Instrumentation for measuring cardiac output by direct Fick method during liquid ventilation

A closed-circuit fluorocarbon oxygenation system was designed and incorporated into an existing liquid breathing system (LBS) to allow measurement of an animal's oxygen consumption during liquid ventilation. This enabled simultaneous determination of cardiac output by the direct Fick method. A series of seven in-vivo experiments were conducted in which the oxygen consumption and cardiac output of adult cats (2.3 +/- 0.1 kg body wt SEM) were measured during both spontaneous gas breathing (Fio2 = 0.80 in the control animals) and fluorocarbon liquid (FC-80) ventilation using the LBS. On conversion to liquid ventilation, cardiac output and oxygen consumption were found to decrease significantly, by 40% (P less than 0.02) and 18.6% (P less than 0.05), respectively, from control values for gas breathing. Use of the closed-loop fluorocarbon oxygenation system provided for total recovery of vaporized fluorocarbon (greater than 750 ml/h) and of oxygen (18 liter/min STPD), which were otherwise discarded in previous experiments with liquid ventilation.