CN100407993C - Digital signal process method for light- frequency conversion type pulse blood oxygen instrument - Google Patents
Digital signal process method for light- frequency conversion type pulse blood oxygen instrument Download PDFInfo
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Abstract
A method for processing the digital signals of a light-frequency conversion type pulse oxyhemograph includes such steps as using a light-frequency converter to directly convert the light signals received by human tissue to the electric pulse signals, using microprocessor to count the electric pulse signals and time, and calculation to digital signals to obtain the blood oxygen saturation degree and cardiac rhythm value.
Description
Technical field
The present invention relates to the digital signal processing method of digital pulse blood oxygen instrument, particularly a kind of digital signal processing method of light-frequency conversion type pulse blood oxygen instrument.
Background technology
Pulse blood oxygen instrument is a kind of medical instrument that does not have wound, continuously monitoring human body arterial oxygen saturation, has become the conventional configuration device of anaesthetizing monitoring and Intensive Care Therapy in the hospital, also is widely used in various mobile monitorings and sleep monitoring outside the hospital.The development of family and community medicine health care system has proposed new requirement to the design and the manufacturing of pulse blood oxygen instrument, and promptly wishing to provide low price, high performance Worn type pulse blood oxygen instrument to be widely used in family and community medicine net.
The operation principle of pulse blood oxygen instrument is according to HbO2 Oxyhemoglobin (HbO
2) with reduced hemoglobin (Hb) HONGGUANG and near infrared light are had different absorption Spectrum characteristic, light with two bundle different wave lengths, as the HONGGUANG of 660nm and the positions such as near infrared light human finger, toe or ear-lobe of 940nm, survey the photoelectricity volume pulsation wave intensity of transmission (or reflection) by light-sensitive element.This class is organized the line and staff control that all is made up of skin, blood, muscle, skeleton etc., and light is to go up less flutter component of superposition (also being called AC compounent AC) at a very big stable component (or claiming DC component DC) by the feature of the photoelectricity volume pulsation wave that this class tissue forms.Its AC compounent is because the blood engorgement tremulous pulse causes, DC component then is blood flow when crossing tremulous pulse, and by non-pulsation part, promptly tissues such as muscle, venous blood, skin, skeleton are to the absorption result of light.Can obtain four variablees by measurement, i.e. HONGGUANG DC component RD_DC, HONGGUANG AC compounent RD_AC, infrared DC component IR_DC and infrared AC compounent IR_AC to the photoelectricity volume pulsation wave of two-beam.Can calculate so-called R-R ratio by these four amounts:
R-R＝(RD_AC/RD_DC)/(IR_AC/IR_DC)
For the pick off of specific emission wavelength configuration, R-R ratio and arterial oxygen saturation have a specific functional relationship.This functional relationship is difficult to express with theoretical formula, generally is by clinical and have wound method control experiment to obtain the calibration curve that the calibration data are drawn out R-R ratio and arterial oxygen saturation relation.The data of calibration curve can be stored in the digital signal processing unit of pulse blood oxygen instrument with the mode of tabulation.Instrument is after measurements and calculations go out R-R ratio, and available look-up method is obtained the arterial oxygen saturation value.
In order to reduce of the influence of factors such as motion artifact and interior external interference to measurement result, can also introduce the three-beam of (for example 880nm) that has specific wavelength or the light beam of more specific wavelengths, the influence that solves variable to be measured and remove disturbance variable according to its mathematical relationship.
Because the difference of human body each several part tissue to be measured and human body individuality, the excursion of photoelectricity volume pulsation wave DC component itself just reaches 100～200 times, and synergetic AC compounent excursion is generally 0.5%～20% of DC component on it.The specialty pulse blood oxygen instrument designing requirement be when AC compounent be DC component 0.1% the time also can trace pulse wave preferably, detect heart rate and calculating detecting sphygmus and blood oxygen saturation.Like this, directly all very high to dynamic range, resolution and the signal to noise ratio of measuring system from primary photoelectricity volume pulse wave measurement alternating current-direct current component.
