Effect of lung volume and positional changes on pulmonary diffusing capacity and its components

J Appl Physiol (1985). 1991 Oct;71(4):1477-88. doi: 10.1152/jappl.1991.71.4.1477.


Normal subjects have a larger diffusing capacity normalized per liter alveolar volume (DL/VA) in the supine than in the sitting position. Body position changes total lung diffusing capacity (DL), DL/VA, membrane conductance (Dm), and effective pulmonary capillary blood volume (Qc) as a function of alveolar volume (VA). These functions were studied in 37 healthy volunteers. DL/VA vs. VA yields a linear relationship in sitting as well as in supine position. Both have a negative slope but usually do not run parallel. In normal subjects up to 50 yr old DL/VA and DL increased significantly when subjects moved from a sitting to a supine posture at volumes between 50 and 100% of total lung capacity (TLC). In subjects greater than 50 yr old the responses of DL/VA and DL to change in body position were not significant at TLC. Functional residual capacity (FRC) decreases and DL/VA increases in all normal subjects when they change position from sitting to supine. When DL/VA increases more than predicted from the DL/VA vs. VA relationship in a sitting position, we may infer an increase in effective Qc in the supine position. In 56% of the volunteers, supine DL was smaller than sitting DL despite a higher DL/VA at FRC in the supine position because of the relatively larger decrease in FRC. When the positional response at TLC is studied, an estimation obtained accidentally at a volume lower than TLC may influence results. Above 80% of TLC, Dm decreased significantly from sitting to supine. Below this lung volume the decrease was not significant. The relationship between Qc and VA was best described by a second-order polynomial characterized by a maximum Qc at a VA greater than 60% of TLC. Qc was significantly higher in the supine position than in the sitting position, but the difference became smaller with increasing age. In observing the sitting and supine positions, we saw a decrease in maximum Qc normalized per square meter of body surface area with age.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aging / physiology
  • Blood Volume / physiology
  • Capillaries / physiology
  • Carbon Monoxide
  • Female
  • Functional Residual Capacity
  • Helium
  • Humans
  • Lung / anatomy & histology
  • Lung / physiology*
  • Male
  • Middle Aged
  • Posture
  • Pulmonary Alveoli / physiology
  • Pulmonary Circulation / physiology
  • Pulmonary Diffusing Capacity / physiology*
  • Respiratory Function Tests
  • Sex Characteristics
  • Smoking / physiopathology


  • Helium
  • Carbon Monoxide