Closing volume (single breath nitrogen test), regional ventilation and perfusion (using intravenous xenon-133), and total lung function (TLC, VC, and FEV) were measured before and after intramuscular administration of 250 mug 15-methyl prostaglandin F2alpha (15-me PGF2alpha) in 10 healthy women. The cardiac output was measured with the Minnesota impedance cardiograph model 304A and the transthoracic impedance was used as an expression of the thoracic fluid volume. The slope of the alveolar plateau on the closing volume tracing showed a 271% increase 20 minutes after the prostaglandin administration, at which time the closing volume per cent (CV%) had decreased (P less than 0-01) and the closing capacity (CC%) had increased (P less than 0-05). Vital capacity (VC) decreased (P less than 0-01), residual volume (RV) increased (P less than 0-01), and the total lung capacity (TLC) remained unchanged. The maximal decrease (9%) in FEV1 was seen after 20 minutes. All these measurements except the slope of the alveolar plateau returned to control levels after 60 minutes. The redistribution of regional ventilation was more pronounced than that of the regional pulmonary blood flow. No change was observed in cardiac output and transthoracic impedance. None of the patients experienced any dyspnoea. Our results are consistent with a more pronounced effect of prostaglandin F2alpha on the small airways (the alveolar plateau) than on the larger airways (FEV1). In cases where an increase in the slope of the alveolar plateau is observed, the closing volume per cent should not be used as a measurement of the lung disease. It is concluded that the single breath nitrogen test (N2 closing volume) is more sensitive than the conventional tests.
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