Experimental Pulmonary Arterial Hypertension in the Newborn Calf

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Abstract
1. The left pulmonary artery was ligated in day-old calves. All animals developed pulmonary arterial hypertension with resting mean pressures as high as 114 mm Hg. This was associated with a reduction in the pulmonary arterial vascular bed of the right lung and right ventricular hypertrophy. The longest survival has been five months; death being associated with congestive heart failure. 2. Pulmonary hypertension developed without concomitant rise of pulmonary arterial wedge pressure. 3. Inhalation of 13% O2 caused an average rise of 45 mm Hg in mean pulmonary arterial pressure, as compared with 21 mm Hg in normal calves and nine in yearling steers. 4. Inhalation of 41% or 100% O2 caused an average decrease of 29 mm Hg in pulmonary arterial pressure, as compared with 14 mm Hg in normal calves. 5. Acetylcholine reduced the elevated pulmonary arterial pressure suggesting that vaso-constriction played an important role in the development of the pulmonary hypertension. Tolazoline was ineffective. 6. The spectrum of reactivity of the pulmonary vascular bed among species as well as within a given species is illustrated.