DEVICE AND METHOD FOR ASSESSING STERNAL COMPRESSION

The evaluation apparatus is an apparatus for evaluating chest compression, and includes a measuring unit, a compression position evaluation unit, and an instruction unit. The measuring unit obtains numerical values relating to temporal changes in a total hemoglobin concentration, an oxygenated hemoglobin concentration, and a deoxygenated hemoglobin concentration of the head. The compression position evaluation unit determines whether compression position on a sternum is appropriate based on a first indicator and a second indicator, the first indicator relating to a temporal change ratio of the oxygenated hemoglobin concentration with respect to the temporal change in the total hemoglobin concentration, and the second indicator relating to a correlation between the temporal change in the oxygenated hemoglobin concentration and the temporal change in the deoxygenated hemoglobin concentration. When the compression position on the sternum is inappropriate, the instruction unit instructs to change the compression position.

TECHNICAL FIELD

The present disclosure relates to an evaluation apparatus and evaluation method for chest compression.

BACKGROUND ART

Patent Literature 1 discloses a device for assisting a rescuer when performing cardio pulmonary resuscitation (CPR) on a cardiorespiratory arrest person. This apparatus comprises at least one of a pulse sensor for measuring the heart rate of the cardiorespiratory arrest person and a SpO2 for measuring blood oxygen, electronics for processing the output of the sensor and determining one or more actions to be taken by a rescuer to improve current CPRs, and a reminder device that transmits one or more actions to the rescuer.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In cardiopulmonary resuscitation, chest compression is performed in combination with an artificial respiration. The chest compression is an action of giving artificial pulsation to a stopped heart by periodically compressing the lower half of the sternum with the hand of another person. The primary purpose of chest compression is to supply blood oxygen to the brain of a cardiorespiratory arrest person. Whether the chest compression is appropriately performed greatly affects the success rate of cardiopulmonary resuscitation. Therefore, there is a need for a useful method and apparatus for objectively evaluating whether the chest compression is being properly performed.

An object of the present disclosure is to provide an apparatus and a method capable of increasing a success rate of cardiopulmonary resuscitation by evaluating whether the chest compression is appropriately performed and notifying the rescuer of the fact that the chest compression is inappropriate in a case where the chest compression is not appropriately performed.

Solution to Problem

An evaluation apparatus according to the present disclosure is an apparatus for evaluating chest compression, and includes a measuring unit, a compression position evaluation unit, and an instruction unit. The measuring unit obtains numerical values relating to temporal changes in a total hemoglobin concentration, an oxygenated hemoglobin concentration, and a deoxygenated hemoglobin concentration in a head, which vary due to repetition of the chest compression. The compression position evaluation unit calculates a first indicator and a second indicator based on the numerical values. The first indicator is relating to a temporal change ratio of one or both of the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration with respect to a temporal change in the total hemoglobin concentration. The second indicator is relating to a correlation between a temporal change in the oxygenated hemoglobin concentration and a temporal change in the deoxygenated hemoglobin concentration. The compression position evaluation unit determines whether a compression position on the sternum is appropriate based on the first indicator and the second indicator. The instruction unit instructs to change the compression position in a case where the compression position on the sternum is inappropriate.

An evaluation method according to the present disclosure is a method for evaluating chest compression, and includes: a step of obtaining numerical values relating to temporal changes in a total hemoglobin concentration, an oxygenated hemoglobin concentration, and a deoxygenated hemoglobin concentration of a head, which vary due to repetition of the chest compression; a step of calculating a first indicator and a second indicator based on the numerical values, the first indicator relating to a temporal change ratio of one or both of the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration with respect to a temporal change in the total hemoglobin concentration, and the second indicator relating to a correlation between a temporal change in the oxygenated hemoglobin concentration and a temporal change in the deoxygenated hemoglobin concentration; a step of determining whether a compression position on a sternum is appropriate based on the first indicator and the second indicator; and a step of instructing to change the compression position in a case where the compression position on the sternum is inappropriate.

Advantageous Effects of Invention

According to the apparatus and the method of the present disclosure, it is possible to increase a success rate of cardiopulmonary resuscitation by evaluating whether the chest compression is appropriately performed and notifying the rescuer of the fact that the chest compression is inappropriate in a case where the chest compression is not appropriately performed.

DESCRIPTION OF EMBODIMENTS

An evaluation apparatus according to the present disclosure is an apparatus for evaluating chest compression, and includes a measuring unit, a compression position evaluation unit, and an instruction unit. The measuring unit obtains numerical values relating to temporal changes in a total hemoglobin concentration, an oxygenated hemoglobin concentration, and a deoxygenated hemoglobin concentration in a head, which vary due to repetition of the chest compression. The compression position evaluation unit calculates a first indicator and a second indicator based on the numerical values and determines whether a compression position on the sternum is appropriate based on the first indicator and the second indicator, the first indicator relating to a temporal change ratio of one or both of the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration with respect to a temporal change in the total hemoglobin concentration, and the second indicator relating to a correlation between a temporal change in the oxygenated hemoglobin concentration and a temporal change in the deoxygenated hemoglobin concentration. The instruction unit instructs to change the compression position in a case where the compression position on the sternum is inappropriate.

An evaluation method according to the present disclosure is a method for evaluating chest compression, and includes: a step of obtaining numerical values relating to temporal changes in a total hemoglobin concentration, an oxygenated hemoglobin concentration, and a deoxygenated hemoglobin concentration of a head, which vary due to repetition of the chest compression; a step of calculating a first indicator and a second indicator based on the numerical values and determining whether a compression position on a sternum is appropriate based on the first indicator and the second indicator, the first indicator relating to a temporal change ratio of one or both of the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration with respect to a temporal change in the total hemoglobin concentration, and the second indicator relating to a correlation between a temporal change in the oxygenated hemoglobin concentration and a temporal change in the deoxygenated hemoglobin concentration; and a step of instructing to change the compression position in a case where the compression position on the sternum is inappropriate.

During cardiopulmonary resuscitation, at least two rescuers may alternately perform the chest compression in order to continuously continue the chest compression for a long time. And when the rescuer changes, a compression position on a sternum naturally changes slightly. The present inventors observed temporal changes in tissue oxygenation index (TOI), oxygen saturation in a pulse wave component (SnO2), R2, the oxygenated hemoglobin concentration, and the deoxygenated hemoglobin concentration in a head undergoing the chest compression. During that time, the rescuer was changed multiple times. As a result, it was found that SnO2, R2, the ratio of an amplitude of the temporal change in the total hemoglobin concentration to an amplitude of the temporal change in the oxygenated hemoglobin concentration, the ratio of an amplitude of the temporal change in the total hemoglobin concentration to an amplitude of the temporal change in the deoxygenated hemoglobin concentration (hereinafter, these are simply referred to as “amplitude ratio”), and a difference between a phase of the temporal change in the oxygenated hemoglobin concentration and a phase of the temporal change in the deoxygenated hemoglobin concentration (hereinafter simply referred to as “phase difference”) varies depending on the compression position on the sternum. Further, the present inventors have found that SnO2and the amplitude ratio indicate a ratio of the temporal change in the oxygenated hemoglobin concentration or the deoxygenated hemoglobin concentration to the temporal change in the total hemoglobin concentration, and R2and the phase difference indicate a correlation between the temporal change in the oxygenated hemoglobin concentration and the temporal change in the deoxygenated hemoglobin concentration. The present inventors have also found that there is a significant correlation between the temporal change ratio of the oxygenated hemoglobin concentration or the deoxygenated hemoglobin concentration to the temporal change in the total hemoglobin concentration and a tendency (ascending tendency, descending tendency, or leveling off tendency) of a temporal change in TOI of the head, and between the tendency of the temporal change in TOI of the head and the correlation between the temporal change in the oxygenated hemoglobin concentration and the temporal change in the deoxygenated hemoglobin concentration.

