Abstract
Twelve infants, 29 ± .62 wks. gestation, 1035 ± 11 g. without apparent respiratory distress were studied within 10 hrs. of birth. Measurements of intraesophageal pressure, air flow, and tidal volume (VT) enabled calculation of lung compliance (CL), lung inspiratory (≥) and expiratory (≥) resistance, and minute volume (V) at 5-10 hr. intervals. Simultaneous blood gases were measured. Mean CL ± SD in ml/cmH2O/kg in the first 24 hrs. varied from 1.12 ± 0.23 to 1.19 ± 0.22 and then decreased to 0.09 ± 0.15 at 72 hrs. Subsequently CL increased to 1.62 ± 0.53 at 150 hrs. The sequential CL values varied from 2%-56% of the individual mean. VT varied from 5.0 ± 0.58 to 7.6 ± 2.09 ml/kg in the first 24 hrs., remaining relatively unchanged at 6.65 ± 0.82 ml/kg at 150 hrs. Mean V ± SD in ml/min ranged from 387 ± 60 to 311 ± 40 at 24 and 72 hrs. respectively and to 366 ± 29 at 150 hrs. The inspiratory (≥) and expiratory (≥) resistance increased in the first 72 hrs. from 73 ± 11 to 149 ± 40 cmH2O/L/sec and 112 ± 21 to 159 ± 30 cmH2O/L/sec respectively, followed by a decrease in ≥ over the next few days to 87 ± 15 cmH2O/L/sec while ≥ remained unchanged. Blood gases and pH were within physiological range. These data indicate the variability of the mechanics of breathing in VLBW infants prone to periodic breathing may reflect unstable lungs due to changes in lung volume or to a degree of immaturity in the control of breathing.
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