fig2 depicts the heart rate variability analytical apparatus 20 as put forth in the present invention . it essentially comprises a signal amplifier 21 , an analog - to - digital converter 22 , a computer 23 , a digital input / output device 24 , an electrocardiogram signal detector 25 , an “ execution ” button 26 , and a case 32 . the case 32 is a rectangular container whose dimensions are 14 cm × 11 cm × 4 . 5 cm , and it contains the signal amplifier 21 , the analog - to - digital converter 22 , the computer 23 and the digital input / output device 24 . the electrocardiogram signal detector 25 is composed of three detection electrodes 251 . one end of each detection electrode 251 is connected to the subject , and the other end passes through the case 32 to be connected to the signal amplifier 21 so as to capture a person electrocardiogram signals and transmit them to the signal amplifier 21 . after being amplified by the signal amplifier 21 , the electrocardiogram signals are converted into digital signals by means of the analog - to - digital converter 22 , and then are entered into the computer 23 . the computer 23 executes a program 231 to carry out a series of analyses and control - related tasks ( for further details , please refer to later description ). the digital input / output device 24 functions as the transmission interface between the computer 23 and the “ execution ” button 26 . in practice , being a user - machine interface intended for external communication , the digital input / output device 24 may be additionally connected to a “ noise ” indicator 33 , a “ no signal ” indicator 34 , a “ print ” indicator 35 , a “ recording ” indicator 36 , and a “ stand by ” indicator 37 , to indicate the status of the heart rate variability analytical apparatus 20 . moreover , the digital input / output device 24 may be connected to a “ cancel ” button 27 for the sake of manual interruption of the process . the above - mentioned buttons 26 and 27 as well as various indicators 33 - 37 may be installed on the same side of the case 32 to facilitate control and surveillance . cables 38 connect the signal amplifier 21 and the analog - to - digital converter 22 , the analog - to - digital converter 22 and the computer 23 , and the computer 23 and the digital input / output device 24 to transmit signals . in addition , the computer 23 may be connected to a display 29 and a printer 30 , so as to display and print the findings of the heart rate variability analysis of the electrocardiogram signals . the signal amplifier 21 may be connected to a battery 31 or an ac power source to meet its electric demand . the process of heart rate variability analysis put forth in the present invention is shown in fig3 . the following is the explanation of the analytical process , with references made to the heart rate variability analytical apparatus 20 depicted in fig2 . the “ stand by ” indicator 37 gets turned on as soon as the power for the heart rate variability analytical apparatus 20 is switched on , telling the user that the heart rate variability analytical apparatus 20 is standing by . all the procedures of the heart rate variability analysis are started by the “ execution ” button 26 . immediately after the user pressed the “ execution ” button 26 , the “ recording ” indicator 36 turns on , and the electrocardiogram signal detector 25 begins to capture a transient electrocardiogram signal which is then amplified by the signal amplifier 21 or additionally undergoes wave filtration performed with a band pass filter before being sent to the analog - to - digital converter 22 . after that , the user performs analog - to - digital conversion , and carries out sampling at a rate of 256 to 2048 times per second on the electrocardiogram signal by means of the analog - to - digital converter 22 , which is under the control of the program 231 . in the meantime , the program 231 may have an additional function of detecting the 50 / 60 hz components of the electrocardiogram signal . the “ noise ” indicator 33 gets turned on whenever the signal is too strong . the peak of the electrocardiogram signal corresponding to each heartbeat , i . e ., the qrs wave , is searched out ( please refer to fig4 ), and it stands for each heartbeat . the “ no signal ” indicator 34 turns on whenever no peak is identified . the program 231 measures parameters such as height and duration of the peak of each heartbeat , and calculates the mean and standard deviation of individual parameters in order to create a standard template . afterward , each of the heartbeat peaks is compared with the template . in comparison , a heartbeat peak found to fall beyond a first predetermined standard deviation of the standard template is deemed a noise and , therefore , should be deleted . in practice , the first predetermined standard deviation is mostly set to three standard deviations . the interval between the respective peaks of two successive heart - beats is measured to be the period of heartbeat at that point . the mean and standard deviation of all the heartbeat intervals are figured out , and then all the heartbeat intervals are verified . a heartbeat interval which falls beyond a second predetermined standard deviation is deemed as either a noise or an unstable signal , and thus it has to be deleted . similarly , the second predetermined standard deviation is generally set to be as large as three standard deviations . all qualified peaks are sampled at an appropriate frequency , e . g ., 7 . 11 hz , and performed interpolation to keep the time consecution , with the program 231 to detect and see whether the “ cancel ” button 27 is pressed . if it is , the heart rate variability analytical apparatus 20 returns to the standby status ; otherwise , the next step proceeds . moreover , the program 231 is used to judge whether the amount of data is enough . if negative , the heart rate variability analytical apparatus 20 continues to capture electrocardiogram signals so as to form a loop ; otherwise , the next step proceeds . fourier transform is adopted in spectrum analysis . in the first place , any linear drift of signal is eliminated to evade the interference from low - frequency band , and the hamming computation is employed to prevent the mutual leakage between individual frequency components of the spectrum . after that , 288 - second data ( 2048 points ) is taken and fast fourier transform is conducted so as to acquire heart rate power spectral density ( hpsd ), and the compensation with regard to any effects of sampling and hamming computation is performed . the powers of the lf ( 0 . 04 - 0 . 15 hz ) and hf ( 0 . 15 - 0 . 4 hz ) bands of the heart rate power spectral density are quantified by integral , and the quantitative parameters like lf / hf or tp are figured out as well , as shown in fig5 . eventually , the findings are displayed on the display 29 or printed out with the printer 30 . the “ print ” indicator 35 turns on whenever the printer 30 is printing . in addition to external installation , the display 29 and the printer 30 may also be built - in , that is , installed inside the heart rate variability analytical apparatus 20 . the program 231 not only measures , filters and analyzes electrocardiogram signals , but , as illustrated with the present embodiment , also has the additional function of controlling the steps of the aforesaid heart rate variability analytical method , so a user merely needs to press the “ execution ” button 26 to accomplish all the steps . unlike a conventional heart rate variability analysis that requires a user to enter a large amount of data , the present invention reduces the number of keystrokes to one during the process of heart rate variability analysis , and even the traditional keyboard can be replaced with a button , under the integrated control of the computer program . the method put forth in the present invention may not only be applied to small machines , but also provide a friendly operating interface . besides tremendously minimizing operational errors , it becomes accessible to laymen . in practice , the heart rate variability analytical apparatus put forth in the present invention is quite time - saving and easy to use , as it prints out a person heart rate variability analytical result and autonomic function data in just five minutes after a button is pressed . the above - described embodiments of the present invention are intended to be illustrative only . numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims .
a user - friendly and statistic based heart rate variability analytical method includes the following steps of capturing an electrocardiogram signal of a person , performing analog - to - digital conversion of the electrocardiogram signal , selecting the peaks of the electrocardiogram signal , calculating the standard deviation of the heights , durations and inter - peak intervals of the peaks , removing the peaks whose heights , durations or inter - peak duration fall beyond a first predetermined standard deviation , sampling and interpolating the qualified peaks to form a consecutive peak signal , and performing spectrum analysis to the peak signal in frequency domain .