A model of the spontaneously breathing patient: applications to intrinsic PEEP and work of breathing

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Abstract
Schuessler, Thomas F., Stewart B. Gottfried, and Jason H. T. Bates. A model of the spontaneously breathing patient: applications to intrinsic PEEP and work of breathing.J. Appl. Physiol. 82(5): 1694–1703, 1997.—Intrinsic positive end-expiratory pressure (PEEPi) and inspiratory work of breathing (Wi) are important factors in the management of severe obstructive respiratory disease. We used a computer model of spontaneously breathing patients with chronic obstructive pulmonary disease to assess the sensitivity of measurement techniques for dynamic PEEPi(PEEPi dyn) and Wi to expiratory muscle activity (EMA) and cardiogenic oscillations (CGO) on esophageal pressure. Without EMA and CGO, both PEEPi dyn and Wi were accurately estimated (r = 0.999 and 0.95, respectively). Addition of moderate EMA caused PEEPi dyn and Wi to be systematically overestimated by 141 and 52%, respectively. Furthermore, CGO introduced large random errors, obliterating the correlation between the true and estimated values for both PEEPi dyn(r = 0.29) and Wi(r = 0.38). Thus the accurate estimation of PEEPi dyn and Wi requires steps to be taken to ameliorate the adverse effects of both EMA and CGO. Taking advantage of our simulations, we also investigated the relationship between PEEPi dyn and static PEEPi(PEEPi stat). The PEEPi dyn/PEEPi statratio decreased as stress adaptation in the lung was increased, suggesting that heterogeneity of expiratory flow limitation is responsible for the discrepancies between PEEPi dyn and PEEPi stat that have been reported in patients with severe airway obstruction.