RIGHT ATRIAL BYPASS MODEL IN THE DOG

In gas exchange studies addressing the storage and transport of CO2 in dogs, a model in which cardiac output (QT) can be precisely controlle d and measured would be beneficial. We identified problems with descri bed extracorporeal circuits and implemented right atrial bypass (RAB) in dogs. In 6 anesthetized (chloralose and urethane), heparinized dogs (mean +/- SD, 24 +/- 4 kg) with open thorax, cannulas were inserted i n both vena cavas to drain venous blood return to a reservoir (anaerob ic bag or bubble oxygenator). A roller pump then drove blood through a heat exchanger back to the right atrial appendage. After 1.8 +/- 1.4 hour of RAB, physiologic variables remained within reference limits fo r dogs (QT, 1.5 +/- 0.3 L/min; blood pressure, 92 +/- 25 mm of Hg; art erial P-co2, 35 +/- 4 mm of Hg; P-o2, 513 +/- 39 mm of Hg; pH, 7.39 +/ - 0.08; and tissue CO2 production, 126 +/- 56 ml/min). To permit study of gas exchange, venous return (and thus, QT) and venous Pc(o2) and P -o2 could be accurately regulated and measured over a wide range. Main tenance of native pulsatile lung perfusion and cardiogenic oscillation s minimizes mismatching of pulmonary ventilation and perfusion and fac ilitates studies addressing pulmonary gas exchange. This RAB model is designed so that investigators can establish the preparation in a few hours.