Continuous distributions of specific ventilation recovered from inert gas washout.

We describe a new technique for recovering continuous distributions of ventilation (V) 
as a function of tidal ventilation/volume ratio (V/V0) from the nitrogen 
washout. The analysis yields a continuous distribution of V as a 
function of V/V0 represented as fractional ventilations of 50 compartments plus 
dead space. The procedure was verified by recovering known distributions from 
data to which noise had been added. Using an apparatus to 
control the subject's tidal volume and FRC, mixed expired N2 data 
gave the following results: a) the distributions of young, normal subjects 
were narrow and unimodal with a mean ln standard deviation of 
0.56 plus or minus 0.13; b) those of subjects over age 
40 were broader (ln SD 0.86 plus or minus 0.19) with 
more poorly ventilated units; c) patients with pulmonary disease of all 
descriptions showed enlarged dead space; d) patients with cystic fibrosis showed 
multimodal distributions with the bulk of the ventilation going to overventilated 
units; and e) patients with obstructive lung diseases fell into several 
classes, three of which are illustrated. These results suggest that our 
approach is well suited for clinical investigation. 