To the Editor .–With regard to the article by Venus et al on continuous positive airway pressure (CPAP) (Archives1980;115:824-828), I and my colleagues recently published the results of a study that compared the respiratory and cardiovascular effects of CPAP, T-piece breathing, and extubation. 1 This study was performed in patients who were recovering from acute respiratory failure and in patients recovering from elective surgery. We found that CPAP and extubation were essentially indistinguishable, whereas T-piece breathing reduced functional residual capacity (FRC), increased shunt, and decreased the Pao 2 . As Venus et al stated, patients who were hemodynamically stable demonstrated no changes in cardiac index or vascular pressures and resistances. In an attempt to explain why CPAP and extubation are physiologically similar, we measured intratracheal pressures in patients while intubated (without end-expiratory pressure) and then while extubated. Mean expiratory pressures increased from 0.81 ± 0.16 to 2.44 ± 0.53 cm