Changes in Thoracic Size Following the Administration of Broncho-constricting or Broncho-dilating Drugs to Dogs. ∗

Abstract

Report has been made of the intrapleural pressure changes occurring after the administration of typical broncho-constricting or broncho-dilating drugs to dogs. 1 It has been suggested that these alterations in intrapleural pressure may be mediated by variations in thoracic girth accompanying the effects of these drugs on the respiratory mechanism, especially as a result of changes in alveolar and blood carbon dioxide tension following broncho-constriction or broncho-dilatation. The experiments here reported were undertaken to determine directly whether alteration in thoracic size actually occurs after the administration of broncho-constricting or broncho-dilating drugs.

The technique used for intrapleural pressure determination was the same as that previously described. In addition we measured directly the circumference of the thorax about 5 cm. above the xiphoid process, and we obtained records of respiratory movement by kymograph and pneumograph. After the subcutaneous injection of solutions of such broncho-constricting drugs as pilocarpine nitrate (2 experiments) and eserine salicylate (4 experiments), we found uniformly an increase in average thoracic girth accompanying a more negative intrapleural pressure (Fig. 1). This corresponds to the change in thoracic size accompanying the more negative intrapleural pressure resulting from the inhalation of 10% CO₂ in oxygen. We found a decrease in mean thoracic girth (Table I) accompanying a more positive intrapleural pressure after the administration of such broncho-dilating drugs as atropine sulphate (3 experiments) and epinephrine hydrochloride (1 experiment).