Association between Heart Rate Recovery following Six-Minute Walk Test and Resting Short-Term Heart Rate Variability in Apparently Healthy Young Male University Students in North India

Abstract

Hear rate recovery (HRR) is not only an indirect measure of cardiorespiratory fitness but also a valid maker of autonomic dysfunction, poor prognosis and mortality. Heart rate variability (HRV) is a non-invasive, reliable and valid assessment of autonomic nervous system, and also a predictor of morbidity and mortality. There is limited data on the correlation of HRR after six-minute walk test (6MWT) with resting short-term HRV in apparently healthy young male university students in north India, and hence the study was planned. 25 young (22.60±1.53 years old) male university students were the volunteers. Following anthropometric variables were measured: height, weight, BMI, waist and hip circumferences, and waist-hip and waist-height ratios. Resting short-term or 5min HRV indices used for analysis were: (a) time domain: RMSSD, LnRMSSD, SDNN and SDSD, (b) frequency domain: LF (ms2), LF (nu), HF (ms2), HF (nu) and LF/HF ratio, and (c) non-linear: SD1, SD2 and SD2/SD1. HRV analysis was done from lead II ECG. Heart rate immediately (RHR0), at 1st min (RHR1) and 2nd min (RHR2) after 6MWT were measured in quiet sitting position, and HRR at 1st min (HRR1) and 2nd min (HRR2) were calculated as HRRi=RHR0-RHRi, i=1 or 2. There were statistically significant positive correlations of HRR1 with RMSSD, LnRMSSD, SDSD, HF (nu), SD1, RHR0 and HRR2. HRR1 correlated significantly and negatively with LF (nu), LF/HF and SD2/SD1. HRR2 showed only statistically significant positive corelation with RHR0 and HRR1. Out of the two HRRs, HRR1 was a better correlate of resting cardiac vagal modulation, and those who recovered faster at 1st min after 6MWT also had higher vagally mediated markers of HRV.