Interaction between hypercapnic and hypoxic respiratory drive during muscular exertion

During the performance of graded muscular exertion against the background of controlled hypercapnia, hypoxia, hyperoxia, and their combinations, the dynamics of the pulmonary ventilation ( ) and the composition of the alveolar gas (p_a CO₂, p_a O₂) were investigated in 12 healthy men. The respiratory response was assessed from the absolute values of ventilation at a given value of p_a CO₂ and from its increase per mm Hg increase in p_a CO₂ ( ) at rest and on transition to and with establishment of stable conditions of exertion. The respiratory response at the beginning of exertion was accompanied by an upward shift and an increase in the slope of the line, independent of the magnitude of exertion. These changes point to multiplicative ineraction between neurogenic and hypercapnic stimuli with the commencement of exertion. In the steady state of exertion a significant role of the hypoxic stimulus was discovered: During hypoxemia the line was found to be appreciably shifted upward, especially during intensive exertion. This proves that positive interaction between hypercapnic and hypoxic stimuli is potentiated during exertion.Group for Physiology of Respiration, I. P. Pavlov Institute of Physiology, Academy of Medical Sciences of the USSR, Leningrad. (Presented by Academician of the Academy of Sciences of the USSR V. N. Chernigovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 87, No. 5, pp. 390–393, May, 1979.