Afferent Feedback Stimulation Via Venous Distention Contributes To Increased Ventilation During Exercise In Healthy Adults

Abstract

Limb congestion may alter ventilation via stimulating afferent feedback from the skeletal muscles during physical activity. Venous distention via sub-systolic occlusion of the lower limbs may simulate limb congestion and has been proposed to stimulate group III/IV afferent neurons. PURPOSE: The purpose of this study was to examine the ventilatory response to graded lower extremity venous occlusion during exercise in healthy adults. METHODS: Nineteen healthy adults (9 men, 25±5 yr) completed two sessions. Session 1 included a maximal cycle ergometry exercise test. Session 2 included constant-load cycling at 30% peak workload for 3 min (baseline) followed by randomized inflation of bilateral thigh pressure tourniquets to 20, 40, 60, 80, 100 mmHg for 2 min with 2 min of deflation between occlusions. Ventilation (VE), gas exchange and dyspnea were measure during each session. RESULTS: VE increased significantly from baseline (exercise only) to each occlusion pressure (base to100 mmHg: 31.5±6.6 to 40.1±10.7 L/min, p<0.05, all pressures). Respiratory rate (RR) increased as well (base to 100 mmHg: 24.8±6.0 to 30.9±11.5 breaths/min, p<0.05, condition effect) with no change in tidal volume (p>0.05). Tidal volume to inspiratory time (VT/TI) increased significantly from baseline to each occlusion pressure (base to 100 mmHg: 1.5±0.3 to 1.8±0.4 L/min, p<0.05, all pressures). Partial pressure of end-tidal carbon dioxide (PETCO2) decreased only with 100 mmHg cuff pressure (base: 24.8±6.0 and 100 mmHg: 36.8±3.9 mmHg, p<0.05 at 100 mmHg). Dyspnea increased from base to 100 mmHg (1.0±1.2 to 2.6±2.0, p<0.05, all pressures). CONCLUSIONS: Graded venous occlusion of the lower extremity muscles increased VE by increasing RR in young healthy adults. Importantly, vascular occlusion of the lower extremity during exercise contributed to increased sensations of breathing during exercise. Stimulation of afferent feedback via limb congestion contributes to ventilatory control and increased dyspnea in healthy humans. Results from this study may be important to clinical populations with exaggerated limb congestion, such as heart failure, who experience increased ventilation and dyspnea during exercise. This work was funded by American Heart Association (AHA) grant 12GRNT1160027 (TPO) and MLKR is supported by a NIH/NIAMS T32 AR056950