WO1999063883A1

WO1999063883A1 - Physiological stress detector device and method

Info

Publication number: WO1999063883A1
Application number: PCT/IL1998/000270
Authority: WO
Inventors: Israel Sarussi
Original assignee: S.P.O. Medical Equipment Ltd.
Priority date: 1998-06-11
Filing date: 1998-06-11
Publication date: 1999-12-16
Also published as: EP1083822A4; CA2334964C; EP1083822A1; AU7672698A; CA2334964A1

Abstract

This invention is a method and device for measurement of a level of at least one blood constituent. The device includes a light source, and a light detector proximate the surface of an organ. The device also includes a pair of adjustable gain amplifiers (A1, A2), and a processor/controller (44) connected within a processing unit. The processing unit operates to separate an AC signal component from a DC signal component. The light source includes at least one light emitting unit. Preferably the light source alternatingly emits light at two different wavelength ranges, and normalizes the AC and DC output signals corresponding with the intensity of the light reflected from the organ and calculates a ratio of the normalized signals for each wavelength range. The device may determine the level of the blood constituent, and may also use this level for monitoring and/or to activate an alarm (48) when the level falls outside a predetermined range. The device, and the method may be applied to monitoring, inter alia, conditions of apnea, respiratory stress, reduced blood flow in organ regions, heart rate, jaundice, and blood flow velocity.

Description

PHYSIOLOGICAL STRESS DETECTOR DEVICE AND METHOD

FIELD OF THE INVENTION

The present invention relates to instruments which operate on the

principle of pulse oximetry, in particular, to non-invasive hemoglobin saturation

detectors and methods, and may be generally applied to other electro-optical

methods of measuring blood constituents.

BACKGROUND OF THE INVENTION

Electro-optical measurement of blood characteristics has been found to

be useful in many areas of blood constituent diagnostics, such as glucose levels,

oxygen saturation, hematocrit, billirubin and others. This method is advantageous

in that it can be performed in a non-invasive fashion. In particular, much research

has been done on oximetry, a way of measuring oxygen saturation in the blood,

as an early indicator of respiratory distress.

Infants during the first year of life are susceptible to breathing

disturbances (apnea) and respiratory distress. Sudden Infant Death Syndrome

(SIDS) is a medical condition in which an infant enters respiratory distress and

stops breathing, leading to the death of the infant. Although the cause and

warning signs of SIDS are not clear, it has been shown that early detection of

respiratory distress can provide the time to administer the aid necessary to

prevent death.

Many types of baby monitors are currently available, from simple motion

detectors to complicated systems which stream oxygen enriched air into the infant's environment. Some of the more accepted monitoring methods include

chest motion monitors, carbon dioxide level monitors and heart rate (pulse)

monitors. Unfortunately these methods often do not give the advance warning

necessary for the caregivers to administer aid. In addition, these monitors are

administered by attaching a series of straps and cords which are cumbersome to

use and present a strangulation risk.

The chest motion monitor gives no warning when the breathing patterns

become irregular or when hyperventilation is occurring, since the chest continues

to move. Distress is only noted once the chest motion has ceased at which point

there may only be a slight chance of resuscitation without brain damage. In

addition these devices are known to have a high level of "false alarms" as they

have no way to distinguish between the lapses in breathing which are normal for

an infant (up to 20 seconds) and respiratory distress. These devices can cause

excessive anxiety for the caregivers or cause them to ignore a signal which is true

after responding repeatedly to false alarms.

Among other symptoms, SIDS causes an irregular heartbeat, resulting

eventually in the cessation of heartbeat with the death of the infant. There are

some instruments which use the EKG principle to monitor this clinical

phenomenon. This is a limited method which has a very high rate of false

positives since the monitors have inadequate algorithms to determine what is a

SIDS event. Obviously, this is not a convenient method, nor is it desirable to have

the infant constantly hooked up to an EKG monitor. In light of these disadvantages a better method to use is a form of

electro-optical measurement, such as pulse oximetry, which is a well-developed

art. This method uses the difference in the absorption properties of

oxyhemoglobin and deoxyhemoglobin to measure blood oxygen saturation in

arterial blood. The oximeter passes light, usually red and infrared, through the

body tissue and uses a photodetector to sense the absorption of light by the

tissue. By measuring oxygen levels in the blood, one is able to detect respiratory

distress at its onset giving sufficiently early warning to allow aid to be administered

as necessary.

Two types of pulse oximetry are known. Until now, the more commonly

used type has been transmission oximetry in which two or more wavelengths of

light are transmitted through the tissue at a point where blood perfuses the tissue

(i.e. a finger or earlobe) and a photodetector senses the absorption of light from

the other side of the appendage. The light sources and sensors are mounted in a

clip which attaches to the appendage and delivers data by cable to a processor.

These clips are uncomfortable to wear for extended periods of time, as they must

be tight enough to exclude external light sources. Additionally, the tightness of the

clips can cause hematomas. Use of these clips is limited to the extremities where

the geometry of the appendages is such that they can accommodate a clip of this

type. The clip must be designed specifically for one appendage and cannot be

used on a different one. Children are too active to wear these clips and

consequently the accuracy of the reading suffers. In another form of transmission oximetry, the light source and detector

are placed on a ribbon, often made of rubber, which is wrapped around the

appendage so that the source is on one side and the detector is on the other. This

is commonly used with children. In this method error is high because movement

can cause the detector to become misaligned with the light source.

It would be preferable to be able to use the other type of pulse oximetry

known as reflective, or backscattering, oximetry, in which the light sources and

light detector are placed side by side on the same tissue surface. When the light

sources and detector can be placed on the tissue surface without necessitating a

clip they can be applied to large surfaces such as the head, wrist or foot. In cases

such as shock, when the blood is centralized away from the limbs, this is the way

meaningful results can be obtained.

One difficulty in reflective oximetry is in adjusting the separation between

the light source and the detector such that the desired variable signal component

(AC) received is strong, since it is in the alternating current that information is

received. The challenge is to separate the shunted, or coupled, signal which is

the direct current (DC) signal component representing infiltration of external light

from the AC signal bearing the desired information. This DC signal does not

provide powerful information. If the DC signal component is not separated

completely, when the AC signal is amplified any remaining DC component will be

amplified with it, corrupting the results. Separating out the signal components is

not a simple matter since the AC signal component is only 0.1% to 1% of the total reflected light received by the detector. Many complicated solutions to this

problem have been proposed.

If the light source and detector are moved further apart, this reduces the

shunting problem (DC), however, it also weakens the already weak AC signal

component. If the light source and detector are moved close together to increase

the signal, the shunting (DC) will overpower the desired signal (AC).

Takatani et al., in US Pat. No. 4,867,557, Hirao et al., in US Pat. No.

5,057,695 and Mannheimer, in US Pat. No.5, 524,617 all disclose reflective

oximeters which require multiple emitters or detectors in order to better calculate

the signal.

A number of attempts have been made to filter out the DC electronically

(see Mendelson et al., in US Pat. No. 5,277,181). These methods are very

sensitive to changes in signal level. The AC remaining after the filtering often

contains a small portion of DC, which upon amplification of the AC becomes

amplified as well, resulting in inaccurate readings. Therefore, this method is only

useful in cases where the signal is strong and uniform.

Israeli patents 114082 and 114080 disclose a sensor designed to

overcome the shunting problem by using optical fibers to filter out the undesired

light. This is a complicated and expensive solution to the problem which requires

a high level of technical skill to produce. In addition, it is ineffectual when the AC

signal is relatively weak.

As can be seen from the above discussion, the prior art methods of

addressing the AC/DC signal separation problem in reflective oximetry techniques are complicated and expensive. Therefore, it would be desirable to provide a

simple, low cost and effective method for achieving accurate reflective or

transmissive oximetry detection of respiratory stress.

SUMMARY OF THE INVENTION

Accordingly, it is the broad object of the present invention to overcome

the problems of separating the shunted light from the signal in order to provide a

physiological stress detector which achieves accurate readings.

A general object of this invention is to overcome the problems of

separating the shunted light from the signal in order to provide a respiratory stress

detector which achieves accurate pulse oximetry readings for respiratory stress

applications.

The present invention discloses a small, independent, sensor, for

invasive and non-invasive applications unencumbered by cables or wires, which is

capable of being attached to different body parts, to comfortably and accurately

monitor blood constituent levels and the pulse of an infant or any other living

organism. The apparatus may be applied to any part of the body without prior

calibration. Accurate readings of blood constituent levels are obtained using the

inventive method in which a precise separation of the AC and DC signal

components has been achieved, allowing each signal component to be amplified

separately. In order to accomplish this precise separation, the signal components

are separated by a novel signal processing technique.

The inventive sensor may be adapted for many health monitoring

situations including infant monitoring for SIDS, fetal monitoring, etc.

In a preferred embodiment adapted for SIDS, the sensor is designed to

apply reflective oximetry techniques, so as to comfortably and accurately monitor

the arterial oxygen levels and the pulse of an infant or any other living organism prone to respiratory distress. This monitor is equipped with a processor capable of

determining the need for an alarm and capable of signalling a distress signal to

further alert to a crisis.

In another embodiment, in addition to the alarm being generated from

the sensor itself, readings will be radio-transmitted to a base station, possibly at a

nurse's station, to allow monitoring of the reading, and another alarm will be

activated from the base station when the readings are outside of the accepted

range.

In another preferred embodiment, the apparatus is mounted in a

sock-type mounting such that the apparatus is properly applied when the sock is

put on in the usual fashion. In addition, the sock-type apparatus blocks entrance

of external light to the area of the sensor apparatus.

In yet another preferred embodiment, the apparatus is mounted on a

ribbon-type mounting such that the apparatus is properly applied when the ribbon

is tied around the head or other body part. In addition, the width of the ribbon is

such that it will block entrance of external light to the area of the sensor

apparatus. Additionally, the ribbon may be of dark color which also blocks

entrance of external light to the area of the sensor apparatus.

In yet another preferred embodiment, the apparatus is mounted on a

bracelet-type mounting such that the apparatus is properly applied when the

bracelet is fastened to the wrist or other body part. In addition, the width of the

bracelet is such that it blocks entrance of external light to the area of the sensor apparatus. Additionally, the bracelet may be of dark color which also blocks

entrance of external light to the area of the sensor apparatus.

There is therefore provided, in accordance with a preferred embodiment

of the present invention, A non-invasive device disposed proximate the surface

of an organ for measurement of a level of at least one blood constituent. The

device includes: at least one light source, providing light directed toward the

surface of the organ, theMight being reflected from the organ, a light detector

spaced apart from the at least one light source and being sensitive to intensity

levels of the reflected light for producing intensity signals in accordance

therewith, and a processing unit for processing the intensity signals received

from the light detector. The processing unit includes: first and second amplifiers

for amplifying the intensity signals, each in accordance with a respective first

and second gain amplification factor, and a processor for automatically

determining the first and second gain amplification factors in adjustable fashion.

During a first stage, the first and second amplifiers amplify a DC signal

component of the intensity signals in accordance with predetermined first and

second gain amplification factors, the DC signal component is subtracted from

the intensity signals at an input of the first amplifier, to isolate an AC signal,

component of the intensity signals. During a second stage, the ^"second

amplifier amplifies the isolated AC signal component in accordance with the

adjustably-determined second gain amplification factor. The processing unit

produces output signals in accordance with the isolated AC signal component and the DC signal component and calculates in accordance therewith, at least

one blood constituent level.

Furthermore, in accordance with another preferred embodiment of the

present invention, the light source and the light detector of the device are held in

a spaced relationship while in contact with the surface of the organ so as to

substantially block entrance of external light therebetween.

Furthermore, in accordance with another preferred embodiment of the

present invention, the processing unit further comprises: means for normalizing

the AC and DC output signal components to produce first and second

normalized signals, and means for forming a ratio of the first and second

normalized signals. The processor calculates the blood constituent level in

accordance with the ratio.

Furthermore, in accordance with another preferred embodiment of the

present invention, the organ is the skin and the device is arranged for mounting

on a ribbon, a bracelet and the like for placement on a part of a human or an

animal body.

Furthermore, in accordance with another preferred embodiment of the

on a tightly-fitted garment to be worn over a part of the body.

Furthermore, in accordance with another preferred embodiment of the

present invention, the device further includes a transmitter for transmitting the output signals to a receiver at a remote location, allowing monitoring of the at

least one blood constituent level from the remote location. The receiver is

equipped with an alarm unit for alerting when the at least one blood constituent

level falls outside of a predetermined range.

Furthermore, in accordance with another preferred embodiment of the

present invention, the processor develops a control signal when the

adjustably-determined sebond gain amplification factor is established in the

second stage, the signal is measured and the control signal shuts off the light

source.

Furthermore, in accordance with another preferred embodiment of the

present invention, the control signal conserves energy by reducing the

operational duty cycle of the light source.

Furthermore, in accordance with another preferred embodiment of the

present invention, the first and second gain amplification factors are determined

by the processor in an iterative process by adjustably setting a gain

amplification factor and measuring a dynamic voltage range of the output

signals to determine if the voltage range falls within a predetermined window

established by the processor.

Furthermore, in accordance with another preferred embodiment of the

present invention, the light source comprises a single light emitting unit capable

of controllably providing light having a wavelength range selected from at least a

first wavelength range and a second wavelength range. The first wavelength range is at least partially different from the second wavelength range. The

single light emitting unit can be switched from emitting light within the first

wavelength range to emitting light within the second wavelength range.

Furthermore, in accordance with another preferred embodiment of the

present invention, the light source includes at least a first light emitting unit

capable of controllably emitting light having a first wavelength range and a

second light emitting unit capable of controllably emitting light having a second

wavelength range. The first wavelength range is at least partially different from

the second wavelength range.

Furthermore, in accordance with another preferred embodiment of the

present invention, the light source provides light having wavelengths in the red

and infrared ranges.

Furthermore, in accordance with another preferred embodiment of the

present invention, the organ is the skin, the blood constituent is hemoglobin,

and measurement of a level of oxygen saturation in the hemoglobin provides an

early indication of respiratory stress.

Furthermore, in accordance with another preferred embodiment of the

present invention, the respiratory stress is associated with Sudden Infant Death

Syndrome.

Furthermore, in accordance with another preferred embodiment of the

present invention, the device produces an output signal sent by the processor to an alarm unit for alerting when the at least one blood constituent level falls

outside of a predetermined range.

Furthermore, in accordance with another preferred embodiment of the

present invention, the device is used to monitor the heart rate.

Furthermore, in accordance with another preferred embodiment of the

present invention, the device is used as an apnea monitor.

Furthermore, in accordance with another preferred embodiment of the

present invention, the device is a portable hand held reflective pulse oximeter.

Furthermore, in accordance with another preferred embodiment of the

present invention, the device is adapted to determine blood billirubin levels.

