WO2015190413A1 - 循環時間測定装置、推定心拍出量算出装置、循環時間測定方法、推定心拍出量算出方法及びプログラム - Google Patents
循環時間測定装置、推定心拍出量算出装置、循環時間測定方法、推定心拍出量算出方法及びプログラム Download PDFInfo
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/0205—Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/026—Measuring blood flow
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/026—Measuring blood flow
- A61B5/029—Measuring or recording blood output from the heart, e.g. minute volume
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/08—Detecting, measuring or recording devices for evaluating the respiratory organs
- A61B5/087—Measuring breath flow
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7235—Details of waveform analysis
- A61B5/7246—Details of waveform analysis using correlation, e.g. template matching or determination of similarity
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7271—Specific aspects of physiological measurement analysis
- A61B5/7278—Artificial waveform generation or derivation, e.g. synthesising signals from measured signals
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
- A61B5/14542—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue for measuring blood gases
Definitions
- the present invention relates to a circulation time measurement device, an estimated cardiac output calculation device, a circulation time measurement method, an estimated cardiac output calculation method, and a program.
- ⁇ Cardiac output is one of the indicators of cardiac function status.
- the cardiac output indicates the amount of blood ejected from the heart in one minute, and this value decreases when the cardiac function decreases.
- There are various ways to measure cardiac output As a typical measurement method, for example, there is a thermodilution method.
- MRI, cardiac ultrasonography, impedance method and the like are also provided.
- Non-patent Document 1 Non-patent Document 1
- Patent Document 1 describes a measurement method that can noninvasively measure the circulation time of oxygen transport in the bloodstream. Patent Document 1 describes that the circulation time for oxygen transport in the bloodstream and the cardiac output correlate well.
- thermodilution method which is often used at present, is an invasive method of inserting a catheter into the heart, and various problems have been pointed out such as physical burden on the subject.
- measurement methods such as cardiac ultrasonography
- the problem is that accuracy cannot be maintained.
- Patent Document 1 does not describe such a method.
- an object of the present invention is to provide a circulation time measurement device, an estimated cardiac output calculation device, a circulation time measurement method, an estimated cardiac output calculation method, and a program that can solve the above-described problems.
- the circulation time measurement device includes a signal acquisition unit that acquires an airflow signal that indicates a temporal change in a respiratory airflow, and an oxygen saturation signal that indicates a temporal change in oxygen saturation, Based on a time difference between a predetermined first time in the airflow signal and a second time in the oxygen saturation signal indicating an increase in oxygen saturation corresponding to resumption of breathing at the first time, the oxygen carrying circulation time of blood
- the circulation time calculation unit shapes the airflow signal into a waveform representing a cycle of stopping and resuming breathing, and the waveform after the shaping and the oxygen saturation signal indicate The oxygen carrying circulation time is measured based on the time lag with the waveform.
- the circulation time calculating unit segments the airflow signal at predetermined time intervals to generate a segmented airflow signal; and the oxygen saturation signal is input to the predetermined value.
- Oxygen saturation segment that generates a segmental oxygen saturation signal by segmenting every time, and a filter applied to the segmental airflow signal, and shaping the segmental airflow signal into a waveform that represents the period of respiratory stop and restart
- a signal shaping processing unit for generating a segmental airflow signal; and calculating a time difference corresponding to a time lag between the waveform indicated by the shaped segmental airflow signal and the waveform indicated by the segmental oxygen saturation signal, and calculating the time difference as the oxygen transport
- a time difference calculation unit that sets the circulation time.
- the time difference calculation unit calculates the time difference using cross-correlation analysis for the shaped segmental airflow signal and the segmental oxygen saturation signal.
- an estimated cardiac output calculating device wherein the circulating time measuring device according to any one of the first to fourth embodiments and the circulating time measuring device measure The obtained oxygen carrying circulation time is obtained, and the estimated cardiac output is calculated based on the predetermined hyperbolic function indicating the relationship between the blood oxygen carrying circulation time and the cardiac output and the obtained oxygen carrying circulation time.
- a cardiac output calculating unit A cardiac output calculating unit.
- the circulation time measuring method includes the steps of: obtaining an airflow signal indicating a time change of a respiratory airflow; and an oxygen saturation signal indicating a time change of oxygen saturation; Measure the oxygen transport circulation time of blood based on the time difference between the predetermined first time in the signal and the second time in the oxygen saturation signal indicating an increase in oxygen saturation corresponding to resumption of breathing at the first time And a step of performing.
- the estimated cardiac output calculation method obtains an airflow signal indicating a temporal change in respiratory airflow and an oxygen saturation signal indicating a temporal change in oxygen saturation. Based on a time difference between a predetermined first time in the airflow signal and a second time in the oxygen saturation signal indicating an increase in oxygen saturation corresponding to resumption of breathing at the first time, the oxygen carrying circulation time of blood.
- the program acquires, from the computer of the circulation time measuring device, an airflow signal indicating a temporal change in respiratory airflow and an oxygen saturation signal indicating a temporal change in oxygen saturation.
- Means for transporting oxygen based on a time difference between a predetermined first time in the airflow signal and a second time in the oxygen saturation signal indicating an increase in oxygen saturation corresponding to resumption of breathing at the first time It functions as a means for measuring the circulation time.
- the program causes the computer of the estimated cardiac output calculation device to execute an airflow signal indicating a temporal change in respiratory airflow and an oxygen saturation signal indicating a temporal change in oxygen saturation.
- Blood based on a time difference between a predetermined first time in the airflow signal and a second time in the oxygen saturation signal indicating an increase in oxygen saturation corresponding to resumption of breathing at the first time
- the estimated cardiac output is calculated based on the means for measuring the oxygen carrying circulation time, the predetermined hyperbolic function indicating the relationship between the blood oxygen carrying circulation time and the cardiac output, and the measured oxygen carrying circulation time. Function as a means to
- FIG. 1 is a block diagram showing a configuration of an estimated cardiac output calculation device according to an embodiment of the present invention.
