DD208297A1 - photoplethysmograph - Google Patents

Abstract

The photoplethysmograph belongs to the medical photometric devices. The device consists of a light source and two photoreceptors arranged in a line one behind the other on a common base element, and a pulse generator connected to the light source and the first input of the comparison circuit whose output is connected to the registration device, the comparison circuit is executed as a measuring device of the ratio or the logarithm of the ratio of the input signals, two sample-and-hold circuits and two differential amplifiers whose first inputs are correspondingly connected to two photoreceivers, the second inputs are with the outputs of the corresponding sample-and-hold circuits and the outputs connected to the second and third inputs of the comparator and the first inputs of the respective sample-and-hold circuits whose second inputs are connected to the output of the pulse generator. The device can be used in medicine and biology as well as in other fields of science and technology.

Description

pilot © plethysmograph.

Field of application of the invention

The proposed photoplethysmograph belongs to the medical photometric devices which are intended for determining the blood filling level of the vessels of biological tissues, without disturbing the occlusion of the tissue covering.

The use of the proposed photoplethysmograph is useful in medicine and biology, as well as in scientific investigations as well as in. Prophylactic screening or in the control of the effectiveness of medical and physiotherapeutic treatments performed, since the device allows the optical To register the characteristics of the tissues and to determine the parameters of the peripheral perfusion (volume pulse, blood filling level and others). The device makes it possible to carry out measurements anywhere on the skin surface or mucous membrane of the human body or in animals under normal illumination or the effect of additional external light sources, without destroying the integrity of the object to be examined *

The device can also be used in the petroleum and chemical industry as well as in other areas _? photometric methods for the determination of the concentration, structure and state of substances that are

be used under normal conditions.

Characteristic of the known technical solutions

Photoplethysmographs are known which operate according to the principle of elemination and are intended for assessing the blood supply level of the vessels in the area of the tissue to be examined (Moschkevitsch V. 8; Fotopletismografija / apparatura i metodui issledovanija; M, Medizina, 1970). This device does not allow to quantify the optical properties of the tissue to be examined. A device has been described (Sajavka Ur .. 2643172/13 j Photographic Letters, M.K. ^, A 61 B 5/02 .Eeschenie WIIGPE ot 26.09 , 1980 ο vuidatsche avtorskovo svidetelstva), which operates on the principle of emission and is intended for the quantitative assessment of the blood supply level of the vessels in the area of the tissue to be examined. A self-stabilizing system was developed (Benoit HJ., Borth E,, Woolever Cl. Self-stabilizing system for measuring infrared light backscattered from vaginal tissue; Med. & Biol.Eng.Sc Gomput., 198o, 18, .265 However, this system works only as long as the level of ambient lighting does not cause the saturation of the input cascade amplifiers. This is the deficiency of the known devices because the measurement information at the saturation of the Amplifier of the input cascade is lost.

The most obvious technical solution to the proposed device is a photoplethysmograph (Sa.javka Nr, 2643172 /

-7

13, photo-digitismograph, .M.kl. ^p , A 61 B 5/02 .Eeschenie VNIIGPE ot 26.09.1980 ο vuidatsche avtorskovo svidetelstva), which contains a pulse generator which is connected to the light source and the first input of the comparison circuit, whose two other inputs with two photoreceivers and their output with are connected to a Segistriereinrichtung, the comparison circuit as a measuring apparatus of the ratio or the logarithm of the ratio of the signals of the Photoem -

W Η W W

pf is executed. The two Piiot ο receiver "and the light source are arranged in a line one behind the other on a common base element.

The lack of the known device is that the measurement result is affected by changing level of Umgebungsbe lighting, wherein the measuring error with too - nehmendem Niveau'dieser'Beleuchtung vergrößert.Wird this exceeded a certain level, then a at the output of the photoreceiver Such a signal is completely lost, the application of a shielding to eliminate the ambient lighting (total 'or local) is usually not useful, since thus the operating convenience significantly reduced, the Control of the position of the transducer difficult, the processes of heat dissipation and ventilation of the body surface are obstructed, In addition, in a number of cases, the application of shielding is generally not possible, such as the control of blood flow under the conditions of surgery, etc.

Object of the invention .

The object of the invention is to determine the optical properties of a substance Eigen- independent of the present at the measuring point external lighting conditions and thus the application possibilities photometrischeas methods to expand.

