DIAPHRAGM AND LUNG AFFERENTS CONTRIBUTE TO INSPIRATORY LOAD COMPENSATION IN AWAKE PONIES

We determined the effect of pulmonary vagal (hilar nerve) denervation (HND) and diaphragm deafferentation (DD) on inspiratory load compensat ion. We studied awake intact (I; n = 10), DD (n = 5), HND (n = 4), and DD + HND (n = 7) ponies at rest and during mild (1.8 mph, 5% grade) a nd moderate (1.8 mph, 15% grade) treadmill exercise before, during, an d after resistance of the inspiratory circuit was increased from simil ar to 1.5 to similar to 20 cmH(2)O.l(-1).s. During the first loaded br eath in I ponies at rest, inspiratory time (TI) increased, expiratory time decreased, and inspiratory drive increased. There were minimal ch anges after the first breath, and inspiratory minute ventilation (VI) and arterial Pco(2) did not change (P > 0.10) from control values. On the first loaded breath during exercise, TI increased but inspiratory drive either did not change or decreased from control values. TI and d rive increased after the first breath, but the increases were insuffic ient to maintain VI and arterial Pco(2) at control levels. First-breat h load compensation remained after DD, HND, and DD + HND, but after DD + HND tidal volume and VI were compensated 5-10% less (P < 0.05) than in I ponies. In all groups inspiratory drive, tidal volume, and VI we re markedly augmented on the first breath after loading was terminated with a gradual return toward control. We conclude that diaphragm and pulmonary afferents contribute to but are not essential for inspirator y load compensation in awake ponies.