Pulmonary vascular pressures of strenuously exercising Thoroughbreds after administration of varying doses of frusemide.

This study investigated the impact of different doses of frusemide on exercise-induced pulmonary capillary hypertension in Thoroughbred horses. It concluded that a linear relationship does not exist between an increased dosage of frusemide and the attenuation of this type of hypertension in vigorously exercising horses.

Research Overview

The research was conducted on seven healthy Thoroughbred horses under vigorous exercise conditions. The scientists administered four different doses of frusemide to test its effect on exercise-induced pulmonary capillary hypertension, a disorder in which the pressure in the blood vessels that lead to or from the lungs becomes overly high.

Methodology

In this study:

• The researchers administered frusemide intravenously, four hours before exercise.
• Four different doses were tested: 250 mg regardless of body weight (equivalent to approximately 0.56 ± 0.03 mg/kg of body weight), 1.0 mg/kg, 1.5 mg/kg, and 2.0 mg/kg.
• The exercise protocol involved treadmill exercises carried out at 14.2 m/s on a 3.5% uphill grade to simulate strenuous exercise conditions.
• Airway endoscopy was performed post-exercise to detect exercise-induced pulmonary haemorrhage (EIPH).

Findings

The results from this research illustrated that the administration of frusemide resulted in:

• A significant decrease in mean pulmonary arterial, pulmonary capillary, and pulmonary artery wedge pressures in standing horses, irrespective of the frusemide dose.
• A significant reduction in the exercise-induced increase in right atrial and pulmonary vascular pressures. However, no notable differences were observed between the frusemide doses of 250 mg, 1.0 mg/kg, and 1.5 mg/kg.
• Although increasing the frusemide dose from 250 mg to 2.0 mg/kg showed a further significant reduction in exercise-induced pulmonary capillary blood pressure, all horses continued to experience EIPH.

Conclusion

Based on their findings, the researchers concluded that a linear response to increasing frusemide dosage for the attenuation of pulmonary capillary hypertension does not exist in Thoroughbred horses undergoing strenuous exercise. This suggests that while the medication can have some effect on decreasing hypertension, an increase in dosage does not necessarily lead to better results.