WO2019158385A1

WO2019158385A1 - A controller and method to determine incident intensity of a light source and total hemoglobin

Info

Publication number: WO2019158385A1
Application number: PCT/EP2019/052657
Authority: WO
Inventors: Kiran Rangaswamy Aatre; Rayaroth DINESH KUMAR; Swaminathan DHIVYA; Sushovan CHAKRABORTY
Original assignee: Robert Bosch Gmbh; Robert Bosch Engineering And Business Solutions Private Limited
Priority date: 2018-02-13
Filing date: 2019-02-04
Publication date: 2019-08-22

Abstract

The present invention discloses a controller (110) and method to determine incident intensity of a light source (108) and total hemoglobin concentration using the Hemoglobin monitoring device (102). The controller (110) is adapted to supply a reduced rated power to the at least one light source (108), when the device (102) is switched ON. The rated power is reduced by a predetermined factor. The controller (110) measures a value of the incident intensity of emitted light from the at least one light source (108) through a photodetector (106). The controller (110) then determines the incident intensity by multiplying the measured value with the predetermined factor. The controller (110) measures attenuated intensities in the presence of the body appendage (114) when the light sources (108) are supplied with rated power. Further, the controller (110) is adapted to determine the total hemoglobin by processing the incident intensity and the attenuated intensity.

Description

TITLE: A Controller And Method To Determine Incident Intensity Of A Light Source And Total Hemoglobin

Field of the invention:

[0001] The present invention relates to a controller and method to determine incident intensity of a light source and Total Hemoglobin Concentration (THC).

Background of the invention:

[0002] According to a patent literature US2004/0176670, an apparatus for measuring concentration of light- absorbing substance in blood is disclosed, in which a light emitter emits light beams to irradiate a living tissue, each of the light beams being associated with one wavelength which is absorbed by the blood. A first instrument measures first intensities of the light beams, which are to be incident on the living tissue. A second instrument measures second intensities of the light beams, which are transmitted through the living tissue. A first calculator calculates an attenuation variation ratio, which is a ratio of attenuation variations of the respective light beams due to variation of a volume of the blood caused by pulsation, based on the second intensities of the light beams. A second calculator calculates the concentration based on the first intensities, the second intensities, and the attenuation variation ratio.

Brief description of the accompanying drawings:

[0003] An embodiment of the disclosure is described with reference to the following accompanying drawings,

[0004] Fig. 1 illustrates a controller for a Hemoglobin monitoring device, according to an embodiment of the present invention;

[0005] Fig. 2 illustrates a method for determining incident intensity, according to the present invention;

[0006] Fig. 3 illustrates the controller to determine Hemoglobin using the Hemoglobin monitoring device, according to an embodiment of the present invention, and

[0007] Fig. 4 illustrates a method for determining the Hemoglobin, according the present invention.

Detailed description of the embodiments: [0008] Fig. 1 illustrates a controller for a Flemoglobin monitoring device, according to an embodiment of the present invention. The Flemoglobin monitoring device 102 is an apparatus to measure Flemoglobin concentration in blood of a living being in a non-invasive manner using pulse oximetry. The Flemoglobin monitoring device 102 comprises at least one light source 108, a photodetector 106, a slot 104 where a body appendage 114 of a living being is inserted, and the controller 110 to process the signals received from the photodetector 106 to determine Flemoglobin. The body appendage 114 comprises a finger of a hand or a foot, an ear lobe and the like of a living being such as human and animals. The light radiated/emitted by the light source 108 is absorbed by the body appendage 114 depending on its red and infrared light absorption characteristics. The attenuated light after absorption is detected by the photodetector 106 and is stored as a Photoplethysmographic (PPG) signal. The Flemoglobin monitoring device 102 employ one or more than one light sources 108 with wavelengths ranging from 470 nm to 1050 nm. The wavelength range is provided for providing clarity and is not limited thereby.

