M. Manohar, PULMONARY VASCULAR PRESSURES OF THOROUGHBREDS INCREASE RAPIDLY AND TOA HIGHER-LEVEL WITH RAPID ONSET OF HIGH-INTENSITY EXERCISE THAN SLOW ONSET, Equine veterinary journal, 26(6), 1994, pp. 496-499
Previous studies of pulmonary vascular pressures have utilised gradual
incremental step exercise protocols, but in competitive racing at the
track, horses perform rapid acceleration high-intensity exercise. The
rate of rise in pulmonary vascular pressures under conditions of quic
k onset high-intensity exercise is unknown. Catheter mounted manometer
s, whose in vivo signals were matched with pressure signals obtained v
ia transducers connected to fluid-filled lumens from same cardiovascul
ar sites, were used to compare right heart and pulmonary vascular pres
sures in 8 healthy Thoroughbreds performing 2 separate exercise protoc
ols on a high speed treadmill (gradually incremental vs. rapid acceler
ation exercise protocol where the belt speed was raised from 8 m/s to
15 m/s in 8 s). Heart rate, right atrial and pulmonary vascular pressu
res at rest were similar for the 2 protocols. Rapid acceleration of ho
rses from 8 to 15 m/s was attended by an equally rapid escalation in t
he right heart and pulmonary vascular pressures such that these pressu
res reached their zenith as belt speed approached 15 m/s. Although exe
rcise at 15 m/s resulted in similar heart rate in the 2 protocols, the
mean +/- s.e. values of mean right atrial pressure, mean pulmonary ar
tery pressure, mean pulmonary artery wedge pressure and mean pulmonary
capillary pressure (91.5 +/- 3.9 mmHg) in the rapid acceleration exer
cise were significantly (P<0.05) higher than respective values at 15 m
/s in the gradual incremental step exercise protocol. It is concluded
that pulmonary capillary blood pressure of Thoroughbreds rapidly accel
erating to high-intensity exercise increases just as rapidly as their
speed and that the values achieved are higher than in incremental step
exercise protocol; thereby playing a potential role in initiating str
ess failure of pulmonary capillaries and exercise-induced pulmonary ha
emorrhage very early in a race.