THE EFFECTS OF BODY POSITION, GANGLIONIC BLOCKADE AND NOREPINEPHRINE ON THE PULMONARY CAPILLARY BED*†

Abstract

The pulmonary capillary blood volume (Vc) and the diffusing capacity of the pulmonary membrane (DM) were calculated from measurements of the diffusing capacity of the lungs for carbon monoxide in normal subjects in the recumbent and 45[degree] head-up tilted positions during a control period and during the infusion of trimethapan (Arfonad) and norepinephrine (Levophed). Vc fell during head-up tilting. The infusion of trimethapan in the recumbent position also decreased Vc and accentuated its decrease during the head-up tilt. DM did not change significantly during these procedures. Norepinephrine did not change Vc in the recumbent position but lead to an increase in DM. The decrease in Vc on tilting was abolished by norepinephrine. Vc changed in the same direction as did the capillary transmural pressure deduced from available hemodynamic data during tilting, trimethapan infusion and exercise. This could be due to passive conformity of the capillary bed to changes in transmural pressure. Active vasomotion, however, can not excluded. Vc did not change although transmural pressure was probably increased during norepinephrine infusion in the recumbent position. This is best explained by active vasomotion in the pulmonary capillaries.