Airway distensibility in normal and asthmatic subjects and partitioning of the Fowler dead space

Authors

David P. Johns
Graham Burns
David W. Reid
Justin Walls
Michael Maskrey
E Haydn Walters, University of Notre Dame AustraliaFollow

Publication Details

Johns, D. P., Burns, G., Reid, D. W., Walls, J., Maskrey, M., & Walters, E. (2006). Airway distensibility in normal and asthmatic subjects and partitioning of the Fowler dead space. Applied Physiology, Nutrition and Metabolism, 31(4), 460-466. doi:10.1139/H06-019

Abstract

Anatomical dead space measured by the Fowler method (VD_F) is the sum of 2 serial volume compartments (VD_F = VD_p1 + VD_p2). VD_F has been shown to increase linearly with end-inspiratory lung volume (EILV) and the gradient of the relationship (ΔVD_F) has been used as an index of airway distensibility. The aim of this study was to partition VD_F into its serial compartments VD_p1 and VD_p2 to test the hypothesis that, given the greater distensibility of distal airways, VD_p2 would demonstrate greater volume dependence than VD_p1. The relationships between each measure of VD (VD_F, VD_p1, and VD_p2) and EILV were studied in 16 healthy subjects and 16 mildly asthmatic subjects. Significant (p < 0.05) linear relationships were obtained between each measure of VD and EILV in both subject groups. Changes in VD_p1 with EILV (ΔVD_p1) accounted for 78.6% ± 5.6% (mean ± SEM) and 72.6% ± 6.3% of ΔVD_F in the healthy and asthmatic groups, respectively. ΔVD_p1 was greater in the healthy subjects than in asthmatic subjects (18.4 versus 13.1 mL/L, p = 0.005). We conclude that in both asthmatic and healthy subjects, the major component of ΔVD_F was ΔVD_p1 and not ΔVD_p2, as originally hypothesized. We believe our results are reflecting the degree of asynchronous airway emptying.

Keywords

peer-reviewed