In the above-described evaluation method and evaluation apparatus, the first indicator relating to the temporal change ratio of the oxygenated hemoglobin concentration or the deoxygenated hemoglobin concentration with respect to the temporal change in the total hemoglobin concentration and the second indicator relating to the correlation between the temporal change in the oxygenated hemoglobin concentration and the temporal change in the deoxygenated hemoglobin concentration are calculated. Based on the first indicator and the second indicator, it is determined whether the compression position on the sternum is appropriate, that is, whether the tendency of the temporal change in TOI of the head is an ascending tendency or a descending tendency or a leveling off tendency. In a case where the compression position on the sternum is inappropriate, an instruction to change the compression position is given. As described above, by evaluating whether the compression position on the sternum is appropriate and notifying the rescuer of the inappropriateness in a case where the compression position is inappropriate, it is possible to bring the tendency of the temporal change in TOI of the head close to the ascending tendency and to increase the success rate of cardiopulmonary resuscitation.

The measuring unit may include: a light incidence portion that makes the measurement light incident on the head; a light detection portion that detects the measurement light having propagated through the head and generates a detection signal corresponding to an intensity of the measurement light; and a calculation portion that calculates the numerical values based on the detection signal. The step of obtaining may include: a step of making measurement light incident on the head; a step of detecting the measurement light having propagated through the head and generating a detection signal corresponding to an intensity of the measurement light; and a step of calculating the numerical values based on the detection signal. In these cases, temporal changes in the total hemoglobin concentration, the oxygenated hemoglobin concentration, and the deoxygenated hemoglobin concentration of the head can be measured non-invasively and simply. Therefore, it is possible to easily measure the temporal changes in the total hemoglobin concentration, the oxygenated hemoglobin concentration, and the deoxygenated hemoglobin concentration of the head while performing the chest compression.

The compression position evaluation unit or the step of calculating may perform first linear regression based on the numerical values by using a numerical value relating to a pulse wave component of the total hemoglobin concentration as an explanatory variable and a numerical value relating to a pulse wave component of the oxygenated hemoglobin concentration as an objective variable, and may use a regression coefficient value (SnO2) obtained by the first linear regression as the first indicator. The compression position evaluation unit or the step of calculating may perform second linear regression, based on the numerical values described above, between the numerical value relating to the pulse wave component of the oxygenated hemoglobin concentration and a numerical value relating to the pulse wave component of the deoxygenated hemoglobin concentration, and use a determination coefficient value (R2) obtained by the second linear regression as the second indicator. For example, by performing evaluation based on SnO2and R2in this manner, it is possible to easily evaluate whether the compression position on the sternum is appropriate.

The compression position evaluation unit or the step of calculating may perform the first linear regression and the second linear regression based on the numerical values obtained during a period from a time of calculation of the first linear regression and the second linear regression to at least 5 seconds before the time of calculation. Considering that the chest compression is recommended to be performed 100 times per minute, the determination accuracy can be improved by securing 5 seconds or more for obtaining the numerical values.

The compression position evaluation unit or the step of determining may determine that the compression position on the sternum is inappropriate when the regression coefficient value (SnO2) served as the first indicator is less than a first threshold value and the determination coefficient value (R2) served as the second indicator is less than a second threshold value. In the case where the value of SnO2is less than a predetermined threshold value, the deoxygenated hemoglobin concentration is dominant over the oxygenated hemoglobin concentration. In the case where R2is low, there is no correlation between the change in oxygenated hemoglobin concentration and the change in deoxygenated hemoglobin concentration. Therefore, it is possible to easily evaluate that the compression position on the sternum is inappropriate.

The first threshold value may be 0.5 or more and 1.0 or less. For example, in this case, it is possible to more accurately evaluate whether the compression position on the sternum is appropriate.

The second threshold value may be 0 or more and 0.7 or less. For example, in this case, it is possible to more accurately evaluate whether the compression position on the sternum is appropriate.

The compression position evaluation unit or the step of calculating may calculate a ratio, based on the numerical values, between an amplitude of a temporal change in the total hemoglobin concentration and an amplitude of a temporal change in one or both of the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration as the first indicator. The compression position evaluation unit or the step of calculating may calculate a difference between a phase of the temporal change in the oxygenated hemoglobin concentration and a phase of the temporal change in the deoxygenated hemoglobin concentration as the second indicator. In this manner, by performing evaluation based on the amplitude ratio and the phase difference, it is possible to easily evaluate whether the compression position on the sternum is appropriate.

The measuring unit may obtain a pulse wave component of the total hemoglobin concentration, a pulse wave component of the oxygenated hemoglobin concentration, and a pulse wave component of the deoxygenated hemoglobin concentration by applying filtering process on the numerical values to extract a component that varies due to repetition of the chest compression. The compression position evaluation unit may calculate the first indicator and the second indicator by using the pulse wave component of the total hemoglobin concentration, the pulse wave component of the oxygenated hemoglobin concentration, and the pulse wave component of the deoxygenated hemoglobin concentration, which are obtained by the measuring unit. The step of obtaining may obtain a pulse wave component of the total hemoglobin concentration, a pulse wave component of the oxygenated hemoglobin concentration, and a pulse wave component of the deoxygenated hemoglobin concentration by applying filtering process on the numerical values to extract a component that varies due to repetition of the chest compression. The step of calculating may calculate the first indicator and the second indicator by using the pulse wave component of the total hemoglobin concentration, the pulse wave component of the oxygenated hemoglobin concentration, and the pulse wave component of the deoxygenated hemoglobin concentration, which are obtained in the step of obtaining. In these cases, it is possible to accurately calculate the first indicator and the second indicator based on only the variation component caused by the repetition of the chest compression.

A time from when the measuring unit starts obtaining of the numerical values to when the compression position evaluation unit determines the compression position based on the obtained numerical values may be 5 seconds or more and 30 seconds or less. A time from the start of obtaining the numerical values in the step of obtaining to the determination in the step of determining based on the obtained numerical values may be 5 seconds or more and 30 seconds or less. By securing 5 seconds or more as this time, the determination accuracy can be improved. By setting this time to 30 seconds or less, it is possible to determine the compression position sufficiently earlier than the change cycle of the rescuer (for example, 2 minutes).

