Changes in lung mechanics following sighs in premature newborns without lung disease

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Abstract
Sighs, the interspersed breaths of larger tidal volume (VT) than those preceding or following them, occur more frequently in the newborn than in adults. It has been postulated that the sigh augments functional residual volume (FRC), increases lung compliance (CJ, and recruits atelectatic alveoli. Since the premature infant has relatively low FRC, we hypothesized that sighs might be more frequent in these babies and that CL could be shown to change before and/or after a sigh. We studied 14 premature infants (gestational age, 30 ± 2.2 weeks; mean ± SD) without lung disease during quiet sleep. Minute ventilation (VE) was measured by pneumotachography and pleural pressure changes via a water‐filled catheter in the esophagus. In the 78 sighs examined, the incidence was 0.71 sighs/min, similar, to previous reports for full‐term newborns. There was no change in respiratory frequency, VT/VE, nor mean inspiratory flow (VT/Tt, where Tt is the inspiratory time) before or after the event. The volume of the sigh increased from 7.8 ± 0.2 mL/kg to 21.5 ± 0.5 mL/kg, in concert with an increase in breath duration (TTOT) from 0.98 ± 0.02 ± to 2.56 ± 0.12 s, resulting in an unchanged VE, VT/TI). and respiratory duty cycle (TI/TTOT/). This suggests that the increased VT was matched by a prolongation in both TI and TTOT. Following the sigh, CL increased from 1.43 ± 0.13 cmH2O/kg to 1.66 ± 0.27 cmH2O/L/s/kg (paired t‐test, P < 0.001) whilst the lung resistance RL, fell from 62 ± 8 cmH2O/L/s/kg to 55 ± 3.8 cmH2O/L/s/kg (P < 0.05). As reflected by the end—expiratory volume (EEV), FRC did not change. This stability of FRC, coupled with the increase in CL and fall in RL, suggests a recruitment of atelectatic acini with a redistribution of lung volume, such that the previously atelectatic and overdistended acini achieve a more optimal pressureivolume relationship following a sigh. Pediatr Pulmonol. 1994; 17:22–25.