Leg Vascular Conductance During Fatiguing Inspiratory Muscle Work Is Not Different Between Females And Males

Background: Fatiguing inspiratory muscle work can trigger the sympathetically-mediated respiratory muscle metaboreflex. Activating this reflex has been shown to increase blood pressure and heart rate while decreasing peripheral blood flow. Studies have shown females have an attenuated mean arterial pressure response (MAP) compared to males despite similar workloads to fatiguing inspiratory muscle work, suggesting females may have an attenuated respiratory muscle metaboreflex. However, the sex difference effects of respiratory muscle metaboreflex effects on resting limb vascular conductance (LVC) remains unknown. The purpose of this study was to investigate whether sex differences exist in LVC responses to fatiguing inspiratory muscle work. We hypothesize that males would exhibit a greater decrease in LVC compared to females. Methods: Eight healthy females (F; 35±11 years) and 8 healthy males (M; 31±6 years) completed the study. Participants completed a 5-minute baseline followed by a 5-minute inspiratory pressure threshold loading (IPTL) trial. The breathing pattern was set to 60% of their maximal inspiratory mouth pressure with a breathing frequency of 15 breaths/minute and an inspired duty cycle of 0.7 to activate the respiratory muscle metaboreflex. CO 2 was introduced into the inspired circuit to prevent hypocapnia. Continuous MAP (finger photoplethysmography) and heart rate (electrocardiogram) were recorded. Continuous blood velocity and diameters of the superficial femoral artery were measured using duplex ultrasonography. Leg blood flow (LBF) was calculated as the product of mean blood velocity and femoral artery cross-sectional area. LVC was calculated as LBF/mean arterial pressure. These data were averaged in 30-second segments and reported from 5-minute mark of IPTL (End-Task % of baseline). Groups were compared using Student’s t -test and analyzed using a two-way repeated-measures ANOVA. Results: Pulmonary function was within predicted ranges for all participants (FEV 1 /FVC: [F vs. M]: 100±8 vs. 100±9%predicted; P=0.919). Heart rate ([Baseline: F vs. M]: 70±13 vs. 73±8 bpm; P=0.571) and MAP (Baseline: [F vs. M]: 90±12 vs. 95±8 mmHg; P=0.378) were not different between females and males at baseline or throughout the IPTL trial (Group Main Effect: p>0.05 for both). Additionally, LBF decreased in response to IPTL but there was no difference between groups (End-Task: [F vs. M]: -31±33 vs. -21±24%baseline; Time Main Effect: P=0.012, Group Main Effect: P=0.352). When accounting for blood pressure, LVC also decreased during IPTL but was not different between females and males (End-Task: [F vs. M]: -37±30 vs. -33±24%baseline; Time Main Effect: p<0.001, Group Main Effect: P=0.655). Conclusion: These preliminary data suggest LVC decreases during a 5-minute period of fatiguing inspiratory work using IPTL; however, IPTL does not elicit variable LVC decreases between females and males. NIH (HL139854); NSERC (PDF-577750-2023) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.