Figure 5. Results obtained in tracheally intubated patients: comparison between the endotracheal tube (ETT)-related work of breathing measured by the catheter method and computed (predicted) using the acoustic-Blasius method, the Blasius formula, and the theoretical ETT diameter given by the manufacturer. Data were obtained from three or four cycles in each of the five patients. (Upper) Inspiratory work per cycle computed using the acoustic-Blasius method versus inspiratory work measured using the catheter method (correlation coefficient = 0.97). The solid line is the identity line. (Lower) As recommended by Bland and Altman, [16]differences between the results of the two methods were plotted versus the mean of the two methods (mean = 0.011 joules; SD = 0.027).