Figure 3
Results from the physical lung model. Shown is the effect of increasing respiratory rates (RRs) on tidal volumes (VTs) in the absence of any endotracheal tube (ETT) and in the presence of an ETT with (compensated) and without (uncompensated) expiratory automatic tube compensation at a test lung compliance of 113 ml/cmH2O, ETT sizes of 7.0 mm (top) and 8.5 mm inner diameter (bottom), and inspiratory pressures of 3.0 (white bars), 4.5 (light grey bars) and 6.0 cmH2O (dark grey bars). 'Ideal' indicates tidal volume calculated on the basis of peak inspiratory pressure and compliance. Bars and whiskers indicate means ± standard deviation. Note that at low RRs, VTs during expiratory automatic tube compensation exceeded those observed in the absence of any ETT, particularly at the larger ETT size. *P < 0.025 versus absent ETT. STPD: standard temperature pressure dry.