Pressures in the right side of the heart and esophagus (pleura) in ponies during exercise before and after furosemide administration.

Pressures in the right side of the heart and esophagus (pleural) have not been determined in the exercising equine subjects. In the present study, 8 healthy ponies were examined to determine the changes in these variables caused by 2 degrees of exercise done on a treadmill (heart rate:183 +/- 5 beats/min [trot] and 220 +/- 6 beats/min [canter]). Measurements were also made during both degrees of exertion 10 minutes and 120 minutes after furosemide (1.0 mg/kg) administration. It was observed that both gaits resulted in significant increases in pulmonary artery, right ventricular, and right atrial pressures. The pulmonary artery systolic, mean, and diastolic pressures during strenuous exertion were 306%, 252%, and 242% of the respective resting values. At canter, when respiratory frequency (138 +/- 4 breaths/min) is synchronized with stride frequency, the delta esophageal pressure approached 30.4 +/- 2.86 cm of water. During exercise 10 minutes after furosemide administration, the increment in right atrial pressure was markedly attenuated. During strenuous exertion 120 minutes after furosemide administration, the right atrial and pulmonary arterial pressures increased, but to a significantly lower level than did the prefurosemide values. However, the mean pulmonary artery pressure was still 240% of the resting value. It is concluded that marked pulmonary hypertension is a consistent feature of moderate, as well as strenuous, exertion in the pony. Although furosemide administration attenuated the pulmonary hypertension somewhat, the significance remains unclear.