- the estimated cardiac output calculation device 20 is a device that calculates an estimated value of the cardiac output of the subject.
- the cardiac output is, for example, CI (cardiac index).
- the estimated cardiac output calculation device 20 of the present embodiment is an apparatus that can calculate an accurate estimated value of cardiac output without requiring an expensive and special medical device.
- the estimated cardiac output calculation device 20 is, for example, a PC (personal computer) or server device provided with a CPU (Central Processing Unit).
- the estimated cardiac output calculation device 20 is connected to a display device, a keyboard, a mouse, and the like.
- the estimated cardiac output calculation device 20 includes a circulation time measurement device 10, a cardiac output calculation unit 21, a graph display unit 22, and a storage unit 23.
- the circulation time measuring device 10 uses the airflow signal measured by the airflow sensor that detects the state of respiration and the oxygen saturation signal measured by the sensor that detects the oxygen saturation in the blood, to thereby carry the oxygen carrying circulation time of the blood of the subject. Measure.
- the oxygen carrying circulation time of blood is the time from the start of breathing of a subject until the blood oxygenated by oxygen sucked by the breathing is carried by the bloodstream and reaches a predetermined position.
- the cardiac output calculation unit 21 acquires the circulation time measured by the circulation time measurement device 10 and calculates the cardiac output using the circulation time.
- a method for calculating a highly accurate estimated value of cardiac output from the oxygen carrying circulation time of blood is provided using an expression representing the correlation between blood oxygen carrying circulation time and cardiac output.
- the graph display unit 22 creates a time-series graph of the estimated value of the cardiac output calculated by the cardiac output calculation unit 21, and the graph is connected to the estimated cardiac output calculation device 20 or the like. Output to.
- storage part 23 memorize
- FIG. 2 is a block diagram showing the configuration of the circulation time measuring apparatus in one embodiment of the present invention.
- the circulation time measuring device 10 is a device that measures the oxygen carrying circulation time of the blood of the subject.
- the circulation time measuring device 10 of this embodiment measures the oxygen transportation circulation time of blood based on the state of breathing during sleep of the subject suffering from sleep disordered breathing and the change in oxygen saturation in the blood at that time.
- a subject suffering from sleep disordered breathing there is time for breathing to stop or weaken during sleep. Meanwhile, the oxygen saturation of the subject's blood decreases. Thereafter, when the subject resumes breathing, blood oxygen saturation increases.
- the circulation time measuring device 10 of this embodiment uses this property to measure the oxygen carrying circulation time of blood.
- the airflow signal and the oxygen saturation signal of the subject measured by the sleep polygraph can be used.
- the airflow signal can be measured by, for example, a pressure sensor attached to the subject's nose.
- a method of detecting a temperature change of air entering and exiting the nasal cavity with breathing, a method of detecting movement of the chest with breathing, and the like can be used.
- the oxygen saturation signal can be measured by, for example, a pulse oximeter attached to the fingertip.
- LFCT lung-to-finger circulation time
- the circulation time measuring apparatus 10 includes a signal acquisition unit 11, a circulation time calculation unit 12, and an output unit 13.
- the signal acquisition unit 11 acquires an airflow signal indicating a temporal change in the breathing state of the subject from the storage unit 23.
- the signal acquisition unit 11 acquires an oxygen saturation signal indicating a temporal change in oxygen saturation in blood flowing through the fingertip of the subject from the storage unit 23.
- the circulation time calculation unit 12 includes a first time (respiration resumption time) in the airflow signal and an oxygen saturation signal indicating a behavior of oxygen saturation (an increase in oxygen saturation) corresponding to the resumption of respiration at the first time.
- the oxygen carrying circulation time of blood is measured based on the time difference from the second time.
- the circulation time calculation unit 12 shapes the airflow signal into a waveform representing the cycle of stop and restart of breathing, and based on a temporal shift between the shaped waveform and the waveform indicated by the oxygen saturation signal. Measure blood oxygen carrying circulation time.
- the output unit 13 outputs information on the oxygen carrying circulation time of the blood calculated by the circulation time calculation unit 12.
- the circulation time calculation unit 12 includes an airflow segment unit 121, an oxygen saturation segment unit 122, a signal shaping processing unit 123, and a time difference calculation unit 124.
- the airflow segment unit 121 segments the airflow signal every predetermined time to generate a segmented airflow signal.
- the oxygen saturation segment 122 generates a segmental oxygen saturation signal by segmenting the oxygen saturation signal every predetermined time.
- the signal shaping processing unit 123 generates a shaped segmental airflow signal by applying a low-pass filter to the segmental airflow signal.
- the time difference calculation unit 124 calculates a time difference corresponding to a time lag between the waveform indicated by the shaped segmental airflow signal and the waveform indicated by the segmental oxygen saturation signal, and sets the time difference as the oxygen transport circulation time of blood. In calculating the time difference, the time difference calculation unit 124 uses cross-correlation analysis for the shaped segmental airflow signal and the segmental oxygen saturation signal.
- FIG. 3 is a first diagram for explaining the outline of the circulation time measurement process in one embodiment of the present invention.
- FIG. 4 is a second diagram for explaining the outline of the circulation time measurement process (detrend process) in the embodiment of the present invention.
- a graph 3A (first graph) in FIG. 3 is a time-series graph of the airflow signal acquired by the signal acquisition unit 11.
- a graph 3B (second graph from the top) in FIG. 3 is a time-series graph of a signal obtained by performing full-wave rectification processing on the airflow signal acquired by the signal acquisition unit 11.
- a graph 3C third graph from the top in FIG.
- a graph 3D (bottom graph) in FIG. 3 is a time-series graph of the oxygen saturation signal acquired by the signal acquisition unit 11.
