The effects of furosemide on pulmonary transmural pressure and exercise-induced pulmonary hemorrhage in supramaximally exercising thoroughbred racehorses.

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&#xa0;&#x2265;&#xa0;2. METHODS: Horses performed a controlled crossover design protocol, completing standardized treadmill tests (120%V&#x307;O2max) before and 4&#xa0;h after intravenous (IV) furosemide injection (0.5&#xa0;mg/kg). Vascular catheters measured PAP and PAW. An esophageal catheter measured intrapleural pressure (Ppl). Pulmonary capillary pressure (Pcap) was estimated (Pcap&#xa0;=&#xa0;[PAP&#xa0;+&#xa0;PAW]/2) to calculate mean and peak Ptm (Ptm&#xa0;=&#xa0;Pcap-Ppl). The percentage of time that Ptm exceeded a stress failure threshold of 75&#xa0;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 (&#x394;BALRBC) were determined 1&#xa0;h post-exercise. Treatment-related differences were compared using a paired t-test (P&#xa0;<&#xa0;.05). RESULTS: Furosemide decreased mean PAP (P&#xa0;=&#xa0;.03), PAW (P&#xa0;=&#xa0;.04), and Pcap (P&#xa0;=&#xa0;.03), but did not affect Ppl. The outcome was decreased maximum (P&#xa0;<&#xa0;.01) and minimum Ptm (P&#xa0;=&#xa0;.04). Transmural pressure exceeded 75&#xa0;mm Hg for 57%&#xa0;&#xb1;&#xa0;8% of the time in the control run and 31%&#xa0;&#xb1;&#xa0;13% after furosemide, reflecting an approximately 45% decrease (P&#xa0;<&#xa0;.01). Furosemide (4&#xa0;h post-treatment) did not affect BV or PV, but significantly lowered EIPH score (P&#xa0;=&#xa0;.03) and &#x394;BALRBC (P&#xa0;=&#xa0;.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.