Specific examples of an apparatus and a method for evaluating chest compression of the present disclosure will be described below with reference to the drawings. In the following description, the same reference numerals will be applied to the same elements in description of the drawings, and redundant description thereof will be omitted.

FIG.1is a conceptual diagram of an evaluation apparatus1according to an embodiment. A total hemoglobin concentration (cHb), an oxygenated hemoglobin concentration (O2Hb), and a deoxygenated hemoglobin concentration (HHb) of a head51vary due to repetition of chest compression (arrow A in the figure) on the cardiorespiratory arrest person50. The evaluation apparatus1continuously measures temporal changes from initial amounts, that is, relative change amounts, in the total hemoglobin concentration (cHb), the oxygenated hemoglobin concentration (O2Hb), and the deoxygenated hemoglobin concentration (HHb) of the head51. The evaluation apparatus1displays the measurement result on the display unit15. In addition, the evaluation apparatus1calculates a first indicator and a second indicator from temporal changes in relative change amounts in the cHb concentration, the O2Hb concentration, and the HHb concentration. The evaluation apparatus1evaluates whether the compression position on the sternum is appropriate based on the first indicator and the second indicator. In a case where the compression position is inappropriate, the evaluation apparatus1displays an element15aon the display unit15, the element15aindicating an instruction to change the compression position, to notify the rescuer that the compression position is inappropriate.

The evaluation apparatus1makes measurement lights having a plurality of wavelengths incident on a predetermined light incident position from a probe30fixed to the surface of the head51. The evaluation apparatus1detects intensities of the measurement lights emitted from the predetermined light detection position on the surface of the head51to examine the magnitude of attenuation by O2Hb and HHb at each wavelength. The evaluation apparatus1calculates temporal relative change amounts of cHb, O2Hb, and HHb based on the magnitude of attenuation at each wavelength. The evaluation apparatus1repeats the incidence of the measurement lights, the detection of the intensities of the measurement lights, and the calculation of the temporal relative change amounts of cHb, O2Hb, and HHb. The evaluation apparatus1performs filtering process on the time-series data, which is the calculation result, to remove low-frequency components, thereby extracting a short-cycle time variation component (a pulse wave component) caused by repetition of chest compression. The wavelengths of the measurement lights are included in the near infrared region and include three wavelengths such as 735 nm, 810 nm, and 850 nm in one example.

FIG.2is a plan view schematically showing the configuration of the probe30. The probe30is fixed to, for example, the forehead without hair or the vicinity of the carotid artery by an adhesive tape, an elastic band, or the like. The probe30includes a light incidence portion31and a light detection portion32. The light incidence portion31and the light detection portion32are arranged at an interval of, for example, 5 cm from each other, and are substantially integrated by a flexible black silicon rubber holder33. The interval between the light incidence portion31and the light detection portion32may be substantially within a range of 3 cm to 4 cm or may be equal to or greater than 4 cm. The material of the holder33may be replaced with another material having flexibility equivalent to that of silicon rubber. The probe30is electrically connected to a main body unit10(seeFIG.1) of the evaluation apparatus1via a cable34.

The light incidence portion31receives a control signal transmitted from the main body unit10and outputs the measurement lights. The measurement lights are pulsed light and enter the cortical layer on the surface of the head51substantially perpendicularly. The light incidence portion31includes a semiconductor light emitting element such as a laser diode (LD), a light emitting diode (LED), or a super luminescent diode (SLD), and a circuit for driving the light emitting element. The light emitting element and the driving circuit may be provided in the main body unit10. In that case, the probe30and the main body unit10are connected via an optical fiber, and the light incidence portion31includes a distal end portion of the optical fiber.

The light detection portion32generates detection signals corresponding to the intensities of the measurement lights that have propagated through the head51and emitted from the surface of the head51. The light detection portion32includes a plurality of photodetectors35arranged in a distance direction from the light incidence portion31. The plurality of photodetectors35are arranged side by side along an arrangement direction of the light incidence portion31and the light detection portion32. Distances from the light incidence portion31to photodetectors35are different for each photodetector35.

Each photodetector35generates the electrical detection signals corresponding to the intensities of the received measurement lights. Each photodetector35includes a semiconductor light receiving element such as a photodiode (PD) or an avalanche photodiode (APD) and a preamplifier that integrates and amplifies a current output from the semiconductor light receiving element. Thus, the photodetector35can detect weak measurement light with high sensitivity to generate the detection signals, and transmit the detection signals to the main body unit10via the cable34. The light detection portion32may be a one-dimensional or two-dimensional optical sensor, and may be configured by, for example, a CCD image sensor or a CMOS image sensor.

As shown inFIG.1, the evaluation apparatus1includes the main body unit10in addition to the probe30described above.FIG.3is a block diagram illustrating a functional configuration example of the main body unit10. The main body unit10includes a concentration calculation portion10a, a compression position evaluation unit10b, and an instruction unit10c. The concentration calculation portion10ais a calculation portion in the present embodiment, and constitutes a measuring unit10dtogether with the light incidence portion31and the light detection portion32described above. The measuring unit10dobtains numerical values relating to temporal changes from initial amounts, in the cHb concentration, the O2Hb concentration, and the HHb concentration in the head51of the cardiorespiratory arrest person50. The compression position evaluation unit10bdetermines whether the compression position on the sternum is appropriate based on the first indicator and the second indicator. The first indicator is relating to a temporal change ratio of the O2Hb concentration or/and the HHb concentration with respect to the temporal change in the cHb concentration. The second indicator is relating to a correlation between the temporal change in the O2Hb concentration and the temporal change in the HHb concentration. The instruction unit10cincludes the display unit15described above, and instructs the rescuer to change the compression position in a case where the compression position on the sternum is inappropriate.

FIG.4is a diagram illustrating a hardware configuration example of the main body unit10. The main body unit10includes a light emission control unit11, a sample and hold circuit12, an A/D conversion circuit13, a CPU14, the display unit15, a ROM16, a RAM17, and a data bus18.

The light emission control unit11is constituted by a circuit that controls the light incidence portion31of the probe30. The light emission control unit11is electrically connected to the data bus18. The light emission control unit11receives a control signal for controlling the light incidence portion31from the CPU14electrically connected to the data bus18. The control signal includes information such as intensities and wavelengths of the measurement lights output from the light incidence portion31. The light emission control unit11controls the light incidence portion31based on the control signal received from the CPU14. The light incidence portion31outputs measurement lights corresponding to the control signal.

