Response of acoustic transmission to positive airway pressure therapy in experimental lung injury

Abstract

Objective: To evaluate the effect of positive end-expiratory pressure on the sound filtering characteristics of injured lungs. Design and setting: Prospective experimental study in the animal laboratory in an academic medical center. Patients and participants: Six 35- to 45-kg anesthetized, intubated pigs. Interventions: Acute lung injury with intravenous oleic acid. Measurements and results: We injected a multifrequency broad-band sound signal into the airway while recording transmitted sound at three locations bilaterally on the chest wall. Oleic acid injections effected a severe pulmonary edema predominantly in the dependent lung regions, with an average increase in venous admixture from 16±14% to 57±13% and a reduction in static respiratory system compliance from 31±6 to 16±3 ml/cmH 2O. A significant concomitant increase in sound transfer function amplitude was seen in the dependent and lateral lung regions; little change occurred in the nondependent areas. The application of PEEP resulted in a decrease in venous admixture, increase in respiratory system compliance, and return of the sound transmission to preinjury levels. Conclusions: Acute lung injury causes regional acoustic transmission abnormalities that are reversed during alveolar recruitment with PEEP. © Springer-Verlag 2005.