Pulmonary edema and upper airway obstruction.

Recently, DE Sofer et al(Chest 1984; 86:401-03)suggested that the pulmonary edema ofpatients with upper airway obstruction (UAO) was roentgenologically invisible because of the increase in lung volume befure the reliefofthe obstruction. In Dr. Sofer’s article, as well as in others,’4 objective dates ofincrease in lung volumes are not reported. Research in patients with chronic UAO showed different results in their volumes. However, in studies ofhealthy volunteers with experimental stenosis,4 a maintenance or a decrease of their dynamic and static lung volumes was observed. Ifwe were to admit an increase ofFRC with orwithout increase in TIC following UAO, a descent of the diaphragm would occur. Consequently, the minimal pleural pressure (Ppl J becomes less. Thus, ifthe descentofthe diaphragm is close to the maximum (TLC), the Ppl will only reach the maximal static recoil pressure. In contrast, the stability of FRC, or its decrease, would permit it to reach a PpL close to the maximal inspiratory muscular pressure. A similar but inverse argument can be applied to the expiratory pressure. It has been suggested that a severe attack ofasthma could favor the fbrmation ofpulmonary edema,5 but wide clinical experience contradicts this hypothesis. Thereibre, it is probable that the mechanical alterations lbllowing hyperinfiation could explain partially this contradiction. In summary, we believe that there are neither objective nor theoretic data to support the notion that these patients experienced an increase in lung volume. If this increase were enough to mask roentgenologically the pulmonary edema, it would be necessary to call in question the effect of the highly negative pressures in the origin ofthe pulmonary edema. On the other hand, we suggest that the appearance of the pulmonary edemabefore”2 orafter’4 the reliefofUAO would have to be related to its fixed or variable behavior. The fixed behavior, on increasingthe expiratorypressure, would counteract the effect of the inspiratory pressure3 and the edema could be developed with the reliefofthe obstruction. In the variable behavior there would exist a clear prevalence of inspiratory pressures and the edema could be developed befbre the reliefofthe obstruction.