The sample and hold circuit12receives detection signals transmitted from the probe30via the cable34and holds the detection signals. The A/D conversion circuit13converts the detection signals into digital signals and outputs the digital signals to the CPU14. The sample and hold circuit12simultaneously holds values of the detection signals corresponding to the number of the photodetectors35. The sample and hold circuit12is electrically connected to the data bus18. The sample and hold circuit12receives sample signals indicating timings for holding the detection signals from the CPU14via the data bus18. Upon receiving the sample signals, the sample and hold circuit12simultaneously holds a plurality of the detection signals input from the plurality of photodetectors35of the probe30. The sample and hold circuit12is electrically connected to the A/D conversion circuit13, and outputs each of the plurality of held detection signals to the A/D conversion circuit13.

The A/D conversion circuit13converts the detection signals from analog signals to digital signals. The A/D conversion circuit13sequentially converts the plurality of detection signals received from the sample and hold circuit12into digital signals. The A/D conversion circuit13is electrically connected to the data bus18, and outputs the converted detection signals to the CPU14via the data bus18.

The CPU14realizes various functions by reading and executing a program stored in the ROM16. As one of the functions, the CPU14calculates, based on the detection signals received from the A/D conversion circuit13, numerical values relating to temporal changes from initial amounts in the O2Hb concentration and the HHb concentration of the head51, and a numerical value relating to a temporal change from an initial amount in the total hemoglobin concentration (cHb) which is a sum of the O2Hb concentration and the HHb concentration. Further, the CPU14applies filtering process on the temporal change in the O2Hb concentration, the HHb concentration, and the cHb concentration, and removes frequency components less than a predetermined frequency from frequency components included in the these temporal changes. As a result, a temporal variation component (a pulse wave component) caused by the repetition of chest compression is extracted. After performing such a process, the CPU14sends the result to the display unit15via the data bus18. The concentration calculation portion10ashown inFIG.3comprises the sample hold circuit12, the A/D conversion circuit13, and the CPU14. A method of calculating the temporal changes in the O2Hb concentration, the HHb concentration, and the cHb concentration based on the detection signals, and a method of filtering will be described later.

FIGS.5and6are diagrams conceptually showing the temporal changes from initial amounts in the O2Hb concentration and the HHb concentration. The horizontal direction represents time, and the vertical direction represents concentration. Curve G11represents the temporal change from the initial amount in the O2Hb concentration. Curve G12represents the temporal change from the initial amount in the HHb concentration. Part (a) ofFIG.5shows a case where an amplitude AO2Hbof the temporal change from the initial amount in the O2Hb concentration is higher than an amplitude AHHbof the temporal change from the initial amount in the HHb concentration (AO2Hb/AHHb>1) is shown. This case is equivalent to a case where a ratio of the amplitude AO2Hbof the temporal change from the initial amount in the O2Hb concentration to an amplitude AcHbof the temporal change from the initial amount in the cHb concentration is more than 0.5 (AO2Hb/AcHb>0.5). Further, this case is equivalent to a case where a ratio of the amplitude AHHbof the temporal change from the initial amount in the HHb concentration to the amplitude AcHbof the temporal change from the initial amount in the cHb concentration is less than 0.5 (AHHb/AcHb<0.5). Conversely, part (b) ofFIG.5shows a case where the amplitude AHHbare higher than the amplitude AO2Hb(AO2Hb/AHHb<1). This case is equivalent to a case where the ratio of the amplitudes AO2Hbto the amplitudes AcHbis less than 0.5 (AO2Hb/AcHb<0.5). Further, this case is equivalent to a case where the ratio of the amplitude AHHbof the temporal change from the initial amount in the HHb concentration to the amplitude AcHbof the temporal change from the initial amount in the cHb concentration is higher than 0.5 (AHHb/AcHb>0.5). Part (a) ofFIG.6shows a case where an absolute value of a phase difference e between the temporal change from the initial amount in the O2Hb concentration and the temporal change from the initial amount in the HHb concentration are low, and part (b) ofFIG.6shows a case where the absolute value of the phase difference φ is high.

As shown in an example described later, in a case where the amplitude AO2Hbis higher than a predetermined ratio with respect to the amplitude AHHb, that is, the amplitude AO2Hbis higher than a predetermined ratio with respect to the amplitude AcHb(part (a) ofFIG.5) and the absolute value of the phase difference φ is less than a certain value (part (a) ofFIG.6), the compression position on the sternum is appropriate and TOI gradually increases. On the other hand, in a case where the amplitude AO2Hbis less than the predetermined ratio with respect to the amplitude AHHb, that is, the amplitude AO2Hbis less than the predetermined ratio with respect to the amplitude AcHb(part (b) ofFIG.5) and the absolute value of the phase difference e is higher than the certain value (part (b) ofFIG.6), the compression position on the sternum is not appropriate, and TOI becomes leveling off or gradually decreases. Therefore, the CPU14calculates the first indicator relating to the ratio (AO2Hb/AHHb) between the amplitudes AO2Hband AHHb, and calculates the second indicator relating to the phase difference φ. The first indicator may be the amplitude ratio (AO2Hb/AHHb) itself, or may be another numerical value (for example, the ratio of time integral values) correlated with the amplitude ratio (AO2Hb/AHHb). The first indicator may be a time-moving mean value of the amplitude ratio (AO2Hb/AHHb) or the another numerical value, or may be another value similar to a mean value. The second indicator may be the phase difference e itself or an absolute value thereof itself, or may be another numerical value (for example, a peak time difference) correlated with the phase difference e or the absolute value thereof. The second indicator may be a time-moving mean value of the phase difference e or the absolute value thereof or the another numerical value, or may be another value similar to a mean value.

From the above-described equivalent relationship, the first indicator may be the amplitude ratio (AO2Hb/AcHb) itself, or may be another numerical value (for example, a ratio of time integral values) having a correlation with the amplitude ratio (AO2Hb/AcHb). The first indicator may be a time-moving mean value of the amplitude ratio (AO2Hb/AcHb) or the another numerical value, or may be another value similar to a mean value. Further, the first indicator may be the amplitude ratio (AHHb/AcHb) itself, or may be another numerical value (for example, a ratio of time integral values) having a correlation with the amplitude ratio (AHHb/AcHb). The first indicator may be a time-moving mean value of the amplitude ratio (AHHb/AcHb) or the another numerical value, or may be another value similar to a mean value.

