Patent Publication Number: US-2021161412-A1

Title: Pulse-Wave Signal Analysis Device, Pulse-Wave Signal Analysis Method and Computer Program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the United States national phase of International Application No. PCT/JP2019/020762 filed May 24, 2019, and claims priority to Japanese Patent Application No. 2018-131025 filed Jul. 10, 2018, the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a pulse wave signal analyzer, a pulse wave signal analysis method and a computer program, and more particularly to a pulse wave signal analyzer using a pulse wave detection function added to an automatic blood pressure monitor and the like, a pulse wave signal analysis method and a computer program. 
     Description of Related Art 
     Atrial fibrillation is a type of arrhythmia in which the entire atrium is excited and contracted very quickly in small steps, and the excitement is randomly transmitted to ventricles, impairing the contraction and expansion of the heart and losing regular beating. 
     Prolonged atrial fibrillation can lead to impaired heart function. In addition, atrial fibrillation makes it easier for blood clots to form, and the blood clots move into the brain by blood flow, increasing the risk of cerebral infarction. 
     Statistically, it is said that 3 to 5% of patients with atrial fibrillation develop cerebral infarction annually. Furthermore, since the prevalence of atrial fibrillation increases with age, atrial fibrillation is considered to be an important disease among heart diseases. Therefore, early detection of atrial fibrillation and initiation of appropriate treatment are important for the prevention of cardiogenic cerebral infarction. 
     Atrial fibrillation can be detected by electrocardiography. For example, Patent Documents 1 and 2 and Non-Patent Document 1 describe the use of electrocardiography for detection and classification of atrial arrhythmias. An electrocardiogram test is a method of measuring a heart rate by electrical pulses generated in the body for each cardiac cycle. However, the electrocardiogram test must be performed at a medical examination, a human dock, or the like, which is time-consuming and complicated. In addition, since the test described in Patent Document 1 is invasive, it is necessary to consider infection control and safety. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Document 1: Japanese Patent Publication No. 2008-504888 
         Patent Document 2: Japanese Patent Application Laid-open No. 2018-11948 
         Patent Document 3: Japanese Patent Application Laid-open No. 2014-42547 
       
    
     Non-Patent Literature 
     
         
         Non-patent Document 1: “Spectral characteristics of ventricular response to atrial fibrillation,” American Physiological Society, 1997 
       
    
     SUMMARY OF THE INVENTION 
     Patent Document 3 discloses that atrial fibrillation is determined using arterial pulsation, that is, a pulse wave signal. The average pulse wave RR interval obtained by averaging the pulse wave signals is calculated, and frequency analysis is performed on this RR pulse wave interval. However, this method requires long-term measurement and complicated calculations because it is necessary to smooth out small fluctuations and to obtain the degree of variation with respect to the average pulse wave RR interval. Therefore, there is a demand for a method for accurately determining atrial fibrillation in a short time. 
     Also, there are individual differences in the symptoms of atrial fibrillation, and it is estimated that 40% of those suffering from atrial fibrillation have no subjective symptoms. Further, some people may feel palpitations and do not mind the symptoms. Thus, if there are no subjective symptoms of atrial fibrillation, or if a client does not mind the symptoms, the client may miss the opportunity to undergo a complicated test to find atrial fibrillation. 
     Moreover, in areas with poor medical service, it is difficult to undergo such tests. As a result of such circumstances, there is a problem that the symptom is left unattended and the opportunity for early detection and treatment is missed. 
     Furthermore, in the case of paroxysmal atrial fibrillation that occurs in the early stages of atrial fibrillation, atrial fibrillation may not be detected at the time of measurement due to the short period of the state of atrial fibrillation. Therefore, a simple inspection method capable of performing repeated inspections is desirable. 
     Therefore, a method for determining atrial fibrillation with a high probability by using a simple method other than the electrocardiography is desired. 
     The present invention has been made in view of such a problem, and an object of the present invention is to provide a pulse wave signal analyzer, a pulse wave signal analysis method and a computer program which can accurately determine the state of atrial fibrillation by a simple method. 
     In order to solve the above problems, according to one aspect of the embodiment, there is provided a pulse wave signal analyzer, including: a signal detection means for non-invasively detecting a pulse wave signal according to heartbeat of a living body; a generation means for generating a frequency spectrum by Fourier transforming the pulse wave signal detected by the signal detection means; and an analysis means for detecting a state of atrial fibrillation based on the frequency spectrum generated by the generation means, in which the generation means repeatedly performs Fourier transform of the pulse wave signal at a predetermined time frame while shifting the time frame in a range of 0.005 seconds to 0.02 seconds. 
