1665 DIAPHRAGMATIC VENTILATION, WORK, AND CHEST WALL DISTORTION IN PREMATURE INFANTS

Abstract

We studied diaphragmatic ventilation, work, and chest wall distortion (CWD) in 7 premature infants (wt. 1510 ± 176g, age 11±6d) who were recovering from hyaline membrane disease. Tidal volume was partitioned into the movement of the chest wall and abdomen using circumferential mercury-in-rubber strain gauges. A multiple linear regression was used to find the best fit between the weighted sum of the circumference changes and the lung volume, measured with a face mask and pneumotachograph. Changes in tidal volume could be estimated to within ±6% on a breath-by-breath basis. Esophageal and gastric pressures were measured using a two-lumen feeding tube with a 3 cm esophageal balloon connected to the proximal lumen. Diaphragmatic work was calculated using the abdominal volume changes and the transdiaphragmatic pressure. The diaphragm provided 53 to 198% of the ventilation of the lungs, being greater than 100% due to CWD in four of the infants. The work done by the diaphragm, however, was 90 to 396% (21 to 121 ml.cm H2O) of that performed on the lungs, increasing roughly in proportion to the square of the diaphragmatic ventilation. The chest wall was stiffer during diaphragmatic contraction than during expiration, being up to 14 times as compliant during expiration. Thus, even small amounts of CWD produce increases in diaphragmatic ventilation, and lead to dramatic increases in the diaphragmatic work. (Supported by HL-24075 and HL-07159)