Effects of growth and breed on direct static measurements of chest wall compliance in cattle

Chest wall compliance (CW) was measured in 59 conscious standing calves, aged six to 162 days, which were breathing air spontaneously through 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 opening and oesophageal pressure (Pes). CW was measured directly from the inspired volume of the occluded breath and changes in Pes generated by the recoil of the relaxed chest wall. This airway-occlusion technique yielded reproducible CW values similar to those measured by classical invasive methods. The ratio of CW to bodyweight in the growing calves (sCW) ranged from 2.2 to 11.5 ml cmH2O-1 kg-1 and was correlated negatively with age: (log sCW = 0.91-0.003 x age, r = 0.68), the rate of decline corresponding well to the multispecies allometric growth relationship.