title: Density-dependent airflow and ventilatory control during exercise.
abstract: The influence of respired gas density on ventilatory control during cycle-ergometer exercise was investigated in six healthy subjects. They underwent constant-load exercise for 10 min both at 50% and 90% of the anaerobic threshold, inhaling air for the first 5 min followed abruptly by 80% helium-20% oxygen (He-O2) for the remaining 5 min (and vice versa). The He-O2 breathing elicited no discernible effect on ventilation (VI) or mean alveolar PCO2 (PACO2) at rest or at the lower work rate. However, at the higher work rate, He-O2 breathing resulted in a clear and sustained hyperventilation in all subjects. A compensatory response to the hypocapnia, consequent to the helium-induced hyperventilation, was not evident even though all subjects demonstrated a normal ventilatory responsiveness to inhaled CO2 while in this condition. These observations suggest that turbulent airflow normally imposes a constraint on the magnitude of the hyperpnea of high-intensity exercise.
mesh_terms: D002245:Carbon Dioxide / Q000494:pharmacology; D006371:Helium / Q000494:pharmacology; D006706:Homeostasis; D006801:Humans; D010100:Oxygen / Q000494:pharmacology; D005082:Physical Exertion; D012123:Pulmonary Ventilation; D012119:Respiration / Q000187:drug effects; D012143:Respiratory Physiological Phenomena; D012146:Rest
chemical_list: D002245:Carbon Dioxide; D006371:Helium; D010100:Oxygen