     Here, the analyzer can further comprise a filter for filtering the pulse wave signal detected by the signal detecting means, and the generation means can generate the frequency spectrum from the pulse wave signal output from the filter. 
     In addition, the analysis means can detect the state of atrial fibrillation when a frequency component corresponding to a cycle of the heartbeat does not have a plurality of peaks in the frequency spectrum. 
     Further, the predetermined time frame can be 2 to 4 seconds. 
     Furthermore, the signal detecting means can detect the pulse wave signal of a pressure pulse wave. 
     In addition, the analysis means can detect the state of atrial fibrillation based on a time change of the frequency spectrum. 
     Here, the analysis means can detect the state of atrial fibrillation based on time duration of a predetermined number of peaks. 
     Here, the analysis means can detect the state of atrial fibrillation further based on an amount in which a frequency of the peak fluctuates. 
     Here, the analysis means can detect the state of atrial fibrillation based on two or more of time duration of a peak at a given frequency, frequency variation of the peak, and a number of occurrences of temporally discontinuous peaks. 
     According to another aspect of the embodiment, there is provided a pulse wave signal analysis method, including the steps of: non-invasively detecting a pulse wave signal according to heartbeat of a living body; generating a frequency spectrum by Fourier transforming the pulse wave signal detected by the signal detection means; and detecting a state of atrial fibrillation based on the frequency spectrum generated by the generation means, in which the generating step repeatedly performs Fourier transform of the pulse wave signal at a predetermined time frame while shifting the time frame in a range of 0.005 seconds to 0.02 seconds. 
     Here, the method can further include the step of filtering the pulse wave signal detected by the signal detecting means, and the generating step can include generating the frequency spectrum from the filtered pulse wave signal. 
     Further, the step of detecting the state of atrial fibrillation can include detecting the state of atrial fibrillation when a frequency component corresponding to a cycle of the heartbeat does not have a plurality of peaks in the frequency spectrum. 
     Further, the predetermined period can be 2 to 4 seconds. 
     In addition, the step of detecting the state of atrial fibrillation can detect the pulse wave signal of a pressure pulse wave. 
     Further, the step of detecting the state of atrial fibrillation can detect the state of atrial fibrillation based on a time change of the frequency spectrum. 
     Here, the step of detecting the state of atrial fibrillation can detect the state of atrial fibrillation based on time duration in which a predetermined number of peaks lasts. 
     In addition, the step of detecting the state of atrial fibrillation can detect the state of atrial fibrillation based on an amount in which a frequency of the peak fluctuates. 
     Further, the step of detecting the state of atrial fibrillation can detect the state of atrial fibrillation based on two or more of time duration of a peak at a given frequency, frequency variation of the peak, and a number of occurrences of temporally discontinuous peaks. 
     According to another aspect of the embodiment, there is provided a computer program that causes a computer to function as the above-mentioned pulse wave signal analyzer. 
     According to the other aspect of the embodiment, there is provided a computer-readable storage medium that stores the above-mentioned computer program. 
     According to the present disclosure, the pulse wave signal is detected non-invasively, and the detected pulse wave signal is repeatedly subjected to Fourier transform for a predetermined period while shifting in the range of 0.005 seconds to 0.02 seconds to obtain a frequency. Generate a spectrum and detect the state of atrial fibrillation based on the generated frequency spectrum. Therefore, the state of atrial fibrillation can be easily detected. 
     In addition, since the state of atrial fibrillation can be detected by a simple method, the probability of detecting paroxysmal atrial fibrillation is improved by performing repeated examinations. 
