INFLUENCE OF CHEST-WALL DISTORTION AND ESOPHAGEAL CATHETER POSITION ON ESOPHAGEAL MANOMETRY IN PRETERM INFANTS

The purpose of this study was to determine the effect of chest wall di stortion on esophageal manometry by measuring simultaneous esophageal pressure changes at two sites in preterm infants. Fourteen infants wer e studied (mean +/- SD: birth weight, 1340 +/- 260 g; age, 8.5 +/- 4 d ). Esophageal pressure was measured through two water-filled catheters , one placed just above the cardia (Pes1) and the other at the level o f the carina (Pes2). Chest wall distortion was measured by inductance plethysmography, and inspiratory and expiratory flow by pneumotachogra phy. No significant differences were found between the peak to peak es ophageal pressure changes measured through the lower and higher cathet ers during both airway occlusion (18.7 +/- 4.4 versus 18.3 +/- 2.6 cm H2O) and spontaneous breathing (9.4 +/- 1.8 versus 9.0 +/- 1.8 cm H2O) , although half of the infants had significant chest wall distortion. Mean pulmonary compliance and resistance measures calculated from the two pressures for individual infants showed small differences consiste nt with the difference between Pes1 and Pes2. For the whole group of 1 4 infants, however, these differences were not significant. The pressu re changes from the lower and higher measuring sites for each breath w ere analyzed using linear regression. The weighted average of the mean slopes of the 14 infants was significantly different from 1.0 (mean /- SD: 0.92 +/- 0.10, range: 0.75-1.10; p < 0.05). In some of the infa nts, the slopes for different breaths were not consistent, but varied from breath to breath. Neither this breath to breath variability in th e relationship between Pes1 and Pes2, nor the mean slopes were related to the degree of chest wall distortion. The results indicate that eso phageal pressure measurements in preterm infants are not as dependent on the position of the catheter tip and the degree of chest wall disto rtion as previously suggested. A tip positioned between the cardia and the level of the carina transmits pleural pressure changes reliably.