Cardiac output effects of high-frequency oscillatory ventilation in normal dogs

We compared the hemodynamic effects of high-frequency oscillatory ventilation (HFOV) with conventional continuous positive pressure ventilation (CPPV). Six mongrel dogs were anesthetized with chloralose and evaluated over a range of mean airway pressures (Pao) during CPPV and HFOV. Pao during HFOV was measured by allowing alveolar pressure to come into equilibrium with airway opening pressure and was set to equal mean Pao during CPPV. Pao during CPPV was set by adding positive end-expiratory pressure (PEEP) of 0, 5, 10, and 15 cm H2O. Transmural pulmonary capillary wedge pressures (Pwp) were maintained at near 11 mm Hg in both groups during all four ventilatory periods. Cardiac output as measured in triplicate by thermal dilution was similar between HFOV and CPPV at each level of mean airway pressure. After matching mean airway pressure and transmural Pwp we were unable to find any sparing effect of HFOV on cardiac output over a wide range of airway pressures. We conclude that there is not an independent effect of HFOV on cardiac output.