- the LFCT is measured using the timing at which the breathing of the subject with sleep disordered breathing stops or weakens during sleep and returns to normal breathing. Specifically, when the subject's breathing returns from the stopped state to the normal breathing state, oxygen taken in at that time causes an increase in oxygen saturation in the blood. In the oxygen saturation signal, an increase in oxygen saturation is recorded with a slight delay. The reason for the slight delay is that it takes time for oxygenated blood to be transported to the fingertips. Even in one airflow signal, when the subject's breathing returns from the stopped state to the normal breathing state, the behavior is clearly shown.
- LFCT is measured for subjects who may stop breathing during sleep, using the behavior of the airflow signal at the time of resumption of breathing in a series of breaths and the behavior of the corresponding oxygen saturation as a landmark.
- LFCT is the time from the start of inhaling oxygen until the pulse oximeter attached to the fingertip detects an increase in oxygen saturation.
- the time difference between the time when the behavior indicating resumption of respiration in the airflow signal appears and the time when the behavior corresponding to resumption of respiration in the oxygen saturation signal is indicated is the cross-correlation of the waveforms indicated by the respective signals. It is done by analyzing.
- the airflow signal indicated by the graph 3A includes a respiratory waveform having a shorter cycle (higher frequency) than the cycle (P) of stopping and restarting breathing. Even if cross-correlation analysis is performed as it is, correct cross-correlation analysis cannot be performed due to the influence of a signal having a high frequency. In view of this, for the airflow signal, only the waveform representing the respiration stop and restart cycle is mainly extracted so that the cross-correlation analysis with the waveform indicated by the oxygen saturation signal can be easily performed.
- the signal shaping processing unit 123 performs full-wave rectification processing. This makes all the values of the airflow signal positive as shown by the graph 3B.
- the signal shaping processing unit 123 applies a low-pass filter to the airflow signal after the full-wave rectification process, and removes a component having a high frequency. Then, it is possible to extract only the waveform representing the breathing stop and restart cycle indicated by the graph 3C. At this stage, detrend processing is performed in addition to frequency cutoff by a low-pass filter.
- Detrend processing will be described with reference to FIG.
- the signal value may tend to gradually increase due to noise accumulation in the airflow sensor.
- Graph 4A shows an example of the airflow signal in such a case.
- a correct cross-correlation analysis cannot be performed if such an upward trend is included.
- the detrend process is performed in order to remove such a tendency of values and extract only a waveform representing a breathing stop and restart cycle.
- the signal shaping processing unit 123 performs linear approximation on the airflow signal by, for example, the least square method, and calculates a straight line 4B indicating the rising tendency of the airflow signal.
- the signal shaping processing unit 123 performs detrend processing for subtracting this straight line from the value of the airflow signal.
- a graph 4C shows a waveform after the detrend processing.
- the signal shaping processing unit 123 performs full-wave rectification processing, low-pass filter application, and detrend processing, and generates a signal shaped into a waveform that represents a cycle of stopping and resuming breathing.
- the signal shaping processing unit 123 similarly performs a detrend process on the oxygen saturation signal.
- FIG. 5 is a third diagram for explaining the outline of the circulation time measurement process according to the embodiment of the present invention.
- a graph 3 ⁇ / b> C is a time-series graph of the airflow signal after shaping into a waveform that represents the cycle of stopping and resuming breathing.
- Graph 3D is a time-series graph of the oxygen saturation signal.
- Graph 3C-10 is a graph obtained by shifting graph 3C to the right by 10 seconds.
- Graph 3C-20 is a graph obtained by shifting graph 3C to the right by 20 seconds.
- both the predetermined time in the shaped airflow signal and the time in the oxygen saturation signal indicating the behavior of the oxygen saturation corresponding to the resumption of breathing at the predetermined time overlap.
- the graph 3C or the graph 3D is shifted by the time difference corresponding to the temporal shift of the graph.
- the shift amount (seconds) at this time is LFCT.
- LFCT is the time it takes to carry oxygen to the fingertip.
- the time difference calculation unit 124 performs cross-correlation analysis. First, the time difference calculation unit 124 shifts either the time-series graph of the airflow signal after shaping or the time-series graph of the oxygen saturation signal in the time axis direction, and each of the two graphs after the shift is shifted. Calculates the product of values at time. The time difference calculation unit 124 sums up the products at each time for all the times. This total value is called a cross-correlation coefficient.
- the time difference calculation unit 124 compares the cross-correlation coefficients calculated for each shift amount, and obtains the shift amount when the value is the largest.
- the cross-correlation coefficient in this case is called the maximum cross-correlation coefficient. That is, the time difference calculation unit 124 obtains the shift amount when the cross-correlation between the waveform of the graph 3C and the waveform of the graph 3D is strongest.
- This process is called cross-correlation analysis in the present embodiment.
- the shift amount obtained by the cross-correlation analysis is a time difference corresponding to a time lag between the waveform of the airflow signal after shaping and the waveform of the oxygen saturation signal, and is LFCT.
- the cross-correlation when graph C is shifted to the right (future direction) for 0 second is low.
- the LFCT to be calculated is 20 seconds. That is, in this example, oxygen taken in by breathing reaches the fingertip with a delay of 20 seconds. As described above, this delay time correlates with an index of the subject's cardiac function.
- the cardiac output calculation unit 21 calculates an estimated value of the cardiac output CI using LFCT. Next, calculation of the cardiac output CI will be described.
- FIG. 6 is a diagram illustrating calculation of cardiac output in one embodiment of the present invention.
- the left figure of FIG. 6 is a graph which shows the relationship between the measured value of CI measured about the same test subject and LFCT by this embodiment measured about several test subjects (31 persons).
- the vertical axis in the left diagram of FIG. 6 is the CI measurement value, and the horizontal axis is LFCT.
