Distribution function of the clearance time constant in lungs.

Abstract

In healthy subjects and patients with chronic obstructive lung disease intrapulmonary helium clearance was measured by the open-circuit method after 20 min. of helium breathing. The clearance curve was found to be expressed in the Laplace transform of the distribution function of the clearance time constant. The distribution function was obtained graphically, using an approximation method to solve the inverse Laplace transform. In normal subjects the log distribution function curve had maximum peak point in time constant about 0.5 min. with roughly symmetrical shape with respect to the time constant of the maximum, whereas the spectra in emphysematous patients showed much flat function with 1 or 2 maximum points of much higher time constant.