Distribution function of lung volume and ventilation determined by lung N2 washout.

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Abstract
The continuous distribution function of lung volume and ventilation was determined by hing N2 washout in 6 healthy subjects and 5 patients showing signs of diffuse obstructive pulmonary syndrome. If the lung N2 elimination curve, measured from mixed expired gas, is the summation of the N2 volume washout curve of each alveolus, it can be represented by an equation similar to the Laplace transform of N(S). To obtain the distribution of lung volume as a function of clearance time constant (T), the Laplace transform is inverted with the aid of an approximation method. The distribution of ventilation as a function of T was determined from the relationship between lung volume and time constant. In normal subjects the frequency distribution curves of lung volume and ventilation are symmetrical with a relatively narrow base. The maximum frequency of both curves is located between 0.35 and 0.60 min. In patients with diffuse pulmonary obstructive syndrome the highest frequency of the lung volume distribution is shifted toward the longer time constants and the range of distribution is much larger than in normal subjects. The ventilation distribution function does not correspond to the lung volume distribution.