WO2017042350A1

WO2017042350A1 - Method and system for monitoring ventilatory parameter

Info

Publication number: WO2017042350A1
Application number: PCT/EP2016/071330
Authority: WO
Inventors: Michel Petitjean; Marcel BONAY; Pauline NIEDZIALKOWSKI; Yann RETORY; Carole DE PICCIOTO
Original assignee: INSERM (Institut National de la Santé et de la Recherche Médicale); Assistance Publique Hopitaux De Paris; Universite De Versailles Saint-Quentin-En-Yvelines
Priority date: 2015-09-11
Filing date: 2016-09-09
Publication date: 2017-03-16

Abstract

METHOD AND SYSTEM FOR MONITORING VENTILATORY PARAMETER Method for monitoring ventilatory quantitative parameters of a person, the method comprising the following steps of performing measurements of breathing-dependant body deformations of the person during breathing, of collecting body deformation data during a time period from said measurement, of performing measurements of a breathing-related physiological parameter of the person, of collecting breathing-related physiological parameter data during the time period from said measurements, of filtering person exercise artifacts out of said body deformation data, using said breathing-related physiological parameter data, thereby generating filtered data and collecting said filtered data, and of calculating ventilatory quantitative parameters of the person from said filtered data.

Description

METHOD AND SYSTEM FOR MONITORING VENTILATORY PARAMETER

FIELD OF THE INVENTION

The instant invention relates to tidal breathing recording. Tidal breathing recording can be used for example for patients of reduced exercise capacity being evaluated for respiratory problems. BACKGROUND OF THE INVENTION

In particular, the instant invention is related to a method for monitoring ventilatory quantitative parameters of a person.

From the prior art, conventional spirometric methods involving pneumotachometers are used in pulmonary testing laboratories to record respiratory flows and to estimate tidal volumes. However, those methods usually require mouthpieces or facemasks, known to introduce biases on respiratory patterns. Moreover, it is often relevant to monitor breathing while the patient is active and, especially, moving.

The aim of the invention is to provide a more reliable measurement of tidal breathing, especially when exercising.

SUMMARY OF THE INVENTION

To this aim, the invention relates to a method for monitoring ventilatory quantitative parameters of a person, the method comprising the following steps:

- performing measurements of breathing-dependant body deformations of the person during breathing,

- collecting body deformation data during a time period from said measurements,

- performing measurements of a breathing-related physiological parameter of the person, - collecting breathing-related physiological parameter data during the time period from said measurements,

- filtering person exercise artifacts out of said body deformation data, using said breathing-related physiological parameter data, thereby generating filtered data and collecting said filtered data,

- calculating ventilatory quantitative parameters of the person from said filtered data.

This method, performing measurements of the body deformation, enables assessing tidal ventilation for a user during submaximal exercise, minimizing biases in the measurement. Moreover, the influence of specific exercise artifacts, due to tissue motions induced by heel strike or arm swing for example, contaminating the respiratory signal, is reduced with the filtering step. The filtered data may enable to obtain a more accurate estimation of tidal ventilatory quantitative parameter changes.

In some embodiments, one might also use one or more of the following features:

- the body deformations comprise thoracoabdominal perimeter changes;

- the physiological parameter of the person comprises the nasal pressure;

- the physiological parameter of the person comprises the nostril and mouth air temperature;

- the method comprises a calibration step wherein filtered data are calibrated on values of the ventilatory quantitative parameter, the breathing- dependant body deformations and the ventilatory quantitative parameter of the person being simultaneously measured in this calibration step; - the ventilatory quantitative parameter comprises the airflow;

- the ventilatory quantitative parameter is the inspiratory duration and/or expiratory duration.

According to another aspect of the present invention, it is disclosed a monitoring system for monitoring ventilatory quantitative parameters of a person, said monitoring system comprising :

a first device adapted to perform measurements of breathing-dependant body deformations of the person during breathing, and to collect breathing-dependant body deformation data during a time period from said measurements, and to provide body deformations data, a second device adapted to perform measurements of a breathing-related physiological parameter of the person, and to collect breathing-related physiological parameter data during the time period from said measurements ,

a filtering device adapted to receive said breathing- dependant body deformation data and said breathing- related physiological parameter data,

and adapted to filter person exercise artifacts out of said body deformation data, using said breathing- related physiological parameter data,

to generate and collect filtered data,

a calculator device adapted to calculate the ventilatory quantitative parameters of the person from said filtered data.

