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Growth of the Lung Parenchyma Early in Life

¹ Department of Pediatrics, James Whitcomb Riley Hospital for Children, Herman B. Wells Center for Pediatric Research, Indianapolis, Indiana; ² Department of Medicine, Division of Biostatistics, Indiana University, Indianapolis, Indiana

Correspondence and requests for reprints should be addressed to Robert S. Tepper, M.D., Ph.D., Department of Pediatrics, Indiana University Medical Center, James Whitcomb Riley Hospital for Children, 702 Barnhill Drive, ROC 4270, Indianapolis, Indiana 46202-5225. E-mail: rtepper{at}iupui.edu

Rationale: Early in life, lung growth can occur by alveolarization, an increase in the number of alveoli, as well as expansion. We hypothesized that if lung growth early in life occurred primarily by alveolarization, then the ratio of pulmonary diffusion capacity of carbon monoxide (DL_CO) to alveolar volume (V_A) would remain constant; however, if lung growth occurred primarily by alveolar expansion, then DL_CO/V_A would decline with increasing age, as observed in older children and adolescents.

Objectives: To evaluate the relationship between alveolar volume and pulmonary diffusion capacity early in life.

Methods: In 50 sleeping infants and toddlers, with equal number of males and females between the ages of 3 and 23 months, we measured DL_CO and V_A using single breath-hold maneuvers at elevated lung volumes.

Measurements and Main Results: DL_CO and V_A increased with increasing age and body length. Males had higher DL_CO and V_A when adjusted for age, but not when adjusted for length. DL_CO increased with V_A; there was no gender difference when DL_CO was adjusted for V_A. The ratio of DL_CO/V_A remained constant with age and body length.

Conclusions: Our results suggest that surface area for diffusion increases proportionally with alveolar volume in the first 2 years of life. Larger DL_CO and V_A for males than females when adjusted for age, but not when adjusted for length, is primarily related to greater body length in boys. The constant ratio for DL_CO/V_A in infants and toddlers is consistent with lung growth in this age occurring primarily by the addition of alveoli rather than the expansion of alveoli.

Key Words: pulmonary diffusion capacity • alveolar volume • lung development

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Current understanding of early lung growth and development is based largely on small numbers of autopsied lungs from infants and toddlers; in vivo physiologic measurements in this age group are scarce. What This Study Adds to the Field Pulmonary diffusing capacity and alveolar volume increases with increasing age among infants and toddlers, but their ratio remains constant. This suggests that, in this age range, lung volume increases by alveolarization rather than expansion.