Postnatal development of pulmonary and bronchial arterial circulations in the calf and the effects of chronic hypoxia

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Abstract
Seven calves were placed in an altitude chamber on the day of birth and were maintained at the simulated high altitude of 11,000 feet for 2 to 5 months. Circulatory measurements during life and structural changes in the lungs after death were compared with findings in 20 normal calves. The normal calves showed a surprising growth of lung parenchyma and pulmonary and bronchial arterial circulations during the first seven days of life. Such a rapid postnatal lung growth has not previously been reported and may account for much of the normal decrease in pulmonary arterial pressure seen during this period of life. By contrast calves maintained from birth at simulated high altitude rapidly increased their pulmonary arterial pressures during the first two weeks of life. The pulmonary arterial circulation remained constricted and at autopsy presented an exaggerated radiographic and histologic pattern seen in normal calves less than 24 hours old. The bronchial arterial circulation in the calves at high altitude became greatly increased. Chronic hypoxia in these calves probably sustained increased tone in the pulmonary, but not systemic arterioles, with the result that the normal growth pattern of the lung vessels was altered. This study emphasizes the different regulation of the two arterial supplies to the same organ, namely, the lung.