Hypercapnia induced by acetazolamide and its effect on pulmonary circulation. Experimental study

: In order to evaluate the isolated hemodynamic effects of acute hypercapnea on pulmonary circulation, we designed a canine model in which vascular pressures. PaO2, and arterial pH were maintained within normal limits. Six mongrel dogs were studied. Hypercapnea was achieved by a single intravenous doses of acetazolamide (120 mg/Kg) while maintaining mechanical ventilation constant. Both arterial and mixed venous PCO2 increased from 27 to 41 mm Hg and from 31 to 46 mm Hg respectively, and remained constant through the rest of the experiment (up to 3 Hs). With hypercapnea, total pulmonary vascular resistance increased from 312 +/- 156 to 435 +/- 173 d.s.cm-5 (p less than 0.05) and the stroke index decreased from 20.7 +/- 8.3 to 13.2 +/- 4.8 ml/beat (p less than 0.05). There were no changes either in pulmonary capillary wedge pressure or in the right ventricular end diastolic pressure. The above changes suggest a pulmonary vasoconstrictor effect of hypercapnea in the absence of other known vasoactive factors.