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

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.