STRUCTURE-FUNCTION IN SMOKERS : WHEN A SMALL AIRWAYS TEST REALLY REFLECTS THE SMALL AIRWAYS

• Published in: Journal of applied physiology (1985) Vol. 137; no. 2; pp. 343 - 348
• Main Authors: Verbanck, Sylvia, Hanon, Shane, Vandemeulebroucke, Jef, Vanderhelst, Eef, Paiva, Manuel
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01-08-2024
• Subjects: Allergic diseases; Computed tomography; Convection; Diffusion rate; Exhalation; Gaseous diffusion; Heterogeneity; Lungs; Respiratory tract diseases; Smoking; Structure-function relationships; diffusion; qCT; small airways; smokers; multiple breath washout
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00209.2024

If Multiple Breath Washout (MBW) derived acinar ventilation heterogeneity (Sacin) really represents peripheral units, the N
phase-III of the first MBW exhalation should be curvilinear. This is due to the superposed effect of gas diffusion and convection resulting in an equilibration of N
concentrations between neighbouring lung units throughout exhalation. We investigated this in smokers with CT-proven functional small airway disease.
Instantaneous N
slopes were computed over 40ms intervals throughout phase-III and normalized by mean phase-III N
concentration. N
phase-III (concave) curvilinearity was quantified as the rate at which the instantaneous N
slope decreases past the phase-II peak over a 1s interval; for a linear N
phase-III unaffected by diffusion, this rate would amount to 0L
/s. N
phase-III curvilinearity was obtained on the experimental curves and on existing model simulations of N
curves from a normal peripheral lung model and one with missing terminal bronchioles (either 50% or 30% TB left).
In forty-six smokers (66 (
8) years; 49 (
26) packyears) with CT-evidence of peripheral lung destruction, instantaneous N
slope decrease was compared between those with (f
+f
)>20% (-0.26
0.14(SD) L
/s;n=24) and those with (f
+f
)<20% (-0.16
0.12(SD)L
/s;n=22) (P=0.014). Experimental values fell in the range predicted by a realistic peripheral lung model with progressive reduction of terminal bronchioles: values of instantaneous N
-slope decrease obtained from model simulations were -0.09L
/s (normal lung;100%TB left), -0.17L
/s (normal lung 50%TB left) and -0.29L
/s (30%TB left).
In smokers with CT-based evidence of functional small airways alterations, it is possible to demonstrate that Sacin really does represent the most peripheral airspaces.