Date of Award
Doctor of Philosophy (PhD)
Extremely low birth weight infants who develop severe chronic lung disease, known as bronchopulmonary dysplasia (BPD), commonly experience long term growth failure. A randomized, blinded study was designed with the objective to enhance growth in this population using aggressive nutritional intervention. Growth and body composition were assessed during four months of formula feeding that was either: (1) enriched in energy, protein and minerals (EF) or (2) enriched in energy (isoenergetic to EF) but with standard concentrations of protein and minerals (SF). We hypothesized that between randomization (37 weeks post-menstrual age) and 3 months corrected age (CA) the EF group would demonstrate a faster rate of growth with greater lean (versus fat) mass deposition, and greater bone mineral accretion. In addition, higher energy expenditure (EE) as determined by the doubly labelled water method (DLW) would accompany the enhanced rate of growth. The measurements continued after the intervention ended to determine if any growth benefits derived from the enhanced nutrition up to 3 mo CA would be sustained to 12 mo CA. Body composition of the infants was measured with dual energy x-ray absorptiometry (DXA), which was validated against the reference method of chemical analysis. Repeated measures and carcass analysis of infant pigs identified that DXA was accurate and precise in determining bone and lean masses of piglets weighing 6 kg; thus, validating the methodology for use in infants of post-term age. At the end of the nutrition intervention (3 mo CA) infants in the EF group were longer, with greater absolute amounts of lean and bone mass compared to the SF group. The highest velocity of growth occurred between 37 wk PMA and 1 mo CA. No differences in EE were detected, but the high variability within treatment groups (for undetermined reasons) likely precluded our ability to detect significant results. Thus, the DLW method requires further validation for use in BPD infants. Nine months after the intervention ended (12 mo CA), EF and SF groups were similar in weight, length and body composition. When plotted on standard reference growth curves, both groups became significantly more negative in weight-for-length between 3 and 12 mo CA, despite energy and protein intakes deemed adequate by current recommendations for term infants. A longer nutritional intervention study would determine whether growth benefits provided by EF are sustainable, such that catch-up is inducible. Alternatively, catch-up growth may not be possible in infants of such extremely low birth weights under the influence of nutrition alone, and investigations of other factors such as the disease process may be warranted.
Brunton, Janet A., "Somatic growth, body composition and energy expenditure in infants with bronchopulmonary dysplasia" (1997). Open Access Dissertations and Theses. Paper 3335.