Effects of glyceryl trinitrate (nitroglycerin) on pulmonary vascular pressures in standing thoroughbred horses.

This research evaluates the impact of nitroglycerin as a potential remedy for exercise-induced lung bleeding in Thoroughbred horses. The experiments showed that nitroglycerin infusion led to an increase in heart rate but a decrease in various pulmonary and arterial pressures, suggesting it may help prevent lung problems in strenuously exercising horses.

Study Overview

• This research investigates the problems faced by Thoroughbreds when identically exercising, one of which is a severe increase in pulmonary capillary blood pressure. This increase, in turn, leads to a condition known as exercise-induced pulmonary hemorrhage (EIPH).
• To find a solution to EIPH, researchers have turned their focus towards lowering the pulmonary capillary blood pressure of exercising horses. Some studies suggest that nitric oxide plays a key role in maintaining a low vascular resistance in the pulmonary system.
• However, the effects of nitrovasodilators, which function the same as nitric oxide, on the equine pulmonary system were not explored. This research, therefore, aims to examine the impact of nitroglycerin, a nitrovasodilator, on the right atrial and pulmonary vascular pressures in Thoroughbred horses.

Methodology

• The study included seven healthy Thoroughbred horses. On these horses, a freshly mixed nitroglycerin solution was infused for 240 seconds directly into the right atrium.
• The dose rates of nitroglycerin varied and were administered in a random manner. The range was 350, 700, 1400, and 2100 µg/min. Each dosage was given in duplicate to the horses while they were standing quietly.
• Different parameters like heart rate, right atrial pressure, pulmonary artery pressure, pulmonary capillary pressure, and pulmonary artery wedge pressures were measured before, during, and after the nitroglycerin infusions. These measurements were done using catheter-mounted manometers.

Results

• The data showed that the nitroglycerin infusions caused an increase in heart rate in a dose-related manner. However, a decrease in mean right atrial pressure, pulmonary artery pressure, pulmonary artery wedge pressure, and pulmonary capillary pressure was observed.
• Further, a reduction in the pulmonary artery wedge pressure due to nitroglycerin was significantly greater than that in the pulmonary artery pressure at the highest dose rate (2100 µg/min).

In conclusion, this research shines a light on the potential of nitroglycerin as a remedy for EIPH in Thoroughbreds, thanks to its apparent effect in reducing pulmonary and arterial pressures while the heart rate increases. Further research could validate these outcomes and assess any practical or long-term side effects.