Rate constant for forced expiration decreases with lung growth during infancy

Robert S. Tepper, Marcus Jones, Stephanie Davis, Jeff Kisling, Robert Castile

Research output: Contribution to journalArticle

31 Scopus citations


Airway caliber and lung volume (V(L)) increase many fold between infancy and adulthood; however, these two components of the lung may not increase proportionately during lung growth and development. We evaluated in infants the rate of emptying during forced expiration from near total lung capacity to residual volume. From the flow-volume curves we calculated (1) a rate constant (k) as the change in flow divided by the change in volume between 50% and 75% of expired forced vital capacity (FVC), and (2) the fraction of the FVC expired in 0.5 s (FEV0.5/FVC). Seventeen normal healthy infants were evaluated twice; mean ages (ranges) at first and second tests were 30 (5 to 76) and 58 (28 to 98) wk. Analysis of cross-sectional and longitudinal data indicated that the rate of emptying during forced expiration measured by both parameters was greatest in the youngest infants and decreased during infancy. Our findings are consistent with the concept that younger infants have large airways relative to their V(L) and that V(L) increases more rapidly than airway caliber early in life.

Original languageEnglish (US)
Pages (from-to)835-838
Number of pages4
JournalAmerican journal of respiratory and critical care medicine
Issue number3
StatePublished - Jan 1 1999


ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine
  • Critical Care and Intensive Care Medicine

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