     Further, by detecting the pulse wave signal using the pressure pulse wave, highly reliable data can be obtained in a short time by using the sphygmomanometer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a functional configuration of a pulse wave analyzer according to an embodiment; 
         FIG. 2  is a diagram showing an example of values detected by an analyzer  100 ; 
         FIG. 3  is a flowchart showing a procedure of a method for detecting atrial fibrillation according to an embodiment; 
         FIG. 4 ( a )  is a measurement result of pulse wave waveform according to an embodiment, (b) is a diagram after a fast Fourier transform, and (c) is a diagram showing a time change of the result of the fast Fourier transform; 
         FIG. 5  is diagrams showing a method of creating a diagram showing a time change of the result of Fourier transform, in which (a) is a pulse wave waveform and (b) is a created diagram; 
         FIG. 6 ( a )  is a pulse wave waveform of a measurement result according to an embodiment, and (b) is a diagram after fast Fourier transform; 
         FIG. 7 ( a )  is a pulse wave waveform of a measurement result according to an embodiment, (b) is a diagram after a fast Fourier transform, and (c) is a diagram showing a time change of the result of the fast Fourier transform; 
         FIG. 8 ( a )  is a pulse wave waveform of a measurement result according to an embodiment, and (b) is a diagram after fast Fourier transform; 
         FIG. 9 ( a )  is a pulse wave waveform of a measurement result according to an embodiment, (b) is a diagram after a fast Fourier transform, and (c) is a diagram showing a time change of the result of the fast Fourier transform; and 
         FIG. 10  is a diagram showing a flow of a method for determining atrial fibrillation according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, a pulse wave refers to the waveform of a volume change of a body part caused by a beating of a heart. Among the pulse waves, those due to changes in blood pressure are referred to as pressure pulse waves, those due to changes in volume are referred to as volumetric pulse waves, and any of these is included in the present embodiment. 
       FIG. 1  is a block diagram showing a functional configuration of a pulse wave analyzer according to an embodiment of the present invention. An analyzer  100  functions as a diagnostic device for atrial fibrillation, and is configured so that a pulse wave detection unit  104  and an analysis unit  101  can be connected to communicate signals. In this case, the communication means may be wired or may be compliant with a wireless communication standard such as Bluetooth (registered trademark). The pulse wave detection unit  104  and the analysis unit  101  may be integrated into one device, may be configured separately, or may be configured to be detachable from each other. 
     The analysis unit  101  includes a calculation unit  102 , a storage unit  114 , an input unit  116 , a notification unit  118 , and a power supply  120 . 
     The pulse wave detection unit  104  non-invasively detects a pulse wave signal according to the heartbeat of a living body, and may be configured as a contact type or non-contact type biological sensor. For example, the analyzer  100  can be configured as a sphygmomanometer, in which case the pulse wave detection unit  104  is configured to include a cuff to be wrapped around a predetermined portion of an arm. The cuff is provided with an inflatable bag-shaped member. The sphygmomanometer is preset with a compression pressure for blocking blood flow in an artery located inside a cuff wrapped around the arm or the like. When detecting a pulse wave, the blood pressure is measured by increasing the pressure inside the bag-shaped member to the compression pressure and then gradually lowering the pressure at a predetermined speed. Since blood vessels compressed by the cuff vibrate in accordance with the heartbeat, the pressure inside the bag-shaped member is sequentially detected in the process of lowering the blood pressure in blood pressure measurement, and the pulse wave is detected from a pressure change. 
     The pulse wave detection unit  104  may be configured as a combination of a sphygmomanometer and a wireless electrocardiographic transmitter, and the analyzer  100  may be configured as an information processing device such as a personal computer. In this case, the pulse wave detection unit  104  may include an input unit such as a button for instructing execution of an operation for measuring blood pressure, and a display unit for displaying the measurement result. 
     Alternatively, the pulse wave detection unit  104  may be configured by any other sensor such as of a tactile sensor or the like, which measures the pulse wave signal by the pressure. 
     Alternatively, the analyzer  100  may be configured as a fingertip pulse wave detector including a pulse oximeter or the like that measures oxygen saturation using laser light. In this case, the pulse wave detection unit  104  detects the pulse wave by irradiating Infrared laser to hands and feet fingertip and measuring changes in the volume of blood flowing through the fingertips. 
     Alternatively, the analyzer  100  may be configured as a non-contact device such as a camera or a mobile terminal. In this case, the pulse wave detection unit  104  detects the pulse wave by measuring change in brightness caused by the blood flow based on the captured image. 
     Alternatively, the analyzer  100  may be configured as another optical heart rate monitor. In this case, the pulse wave detection unit  104  includes an optical heart rate sensor. The pulse wave detection unit  104  irradiates light using an LED to a predetermined position such as an arm, and detects the pulse wave by measuring an amount of scattered light reflected by the blood flow. 
