Effect of thoracoabdominal configuration on the diaphragmatic contribution to rib cage motion

Owing to the diaphragm-rib cage interaction the diaphragm can reduce the load on the intercostal muscles. The extent of this load reduction was evaluated by analyzing the EMG activity of intercostal muscles as an index of the pressure generated by the intercostal muscles. Three trained subjects shifted their breathing configuration while the rib cage volume and flow were kept constant. Analysis of data thus obtained indicated that the diaphragmatic contribution to the rib cage motion improved with a thoracic shift of breathing. The significance of this effect was further evaluated by performing respiratory maneuvers at constant tidal volume and flow at normal and elevated functional residual capacity. At both lung volumes, a substantial saving of diaphragmatic activity attained by the thoracic shift of breathing was associated with a moderate increase or even a decrease in the intercostal EMG activity, suggesting an overall mechanical advantage of inspiratory muscles during thoracic breathing. Support by National Institute of Health Grant HL 25230 Preliminary results have been reported at the 66th annual FASEB meeting in New Orleans, 1982