Left ventricular systolic function during isometric handgrip exercise and postexercise circulatory occlusion in...

Postexercise circulatory occlusion (PECO) stimulates metabolically sensitive afferents, activating the muscle metaboreflex and eliciting a greater blood pressure response in males than females, possibly owing to greater absolute exercise workloads that contribute to disproportionate increases in stroke volume (SV). We tested the hypotheses that isometric handgrip exercise (EX) and PECO would increase SV greater in males than females, and accounting for strength would negate differences. Ten males and 10 females underwent cardiac MRI during rest, EX, and PECO. SV, end-systolic (ESV) and end-diastolic volume (EDV), all indexed to body surface area, and wall stress, systolic blood pressure (SBP), and total peripheral resistance (TPR) were measured. EX and PECO lowered stroke volume index (SVi) in males (both P < 0.001) but not females (both P = 0.998). The reduction in SVi during EX and PECO in males remained with analysis of covariance (covariate handgrip strength; P = 0.020). EX increased end-systolic volume index (ESVi) in both sexes (P ≤ 0.018), whereas ESVi increased during PECO in males (P < 0.001) but not females (P ≥ 0.092). EX and PECO increased end-diastolic volume index, SBP, TPR, and wall stress (all P ≤ 0.015) in both sexes. The SVi response to PECO was negatively related to ESVi responses in males (r = -0.822, P = 0.004) but not females (P = 0.216). PECO lowers SVi in males but not females independent of handgrip strength, despite comparable pressor responses. These novel findings support differential afterload sensitivity on SV between sexes in response to the exercise pressor and muscle metaboreflex. Remarkably, SV is not augmented as part of the pressor response elicited by isometric handgrip exercise or muscle metaboreflex activation in either sex.NEW & NOTEWORTHY Moderate-intensity isometric handgrip exercise and postexercise circulatory occlusion decrease stroke volume in males but not females, even after accounting for handgrip strength. Sex differences in the stroke volume response to isometric handgrip exercise and the muscle metaboreflex appear driven by greater male sensitivity to ventricular afterload. In an isolated handgrip exercise-circulatory occlusion model, stroke volume does not increase as a component of the pressor response elicited by exercise or the muscle metaboreflex in either sex.