Analysis of static pulmonary mechanics helps to identify functional defects in survivors of acute respiratory distress syndrome.

OBJECTIVE

To assess the utility of static lung pressure-volume measurements in identifying and categorizing pulmonary function test defects in survivors of acute respiratory distress syndrome (ARDS).

DESIGN

Cross-sectional.

SETTING

Pulmonary function laboratory at a tertiary referral hospital in northern India.

PATIENTS

Six survivors of ARDS reporting for their first follow-up visit after discharge.

MEASUREMENTS AND MAIN RESULTS

Spirometry and whole body plethysmography were performed to evaluate lung volumes and to collect static lung pressure-volume data; the latter were subjected to monoexponential analysis. Three patients had a restrictive ventilatory defect as evidenced by diminished vital capacity and total lung capacity, but only one had reduced static lung compliance. The other two patients had reduced recoil pressure at total lung capacity, suggestive of respiratory muscle weakness. Two other patients with normal lung volumes had reduced static lung compliance. Exponential analysis of pressure-volume data in the three patients with reduced static lung compliance was consistent with reduced distensibility and loss of lung units in one patient each. Additionally, two patients had high values for shape constant of the exponential curve, indicative of air space distention.

CONCLUSIONS

Detailed analysis of static pressure-volume data can identify pulmonary function abnormality and categorize the dominant mechanism responsible for restrictive ventilatory defects in survivors of ARDS, even in patients with normal lung volumes. In addition to lung fibrosis, neuromuscular weakness also contributes to decline in pulmonary function.