- LFCT it measured using the airflow signal and oxygen saturation signal in the night measured with respect to the some test subject, and the average value was employ
- the measured value of CI it measured using the invasive measuring method (for example, the thermodilution method and the Fick method) with the highest precision at present.
- the right figure of FIG. 6 is a graph which shows the relationship between the CI estimated value calculated by said Formula (1) about the some test subject, and the CI measured value measured about the same test subject.
- the vertical axis represents the CI measured value
- the horizontal axis represents the CI estimated value.
- the cardiac output calculation unit 21 acquires the LFCT measured by the circulation time measuring device 10 and calculates the estimated value of the cardiac output (CI) by the equation (1). To do. Next, the flow of processing for calculating the estimated value of cardiac output (CI) in this embodiment will be described.
- FIG. 7 is a flowchart of the cardiac output calculation process according to an embodiment of the present invention.
- the storage unit 23 stores a series of airflow signals and a series of oxygen saturation signals measured during sleep of the subject. Further, it is assumed that the measured value of the pulse of the subject measured in parallel with the airflow signal or the like is stored in the storage unit 23.
- the signal acquisition part 11 reads and acquires a test subject's series of airflow signals and oxygen saturation signals from the memory
- the signal shaping processing unit 123 included in the circulation time calculation unit 12 performs full-wave rectification processing on the read series of airflow signals (step S12).
- the oxygen saturation segment 122 provided in the circulation time calculation unit 12 segments the series of oxygen saturation signals into the same time unit (for example, 2 minutes) as the length used by the airflow segment 121 for the segment.
- These segmental airflow signal n and segmental oxygen saturation signal n are collectively referred to as segment signal n.
- the circulation time calculation unit 12 performs the following steps S15 to S17 for each segment (step S14).
- the signal shaping processing unit 123 performs a detrend process on the first segmental airflow signal 1 and the first segmental oxygen saturation signal 1 (step S15).
- the signal shaping processing unit 123 applies a low-pass filter to the first segmental airflow signal 1 after the detrend processing (step S16), and removes high-frequency components.
- the signal shaping processing unit 123 applies a plurality of low-pass filters to the first segmental airflow signal 1 after the detrend processing.
- Primary low-pass filter, dead time 0, cutoff frequency 0.015Hz
- the signal shaping processing unit 123 generates a shaped segmental airflow signal A1, a shaped segmental airflow signal B1, and a shaped segmental airflow signal C1 obtained by applying the low-pass filters A, B, and C to the first segmental airflow signal 1, respectively.
- the time difference calculation unit 124 included in the circulation time calculation unit 12 performs cross-correlation on each of the shaped segmental airflow signal A1, the shaped segmental airflow signal B1, and the shaped segmental airflow signal C1 and the first segmental oxygen saturation signal 1. Analysis is performed (step S17), and a cross-correlation coefficient is calculated.
- the time difference calculation unit 124 sets the shift amount of the shaped segmental airflow signal or the segmental oxygen saturation signal in the time axis direction in the cross-correlation analysis, for example, from 10 seconds to This is limited to a range of 60 seconds.
- the time difference calculation unit 124 has a point indicating a behavior (the point indicating resumption of respiration and the point indicating an increase in oxygen saturation) indicating that the shaped segmental airflow signal or the segmental oxygen saturation signal is a mutual marker while changing the shift amount. By shifting in the overlapping direction, the cross-correlation coefficient is calculated for each shift amount, and the case where the value is maximized is obtained. Finally, the time difference calculation unit 124 calculates the maximum cross-correlation coefficient A′1 between the shaped segment airflow signal A1 and the segmental oxygen saturation signal. The time difference calculation unit 124 calculates the maximum cross-correlation coefficient B′1 between the shaped segmental airflow signal B1 and the segmental oxygen saturation signal.
- the time difference calculation unit 124 calculates the maximum cross-correlation coefficient C′1 between the shaped segmental airflow signal C1 and the segmental oxygen saturation signal. Next, the time difference calculation unit 124 selects the maximum value D′ 1 among the calculated A′1, B′1, and C′1. Next, the time difference calculation unit 124 sets the shift amount corresponding to the maximum value D′ 1 of the selected maximum cross-correlation coefficient as LFCT1 for this segment signal.
- the time difference calculation unit 124 records a predetermined time included in the segmented airflow signal (for example, the first measurement time of the airflow signal included in the segmented airflow signal) and the LFCT 1 in association with each other in the storage unit 23.
- the signal shaping processing unit 123 and the time difference calculation unit 124 repeat the processes of steps S15 to S17 for the second segment airflow signal and the second segmental oxygen saturation signal. For example, even if the time difference calculation unit 124 selects the maximum cross-correlation coefficient C′1 for the first segment signal and sets it as the shift amount LFCT1, the cross-correlation of the second segment signal In the analysis, if the maximum cross-correlation coefficient A′2 becomes the maximum value, the shift amount in that case is selected and set as the circulation time LFCT2 in this segment signal.
- a high-precision (high maximum cross-correlation coefficient) LFCT can be obtained for each segment signal.
- the time difference calculation unit 124 records the predetermined time included in the second segmental airflow signal and LFCT2 in association with each other in the storage unit 23.
- the cardiac output calculation unit 21 records the calculated CIn in the storage unit 23 in association with the time associated with LFCTn.
- the cardiac output calculation unit 21 performs a process of removing outliers from the time-series CIn (step S20). For example, if there is a portion where CIn changes rapidly, the cardiac output calculation unit 21 removes CIn that has changed rapidly. The case where CIn changes rapidly is, for example, the case where ⁇ CI ⁇ 0.5 L / min / m 2 . Further, if there is a value significantly deviating from the average value of CIn, the cardiac output calculation unit 21 removes the CIn. The value greatly deviated is, for example, a case where the value is shifted by 1.0 L / min / m 2 or more. The cardiac output calculation unit 21 deletes the outlier from the time-series CIn data recorded in the storage unit 23.