     Next, various functions of the analysis unit  101  will be described. The calculation unit  102  performs calculation processing based on an electric signal of the pulse wave output from the pulse wave detection unit  104 , and is composed of one or more processors. The calculation unit  102  is further communicably connected to the storage unit  114 , the input unit  116 , and the notification unit  118 . The storage unit  114  is configured to store a program for executing the processing according to the present embodiment, data used in arithmetic processing, or arithmetic result data. Specifically, the storage unit  114  may be configured as a USB flash drive, a removable hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, an optical disk, or the like. 
     The input unit  116  is configured as a keyboard, buttons, dials or switches for inputting commands and information of set values for information processing from a user, an input interface for inputting data, and the like. The notification unit  118  is configured as a liquid crystal display, a lamp, a speaker, or the like for outputting notification information based on the calculation result of the calculation unit  102 . In addition, the analyzer  100  includes the power supply  120  for supplying power to each component in the device. 
     Next, each component included in the calculation unit  102  will be described. The calculation unit  102  includes a filter  105 , a spectrum generation unit  108 , and an atrial fibrillation detection unit  113 . 
     The filter  105  is for passing frequencies associated with pulse waves. The frequency passed here can be a frequency equal to or lower than an audible frequency. The filter  105  may also be configured as a low frequency filter designed to remove high frequency pressure signals that are considered to be associated with atrial flutter. 
     The spectrum generation unit  108  performs a Fourier transform on time series data of the pulse wave signal in order to perform spectrum analysis. As the Fourier transform, for example, a fast Fourier transform (FFT) may be performed. As a result, the spectrum generation unit  108  acquires a frequency spectrum of a signal waveform. It should be noted that the fast Fourier transform is an example, and another Fourier transform for generating the frequency spectrum can be used. 
     The atrial fibrillation detection unit  113  is configured to analyze the signal waveform, and at least detects a state of atrial fibrillation in the living body from the frequency spectrum acquired by the spectrum generation unit  108 . 
     In addition, one or more functions included in the calculation unit  102  in the analysis unit  101  may be implemented in the pulse wave detection unit  104 . For example, the pulse wave detection unit  104  may be provided with the function of the filter  105 , and the pulse wave signal filtered by the pulse wave detection unit  104  may be supplied to the calculation unit  102 . 
     Next, the detection process of atrial fibrillation will be specifically described. As an example, a case where the pulse wave detection unit  104  is configured as a combination of an electrocardiographic transmitter and an automatic sphygmomanometer to measure an electrocardiogram and blood pressure simultaneously will be described.  FIG. 2  shows an example of values detected by the analyzer  100 . In the figure, the horizontal axis represents time (s). The curved broken line  302  shows a cuff pressure (mmHg) of the automatic blood pressure monitor, and the curved solid line  304  shows an amplitude of the pressure pulse wave (mmHg) output from the electrocardiographic transmitter. During the period when an internal pressure of the blood vessel exceeds the pressure of the cuff, the blood vessel dilates, and change in the volume of the blood vessel increases the internal pressure of the cuff. In the oscillometric method, blood pressure is obtained by observing fluctuations in cuff pressure synchronized with the heartbeat in the process of decompressing the cuff. The fluctuation of the cuff pressure observed here is measured as a pressure pulse wave. 
     The pulse wave waveform obtained from the patient is filtered. The filtered waveform is then Fourier transformed. The section to be converted here is preferably about 2 to 20 seconds. In this section, data having a frame time (interval) of 2 to 4 seconds is acquired at a frequency of 50 to 200 times per second (every 0.005 to 0.02 second) while shifting the time axis. 
     The atrial fibrillation detection unit  113  analyzes the value of the frequency spectrum output from the spectrum generation unit  108 . For example, as shown in  FIG. 4( b ) , when there are two or three distinct peaks at equal intervals on the horizontal axis, it is detected that the patient is not in a state of atrial fibrillation (negative). Here, the “peak” of the frequency spectrum refers to the peak of the amplitude of the pressure pulse wave. Specifically, this peak exists at the position of the frequency component of the fundamental frequency corresponding to a cycle of the heartbeat of the living body and its harmonic. On the other hand, as shown in  FIG. 7( b ) , when the value of the frequency spectrum does not have a clear peak at the position of the frequency component corresponding to the cycle of the heartbeat, the state of atrial fibrillation (positive) is detected. 
     Next, a method for detecting atrial fibrillation executed by the analyzer according to the present embodiment will be described with reference to the flowchart of  FIG. 3 . 
