Effects of Typical Broncho-Dilating Drugs on Intrapleural Pressure. ∗

Abstract

By means of suitable trochars and rubber tubing, one may observe intrapleural pressures from both sides of the chest of normal unanesthetized dogs. The tubing may be branched so that both manometric and kymographic records may be obtained for intrapleural pressure changes from each side of the chest. With such an arrangement we have noted the effects on intrapleural pressure of the administration of (1) epinephrin, a typical stimulant of the thoraco-lumbar autonomics and (2) atropine, a drug acting by peripheral paralysis of the cranio-sacral autonomics. Both drugs cause bronchodilatation.

Examples of approximate intrapleural pressure changes in dogs following the administration of these drugs are offered in the tables. The mean pressure, which is given in a separate column, is the average of the intrapleural pressure at inspiration and expiration. It is difficult to obtain satisfactory manometric readings with a rapidly moving column of water and, therefore, the kymograph tracings probably present a better picture of the changing intrapleural pressure.

Examination of the kymographic tracings and of the data presented in the tables shows that the administration of epinephrin or atropine is followed by a definite increase in intrapleural pressure. The effect seems quite prolonged, and in the case of epinephrin, does not become apparent until the action of the drug on blood pressure has practically disappeared. With broncho-dilatation, less resistance is offered to the movement of air in and out of the lungs and this seems to be accompanied by less suction on expansion of the chest.