In some embodiments, one might also use one or more of the following features:

the first device comprises a sensor device set on the thorax of the person, the sensor device being adapted to detect the body deformation of the person during inspiration and expiration phases;

the first device is a respiratory inductive plethysmography device and the sensor device is a thoracic belt set around the thorax of the person, the thoracic belt connected to a polygraph;

the second device comprises a nasal pressure sensor, the nasal pressure sensor comprising a nasal sensor device, the nasal sensor device comprising a nasal cannula equipping the person;

the second device comprises a temperature sensor, the temperature sensor comprising a temperature sensor device, the temperature sensor device comprising a probe set at the nose and mouth entrance of the person ;

the monitoring system also comprises a calibration device, the said calibration device comprising a sensor sensing a ventilatory quantitative parameter, said calibration device being also adapted to collect said filtered data or said body deformation data, said calibration device being also adapted to provide a calibration law connecting body deformation data to values of the ventilatory quantitative parameter;

the sensor is a pneumotachometer , said sensor being adapted to perform measurements of the instantaneous air flowing through the mouth of the person;

the body deformations data are collected at a sampling frequency of 20 - 1000 Hz and the physiological parameter data are collected at a sampling frequency of 200- 1000 Hz. BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will readily appear from the following description of one of its embodiments, provided as a non-limitative example, and of the accompanying drawings .

On the drawings :

Fig. 1 is a schematic diagram of a monitoring device according to one embodiment,

Fig.2 is a diagram similar to Figure 1, but with more details,

Figs. 3 and 4 are schematic views of two embodiments of some parts of the monitoring device of Figs. 1 and 2,

Figs. 5a-5c are time-domain graphs illustrating an example of a filtering step,

Figs. 6a-6c are time-domain graphs illustrating another example of a filtering step.

On the different Figures, the same reference signs designate like or similar elements.

DETAILED DESCRIPTION

In a general overview of the invention, the body deformations of a person, exercising for example, are monitored to assess tidal ventilatory parameters of the person. The body deformation data 10 are filtered using simultaneously-collected values of a breathing-related physiological parameter 20 of the person. These body deformation filtered data 50 are then used to extract ventilatory quantitative parameters 60 for the exercising person.

The monitoring device is for example used during a six minutes walking test to obtain ventilatory parameters of the person, for evaluating submaximal exercise capacity for example.

The method for monitoring ventilatory quantitative parameters 60 of a person comprises several steps.

As illustrated on figure 1 , a first device 1 is adapted to perform measurements of breathing-dependent body deformations of the person during breathing, notably during inspiration and expiration phases. This first device 1 collects those body deformation data 10 during a time period At. The body deformations could be thorax deformations. More precisely, it could be thoracoabdominal perimeter changes. As illustrated on figure 2, this first device 1 comprises a sensor device 1' set on the thorax of the person, the sensor device 1' being adapted to detect the body deformations of the person during inspiration and expiration phases.

In an embodiment, illustrated on figure 3 , the first device 1 is a respiratory inductive plethysmography (RIP) device comprising a sensor device 1', the sensor device 1' being a thoracic belt set around the person's thorax, the thoracic belt being connected to a polygraph 500.

The respiratory inductive plethysmography device relies on measurements of the variations of current induced in coils surrounding the person's thorax by an alternating magnetic field, which is a function of the surface area encircled by the coil, during inspiration and expiration phases. The variation of current is converted in a variation of potential for a given resist value. Alternatively or additionally, such coils could be installed around the abdomen. More precisely, the respiratory inductance plethysmography device can comprise two sinusoid wire coils insulated from one another and placed within two 2.5 cm wide, lightweight elastic and adhesive bands. The transducer bands are placed around the rib cage under the armpits for exemple or around the abdomen at the level of the umbilicus for example. Bands are connected to an oscillator and subsequent frequency demodulation electronics to obtain digital waveforms. During inspiration, the cross-sectional area of the ribcage or of the abdomen increases, altering the self-inductance of the coils and the frequency of their oscillation. The electronics convert this change in frequency to a digital respiration waveform where the amplitude of the waveform is proportional to the inspired breath volume.

The thorax deformation data 10 are collected with the polygraph 500 during the time period At, at a sampling frequency of 20- 1000 Hz.

The above method works well when the patient is still. However, it is often required to monitor breathing of an exercising patient. A typical exercise includes walking. As the respiratory inductance plethysmography signal can be easily contaminated by motion artifacts during walking (exercising artifacts), the present method uses a simultaneous monitoring of a breathing-related physiological parameter, less sensitive to exercising motions as a time reference for the filtering step. By itself, this breathing-related physiological parameter does not enable to provide relevant ventilatory quantitative parameter of the person.

