We obtained chest computed tomography (CT) sections in 12 normal subjects (controls) and 17 patients with the adult respiratory distress syndrome (ARDS) to investigate regional lung inflation. A basal CT section (just above the diaphragm) was obtained in the supine position at zero cm H2O end- expiratory pressure. In each CT section the distance from ventral to dorsal surface (hT) was divided into 10 equal intervals, and 10 lung levels from ventral (no. 1) to dorsal (no. 10) were defined. Knowing the average density and the volume of each level, we computed: (1) the tissue volume; (2) the gas/tissue (g/t) ratio (index of regional inflation); (3) the hydrostatic pressure superimposed on each level (SPL), estimated as density x height. The total volume of the basal CT section was 49 ± 2.5 ml x m-2 (mean ± SE) in control subjects and 43 ± 2.3 ml x m-2 in patients with ARDS (p = not significant [NS]). The tissue volume, however, was 16.7 ± 0.8 ml x m-2 in control subjects and 31.6 ± 1.7 ml x m-2 in patients with ARDS (p <0.01). The g/t ratio in level 1 averaged 4.7 ± 0.5 in control subjects and 1.2 ± 0.2 in patients with ARDS (p <0.01), and this ratio decreased exponentially from level 1 to level 10, both in controls and patients with ARDS. The Kd constant of the exponential decrease was 13.9 ± 1.3 cm in control subjects and 7.8 ± 0.8 cm in patients with ARDS (p <0.01). This indicates a greater rate of change of g/t with hT in ARDS. The SPL in level 10 was 4.5 ± 0.2 cm H2O in control subjects and 10.5 ± 0.4 cm H2O in patients with ARDS (p <0.01). In conclusion: (1) the ARDS lung is characterized by decreased gas volume and increased tissue volume, whereas total lung volume is similar to controls; (2) along the vertical gradient the g/t ratio decreased and SPL increased at a greater rate than controls; (3) The increased SPL, caused by the increased tissue volume, may be one of the major factors responsible for the increased regional inflation gradient in ARDS.
|Number of pages||6|
|Journal||American Journal of Respiratory and Critical Care Medicine|
|Publication status||Published - Jan 1994|
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine