INTERACTION BETWEEN THE DIAPHRAGM, INTERCOSTAL-ACCESSORY MUSCLES OF INSPIRATION AND THE RIB CAGE

During Mueller maneuvers (MM), the volume change of rib cage, ΔVrc, and abdomen, ΔVab, are equal and opposite. Thus ΔVrc = ΔVab. Substituting ΔPrc · Crc for ΔVrc and ΔPab · Cab for ΔVab yields: ΔPrc = -ΔPab · Cab/Crc, where ΔPrc, ΔPab, Crc and Cab are applied pressures and compliances of rib cage and abdomen respectively. MM performed solely with the diaphragm permits calculatins of Prc in terms of observed changes in Pab and pleural pressure, Ppl. Three trained subjects performed MM with no evidence of inspiratory intercostal or abdominal muscle contraction. During the diaphragmatic MM ΔPab was positive and ΔPrc negative. The magnitude of ΔPrc/ΔPab was 2-6 times greater than that of ΔPpl/ΔPab. We conclude that neither Pab nor Ppl by themselves displace the relaxed rib cage during Mueller maneuvers. A model in which the diaphragm acts both in parallel and in series with the rib cage, and in which Prc is the sum of Pab and a pressure lying between Pab and Ppl explains these results as well as the hypothesis that Pab displaces the relaxed rib cage during quiet breathing. © 1979.