Furthermore, in accordance with another preferred embodiment of the

present invention, the device is adapted for mapping the intensity of the AC

signal along the surface of the organ to detect regions of the organ having a

reduced blood flow.

There is further provided, in accordance with another preferred

embodiment of the present invention, a method for non-invasive measurement

of a level of at least one blood constituent. The method includes the steps of:

providing light from at least one light source disposed proximate the skin,

directing the light toward the skin surface, the light being reflected from the skin,

providing a light detector spaced apart from the light source and being sensitive

to intensity levels of the light reflected from the skin for producing intensity signals in accordance therewith, and processing the intensity signals received

from the light detector. The processing step includes the steps of amplifying the

intensity signals in first and second amplifiers, each in accordance with a

respective first and second gain amplification factor, and automatically

During a first stage, the first and second amplifier amplify a DC signal

component of the intensity signals in accordance with predetermined first and

second gain amplification factors, the DC signal component being subtracted

from the intensity signals at an input of the first amplifier, thereby isolating an

AC signal component of the intensity signals. During a second stage, the

second amplifier amplifies the isolated AC signal component in accordance with

the adjustably-determined second gain amplification factor. The processing

step produces output signals in accordance with the isolated AC signal

component and the DC signal component and calculates in accordance

therewith, the at least one blood constituent level.

Furthermore, in accordance with another preferred embodiment of the

present invention, the method further includes the step of transmitting the output

signals to a receiver at a remote location, allowing monitoring of the at least one

blood constituent level from the remote location. The receiver is equipped with

an alarm unit for alerting when the at least one blood constituent level falls

outside of a predetermined range. Furthermore, in accordance with another preferred embodiment of the

present invention, the step of processing further includes normalizing the AC

and DC output signal components to produce first and second normalized

signals, forming a ratio of the first and second normalized signals, and

calculating the blood constituent level in accordance with the ratio.

Furthermore, in accordance with another preferred embodiment of the

present invention, the method further includes the steps of developing a control

signal when the adjustably-determined second gain amplification factor is

established in the second stage,

measuring the signal and shutting off the light source in response to the

control signal.

Furthermore, in accordance with another preferred embodiment of the

present invention, the method further includes the steps of determining the first

and second gain amplification factors by a processor in an iterative process by

adjustably setting a gain amplification factor, and measuring a dynamic voltage

range of the output signals to determine if the voltage range falls within a

predetermined window established by the processor.

Furthermore, in accordance with another preferred embodiment of the

present invention, the blood constituent is hemoglobin, the method further

includes the step of measuring a level of oxygen saturation in the hemoglobin

providing an early indication of respiratory stress. Furthermore, in accordance with another preferred embodiment of the

Syndrome.

Furthermore, in accordance with another preferred embodiment of the

present invention, the method further includes the step of initiating an alarm for

alerting when the blood constituent level falls outside of a predetermined range.

Furthermore, in accordance with another preferred embodiment of the

present invention, the alarm is selected from an audible alarm, a visual alarm, a

tactile alarm, dialing a telephone number and any combination thereof.

Furthermore, in accordance with another preferred embodiment of the

present invention, the light is altematingly selected from at least a first

wavelength range and a second wavelength range. The first wavelength range

is at least partially different from the second wavelength range.

Furthermore, in accordance with another preferred embodiment of the

present invention, the first wavelength range includes wavelength of red light

and the second wavelength range includes wavelength of infra-red light, the

blood constituent is hemoglobin and the method determines the level of oxygen

saturation of the hemoglobin.

Furthermore, in accordance with another preferred embodiment of the

present invention, the method is used for monitoring the heart rate. Furthermore, in accordance with another preferred embodiment of the

present invention, the method is used for monitoring a condition of apnea.

Furthermore, in accordance with another preferred embodiment of the

present invention, the method is used for monitoring the level of billirubin in

blood.

Furthermore, in accordance with another preferred embodiment of the

present invention. The method further includes the step of repeating the steps of

providing light, providing a light detector and processing at a plurality of

positions along the skin for mapping the levels of the AC signal component

along the surface of the skin to detect regions of reduced blood flow.

There is still further provided, in accordance with another preferred

embodiment of the present invention, a method for measurement of a level of at

least one blood constituent. The method includes the steps of providing light

from at least one light source disposed proximate the surface of an organ,

directing the light toward the surface of the organ, the light being reflected from

the organ, providing a light detector spaced apart from the light source. The light

detector is sensitive to intensity levels of the light reflected from the organ for

producing intensity signals in accordance therewith, and processing the intensity

signals received from the light detector. The processing step includes the steps

of amplifying the intensity signals in first and second amplifiers, each in

accordance with a respective first and second gain amplification factor, and

automatically determining the first and second gain amplification factors in adjustable fashion. During a first stage, the first and second amplifier amplify a

DC signal component of the intensity signals in accordance with predetermined

first and second gain amplification factors, the DC signal component is

subtracted from the intensity signals at an input of the first amplifier, thereby

isolating an AC signal component of the intensity signals. During a second

stage, the second amplifier amplifies the isolated AC signal component in

accordance with the adjustably-determined second gain amplification factor.

The processing step produces output signals in accordance with the isolated AC

signal component and the DC signal component, and calculating in accordance

therewith, the blood constituent level.

Furthermore, in accordance with another preferred embodiment of the

present invention, the organ is an internal organ and the method further

includes the step of repeating the steps of providing light, providing a light

detector, and processing, at a plurality of positions along the surface of the

internal organ for mapping the levels of the AC signal component along the

surface of the internal organ to detect regions of reduced blood flow.

There is also provided, in accordance with another preferred embodiment

of the present invention, a method for non-invasively determining the blood flow

velocity in a region of an organ. The method includes the steps of positioning a

first pulse-oximetry device and a second pulse-oximetry device proximate the

surface of the region. The first and the second device are separated from each

other by a predetermined distance, simultaneously obtaining a first and a second sets of data representing the pulsatile variation at the locations of the

first and the second device, respectively, as a function of time, each of the first

set and the second set of data includes at least one extremum data value, the

extremum data value of the first set of data corresponds to the extremum data

value of the second set of data, calculating the time interval between the

extremum data value of the first set of data and the extremum data value of the

second set of data, dividing the value of the predetermined distance by the

value of the time interval to obtain a value representing the approximate blood

flow velocity in the region of the organ, wherein each of the first device and the

second device includes at least one light source, providing light directed toward

the surface of the organ, the light being reflected from the organ, a light detector

levels of the reflected light for producing intensity signals in accordance

therewith, and a processing unit for processing the intensity signals received

from the light detector. The processing unit includes first and second amplifiers

and second gain amplification factor, and a processor for automatically

During a first stage, the first and second amplifiers amplify a DC signal

component of the intensity signals in accordance with predetermined first and

second gain amplification factors, the amplified DC signal component being

subtracted from the intensity signals at an input of the first amplifier, to isolate

an AC signal component of the intensity signals. During a second stage, the second amplifier amplifies the isolated AC signal component in accordance with

the adjustably-determined second gain amplification factor. The processing unit

produces output signals in accordance with the isolated AC signal component

and the DC signal component and calculates in accordance therewith.

Furthermore, in accordance with another preferred embodiment of the

present invention, the organ is the skin.

Finally, in accordance with another preferred embodiment of the present

invention, the extremum data value is selected from a minimum data value and

a maximum data value.

Other features and advantages of he invention will become apparent

from the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding, the invention will now be described, by way

of example only, with reference to the accompanying drawings in which like

numerals designate like components throughout the application, and in which:

Fig. 1 is a schematic layout diagram of a physiological stress detector

device, constructed and operated in accordance with the principles of the present

invention;

Fig. 2 is an electronic schematic diagram of a prior art signal processing

technique, for use with the device of Fig. 1 ;

Figs. 3a- 3b show, respectively, a prior art signal waveform representing

emitted and received light;

Figs. 4 and 5a-b show, respectively, arrangements for wearing the

device of Fig. 1 on the body of an infant on a leg, foot or head;

Fig. 6 is an electronic block diagram showing the signal processing

components of the device ofthe present invention;

Fig. 7 is an algorithm of a signal processing technique performed in

accordance with the principles of the present invention;

Figs. 8a-b are, respectively, signal waveforms representing emitted red

and infrared light used in the device of Fig. 1 ;

Fig. 9 is a timing diagram applied in an automatic gain adjustment

procedure during signal processing; Fig. 10 is a schematic illustration of a device for determining blood flow

velocity in accordance with another preferred embodiment of the present

invention; and

Fig. 11 is a schematic graph useful in understanding the method of

determining blood flow velocity used by the device of Fig. 10.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following description presents a detailed construction of a

physiological stress detector device adapted for use in monitoring arterial oxygen

levels. In this particular application, the reflective oximetry method uses light

wavelengths in the red and infrared ranges, since these are most suitable for

detecting oxygen saturation in hemoglobin. As will be understood by those skilled

in the art, particular desigYi features used for this application can be varied for

different applications. For example, in an application for monitoring jaundice

through bilirubin levels, other suitable, light wavelengths would be used.

Therefore, the light wavelengths discussed in the following description are not

intended to limit the scope of the present invention, and are to be understood as

pertaining to the subject example only.

Referring now to Fig. 1 , there is shown a preferred embodiment of a

physiological stress detector device 10 constructed and operated in accordance

with the principles of the present invention. Device 10 comprises a housing 12

arranged for placement in close proximity to a skin surface 14. Housing 12 may

be provided as a casing enclosing a light source 16 emitting two wavelengths, red

and infrared, and a photodetector 18 spaced apart from the light source 16.

Device 10 is designed to be operated such that when light source 16 emits^* light of

a red or infrared wavelength, the light penetrates skin tissue (arrow A) and a

portion of the light is reflected back to light detector 18, along a path defined by

line 20. The light source 16 may be implemented as a single component which

can controllably emits red or infrared light. A non limiting example of the light

source 16 is the selectable wavelength light emitting diode (LED) component

model L122R6IR880, or for pediatric or prematurely born baby applications the

component model SML12R6IR880, both components are commercially available

from Ledtronics, CA, U.S.A. However, The light source 16 may also include two

separate suitable light sources. For example, the light source 16 may include two

separate light sources (not shown) such as an LED emitting red light and another

different LED emitting infrared light.

It is noted that, while, preferably, the light source 16 includes one or

more LEDs emitting in the suitable red and infrared ranges, other light sources

may be used such as incandescent lamps in combination with suitable optical

filters, various types of gas discharge or arc lamps, with or without optical filters,

diode laser devices, or any other.

For the pulse-oximetry application the light detector 18 may be a

photodiode, such as the model BPW34 photodiode, or for pediatric and premature

born babies the model BPW34S photodiode, both commercially available from

Siemens Semiconductor Group, Germany. However, many other types of

photo-detecting devices may be used such as resistive photocells, or any other

type of photodetector which has the required sensitivity at the wavelengths used

for the specific application of the device 10. It is noted that the device 10 of Fig. 1 also includes further electronic

components (not shown in Fig. 1 ) which are disclosed in detail hereinbelow ( as

best seen in Fig. 6).

As described in the background of the invention, the device 10 employs

non-invasive reflective oximetry techniques to provide measurement of blood

characteristics useful in diagnostic procedures and detection of physiological

stress. As mentioned, one difficulty in reflective oximetry is in adjusting the

separation between light source 16 and detector 18 such that the desired signal

received by light detector 18 is strong and not affected by shunted, or coupled,

light from source 16. Figs. 2 and 3a-3b illustrate this problem and the prior art

techniques currently available for its solution.

In Fig. 2 there is shown an electronic schematic diagram of a signal

processing filter 22 used to separate the variable signal (AC) component of

received light from the shunted (DC), or coupled, light. The separation is

achieved by a blocking capacitor 24 on the input of an operational amplifier 26

used to amplify the variable signal portion. The DC signal component of the

received light, which does not pass through blocking capacitor 24, forms the input

of, and is amplified by operational amplifier 28.

As illustrated in Figs 3a-3b, the signal waveform representing the

emitted light, (Fig. 3a) is substantially reproduced as a received signal waveform

(Fig. 3b). Even after filtering by signal processing filter 22, the AC signal

component remaining ΔSIG is only a small portion of a larger signal which has

been amplified by operational amplifier 26, and therefore dominates the variable signal portion. Thus, this method of signal separation results in inaccurate

readings of reflected light, and cannot provide accurate information in oximetry

measurements.

In Figs. 4 and 5a-b there are shown alternative configurations of device

10, respectively, provided in a foot bracelet 30, a sock 32 worn around the ankle,

and a ribbon 34 worn around the head. In each arrangement, casing 12 is

designed to be held tightly against skin surface 14 to reduce the amount of stray

light entering into the optical path between light source 16 and detector 18.

Preferably, the casing 12 is made from a material opaque to light in the

relevant spectral range to which the detector 18 is sensitive, such as an opaque

plastic material, metal or the like. The foot bracelet 30, the sock 32 and the ribbon

34 may be made of a material which allows the casing 12 to be tightly pressed

against the skin. This material may be a flexible material such as a flexible fabric.

The material may also be a porous or woven material to prevent excessive

perspiration of the skin thereunder.

Referring now to Fig. 6 , there is shown an electronic schematic block

diagram of device 10. Device 10 comprises a sensor 35 incorporating light source

16 and detector 18. The sensor 35 may also include a preamplifier circuit (not

shown) for amplifying the output signals of the detector 18 and feeding the

amplified signals to the processing unit 40. It will be appreciated by those skilled

in the art that the numbers of light sources and detectors can be varied while

keeping the same processing method. In addition, device 10 comprises a signal

processing unit 40 including a pair of operational amplifiers A1 and A2, an analog to digital converter 42, a central processing unit (CPU)/controller 44, and a digital

to analog converter 46. In critical applications, such as SIDS, when there exists a

need for emergency first aid availability, when CPU 44 has determined that the

value obtained is not within the acceptable range an output signal 47 is fed to an

alarm unit 48 causing an alarm to be activated. Optional connections to an RF

transmitter 50 and PC computer 52 are available. Sensor 35 is designed to be

powered by a small battery (not shown).

According to another embodiment of the present invention, processing

unit 40 with or without alarm 48, RF transmittor 50 and/or PC 52 are connected to

the sensor 35 via a cable or by wireless transition. In this case sensor 35 does not

require a battery.

It is noted that, the alarm unit 48 may activate a visual alarm, an audio

alarm, a tactile alarm (such as a vibratory signal), or an audio-visual alarm. The

alarm unit 48 may also initiate the automatic dialing of a telephone number and

may also activate any combination of any of the above types of alarms, or of other

types of alarms.

