Diaphragm Function in Very Preterm Infants at 36 Weeks' Postmenstrual Age.

OBJECTIVES

Understand how bronchopulmonary dysplasia (BPD) and antenatal and postnatal factors influence diaphragmatic functional effectiveness in very preterm infants.

WORKING HYPOTHESIS: Diaphragmatic functional effectiveness during spontaneous breathing is impaired in infants with BPD. Moreover, diaphragmatic functional effectiveness is influenced by adverse antenatal and postnatal factors.

METHODOLOGY: Diaphragmatic functional effectiveness was assessed in a single-centre, prospective observational study in preterm infants. Transdiaphragmatic pressure (Pdi) and respiratory flow were measured during quiet sleep at 36 weeks' postmenstrual age (PMA). Pdi was normalized to tidal volume (Pdi/VT). Diaphragmatic work of breathing per minute was calculated from the inspiratory pressure time integral (PTIdi) and respiratory rate. Factors predictive for each outcome were identified from multivariable linear regression.

RESULTS

Very preterm infants (n = 182) were measured at a median (IQR) 35.6 (1.3) weeks' PMA. Infants with BPD had a lower Pdi/VT (p = 0.007) and lower PTIdi·min-1 (p = 0.022) but higher minute ventilation (p = 0.032) and similar respiratory rates (p = 0.419) compared to infants without BPD. Birthweight Z score (R2 = 0.08, p < 0.001) and BPD (R2 = 0.04, p = 0.022) were independent negative predictors for Pdi/VT while gestational age (R2 = 0.04, p = 0.01) and average early postnatal energy intake (R2 = 0.03, p = 0.026) were independent positive predictors for PTIdi·min-1 on multivariable analysis. Chorioamnionitis and duration of mechanical ventilation did not contribute to the final model.

CONCLUSIONS

Contrary to our hypothesis, diaphragm functional effectiveness appears improved in infants with BPD. We speculate this finding may reflect an adaptive process, or alternatively indicate an increased recruitment of accessory muscles to achieve required ventilation in BPD infants. Adverse antenatal and postnatal factors only explain a small proportion of variance in diaphragm effectiveness.