Nonhomogeneous alveolar pressure swings: effect of different respiratory muscles

We tested the hypothesis in dogs that during isovolumic inspiratory efforts the degree of nonhomogeneity of alveolar pressure changes is influenced by regional differences in respiratory muscle activity. Pressure distal to an occluded right lower lobe bronchus (PRLL) was compared with pressure in the occluded airway opening (PaO) during spontaneous inspiratory efforts (S), during right (RP), left (LP), and bilateral (BP) phrenic nerve stimulation, and during spontaneous inspiratory efforts after cutting both phrenic nerves (SCP), Upper and lower rib cage and abdominal dimensional changes were monitored by magnetometers. PRLL was greater than Pao during S and the difference was greater during BP and greater during RP, whereas with LP and SCP Pao exceeded PRLL. Compared with S, during RP, LP, and BP there was greater upper rib cage inward motion relative to abdominal outward motion. SCP resulted in opposite upper rib cage-abdomen relative motions. Thus activities of various muscle groups produced different regional pressures and deformations of rib cage and abdomen. These results may relate to potential errors in plethysmographic determination of thoracic gas volume in the presence of airway closure.