The compression position evaluation unit10bshown inFIG.3is configured by the CPU14. That is, the CPU14determines whether the compression position on the sternum is appropriate based on the first indicator and the second indicator described above. For example, in a case where the first indicator indicates that the amplitude ratio (AO2Hb/AHHbor AO2Hb/AcHb) is less than a first threshold value and the second indicator indicates that the absolute value of the phase difference φ converted to R2is less than a second threshold value, the CPU14determines that the compression position on the sternum is inappropriate. The first threshold value is, for example, 0.5 or more and 1.0 or less in terms of SnO2. In one example, the first threshold value is 1. The CPU14may determine that the compression position on the sternum is inappropriate in a case where the first indicator indicates that the amplitude ratio (AHHb/AcHb) is higher than a first threshold value and the second indicator indicates that the absolute value of the phase difference p converted into R2is less than the second threshold value. In a case where the first threshold value is 1, the CPU14determines that the compression position is inappropriate when the amplitude AO2Hbis less than the amplitude AHHb. The second threshold value is, for example, 0 or more and 0.7 or less in terms of R2

Reference is again made toFIG.4. The display unit15is electrically connected to the data bus18, and visually displays calculation results relating to temporal changes from initial amounts in the O2Hb concentration and the HHb concentration transmitted from the CPU14via the data bus18. Furthermore, in a the case where the CPU14determines that the compression position on the sternum is inappropriate, the display unit15displays the element15a. The element15ais a character, a figure, a symbol, a picture, or the like, or a combination thereof for instructing the rescuer to change the compression position. The evaluation apparatus1may include a speaker that outputs a voice and/or a warning sound for instructing the rescuer to change the compression position instead of or together with the display on the display unit15for instructing the rescuer to change the compression position. The instruction unit10cillustrated inFIG.3includes the CPU14and one or both of the display unit15and the speaker.

In the present embodiment, “instruct to change the compression position” means prompting the rescuer to change the compression position. The instruction to change the compression position conceptually includes an active instruction that explicitly instructs that the compression position should be changed and a passive instruction that conveys that the compression position is inappropriate. As a system of instructing the change of the compression position, various systems by which the rescuer can recognize the necessity of changing the compression position can be applied.

Next, an operation of the evaluation apparatus1will be described. In addition, an evaluation method according to the present embodiment will be described.FIG.7is a flowchart showing an evaluation method according to the present embodiment. In the following description, a case where three measurement lights having wavelengths λ1to λ3are used will be described as an example.

First, the light emission control unit11sequentially outputs measurement lights having wavelengths λ1to λ3from the light incidence portion31based on an instruction signal from the CPU14. These measurement lights enter the head51from the light incident position (light incidence step ST11). The measurement lights incident on the head51are scattered in the head51and propagates while being absorbed by the component to be measured, and a part thereof reaches the light detection position of the head51. The measurement lights having reached the light detection position are emitted from the head51and detected by the plurality of photodetectors35(light detection step ST12). Each photodetector35generates the detection signals corresponding to the intensities of the detected measurement lights. These detection signals are sent to and held by the sample and hold circuit12of the main body unit10, and then converted into digital signals by the A/D conversion circuit13.

Part (a) ofFIG.8is a diagram illustrating the incident timings of the measurement lights having wavelengths λ1to λ3. Part (b) ofFIG.8is a diagram illustrating the output timings of the digital signals from the A/D conversion circuit13. As shown inFIG.8, when the measurement light having wavelength λ1is made incident, N (N is the number of photodetectors35) digital signals D1(1) to D1(N) respectively corresponding to the N photodetectors35are sequentially output from the A/D conversion circuit13. Subsequently, when the measurement light having wavelength λ2is made incident, N digital signals D2(1) to D2(N) respectively corresponding to the N photodetectors35are sequentially output from the A/D conversion circuit13. Subsequently, when the measurement light having wavelength λ3is made incident, N digital signals D3(1) to D3(N) respectively corresponding to the N photodetectors35are sequentially output from the A/D conversion circuit13.

Subsequently, the CPU14calculates TOI based on the digital signals D1(1) to D1(N), D2(1) to D2(N), and D3(1) to D3(N). The CPU14uses at least one of the digital signals D1(1) to D1(N), at least one of the digital signals D2(1) to D2(N), and at least one of the digital signals D3(1) to D3(N) to obtain a numerical value relating to the temporal change amount in the O2Hb concentration from the initial value (ΔO2Hb), a numerical value relating to the temporal change amount in the HHb concentration from the initial value (ΔHHb), and a numerical value relating to the temporal change amount in the total hemoglobin concentration from the initial value (ΔcHb) (calculation step ST13). The CPU14removes frequency components lower than a predetermined frequency among frequency components included in these change amounts (ΔcHb, ΔO2Hb, ΔHHb) by filtering process, and extracts pulse wave components of the respective change amounts (filtering process step ST14). These change amounts (ΔcHb, ΔO2Hb, ΔHHb) after the filtering process are displayed on the display unit15(display step ST15). The light incidence step ST11, the light detection step ST12, the calculation step ST13, the filtering process step ST14, and the display step ST15described above are included in the measurement step ST1for obtaining the numerical values relating to ΔcHb, ΔO2Hb, and ΔHHb in the head51.

CPU14calculates the first indicator relating to the ratio of one or both of ΔO2Hb and ΔHHb to ΔcHb, and calculates the second indicator relating to the correlation between ΔO2Hb and ΔHHb (step ST2). For example, the first indicator is an amplitude ratio of ΔO2Hb to ΔcHb, an amplitude ratio of ΔHHb to ΔcHb, or an amplitude ratio of ΔO2Hb to ΔHHb, and the second indicator is a phase difference between ΔO2Hb and ΔHHb. The CPU14determines whether the compression position on the sternum is appropriate based on the first indicator and the second indicator (compression position evaluation step ST3). As described above, for example, the CPU14determines that the compression position on the sternum is inappropriate when the first indicator indicates that the amplitude ratio (AO2Hb/AHHb) or the amplitude ratio (AO2Hb/AcHb) is less than the first threshold value and the second indicator indicates that the absolute value of the phase difference (p converted to R2is less than the second threshold value.

In a case where the CPU14determines that the compression position on the sternum is inappropriate (step ST3: NO), the CPU14instructs the display unit15to display the element15afor instructing the rescuer to change the compression position (instruction step ST4). Alternatively, in a case where the evaluation apparatus1comprises a speaker, the CPU14may cause the speaker to output a voice and/or a warning sound for instructing the rescuer to change the compression position. In a case where the CPU14determines that the compression position on the sternum is appropriate (step ST3: YES), the instruction step ST4is not performed.

In the evaluation apparatus1and the concentration measuring method according to the present embodiment, the above-described steps ST1to ST4are repeated until the chest compression ends (step ST5).

Here, contents of the calculation by CPU14in the calculation step ST13and the filtering process step ST14will be described in detail.

At a certain light detection position, when the values of the detection signals corresponding to the measurement light wavelengths λ1to λ3at the time T0are Dλ1(T0) to Dλ3(T0) and the values at the time T1are Dλ1(T1) to Dλ3(T1), change amounts of detected light intensities at a time T0to T1is expressed by following formulas (1) to (3).

In the formulas (1) to (3), ΔOD1(T1) is the temporal change amount of the detected light intensity at wavelength λ1, ΔOD2(T1) is the temporal change amount of the detected light intensity at wavelength λ2, and ΔOD3(T1) is the temporal change amount of the detected light intensity at wavelength λ3.

Temporal relative change amounts of the concentrations of O2Hb and HHb over time from time T0to time T1are denoted by ΔO2Hb(T1) and ΔHHb(T1), respectively. ΔO2Hb(T1) and ΔHHb(T1) can be obtained by following formula (4).