Explanation of the essence of the invention

The object of the invention is to reduce the influence of the changing external illuminance on the measurement result of the pptischen properties of a substance.

According to the invention. Problem solved in that in the known device, two differential amplifiers and two sample-and-hold circuits are inserted, wherein the first inputs of the differential amplifier according to two photoreceivers, the second inputs of the differentiation

are more strongly connected to the outputs of the respective sample-and-hold circuits and the outputs of the differential amplifiers to the second and third inputs of the comparator and the first inputs of the respective sample-and-hold circuits, the second inputs of the sample-and-hold circuits are connected to the output of the pulse generator.

The advantage of the proposed device in comparison with known United States is that in the proposed device, the influence of the changing external illuminance on the measurement of the optical properties of the tissue surface of the body is substantially reduced.

Let us prove this. Assumed in the proposed device, the ¹ . After absorption and scattering, part of the plus F ₁ * i ^ "f _{i1 reaches} the photoreceiver 8 and another part \ ~ Κ, -Τ-ΐ reaches the photoreceiver 9. The coefficients % and X _x characterize the optical properties of the sch Gewebeab ni Gd between the light source 2 and the receiver 8 and 9 Phot © .The optical properties of the Gewebeab ^ chnittes between the photoreceptors 8 and 9 can be defined as the ratio

t * \ / _Τ Λ - ^ x / _Χ Λ we ausdrücken.Nehmen to that due to external light sources f to the Photοempfänger 8 and 9 of the light flux _A fällt.Zur simplification we thereof, assume that both photoreceptor 8 and 9 from the external sources of light the same flux of light falls and the sensitivity S of the photoreceptors 8 and 9 is the same. Then one can write for the first working cycle of the proposed device

Up ₁ = Uf ₁ - 5F _A , where U. ^ and Uf _{1 are} the electrical signals formed at the outputs of the photoreceivers 8 and 9. These signals are stored in the sample-and-hold circuits 3 and 4, where U ₅ = li _fi and Us ^ U _fi. During the second working cycle of the device, the photon receivers 8 and 9 form the following signals:

UjJ ₁ * 5 (Ρ, +. Ρ ^ ν ^unci Up ₁ ⁼ 5 (F _5. + F _A ) .These signals go on, the first inputs of the corresponding differential amplifiers 6 and 7, respectively, reach the second inputs of these amplifiers the signals U ^ and U ₅₁ , which are stored in the sampleand-hold circuits 3 and 4. To the Aus -

The differential amplifiers 6 and 7 , which have the amplification factor k, form the signals

U _{A /} k (U _f ' _r u; j = k [S (F, tF _A } -SF _A ] »IcSr, and U ^ k (Uf ₁ -Up ¹ J * k [S (F ^) -Sh ] 'ICSF ₁ ..The ratio which is determined in the comparison circuit 5 of the signals corresponding to f: _x ^ a / ^ _α λ ^B k <SFi / K5F ₁ - f It follows that in the proposed device, the outer flux F ^ does not affect the determination of the optical properties of the surface tissues of the body.

Now show that in the known device (Sa.jav-, no. 2643172/13, Potopletismograf, M.kl. ^, A 61 B 5/02, Reschenie VNIIGPE ot 26.09.1980 ο vuidatsche avtorskovo svidetelstva) the ratio the signals, which is determined in the same circuit Ver not reach entspricht.Da V, in the presence of external light in the known device the signals of the photodetectors directly to the inputs of the comparison circuit, one can write:

^ B ^{s U} Fi / Fi Fi ⁼ ^ (j j ⁺ Pa) / S ί ^ ^{+ p} A) j where T ^ represents the ratio of the signals determined in the comparison circuit of the known device, and U _Fij and up _x the signals from the photodetector are applied to the inputs of the comparison circuit we gelangen.Bestimmen the relative Pehler (TTj $ of the ratio of the signals of Phot ο receiver in the known device, taking into account that x =

-Fz '

After some algebraic transformations we get

ϊΜ- ' ^where * -VFa "·

The table shows the relative errors (in percent) as a function of the size of the coefficient CL-F ₁ / F ^ at different values of X.

