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.

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 ¼ 61); (2) mild preterm (32-36 wk; n ¼ 21); (3) extreme preterm (,32 wk, not oxygen dependent at 4 wk; n ¼ 19); and (4) extreme preterm with chronic lung disease (,32 wk and oxygen dependent beyond 4 wk; n ¼ 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 FEV 1 (P ¼ 0.017) compared with term-born and mild preterm children. Apparent diffusion coefficient was 0.092 cm 2 /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.Keywords: alveolar structure; lung acinus; bronchopulmonary dysplasia; neonatal chronic lung disease Advances in preterm care have led to increased survival of extremely premature babies, with increasing numbers reaching adulthood. This has shifted the focus of research from survival toward long-term sequelae of prematurity (1, 2). Infants born extremely preterm are known to have arrested alveolar development, manifesting as fewer and larger alveoli (3, 4). Schoolage and adult survivors of extreme preterm birth are known to have long-term respiratory problems, particularly decreased forced expiratory volumes and increased residual lung volumes, suggesting airway damage (5, 6). There are insufficient data regarding structure and development of the periphery of the lung in long-term survivors of preterm birth because studies on this cohort have relied on traditional lung function tests that only provide an overall estimate of function.The short-and long-term outcomes described previously correlate with gestational age (GA) at birth and the presence of chronic lung disease of prematurity (CLD), one of the early pulmonary sequelae of extreme preterm birth (6-8). Most evidence regard...

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Rationale: Asthma is characterized by disease within the small airways. Several studies have suggested that forced oscillation technique-derived resistance at 5 Hz (R5) 2 resistance at 20 Hz (R20) is a measure of small airway disease; however, there has been limited validation of this measurement to date. Objectives: To validate the use of forced oscillation R5 2 R20 as a measure of small airway narrowing in asthma, and to investigate the role that small airway narrowing plays in asthma. Methods: Patient-based complete conducting airway models were generated from computed tomography scans to simulate the impact of different degrees of airway narrowing at different levels of the airway tree on forced oscillation R5 2 R20 (n = 31). The computational models were coupled with regression models in an asthmatic cohort (n = 177) to simulate the impact of small airway narrowing on asthma control and quality of life. The computational models were used to predict the impact on small airway narrowing of type-2 targeting biologics using pooled data from two similarly design randomized, placebo-controlled biologic trials (n = 137). Measurements and Main Results: Simulations demonstrated that narrowing of the small airways had a greater impact on R5 2 R20 than narrowing of the larger airways and was associated (above a threshold of approximately 40% narrowing) with marked deterioration in both asthma control and asthma quality of life, above the minimal clinical important difference. The observed treatment effect on R5 2 R20 in the pooled trials equated to a predicted small airway narrowing reversal of approximately 40%. Conclusions: We have demonstrated, using computational modeling, that forced oscillation R5 2 R20 is a direct measure of anatomical narrowing in the small airways and that small airway narrowing has a marked impact on both asthma control and quality of life and may be modified by biologics.