An effect of isoproterenol on ventilation-perfusion in asthmatic versus normal subjects

Abstract

A fall in PaO2 was observed following the inhalation of isoproterenol aerosol in 10 symptomatic asthmatics. In 4 asthmatic and 2 normal subjects, measurements were made of VC and FEV1 %,RA, and FRC in the body plethysmograph, and resting steady-state PAO2, PaO2, (A-a)D, VD, DLCO and FCO. The studies were repeated after administration of isoproterenol aerosol. In the asthmatics there was improvement of the RA and FEV1 %, but an increase in the already large (A-a)D and a fall in the FCO and DLCO. These effects were not seen in the normal subjects. It is suggested that the administration of isoproterenol aerosol to asthmatics increases the ventilation of the already well-ventilated portions of lung to the detriment of the poorly ventilated portions, further increasing the unevenness of distribution VA/Q ratios throughout the lung.