- the graph display unit 22 reads the time-series LFCT and CI estimated values after outlier removal, and generates an image displaying a time-series graph such as LFCT and CI estimated values.
- the graph display unit 22 outputs and displays the generated image on the display device (step S21). An example of the graph output by the graph display unit 22 is shown in FIG.
- FIG. 8 is a first diagram illustrating an example of a graph output by the estimated cardiac output calculation device according to the embodiment of the present invention.
- a graph 8A (first graph) in FIG. 8 is a time-series graph of oxygen saturation (SpO 2 ).
- a graph 8B (second graph from the top) is a time-series graph of LFCT measured by the circulation time measuring device 10 of the present embodiment.
- a graph 8C (third graph from the top) is a time-series graph of CI estimated values calculated by the estimated cardiac output calculating device 20 of the present embodiment.
- Graph 8D bottom graph is a time-series graph of the pulse. According to this embodiment, the graph illustrated in FIG. 8 can be output using data measured by the sleep polygraph test.
- the graph display unit 22 may calculate each average value from the time-series LFCT and the cardiac output, and output the average value.
- the estimated value of CI is calculated as the cardiac output
- CO Estimated value CI estimated value ⁇ subject's body surface area.
- the outlier is removed from the estimated CI value.
- the time-series LFCT measurement value is significantly different from the rapidly changed value or the average value. You may perform the process which removes a new value.
- FIG. 9 is a second diagram illustrating an example of a graph output by the estimated cardiac output calculation device according to the embodiment of the present invention.
- FIG. 9 shows the measurement of LFCT using the circulation time measuring device 10 of the present embodiment and the CI using the estimated cardiac output calculating device 20 for a subject who has atrial fibrillation combined with heart failure with preserved contractility. It is the graph which displayed the result of having calculated the estimated value. The subject complained of dyspnea, and a cardiac ultrasonography showed that the subject had good cardiac function.
- the estimated cardiac output calculation device 20 of the present embodiment used the CI estimated value. As a result, a decrease in the CI estimated value was observed (the left diagram in FIG. 9).
- the CI estimated value is calculated again by the estimated cardiac output calculating device 20 of the present embodiment.
- the right figure of FIG. 9 was obtained. According to the right figure of FIG. 9, it can be seen that the CI estimated value of the subject has recovered. From this example, even if the subject's cardiac function state cannot be detected by cardiac ultrasonography or the like, the estimated cardiac output calculation device 20 of the present embodiment may be able to grasp the cardiac function state. I know that there is. Moreover, since patients with heart failure often have sleep disordered breathing, the CI, which is an important index of cardiac function, can be estimated from the airflow signal and oxygen saturation signal measured during sleep. The morphological method is also suitable for daily examinations on patients such as heart failure.
- the cardiac output CI can be estimated by a non-invasive method based on the measured value of LFCT.
- the LFCT measurement does not require special equipment or specialized skills, and can be carried out if there is a PC with the functions of the existing inspection equipment and the circulation time measuring device 10, so that it can be introduced and operated. Is easy. Further, in daily medical practice, it is not realistic to manually measure LFCT from a large amount of data of airflow signals and oxygen saturation signals measured overnight for a plurality of subjects.
- a waveform representing a breathing stop and restart period is extracted from the airflow signal, and the LFCT can be automatically measured by performing a cross-correlation analysis with the oxygen saturation signal. Therefore, the measurement of LFCT can be continued without difficulty every day.
- the present embodiment not only the LFCT and the CI estimated value at a certain point in time, but also a graph showing the variation of the LFCT and the CI estimated value in a predetermined period (for example, overnight) can be displayed. Significant data about the subject can be obtained.
- a program for realizing all or part of the functions of the circulation time measuring device 10 and the estimated cardiac output calculating device 20 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is recorded.
- the processing of each unit may be performed by being read and executed by a computer system.
- the “computer system” includes an OS and hardware such as peripheral devices. Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
- the “computer-readable recording medium” refers to a storage device such as a portable medium such as a CD, a DVD, or a USB, or a hard disk built in a computer system.
- the program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.
- the storage unit 23 may be provided in an external storage device.
- LFCT is an example of oxygen oxygen circulation time of blood.
- Expression (1) is an example of a predetermined hyperbolic function indicating the relationship between the blood oxygen carrying circulation time and the cardiac output.
- the estimated CI value is an example of the estimated cardiac output.
- time series data of the subject's respiratory cycle and oxygen saturation in the blood is obtained. It can be used to measure blood oxygen carrying circulation time and estimate cardiac output.
