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2.  Catch-up Alveolarization in Ex-Preterm Children. Evidence from 3He Magnetic Resonance 
Rationale: Histologic data from fatal cases suggest that extreme prematurity results in persisting alveolar damage. However, there is new evidence that human alveolarization might continue throughout childhood and could contribute to alveolar repair.
Objectives: To examine whether alveolar damage in extreme-preterm survivors persists into late childhood, we compared alveolar dimensions between schoolchildren born term and preterm, using hyperpolarized helium-3 magnetic resonance.
Methods: We recruited schoolchildren aged 10–14 years stratified by gestational age at birth (weeks) to four groups: (1) term-born (37–42 wk; n = 61); (2) mild preterm (32–36 wk; n = 21); (3) extreme preterm (<32 wk, not oxygen dependent at 4 wk; n = 19); and (4) extreme preterm with chronic lung disease (<32 wk and oxygen dependent beyond 4 wk; n = 18). We measured lung function using spirometry and plethysmography. Apparent diffusion coefficient, a surrogate for average alveolar dimensions, was measured by helium-3 magnetic resonance.
Measurements and Main Results: The two extreme preterm groups had a lower FEV1 (P = 0.017) compared with term-born and mild preterm children. Apparent diffusion coefficient was 0.092 cm2/second (95% confidence interval, 0.089–0.095) in the term group. Corresponding values were 0.096 (0.091–0.101), 0.090 (0085–0.095), and 0.089 (0.083–0.094) in the mild preterm and two extreme preterm groups, respectively, implying comparable alveolar dimensions across all groups. Results did not change after controlling for anthropometric variables and potential confounders.
Conclusions: Alveolar size at school age was similar in survivors of extreme prematurity and term-born children. Because extreme preterm birth is associated with deranged alveolar structure in infancy, the most likely explanation for our finding is catch-up alveolarization.
doi:10.1164/rccm.201210-1850OC
PMCID: PMC3734619  PMID: 23491406
alveolar structure; lung acinus; bronchopulmonary dysplasia; neonatal chronic lung disease
3.  Alveolarization Continues during Childhood and Adolescence 
Rationale: The current hypothesis that human pulmonary alveolarization is complete by 3 years is contradicted by new evidence of alveolarization throughout adolescence in mammals.
Objectives: We reexamined the current hypothesis using helium-3 (3He) magnetic resonance (MR) to assess alveolar size noninvasively between 7 and 21 years, during which lung volume nearly quadruples. If new alveolarization does not occur, alveolar size should increase to the same extent.
Methods: Lung volumes were measured by spirometry and plethysmography in 109 healthy subjects aged 7–21 years. Using 3HeMR we determined two independent measures of peripheral airspace dimensions: apparent diffusion coefficient (ADC) of 3He at FRC (n = 109), and average diffusion distance of helium (Xrms¯) by q-space analysis (n = 46). We compared the change in these parameters with lung growth against a model of lung expansion with no new alveolarization.
Measurements and Main Results: ADC increased by 0.19% for every 1% increment in FRC (95% confidence interval [CI], 0.13–0.25), whereas the expected change in the absence of neoalveolarization is 0.41% (95% CI, 0.31–0.52). Similarly, increase of (Xrms¯) with FRC was significantly less than the predicted increase in the absence of neoalveolarization. The number of alveoli is estimated to increase 1.94-fold (95% CI, 1.64–2.30) across the age range studied.
Conclusions: Our observations are best explained by postulating that the lungs grow partly by neoalveolarization throughout childhood and adolescence. This has important implications: developing lungs have the potential to recover from early life insults and respond to emerging alveolar therapies. Conversely, drugs, diseases, or environmental exposures could adversely affect alveolarization throughout childhood.
doi:10.1164/rccm.201107-1348OC
PMCID: PMC3410735  PMID: 22071328
growth and development; lung development; alveolarization

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