Effect of rib cage or abdomen compression at iso-lung volume on breathing pattern.

In anesthetized rabbits a small compression of the rib cage (RC) caused a marked increase of breathing frequency (f), a marked reduction of expiratory duration (Te), a reduction of inspiratory duration (Ti) and tidal volume (VT), while an equal decrease of lung volume produced by abdominal compression(AC) caused a smaller increase of f and no change of Ti, and a slight increase of VT. Similar results occurred when normal end-expiratory volume was maintained during compression. The phenomena disappeared after bilateral vagotomy, whereas persisted after cordotomy in T1. Similar results occurred in dogs (with the exception that VT decreased during AC), whereas in cats only RC increased f by shortening Te. RC caused a marked increase of discharge in 11 out of 19 irritant receptor fibers, whereas AC caused an increase only in 2. In most of the pulmonary stretch receptor fibers the change of activity produced by compression paralleled the lung volume change. The effects of vagal cooling on Ti, Te and the VT-Ti relationship with and without compression suggest irritant receptors as responsible for the different ventilatory pattern during RC and AC.