The comparison of work of breathing methodologies on a patient model

Pressure volume curves were obtained from a surgical patient during the weaning period to determine the inspiratory Work Of Breathing (WOB). The methodologies of Otis (1950, 1977) and Campbell (1958, 1970) were used to derive the work per breath. There were differences recorded by these methods, which are explained with the use of an electrical RLC model of the respiratory system. The patient was spontaneously breathing during the ventilated support period and then breathing through the ET tube during an unsupported stage, just prior to extubation. The inspiratory work derived from: the airway pressures (Wpaw) were 0.23±0.03 Joules per breath (Jpb) and 0.00 Jpb; transpulmonary pressures were 0.31±0.04 Jpb and 0.27±0.08 Jpb; Campbell Diagram were 0.30±0.06 Jpm and 0.42±0.14 Jpb; and a simplified Campbell´s method (WcampRO) were 0.24 ±0.05 Jpb and 0.33 ±0.13 Jpb, during supported and unsupported periods, respectively. The simplistic approach of Wpaw and WcampRO methods produced work levels that were significantly lower than their standard methods during both phases (p<0.001). Otis methods show a decrease in the levels of work when the work should have increased due to imposed WOB during the unsupported period, as recorded by using Campbell´s methods.