The effects of respiration on heart rate and blood pressure spectra during exercise below the ventilatory threshold

The purpose of this study was to determine how heart rate and blood pressure variabilities (HRV and BPV) change with steady-state exercise up to the ventilatory threshold (VT). The VT was determined using the V-slope method of computer regression analysis of the plot of carbon dioxide production versus oxygen consumption (VO2max). Twelve healthy subjects performed 1) cycle ergometry (exercise protocol) at 50%, 75% and 100% of previously determined VT and 2) sitting at rest and breathing at matched respiratory rates and volume (controlled breathing, CB) as during the exercise protocol. Throughout the CB protocol carbon dioxide was added to maintain normal gas homeostasis. Heart rate and blood pressure spectra for both protocols were derived from 3-minute epochs of stationary data using frequency domain analyses. These data were analyzed by repeated measures ANOVA and coherence analyses between heart rate and respiration as well as blood pressure and respiration. The ANOVA revealed significant changes in heart rate and blood pressure spectra for both low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.4 Hz) modulations between all stages of the exercise protocol (p<0.05) but no significant changes for any of the CB protocol. Coherence analyses showed significant decrease in heart rate and blood pressure coherences during exercise than during control breathing.