Sympathetically-mediated cardiac responses to isolated muscle metaboreflex activation following exercise are modulated by body position in humans

Abstract

Isolated muscle metaboreflex activation with posthandgrip exercise ischemia (PEI) increases sympathetic nerve activity and partially maintains the exercise-induced increase in blood pressure, but a smaller heart rate (HR) response occurs. The cardiopulmonary baroreceptors, mechanically sensitive receptors that respond to changes in central blood volume and pressure, are strongly associated with changes in body position and upon activation elicit reflex sympathoinhibition. Here, we tested the hypothesis that postural changes modulate the sympathetically mediated cardiac response to PEI in humans. Beat-to-beat HR (electrocardiography) and blood pressure (finger photoplethysmography) were continuously measured, and cardiac function was assessed by echocardiography in 13 healthy men (21 ± 3 yr). After a 15-min rest period, 90-s static handgrip at 40% maximum voluntary contraction was performed followed by 3 min of PEI. Four trials were randomly conducted during either seated or supine position with and without β-adrenergic blockade (25 mg atenolol). During PEI under control conditions, HR remained elevated from baseline in the seated [change (Δ): 4 ± 1 beats/min] but not in the supine (change: -1 ± 1 beats/min) position. Similarly, stroke volume and cardiac output were increased from baseline in the seated (∆13.0 ± 2.4 ml and ∆1.1 ± 0.2 l/min, respectively) but not in the supine (∆2.5 ± 2.9 ml and ∆0.13 ± 0.20 l/min, respectively) position. During β-adrenergic blockade, HR, stroke volume, and cardiac output remained unchanged in both conditions. We conclude that sympathetically mediated cardiac responses to PEI are influenced by changes in body position. These findings indicated that muscle metaboreflex and cardiopulmonary baroreflex have an interactive influence on the neural control of cardiovascular function in humans. NEW & NOTEWORTHY In the present study, we demonstrated that muscle metaboreflex activation increases heart rate, stroke volume, and cardiac output in the seated position but not in the supine position and not after β-adrenergic blockade. These findings indicate that sympathetically mediated cardiac responses to isolated muscle metaboreflex activation after exercise are modulated by central blood volume mobilization.

Sex differences in the ventilatory and cardiovascular response to supine and tilted metaboreflex activation

“…; Teixeira et al. ). Recent studies have established that men have an enhanced sympathetic and pressor response to metaboreflex activation compared to women (Jarvis et al.…”

“…; Teixeira et al. ). While there are no sex differences in sympathetic baroreflex function in upright posture (Fu et al.…”

“…Teixeira et al. () have recently concluded that sitting in an upright posture unloads the cardiopulmonary baroreceptors leading to increased activation of the metaboreflex. Similarly, Ichinose et al.…”

GABAA receptors modulate sympathetic vasomotor outflow and the pressor response to skeletal muscle metaboreflex activation in humans

“…; Teixeira et al . ). Human investigations have demonstrated that the return of HR to resting levels is a consequence of cardiac parasympathetic reactivation possibly overcoming the effect of metaboreflex‐induced sympathoexcitation to the heart (Nishiyasu et al .…”

“…), and participant body position (Teixeira et al . ). We acknowledge that, because we have only used ischaemic IHG at 30% MVC, care should be taken when extrapolating our findings to the exercise of other muscle groups (i.e.…”