The signal processing method that early stage analog pulse blood oxygen instrument is taked is to shine tissue to be measured with time-multiplexed HONGGUANG and infrared light pulse signal sequence, with current-to-voltage convertor the detected photoelectric current pulse signal of light-sensitive device is converted to voltage pulse signal, time-multiplexed HONGGUANG is separated with the infrared light pulse sequence, respectively two-way pulse train is reduced to successive volume ripple signal with high-order low-pass filter then, at last the alternating current-direct current component on each road is separated and the gain of regulating each road is respectively satisfied the requirement of follow-up analog-digital converter certainty of measurement to guarantee signal amplitude.The gain-adjusted of direct current channel also can partly or entirely replace with regulating the method that drives light intensity.The shortcoming of this method is the analog circuit complexity, the parameter matching requirement height of each analog channel, and the performance indications that reached also are very limited.
At this defective of board design, people begin to attempt directly the detected photoelectric current pulse signal of light-sensitive device being converted to digital signal with high-resolution analog-digital converter, and process after this can be finished by Digital Signal Processing.Want the direct requirement that the detected photoelectric current pulse signal of light-sensitive device is converted to digital signal and satisfies certainty of measurement, the resolution of the analog-digital converter that is adopted will reach 20 at least, is preferably in more than 22.Though the Sigma-Delta ∑-Δ pattern number converter that generally uses can satisfy the requirement of voltage resolution at present, because its lag characteristic when pulse signals is sampled has limited the application in this occasion.Existing digital pulse blood oxygen instrument still adopts the pattern number converter relatively one by one more than 16, and for denoising with improve interference free performance, the signal input stage before the analog-digital converter often adopts charge integrator to replace current-to-voltage convertor.For remedying the deficiency of system dynamics scope, just selected 20 charge integration pattern number converters as Chinese invention patent ZL99813986.6 disclosed " Direct Digital formula blood oxygen instrument and be used for the method for calculating oxygenation levels value ", the method for regulating the drive current of luminous tube with digital to analog converter simultaneously and adding controlled diverter before analog-digital converter strengthens the system dynamics scope.This Design of digital scheme has been simplified hardware designs and debugging, has improved systematic function, but because the high-resolution analog-digital converter price that adopted is higher, so this design also lacks cost advantage to the application scenario of community medicine and family health care.
The other method of Direct Digital pulse blood oxygen instrument design is directly will convert its frequency and transmission (or reflection) the proportional electric impulse signal of light intensity from the optical signal that tissue receives to light frequency converter (LFC), electric impulse signal is carried out frequency counting and carries out digital signal processing, obtain blood oxygen saturation and heart rate value.Document JeffBachiochi, TSL230R-Based Pulse Oximeter, CIRCUITCELLAR, Issue 173, and December 2004, introduced the experimental program of this design among the P26..This scheme adopts decide sampling time driven for emitting lights diode and simultaneously the pulse of LFC output is counted, and the step-by-step counting meansigma methods in usefulness continuous sampling cycle is represented DC component, and the variable quantity of each sampling period counted number of pulses is then represented AC compounent.But the frequency range of present available LFC is below the 1MHz, in order under limited LFC output impulsive condition, to obtain enough resolution to AC compounent, testing program has been selected 31.25 milliseconds sampling time for use, selects for use manual mode to regulate the luminous tube drive current to guarantee obtaining suitable counted number of pulses in the sampling time simultaneously.What the document provided obviously only is the most preliminary a kind of conception, and for practical application, Chang sampling time all is unacceptable to certainty of measurement and power consumption like this, and the adjusting of dynamic range also must be carried out automatically in real time by measuring system.If the method that adopts the pulse period to measure replaces the frequency measurement method of above-mentioned document, the feasible LFC output pulse of organizing for any thickness of drive current that then will regulate luminous tube automatically all has the precision that enough width are measured with hold period, but accomplish this point, when when measuring than thin tissue, the drive current of luminous tube and pulsed light intensity can be adjusted to very little value, and this will cause the serious reduction of signal to noise ratio.Timing resolution is low more, and desired pulse width values is big more, and the decline of signal to noise ratio is also serious more.Therefore, adopt the Direct Digital pulse blood oxygen instrument of LFC will reach the actual applicable degree of energy, solve because the problems such as power consumption, pulse wave detection sensitivity and dynamic range adjustment that the restriction of LFC inversion frequency brings with regard to needs.
Summary of the invention
The inversion frequency scope that the present invention is directed to existing LFC limits the measuring technique difficulty of being brought, a kind of digital signal processing method based on fixed number train of pulse accumulation timing has been proposed, this method can effectively solve the problem of speed, power consumption and dynamic range adjustment that aforementioned measurement LFC output pulse frequency and period measurement run into, and available very low cost has reached the requirement of certainty of measurement under professional pulse blood oxygen instrument noiseproof feature and the weak perfusion condition.
