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# The association of tidal EFL with exercise performance, exacerbations, and death in COPD

Dove Medical Press

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### Abstract

##### Background

Tidal expiratory flow limitation (EFL T) is frequently found in patients with COPD and can be detected by forced oscillations when within-breath reactance of a single-breath is ≥0.28 kPa·s·L −1. The present study explored the association of within-breath reactance measured over multiple breaths and EFL T with 6-minute walk distance (6MWD), exacerbations, and mortality.

##### Methods

In 425 patients, spirometry and forced oscillation technique measurements were obtained on eight occasions over 3 years. 6MWD was assessed at baseline and at the 3-year visit. Respiratory symptoms, exacerbations, and hospitalizations were recorded. A total of 5-year mortality statistics were retrieved retrospectively. We grouped patients according to the mean within-breath reactance $( Δ Xrs ¯ )$ , measured over several breaths at baseline, calculated as mean inspiratory–mean expiratory reactance over the sampling period. In addition to the established threshold of EFL T, an upper limit of normal (ULN) was defined using the 97.5th percentile of $Δ Xrs ¯$ , of the healthy controls in the study; 6MWDs were compared according to $Δ Xrs ¯$ , as normal, ≥ ULN < EFL T, or ≥ EFL T. Annual exacerbation rates were analyzed using a negative binomial model in the three groups, supplemented by time to first exacerbation analysis, and dichotomizing patients at the ULN.

##### Results

In patients with COPD and baseline $Δ Xrs ¯$ below the ULN (0.09 kPa·s·L −1), 6MWD was stable. 6MWD declined significantly in patients with $Δ Xrs ¯ ≥ ULN$ . Worse lung function and more exacerbations were found in patients with COPD with $Δ Xrs ¯ ≥ ULN$ , and patients with $Δ Xrs ¯ ≥ ULN$ had shorter time to first exacerbation and hospitalization. A significantly higher mortality was found in patients with $Δ Xrs ¯ ≥ ULN$ and FEV 1 >50%.

##### Conclusion

Patients with baseline $Δ Xrs ¯ ≥ ULN$ had a deterioration in exercise performance, more exacerbations, and greater hospitalizations, and, among those with moderate airway obstruction, a higher mortality. $Δ Xrs ¯$ is a novel independent marker of outcome in COPD.

### Most cited references27

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### Prevalence and outcomes of diabetes, hypertension and cardiovascular disease in COPD.

(2008)
Chronic obstructive pulmonary disease (COPD) is associated with important chronic comorbid diseases, including cardiovascular disease, diabetes and hypertension. The present study analysed data from 20,296 subjects aged > or =45 yrs at baseline in the Atherosclerosis Risk in Communities Study (ARIC) and the Cardiovascular Health Study (CHS). The sample was stratified based on baseline lung function data, according to modified Global Initiative for Obstructive Lung Disease (GOLD) criteria. Comorbid disease at baseline and death and hospitalisations over a 5-yr follow-up were then searched for. Lung function impairment was found to be associated with more comorbid disease. In logistic regression models adjusting for age, sex, race, smoking, body mass index and education, subjects with GOLD stage 3 or 4 COPD had a higher prevalence of diabetes (odds ratio (OR) 1.5, 95% confidence interval (CI) 1.1-1.9), hypertension (OR 1.6, 95% CI 1.3-1.9) and cardiovascular disease (OR 2.4, 95% CI 1.9-3.0). Comorbid disease was associated with a higher risk of hospitalisation and mortality that was worse in people with impaired lung function. Lung function impairment is associated with a higher risk of comorbid disease, which contributes to a higher risk of adverse outcomes of mortality and hospitalisations.
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### The forced oscillation technique in clinical practice: methodology, recommendations and future developments.

(2003)
The forced oscillation technique (FOT) is a noninvasive method with which to measure respiratory mechanics. FOT employs small-amplitude pressure oscillations superimposed on the normal breathing and therefore has the advantage over conventional lung function techniques that it does not require the performance of respiratory manoeuvres. The present European Respiratory Society Task Force Report describes the basic principle of the technique and gives guidelines for the application and interpretation of FOT as a routine lung function test in the clinical setting, for both adult and paediatric populations. FOT data, especially those measured at the lower frequencies, are sensitive to airway obstruction, but do not discriminate between obstructive and restrictive lung disorders. There is no consensus regarding the sensitivity of FOT for bronchodilation testing in adults. Values of respiratory resistance have proved sensitive to bronchodilation in children, although the reported cutoff levels remain to be confirmed in future studies. Forced oscillation technique is a reliable method in the assessment of bronchial hyperresponsiveness in adults and children. Moreover, in contrast with spirometry where a deep inspiration is needed, forced oscillation technique does not modify the airway smooth muscle tone. Forced oscillation technique has been shown to be as sensitive as spirometry in detecting impairments of lung function due to smoking or exposure to occupational hazards. Together with the minimal requirement for the subject's cooperation, this makes forced oscillation technique an ideal lung function test for epidemiological and field studies. Novel applications of forced oscillation technique in the clinical setting include the monitoring of respiratory mechanics during mechanical ventilation and sleep.
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### Author and article information

###### Journal
Int J Chron Obstruct Pulmon Dis
Int J Chron Obstruct Pulmon Dis
International Journal of COPD
International Journal of Chronic Obstructive Pulmonary Disease
Dove Medical Press
1176-9106
1178-2005
2017
26 July 2017
: 12
: 2179-2188
###### Affiliations
[1 ]Department of Clinical Science, University of Bergen
[2 ]Department of Thoracic Medicine, Haukeland University Hospital, Bergen, Norway
[3 ]Clinical Science Centre, University Hospital Aintree, Liverpool, UK
[4 ]LDS Hospital, Pulmonary Division, Salt Lake City, UT, USA
[5 ]TBM-Lab, Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano University, Milano, Italy
###### Author notes
Correspondence: Bernt Boegvald Aarli, Department of Thoracic Medicine, Postboks 1400, Haukeland University Hospital, 5021 Bergen, Norway, Tel +47 9203 7838, Email bernt_aarli@ 123456me.com
###### Article
copd-12-2179
10.2147/COPD.S138720
5536237
© 2017 Aarli et al. This work is published and licensed by Dove Medical Press Limited

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###### Categories
Original Research

Respiratory medicine