The coupling of operational amplifiers A1 and A2 is between the output

of amplifier A1 and the input of amplifier A2. The gain amplification factor of each

amplifier is set by the central processing unit 44 via a signal in accordance with an

automatic adjustable gain technique described further herein. Analog to digital

converter 42 provides a digital input signal 54 based on the level of output signal

56 from amplifier A2. The central processing unit 44 is programmed to process

the information contained in input signal 54, and thereby determine blood oxygen saturation levels detected by sensor 35. The output signal 47 from CPU 44 may

be used to trigger alarm 48, or its information can be transmitted by an RF

transmitter 50 to a receiver 60 for remote station processing. Data analysis can

be performed by PC 52 based on a data output signal 53.

Based on the block diagram of Fig. 6, device 10 can be constructed in

accordance with state of the art electronic design techniques employing, for

example a 8051 micro-controller, commercially available from Intel Corp, U.S.A.,

or any other suitable processor or controller to implement the CPU/controller 44.

The properties of amplifiers A1 and A2 are selected in accordance with

electronic design rules well known in the art. In a non-limiting example, amplifier

A1 is the model PGA205AU programmable gain instrumentation amplifier, and

amplifier A2 is the model PGA204AU programmable gain instrumentation

amplifier, commercially available from Burr-Brown, AZ, U.S.A. However, the

amplifiers A1 and A2 may be any other suitable type of amplifier. For example,

while in the preferred embodiment disclosed hereinabove each of the amplifiers

A1 and A2 is shown as an operational amplifier unit, each of the amplifiers A1 and

A2 may be implemented as a multi-stage amplifier device containing more than

one amplification stages.

As mentioned in the background of the invention, problems with prior art

reflective oximetry techniques are related to the measurement of the AC signal

component which forms a small part of the larger DC signal component provided

by light sensor 35. Whereas the previous techniques involved use of a blocking

capacitor 24 as described in Figs. 2 and 3a-3b, the present invention provides a novel solution to the signal amplification problem such that more accurate

oximetry measurement may be obtained.

It is noted that, depending on the specific detector used, the AC and DC

signal components generated by the detector 18 may be current or voltage AC

and DC signal components, and that the terms AC signal component and DC

signal component throughout the specification and claims define AC and DC

components of the output signal of the detector 18 and may include voltage signal

components and current signal components. However, the AC and DC signal

components may also include any other type of electrical or photonic (optical)

signal which may be the output of any suitable detector type useful with the

device of the present invention.

In accordance with the principles of the present invention, processing

unit 40 applies a novel technique for separating the AC signal component from

the DC signal component. The steps carried out by CPU 44 in this technique are

illustrated in the flow chart of Fig 7.

In start block 62, CPU 44 begins its operation by initializing the gain of

analog amplifiers A1 and A2 automatically. In block 64 the detected signal from

sensor 35 is measured, and this is performed by providing output signal 56 from

signal processing unit 40 to the analog to digital converter 42, so that it is

converted to a digital input signal 54 for input to CPU 44. In block 66, CPU 44

calculates the DC signal component of the detected signal. This is achieved by a

two-stage process. In the first stage, output signal 56 is treated as a pure DC signal, such

that CPU 44 takes the average of this signal level, and generates a digital output

signal 67 which is converted by the digital to analog converter 46 to an analog

reference shift signal 68. In block 70, reference shift signal 68 is fed into the

negative input of amplifier A1 and amplifier A1 effectively neutralizes the DC

component by applying reference shift signal 68 against the detected signal from

sensor 35. This produces a null output for input to amplifier A2.

In the second stage, in block 72, amplifier A2 receives the AC signal

component of the detected signal and amplifies it, thereby producing an output

signal 56 containing information based on the reflective oximetry technique. This

information, when converted to a digital signal in analog to digital converter 42,

provides digital input signal 54 to CPU 44. In block 74, the oximetry calculation is

performed by the CPU/controller 44 based on measurements derived from sensor

35, in accordance with the information provided by digital input signal 54. The

results of the oximetry calculation are provided as output signal 47 or in the form

of a data signal 35 fed to a PC computer 52. Output signal 47 may be used to

activate an alarm 48 or it may be provided as the signal for transmission via RF

transmitter 50 to a remote receiver 60, to allow base station monitoring of the

reading.

Referring now to Figs. 8a-b, there are shown respectively, pulse signal

waveforms representing light received in the red and infrared ranges by light

detector 18 in sensor 35. Light is provided by light source 16 in pulses each

having, for example, a duration of 1.6 milliseconds and a period of 15.6 milliseconds. The analysis of a typical light pulse is provided in Fig. 9, showing

the time scale division of the 1.6 millisecond pulse into two cyclical gain

adjustment periods 76 and 78, respectively. The red and infrared pulses are

staggered so as to minimize interference between them.

In Fig. 9, a time division scale is developed in which each of the pulsed

light waveforms is divided into two periods 76 and 78, each having, for example, a

maximum duration of 800 microseconds, during which the gain amplification factor

is set for each of operational amplifiers A1 and A2. The first period is used to set

the gain for and measure the DC signal component, and the second period is

used to set the gain for and measure the AC signal component.

The gain amplification factor is automatically adjusted in an iterative

process. After a predetermined delay, for example 50 microseconds, the gain

amplification factor is set during interval 80, and the output signal 56 of signal

processing unit 40 is measured to determine if it falls within the window defined by

CPU 44. For example, a dynamic voltage range of between 0.4-4 volts is

established by CPU 44, and output signal 56 is measured during interval 82, to

see if it falls within this window. If it does, the gain amplification factor is fixed at

its current value. If, on the other hand, output signal 56 does not fall within this

window, another setting is provided by CPU 44 and again the output signal 56 is

measured. This process is repeated, in iterative fashion, within the first period of

the cyclical gain adjustment procedure until the output signal 56 falls within the

desired window. If the desired window for the DC signal component is obtained before

the 800 microseconds of the first period has elapsed, the first period is shortened

accordingly, and the second period is commenced, during which the same

procedure is performed for the AC signal component. Once a desirable window is

attained for the AC signal component, the second period may be shortened

accordingly, and CPU 44 sends a control signal 84 to sensor 35, to shut off the

light source for that pulse. In this fashion, an energy savings is achieved by

reducing the duty cycle of light source 16, and reducing the current drain from the

battery and extending its useful life. Control signal 84 is provided for each

individual light pulse, so that the maximum energy savings is achieved. If the 800

microseconds has elapsed without establishing the gain amplification factor, the

signal is ignored.

It is noted that, the values disclosed hereinabove for the pulse duration

and pulse interval of Figs. 8a and 8b and for the two periods 76 and 78 of Fig. 9

are given as a non-limiting example only and may be replaced by other suitable

values depending, inter alia, on the available electronic component speed, the

processing speed of the processor/controller 44 and the specific application type.

For example, the pulse duration and pulse interval of Figs. 8a and 8b can have

the values of 0.6 milliseconds and 15.6 milliseconds, respectively, and the two

periods 76 and 78 of Fig. 9 may each have the value of 300 microseconds.

It is further noted that, while in the embodiment disclosed hereinabove

(Figs. 8a, 8b and 9) a DC gain correction procedure is performed for each first

time period 76 as disclosed in detail hereinabove, it was found that the DC correction can be performed much less often with no deterioration of the devices

performance and in some cases with a resulting improvement of measurement

stability. For example, if a typical measurement cycle lasts approximately 4-5

seconds, in order to include a few heart pulse cycles, and includes 256 infrared

and red light measurement periods (each of the light measurement periods

comprising the time periods 76 and 78), performing the DC correction procedure

only once for every 256 measurement periods (i.e once for each measurement

cycle) results with a better stability. Thus, the number of times of performing the

DC correction procedure of the present invention per measurement cycle may be

varied for optimizing the stability and accuracy of the measurements. The optimal

number of times of performing the DC correction procedure of the present

invention per measurement cycle may depend, inter alia, on the optical

parameters of the light source 16 and the detector 18 of the device 10 and on the

specific wavelengths implemented in the specific application.