For example, the physiological parameter data 20 gives a time reference for identification of respiratory cycles. This temporal reference allows exclusion of exercising artifacts by keeping only maximum and minimum values localized on ranges corresponding to respiratory cycles on physiological parameter signal (exemplary algorithm described below) .

As illustrated on figure 1, the monitoring device thus also comprises a second device 2. During the same time period At, the second device 2 measures the physiological parameter of the person and collects physiological parameter data 20 during this time period At.

In an embodiment illustrated on figure 3, the physiological parameter of the user comprises the nasal air pressure. The second device 2 comprises a nasal pressure sensor less sensitive to exercising motions, the nasal pressure sensor comprising a nasal sensor device 2', the nasal sensor device 2' comprising a small nasal cannula equipping the person. Nasal pressure is recorded with the polygraph 500, allowing measurement of nasal pressure at a sampling frequency of 200Hz and above. Alternatively, the physiological parameter of the user is the nose and mouth air temperature (air temperature at the nasal and oral entrance) , less sensitive to exercising motions and allows exclusive mouth breathing.

In another embodiment illustrated on figure 4, the second device 2 is a temperature sensor, the temperature sensor comprising a temperature sensor device 2'', the temperature sensor device 2 ' ' comprising a probe set at the mouth and nose of the person. The temperature is recorded with the polygraph 500, allowing measurement of temperature at a sampling frequency of 200 Hz or above.

The collected thorax deformations data 10 are filtered, using the physiological parameter data 20, to remove artifacts from thorax deformations data 10. The nasal pressure signal for example is used as a time reference for identification of respiratory cycles on thoracoabdominal signals, to remove artifacts from the respiratory inductive plethysmography signals. More precisely, this temporal reference allows exclusion of artifacts by keeping only maximum and minimum values localized on ranges corresponding to respiratory cycles on nasal signal (an exemplary algorithm is described below) .

Data from respiratory inductive plethysmography (thoracic signal) and nasal pressure are analyzed off line, for example after the end of the exercise, by extracting them from the polygraph 500 by using a dedicated software. Data are then converted into ASCII format in order to be importable in the software. The monitoring device comprises a filtering device 5 to perform these calculations. The filtering device 5 runs an algorithm designed in time domain to remove artifacts.

An example of this algorithm in case of a respiratory inductive plethysmography first device 1 and a nasal pressure signal sensor 2 is illustrated on figures 5a-5c.

Fig. 5a is a graph representing the breathing- related physiological parameter data 20, in the present example as the measured nasal pressure (expressed in cm H₂0) as a function of time (expressed in seconds) . This figure shows only a little part of the physiological parameter data 20, which can be collected during many minutes .

Fig. 5b is a graph representing the body deformation data 10, in the present example as a measured tension (expressed in micro-Volts) as a function of time (expressed in seconds) . This figure shows only a little part of the body deformation data 10, which can be collected during many minutes. Especially, the times of Figs. 5a and 5b are synchronized, for example by collecting data with the same polygraph.

Fig. 5c corresponds to Fig. 5b to which filtered data are superimposed.

The first step (figure 5a) is to determine the time (a, b) of the onset of each respiratory cycle based on the nasal pressure signal, characterized by a zero-crossing value going positive as:

. r ^xi ≥ o

I H - l< 0

where x_± is the value x of nasal pressure signal for time index i corresponding to the onset of a respiratory cycle.

The second step (figure 5b) is to search for local maximums (M) of the respiratory inductive plethysmography signal between respiratory cycle onsets t_Q determined in the first step as:

Vx-e [a, b] , f(x) < f(M)

where a and b are time indices of the respiratory inductive plethysmography signal corresponding to onsets of two consecutive respiratory cycles of the nasal pressure signal. M is the local maximum of a respiratory cycle on the respiratory inductive plethysmography signal, and the time t_M at which M is measured can also be recorded.

The third step (figure 5c) is to determine local minimum values (m) between maximum values found in second step as:

V e [c, d], f (x)≥ f (m)

where c and d are time indices corresponding to two consecutives local maximums determined in the previous step and m is the local minimum of a respiratory cycle on the respiratory inductive plethysmography signal. The time t_m at which m is measured can also be recorded.

By keeping only local minimums m and maximums M determined in the previous steps, a filtered curve can be generated by straight lines as shown on Fig. 5c. Artifacts, which are of smaller amplitude, are not taken into account for calculation of ventilatory parameters.

