Variabilidad De La Frecuencia Cardiaca

Journal of Medical and Biological Engineering, 25(2): 67-71

67

Comparison of Heart Rate Variability Measured by ECG in Different Signal Lengths
Geng Hong Lin
1

Yuh Huu Chang

Kang Ping Lin1,*

Department of Electronic Engineering, Chung Yuan Christian University, Chung-Li, Taiwan, 320, ROC Department of Electrical Engineering, Chung Yuan Christian University, Chung-Li, Taiwan, 320,ROC Received 7 May 2005; Accepted 28 Jan 2005

Abstract
The measurement of heart rate variability, HRV, provides a noninvasive measurement of the autonomic nervous system (ANS) activity. HRV can be measured with the variation of RR intervals exhibited in a sequence of ECG sample. For a short-term HRV, the measuring time is usually five minutes. However, there are still many expectations ofshortening the measuring time to evaluate the ANS. In this paper we analyzed and compared three minute HRV measurement to five minute standard short-term HRV. In order to evaluate the measurement results based on three minute and five minute HRVs, four major measurements were calculated in this study. The first is the standard deviation of normal-beat to normal-beat intervals (SDNN). The second isthe square root of the mean squared differences of successive difference normal-beat to normal-beat intervals (RMSSD). The third is the proportion of interval differences of successive normal-beat to normal-beat intervals greater than 50 ms (pNN50). The fourth is the ratio of low frequency energy to high frequency energy (LF/HF) based on Fourier analysis method. Results show that the HRV presentedby both SDNN and LF/HF using the three-minute measuring data differs significantly from that using the five-minute measuring data. In addition, the characteristics of HRV under different heart rate conditions shows that faster heart rate will come out smaller HRV. In conclusion, the HRV analyzed based on three minutes measuring data would not be equaled to that of five minutes measuring data. Atthe same time, the conditions of heart rate need to be considered when heart rate variability was analyzed.. Keywords: Short-term HRV, Activity of autonomic Nervous system, ECG.

Introduction
The ANS comprises two basic components: the sympathetic and parasympathetic. The sympathetic influences heart rate (HR) and can be mediated by releasing s epinephrine and norepinephrine. The parasympatheticinfluences on heart rate, but it is mediated via the acetylcholine release from vagus nerve. The heart rate may be increased by acting sympathetic activity or decreased by acting parasympathetic activity. Changes in the balance of sympathetic/parasympathetic control of heart rate will result in measurable changes in heart rate variability, HRV. The analysis of HRV is one of the useful non-invasivetools for measuring the status of autonomic nervous system. To measure the HRV information can be obtained using the variations of heart-beat to heart-beat intervals that can be measured by any cardiac related signal such as electrocardiogram (ECG). [1] HRV analysis has been applied widely to many clinical studies including sudden death, cardiovascular diseases, hypertension, and diabetes [2-5].The clinical importance of
* Corresponding author: Kang Ping Lin Tel: +886-3-2654826; Fax: +886-3-2654899 E-mail: kplin@cycu.edu.tw

HRV has been known since the publication of studies established that HRV was an independent and strong predictor of mortality after myocardial infarction [6-7]. In addition, low heart rate variability has been implicated as a risk factor for sudden death.Moreover, low parasympathetic active have an increased risk for sudden death [4]. HRV measures are usually divided into short-term and long-term recording. For short-term HRV measures, the measuring time length is five minutes which has been found valid and with clinical significance. However, in the existing studies, there is no information to show the differences of short-term HRV based on different...