Effect Of Arm Powered Passive Leg Cycling On Heart Rate Variability In Spinal Cord Injured

Abstract

Heart rate variability (HRV) has emerged as a reproducible, non-invasive technique to assess autonomic influences on the heart. Studies have shown that exercise in ablebodied individuals decreases high frequency (HF) and low frequency (LF) components of HRV. The effect of arm powered passive leg exercise on HRV in spinal cord injured (SCI) individuals is not known. PURPOSE The purpose of this investigation was to determine the effects of an acute bout of exercise on cardiac autonomic function in SCI as indicated by time and frequency-domain measures of HRV. METHODS HRV values were obtained (Welch Allyn CardioPerfectTM, Skareateles Falls, NY) during 300 sec recordings from three paraplegic and two tetraplegic SCI subjects (mean age: 33.4 ± 20.1 yrs, range 21–69 yrs) at rest (W0) and immediately following an acute bout of passive exercise on the PsycleTM (Intellifit, Inc., Wichita Falls, TX) at a target heart rate of 65% of age-adjusted maximum (W1). Frequency domain measures were calculated by Fast Fourier Transform including high frequency (HF, 0.15–0.4 Hz), low frequency (LF, .04−.15 Hz), and the ratio of LF to HF (LF/HF). A 2X2 ANOVA was used to identify changes in LF, HF, LF/HF and the raw time domain data obtained from R-R intervals from W0 to W1. RESULTS No significant difference (P >.05) was determined between paraplegic and tetraplegic individuals on criterion measures from W0 to W1. Arm powered passive leg cycling was accomplished for 35 min at 35±17.5 rpm, for 1227±663 total revolutions, at 9.7±6.8 W, and at heart rates of 122±22 bpm. Mean HF values (ms2) were reduced from 423±427 to 30±30 [F 1,6) = 12.1, p< 0.05] for W0 and W1, respectively. Mean LF values (ms2) were 692±841 and 104±142 [F(1,6) = 2.3, P>.05), respectively for W0 and W1. Mean LF/HF values were 1.8±1.3 and 2.7±1.3 [F (1,6) = 2.4, P>.05) for W0 and W1, respectively. Mean R-R intervals were reduced from 810±60 to 655±109 ms [F (1,6) = 7.8, p<.05] for W0 and W1, respectively. Although LF did not reach statistical significance, the tendencies of reduced HF and LF values with exercise is consistent with reported responses from able-bodied subjects. CONCLUSION These data suggest that arm powered passive leg cycling produces a shift in autonomic influences on the heart of spinal cord injured.