In another embodiment, illustrated on figures 6a- 6c, one uses a database of signals in order to provide the filtered data. The database is shown on Fig. 6b and comprises many candidates l_lr 7₂, 7₃, ... of plethysmography data which can be associated to the reference nasal pressure cycle. One first step is to determine the onset of respiratory cycles like above. One may also use the maximum value for the nasal pressure data, so as to provide a descriptor of the nasal pressure data, as shown on Fig. 6a superimposed on the actual signal. The algorithm could thus comprise a characterization step of all respiratory cycles through the nasal signal (figure 6a - in dotted line except for one of the signals where it is shown in straight lines) . The next step is to characterize every possible cycle of respiratory inductive plethysmography signal, whatever the amplitude might be (figure 6a - bottom) . Then, a selection step relies on a comparison based on similarity between nasal signal reference (top of Fig. 6b), and the candidates of the database (figure 6b - bottom) . Any suitable distance could be applied. The selected candidate 7₃ is framed on Fig. 6b. The selected filtered plethysmography signal for the cycle is shown superimposed on the actual signal on figure 6c. (

In either embodiment, the monitoring device comprises a calculator device 6 to determine ventilatory quantitative parameters of the person. After the artifact removal step, ventilatory quantitative parameters 60 are calculated from the filtered data 50 by the calculator device 6. Ventilatory quantitative parameters comprise for example the inspiratory time duration (Ti), the expiratory time duration (Te) , the tidal volume (V_t) and/or combinations thereof, determined as explained below. These parameters could be determined for each breathing cycle, as a function of time. Alternatively, other treatments can be applied, such as averages, maximum, minimum, differences between maximum and minimum, evolution with time, ...

To determine the tidal volume (V_t) , a calibration step can be used. Filtered data 50 are calibrated on values of a ventilatory quantitative parameter 30, the filtered data 50 and the ventilatory quantitative parameter 30 of the user being simultaneously measured in this calibration step. The ventilatory quantitative parameter 30 is for example the airflow.

The monitoring device comprises a calibration device 3, said calibration device 3 comprising a sensor 4 sensing a ventilatory quantitative parameter 30. The sensor can be a pneumotachometer for example, for an airflow measurement. The pneumotachometer is adapted to perform measurements of the instantaneous air flow flowing through the mouth of the person. The calibration device 3 is adapted to collect data from the sensor 4, the calibration device 3 being also adapted to collect body deformation data. Using various respiration cycles, and the measured deformation data and associated measured value for the ventilatory quantitative parameter, the said calibration device 3 establishes a calibration law connecting body deformations data to values of the ventilatory quantitative parameter . Note that this calibration step is carried out before starting the monitoring described above. Especially, during calibration, the body deformation is monitored as the person is not walking. In other words, body deformation data during the calibration process is not filtered, but is similar to the filtered data (since during calibration, no exercising movement is performed, and since the filtering aims at removing the exercising movement artefact) . The calibration step can be carried out both before and after the exercise to check that the law established before the exercise is still applied after the exercise (the law may unfortunately have changed due to permanent moves of the body deformation measurement system during the exercise) . If the calibration step performed after exercise reveals a change of law, compared to the one performed before exercise, the exercise data might be discarded.

The calibration is carried out by simultaneously measuring volume change by the pneumotachometer and perimeter change by the respiratory inductive plethysmography measurement, while the subject remained standing still for example. The relationship between the perimeter changes measured by respiratory inductive plethysmography and the volume measured by the pneumotachometer can be determined by hypothesizing a linear regression model, or any law deemed suitable. Slopes of these relationships are calculated a posteriori to predict volumes changes from perimeter changes between calibration maneuvers.

Other ventilatory quantitative parameters may include inspiratory and expiratory durations.

The difference between end and onset of inspiratory phase reveals inspiratory duration (Ti), whereas the difference between end of expiratory time and end of inspiratory time reveals expiratory duration (Te) .

The above-describes process could be applied for these parameters as well, and/or to combinations of these parameters .

At rest the tidal volume may vary around 500 ml related to biometrics parameters like height or ribcage geometry. At rest, the inspiratory time may vary around 1 second whereas the expiratory time may vary around 2 seconds.

In a variant, the monitoring device may additionally comprise an associated accelerometer , acting as an activity witness, to discriminate rest from walking, the data from actimetry being for example collected by using the accelerometer included in the polygraph, at a sampling frequency of 10 Hz. The accelerometer could therefore be used by the system to discriminate the calibration step from the exercise time in an automatic process .

