PULMONARY VASCULAR PRESSURES OF EXERCISING THOROUGHBRED HORSES WITH AND WITHOUT ENDOSCOPIC EVIDENCE OF EIPH

Exercise-induced pulmonary hemorrhage (EIPH) is a common occurrence in racehorses. The objective of this study was to compare pulmonary vasc ular pressures of healthy Thoroughbred horses with and without postexe rtion endoscopically detectable fresh blood in the trachea. The nasoph arynx, larynx, and trachea (down to the carina) of horses were examine d weekly with an endoscope 55-60 min postexertion, and the diagnosis o f EIPH was confirmed by the presence of fresh blood in the trachea. Me asurements of heart rate and right atrial, pulmonary arterial, and pul monary arterial wedge pressures were made during quiet rest and during treadmill exercise performed at 14.5 m/s on a 5% uphill grade. This w orkload elicited maximal heart rate of the horses. Mean pulmonary capi llary pressure was estimated to be halfway between the mean pulmonary arterial pressure and the mean pulmonary arterial wedge pressure. Thes e data from 7 healthy sound exercise-trained horses that were positive on 12 consecutive occasions (at 1-wk intervals) for the postexercise presence of fresh blood in the trachea were compared with those in 8 h ealthy horses that were consistently negative for the evidence of fres h blood in the trachea on postexercise endoscopic examination over 12- 16 wk. The heart rate and the right heart and/or pulmonary vascular pr essures in the two groups of horses were similar at rest. Exercise was attended by a large significant (P < 0.05) increase in these pressure s and heart rate in both groups. However, statistically significant di fferences between endoscopically EIPH-positive and endoscopically EIPH -negative horses for heart rate and right atrial and pulmonary vascula r pressures were not found during exercise. Thus these data revealed t hat the magnitude of exercise-induced right atrial as well as pulmonar y arterial, capillary, and venous hypertension in endoscopically EIPH- positive horses that are otherwise healthy is quite similar to that in endoscopically EIPH-negative horses during comparable exertion.