[0009] In one embodiment, the non-invasive Flemoglobin monitoring device 102 comprises four light sources 108, and generates a set of four PPG signals of predetermined duration for a subject/patient for the four light sources 108 of different wavelengths (for example 590nm, 660nm, 8l0nm and 940nm). The light source 108 may be a Light Emitting Diode (LED). The light sources 108 used are corresponding to the components of the Flemoglobin, i.e. two major moieties comprising oxygenated Flemoglobin (Flb) and de-oxygenated/reduced Flb, and two minor moieties comprising carboxy-Flb and methemoglobin. The incident light from the light source 108 is made to pass through the subject’s body appendage 114 and the attenuated intensity of light is detected using a photodetector 106. The four light sources 108 are switched ON at pre-programmed intervals. Only one light source 108 is ON at any point of time. The PPG signals are recorded and analyzed by the controller 110 to determine Flemoglobin concentration. The wavelength of the light are mentioned for explanatory purpose and the same must not be understood in limiting manner. Similarly, the number of light sources 108 is given as an example and must not be limited by the same, the Flemoglobin monitoring device 102 is adaptable/configurable to be used with one, two, or plurality of light sources 108.

[0010] In accordance to an embodiment, the controller 110 is provided to determine incident intensity of the light source 108 for the Flemoglobin monitoring device 102. The controller 110 is adapted to supply a reduced rated power to the all the light source 108, when the device 102 is switched ON. The reduced rated power supply may be provided in a predetermined sequence based on the number of light sources 108, such as one at a time, two at time and the like. The rated power is reduced by a predetermined factor with the use of electrical and electronic circuits. The controller 110 measures a value of the incident intensity of emitted light from the light source 108 through the photodetector 106. The controller 110 then determines the incident intensity by multiplying the measured value with the predetermined factor, and then stores the value in the memory element 112.

[0011] In one embodiment, once the Hemoglobin monitoring device 102 is switched ON, the light source 108 (at least one) is not immediately supplied with the electrical power. Only other components of the device 102 such as display (not shown), the controller 110, etc. are energized. The light source 108 is powered only after a dedicated action or button press by an operator. The power supply is either from a battery or from a standard wall socket. Thus, this embodiment, provides a safety feature/check for the photodetector 106, as the output signal of the photodetector 106 may saturate on being exposed to high intensity of light under rated power supply.

[0012] In another embodiment, the Hemoglobin monitoring device 102 is switched ON and the body appendage 114 is inserted inside the slot 104. The rated power is supplied to the light sources 108 and the attenuated intensities are measured. Now, once the body appendage 114 is removed from the slot 104, the user/operator presses a button to measure the incident intensity. The controller 110 on receiving the input from the button, supplies the reduced rated power to each of the light source 108, one by one, and measures the incident intensity. The controller 110 calculates the true/actual value of the incident intensity by multiplying with the predetermined factor and stores in the memory element 112. The incident intensity is determined either before or after the measurement of the attenuated intensities.

[0013] In an alternative, a proximity sensor (not shown) is provided in the slot 104, and is electrically connected to the controller 110. The proximity sensor enables an automated operation for supplying power to the light sources 108. The controller 110 does not control the supply of the rated power to the light source 108, unless the body appendage 114 is detected in the slot 104. On insertion of body appendage 114, the proximity sensor signals the controller 110. The controller 110 then controls the supply of the rated power to the at least one light source 108, followed by storing the attenuated intensities. Thus, in the absence of the body appendage 114, the incident intensity is automatically determined by the controller 110 and stores in the memory element 112.

[0014] Fig. 2 illustrates a method for determining incident intensity, according to the present invention. The method is provided for determining incident intensity of the light source 108 in the Flemoglobin monitoring device 102, comprising plurality of steps. A first step 202 comprises supplying a reduced rated power to at least one light source 108 after switching ON the device 102. The rated power is reduced by the predetermined factor. The rated power supply is reduced by using electrical and electronic circuits. A step 204 comprises emitting light from the light source 108 towards a photodetector 106, with reduced intensity. A step 206 comprises measuring the value of the incident intensity from the photodetector 106, and determining the incident intensity by multiplying with the predetermined factor. The steps 202 through 206 are carried out based on the control signals from the controller 110. The incident intensity is then stored in the memory element 112.

[0015] Fig. 3 illustrates the controller to determine Flemoglobin using the Flemoglobin monitoring device, according to an embodiment of the present invention. The controller 110 is also provided to determine Total Flemoglobin Concentration (TF1C) using the Flemoglobin monitoring device 102. The controller 110 is a single board computer (SBC) which performs the computing and connectivity requirements for the Flemoglobin monitoring device 102. The controller 110 is built on a single circuit board with a processor, the memory element 112, an input/output ports and other features required for a computer. The memory element 112 comprises a Random Access Memory (RAM), Read Only Memory (ROM), etc. The controller 110 is adapted to supply a reduced rated power to plurality of light sources 108 of different wavelengths, after switching ON the device 102. The rated power is reduced by a predetermined factor before supplying to the plurality of light sources 108. The controller 110 detects, by the photodetector 106, the incident intensity of the light emitted by each of the plurality of light source 108, and stores in the memory element 112. Once the incident intensity is recorded, and when the body appendage 114 is inserted inside the slot 104 of the device 102, the controller 110 supplies the rated power to the plurality of light sources 108. The controller 110 further detects, by the photodetector 106, an attenuated intensity of light transmitted through the body appendage 114, and stores an output (PPG) signal in the memory element 112. The output signal comprises attenuated intensity for the plurality of light sources 108. The controller 110 then determines the TF1C by processing the incident intensity and the attenuated intensity stored in the memory element 112 corresponding to plurality of light sources 108, based on Beer-

Lambert law. The equation for Beer- Lambert’ s law is represented as:

I I p- c.d

L h = ¹ o (1) where,

I_n is the transmitted/attenuated intensity,

I₀ is the incident intensity,

e is the extinction coefficient,

c is the concentration of the material, and

d is the distance travelled by the light.

[0016] The intensity of the light received by the photodetector 106 depends on absorptivity of each of the four components in the hemoglobin after the incident light passes through the body appendage 114. Each component in the hemoglobin has maximum absorption co-efficient of light at a particular wavelength. Therefore, intensity of light transmitted by the light source 108 such as Light Emitting Diode (LED) having a particular wavelength decreases once it passes through the body appendage 114, since one component of the hemoglobin has absorbed maximum light emitted by that particular LED. Therefore, based on the concentration of each component in the hemoglobin, the intensity of light received by the photodetector 106, varies as the light passes through the body appendage 114. The controller 110 detects these values through the photodetector 106 accordingly. For light emitted by four light sources 108, four different voltage values or current values are obtained by the photodetector 106 and the same is stored in the memory element 112. These four different values collectively determines the hemoglobin concentration in the blood.

[0017] A total of four sets of absorption values are calculated for the subject, i.e. A₅₉₀, A₆₆o,

Asm, and A₉₄₀ corresponding to the four wavelengths.

[L\_l = [log(I₀) - log(I_n( i) ) ]_x . (2) where, l is the wavelength.

[0018] Now, applying logarithmic function to equation (1), the below equation is received.

log(I₀) - log(I_n) = e. c. d ... (3)

[0019] Substituting, e and c with respective components, the below equation is received.

log(I₀) - log(I_n) = ( e^ + e₂c₂ + e₃c₃ + £₄c₄) d ... (4) where,

e₁ , e₂, e₃, e₄ represents extinction coefficients, and

ci, c₂, c₃, c₄ represents concentration of CHbCk, CRHb, CHbCO and CHbMet respectively.

[0020] The values of e for the four moieties are referenced from an empirically derived table. Similarly, the value for d is taken as the change in the arterial diameter after inflow and outflow of blood for the subject, such as 1.7 ± 0.1 mm.

