Journal of thoracic imaging
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The anatomic and physiologic response to positive end-expiratory pressure (PEEP) was investigated using computed tomography (CT) in patients with adult respiratory distress syndrome (ARDS). The lesions (densities) in ARDS are distributed inhomogeneously but tend to concentrate in the dependent regions. The estimated lung weight (by CT scan, quantitative analysis, and lung gas volume measured with helium dilution) is, on the average, 200% higher than expected. ⋯ The main effect of PEEP is to clear the densities through alveolar anatomic recruitment. Anatomic recruitment changes the mechanical characteristics of the lung and parallels the improvement in gas exchange. The effects of PEEP on pulmonary arterial pressure appear to be related to anatomic recruitment.
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Several acute and chronic conditions that alter the integrity of the pulmonary epithelium increased the rate of absorption or clearance into the circulation of small solutes deposited in the alveoli. Technetium 99m diethylenetriamine pentaacetic acid can be deposited in the lungs as a submicronic aerosol and its rate of clearance measured with a gamma camera or simple probe. This clearance technique is currently being used to evaluate patients who have developed pulmonary edema and also to detect those patients from a high risk group who are likely to develop adult respiratory distress syndrome (ARDS). ⋯ It is clear that a single measurement in patients who smoke is not useful, but repeated measurements may provide important information. The lung clearance measurement is very sensitive to changes in epithelial integrity but is not specific for ARDS. It may be most useful in combination with other predictive tests or when the clearance rate is normal.