Effect of maturity on maximal transdiaphragmatic pressure in infants during crying

The aim of this study was to determine the effect of maturation on diaphrag matic function. In addition, we investigated whether noninvasive assessment yielded similar results to invasive measurement. Twenty-eight infants, med ian gestational age (GA) 35.5 wk (range, 25 to 42 wk) and postconceptional age (PCA), 37.6 wk (range, 32 to 44 wk), were examined. Diaphragmatic funct ion was assessed by measuring the maximal transdiaphragmatic pressure durin g crying (cPdi) using balloon catheters in the midesophagus (Pes) and the s tomach (Pgas). In 14 of the infants, a noninvasive measurement of inspirato ry muscle strength, maximal inspiratory pressure (Pimax), was also made. cP di and Pimax were recorded during a crying effort with the airway occluded at end-expiration. The median cPdi and Pes during crying (cPes), but not Pg as during crying (cPgas), were significantly lower in those studied at a PC A of less than term compared with those studied at an older age (p < 0.05). cPdi and cPes, but not cPgas, correlated significantly with PCA (r = 0.44, p < 0.02; r = 0.43, p < 0.03; respectively) and gestational age (r = 0.46, p < 0.02 and r = 0.56, p < 0.01; respectively). In the 14 infants, the med ian Pimax was lower, but it correlated significantly with cPdi (r = 0.79, p < 0.01). We conclude maturation does affect diaphragm function, and Pimax may provide a noninvasive index of diaphragm strength.