Impact of Positive End-expiratory Pressure on Chest Wall and Lung Pressure–Volume Curve in Acute Respiratory Failure

To investigate whether chest-wall mechanics could affect the total respiratory system pressure–volume (P–V) curve in patients with acute respiratory failure (ARF), and particularly the lower inflection point (LIP) of the curve, we drew the total respiratory system, lung, and chest-wall P–V curves (P–Vrs, P–Vl, and P–Vw, respectively) for 13 patients with ARF, using the supersyringe method together with the esophageal balloon technique. Measurements were randomly repeated at four different levels of positive end-expiratory pressure (PEEP) (0, 5, 10, 15 cm H2O) and from each P–V curve we derived starting compliance (Cstart), inflation compliance (Cinf), and end compliance (Cend). With PEEP of 0 cm H2O (ZEEP), an LIP on the P–Vrs curve was observed in all patients (7.5 ± 3.9 cm H2O); in two patients an LIP was detected only on the P–Vl curve (8.6 and 8.7 cm H2O, respectively); whereas in seven patients an LIP was observed only on the P–Vw curve (3.4 ± 1.1 cm H2O). In four patients, an LIP was detected on bot...