Passive limb movement: evidence of mechanoreflex sex specificity

Abstract

Previous studies have determined that premenopausal women exhibit an attenuated metaboreflex; however, little is known about sex specificity of the mechanoreflex. Thus, we sought to determine if sex differences exist in the central and peripheral hemodynamic responses to passive limb movement. Second-by-second measurements of heart rate, stroke volume, cardiac output (CO), mean arterial pressure, and femoral artery blood flow (FBF) were recorded during 3 min of supine passive knee extension in 24 young healthy subjects (12 women and 12 men). Normalization of CO and stroke volume to body surface area, expressed as cardiac index and stroke index, eliminated differences in baseline central hemodynamics, whereas, peripherally, basal FBF and femoral vascular conductance were similar between the sexes. In response to passive limb movement, women displayed significantly attenuated peak central hemodynamic responses compared with men (heart rate: 9.0 ± 1 vs. 14.8 ± 2% change, stroke index: 4.5 ± 0.6 vs. 7.8 ± 1.2% change, cardiac index: 9.6 ± 1 vs. 17.2 ± 2% change, all P < 0.05), whereas movement induced similar increases in peak FBF (167 ± 32 vs. 193 ± 17% change) and femoral vascular conductance (172 ± 31 vs. 203 ± 16% change) in both sexes (women vs. men, respectively). Additionally, there was a significant positive relationship between individual peak FBF and peak CO response to passive movement in men but not in women. Thus, although both sexes exhibited similar movement-induced hyperemia and peripheral vasodilatory function, the central hemodynamic response was blunted in women, implying an attenuated mechanoreflex. Therefore, this study reveals that, as already recognized with the metaboreflex, there is likely a sex-specific attenuation of the mechanoreflex in women.

Fig. 1.

Central hemodynamic responses to passive limb movement between women and men. A–C: cardiac index (CI; A), heart rate (HR; B), and stroke index (SI; C) responses to passive movement in women and men. CO, cardiac output; BSA, body surface area; SV, stroke volume. Note: these data are temporally aligned and thus underrepresent true individual peak responses. Data are expressed as means ± SE. *P < 0.05, sex × time interaction.

Fig. 2.

Individual peak relative changes in central and peripheral hemodynamic of women and men. MAP, mean arterial pressure; FBF, femoral blood flow; FVC, forearm vascular conductance. Note: these data represent individual peak responses, which are underrepresented in Figs. 1 and 3. Data are expressed as means ± SE. *P < 0.05, men vs. women.

Fig. 3.

Peripheral hemodynamic responses to passive limb movement in women and men. A–C: absolute FBF (A), MAP (B), and FVC (C) in response to passive movement in women and men. Note: these data are temporally aligned and thus underrepresent true individual peak responses. Data are expressed as means ± SE.

Fig. 4.

Relationship between peak FBF and peak CO responses to passive movement in women and men.