Augmentation of the exercise pressor reflex in prehypertension: roles of the muscle metaboreflex and mechanoreflex

This study investigated the hemodynamic mechanisms underlying the exaggerated blood pressure response to muscle contraction in prehypertensive humans and the potential role of skeletal muscle metabo- and mechanoreceptors in this response. To accomplish this, changes in peak mean arterial blood pressure (Delta MAP), cardiac output, and total peripheral resistance (Delta TPR) were compared between prehypertensive (n = 23) and normotensive (n = 19) male subjects during 2 min of static contraction (at 50% of maximal tension), 2 min of postexercise muscle ischemia (metaboreflex), and 1 min of passive dorsiflexion of the foot (tendon stretch, mechanoreceptor reflex). These variables were assessed before and during the interventions. Percentage increases from baseline in MAP and TPR in response to the exercise pressor reflex were augmented in the prehypertensives, compared with the normotensives (44% +/- 5% vs. 33% +/- 4% and 34% +/- 15% vs. 2% +/- 8%, respectively) (p < 0.05). Metaboreflex-induced increases in MAP and TPR were also augmented in the prehypertensives (28% +/- 5% vs. 14% +/- 4% and 36% +/- 12% vs. 14% +/- 9%, respectively) (p < 0.05). In response to the mechanoreflex, no differences in the percentage increase in MAP or TPR were seen between groups. The results indicate that the reflex pressor response to static contraction is augmented in prehypertension and suggest that this phenomenon is due, at least in part, to enhanced activation of metaboreceptors.