Pulmonary hemodynamics following acute atelectasis

¹ Department of Surgery, University of Minnesota, and Veterans Administration Hospital, Minneapolis, Minnesota

Locally induced alterations in pulmonary lobar blood flow and vascular resistance produced by atelectasis, hypoxia, or hypercarbia were studied in the autoperfused, innervated, separately ventilated right lower lobes of 14 dogs. Systemic effects of hypoxia or hypercarbia were excluded by shunting the lobar blood back to the vena cava; a second shunt between the internal mammary artery and the lobar artery permitted perfusion with either oxygenated or desaturated blood. Lobar blood flow was monitored with a magnetic flowmeter, and pressures were measured in the lobar artery, lobar vein, and femoral artery. Oxygen saturation was measured at these sites in nine of the dogs with a cuvette oximeter. Although systemic arterial pressure and oxygen saturation remained normal throughout these studies, hypoxia secondary to nitrogen ventilation produced average flow decreases of 19% and 14% with desaturated and saturated blood, respectively, and resistance increases of 26% and 15%. Atelectasis decreased flow by 37% and 23% and caused resistance to rise 93% and 65%. Ventilation of the lobe with 5% and 30% carbon dioxide in oxygen was without apparent effect.