Density-dependent airflow and ventilatory control during exercise

Respir Physiol. 1982 Sep;49(3):267-77. doi: 10.1016/0034-5687(82)90116-5.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbon Dioxide / pharmacology
  • Helium / pharmacology
  • Homeostasis
  • Humans
  • Oxygen / pharmacology
  • Physical Exertion*
  • Pulmonary Ventilation*
  • Respiration / drug effects
  • Respiratory Physiological Phenomena*
  • Rest


  • Carbon Dioxide
  • Helium
  • Oxygen