[Control of pulmonary ventilation during muscular exercise (author's transl)]

The ventilatory changes as function of time or power depend on the type of exercise. However, in any case, two kinds of factors are involved in these changes : fast, neurogenic, factors and other factors, slower, which are thought to be humoral. Neurogenic stimuli arise from the periphery and from the central nervous system. Peripheral stimuli are induced by the repetitive changes of muscle length and by the motion of articulations. Ventilatory output is also increased by stimuli coming from motor centers. These two kinds of factors induce a ventilatory increase at the start of exercise ("accrochage ventilatoire"). Both chemical and physical stimuli act as humoral factors. The arterial PO2 is scarcely reduced even during maximal exercise, but the increased blood level of norepinephrine may account for the enhanced sensitivity of the centers to the oxygen drive. The sensitivity of the respiratory centers to PaCO2 is not increased. The pH is lowered and can reach 7.15 during very intense exercise. tthis acidity may account for the increased ventillatoy output under these circumstances. The increased body temperature may partly explain the progressive increase of ventilatory output during long lasting exercise, but it does not change the alveolar ventilation. It thus appears that the exercise ventilatory behaviour meets the metabolic, acid-base balance and thermolytic requirements.