Ventilation in dogs on cardiopulmonary bypass with and without lungs

In 13 anesthetized or awake dogs, on cardiopulmonary bypass, we varied PaO2 and PaCO2 while continuously monitoring ventilatory responses and mechanics, to assess the dog's ability to maintain eupneic ventilation for any chemical drive. In a second group of 13 dogs on cardiopulmonary bypass we repeated the tests after removal of both lungs, to assess the importance of pulmonary feedback and mechanics. The VE/PO2 plot formed two hyperbolas, asymptotic to 39 Torr PO2 with lungs, and to 27 without; both intercepted zero ventilation near 200 Torr. Hyperoxic apnea occurred at, or below, PCO2 30 +/- 7 Torr under barbiturate and 20 +/- 4 Torr under morphine. Steady-state low PCO2 (10 Torr) turned off hypoxic drives as low as 20 Torr PO2. Empty-chest dogs had a low respiratory frequency (18 vs. 40), and near zero dynamic elastance; ventilatory work per minute and airway resistance were the same with and without lungs. Chest wall ventilatory responses are grossly independent of the presence of absence of lungs.

Continuous in vivo measurement of arterial PO2 in humans

A system suitable for prolonged continuous in vivo measurement of human arterial PO2 is described. The system uses a polarographic electrode developed by Kimmich and Kreuzer, inserted in a specially made shunt between the radial artery and an antecubital vein. Nhe electrode surface is maintained in a fixed position parallel to the flow of blood; blood velocity dependency is small owing to the high flow rate achieved (more than 40 cm/s); clotting is prevented by the material used and the continuous instillation of heparin through the arterial end of the shunt. The system has been tested in vitro; it is stable (variation less than 0.5% in 24 h), linear and precise (plus or minus 0.2%) in a broad range of PO2 values (from about 10 mmHg to more than 700 mmHg); its response time is 0.4 s per 95% of deflection. It has been applied to 35 patients for periods ranging between 6 and 24 h; most of the patients were ventilated by an Engstrom respirator.