An advantage of reducing the number of DC corrections per

measurement cycle is that it reduces the computational load of the CPU 44,

enabling increasing the number of light measurement time periods within each

given measurement cycle or, alternatively, using a less powerful CPU 44 to

reduce the overall cost of the device 10 while conserving or even improving the

accuracy and stability of the measurements.

The gain amplification factors are selected from a set of preselected

values. Amplifier A1 , which acts to amplify the DC signal component, can have gain amplification factors of 1 , 2, 4 or 8. Amplifier A2, which amplifies the AC

signal component, operates in the amplification ranges of 1 , 10, 100 or 1000.

An advantage of the ability to automatically switch between the gain

amplification factors based on the iterative process performed by CPU 44, is that

it allows the device 10 to obtain oximetry measurements in different parts of the

body without recalibrating the gain amplification factor for each area.

The separated AC and DC signals are calibrated using the formulas:

V_AC =

A AC * ADC

v_DC= 0 K v_DC=

where V-,_d is the signal from the analog to digital converter and A_AC and

A_DC represent the gain of the A2 and A1 amplifiers, respectively. Using these

calibration equations it is possible to calculate a value for each of the signal

components (V_AC and V_DC) which is substantially separated from the other signal

component. Once the AC and DC signal components are calibrated, calculations for

purposes of determining oxygen saturation are performed by taking the AC and

DC values for each wavelength and forming a ratio:

V(AC)_redΛ/(DC)_red

G=

V(AC)_infr-_red/V(DC)_infrar-_d

This ratio is used to calculate the oxygen saturation in the formula:

SatO₂= B - A ^* G

where B and A are constants. CPU 44 determines whether or not this

value falls within the desired window, and in cases where the value is

unacceptable and stress is detected, an output signal 47 is sent to alarm 48 and

the alarm willturn on. Alternatively, or in addition, the output signal 47 can be

sent to RF transmitter 50 for transmission to receiver 60. Additional information,

such as a log of all readings, may be sent from CPU 44 as a data output signal 53

to PC 52.

In summary, the physiological stress detector device of the present

invention provides a non-invasive method for more accurately measuring blood

constituents in a compact, easily utilized design. It is especially useful for

application in SIDS monitoring systems due to its compact light weight design

which is provided with no cumbersome, dangerous cable connections.

An advantage of the devices and methods of the present invention is

that the sensitivity and improved signal to noise ratio of the present method

enables use of transmissive methods of pulse oximetry under conditions where the signals are of low amplitude relative to the noises. In a non-limiting example,

the method and devices may be particularly useful for transmissive oximetry

under conditions of low blood perfusion such as in systemically shocked patients

or in cases of severe hypothermia.

A major advantage of the present invention is in its application to

reflective oximetry where the signals are usually of a relatively low amplitude. In

particular, the sensitivity of the method and the devices may enable performing

reflective pulse oximetry on regions of the body which exhibit particularly low

amplitude signals such as the wrist region, or the ankle region of adults and

babies.

Reference is now made to Fig. 10 which is a schematic illustration of a

device 90 for determining blood flow velocity in accordance with another preferred

embodiment of the present invention.

The device 90 includes a housing 92 and two pulse oximetry devices

10a and 10b attached thereto. The devices 10a and 10b are constructed as the

device 10 disclosed hereinabove and are simultaneously operated to provide an

amplified pulse oximetry AC signal as disclosed in detail for the device 10

hereinabove. The fixed distance D between the device 10a and the device 10b is

represented by the double headed arrow labeled D. The device 90 is placed on a

region of skin A and the pulse oximetry AC signal is simultaneously determined

for each of the devices 10a and 10b.

Reference is now made to Fig. 11 which is a schematic graph useful in

understanding the method of determining blood flow velocity used by the device 90 of Fig. 10. The horizontal axis represents time and the vertical axis represents

the amplitude of the reflective oximetry AC signals. The curve 94A represents the

AC signal output from the device 10a and the curve 94B represents the AC signal

output from the device 10b. The minima 96A and 96B of the curves 94A and

94B, respectively represent the minima of the reflected AC signal due to the

pulsation of the blood flow. The time delay ΔT between the reflection minima

96A and 96B represent the time delay between the registration of a minimum

reflectance by the device 10a and its registration by the device 10b. The delay

results from the finite blood velocity and the distance D separating the devices.

Since the distance D between the devices 10a and 10b is known, the

approximate blood flow velocity V can be determined by calculating the value

V = D/ ΔT.

The processing unit 40 of one of the devices 10a or 10b thus acquires

two data sets. The first data set represents the AC signal component of the

device 10a and the second data set represents the AC signal component of the

device 10b. Preferably, both of the data sets are digital data sets and are

sampled simultaneously. The data sets are sampled such that each data set

includes at least one extremum data value corresponding to a minimum or a

maximum value of the AC signal component, the processing unit 40 detects the

extremum point for each of the data sets using any method known in the art for

detecting an extremum point. The processing unit then calculates the time

interval ΔT between the corresponding extremum points of the first and the

second data sets and calculates the blood flow velocity from the ratio ΔT/D. Preferably, for devices using reflective pulse oximetry of the present

invention, the extremum data values used are minimum values representing

minimal values of reflected light due to maximal absorption of the light from the

light sources 16 of the devices 10a and 10b. However, the extremum values

may also be maxima. For example, in an embodiment where transmissive pulse

oximetry devices are used, the extremum values may be maxima.

It is noted that, while each of the devices 10a and 10b may have a CPU

44 as disclosed hereinabove, in accordance with another preferred embodiment

of the present invention, the device 90 may include a single CPU unit (not shown)

which may be shared for performing all the calculations and control functions

disclosed hereinabove for the operation of each of the devices 10a and 10b and

for additionally performing the determination of ΔT and the calculation of the

approximate blood flow velocity therefrom.

It will be appreciated by those skilled in the art that suitable methods for

detecting and timing the reflection minima 96A and 96B are well known in the art

and are not included in the subject matter of the present invention, and will

therefore not be described herein in detail.

It is noted that while the device and method for determining blood flow

velocity disclosed hereinabove is adapted for use with a pair of devices 10a and

10b, a larger number of devices (not shown) may be used together either as a

multiplicity of device pairs or in any other geometrical configuration for improving

the accuracy of the measurement by averaging the results of multiple pair

determinations or by any other suitable computational method known in the art. It is noted that, while the preferred embodiments of the present invention

are particularly adapted for reflective pulse oximetry applications, it may be also

implemented in many other applications. For example, the method and the

device of the present invention may be adapted to the monitor bilirubin levels for

the detection and monitoring of jaundice, by suitably selecting a light source which

emits wavelengths of light in the range selectively absorbed by bilirubin,

(approximately between 400 - 600 nanometer).

In another example, the present invention may also be used to detect

and monitor blood constituents which have distinct absorbance peaks in the

visible range, the near ultraviolet (UV) range or in both the visible and the near UV

range. For this type of applications one or more of the light wavelengths used

may be obtained from a gas discharge lamp or from any another suitable source

of light in the near UV range.