Another object of the present invention provides a kind of light-frequency change type digital pulse blood oxygen instrument of realizing said method.
For reaching above purpose, the present invention takes following technical scheme to be achieved:
A kind of digital signal processing method of light-frequency conversion type pulse blood oxygen instrument comprises the steps:
A. behind the instrument electrification reset, microprocessor is preset a train of pulse predetermined count value CNT0, drive red light-emitting pipe and infraluminescence pipe successively by I, II sequential, measure the corresponding light frequency transducer LFC output pulse period, just obtain predetermined count value RD_CNT and IR_CNT respectively divided by the light frequency transducer LFC output pulse period corresponding to HONGGUANG and infrared light with the intermediate value of being scheduled to timing window T ± Δ T.
B. in the follow-up sampling period, microprocessor drives red light-emitting pipe and infraluminescence pipe successively and the train of pulse of light frequency transducer LFC output is carried out the pulse stored counts simultaneously and catches timing.
C. when counted number of pulses reaches predetermined number RD_CNT and IR_CNT respectively, microprocessor is just write down the driving of catching clocking value and stopping corresponding luminous tube immediately, catches accumulative total cycle that clocking values equal the HONGGUANG of predetermined number and infrared light pulse string respectively when accounting for for resulting two.
D. export T_DARK remaining time in sampling period of pulse III sequential at the light frequency transducer, the low-frequency pulse string that dark current is produced carries out the pulse capture counting, when this end cycle, write down and catch count value DARK_CNT, by data computation, draw the alternating current-direct current component of cycle, frequency and the representative of light frequency transducer LFC output pulse by microprocessor.
E. in measuring process, the dynamic range of photoelectricity volume pulse wave measurement is carried out regulating in real time automatically, promptly in each sampling period, whether drop among timing window T ± Δ T when all detecting the accounting for of light frequency transducer output pulse string.In this window, measurement will normally be carried out, and calculate predetermined count value RD_CNT and IR_CNT again otherwise will return step a when the accounting for of train of pulse.
Among the above-mentioned steps a, the obtaining value method of time window T ± Δ T is: intermediate value T should guarantee that there are enough timing resolution and lower power consumption in system, and the ratio of Δ T and intermediate value T should be greater than 20%.
In steps d, the present invention gives according to fixed number train of pulse accumulation clocking value to come computed volume pulse wave intensity and eliminate a kind of data fast algorithm that dark current influences, if the predetermined count value corresponding to HONGGUANG and infrared light pulse string is RD_CNT and IR_CNT, to arbitrary sampling period n, measured HONGGUANG and infrared light pulse string accumulative total are T_RD (n) and T_IR (n) when accounting for, the time that the low-frequency pulse string of dark current generation is counted is T_DARK (n), count value is DARK_CNT (n), then HONGGUANG and infrared light the value of calculation of the corresponding sampled point n of pulse frequency be respectively:
RD_X(n)＝K*RD_CNT/T_RD(n)-K*DARK_CNT(n)/T_DARK(n)
IR_X(n)＝K*IR_CNT/T_IR(n)-K*DARK_CNT(n)/T_DARK(n)；
In the formula, subtrahend is the pulse wave amplitude sampled value error term of the pulse frequency representative of dark current generation, minuend is the pulse wave amplitude sampled value of the pulse frequency representative that records between action period of driving pulse, and COEFFICIENT K is a constant relevant with the timer clock frequency; The value of K should be a size to fit, the non-vanishing hexadecimal number of highest order only, make in the above-mentioned formula every multiplying can by minority several times simple shift realize, can guarantee operational precision again.
Advantage of the present invention is: pulse blood oxygen instrument to the Measurement Resolution of transmission (or reflection) light intensity only depend on system to the accuracy of timekeeping of T ± Δ T and and the LFC output frequency irrelevant.For example, the present invention can adopt general 8MHz clock frequency, timing resolution is the low price microprocessor of 125ns, as long as the timing window of T ± Δ T=1 ± 0.3ms is set and determines RD_CNT and IR_CNT thus, then no matter how many LFC output pulse periods is, can both guarantee the timing resolution of system to the fixed number train of pulse, promptly the Measurement Resolution to the pulsation light intensity reaches more than 0.02%.Obviously, pulse blood oxygen instrument by concept of the present invention does not need to regulate the driving light intensity, this has also simplified design, improved signal to noise ratio, assurance can use the limited operational capability of low price microprocessor and memory source to realize the real-time processing of measurement data and the real-time demonstration and the transmission of pulse frequency and blood oxygen levels.