Abstract
Description
本願は、2014年6月13日に米国に出願された米国特許仮出願第62/011590号に基づいて優先権を主張し、その内容をここに援用する。
以下、本発明の一実施形態による推定心拍出量算出装置を図面を参照して説明する。
図1は、本発明の一実施形態における推定心拍出量算出装置の構成を示すブロック図である。
推定心拍出量算出装置20は、被験者の心拍出量の推定値を算出する装置である。心拍出量とは、例えばCI(cardiac index)である。またはCO(cardiac output:CO/体表面積=CI)を用いることもできる。以下の説明では、心拍出量にCIを用いた場合を例に説明を行う。本実施形態の推定心拍出量算出装置20は、高価で特別な医療機器を必要とせず、かつ精度の高い心拍出量の推定値を算出することができる装置である。推定心拍出量算出装置20は、例えばCPU(Central Processing Unit)を備えたPC(パーソナルコンピュータ)やサーバ装置である。推定心拍出量算出装置20は、ディスプレイ装置、キーボード、マウスなどと接続されている。
循環時間測定装置10は、呼吸の状態を検出する気流センサによって測定した気流信号、血液中の酸素飽和度を検出するセンサで測定した酸素飽和度信号を用いて、被験者の血液の酸素運搬循環時間を測定する。血液の酸素運搬循環時間とは、被験者の呼吸の開始から、その呼吸によって吸い込んだ酸素によって酸素化された血液が血流によって運ばれ、所定の位置に至るまでの時間である。
心拍出量算出部21は、循環時間測定装置10が測定した循環時間を取得し、循環時間を用いて心拍出量を算出する。正常な被験者の場合、心臓が送り出す血液の量に問題がなく、その場合、血液の酸素運搬循環時間は正常な値を示す。ところが心機能に問題を抱える患者の場合、心臓の働きが弱く、心臓が送り出す血液の量が正常な被験者に比べ少なくなる。そのため、酸素が所定の位置に至るまでに時間がかかり、血液の酸素運搬循環時間は正常な被験者の値に比べ長くなる。このような血液の酸素運搬循環時間と心拍出量との相関はこれまでにも知られていたが、両者の正確な関係についての情報は無かった。本実施形態では、血液の酸素運搬循環時間と心拍出量の相関関係を表す式を用いて、血液の酸素運搬循環時間から精度の高い心拍出量の推定値を算出する方法を提供する。
グラフ表示部22は、心拍出量算出部21が算出した心拍出量の推定値の時系列のグラフを作成し、そのグラフを推定心拍出量算出装置20に接続されたディスプレイ装置などに出力する。
記憶部23は、心拍出量の算出に必要な関数、気流信号、酸素飽和度信号など種々の情報を記憶する。
循環時間測定装置10は、被験者の血液の酸素運搬循環時間を測定する装置である。本実施形態の循環時間測定装置10は、睡眠時呼吸障害を患う被験者の睡眠時の呼吸の状態とそのときの血液中の酸素飽和度の変化に基づいて血液の酸素運搬循環時間を測定する。睡眠時呼吸障害を患う被験者の場合、睡眠中に呼吸が停止したり弱まったりする時間が存在する。その間、被験者の血液の酸素飽和度は低下する。その後、被験者が呼吸を再開すると血液の酸素飽和度は上昇する。睡眠時呼吸障害を患う被験者の場合、呼吸の再開やそれに伴う血液の酸素飽和度の上昇が、その被験者について測定した気流信号や酸素飽和度信号にはっきりと表れる。本実施形態の循環時間測定装置10は、この性質を利用し、血液の酸素運搬循環時間を測定する。
信号取得部11は、記憶部23から被験者の呼吸状態の時間変化を示す気流信号を取得する。また、信号取得部11は、記憶部23から被験者の指先を流れる血液中の酸素飽和度の時間変化を示す酸素飽和度信号を取得する。
循環時間算出部12は、気流信号における第一時刻(呼吸の再開時刻)と、第一時刻での呼吸再開に対応した酸素飽和度の挙動(酸素飽和度の上昇)を示す酸素飽和度信号における第二時刻と、の時間差に基づいて血液の酸素運搬循環時間を測定する。この算出において、循環時間算出部12は、気流信号を呼吸の停止と再開の周期を表す波形に整形し、整形後の波形と、酸素飽和度信号が示す波形との時間的なずれに基づいて血液の酸素運搬循環時間を測定する。
出力部13は、循環時間算出部12が算出した血液の酸素運搬循環時間の情報を出力する。
気流分節部121は、気流信号を所定の時間毎に分節して分節気流信号を生成する。
酸素飽和度分節部122は、酸素飽和度信号を所定の時間毎に分節して分節酸素飽和度信号を生成する。
信号整形処理部123は、分節気流信号にローパスフィルタを適用するなどして整形分節気流信号を生成する。
時間差算出部124は、整形分節気流信号が示す波形と分節酸素飽和度信号が示す波形との時間的ずれに対応する時間差を算出し、その時間差を血液の酸素運搬循環時間とする。この時間差の算出において、時間差算出部124は、整形分節気流信号および分節酸素飽和度信号について相互相関分析を用いる。
図4は、本発明の一実施形態における循環時間測定処理(デトレンド処理)の概要を説明する第二の図である。
図3のグラフ3A(1番上のグラフ)は、信号取得部11が取得した気流信号の時系列のグラフである。図3のグラフ3B(上から2番目のグラフ)は、信号取得部11が取得した気流信号に対して全波整流処理を行った信号の時系列のグラフである。図3のグラフ3C(上から3番目のグラフ)は、全波整流処理を行った気流信号に対してローパスフィルタを適用することにより、呼吸の停止と再開の周期を表す波形に整形された信号の時系列のグラフである。図3のグラフ3D(1番下のグラフ)は、信号取得部11が取得した酸素飽和度信号の時系列のグラフである。
まず、信号整形処理部123は、全波整流処理を行う。これにより、グラフ3Bが示すように気流信号の値を全て正にする。次に、信号整形処理部123は、全波整流処理後の気流信号に対してローパスフィルタを適用し、周波数の高い成分を取り除く。すると、グラフ3Cが示す呼吸の停止と再開の周期を表す波形だけを抽出することができる。なお、この段階では、ローパスフィルタによる周波数遮断の他にデトレンド処理を行う。
