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A B S T R A C r We investigated the effects of isoproterenol on the pulmonary mechanics of eight healthy male subjects. We measured the flow-volume, pressurevolume, resistance-volume, and pressure-flow relationships of the lungs of our subjects in addition to the forced expiratory volume (FEV1). The results of this study confirm earlier observations that isoproterenol produces a considerable decrease in airway resistance but only small changes in maximum expiratory flow. Measurements of static pressure-volume curves showed that isoproterenol caused a temporary decrease in the elastic recoil pressure of the lungs. In five men there were mean falls in recoil pressure of 4.1 cm H2O at 85% total lung capacity (TLC), 2.6 cm H2O at 75% TLC, and 1.5 cm HMO at 50% TLC. We postulate that the reason for the relatively small increments in maximum expiratory flow after isoproterenol is primarily that the effects of airway dilatation are in large part negated by the reduction in lung recoil pressure, which results in a fall in the maximum effective driving force for expiratory air flow, and secondly that there is an increase in the compliance of the flow-limiting airways. These studies emphasize that tests of maximum flow and of airway resistance should not be regarded as invariably interchangeable in the assessment of airway reactions or mild disease of the airways.

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Increasing doses of histamine, 0.00025-0.001 mg of the phosphate/kg body weight, were given intravenously to five normal subjects, seven asthmatics and five chronic bronchitics. Changes in specific airway conductance (SGaw) were measured with a body plethysmograph.In all groups there was significant depression of SGaw following injection of all three doses of histamine but no group was significantly different from another.It is concluded that bronchial reactivity to intravenous injection of histamine does not provide a diagnostic test for separating chronic bronchitis from asthmatics.