The Cardiovascular Consequences Of Fatiguing Expiratory Muscle Work In Otherwise Resting Healthy Humans

In 11 healthy adults (25 +/- 4yr; 2 female, 9 male subjects), we investigated the effect of expiratory resistive loaded breathing [65% maximal expiratory mouth pressure (MEP), 15 breaths.min(-1), duty cycle 0.5; ERLPm] on mean arterial pressure (MAP), leg vascular resistance (LVR), and leg blood flow ((Q) over dot (L)). On a separate day, a subset of five male subjects performed ERL targeting 65% of maximal expiratory gastric pressure (ERLPga). ERL-induced expiratory muscle fatigue was confirmed by a 17 +/- 5% reduction in MEP (P < 0.05) and a 16 +/- 12% reduction in the gastric twitch pressure response to magnetic nerve stimulation (P = 0.09) from before to after ERLPm and ERLPga, respectively. From rest to task failure in ERLPm and ERLPga, MAP increased (ERLPm = 31 +/- 10 mmHg, ERLPga = 18 +/- 9 mmHg, both P < 0.05), but group mean LVR and (Q) over dot(L) were unchanged (ERLPm: LVR=0.78 +/- 0.21 vs. 0.97 +/- 0.36mmHg.mL(-1)-min, (Q)over dot(L) = 133 +/- 34 vs. 152 +/- 74 mL.min(-1); ERLPga: LVR=0.70 +/- 0.21 vs. 0.84 +/- 0.33mmHg.mL(-1).min, (Q) over dot(L) = 160 +/- 48 vs. 179 +/- 110 mL.min(-1)) (all P >= 0.05). Interestingly, (Q) over dot(L) during ERLPga oscillated within each breath, increasing (similar to 66%) and decreasing (similar to 50%) relative to resting values during resisted expirations and unresisted inspirations, respectively. In conclusion, fatiguing expiratory muscle work did not affect group mean LVR or (Q) over dot(L) in otherwise resting humans. We speculate that any sympathetically mediated peripheral vasoconstriction was counteracted by transient mechanical effects of high intra-abdominal pressures during ERL.NEW & NOTEWORTHY Fatiguing expiratory muscle work in otherwise resting humans elicits an increase in sympathetic motor outflow; whether limb blood flow ((Q) over dot(L)) and leg vascular resistance (LVR) are affected remains unknown. We found that fatiguing expiratory resistive loaded breathing (ERL) did not affect group mean (Q) over dot(L) or LVR. However, within-breath oscillations in (Q) over dot(L) may reflect a sympathetically mediated vasoconstriction that was counteracted by transient increases in (Q) over dot(L) due to the mechanical effects of high intra-abdominal pressure during ERL.