A system was devised combining means of a) automatic sampling of end-tidal gas, b) rapid analysis of samples gas for Co2 concentration and c) manual or automatic modification of per cent Co2 in succeeding inspirations to permit maintenance of alveolar pCo2 at desired levels above the Co2 tension natural for a particular experimental situation. By imposing a fixed, elevated alveolar pCo2 upon a subject, effects of drugs or physiological stresses upon Co2-sensitive functions can be evaluated, unmasked by the compensatory alterations of alveolar and arterial pCo2 which normally result from changes in alveolar ventilation or metabolism. Validation of alveolar pCo2 control in 16 normal subjects, using arterial pCo2 as a reference standard, revealed no significant difference between the imposed end-tidal pCo2 and the pCo2 of arterial blood. Use of the pCo2 control system to evaluate the dynamics of meperidine effect on respiration in normal men indicated sufficient magnification of the effect of meperidine on respiratory minute volume to permit use of the method for comparative studies of rate of onset, time of peak effect and rate of disappearance of the action of meperidine on respiration.
Submitted on July 9, 1959
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