Pediatric research
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Total lung capacity (TLC), inspiratory capacity (IC), functional residual capacity (FRC), and deflation pressure-volume (P-V) curves were studied in 16 intubated neonates (540-3300 g), 10 with severe respiratory distress syndrome (RDS) and 6 air-ventilated with normal chest radiograms. FRC was measured using washout of a tracer gas (sulfur hexafluoride), and TLC and IC were calculated after inflating the lungs to 30 cm H2O. P-V curves were obtained during expiration from TLC using an interrupter technique, and the steepest slope of the curve, i.e. the maximum compliance (Crs-max), was calculated. ⋯ The flatter P-V curve in the RDS group was reflected also in a lower Crs-max (median 0.7 and range 0.4-1.7 cm H2O-1 kg-1) than in the air-ventilated group (2.3 and 2.0-3.1 mL cm H2O-1 kg-1, respectively; p < 0.01). Thus, there was no overlap in IC or Crs-max between the groups, suggesting that reductions in these measures may be main characteristics of RDS. On the other hand, no difference in PCD was found, indicating that, in infants with RDS, the tidal volume is distributed fairly homogeneously to the ventilated parts of the lungs.