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Evidence for an intramuscular ventilatory stimulus during dynamic exercise in man
J W Williamson1, P B Raven, B H Foresman
1Department of Physiology, Texas College of Osteopathic Medicine, Fort Worth 76107.
Respiration Physiology
|November 1, 1993
Summary
Lower body positive pressure (LBPP) reduces the ventilatory threshold during exercise. This suggests LBPP may alter exercise-induced hyperpnea by affecting muscle perfusion and metabolite accumulation.
Area of Science:
- Exercise Physiology
- Cardiopulmonary Function
- Respiratory Control
Background:
- Ventilation (VE) typically increases with metabolic rate during exercise.
- Metabolic acidemia triggers compensatory hyperpnea, raising the ventilatory threshold.
- The control mechanisms of this compensatory response require further investigation.
Purpose of the Study:
- To investigate the effect of lower body positive pressure (LBPP) on the ventilatory threshold during incremental exercise.
- To determine if LBPP alters the occurrence and characteristics of the ventilatory threshold.
Main Methods:
- Seven healthy subjects performed incremental cycle ergometry with varying levels of LBPP (0-45 Torr).
- Ventilatory responses and pulmonary gas exchange were measured breath-by-breath.
- Arterialized-venous blood was sampled for lactate, pH, and potassium ([K+]) analysis.
Main Results:
- The ventilatory threshold was progressively reduced with increasing LBPP (Ventilatory threshold = 2.33 - 0.0173*LBPP).
- Ventilatory equivalents for oxygen (VE/VO2) and carbon dioxide (VE/VCO2) increased at higher work rates.
- Lactate and pH levels remained largely unchanged, suggesting chemoreceptors were not the primary drivers of the LBPP-induced hyperpnea.
Conclusions:
- LBPP reduces the ventilatory threshold during incremental exercise.
- The observed hyperpnea is unlikely due to peripheral or central chemoreceptor activation.
- Potential mechanisms include LBPP-induced reduction in muscle perfusion and/or increased intramuscular tissue pressure.