Background
Cystic fibrosis (CF) airway secretions are abnormal, contributing to decreased clearance
and a cycle of infection and inflammation. CF sputum properties may predict disease
progression. We hypothesized that sputum viscoelasticity and clearance abnormalities
would inversely correlate with pulmonary function during exacerbation and that sputum
properties would return to baseline after therapy.
Methods
We collected sputa longitudinally from 13 subjects with CF with moderate to severe
lung disease during both clinical stability and exacerbation. Dynamic rheology was
analyzed, using a cone-and-plate rheometer. Mucociliary clearability was measured
on mucus-depleted frog palate, cough clearability in a simulated cough machine, and
sputum hydration as percent solids was measured following lyophilization.
Results
Elastic modulus
G′ and viscous modulus
G′′ increased during exacerbation and returned to baseline levels with recovery (
P < .05 for both). Solid content did not change. Sputum mucociliary clearability decreased
during exacerbations (
P < .01) but not cough clearance. FEV
1 % predicted was inversely correlated with
G′ and
G′′ (
P < .01 for both). The regression slope of the natural log–transformed
G′ and
G′′ vs FEV
1 % predicted was statistically homogeneous among subjects (estimated common slope
m = –3.84,
P < .001 and m = –8.53,
P < .0001, respectively).
Conclusions
Among these subjects with CF, there is a striking identity of the slope defining the
relationship between ln
G′ or ln
G′′ and FEV
1. There are dramatic increases in dynamic viscosity and elasticity during a pulmonary
exacerbation with return to baseline at recovery. This suggests that sputum viscoelastic
properties are tightly associated with lung function and disease status.
Key Words
Abbreviations:
CF ( cystic fibrosis), CFTR ( cystic fibrosis transmembrane conductance regulator), G′ ( elastic or storage modulus), G′′ ( for ideal (Newtonian) liquids, the viscous or loss modulus), LMM ( linear mixed-effects model), PFT ( pulmonary function test)To read this article in full you will need to make a payment
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Article Info
Publication History
Published online: March 17, 2018
Footnotes
FUNDING/SUPPORT: This study was supported by the Denny Hamlin Foundation and by a CF Foundation development grant (B. K. R.).
Identification
Copyright
© 2018 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.