Another application of the present invention is the application of the

method for the determination and mapping of areas of organs suspected of a

reduced blood flow due to chronic or temporary clinical condition. For example if

an internal or external organ is suspected to have developed gangrene the device

10 of the present invention may be used to map areas having low or reduced

blood flow by moving the device 10 along the organ and in contact therewith and

mapping areas of reduced blood flow by recording and mapping the amplitude of

the minima of the pulse oximetry AC component as disclosed hereinabove along

the surface of the organ. This method may be particularly useful in mapping of such reduced flow areas in cases where regular transmissive pulse oximetry is not applicable due to inaccessibility problems or due to very noisy signal

conditions.

One exemplary application is mapping the external surface of the

intestines using a small pre-sterilized reflective oximetry device such as the device

10 of the present invention. In such a case transmissive oximetry devices cannot

be used because it is not possible to position a light source and a light detector on

opposite sides of the intestinal wall. The device 10 is particularly advantageous

here because it can be simply moved along the external surface of the suspected

intestinal part and because of its improved sensitivity and reduced noise level.

The above mapping method may be applied to many other organs such

as limbs suspected of blood flow disturbances due to a gangrene condition or

other diseases.

It is noted that the devices of the present invention may be implemented

in a variety of different configurations. The devices 10 or 90 of Figs. 1 and 10,

respectively may be connected to a computer (not shown) or a monitor (not

shown). The computer or monitor may include a display device (not shown).

An alternative configuration may include the device 10, connected to a

housing(not shown) wirelessly or by suitable wires. The housing may also include

a liquid crystal display device (LCD), such as the LCD display model

G1216001 N000-3D0E, commercially available from Seiko Instruments Inc.,

Japan, suitably connected to the CPU 44 for displaying alphanumeric symbols

representative of one ore more parameters of the pulse oximetry signal such as the pulse frequency , or amplitude or any other data. The LCD display may also

display the AC signal graphically with or without the alphanumeric data.

In a third configuration of the device of the present invention the pulse

oximetry device includes all the optical and electronic components within one

single device shaped as a wrist watch like device to be worn as a self contained

unit. One non-limiting example (not shown) is a device worn on the wrist and

shaped like a wrist watch. All the components of the device 10 are integrated

within the device such that the light source 16 and the detector 18 are attached to

the device so as to be in contact with the skin when the device is worn. All the

necessary electronic components disclosed hereinabove are also integrated in

the device including a power source such as a battery. The device may thus

monitor signals, may or may not collect and store data and may or may not

activate an alarm unit or transmit a distress signal as disclosed hereinabove in

detail. It is noted that this self contained integrated device configuration may also

be shaped to be placed in contact with the skin on the limbs, forehead or any

other organ of the patient by suitable means such as strips bands of flexible

material, adhesives or any other suitable attachment means known in the art.

The self contained integrated device configurations may be used for a

variety of applications. For example, in a preferred embodiment of the preseni

invention, the device may determine the pulse rate of the wearer. It is known that

during a meal the pulse rate increases. The pulse rate may thus be used for diet

control by reporting to the user when the pulse rate reaches a predetermined

value or when the increase in the pulse rate following the beginning of a meal is within a predetermined rate. The user may thus use the device for obtaining an

indication of when to stop consuming food.

The device may also be used for radial pulse measurement in cardiac

measurements and for various bio-feedback application.

In all of the above applications of the self contained integrated device

configurations, such as a bracelet-like device or the like the device has an

advantage of being a compact, lightweight and convenient wearable device while

still providing the high sensitivity, accuracy and relative immunity to movement

artifacts of the present invention.

It is noted that the devices of the present invention, as used in the

various applications disclosed herein above, may also be configured and used as

monitoring devices in a hospital environment, as well as for domestic use.

It is further noted that the devices and methods of the present invention

may be adapted for use of humans and animals.

Having described the invention with regard to certain specific

embodiments thereof, it is to be understood that the description is not meant as a

limitation, since further modifications will now become apparent to those skilled in

the art, and it is intended to cover such modifications as fall within the scope of

the appended claims.

Claims

1. A non-invasive device disposed proximate the surface of an organ for

measurement of a level of at least one blood constituent, comprising:

at least one light source, providing light directed toward said

surface of said organ, the light being reflected from said organ;

a light detector spaced apart from said at least one light source

and being sensitive to intensity levels of said reflected light for

producing intensity signals in accordance therewith; and

a processing unit for processing said intensity signals received

from said light detector, said processing unit comprising:

first and second amplifiers for amplifying said intensity

signals, each in accordance with a respective first and

second gain amplification factor; and

a processor for automatically determining said first and

second gain amplification factors in adjustable fashion;

wherein during a first stage, said first and second amplifiers

amplify a DC signal component of said intensity signals in

accordance with predetermined first and second gain amplification

factors, said amplified DC signal component being subtracted from

said intensity signals at an input of said first amplifier, to isolate an

AC signal component of said intensity signals, and wherein during a second stage, said second amplifier

amplifies said isolated AC signal component in accordance with said

adjustably-determined second gain amplification factor,

said processing unit producing output signals in accordance with

said isolated AC signal component and said DC signal component

and calculating in accordance therewith, at least one blood

constituent level.

2. The device according to claim 1 wherein said at least one light source

and said light detector are held in a spaced relationship while in contact

with the surface of said organ so as to substantially block entrance of

external light therebetween.

3. The device according to claim 1 wherein said processing unit further

comprises:

means for normalizing said AC and DC output signal components

to produce first and second normalized signals; and

means for forming a ratio of said first and second normalized

signals,

said processor calculating said blood constituent level in

accordance with said ratio.

4. The device according to claim 1 wherein said organ is the skin and said

device is arranged for mounting on a ribbon, a bracelet and the like for

placement on a part of a human or an animal body.

5. The device according to claim 1 wherein said organ is the skin and said

device is arranged for mounting on a tightly-fitted garment to be worn

over a part of the body.

1.

6. The device according to claim 1 further comprising a transmitter for

transmitting said output signals to a receiver at a remote location,

allowing monitoring of said at least one blood constituent level from said

remote location,

said receiver being equipped with an alarm unit for alerting when

said at least one blood constituent level falls outside of a

predetermined range.

7. The device according to claim 1 wherein said processor develops a

control signal when said adjustably-determined second gain amplification

factor is established in said second stage, said signal being measured

and said control signal shutting off said light source.

8. The device according to claim 7 wherein said control signal conserves

energy by reducing the operational duty cycle of said at least one light

source.

9. The device according to claim 1 wherein said first and second gain

amplification factors are determined by said processor in an iterative

process by adjustably setting a gain amplification factor and measuring a

dynamic voltage range of said output signals to determine if said voltage

range falls within a predetermined window established by said processor.

10. The device according to claim 1 wherein said at least one light source

comprises a single light emitting unit capable of controllably providing

light having a wavelength range selected from at least a first wavelength

range and a second wavelength range, said first wavelength range being

at least partially different from said second wavelength range, said single

light emitting unit can be switched from emitting light within said first

wavelength range to emitting light within said second wavelength range.

11. The device according to claim 1 wherein said light source comprises at

least a first light emitting unit capable of controllably emitting light having

a first wavelength range and a second light emitting unit capable of

controllably emitting light having a second wavelength range, said first

wavelength range being at least partially different from said second

wavelength range.

12. The device according to claim 1 wherein said at least one light source

provides light having wavelengths in the red and infrared ranges.

13. The device according to claim 12 wherein said organ is the skin, said

blood constituent is hemoglobin, and wherein measurement of a level of oxygen saturation in said hemoglobin provides an early indication of

respiratory stress.

14. The device according to claim 13 wherein said respiratory stress is

associated with Sudden Infant Death Syndrome.