\. α. 0.1 0.5 1.0 5 10 50 100 1000 0.001 9x10 ⁴ 7x10 ⁴ 5x10 ⁴ 2x10 ^ 9x10 ^ 10 ³ 10 ^ 10U 0.005 2x10 ⁴ 10 ⁴ 10 ⁴ 3x10 ^ 2x10 ^ 390 190 20 0,010 9x1 ο ³ 7x1 O ^ 5x1 O ^ 2x1.0 ⁵ 9x10 ² 190 98 10 0,050 2x10 ^ 10 ⁵ 9x10 ² 3x10 ² 170 37 19 1.9 0,100 800 600 400 150 81 18 8.9 0.8 0, $ 00 90 67 50 17 9 2 1 0.1 0.900 10 7.4 5.6 1.8 1 0.2 0.1 .0,01

As can be seen from this table, in the known device for the real values τοη T = O ₁ OOS? 0.1, one must increase the coefficient a to the value 1000 and more in order to obtain an acceptable error in the determination of.

However, such an increase in the coefficient a means to increase the light flux of the light source so that it is 4-5 orders of magnitude larger than the light flux of the external light sources. Such an increase in the beam power of the light source can lead to unwanted effects lead the biological tissue to be examined.

From the comparison of the known and proposed photoplethysmographs it can be seen that the proposed device makes it possible to determine the optical properties of the surface tissue of the body in the presence of changing external illuminance and low radiation powers of the light source 2.

Bearing does not affect the tissue to be examined and allows a quantitative determination of the optical properties due to the two-beam optical system. the tissue. anywhere on the body surface,

Ausfi'ihruiigsbeispiel

The invention is explained in more detail by an exemplary embodiment, in which:

Figure 1 - Structure diagram of the photoplethysmograph Figure 2 - Timing diagrams describing the work of the device.

The proposed photoplethysmograph. Fig. 1 includes a pulse generator 1 connected to the light source 2, the wide inputs of the sample-and-hold circuits 3 and 4 and the first input of the comparator 5. The two other inputs of the comparator 5 are connected to the outputs the differential amplifier 6 and 7 ^ and the output of the comparison circuit 5 is connected to the Hegistrier device 10. The outputs of the differential amplifiers 6 and 7 are connected to the first inputs of the sample-and-hold circuits 3 and 4, the output of the sample-and-hold circuit 3 is connected to the second input of the differential amplifier 6, whose first input is connected to the photoreceptor 8. The output of the 3 ample-and- hold ' circuit 4 is connected to the second input of the Differenzver amplifier 7, whose first input to the photo receiver 9 is connected. The light source 2 and the photo receivers 8 and 9 are in a line behind one another on a common base element angeo For example, one luminescence and two photodiodes may be used as the light source 2 and the photoreceptors 8 and 9. The comparison circuit 5 is implemented as a measuring device of the ratio or the logarithm of the ratio of the signals of the photoreceptors 8 and 9.

The photoplethysmograph operates in the following manner. The pulse generator 1 forms a rectangular pulse signal (FIG. 2 a) which arrives at the light source 2 and

the radiation of a corresponding Strahienflusses forth ago, Let's look at two strokes of the device. During the first clock pulse generator 1 forms no signal (time interval 0 ~ t ₁ in Figure 2a) and the light source 2 emits no Strahlfluß aus.An the second inputs of the sample-and-hold circuits 3 and 4 also get no signals and circuits operate in a regime in which they continuously the changing level of the external illuminance registrieren.Dies happens folgendermaßen.Der light flux of the external light source (natural or artificial) reaches the photodetector 8 and 9, transform electrical signals, the illuminance of be their photosensitive elements are proportional (for one of the photoreceivers, such a signal is shown in Fig. 2b, time interval 0 ~ t ₁ ). These signals reach the first inputs of the corresponding difference; amplifiers 6 and 7 "From the outputs of the differential amplifiers 6 and 7, the signals are applied to the first inputs of the respective sample-and-hold circuits 3 and 4 and to the second and third inputs of the comparison circuit 5 Sigmal formed, no signal reaches the first input of the comparator 5, so that the comparison circuit does not work 5. At the second inputs of the sample-and-hold circuits 3 and 4 also passes during the first power stroke, no signal of the pulse generator. 1 , and these circuits work like inverting amplifiers. They transmit in opposite phase the signals from the outputs of the differential amplifiers 6 and 7 to their second non-inverting inputs. Since the Differenzver stronger 6 and 7 form at their outputs signals that are proportional to the difference of the voltages at their two inputs, u u u u assume that with a sufficiently large amplification factor. the amplifier of the sample-and-hold circuits 3 and 4 during the first working cycle at both inputs of each difference amplifier 6 and 7, the signals are the same size. In this way, any signal which is from the Photoreceivers 8 and 9 due to external illumination

