Airway occlusion pressure and respiratory nerve and muscle activity in studies of respiratory control.

M.D.; Gabriel Zubillaga, M.D.; and Ruy V. Louren#{231}o, M.D. W e have evaluated the relationship between respiratory nerve and muscle electrical activity and airway occlusion pressure in both anesthetized animals and conscious humans. This relationship which reflects the coupling of the neuromuscular components of the respiratory control system was studied under conditions of unloaded and loaded breathing. In anesthetized cats, changes in phrenic nerve activity, quantified as a moving time average ( N 1 were compared to changes in intratracheal pressure (PiT) obtained during complete airway occlusion at functional residual capacity (FRC) . PiT plotted against PNG(t) during the course of an inspiratory effort while breathing room air, and at different levels of PACO2 during CO2 rebreathing showed an approximately linear relationship. During the course of CO2 rebreathing, increases in PIT and N (t) , both obtained 150 msec after the onset of the occluded breath, were linearly related with high correlation coefficients. Therefore, both during single breaths at different levels of PACO2, and during the course of CO2 rebreathing, inspiratory muscle pressure appears to be linearly related to phrenic nerve activity. During room air breathing in the intact cat, the relationship between PIT and PNG(t) usually became somewhat alinear with positive pressure breathing (PPB), but the overall slope, though slightly diminished, was similar to that at FRC (Fig 1) . At low lung volumes induced by negative pressure breathing (NPB), PIT/