Therefore in addition, blood oxygen instrument of the present invention has only been used a LFC device and a microprocessor, has that volume is little, cost and an advantage low in energy consumption, is particularly suitable for the application scenario of community health and mobile monitoring.
Description of drawings
Fig. 1 is a light-frequency conversion type digital pulse blood oxygen instrument structured flowchart of the present invention.
Fig. 2 is the driving pulse of luminous tube and the sequential chart of corresponding light frequency transducer output pulse.Wherein I is a red light-emitting pipe driving pulse; II is an infraluminescence pipe driving pulse; III is a light frequency transducer output pulse string.
The specific embodiment
The present invention is described in further detail below in conjunction with drawings and Examples:
As shown in Figure 1, a kind of light-frequency conversion type digital pulse blood oxygen instrument, comprise red light-emitting pipe 3, infraluminescence pipe 4, liquid crystal display 6, described red light-emitting pipe 3, infraluminescence pipe 4 is electrically connected with the two-way output of luminous tube driver 2 respectively, the input of luminous tube driver 2 is connected with microprocessor 1 signal, this microprocessor 1 is one and includes seizure logic interfacing, the microprocessor of USB (universal serial bus) and liquid crystal display drive circuit, the seizure logic interfacing of microprocessor 1 connects light frequency transducer 5, the liquid crystal display drive output port of microprocessor 1 connects liquid crystal display 6 display driver input ports, the USB (universal serial bus) of microprocessor 1 can connect central processing system or wireless transmitting unit, when measuring, tissue 7 places red light-emitting pipe 3, between infraluminescence pipe 4 and the light frequency transducer 5.
Microprocessor 1 can be any microprocessor of catching logic interfacing, USB (universal serial bus) and including liquid crystal display drive circuit that has, and should select the higher system clock frequency as far as possible for use.In the present embodiment, system clock is 8MHz, and timing resolution is 125ns.Microprocessor 1 is periodically exported two pulse signals chronologically, drive red light-emitting pipe 3 successively and infraluminescence pipe 4 is luminous by driver 2, the light pulse of sending is received by light frequency transducer 5 after tissue 7 decay and modulation, and converts the pulse capture input port that frequency and the linearly proportional train of pulse of pulse light intensity are sent to microprocessor 1 to.The train of pulse that microprocessor 1 utilizes clock internal and timer that light frequency transducer 5 is exported carries out stored counts simultaneously and catches timing.When counted number of pulses reaches predetermined number RD_CNT and IR_CNT, write down the driving of catching clocking value and stopping 2 pairs of corresponding luminous tubes of luminous tube driver immediately.Microprocessor 1 calculates corresponding DC component and AC compounent according to detected every road light pulse cycle and undulate quantity thereof, thereby try to achieve volume pulsation wave datum, detecting sphygmus and blood oxygen saturation and heart rate value by common pulse blood oxygen instrument algorithm, the gained result can drive liquid crystal display 6 by liquid crystal display drive circuit on the one hand and show heart rate, blood oxygen saturation and pulse wave rod figure, can send data to central processing system or wireless transmitting unit by general serial line interface on the other hand, realize telemetry function.
Luminous tube driver 2 is made up of two single-pole single-throw(SPST MOS switches, adopts fixed pulse voltage and current drives red light-emitting pipe 3 and infraluminescence pipe 4 luminous.The method of this fixed pulse current drives can be simplified hardware designs, saves volume and cost, is particularly suitable for the Worn type application scenario.Determining of the driving pulse current value of luminous tube driver 2: when measuring the thinnest organizing, the output pulse frequency of light frequency transducer 5 should be in the better linearity scope, in the present embodiment, the output pulse highest frequency of light frequency transducer 5 is defined as 400KHz, and the corresponding output pulse period is 2.5 μ S.Though present embodiment has only provided a kind of specific design of drive circuit, do not get rid of and to select similar fashion realization above-mentioned functions for use or add the 3rd luminous tube as previously mentioned to improve capacity of resisting disturbance.