In the formula (4), coefficients an to a23are constants obtained from the extinction coefficients of O2Hb and HHb with respect to lights having wavelengths λ1, λ2, and λ3. The temporal relative change amount ΔcHb(T1) of cHb in the head51can be obtained by following formula (5).

The CPU14performs the above-described calculation with respect to one detection signal among the N light detection positions, and calculates temporal relative change amounts (ΔO2Hb, ΔHHb, ΔcHb) of the O2Hb concentration, the HHb concentration, and the cHb concentration. Further, the CPU14performs, any one of the following filtering processes, for example, on the temporal relative change amounts (ΔO2Hb, ΔHHb, ΔcHb) calculated in this manner.

(1) Filtering Process by Digital Filter

An data sequence relating to the temporal relative change amounts (ΔO2Hb, ΔHHb, ΔcHb) obtained in a predetermined cycle is denoted by X(n). N is an integer. A non-cyclic linear phase digital filter is realized by multiplying each data in the the data sequence X(n) by, for example, the following filter coefficient A(n) with n=0 as a temporal center.

To explain in more detail, the delay operator of the data sequence X(n) is expressed by following formula (6). F is a temporal frequency (the unit is 1/sec). Ω is an angular frequency, and ω=2πf. T is a cycle at which the data sequence X(n) is obtained, and is set to a cycle of, for example, 1/20 second in order to measure a variation waveform up to about 150 times per minute (2.5 Hz).

In this case, characteristics of the digital filter when the above-described filter coefficient A(n) is used is described by following formula (7).

In this manner, the digital filter is represented by a product-sum operation of the data sequence X(n) and each corresponding coefficient. When the temporal frequency f in the formula (7) is converted into a temporal frequency F per minute (the unit: 1/min), following formula (8) is obtained.

FIG.9is a graph showing this R(F) and shows the filter characteristics of the digital filter. InFIG.9, the horizontal axis represents the heart rate per minute, and the vertical axis represents the value of R(F).FIG.10is a graph showing an example of a result obtained by removing (or reducing) frequency components less than a predetermined frequency from frequency components included in a temporal relative change amount of O2Hb (ΔO2Hb) by using the digital filter shown inFIG.9to extract a temporal variation component caused by a spontaneous heart beat simulating repetition of chest compression. InFIG.10, a graph G21indicates the relative change amount (ΔO2Hb) before the filtering process, a graph G22indicates long-period components (frequency components less than the predetermined frequency) included in the relative change amount (ΔO2Hb) before the filtering process, and a graph G23indicates the relative change amount (ΔO2Hb) after the filtering process. As shown inFIG.10, the temporal variation component (the pulse wave component) caused by repetition of spontaneous heartbeat or chest compression can be suitably extracted by the above-described digital filter.

(2) Filtering Process by Smoothing Operation (Least Square Error Curve Fitting)

With n=0 as the temporal center in the data sequence X(n) described above, the least square error curve fitting using a high-order function (for example, a fourth order function) is performed on the data sequence X(n) obtained during a predetermined period of time (for example, 3 seconds, 5 beats) before and after the temporal center. The constant term of the obtained high-order function is regarded as a smoothed component (frequency component less than the predetermined frequency) at n=0. That is, by subtracting the smoothed frequency component from the original data X(0), it is possible to remove the frequency components less than the predetermined frequency from the frequency components included in the relative change amount to separate and extract the temporal variation component (the pulse wave component) caused by the repetition of the chest compression.

FIG.11is a graph showing a result obtained by removing (or reducing) the frequency components less than the predetermined frequency from frequency components included in the temporal relative change amount of cHb (ΔcHb) to extract the temporal variation component (the pulse wave component) caused by the spontaneous heart beat simulating repetition of the chest compression by using such filtering process. InFIG.11, a graph G31shows the relative change amount (ΔcHb) before the filtering process, a graph G32shows long-period components (frequency component less than the predetermined frequency) included in the relative change amount (ΔcHb) before the filtering process, a graph G33shows the relative change amount (ΔcHb) after the filtering process, and a graph G34shows a mean amplitude for five seconds of the relative change amount (ΔcHb) after the filtering process. As shown inFIG.11, it is possible to preferably extract the temporal variation component (the pulse wave component) caused by the repetition of the spontaneous heartbeat or the chest compression by the filtering process by the smoothing operation described above.

(3) Filtering Process for Making the Local Maximum Part and the Local Minimum Part of Variation Constant

Parts (a) and (b) ofFIG.12are diagrams for explaining the concept of the present filtering process. In this filtering process, for example, the local maximum values in the temporal changes of the relative change amounts (ΔO2Hb, ΔHHb, or ΔcHb) is obtained, and as shown in part (a) ofFIG.12, the local maximum value P1of the temporal change graph G41is regarded as a constant value, thereby removing frequency components less than the predetermined frequency included in the relative change amounts (ΔO2Hb, ΔHHb, or ΔcHb). Alternatively, for example, the local minimum values in the temporal changes of the relative change amounts (ΔO2Hb, ΔHHb, or ΔcHb) are obtained, and as shown in part (b) ofFIG.12, the local minimum value P2of the temporal change graph G41is regarded as a constant value, thereby removing frequency components less than the predetermined frequency included in the relative change amounts (ΔO2Hb, ΔHHb, or ΔcHb). In this manner, by bringing the local maximum value P1and/or the local minimum value P2close to a constant value, it is possible to suitably extract the temporal variation component (the pulse wave component) caused by the repetition of the chest compression.

Effects obtained by the evaluation apparatus1and the evaluation method of the present embodiment described above will be described. As is clear from examples described later, the ratio of the temporal change in the O2Hb concentration and the HHb concentration to the temporal change in the cHb concentration, and the correlation between the temporal change in the O2Hb concentration and the temporal change in the HHb concentration vary depending on the compression position on the sternum. In addition, there is a significant correlation between both the ratio and the correlation and the tendency (ascending tendency, descending tendency, or leveling off tendency) of the temporal change in TOI of the head51.

In the evaluation method and the evaluation apparatus1of the present embodiment, it is determined whether the compression position on the sternum is appropriate, that is, whether the tendency of the temporal change in TOI of the head51is the ascending tendency, the descending tendency, or the leveling off tendency, based on the first indicator relating to the above-mentioned ratio and the second indicator relating to the above-mentioned correlation. And then, in a case where the compression position on the sternum is inappropriate, an instruction to change the compression position is given. In this manner, by evaluating whether the compression position on the sternum is appropriate and notifying the rescuer of the fact that the chest compression position is inappropriate in a case where the chest compression is not appropriately performed, it is possible to bring the tendency of the temporal change in TOI of the head51close to an ascending tendency and to increase the success rate of cardiopulmonary resuscitation.