In another embodiment, a capnograph could be added to the monitoring device for monitoring the partial pressure of carbon dioxide (C02) in the respiratory gases. It would provide a direct monitoring of the inhaled and exhaled partial pressure of C02, and an indirect monitoring of the C02 partial pressure in the arterial blood. This additional measurement provides additional information on the spontaneous breathing of the person. This information can be used along with or in place of the nasal pressure measurement data as a guide for filtering the body deformation data.

In another embodiment, a transcutaneous C02 pressure monitoring equipment could be added to the monitoring device.

In another embodiment, a Sp02 ear captor could be added to the monitoring device to improve oximetry data because the ear signal is less contaminated by arm swing.

Claims

1. A method for monitoring ventilatory quantitative parameters (60) of a person,

the method comprising the following steps:

A/ performing measurements of breathing-dependant body deformations of the person during breathing,

B/ collecting body deformation data (10) during a time period from said measurement,

C/ performing measurements of a breathing-related physiological parameter of the person,

D/ collecting breathing-related physiological parameter data (20) during the time period from said measurements ,

E/ filtering person exercise artifacts out of said body deformation data, using said breathing-related physiological parameter data (20), thereby generating filtered data (50) and collecting said filtered data (50) ,

F/ calculating ventilatory quantitative parameters (60) of the person from said filtered data (50) .

2. A method according to claim 1, wherein body deformations comprise thoracoabdominal perimeter changes.

A method according to any of claims 1 to 2, wherein the physiological parameter of the person comprises the nasal pressure.

4. A method according to any of claims 1 to 3, wherein the physiological parameter of the person comprises the nostril and mouth air temperature.

A method according to any of claims 1 to 4, comprising a calibration step before the step F/,

Wherein, during step F/ filtered data (50) are calibrated on values of the ventilatory quantitative parameter (30),

the breathing-dependant body deformations and the ventilatory quantitative parameter (30) of the person being simultaneously measured in this calibration step .

A method according to claim 5, wherein the ventilatory quantitative parameter (30) comprises the airflow.

A method according to any of claims 1 to 6, wherein a ventilatory quantitative parameter (60) is the inspiratory duration and/or expiratory duration.

8. A monitoring system for monitoring ventilatory quantitative parameters (60) of a person,

said monitoring system comprising:

- a first device (1) adapted to perform measurements of breathing-dependant body deformations of the person during breathing, and to collect breathing-dependant body deformation data (10) during a time period from said measurements, and to provide body deformations data (10),

a second device (2) adapted to perform measurements of a breathing-related physiological parameter of the person, and to collect breathing-related physiological parameter data (20) during the time period from said measurements ,

a filtering device (5) adapted to receive said breathing-dependant body deformation data (10) and said breathing-related physiological parameter data (20) ,

and adapted to filter person exercise artifacts out of said body deformation data (10), using said breathing- related physiological parameter data (20),

to generate and collect filtered data (50),

a calculator device (6) adapted to calculate the ventilatory quantitative parameters (60) of the person from said filtered data (50) .

A monitoring system according to claim 8 wherein the first device (1) comprises a sensor device ( 1 ' ) set on the thorax of the person, the sensor device ( 1 ' ) being adapted to detect the body deformation of the person during inspiration and expiration phases.

A monitoring system according to claim 9, wherein the first device (1) is a respiratory inductive plethysmography device and the sensor device ( 1 ' ) is a thoracic belt set around the thorax of the person, the thoracic belt connected to a polygraph.

A monitoring system according to any of claims 8 to 10 wherein the second device (2) comprises a nasal pressure sensor, the nasal pressure sensor comprising a nasal sensor device (2'), the nasal sensor device (2') comprising a nasal cannula equipping the person. A monitoring system according to any of claims 8 to 11 wherein the second device (2) comprises a temperature sensor, the temperature sensor comprising a temperature sensor device (2''), the temperature sensor device (2'') comprising a probe set at the nose and mouth entrance of the person.

13. A monitoring system according to any of claims 8 to 12 also comprising a calibration device (3), the said calibration device (3) comprising a sensor (4) sensing a ventilatory quantitative parameter (30), said calibration device (3) being also adapted to collect said filtered data (50) or said body deformation data (10),

said calibration device (3) being also adapted to provide a calibration law connecting body deformation data to values of the ventilatory quantitative parameter (30).

A monitoring system according to claim 13 wherein the sensor (4) is a pneumotachometer , said sensor being adapted to perform measurements of the instantaneous air flowing through the mouth of the person.

A monitoring system according to any of claims 8 to 14 wherein the body deformations data (10) are collected at a sampling frequency of 20 - 1000 Hz and the physiological parameter data (20) are collected at a sampling frequency of 200- 1000 Hz.