[Exhaled tidal volume is overestimated due to cardiogenic oscillation: effects of ventilator and mode]

We investigated effects of cardiogenic oscillation on overestimation of tidal volume using a lung model, with three ventilators and two ventilatory modes.

We simulated cardiogenic oscillation at a rate of 90 breaths x min(-1) by ventilating one bellow of a two-bellow-type lung model. The magnitude of cardiogenic oscillation was defined as peak expiratory flow fluctuation when the airway was opened to the atmosphere. The lung model was mechanically ventilated with three ventilators (Bird 8400 STi, Servo-300, and Nellcor Puritan-Bennett 840), two ventilatory modes (volume- and pressure-controlled ventilation), and two respiratory rates (5 and 10 breaths x min(-1)) in random order. We recorded tidal volume on a ventilator monitor and calculated the discrepancy from the set tidal volume.

With Bird 8400 STi, monitored tidal volume exceeded set tidal volume, regardless of volume- or pressure-controlled ventilation. The overestimation in tidal volume was larger with smaller respiratory rate and with larger cardiogenic oscillation. In contrast, with the other ventilators, the discrepancy was small.

Exhaled tidal volume is overestimated during mechanical ventilation when cardiogenic oscillation is large.