Lung emptying patterns in diffuse obstructive pulmonary syndromes

Abstract

A lung model that analyzes an 18-breath washout for the distribution of ventilation, the functional residual capacity, the dead-space volume and the pattern of compartmental emptying, has been used in a study of normal subjects and those with irreversible obstructive pulmonary syndromes. Lung compartments are defined in terms of their alveolar dilution ratio (ω) as determined from endtidal nitrogen concentrations. Simulating the nitrogen washout at specific volumes expired in each breath gives the contribution at that volume coming from each compartment. Dead space is treated as one of these compartments, having a dilution ratio of zero. The emptying pattern in subjects with moderate and severe obstructive syndromes is altered when compared with that of normals. Dead space is not delivered within one tidal volume and the late delivery served to distinguish normal subjects from those with an obstructive syndrome. The relative flow from compartments other than dead space progressively increases throughout expiration in severe obstructive syndromes. The nitrogen rise on the alveolar plateau with normal tidal volumes in obstructive syndromes is principally a function of the dead-space delivery. On the average, the flow from the well-ventilated compartment increased throughout expiration in those with obstructive syndromes, whereas it fell off from an early peak in normal subjects.