Further specify the operation principle of fixed number train of pulse accumulation clocking method and the fast algorithm that corresponding digital signal is handled below in conjunction with accompanying drawing 2.
Pulse train I is the red light-emitting pipe driving pulse that microprocessor 1 sends among the figure, and its period T 0 is the sampling period of pulse wave measurement.In order to make measuring system to the power frequency interference that civil power produces the ability that suppresses preferably be arranged, the frequency of this driving pulse is typically chosen in the integral multiple of power frequency.To work frequency is the area of 50Hz, and the optional frequency of this driving pulse is 100Hz, is the area of 60Hz to work frequency, and the frequency of this driving pulse then is chosen as 120Hz.For system clock is 8MHz, and timing resolution is the application scenario of 125ns, and the pulsewidth of this driving pulse is predeterminable to be 1ms, and its pulsewidth fluctuates in can be along with the time window of variation at 1 ± 0.3ms of pulse wave when normal the measurement.
Pulse train II is the infraluminescence pipe driving pulse that microprocessor 1 sends among the figure, and the preset value of its cycle and pulsewidth is the same with the HONGGUANG driving pulse, and there is the time-delay of a 0.2ms in the forward position of this pulse to the tailing edge of HONGGUANG driving pulse.
Pulse train III is the train of pulse of light frequency transducer 5 outputs among the figure.The time of corresponding HONGGUANG and infrared light driving pulse, light frequency transducer 5 will be exported the train of pulse of two string upper frequencies (being about 100KHz usually), represent with two black rectangle among the figure.T_RD and T_IR equal corresponding HONGGUANG and infrared light driving pulse width respectively during the accounting for of this two black rectangle, and the pulse number that is comprised equals HONGGUANG and infrared light pulse predetermined count value RD_CNT and IR_CNT respectively.At the T_DARK remaining time in a sampling period, light frequency transducer 5 will be exported the train of pulse of lower frequency (usually below 100Hz), represent with square wave among the figure.The frequency of this train of pulse and the umber of pulse DARK_CNT that is comprised should eliminate this influence by the dark current and the decision of external interference light intensity of photoelectric device to Measurement and Data Processing the time.
Below describe the fix a number digital signal processing method of train of pulse accumulation timing of the present invention in detail: comprise the steps:
A is behind the instrument electrification reset, microprocessor 1 default train of pulse predetermined count value CNT0, drive red light-emitting pipe 3 and infraluminescence pipe 4 successively by Fig. 2 sequential, measure the 5 output pulse periods of corresponding light frequency transducer, just obtain predetermined count value RD_CNT and IR_CNT divided by the 5 output pulse periods of light frequency transducer corresponding to HONGGUANG and infrared light with the intermediate value 1ms of predetermined timing window 1 ± 0.3ms.
B. in the follow-up sampling period, microprocessor 1 drives red light-emitting pipe 3 and infraluminescence pipe 4 successively by Fig. 2 sequential and the train of pulse of light frequency transducer 5 outputs is carried out the pulse stored counts simultaneously and catches timing,
C. when counted number of pulses reaches predetermined count value RD_CNT and IR_CNT respectively, microprocessor 1 is just write down immediately and is caught clocking value T_RD and T_IR and stop the driving of corresponding luminous tube by luminous tube driver 2, catches accumulative total cycle that clocking values equal the HONGGUANG of predetermined number and infrared light pulse string respectively when accounting for for resulting two.
D. at T_DARK remaining time in sampling period, the low-frequency pulse string that dark current is produced carries out the pulse capture counting, when this end cycle, write down and catch count value DARK_CNT, by these measurement data, microprocessor 1 can be exported the alternating current-direct current component of cycle, frequency and the representative of pulses by calculating light frequency transducer 5.
E. the pulsed light intensity that is received owing to light frequency transducer 5 is the pulsating quantity that changes with pulse wave, so train of pulse accumulative total of its output predetermined number also is a pulsating quantity that changes with pulse wave when accounting for.Data rule of thumb, the flutter component maximum of photoelectricity volume pulsation wave may reach 20% of basic DC quantity.
For this reason, setting a time window in the present embodiment is 1 ± 0.3ms.In each follow-up sampling period, whether drop in this timing window when all detecting the accounting for of light frequency transducer 5 output pulse strings.If in this window, measurement will normally be carried out, and calculate predetermined count value RD_CNT and IR_CNT again otherwise will return step a during the accounting for of train of pulse, this process is the real-time adjustment process of dynamic range of photoelectricity volume pulse wave measurement just.
