PULMONARY-LOCOMOTORY INTERACTIONS IN EXERCISING DOGS AND HORSES

In exercising quadrupeds, limb movement is often coupled with breathin g frequency. This finding has lead some investigators to conclude that locomotory forces, associated with foot plant, abdominal visceral dis placements or lumbo-sacral flexion, are the primary determinants of ai rflow generation. Analysis of respiratory muscle electrical activation (EMG) and contraction profiles in chronically instrumented dogs and h orses, along with measurements of esophageal pressure (P-es) changes a nd limb movements, provide evidence that each breath during the exerci se hyperpnea is determined by respiratory neuromuscular events. Specif ically: (1) Phasic diaphragmatic EMG and tidal shortening are always s ynchronous with decreases in P-es; (2) decrements in P-es are always a ssociated with inspiratory flow generation; and (3) strict phase coupl ing between breathing and stride frequency is not obligatory. Thus, al though locomotory-associated forces may minimally assist with flow gen eration, they are not the primary determinants of breathing during exe rcise. (C) 1997 Elsevier Science B.V.