[0021] Taking a median of the Attenuation values for the subject, four different equations are obtained for the four wavelengths using equation (2) and (4):

median[A]_A = [( e_ίe_ί + e₂e₂ + e₃e₃ + e₄e₄) ά]_l ... (5)

[0022] The controller 110 is programmed to solve the four equations for the four wavelengths forc₁, c₂, c₃, c₄, and is adapted to calculate the theoretical concentrations of the Hb moieties. The total hemoglobin concentration (THC) is determined as the sum of these individual concentrations:

THC = c₄ + c₂ + c 3 + c₄ (6)

[0023] The controller 110 is further adapted to process the determined THC along with at least one parameter using a computing model 302. The controller 110 then determines a revised THC. The said at least one parameter is selected from a group comprising, ratios of different hemoglobin moieties against each other across different combination of wavelengths, absorption values of each of said at least four sources of light, age of subject and a pregnancy status of said subject. The ratios of different hemoglobin moieties are obtained by following:

A ratio R , defined as the median of the set of natural logarithms of ratios of peak amplitude to trough amplitude is calculated for all required wavelengths, from the PPG signal.

[0024] Subsequently, pairwise ratios of these ratios (Rii ) for the red (590nm and 660nm) to infrared (8l0nm and 940nm) wavelengths are calculated - R590/810, R590/940, R660/810, R660/940. A function of Sp0₂, i.e. S is defined in the below equation:

CHb0₂

S = CHb0₂+CRHb . . . (8) where, S is a function of Sp02 and not Sp02 itself.

[0025] Now, by using the Beer- Lambert’ s law,

The above equation is solved for S for four pairwise ratios - 5)5_90/810), 5_(590/940), 5₍₆₆o/8io₎, 5_(660/940) and a set of four feature/ parameters are defined and used.

[0026] The controller 110 processes the THC and the at least one parameter using a computing model 302 stored in the memory element 112. The computing model 302 comprises a Machine Learning Model (MLM) comprising at least one regression model, and a meta regressor model. The output of the at least one regression model is provided as input to the meta regressor model, to obtain the revised THC. The meta regressor model comprises but not limited to a Support Vector Regressor (SVR).

[0027] Further, the at least one regression model is selected from but not limited to a Least Absolute Shrinkage and Selection Operator (LASSO) 304, a Ridge regression 306, an Elastic Net Regression model 308 and an Ada boost model 310.

[0028] Fig. 4 illustrates a method for determining the Hemoglobin, according the present invention. The method for determining THC using a Hemoglobin monitoring device 102 comprises plurality of steps. A first step 402 comprises, supplying a reduced rated power to plurality of light sources 108 of different wavelengths, after switching ON of the device 102. The rated power is reduced by a predetermined factor before supplying to the light source 108 to prevent saturation of the output of the photodetector 106. A step 404 comprises, emitting light from the plurality of light sources 108 and storing in a memory element 112, the incident intensity detected by the photodetector 106 for each of the plurality of light sources 108. A step 406 comprises supplying rated power to the plurality of light sources 108 in the presence of the body appendage 114. A step 408 comprises emitting and transmitting light from the plurality of light sources 108 through the body appendage 114, and storing an output (PPG) signal in the memory element 112, as detected by the photodetector 106. The output signal comprises attenuated intensity for the plurality of light sources 108. A step 410 comprises determining THC by processing the incident intensity and the attenuated intensity stored in the memory element 112 corresponding to plurality of light sources 108, based on Beer-Lambert law. [0029] The method further comprises a step 412 comprising, processing the THC and the at least one parameter using the computing model 302 and revising the THC. The at least one parameter is selected from a group comprising, ratios of different hemoglobin moieties against each other across different combination of wavelengths, absorption values of each of the at least four sources of light, age of subject and a pregnancy status of the subject and the like.

[0030] For determining the hemoglobin concentration in the blood, the body appendage 114 is positioned into the slot 104 of the device 102. The controller 110 then operates each of the light sources 108 sequentially and at pre-programmed intervals. That is, the controller 110 turns ON each light source 108 for a fixed time period and then turns OFF. All the LEDs are therefore operated in this manner.

[0031] Further, the light emitted by the light source 108, penetrates through the body appendage 114 and is absorbed by at least one component of the hemoglobin. Based on the wavelength of the light incident on the body appendage 114, one particular component, out of the four components in the hemoglobin, absorbs maximum light. The method follows the execution of instructions by the controller 110 as per the aforementioned equations from (1) through (9).