Be different from the existing pulse blood oxygen instrument that the amplitude of photoelectricity volume pulsation wave is carried out digitized sampling, blood oxygen instrument of the present invention is that the accumulation of fixed number train of pulse is measured when accounting for, this measured value can not the direct representation pulse wave amplitude, need just to obtain representing the amount of pulse wave amplitude through certain calculating.The data processing speed and the certainty of measurement of this additional amount of calculation and system have direct relation.
In the above-mentioned steps d kind, the present invention is according to the data processing method of fixed number train of pulse accumulation clocking value, and a kind of fast algorithm of computed volume pulse wave intensity and the influence of elimination dark current is as follows:
If the predetermined count value corresponding to HONGGUANG and infrared light pulse string is respectively RD_CNT and IR_CNT, to arbitrary sampling period n, measured HONGGUANG and infrared light pulse string accumulative total are T_RD (n) and T_IR (n) when accounting for, the time that the low-frequency pulse string of dark current generation is counted is T_DARK (n), and count value is DARK_CNT (n).Therefore according to the operation principle of light frequency transducer 5, the light intensity of its output pulse frequency and reception is directly proportional, and only requires to such an extent that output pulse frequency just can be represented the relative amplitude of photoelectricity volume pulsation wave.With HONGGUANG and infrared light the value of calculation of the corresponding sampled point n of pulse frequency be made as RD_X (n) and IR_X (n) respectively, then have:
RD_X(n)＝K*RD_CNT/T_RD(n)-K*DARK_CNT(n)/T_DARK(n)
IR_X(n)＝K*IR_CNT/T_IR(n)-K*DARK_CNT(n)/T_DARK(n)
On two equatioies the right, subtrahend is the pulse wave amplitude sampled value error term of the pulse frequency representative of dark current generation, minuend is the pulse wave amplitude sampled value of the pulse frequency representative that records between action period of driving pulse, COEFFICIENT K is a constant relevant with the timer clock frequency, if the absolute value of calculated rate, K equals clock frequency value 8*10
6
Consider K*RD_CNT/T_RD (n) algorithm in the equation.If get K=8*10
6, then K is one 32 a binary number.RD_CNT changes between 0-400, represents with one 16 bit.T_RD (n) also represents with one 16 bit 8000 ± 30% variations.In order not lose Measurement Resolution when the calculated rate, should at first do 16 multiplication of 32 * of K*RD_CNT, do 32/16 divisions then.In each sampling period, also to do similar computing to K*IR_CNT/T_IR (n) and K*DARK_CNT (n)/T_DARK (n).For general low price microprocessor, these additional operands are bigger, may influence the real-time of date processing, need do further simplification.
At first, according to the detecting sphygmus and blood oxygen saturation measuring principle analysis that background technology is introduced, the R-R ratio calculation be that the value of the relative ratio of two-beam alternating current-direct current component and COEFFICIENT K is irrelevant.Therefore we can be taken as a specific number to COEFFICIENT K, make 16 binary multiplications of 32 * of K*RD_CNT to realize with simple displacement.Secondly, the size of COEFFICIENT K is suitable again, as less than the timer clock frequency, pass through the resolution that computing may reduce measurement, and too conference makes K*RD_CNT surpass 32, makes troubles to subsequent treatment.In conjunction with the consideration of two aspects,, the value of K can be decided to be hexadecimal number 800000H for the timer clock frequency of 8MHz.Like this, the computing of K*RD_CNT can be carried out like this: with RD_CNT 7 the high sixteen bits as product that move to left, the low sixteen bit of product is changed to zero; After trying to achieve 32 products of K*RD_CNT, can carry out the result that 32/16 divisions are tried to achieve K*RD_CNT/T_RD (n) computing item by conventional method; In like manner can ask the result of K*IR_CNT/T_IR (n) and K*DARK_CNT (n)/T_DARK (n) computing item; After obtaining RD_X (n) and IR_X (n) value, just can calculate the alternating current-direct current component of two-beam volume pulsation wave as common blood oxygen instrument, obtain detecting sphygmus and blood oxygen saturation and pulse frequency value.If change the requirement of Measurement Resolution or select other timer clock frequency for use, also the K value can be decided to be other only non-vanishing hexadecimal number of highest order.
