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/cm H(2)O. 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.