Journal of Applied Physiology, Vol 48, Issue 2 265-272, Copyright © 1980 by American Physiological Society
A new method for analyzing multiple-breath nitrogen washout curves
R. W. Light, R. B. George, G. R. Meneely, L. J. Chouest and R. H. Rosekrans
Multiple-breath nitrogen washout (MBNW) curves from 39 normal and 45
patients with varying degrees of airway obstruction were analyzed with the
following equation: log log [(F0N2 - F infinity N2)/(FN2 - F infinity N2)]
= B log (V/FRC) +A, where F0N2 is the initial, F infinity N2 is the
equilibrium, and FN2 is the end-tidal fractional nitrogen concentration
after a volume (V) of air in liters have been exchanged, and FRC is the
measured functional residual capacity of the individual. All 84 curves were
well described with the equation when all points corresponding to FN2 below
0.40 were used. The coefficient of determination (r2) exceeded 0.990 in
56/84 (67%) of the transformed curves and the lowest coefficient of
determination was 0.946. This suggests that the MBNW can be described by
two numbers, B called the index of uniformity, and A the index of
efficiency. The ability of these two indices and the lung clearance index
(LCI) to identify individuals as abnormal and to separate groups with
varying degrees of airway obstruction was compared. B identified more
individuals (33/45) as abnormal than did A(15/45) or LCI (19/45). B was
also superior to A or LCI in separating groups with varying degrees of
airway obstruction. This analysis allows the complex MBNW curve to be
described by two numbers that vary depending on the degree of airway
obstruction.
