Effect of lung volume and positional changes on pulmonary diffusing capacity and its components.
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.
Stam
H
H
Department of Pulmonary Diseases, University Hospital Dijkzigt, Erasmus University, Rotterdam, The Netherlands.
Kreuzer
F J
FJ
Versprille
A
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D002196:Capillaries / Q000502:physiology; D002248:Carbon Monoxide; D005260:Female; D005652:Functional Residual Capacity; D006371:Helium; D006801:Humans; D008168:Lung / Q000033:anatomy & histology / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011187:Posture; D011650:Pulmonary Alveoli / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D012129:Respiratory Function Tests; D012727:Sex Characteristics; D012907:Smoking / Q000503:physiopathology
D006371:Helium; D002248:Carbon Monoxide