Using Spirometry to Rule Out Restriction in Patients with Concomitant Low Forced Vital Capacity and Obstructive Pattern
Imran Khalid*, 1, Zachary Q Morris2, Tabindeh J Khalid1, 3, Amina Nisar4, Bruno DiGiovine5
Identifiers and Pagination:Year: 2011
First Page: 44
Last Page: 50
Publisher Id: TORMJ-5-44
Article History:Received Date: 20/12/2010
Revision Received Date: 2/5/2011
Acceptance Date: 18/5/2011
Electronic publication date: 23/6/2011
Collection year: 2011
open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.
Different formulas have been proposed to exclude restriction based on spirometry, however none of them have specifically tested the patients whose spirometry show both obstruction and a low forced vital capacity (FVC).
The study was designed to create an algorithm that would better predict the absence of restriction in such patients.
Retrospective analysis of prospectively collected data.
A cohort of consecutive adults that underwent complete pulmonary function testing from 2002-2004 was analyzed. The data was randomly split into two groups to allow for derivation and then validation of a predictive formula. Patients were randomly assigned into either a “derivation” or “validation” group. In the derivation group, stepwise logistic regression was used to determine a formula and optimal cut-off value for the variable with the best discriminative capacity. The formula was applied subsequently to the validation group to test the results and compared to previously published formula.
The study group contained 766 patients. We determined that the variable with the highest association with TLC was [(FEV1/FVC) % predicted/FVC % predicted]. A value of ≥1.11 was found to be the maximal cutoff to predict the absence of restriction.
The formula was applied to a validation group (n=397) and performed better than prior published algorithm with a sensitivity, specificity, positive predictive value and negative predictive value of 95%, 44%, 22%, and 98%, respectively.
Our formula performs superior to the previously published algorithms in patients with concomitant low FVC and obstruction to exclude restriction.