[0032] In accordance to an embodiment of the present invention, the controller 110 is adapted to calculate the total absorbance using incident intensity and the attenuated intensity, in contrary to the calculation where the ratio of the absorbance eliminates the incident intensity.

[0033] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.

Claims

We claim:

1. A controller (110) to determine incident intensity of a light source (108) for a Hemoglobin monitoring device (102), said controller (110) adapted to:

supply a reduced rated power to at least one light source (108), when said device (102) is switched ON, said rated power is reduced by a predetermined factor; measure a value of said incident intensity of emitted light from said at least one light source (108) through a photodetector (106);

determine said incident intensity by multiplying said measured value with said predetermined factor.

2. A method for determining incident intensity of a light source (108) in a Hemoglobin monitoring device (102), said method comprising the steps of:

supplying (202) a reduced rated power to at least one light source (108) after switching ON said device (102), said rated power is reduced by a predetermined factor;

emitting (204) light from said at least one light source (108) towards a photodetector (106), and

measuring (206) a value of an incident intensity from said photodetector (106), and determining said incident intensity by multiplying with said predetermined factor.

3. A controller (110) to determine Total Hemoglobin Concentration (THC) for a Hemoglobin monitoring device (102), said controller (110) is adapted to:

supply a reduced rated power to plurality of light sources (108) of different wavelengths after switching ON said device (102), said rated power is reduced by a predetermined factor;

detect, by a photodetector (106), an incident intensity of the light emitted by said plurality of light sources (108), and store in a memory element (112);

supply said rated power to said plurality of light sources (108) in the presence of a body appendage (114) inside a slot (104) of said device (102); detect an attenuated intensity of light transmitted through said body appendage (114), by said photodetector (106), and store an output signal in said memory element (112), said output signal comprises attenuated intensity for said plurality of light sources (108), and determine said THC by processing incident intensity and said attenuated intensity stored in said memory element (112) corresponding to plurality of light sources (108), based on Beer-Lambert law.

4. The controller (110) as claimed in claim 3 further adapted to:

process said THC along with at least one parameter using a computing model (302), and

determine a revised THC.

5. The controller (110) as claimed in claim 4, wherein said at least one parameter is selected from a group comprising, ratios of different hemoglobin moieties against each other across different combination of wavelengths, absorption values of each of said light sources (108), age of subject and a pregnancy status of said subject.

6. The controller (110) as claimed in claim 4, wherein said computing model (302) comprises Machine Learning Model (MLM) comprising at least one regression model and a meta regressor, wherein output of said at least one regression model is provided as input to said meta regressor.

7. The controller (110) as claimed in claim 6, wherein said at least one regression model is selected from a Least Absolute Shrinkage and Selection Operator (LASSO) (304), a Ridge regression (306), an Elastic Net Regression model (308) and an Ada boost model (310).

8. A method for determining Total Hemoglobin Concentration (THC) using a Hemoglobin monitoring device (102), comprising the steps of:

supplying (402) a reduced rated power to plurality of light sources (108) of different wavelengths after switching ON said device (102), said rated power is reduced by a predetermined factor;

emitting (404) light from said plurality of light sources (108) and storing an incident intensity detected by a photodetector (106) for each of said plurality of light sources (108) in a memory element (112);

supplying (406) rated power to said plurality of light sources (108) in the presence of a body appendage (114); emitting (408) and transmitting light from said plurality of light sources (108) through said body appendage (114), and storing an output signal as detected by said photodetector (106) in said memory element (112), said output signal comprises attenuated intensity for said plurality of light sources (108); determining (410) THC by processing said incident intensity and said attenuated intensity stored in said memory element (112) corresponding to plurality of light sources (108), based on Beer-Lambert law.

9. The method as claimed in claim 8, further comprises processing (412) said THC and at least one parameter using a computing model (302), and revising said THC.

10. The method as claimed in claim 9, wherein said at least one parameter is selected from a group comprising, ratios of different hemoglobin moieties against each other across different combination of wavelengths, absorption values of each of said light sources (108), an age of subject and a pregnancy status of said subject.