15. The device according to claim 1 further produces an output signal sent by

said processor to an alarm unit for alerting when said at least one blood

constituent level falls outside of a predetermined range.

16. The device according to claim 13 used to monitor the heart rate.

17. The device according to claim 13 used as an apnea monitor.

18. The device according to claim 13 wherein the device is a portable hand

held reflective pulse oximeter.

19. The device according to claim 1 adapted to determine blood billirubin

levels.

20. The device according to claim 1 used for mapping the intensity of said

AC signal along the surface of said organ to detect regions of said organ

having a reduced blood flow.

21. A method for non-invasive measurement of a level of at least one blood

constituent, the method comprising the steps of: providing light from at least one light source disposed proximate

the skin, directing said light toward the skin surface, said light being

reflected from said skin;

providing a light detector spaced apart from said at least one light

source and being sensitive to intensity levels of said light reflected

from said skin for producing intensity signals in accordance therewith;

and

processing said intensity signals received from said light detector,

said processing step comprising the steps of:

amplifying said intensity signals in first and second

amplifiers, each in accordance with a respective first and

second gain amplification factor; and

automatically determining said first and second gain

amplification factors in adjustable fashion;

wherein during a first stage, said first and second amplifier amplify

a DC signal component of said intensity signals in accordance with

predetermined first and second gain amplification factors, said DC

signal component being subtracted from said intensity signals at an

input of said first amplifier, thereby isolating an AC signal component

of said intensity signals, and wherein during a second stage, said second amplifier

amplifies said isolated AC signal component in accordance with said

adjustably-determined second gain amplification factor,

said processing step producing output signals in accordance with

said isolated AC signal component and said DC signal component;

and

calculating $n accordance therewith, said at least one blood

constituent level.

22. The method according to claim 21 further comprising the step of

transmitting said output signals to a receiver at a remote location,

allowing monitoring of said at least one blood constituent level from said

remote location,

said receiver being equipped with an alarm unit for alerting when

said at least one blood constituent level falls outside of a

predetermined range.

23. The method according to claim 21 wherein said step of processing further

comprises:

normalizing said AC and DC output signal components to produce

first and second normalized signals;

forming a ratio of said first and second normalized signals; and calculating said blood constituent level in accordance with said

ratio.

24. The method according to claim 21 further comprising the steps of:

developing a control signal when said adjustably-determined

second gain amplification factor is established in said second stage;

and

shutting off said at least one light source in response to said

control signal.

25. The method according to claim 21 further comprising the steps of:

determining said first and second gain amplification factors by a

processor in an iterative process by adjustably setting a gain

amplification factor; and

measuring a dynamic voltage range of said output signals to

determine if said voltage range falls within a predetermined window

established by said processor.

26. The method according to claim 21 wherein said blood constituent is

hemoglobin, the method further comprising the step of measuring a level

of oxygen saturation in said hemoglobin providing an early indication of

respiratory stress.

27. The method according to claim 26 wherein said respiratory stress is

associated with Sudden Infant Death Syndrome.

28. The method according to claim 21 further comprising the step of initiating

an alarm for alerting when said at least one blood constituent level falls

outside of a predetermined range.

29. The method according to claim 28 wherein said alarm is selected from an

audible alarm, a visual alarm, a tactile alarm, dialing a telephone number

and any combination thereof.

30. The method according to claim 21 wherein said light is altematingly

selected from at least a first wavelength range and a second wavelength

range, said first wavelength range being at least partially different from

said second wavelength range.

31. The method according to claim 30 wherein said first wavelength range

includes wavelength of red light and said second wavelength range

includes wavelength of infra-red light, said at least one blood constituent

is hemoglobin and wherein said method determines the level of oxygen

saturation of said hemoglobin.

32. The method according to claim 31 used for monitoring the heart rate.

33. The method according to claim 31 used for monitoring a condition of

apnea.

34. The method according to claim 21 used for monitoring the level of

billirubin in blood.

5. The method according to claim 31 further including the step of repeafing

said steps of providing light, providing a light detector and processing, at

a plurality of positions along said skin for mapping the levels of said AC

signal component along the surface of said skin to detect regions of

reduced blood flow.

36. A method for measurement of a level of at least one blood constituent,

the method comprising the steps of:

providing light from at least one light source disposed proximate

the surface of an organ, directing said light toward the surface of said

organ, said light being reflected from said organ;

providing a light detector spaced apart from said at least one light

source and being sensitive to intensity levels of said light reflected

from said organ for producing intensity signals in accordance

therewith; and

processing said intensity signals received from said light detector,

said processing step comprising the steps of:

amplifying said intensity signals in first and second

amplifiers, each in accordance with a respective first and

second gain amplification factor; and

automatically determining said first and second gain

amplification factors in adjustable fashion; wherein during a first stage, said first and second amplifier amplify

a DC signal component of said intensity signals in accordance with

predetermined first and second gain amplification factors, said DC

signal component being subtracted from said intensity signals at an

input of said first amplifier, thereby isolating an AC signal component

of said intensity signals,

and whereiri during a second stage, said second amplifier

amplifies said isolated AC signal component in accordance with said

adjustably-determined second gain amplification factor,

said processing step producing output signals in accordance with

said isolated AC signal component and said DC signal component;

and

calculating in accordance therewith, said at least one blood

constituent level.

37. The method according to claim 36 wherein said organ is an internal

organ and wherein said method further includes the step of repeating

said steps of providing light, providing a light detector and processing, at

a plurality of positions along the surface of said internal organ for

mapping the levels of said AC signal component along the surface of said

internal organ to detect regions of reduced blood flow.

38. A method for non-invasively determining the blood flow velocity in a

region of an organ, the method comprising the steps of: positioning a first pulse-oximetry device and a second pulse-oximetry

device proximate the surface of said region, said first and said second

device being separated from each other by a predetermined distance;

simultaneously obtaining a first and a second sets of data representing

the pulsatile variation of the level of oxygen saturation at the locations of

said first and said second device, respectively, as a function of time, each

of said first set and second set of data including at least one extremum

data value, said at least one extremum data value of said first set of data

corresponding to said at least one extremum data value of said second set

of data;

calculating the time interval between said at least one extremum data

value of said first set of data and said at least one extremum data value of

said second set of data;

dividing the value of said predetermined distance by the value of said

time interval to obtain a value representing the approximate blood flow

velocity in said region of said organ,

wherein each of said first device and said second device includes:

at least one light source, providing light directed toward the

surface of said organ, said light being reflected from said organ; a light detector spaced apart from said at least one light source

and being sensitive to intensity levels of said reflected light for

producing intensity signals in accordance therewith; and

a processing unit for processing said intensity signals received

from said light detector, said processing unit comprising:

first and second amplifiers for amplifying said intensity

signals, each in accordance with a respective first and

second gain amplification factor; and

a processor for automatically determining said first and

second gain amplification factors in adjustable fashion;

wherein during a first stage, said first and second amplifiers

amplify a DC signal component of said intensity signals in

accordance with predetermined first and second gain amplification

factors, said amplified DC signal component being subtracted from

said intensity signals at an input of said first amplifier, to isolate an

AC signal component of said intensity signals,

and wherein during a second stage, said second amplifier

amplifies said isolated AC signal component in accordance with said

adjustably-determined second gain amplification factor,

said processing unit producing output signals in accordance with said

isolated AC signal component and said DC signal component and

calculating in accordance therewith, said level of oxygen saturation.

39. The method according to claim 38 wherein said organ is the skin.

40. The method according to claim 38 wherein said at least one extremum

data value is selected from a minimum data value and a maximum data

value.