As in the present embodiment, the measuring unit10dmay include the light incidence portion31that makes the measurement lights incident on the head51, the light detection portion32that detects the measurement lights having propagated through the head51and generates the detection signals corresponding to the intensities of the measurement lights, and the concentration calculation portion10athat calculates the numerical values relating to the temporal changes in the cHb concentration, the O2Hb concentration, and the HHb concentration based on the detection signals. The measurement step ST1may include the light incidence step ST11of making the measurement lights incident on the head51, the light detection step ST12of detecting the measurement lights having propagated through the head51and generating detection signals corresponding to the intensities of the measurement lights, and the calculation step ST13of calculating the numerical values relating to temporal changes in the cHb concentration, the O2Hb concentration, and the HHb concentration based on the detection signals. In these cases, temporal changes in the cHb concentration, the O2Hb concentration, and the HHb concentration of the head51can be measured non-invasively and simply. Therefore, it is possible to easily measure the temporal changes in the cHb concentration, the O2Hb concentration, and the HHb concentration of the head51while performing the chest compression.

As in the present embodiment, the compression position evaluation unit10bor the compression position evaluation step ST3may calculate the ratio (AO2Hb/AcHb, AHHb/AcHb) of amplitudes of temporal changes of one or both of the O2Hb concentration and the HHb concentration to an amplitude of the temporal change of the cHb concentration as the first indicator, and calculate phase difference φ between the phase of the temporal change of the O2Hb concentration and the phase of the temporal change of the HHb concentration as the second indicator. In this case as well, by evaluating whether the compression position on the sternum is appropriate, and notifying the rescuer the fact that the compression position is inappropriate in the case where the compression position is inappropriate, it is possible to bring the tendency of the temporal change in TOI of the head51close to an ascending tendency to increase the success rate of cardiopulmonary resuscitation.

As in the present embodiment, the compression position evaluation unit10bor the compression position evaluation step ST3may determine that the compression position on the sternum is inappropriate in the case where the first indicator indicates that the ratio (AO2Hb/AcHb) of the amplitude AO2Hbof the temporal change in the O2Hb concentration to the amplitude AcHbof the temporal change in the cHb concentration is less than the first threshold value and where the second indicator indicates that the absolute value, which is a value in terms of R2, of the phase difference φ between the temporal change in O2Hb concentration and the temporal change in HHb concentration are less than the second threshold. For example, in this manner, by comparing the magnitude between the amplitude ratio and the first threshold value and comparing the magnitude between the absolute value of the phase difference and the second threshold, it is possible to easily evaluate whether the compression position on the sternum is appropriate.

As in the present embodiment, the first threshold value may be 0.5 or more and 1.0 or less in terms of SnO2. For example, in this case, it is possible to more accurately evaluate whether the compression position on the sternum is appropriate.

As in the present embodiment, the second threshold value may be 0 or more and 0.7 or less in terms of R2. For example, in this case, it is possible to more accurately evaluate whether the compression position on the sternum is appropriate.

As in the present embodiment, the concentration calculation portion10amay obtain the pulse wave component of the cHb concentration, the pulse wave component of the O2Hb concentration, and the pulse wave component of the HHb concentration by performing filtering process on the numerical values to extract the component that vary due to the repetition of chest compression. The compression position evaluation unit10bmay calculate the first indicator and the second indicator using the pulse wave component of the cHb concentration, the pulse wave component of the O2Hb concentration, and the pulse wave component of the HHb concentration. The measurement step ST1may include the step ST14of performing filtering process on the numerical values to extract components that vary due to the repetition of chest compression to obtain the pulse wave component of the cHb concentration, the pulse wave component of the O2Hb concentration, and the pulse wave component of the HHb concentration. The step ST2may calculate the first indicator and the second indicator using the pulse wave component of the cHb concentration, the pulse wave components of the O2Hb concentration, and the pulse wave components of the HHb concentration. In these cases, it is possible to accurately calculate the first indicator and the second indicator based on only the variation component (the pulse wave component) caused by the repetition of the chest compression.

In the evaluating method and the evaluation apparatus1of the present embodiment, SnO2may be calculated as the first indicator relating to the temporal change ratio of the O2Hb concentration with respect to the temporal change in the cHb concentration, and R2may be calculated as the second indicator relating to the correlation between the temporal change in the O2Hb concentration and the temporal change in the HHb concentration. Then, based on SnO2and R2, it may be determined whether the compression position on the sternum is appropriate, that is, whether the tendency of the temporal change in TOI of the head51is ascending tendency, descending tendency or leveling off tendency. In the case where the compression position on the sternum is inappropriate, a change in the compression position is indicated. In this manner, by evaluating whether the compression position on the sternum is appropriate and notifying the rescuer that the compression position is inappropriate when the compression position is inappropriate, it is possible to bring the tendency of the temporal change in TOI of the head51close to ascending tendency and increase the success rate of cardiopulmonary resuscitation.

The SnO2can be obtained from a linear regression between a numerical value relating to the pulse wave component of the cHb concentration and a numerical value relating to the pulse wave component of the O2Hb concentration, which are obtained in a predetermined period (for example, up to 5 seconds retroactively from the calculation timing). The SnO2is a slope (regression coefficient) of a regression line obtained by performing linear regression using a numerical value relating to the pulse wave component of the cHb concentration obtained in the predetermined period as an explanatory variable and a numerical value relating to the pulse wave component of the O2Hb concentration obtained in the predetermined period as an objective variable. The R2can be obtained from a linear regression between a numerical value relating to the pulse wave component of the O2Hb concentration and a numerical value relating to the pulse wave component of the HHb concentration, which are obtained in a predetermined period (for example, up to 5 seconds retroactively from present time). The R2is a determination coefficient obtained by performing linear regression using a numerical value relating to the pulse wave component of the O2Hb concentration obtained in the predetermined period as an explanatory variable and a numerical value relating to the pulse wave component of the HHb concentration obtained in the predetermined period as an objective variable. As described later, the changes in SnO2and R2have correlations with TOI of the head51.

Even in a case where the first indicator and the second indicator are calculated using mean values such as moving averages of the numerical values, it is preferable that the time from when the measuring unit10dor the measurement step ST1starts obtaining the numerical values to when the compression position evaluation unit10bor the compression position evaluation step ST3determines the compression position based on the obtained numerical values is 5 seconds or more and 30 seconds or less. By securing 5 seconds or more as the time, it is possible to sufficiently secure the number of numerical values used for calculation of mean values or the like and regression calculation to improve determination accuracy. By setting this time to 30 seconds or less, it is possible to prompt the change of the compression position sufficiently earlier than the change cycle (for example, 2 minutes) of the rescuer.

Example

Next, an example in which temporal changes in TOI, the cHb concentration, the O2Hb concentration, and the HHb concentration in cardiopulmonary resuscitation were actually observed will be described. In the present example, in order to continue chest compression for a long period of time during cardiopulmonary resuscitation, two rescuers performed chest compression while alternating about every two minutes. When the rescuer changes, the compression position on the sternum will of course change slightly.

