Pulmonary vascular pressures of strenuously exercising Thoroughbreds during intravenous infusion of nitroglycerin.

This research article investigates whether intravenous nitroglycerin could affect pulmonary arterial, capillary, or venous hypertension in strenuously working Thoroughbred horses. The conclusion was that nitroglycerin administration did not change exercise-induced hypertension and is unlikely to impact the degree or frequency of exercise-induced pulmonary hemorrhage in these horses.

Methods

• Five healthy Thoroughbred horses were analyzed in this study. The sequence of treatments was randomized for each horse and they were administered a week apart.
• Both resting and exercising state of the horses were examined. Exercise included running on a treadmill, with galloping at a speed of 14.2 m/s on a 5% uphill grade, which could not be sustained for more than 90 seconds.
• The vital observations included measuring right atrial, right ventricular, and pulmonary vascular pressures in each horse. These parameters were recorded during a control treatment (where the horses were not medicated) and a nitroglycerin infused state.
• The dosage of nitroglycerin was carefully chosen. Maximal pulmonary and systemic hemodynamic effects of intravenous nitroglycerin were seen at 5 microg/kg/min, so a quadruple dose (20 microg/kg/min) was used, as it did not cause any adverse effects.

Results

• During the control treatment, exercise that pushed the horses’ heart rates to maximum led to a significant increase in right atrial and pulmonary arterial, capillary, and wedge pressures.
• Infusion of nitroglycerin in a standing horse significantly reduced right atrial and pulmonary vascular pressures. However, an increase in heart rate was observed.
• For the horses that were administered nitroglycerin and made to exercise, similar increases in right atrial and pulmonary arterial, capillary, and wedge pressures were observed. These parameter values were not significantly different from the control treatment data.
• In both the treatments, all horses showed signs of exercise-induced pulmonary hemorrhage.

Conclusions

• The findings conclude that intravenously administered nitroglycerin does not affect exercise-induced pulmonary hypertension.
• Furthermore, it is unlikely to have any impact on the incidence or severity of exercise-induced pulmonary hemorrhage in Thoroughbreds.