Exercise tolerance in dogs with pulmonary hypertension treated with sildenafil

This study aims to establish the effect of sildenafil on the distance covered during the six-minute-walk-test (6MWT) in dogs with pulmonary hypertension (PH) and in healthy ones on heart rate (HR) and respiratory rate (RR) in a high altitude geographic zone (2650 m above sea level). A group of nine dogs diagnosed with PH and other of 10 healthy dogs walked in a flat track of 30 meters without control of temperature and humidity. After the test, dogs received 1 mg/kg of oral sildenafil. One hour later the test was repeated. HR and RR were measured before and after each test by auscultation. Dogs with PH walked 470 ± 122.6 and 407.8 ± 137.4 m before and after sildenafil respectively (p=0.027) and the RR was higher after the walk than before the test (p\u3c0.05). The group of healthy dogs walked 560 ± 55 and 613 ± 36 3 m before and after sildenafil respectively (p=0.03) and reduced the RR before and after the second test where received sildenafil. The dogs with PH drastically reduced the tolerance to exercise and showed increased RR, while the healthy dogs increased the walked distance possibly due to a reduction in oxygen requirements. These results challenge the usefulness of sildenafil in the reduction of clinical signs in dogs with PH living in high altitude areas and suggest its use to improve tolerance to acute exercise in healthy dogs