Ventilatory responses to dynamic exercise elicited by intramuscular sensors

• Published in: Medicine and science in sports and exercise 1999-02, Vol.31 (2), p.277-286
• Main Authors: Smith, S. A., Gallagher, K. M., Norton, K. H., Querry, R. G., Welch-O'Connor, R. M., Raven, P. B.
• Format: Article
• Language: English
• Subjects: Adult; Analysis of Variance; Biological and medical sciences; Cardiac Output - physiology; Cardiorespiratory control. Arterial mecano- and chemoreceptor; Exercise - physiology; Exercise Test; Female; Fundamental and applied biological sciences. Psychology; Heart Rate - physiology; Humans; Least-Squares Analysis; Life Sciences (General); Male; Mechanoreceptors - physiology; Muscle, Skeletal - physiology; Oxygen Consumption - physiology; Pressure; Pulmonary Gas Exchange; Respiration; Space life sciences; Vertebrates: respiratory system
• ISSN: 0195-9131; 1530-0315
• DOI: 10.1097/00005768-199902000-00012

PURPOSE: Eight subjects, aged 27.0+/-1.6 yr, performed incremental workload cycling to investigate the contribution of skeletal muscle mechano- and metaboreceptors to ventilatory control during dynamic exercise. METHODS: Each subject performed four bouts of exercise: exercise with no intervention (CON); exercise with bilateral thigh cuffs inflated to 90 mm Hg (CUFF); exercise with application of lower-body positive pressure (LBPP) to 45 torr (PP); and exercise with 90 mm Hg thigh cuff inflation and 45 torr LBPP (CUFF+PP). Ventilatory responses and pulmonary gas exchange variables were collected breath-by-breath with concomitant measurement of leg intramuscular pressure. RESULTS: Ventilation (VE) was significantly elevated from CON during PP and CUFF+PP at workloads corresponding to > or = 60% CON peak oxygen uptake (VO2peak) and during CUFF at workloads > or = 80% CON VO2peak, P < 0.05. The VO2 at which ventilatory threshold occurred was significantly reduced from CON (2.17+/-0.28 L x min(-1)) to 1.60+/-0.19 L x min(-1), 1.45+/-0.15 L x min(-1), and 1.15+/-0.11 L x min(-1) during CUFF, PP, and CUFF+PP, respectively. The slope of the linear regression describing the VE/CO2 output relationship was increased from CON by approximately 22% during CUFF, 40% during PP, and 41% during CUFF+PP. CONCLUSIONS: As intramuscular pressure was significantly elevated immediately upon application of LBPP during PP and CUFF+PP without a concomitant increase in VE, it seems unlikely that LBPP-induced increases in VE can be attributed to activation of the mechanoreflex. These findings suggest that LBPP-induced reductions in perfusion pressure and decreases in venous outflow resulting from inflation of bilateral thigh cuffs may generate a metabolite sensitive intramuscular ventilatory stimulus.