Abstract Background Maximal intensity exercise in equine athletes induces pulmonary capillary stress failure and exercise-induced pulmonary hemorrhage (EIPH) secondary to excessive transmural pressure (Ptm). Furosemide decreases EIPH severity and pulmonary arterial (PAP) and pulmonary wedge (PAW) pressures. Hypothesis/Objectives Assess the effects of furosemide on Ptm and EIPH during supramaximal exercise. Animals Six fit retired Thoroughbreds with consistent EIPH Grade ≥ 2. Methods Horses performed a controlled crossover design protocol, completing standardized treadmill tests (120%V̇O2max) before and 4 h after intravenous (IV) furosemide injection (0.5 mg/kg). Vascular catheters measured PAP and PAW. An esophageal catheter measured intrapleural pressure (Ppl). Pulmonary capillary pressure (Pcap) was estimated (Pcap = PAP + PAW/2) to calculate mean and peak Ptm (Ptm = Pcap-Ppl). The percentage of time that Ptm exceeded a stress failure threshold of 75 mm Hg was calculated. Blood and plasma volumes (BV, PV) were measured. Tracheoendoscopic EIPH score and the difference between pre- and post-exercise bronchoalveolar lavage red blood cell count (ΔBALRBC) were determined 1 h post-exercise. Treatment-related differences were compared using a paired t-test (P .05). Results Furosemide decreased mean PAP (P = .03), PAW (P = .04), and Pcap (P = .03), but did not affect Ppl. The outcome was decreased maximum (P .01) and minimum Ptm (P = .04). Transmural pressure exceeded 75 mm Hg for 57% ± 8% of the time in the control run and 31% ± 13% after furosemide, reflecting an approximately 45% decrease (P .01). Furosemide (4 h post-treatment) did not affect BV or PV, but significantly lowered EIPH score (P = .03) and ΔBALRBC (P = .03). Conclusions and clinical importance Furosemide decreased EIPH severity and Ptm. However, Ptm remained above the pulmonary capillary stress failure threshold, and some EIPH was observed.
Massie et al. (Thu,) studied this question.