Part (a) ofFIG.13is a graph showing a temporal change in the cHb concentration of the head in the cardiopulmonary resuscitation. Part (b) ofFIG.13is a graph showing a temporal change in TOI of the head in the cardiopulmonary resuscitation. In these figures, the horizontal axis represents time (hour: minute). The vertical axis of part (a) ofFIG.13represents a relative value of the cHb concentration, and the vertical axis of part (b) ofFIG.13represents the magnitude of TOI (unit: %). In the figure, periods A in which one of the two rescuers performs chest compression and periods B in which the other rescuer performs chest compression are shown. In the figure, arrows C indicating the timing at which the pulse check was performed and arrows D indicating the timing at which adrenaline (epinephrine) was administered are shown together.

Each ofFIGS.14to17is a graph showing temporal changes of (a) change amounts in O2Hb concentration and HHb concentration, (b) pulse wave oxygen saturation, that is, a slope in linear regression between the pulse wave component of the cHb concentration and the pulse wave component of the O2Hb concentration (regression coefficient: SnO2), (c) determination coefficient (R2) obtained by linear regression between the pulse wave component of the O2Hb concentration and the pulse wave component of the HHb concentration, and (d) tissue oxygen saturation (TOI), in each of the parts E1to E4ofFIG.13. The horizontal axis of these graphs represent time (hour: minute: second), the unit of the vertical axis of part (a) is arbitrary unit, and the unit of the vertical axes of parts (b) and (d) is %. In part (a), the broken line indicates the change amount of the O2Hb concentration, and the solid line indicates the change amount of the HHb concentration.

Referring toFIGS.13to17, it can be seen that there are a period in which TOI has ascending tendency, a period in which TOI has descending tendency, and a period in which TOI has leveling off tendency, in a plurality of periods including the period A and the period B. The period in which TOI has ascending tendency is, for example, a period including the part E2, and is illustrated inFIG.15. The period in which TOI has descending tendency is, for example, a period including the part E3, and is illustrated inFIG.16. The period in which TOI has leveling off tendency is, for example, a period including the part E1and a period including the part E4, and is illustrated inFIGS.14and17. Referring to parts (a) and (b) ofFIG.15, it is understood that the value of SnO2is higher than 50% and the ratio of the pulse wave component of the O2Hb concentration to the pulse wave component of the cHb concentration is high, in the period in which TOI has ascending tendency. On the other hand, referring to parts (a) and (b) ofFIGS.14,16, and17, it can be seen that the value of SnO2is at least partially less than 50% and the ratio of the pulse wave component of the O2Hb concentration to the pulse wave component of the cHb concentration is low, in the period in which TOI has descending tendency or leveling off tendency. As shown in part (c) ofFIG.15, in a period in which TOI has ascending tendency, the value of R2is relatively high, and it can be said that the correlation between the pulse wave component of the O2Hb concentration and the pulse wave component of the HHb concentration is high. On the other hand, as shown in part (c) ofFIGS.14,16, and17, in a period in which TOI has descending tendency or leveling off tendency, the value of R2is relatively low, and the correlation between O2Hb pulse wave component and HHb pulse wave component is low.

As described above, there is a significant correlation between the ratio of the pulse wave component of the O2Hb concentration to the pulse wave component of the cHb concentration and the tendency (ascending tendency, descending tendency, or leveling off tendency) of the temporal change in TOI of the head. There is also a significant correlation between the tendency of the temporal change of TOI of the head and the correlation between the pulse wave component of the O2Hb concentration and the pulse wave component of the HHb concentration. That is, as the ratio of the pulse wave component of the O2Hb concentration to the pulse wave component of the cHb concentration is higher and the correlation between the temporal change in the O2Hb concentration and the temporal change in the HHb concentration is lower, the tendency of TOI becomes ascending tendency. On the other hand, as the ratio of the pulse wave component of the O2Hb concentration to the pulse wave component of the cHb concentration is lower and the correlation between the temporal change in the O2Hb concentration and the temporal change in the HHb concentration is higher, the tendency of TOI becomes leveling off tendency or descending tendency. Even in a case where the ratio of the temporal change in the O2Hb concentration to the temporal change in the cHb concentration is low, when the ratio is higher than a predetermined ratio, there is a possibility that the TOI becomes ascending tendency.

Since the cHb concentration is the sum of the O2Hb concentration and the HHb concentration, it is estimated from the above results that there is a significant correlation between the ratio of the pulse wave component of the HHb concentration to the pulse wave component of the cHb concentration and the tendency (ascending tendency, descending tendency, or leveling off tendency) of the temporal change of TOI of the head. That is, as the ratio of the pulse wave component of the HHb concentration to the pulse wave component of the cHb concentration is lower, TOI becomes ascending tendency. On the other hand, as the ratio of the pulse wave component of the HHb concentration to the pulse wave component of the cHb concentration is higher, TOI becomes leveling off tendency or descending tendency. Even in a case where the ratio of the temporal change in the HHb concentration to the temporal change in the cHb concentration is high, when the ratio is less than a predetermined ratio, there is a possibility that the TOI becomes ascending tendency.

Among a plurality of periods in which the same rescuer performs chest compression, there are a period in which TOI has ascending tendency and a period in which TOI has descending tendency or leveling off tendency. Therefore, it can be said that such a difference in the tendency of the temporal change in TOI is not caused by the individual difference of the chest compression technique. As discussed above, when the rescuers change, the compression position on the sternum of course changes slightly. Therefore, it is considered that such a difference in the tendency of the temporal change in TOI is caused by a change in the compression position on the sternum at the time of alternation. That is, it is possible to suitably determine whether the compression position on the sternum is appropriate based on the ratio of the pulse wave component of the O2Hb concentration or/and the HHb concentration to the pulse wave component of the cHb concentration and the correlation between the temporal change in the O2Hb concentration and the temporal change in the HHb concentration. The above example shows that even if the chest compression is performed at an appropriate cycle and power, TOI of the head is not improved unless the compression position is appropriate.

The evaluation apparatus and evaluation method for chest compression according to the present disclosure are not limited to the embodiments described above, and various other modifications are possible. For example, in the above embodiment, near-infrared spectroscopy is exemplified as a method of measuring temporal changes in the cHb concentration, the O2Hb concentration, and the HHb concentration. The method of measuring temporal changes in the cHb concentration, the O2Hb concentration, and the HHb concentration is not limited to this, and various other methods can be used.

In the above-described embodiment, the instruction to change the compression position is given to the rescuer. The target to be instructed is not limited to the rescuer. For example, in a case where the chest compression is performed mechanically and automatically, an instruction signal for changing the position of the arm that compresses the sternum may be output from the instruction unit of the evaluation apparatus to the device that performs the chest compression.

INDUSTRIAL APPLICABILITY

The embodiment can be used as an apparatus and a method capable of increasing the success rate of cardiopulmonary resuscitation by evaluating whether the chest compression is appropriately performed and notifying a rescuer of the fact that the chest compression is inappropriate in a case where the chest compression is not appropriately performed.

REFERENCE SIGNS LIST