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. 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).