Muscle chemoreflex control of heart rate during static exercise in healthy humans

In this study we tested the hypothesis that the muscle chemoreflex contributes to heart rate (HR) rise during static exercise through an increase in sympathetic drive to sinus node. To this aim, 10 healthy males performed 4 min static leg extension at 30% MVC (SLE) followed by 4 min of arrested leg circulation (ALC) to isolate the muscle chemoreflex. Arterial pressure (MAP) and RK-inicrval (RR-int) were measured by FINAPRES and ECG. Power spectral analysis of RR-int variability, employing an autoregressive algorithm, was used to evaluate the autonomie modulation of sinus node. The magnitudes of low (RR-_LF) and high (RR-_HF) frequency spectral components (expressed in normalized units, NU) of RR-int variability have been taken as indexes of sympathetic and, respectively, vagal modulation to sinus node. RR-_LF significantly increased during SLE remaining significantly elevated during ALC at the time when RR-int returned to rest. RR-_HF significantly fell during SLE returning toward rest during ALC. REST EXE ALC (1 PLF (NU) 65.1±6.6 81.2±4.6 1 76.0±7.6 1 RR-_HF (NU) 28.0±6.8 15.3±4.2 ±20.7±6.6 These results suggest that muscle chemoreflex contributes to the rise in HR during static exercise via an increase in sympathetic activity to sinus node.