![]() ![]() Transmural pressure (intravascular minus alveolar pressure) across pulmonary capillaries may be even higher because of the large negative pleural pressure swings in galloping horses. Pulmonary arterial hypertension is a more specific diagnostic term that requires a pulmonary capillary wedge pressure of 15 mm Hg or less with a pulmonary vascular resistance of greater than 3 Wood units (mm Hg/liters/minute) in the setting of an elevated mean pulmonary artery pressure (McLaughlin et al., 2009). Assuming mean intravascular pulmonary capillary pressure to be halfway between the mean pulmonary arterial and venous pressures, its value during exercise at 13 m/s may have approached 72.5 mm of Hg. ![]() During exercise at belt speed of 13 m/s, heart rate, mean right atrial pressure, mean pulmonary artery pressure, pulmonary artery pulse pressure, and mean pulmonary artery wedge pressure were 213 (+/- 5) beats/min, 44 (+/- 4) mm of Hg, 89 (+/- 5) mm of Hg, 69 (+/- 4) mm of Hg, and 56 (+/- 4) mm of Hg, respectively. Pulmonary artery diastolic pressure was, however, not different among the 3 work intensities. All these variables registered further significant (P < 0.05) increments as work intensity increased to 10 m/s, and then to 13 m/s. Exercise at treadmill belt speed of 8 m/s resulted in significant (P < 0.05) increments in heart rate, right atrial pressure, pulmonary artery systolic, mean, diastolic and pulse pressures, and pulmonary artery wedge pressure. At rest, mean (+/- SEM) heart rate, mean right atrial pressure, mean pulmonary artery pressure, and mean pulmonary artery wedge pressure were 37 (+/- 2) beats/min, 8 (+/- 2) mm of Hg, 31 (+/- 2) mm of Hg, and 18 (+/- 2) mm of Hg, respectively. Using catheter mounted microtip manometers, right atrial, pulmonary artery, and pulmonary artery wedge pressures were studied in 8 horses while they were standing quietly (rest), and during galloping at treadmill speeds of 8, 10, and 13 m/s. ![]()
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