EFFECTS OF GROWTH AND BREED ON DIRECT STATIC MEASUREMENTS OF CHEST-WALL COMPLIANCE IN CATTLE

Chest wall compliance (C-W) was measured in 59 conscious standing calv es, aged six to 162 days, which were breathing air spontaneously throu gh a face mask. The airways were occluded at the end of inspiration in order to elicit the Hering-Breuer reflex, the effectiveness of which was ensured by the presence of a plateau on the tracings of airway ope ning and oesophageal pressure (Pes). C-W was measured directly from th e inspired volume of the occluded breath and changes in Pes generated by the recoil of the relaxed chest wall. This airway-occlusion techniq ue yielded reproducible C-W values similar to those measured by classi cal invasive methods. The ratio of C-W to bodyweight in the growing ca lves (sC(W)) ranged from 2.2 to 11.5 ml cmH(2)O(-1) kg(-1) and was cor related negatively with age: (log sC(W) = 0.91-0.003 x age, r = 0.68), the rate of decline corresponding well to the multispecies allometric growth relationship.