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Membrane and Capillary Components of Lung Diffusion in Infants with Bronchopulmonary Dysplasia
Daniel V Chang1, Santiago J Assaf1, Christina J Tiller1
1Department of Pediatric Pulmonology, James Whitcomb Riley Hospital for Children at Indiana University, Indianapolis, Indiana.
Insights
Infants with bronchopulmonary dysplasia (BPD) have reduced pulmonary diffusing capacity (DLCO) due to impaired alveolar development, affecting both membrane diffusing capacity (DM) and capillary volume (Vc). The DM/Vc ratio remained unchanged in BPD infants compared to full-term controls.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
- Neonatal Medicine
Background:
- Infants with bronchopulmonary dysplasia (BPD) exhibit impaired alveolar development, characterized by fewer and larger alveoli.
- This structural abnormality correlates with reduced pulmonary diffusing capacity for carbon monoxide (DLCO) in BPD patients compared to healthy full-term (FT) infants.
- The specific contributions of pulmonary membrane diffusing capacity (DM) and capillary volume (Vc) to the decreased DLCO in BPD remain unclear.
Purpose of the Study:
- To investigate whether the reduced DLCO in infants with BPD is attributable to decreases in both DM and Vc.
- To determine if the ratio of DM to Vc differs between infants with BPD and FT controls.
Main Methods:
- Pulmonary diffusing capacity for carbon monoxide (DLCO) was measured in infants under room air and high inspired oxygen (90%) conditions.
- These measurements allowed for the separate calculation of pulmonary membrane diffusing capacity (DM) and capillary volume (Vc).
Main Results:
- Both DM and Vc demonstrated a positive correlation with increasing body length.
- Infants with BPD showed significantly lower DM and Vc values compared to FT infants, even after adjusting for covariates.
- The DM/Vc ratio was found to be independent of body length and did not differ between the BPD and FT groups.
Conclusions:
- The findings support the hypothesis of impaired alveolar development in BPD, leading to fewer but larger alveoli.
- A reduced capillary volume (Vc) is a significant factor contributing to the decreased DLCO observed in infants with BPD.
- The consistent DM/Vc ratio suggests that the impairment in BPD affects both diffusion and volume proportionally.
Rationale:
Autopsied lungs of infants with bronchopulmonary dysplasia (BPD) demonstrate impaired alveolar development with larger and fewer alveoli, which is consistent with our previous physiologic findings of lower pulmonary diffusing capacity of the lung for carbon monoxide (DL(CO)) in infants and toddlers with BPD compared with healthy controls born at full term (FT). However, it is not known whether the decreased DL(CO) in infants with BPD results from a reduction in both components of DL(CO): pulmonary membrane diffusing capacity (D(M)) and Vc.
Objectives:
We hypothesized that impairment of alveolar development in BPD results in a decrease in both D(M) and Vc components of DlCO but that the D(M)/Vc ratio would not differ between the BPD and FT groups.
Methods:
DL(CO) was measured under conditions of room air and high inspired oxygen (90%), which enabled D(M) and Vc to be calculated.
Measurements And Main Results:
D(M) and Vc increased with increasing body length; however, infants with BPD had significantly lower D(M) and Vc than FT subjects after adjustment for race, sex, body length, and corrected age. In contrast to D(M) and Vc, the D(M)/Vc ratio remained constant with increasing body length and did not differ for infants with BPD and FT subjects.
Conclusions:
Our findings are consistent with infants with BPD having impaired alveolar development with fewer but larger alveoli, as well as a reduced Vc.
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