図5において、グラフ3Cは、呼吸の停止と再開の周期を表す波形に整形した整形後の気流信号の時系列のグラフである。グラフ3Dは、酸素飽和度信号の時系列のグラフである。グラフ3C-10は、グラフ3Cを右に10秒分シフトしたグラフである。グラフ3C-20は、グラフ3Cを右に20秒分シフトしたグラフである。
LFCTを測定するために、整形後の気流信号における所定の時刻と、その所定の時刻での呼吸再開に対応した酸素飽和度の挙動を示す酸素飽和度信号における時刻とが重なるように、両方のグラフの時間的なずれに対応する時間差分だけグラフ3Cまたはグラフ3Dをシフトさせる。このときのシフト量(秒)がLFCTである。LFCTは、指先までの酸素運搬に掛かる時間である。このときのシフト量を求めるために時間差算出部124は、相互相関分析を行う。まず、時間差算出部124は、整形後の気流信号の時系列のグラフと酸素飽和度信号の時系列のグラフの何れか一方を、時間軸方向にシフトさせて、シフト後の2つのグラフの各時刻における値の積を計算する。時間差算出部124は、各時刻における積を全ての時刻について合計する。この合計値を相互相関係数と呼ぶ。時間差算出部124は、シフト量ごとに計算した相互相関係数を比較し、最も値が大きかった場合のシフト量を求める。この場合の相互相関係数を最大相互相関係数と呼ぶ。つまり、時間差算出部124は、グラフ3Cの波形とグラフ3Dの波形の相互相関関係が最も強くなる場合のシフト量を求める。この処理を、本実施形態における相互相関分析と呼ぶ。この相互相関分析によって求めたシフト量が、整形後の気流信号の波形と酸素飽和度信号の波形の時間的なずれに対応する時間差であり、LFCTである。
図6の左図は、複数の被験者(31人)について測定した本実施形態によるLFCTと同じ被験者について測定したCIの測定値との関係を示すグラフである。図6の左図の縦軸がCI測定値、横軸がLFCTである。LFCTについては、複数の被験者に対して測定した一晩中の気流信号および酸素飽和度信号を用いて測定し、その平均値を採用した。CIの測定値については、現状で最も精度の高い侵襲的測定方法(例えば熱希釈法やフィック法)を用いて測定を行った。このようにして得られたLFCTの平均値とCI測定値との相関を回帰分析すると、R2=0.53、p値<0.001が得られた。これは両者の間に相関関係があることを示す有意な値といえる。また、図6の左図のグラフを解析すると本実施形態によるLFCTとCIの測定値との関係は、双曲線関数の関係に近似できることがわかった。LFCTとCIの関係は以下の式で表すことができる。
以上の分析に基づいて、本実施形態では心拍出量算出部21が、循環時間測定装置10が測定したLFCTを取得し、式(1)によって心拍出量(CI)の推定値を算出する。
次に、本実施形態における心拍出量(CI)の推定値の算出処理の流れについて説明する。
前提として、記憶部23には、被験者の睡眠中に測定された一連の気流信号と一連の酸素飽和度信号が格納されているとする。また、記憶部23には、気流信号などと並行して測定された被験者の脈拍の測定値が格納されているとする。
まず、信号取得部11が、記憶部23から被験者の一連の気流信号および酸素飽和度信号を読み出して取得する(ステップS11)。信号取得部11は循環時間算出部12に、読み出した気流信号および酸素飽和度信号を出力する。次に、循環時間算出部12が有する信号整形処理部123が、読み出した一連の気流信号に対して全波整流処理を行う(ステップS12)。次に、循環時間算出部12が有する気流分節部121が、全波整流処理後の気流信号を所定の時間単位(例えば2分単位)に分節しN個の分節気流信号n(n=1~N)を生成する(ステップS13)。また、循環時間算出部12が有する酸素飽和度分節部122が、一連の酸素飽和度信号を、気流分節部121が分節に用いた長さと同じ時間単位(例えば2分単位)に分節しN個の分節酸素飽和度信号n(n=1~N)を生成する。これら分節気流信号nと分節酸素飽和度信号nとを総称して分節信号nと呼ぶ。次に、循環時間算出部12は、分節ごとに以下のステップS15~ステップS17の処理を行う(ステップS14)。
A.1次ローパスフィルタ、むだ時間=0、遮断周波数 0.010Hz
B.1次ローパスフィルタ、むだ時間=0、遮断周波数 0.015Hz
C.1次ローパスフィルタ、むだ時間=0、遮断周波数 0.020Hz
信号整形処理部123は、1つ目の分節気流信号1にローパスフィルタA、B、Cのそれぞれを適用した整形分節気流信号A1、整形分節気流信号B1、整形分節気流信号C1を生成する。
分節信号に対する処理を全ての分節信号(n=1~N)について行うと、記憶部23には時系列のLFCTn(n=1~N)が記録される。次に出力部13が、記憶部23から時系列のLFCTn(n=1~N)を読み出して心拍出量算出部21へ出力する。
図8のグラフ8A(1番上のグラフ)は、酸素飽和度(SpO2)の時系列のグラフである。グラフ8B(上から2番目のグラフ)は、本実施形態の循環時間測定装置10によって測定したLFCTの時系列のグラフである。グラフ8C(上から3番目のグラフ)は、本実施形態の推定心拍出量算出装置20によって算出したCI推定値の時系列のグラフである。グラフ8D(1番下のグラフ)は、脈拍の時系列のグラフである。本実施形態によれば睡眠時ポリグラフ検査によって測定したデータを利用して図8で例示したグラフを出力することができる。
なお、グラフ表示部22は、時系列のLFCTおよび心拍出量からそれぞれの平均値を算出して、それらの平均値を出力するようにしてもよい。
また、図7の処理フローでは、CIの推定値に対して外れ値を除去する処理を行ったが、時系列のLFCTの測定値に対して、急激に変化した値や平均値から大幅に外れた値を除去する処理を行ってもよい。
図9は、収縮能の保たれた心不全に心房細動を合併したある被験者について、本実施形態の循環時間測定装置10を用いたLFCTの測定および推定心拍出量算出装置20を用いたCI推定値の算出を行った結果を表示したグラフである。この被験者は呼吸困難感を訴えており、心臓超音波検査を行ったところ良好な心機能を有するとの結果が得られたが、本実施形態の推定心拍出量算出装置20でCI推定値を算出したところ、CI推定値の低下がみられた(図9左図)。
