Comparison of airway closure measured in vivo and from single-breath washout curve.
The volume of air trapped (Vat) in alveoli subtended by airways closed at residual volume (RV) was correlated with the volume of air left in the lungs at the start of airway closure (CC) in a clinical study of 13 patients with a variety of pulmonary disorders and 5 normal subjects. Vat was quantitated at RV from the in vivo distribution differences between 127Xe inspired as a bolus and again after equilibrium; CC was measured from the inflection point on the single-breath washout curve at the onset of phase IV. 127Xe activity was measured with a scintillation camera, and activity profiles were obtained for 28-45 consecutive 6.5-mm horizontal lung slices between base and apex. Three well-defined regions were found: A, in the upper lung, all of whose airways remained completely open; B, located above the base and containing both open and closed airways; and C, above the base, all of whose airways were closed. Of the Vat of 0.43 liter for the normals, 41% was located in region C. For the patients, the values were 59% of 0.59 liter. The relationship between the onset of phase IV and regional airway closure was confirmed for normals as well as patients. A statistically significant increase in closure was found for the patients over the normals. Excellent agreement was obtained between Vat/TLC (total lung capacity) and CC/TLC (r = 0.79, P less than 0.001) for normals as well as patients, and CC appears to reflect regional airway closure in both health and disease. Similar excellent agreement was obtained for the normals between lung height with closed airways and CC/TLC (r = 0.88, P less than 0.001). Vat appears to be the most important physiological determinant of phase IV, the value at RV representing the limiting case.
D000328:Adult; D000368:Aged; D000402:Airway Obstruction / Q000503:physiopathology*; D003011:Closing Volume; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008171:Lung Diseases / Q000503:physiopathology*; D008433:Mathematics; D008875:Middle Aged; D012115:Residual Volume; D012119:Respiration