Constancy of functional residual capacity in the supine position during hypoxia and hyperoxic hypercapnia

Because of the mechanical interrelationship of the respiratory muscles, changes in lung volume may affect the values of mouth occlusion pressures (P(0.1)). Because we wanted to verify the value of P(0.1) in both research and clinical studies, we investigated the effect of hypoxia and hyperoxic hypercapnia of functional residual capacity (FRC) in 6 supine normal male subjects on five separate occasions. The P(0.1) and minute ventillation were highly correlated, and there were no significant changes in FRC at any time. We concluded that P(0.1) can be interpreted as a valid parameter of central respiratory drives in supine subjects during hypoxia and hyperoxic hypercapnia.