次に、この被験者に対して電気的除細動の措置を行い、その後、症状が軽快した時点で、再度、本実施形態の推定心拍出量算出装置20でCI推定値を算出したところ、図9右図が得られた。図9右図によればこの被験者のCI推定値が回復していることがわかる。この例から、心臓超音波検査などで被験者の心機能の状態を検出できない場合でも、本実施形態の推定心拍出量算出装置20であれば心機能の状態を把握することができる可能性があることがわかる。また、心不全などの患者は睡眠時呼吸障害を併発していることが多いので、睡眠時に測定した気流信号と酸素飽和度信号によって心機能の重要な指標であるCIを推定することができる本実施形態の方法は、心不全などの患者に対する日々の検査にも好適である。
また、「コンピュータシステム」は、WWWシステムを利用している場合であれば、ホームページ提供環境(あるいは表示環境)も含むものとする。
また、「コンピュータ読み取り可能な記録媒体」とは、CD、DVD、USB等の可搬媒体、コンピュータシステムに内蔵されるハードディスク等の記憶装置のことをいう。また上記プログラムは、前述した機能の一部を実現するためのものであっても良く、さらに前述した機能をコンピュータシステムにすでに記録されているプログラムとの組み合わせで実現できるものであってもよい。
11 信号取得部
12 循環時間算出部
121 気流分節部
122 酸素飽和度分節部
123 信号整形処理部
124 時間差算出部
13 出力部
20 推定心拍出量算出装置
21 心拍出量算出部
22 グラフ表示部
23 記憶部
Claims (9)
- 呼吸の気流の時間変化を示す気流信号、及び、酸素飽和度の時間変化を示す酸素飽和度信号を取得する信号取得部と、
前記気流信号における所定の第一時刻と、前記第一時刻での呼吸再開に対応した酸素飽和度の上昇を示す前記酸素飽和度信号における第二時刻との時間差に基づいて血液の酸素運搬循環時間を測定する循環時間算出部と、
を有する循環時間測定装置。 - 前記循環時間算出部は、前記気流信号を呼吸の停止と再開の周期を表す波形に整形し、当該整形後の波形と、前記酸素飽和度信号が示す波形との時間的なずれに基づいて前記酸素運搬循環時間を測定する、
請求項1に記載の循環時間測定装置。 - 前記循環時間算出部は、
前記気流信号を所定の時間毎に分節して分節気流信号を生成する気流分節部と、
前記酸素飽和度信号を前記所定の時間毎に分節して分節酸素飽和度信号を生成する酸素飽和度分節部と、
前記分節気流信号にフィルタを適用し、前記分節気流信号を呼吸の停止と再開の周期を表す波形に整形した整形分節気流信号を生成する信号整形処理部と、
前記整形分節気流信号が示す波形と前記分節酸素飽和度信号が示す波形との時間的なずれに対応する時間差を算出し、その時間差を前記酸素運搬循環時間とする時間差算出部と、
を有する請求項1または請求項2に記載の循環時間測定装置。 - 前記時間差算出部は、前記整形分節気流信号および前記分節酸素飽和度信号に対して相互相関分析を用いて前記時間差を算出する、
請求項3に記載の循環時間測定装置。 - 請求項1から請求項4のいずれか一項に記載の循環時間測定装置と、
前記循環時間測定装置が測定した前記酸素運搬循環時間を取得し、血液の酸素運搬循環時間と心拍出量との関係を示す所定の双曲線関数と前記取得した酸素運搬循環時間とに基づいて、推定心拍出量を算出する心拍出量算出部と、
を有する推定心拍出量算出装置。 - 呼吸の気流の時間変化を示す気流信号、及び、酸素飽和度の時間変化を示す酸素飽和度信号を取得し、
前記気流信号における所定の第一時刻と、前記第一時刻での呼吸再開に対応した酸素飽和度の上昇を示す前記酸素飽和度信号における第二時刻との時間差に基づいて血液の酸素運搬循環時間を測定する、
循環時間測定方法。 - 呼吸の気流の時間変化を示す気流信号、及び、酸素飽和度の時間変化を示す酸素飽和度信号を取得し、
前記気流信号における所定の第一時刻と、前記第一時刻での呼吸再開に対応した酸素飽和度の上昇を示す前記酸素飽和度信号における第二時刻との時間差に基づいて血液の酸素運搬循環時間を測定し、
血液の酸素運搬循環時間と心拍出量との関係を示す所定の双曲線関数と前記測定した酸素運搬循環時間とに基づいて、推定心拍出量を算出する、
推定心拍出量算出方法。 - 循環時間測定装置のコンピュータを、
呼吸の気流の時間変化を示す気流信号、及び、酸素飽和度の時間変化を示す酸素飽和度信号を取得する手段、
前記気流信号における所定の第一時刻と、前記第一時刻での呼吸再開に対応した酸素飽和度の上昇を示す前記酸素飽和度信号における第二時刻との時間差に基づいて血液の酸素運搬循環時間を測定する手段、
として機能させるためのプログラム。 - 推定心拍出量算出装置のコンピュータを、
呼吸の気流の時間変化を示す気流信号、及び、酸素飽和度の時間変化を示す酸素飽和度信号を取得する手段、
前記気流信号における所定の第一時刻と、前記第一時刻での呼吸再開に対応した酸素飽和度の上昇を示す前記酸素飽和度信号における第二時刻との時間差に基づいて血液の酸素運搬循環時間を測定する手段、
血液の酸素運搬循環時間と心拍出量との関係を示す所定の双曲線関数と前記測定した酸素運搬循環時間とに基づいて、推定心拍出量を算出する手段、
として機能させるためのプログラム。
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JP2016527782A JP6628720B2 (ja) | 2014-06-13 | 2015-06-05 | 循環時間測定装置、推定心拍出量算出装置、循環時間測定方法、推定心拍出量算出方法及びプログラム |
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JP2019166148A (ja) * | 2018-03-23 | 2019-10-03 | 富士ゼロックス株式会社 | 生体情報測定装置、及び生体情報測定プログラム |
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