Xenon and nitrogen single-breath washout curves in patients with airway obstruction

Abstract

In patients with chronic obstructive lung disease, we determined single-breath N2 and 133 Xe washout curves, and regional distributions of volumes (Vr) and of 133Xe boluses inhaled at residual volume (VIRV). Patients suffering from emphysema with minimal airway obstruction demonstrated large closing volumes and apicobasal distribution gradients, apparently because of a steep pulmonary recoil pressure-volume curve. In one subject with basal small airway disease there was no vertical gradient in regional residual volume; closing volume was increased with the 133Xe technique but almost absent with the N2 technique. Patients with moderate-to-severe airway obstruction had upward-sloping alveolar plateaus without distinct phase IV, and small apicobasal differences in Vr and VIRV. The latter resulted probably from increased regional differences in time constants counteracting the influence of gravity. Finally, patients with severe airway obstruction and basal emphysema demonstrated a rising N2 but a descending 133Xe plateau; the gradient for VIRV was normal, and reversed for Vr. This pattern was attributed to nongravitational differences in time constants causing a first in-first out distribution.

Emphysema with Minor Airway Obstruction and Abnormal Tests of Small Airway Disease

“…5). In contrast, the latter gradient tends to decrease in small airway disease, where basal airways close off at a high regional volume [11]. Similar ly, the steeper alveolar plateau on the wash out curve observed in our patients may be explained by the altered shape of the Pst-V curve and the resulting large apicobasal vol ume gradient for RV [30].…”

“…In fact, this is not unexpected and can be attributed to the loss of elastic recoil. It is well known that CV is influenced by a decrease of the re tractive forces of the lungs [11,14], as well as by intrinsic small airway lesions [17], It is likely that the mechanism responsible for the higher CV is the increased steepness of the Pst-V curve rather than an abnormal collapsibility of the small airways (due, for instance, to a loss of support). Indeed, in the latter case one would expect an increase in Rus for a given Pst value.…”

“…Indeed, in the latter case one would expect an increase in Rus for a given Pst value. A steeper Pst-V curve will result, in the presence of a normal vertical pleural pressure gradient, in a larger apicobasal volume gradient and an enhanced sequential ventilation in the mid volume level [11]; therefore, basal airway closure may occur at a normal regional vol ume (while it occurs at a high regional vol ume in the presence of intrinsic disease or lack of support of the small airways) and appear at an increased overall lung volume on the single breath washout curve. This ex planation is substantiated by the observa tion of a high apicobasal gradient in region al RV in our subjects ( fig.…”

Comparison of ¹³³Xe Washout Curves after Bolus Inhalation, Perfusion, and Equilibration

“…Finally, the apico-basal distributions of venti lation index (V,), perfusion index (0,), V/Q ra tio, and residual volume (RV/TLC) were mea sured with methods described previously [Demedts et al, 1975[Demedts et al, , 1976,…”

Mechanics of the Lung in the 20th Century

“…Several experimental studies in humans have provided good evidence of airway closure at volumes below FRC (18, 35). The functional effect of airway closure was also assessed in humans by measuring the “closing volume,” an index initially derived from the tail of a washout of tracer gas (30, 81), and later from the tail of the nitrogen washout curve (29), a procedure first described in 1949 by Ward Fowler (40). This index was used for the early detection of small airways disease (17, 99), since it was assumed that the sudden change in slope represented the start of airway closure.…”