strength is compensated with an opposite polarity signal which passes from the outputs of the respective sample-and-hold circuits 3 and 4 to the second inputs of the respective Dijfferenz.verstar.feer 6 and 7. The sample-and- hold circuits 3 and 4 formed signals are continuously registered during the first power stroke (for one of the sample-and-hold circuits, such a signal is shown in Fig.2c).

During the second working cycle of the device, the pulse generator 1 forms a pulse having the pulse duration t 1 -t i. (Fig.1a). This pulse is applied to the light source 2, the second inputs of the sample-and-hold circuits, 3 and 4 and the first input of the comparator 5. During the second clock cycle go the sample-and-hold circuits 3 and 4 into a storage regime and store the external light intensity in the photoreceptors 8 and caused electrical signal (U _s Fig.2c), which corresponds to the level of this external illuminance. The light source 2 emits a beam flux in the predetermined wavelength range, which by the Since the light flux is absorbed and scattered by the biological tissue of the body surface to be examined, it is incident on both photoreceptors 8 and 9, since the light source 2 and the photoreceivers 8 and 9 are in line with each other a common base element 11 is arranged, the distance z Consequently, the light flux which reaches the photoreceiver 9 will be less than the light flux which reaches the photoreceiver 8. Apart from the light flux of the light source 2, the light flux 2 and photoreceiver 8 are less than the distance between light source and photon receiver 9. the photoreceivers 3 and 9 continue to soak the light flux of the external illumination with sufficient accuracy for the duration of the light pulse of the light source 2. As in the sample-and-hold circuits 3 and 4 the signal is stored, which is the Level of the external illuminance corresponds to the moment in which the light source 2 a light -

pulse begins to form during the second working cycle of this caused by the external illumination signal of the photoreceptors 8 and 9 is compensated by being given to the second inputs of the respective differential amplifiers 6 and 7. As a result, during the second power stroke at the outputs the differential amplifier 6 and 7 formed signals which are proportional to the caused by the radiation of the light source 2 illuminance of the photo receivers 8 and 9, (3 ig ig 2d) tone go from the differential amplifiers 6 and 7, the signals to the second and third input of the comparator circuit 5, at the first input of which the permitting signal of the pulse generator 1 arrives during the second operating cycle,

In the comparison circuit 5, the ratio of the amplified by the differential amplifiers 6 and 7 electronic signals of the photoreceptor 8 and 9 is determined, which ratio 'provides a quantitative characteristic of the optical Ei. Comforts of the tissue to be examined, If z.3, in the Comparative circuit 5 <3.asas the ratio of the signal of the photoreceptor 9 to the signal of the Photοempfängers 8 is determined, then a signal is formed at the output of the comparison circuit 5, which the. If the magnitude of the logarithm of the ratio of the signal, the photoreceptor 8 to the signal of the photoreceptor 9 is determined in the comparison circuit 5, a signal is formed at the output of the comparison circuit 5, which From the output of the comparison circuit 5, the signals enter the registering device 10 · '

Claims (1)

Erfindungsansprush A photoplethysmograph comprising a light source (2) and two photoreceivers (8, 9) arranged in a line one after another on a common base (11), a pulse generator (1) connected to the light source (2) and the first one Input of the comparison circuit (5)> whose output is connected to an Eegistriereinrichtung (10), wherein the comparison circuit (5) is designed as a measuring apparatus of the ratio or the logarithm of the ratio of the Singangssignale, characterized in that two differential amplifier (6,7 ) and two sample-and-hold circuits (3.4 ·) are inserted, wherein the first inputs of the differential amplifier (6,7) with two photoreceivers (8,9), the second inputs of the differential amplifier (6,7) with the outputs of the ent-speaking sample-and-hold circuits (3.4 ·) and the outputs of the differential amplifier (6,7) with the second and third inputs of the comparison circuit (5) and the first inputs are connected to the corresponding sample-and-hold circuits (3j4), the second inputs of the sampleand-hold circuits (3j40 JHit the output of the pulse generator. tors' (1) are connected. For this 1 page