Maximal airway pressures during crying in healthy preterm and term neonates

Respiratory muscle strength can be assessed by measurement of maximal inspiratory (P-IMAX) and maximal expiratory pressure (P-EMAX) during crying. There are, however, relatively few data on P-IMAX and P-EMAX in infancy, particularly fr om those born preterm. Our aim was to investigate which factors influenced P-IMAX and P-EMAX in preterm and term infants. Forty infants, median gestational age 37 weeks (range 26-43) and birthweight 2.579 kg (range 0.956-5.180) were studied at a postconceptional age (PCA) of 38 weeks (range 32-44). None had respiratory problems. A facemask was placed firmly over the infant's mouth and nose and the infant studied during spontaneous crying. A pneumotachograph fitted snugly into the facemask and from a sideport airway pressure changes were measured. During crying, the distal end of the pneumotachograph was occluded for five breaths and at least three separate occlusions were made. The highest P-EMAX value sustained for at least 1 s and the highest peak inspiratory pressure P-IMAX were recorded. The mean P-IMAX and P-EMAX were higher in the term compared to the preterm infants (70 cmH(2)O +/-S.D. 19 versus 58 cmH(2)O +/-S.D. 17 P-IMAX and 53 cmH(2)O +/-S.D. 13 versus 44 cmH(2)O +/-S.D. 19 P-EMAX, P <0.05). Both P-IMAX and P-EMAX related significantly with postconceptional age, gestational age and weight, but not postnatal age. Stepwise regression analysis demonstrated P-IMAX related independently with PCA and P-EMAX with weight. These results suggest respiratory muscle strength is influenced by maturation at birth. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.