In five mechanically ventilated dogs, effect of 70 min of RPA occlusion on the following: (a) carbon dioxide volume exhaled per breath (VCO2,br); (b) PCO2; (c) dead space (VD); (d) ascending aortic cardiac output ( T); and (e) mean pulmonary artery pressure (Ppa). RPA occlusion began after time 0 (baseline). Solid symbol denotes significant difference (P < 0.05) from baseline measurement. *All stages during RPA occlusion were significantly different from baseline. PaCO2, arterial PCO2; PETCO2, end-tidal PCO2; P CO2, mixed venous PCO2; VDalv/VTalv, alveolar dead space : tidal volume fraction; VDphy, physiologic dead space. From Breen et al .