Frusemide attenuates the exercise-induced rise in pulmonary capillary blood pressure in horses

Catheter mounted micro-tip-manometers (the signals from which were matched with fluid-filled pressure signals from same cardiovascular sites and zeroed at the point of the shoulder), were used to study pulmonary haemodynamics in 8 healthy sound horses at rest and during exercise performed at 8, 10, 12 and 14 m/s on a treadmill. Measurements were made without frusemide (control) and 4 h after iv administration of 250 mg frusemide. Post-frusemide data were also obtained on a separate day, and these observations were not significantly different from those made on the same day as controls. Pre-frusemide values of heart rate, mean right atrial pressure, mean pulmonary artery pressure, mean pulmonary artery wedge pressure and mean pulmonary capillary pressure at 14 m/s were 214 +/- 5 beats/min, 54 +/- 4, 92 +/- 4, 65 +/- 6 and 79 +/- 5 mmHg, respectively. Exercise at 14 m/s after frusemide resulted in a similar heart rate (216 +/- 4 beats/min), but the mean right atrial, pulmonary arterial, pulmonary artery wedge and pulmonary capillary pressures were all significantly lower, i.e. 34 +/- 5, 79 +/- 4, 45 +/- 4, and 62 +/- 3 mmHg, respectively. Attenuation, by frusemide, of the exercise-induced rise in pulmonary capillary pressure would lower the magnitude of the transmural force exerted on the pulmonary capillaries. If, therefore, exercise-induced pulmonary haemorrhage (EIPH) is caused by stress failure of pulmonary capillaries, frusemide pretreatment has the potential for reducing/limiting the extent of EIPH.