EFFECT OF INTRAVENOUS AMINOPHYLLINE ON DISTRIBUTION OF PULMONARY BLOOD FLOW IN OBSTRUCTIVE LUNG DISEASE

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Abstract
The effect on arterial O2 tension of 250 mg aminophylline injected intravenously over 3 min. was studied in 58 patients with obstructive lung disease. Arterial O2 tension was measured at 30-sec. intervals for 3 min. and less frequently thereafter for up to 17 min. Ventilation was monitored continuously. The results in 32 patients (defined by their ventilatory response and the technical adequacy of the experiments) were analyzed. Twenty patients showed a fall of arterial O2 tension of 4 mm Hg or more, or of O2 saturation of 2% or more, after administration of aminophylline. The falls of O2 tension or saturation resulted from a worsening of ventilation-perfusion ratio distribution in the lungs. The direction of the change was such that it reflected increased blood flow through poorly ventilated alveolar populations. Because aminophylline is a pulmonary vasodilator, this was thought due to reversal of pre-existing regional pulmonary vaso-contriction, present in some patients (responders) but not in others (nonresponders). Initial arterial O2 saturation and physiologic dead space/tidal volume ratio among responders were less abnormal for a given value of FEV1 [forced expiratory volume] and VE [minute volume of expired gas] than among nonresponders. This confirms the "compensatory" nature of the regional pulmonary vasoconstriction. The presence or absence of this local vasoconstriction in different patients may be related to similar reproducible differences in pulmonary vascular response to hypoxia among normal subjects.