Developmental pattern of maximal transdiaphragmatic pressure in infants during crying.

Diaphragm strength was measured as maximal transdiaphragmatic pressure (Pdi) during airway occlusion in 38 infants aged 11.6 +/- 0.5 (S.E.) months postconception (mpc), range 8-21 mpc. All infants were asymptomatic at the time of study and required no mechanical ventilatory assistance. Ten infants had previous surgical correction of abdominal wall defects (gastroschisis/omphalocele); 10 infants had previous surgical correction of congenital diaphragmatic hernia; and 18 infants had no thoracic or abdominal surgery. The mean maximal Pdi for all infants was 72 +/- 3 cmH2O. There were no significant differences between the three groups. All infants with a maximal Pdi of less than 60 cmH2O were aged less than 10 mpc. After 13 mpc there was no significant increase in maximal Pdi. Between the ages 8-13 mpc there was a significant positive correlation between maximal Pdi and age postconception (r = 0.87, P less than 0.0005), reflecting a developmental pattern of increasing maximal transdiaphragmatic pressure in infants during crying.