心率變異度HRV (Heart Rate Variability) 在近年來為國際上被大家熱烈的討論及研究的議題，是一種量測連續心跳速率變化過程的方法。目前心律變異度(HRV)的研究都是分析心電圖(ECG)中R波與R波的時間間距(R-R interval， RRI)，並分析R-R間距的頻譜中極低頻(Very-low frequency)、低頻(Low frequency)、與高頻(Hight frequency)的能量，計算低頻與高頻的能量比例(LF/HF ratio)，作為估測受試者交感/副交感神經活性的依據。而許多時間域的指標，如心跳間隔均方根值(RMSSD)與心跳變異(SDNN)在本研究中也有被研究。然而，使用心電圖進行心律變異度(HRV)量測，通常需要量測受試者的左手與右手，此部分經常造成使用者的不方便，也比較難以實現穿戴式裝置的連續量測情境。因此，在本研究中，我們試圖嘗試使用光體積血容積(PPG)作為取代心電圖(ECG)心律變異度量測的手段，藉由使用光體積血容積(PPG)與心電圖(ECG)的同步量測評估，我們發現PPG與ECG具有十分高的相關性，因此證明使用PPG取代ECG的可能性。另外，本研究也量測SDNN/RMSSD，並討論使用時間域參數取代頻率域LF/HF的可能性。;Heart-rate variability (HRV) is a popular issue which has been widely discussed in academic heart studies. In the HRV, the changes of heart-rate information is continuously analyzed. Current HRV measurements analyze R-R intervals of electrocardiogram (ECG) and calculate the spectral density of very low-frequency, low-frequency, and high-frequency bands for estimating the sympathetic/parasympathetic activities. Indicators, such as RMSSD, SDNN, and SDANN, are proposed as indexes for risk factor estimations. Though ECG-based HRV has been widely studied, however, the ECG measurement requires the electrodes to be contacted on both hands which causes inconveniency and is not suitable to be designed for continuous measurement using wearable devices. Accordingly, in our study, we intend to test the feasibility of using photoplethysmogram (PPG) to replace ECG in HRV measurement. Both ECG and PPG signals were measured simultaneously and compared. The ratio between HRV low-frequency and high-frequency components (LF/HF) in each subject was calculated and compared with the value of ECG LF/HF. We found there was a high linear correlation between PPG and ECG -based HRV which demonstes its feasibitliy of replacing ECG by PPG. In addition, in our stud, the feasibility of time-domain parameter SDNN/RMSSD was also calculated for HRV study.
