Control of ventilation during exercise in man with special reference to the feature at the onset

Abstract

When exercise starts, various cardiorespiratory adjustments take place for accommodating the greatly increased metabolic requirements. A rapid response in ventilation (Phase I) may be at least useful for preventing oxygen deficiency and for increasing alveolar ventilation, oxygen tension, and oxygen uptake even if it is minimal. But why is the increasing tidal volume and respiratory frequency elicited so quickly just at the onset of exercise? Dose rapid ventilatory response play an important role as a trigger for surviving in exercising man? It has hitherto been reported that phase I response is observed during not only voluntary and passive movement, but also during electrically induced muscle contraction in man. In addition, it was observed that ventilation in phase I is not affected by hypoxia and is not causally linked to cardiac output. Although these mechanisms have extensively been explored by many investigators, they have still remained obscure until now. At present, the causal factors of phase I are classified as central (descending) and peripheral (ascending) neurogenic stimulus, or as both. In the awake condition, abrupt ventilatory increment immediately after voluntary and passive exercise in man could be attributed to the drives from the central command including cortical and hypothalamic activities as well as some peripheral afferent information mainly through group III and IV fibers. However, further investigations to clarify many unsolved problems should be advanced in future.