Claims (5)
1. the digital signal processing method of a light-frequency conversion type pulse blood oxygen instrument is characterized in that, comprises the steps:
A. behind the instrument electrification reset, microprocessor (1) is preset a train of pulse predetermined count value CNT0, drive red light-emitting pipe (3) and infraluminescence pipe (4) successively by I, II sequential, output pulse period when measuring light frequency converter (5) corresponding red light-emitting pipes (3) and infraluminescence pipe (4) are luminous respectively, just obtain predetermined count value RD_CNT and IR_CNT respectively divided by light frequency transducer (5) the output pulse period corresponding to HONGGUANG and infrared light with the intermediate value of being scheduled to timing window T ± Δ T;
B. in the follow-up sampling period, microprocessor (1) drives red light-emitting pipe (3) and infraluminescence pipe (4) successively and the train of pulse of light frequency transducer (5) output is carried out the pulse stored counts simultaneously and catches timing;
C. when counted number of pulses reaches predetermined number RD_CNT and IR_CNT respectively, microprocessor (1) is just write down the driving of catching clocking value and stopping corresponding luminous tube immediately, catches accumulative total cycle that clocking values equal the HONGGUANG of predetermined number and infrared light pulse string respectively when accounting for for resulting two;
D. at the T_DARK remaining time in sampling period of III sequential, the low-frequency pulse string that dark current is produced carries out the pulse capture counting, when this end cycle, write down and catch count value DARK_CNT, draw the alternating current-direct current component of cycle, frequency and the representative of light frequency transducer (5) output pulse by microprocessor (1) by data computation;
E. in measuring process, the dynamic range of photoelectricity volume pulse wave measurement is carried out regulating automatically in real time, promptly in each sampling period, whether drop among timing window T ± Δ T when all detecting the accounting for of light frequency transducer (5) output pulse string, when the accounting for of train of pulse in this window, measurement will normally be carried out, and calculate predetermined count value RD_CNT and IR_CNT again otherwise will return step a.
2. the digital signal processing method of light-frequency conversion type pulse blood oxygen instrument according to claim 1 is characterized in that, among the described step a, the Δ T of time window T ± Δ T and the ratio of intermediate value T should be greater than 20%.
3. the digital signal processing method of light-frequency conversion type pulse blood oxygen instrument according to claim 1 and 2, it is characterized in that, in the steps d, the method of described data computation is, if the predetermined count value corresponding to HONGGUANG and infrared light pulse string is RD_CNT and IR_CNT, to arbitrary sampling period n, measured HONGGUANG and infrared light pulse string accumulative total are T_RD (n) and T_IR (n) when accounting for, the time that the low-frequency pulse string of dark current generation is counted is T_DARK (n), count value is DARK_CNT (n), then HONGGUANG and infrared light the value of calculation of the corresponding sampled point n of pulse frequency be respectively:
RD_X(n)＝K*RD_CNT/T_RD(n)-K*DARK_CNT(n)/T_DARK(n)
IR_X(n)＝K*IR_CNT/T_IR(n)-K*DARK_CNT(n)/T_DARK(n)；
In the formula, subtrahend is the pulse wave amplitude sampled value error term of the pulse frequency representative of dark current generation, minuend is the pulse wave amplitude sampled value of the pulse frequency representative that records between action period of driving pulse, and COEFFICIENT K is a constant relevant with the timer clock frequency.
4. the digital signal processing method of light-frequency conversion type pulse blood oxygen instrument according to claim 3 is characterized in that, described COEFFICIENT K is for the timer clock frequency of 8MHz, and the value of K is hexadecimal number 800000H.
5. the digital signal processing method of light-frequency conversion type pulse blood oxygen instrument according to claim 4 is characterized in that, the computing of K*RD_CNT is with RD_CNT 7 the high sixteen bits as product that move to left, and the low sixteen bit of product is changed to zero; After trying to achieve 32 products of K*RD_CNT, can carry out the result that 32/16 divisions are tried to achieve K*RD_CNT/T_RD (n) computing item by conventional method; In like manner can ask the result of K*IR_CNT/T_IR (n) and K*DARK_CNT (n)/T_DARK (n) computing item.
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| CN101627902B (en) * | 2009-07-15 | 2011-12-28 | 深圳先进技术研究院 | Low-power consumption and high-precision front processing module of photoelectric plethysmograph signal based on ambient light |
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