     First, in step S 202 , the analysis unit  101  inputs the pulse wave signal of the living body from the pulse wave detection unit  104 . In step S 204 , the filter  105  performs filtering to pass frequencies associated with the pulse wave. In step S 206 , the spectrum generation unit  108  inputs the time series data of the signal input from the filter  105 , performs a fast Fourier transform, and acquires a frequency spectrum. 
     In step S 208 , the atrial fibrillation detection unit  113  detects that the living body is in the state of atrial fibrillation (positive) from the frequency spectrum acquired by the spectrum generation unit  108 . Specifically, if the frequency spectrum does not have a clear peak in the frequency component corresponding to the heartbeat cycle, it is detected that the patient is in the state of atrial fibrillation (positive), and if it has a clear peak in the frequency component corresponding to the heartbeat cycle, it is detected that the patient is not in the state of atrial fibrillation (negative). After that, when the state of atrial fibrillation is detected, the analysis unit  101  stores the detection result in the storage unit  114 , notifies through the notification unit  118  that atrial fibrillation may have occurred, and ends the process. 
     EXAMPLES 
     Example 1 
     Next, examples of the present invention will be described. This example targeted patients with sinus rhythm, persistent atrial fibrillation or extrasystoles. As a component corresponding to the pulse wave detection unit  104 , Health Patch MD (electrocardiographic transmitter) and a HEM-6310F/M6 (automatic sphygmomanometer) manufactured by OMRON HEALTHCARE Co., Ltd. were used. In addition, a personal computer was used as a configuration corresponding to the analysis unit  101 . Then, with reference to  FIG. 2 , simultaneous measurement of the above-mentioned electrocardiogram and blood pressure was performed on a total of 280 subjects (sinus rhythm: 197, atrial fibrillation: 40, other arrhythmias: 43). 
     Next, the pulse wave waveform obtained from the patient was subjected to a fast Fourier transform to obtain a frequency spectrum. Since the automatic sphygmomanometer takes about 20 to 30 seconds for a measurement of blood pressure and pulse rate, the entire 20 to 30 seconds was used as the analysis target of the fast Fourier transform. 
       FIG. 4  shows the measurement results obtained for patients with sinus rhythm. (a) is a pulse wave waveform in which the horizontal axis is time (×0.01 second) and the vertical axis is the amplitude of pressure pulse wave. Further, (b) shows a figure after the fast Fourier transform in which the horizontal axis shows the heart rate (times/minute) and the vertical axis shows the amplitude of the pressure pulse wave. Since the number of samplings of the data measured by the automatic sphygmomanometer was small, the actual number of horizontal axis data was increased about 100 times in order to match characteristics of an electronic circuit for the fast Fourier transform. In the frequency spectrum diagram shown in  FIG. 4( b ) , an arrow  401  indicates a peak of a fundamental wave, and arrows  402  and  403  indicate the peak of the harmonic band. As shown in the figure, sharp peak waveforms with three peaks of frequency is observed in patients with sinus rhythm, in about 65 (times/minute) corresponding to the heartbeat cycle, and about 130 (times/minute) and about 190 (times/minute) which are the harmonic bands thereof. 
       FIG. 4( c )  is a diagram showing a time change of the result of the fast Fourier transform. The method of creating this figure will be described with reference to  FIG. 5 .  FIG. 5( a )  shows a pulse wave waveform, with the horizontal axis representing time (seconds/20) and the vertical axis representing cuff pressure (mmHg/2). A range of 20 seconds was specified in the pulse wave waveform, and the Fourier transform with a frame time of 3 seconds was repeated in this range while shifting by 0.01 seconds. Next, 17 seconds were cut out from the obtained Fourier transform results, arranged on the time axis, and the peaks of the heartbeat information were mapped to obtain the graph shown in  FIG. 5 ( b ) . In  FIG. 5( b ) , the horizontal axis represents time, and 1700 pieces (17 seconds/0.01 seconds=1700) of data are arranged. The vertical axis shows frequency. Spectral intensity in the result of the Fourier transform is represented by the shade of color, with the highest value being 1 and the range of 0.8 to 0.9 represented by shade. 
       FIG. 6  shows the measurement results obtained for another patient of sinus rhythm, in which (a) shows the pulse wave waveform, and (b) shows the figure after the fast Fourier transform. In the frequency spectrum diagram shown in  FIG. 6( b ) , an arrows  501  indicates a peak of the fundamental wave, and arrows  502  and  503  indicate peaks of the harmonic band. Also in the figure, as in  FIG. 4 , sharp peak waveforms with three peaks of frequency is observed in about 55 (times/minute) corresponding to the patient&#39;s heartbeat cycle, and about 110 (times/minute) and about 165 (times/minute) which are the harmonic bands thereof. 
