Interaction between left and right intercostal muscles in airway pressure generation

The interactions between the different rib cage inspiratory muscles in the generation of pleural pressure remain largely unknown. In the present study, we have assessed in dogs the interactions between the parasternal intercostals and the interosseous intercostals situated on the right and left sides of the sternum. For each set of muscles, the changes in airway opening pressure (Delta Pao) obtained during separate right and left activation were added, and the calculated values (predicted Delta Pao) were then compared with the Delta Pao values obtained during symmetric, bilateral activation (measured Delta Pao). When the parasternal intercostals in one or two interspaces were activated, the measured Delta Pao was commonly greater than the predicted value. The difference, however, was only 10%. When the interosseous intercostals were activated, the measured Delta Pao was nearly equal to the predicted value. These observations strengthen our previous conclusion that the pressure changes produced by the rib cage inspiratory muscles are essentially additive. As a corollary, the rib cage can be considered as a linear elastic structure over a wide range of distortion.