Muscle metaboreflex and exercise heart rate: insights from studies in subjects with and without heart failure.

摘要

We read with interest the recent work of Fisher et al. (2010), who demonstrated, in healthy young men, that muscle metaboreflex-induced sympathetic excitation contributes to the heart rate response to ischaemic handgrip exercise in a graded manner. This effect, masked at lower intensity of exercise by parasympathetic reactivation at the cessation of handgrip, was unmasked by glycopyrrolate during post-handgrip ischaemia, which prolongs metaboreflex stimulation of muscle afferents independently of central command and muscle mechanoreflex influences, and abolished by beta-blockade. The authors interpret their findings as indicating that heart rate returns to resting values during ischaemia after moderate exercise because of an overwhelming effect of parasympathetic reactivation, which counters metaboreflex increases in cardiac sympathetic activity. However, after more intense handgrip, cardiac sympathetic activity predominates and the impact of parasympathetic restoration is less obvious. Although this concept has been supported by animal work (O'Leary, 1993), it has not been investigated directly in humans as in the present study (Fisher et al. 2010).