       FIG. 7  shows the measurement results obtained for the patient with atrial fibrillation, in which (a) shows the pulse wave waveform, (b) shows the figure after the fast Fourier transform, and (c) shows a time change of the result of the fast Fourier transform. In the frequency spectrum diagram shown in  FIG. 7( b ) , the sharp peak waveforms with three peaks disappeared. 
       FIG. 8  shows the measurement results obtained for another patient with atrial fibrillation, in which (a) shows the pulse wave waveform, and (b) shows the figure after the fast Fourier transform. In the frequency spectrum diagram shown in  FIG. 8 ( b ) , the sharp peak waveforms with three peaks disappeared as in  FIG. 7 . 
       FIG. 9  shows the measurement results obtained for the patient with extra systole, in which (a) shows the pulse wave waveform, (b) shows the figure after the fast Fourier transform, and (c) shows a time change of the result of the fast Fourier transform. In the frequency spectrum diagram shown in  FIG. 9 ( b ) , two-peak waveforms are found in about 70 (times/minute) corresponding to the patient&#39;s heartbeat cycle and about 140 (times/minute) which is the harmonic band thereof. 
     When the above consideration was applied to the measurement results of other patients, it was found that the following judgment can be made. That is, according to the measurement results of patients with atrial fibrillation, there is no clear peak in the frequency component corresponding to the cycle of the patient&#39;s heartbeat in the frequency spectrum. On the other hand, the measurement results of patients without atrial fibrillation have multiple clear peaks. The positions of these peaks correspond to frequency components of the fundamental frequency that corresponds to the patient&#39;s heartbeat cycle and its harmonic. 
     Example 2 
     The images shown in  FIGS. 4 ( c ) ,  7  ( c ), and  9  ( c ) obtained in the above-described examples were analyzed, and atrial fibrillation was determined as shown in  FIG. 10 . 
     First, determination was made based on time duration of a predetermined number of peaks and amount of fluctuation of the peak frequency. That is, it was determined whether three light-colored lines were continuous horizontally over ¾ or more of the width of the screen in the image, and the vertical fluctuation was less than twice the thickness of the lines (S 902 ). When this condition was met, it was determined to be sinus rhythm (S 908 ). 
     When the condition of step S 902  was not met, the next determination was made based on the time duration of a predetermined number of peaks. Specifically, it was determined whether one or more of the light-colored lines were continuous over two-thirds or more of the width (S 904 ). When this condition was met, it was determined to be an arrhythmia other than atrial fibrillation (S 912 ). 
     Then, if the condition of step S 904  was not met, the next determination was made based on two or more of the time duration of the peak at a predetermined frequency, the fluctuation of the frequency of the peak, and the number of occurrences of temporally discontinuous peaks. Specifically, it was determined whether or not two or more of the following three conditions were satisfied (S 906 ).
         (1) Two or more light-colored lines remain in a row of ½ or less of the width of the screen.   (2) Two or more light-colored lines fluctuate up and down more than twice the thickness of the line.   (3) There are two or more island-shaped light color regions with no continuity on the screen.       

     When the condition of S 906  was met, it was determined to be atrial fibrillation. 
     In this example, the measurement results of 280 persons were observed, and the case where atrial fibrillation was determined 2 or more times out of 3 measurements was determined to be positive. As a result, the above characteristics were applied to all of the measurement results. 
     Although the embodiment of the present invention has been described above, the apparatus according to the present embodiment, its components, and the steps of the method described above can be carried out by hardware or by a combination of software and hardware. Whether functions of the device or its components are performed by hardware or software is subject to the constraints in design of the above embodiments. Although those skilled in the art can perform the functions of the components described above for specific applications using various methods, such changes are also within the scope of the present invention. 
     The apparatus described in the above embodiments is merely an example, and other methods can be used. For example, the above-mentioned components are logically divided functions, and the components may be divided by other methods in implementation. Further, two or more of the above-mentioned components may be integrated into one component, and each of the components may physically exist independently. 
     When the function described in the above embodiments is performed in the form of software, a computer program for realizing the function can be stored in a computer-readable storage medium. The computer program includes several instructions for instructing the computer to function as all or part of the components described in the above embodiments.