Abstract
Many patients with severe chronic obstructive pulmonary disease (COPD) report an unpleasant respiratory sensation at rest, which is further amplified by adoption of a supine position (orthopnoea). The mechanisms of this acute symptomatic deterioration are poorly understood.
Sixteen patients with advanced COPD and a history of orthopnoea and 16 age- and sex-matched healthy controls underwent pulmonary function tests (PFTs) and detailed sensory–mechanical measurements including inspiratory neural drive (IND) assessed by diaphragm electromyography (EMGdi), oesophageal pressure (Pes) and gastric pressure (Pga), in both sitting and supine positions.
Patients had severe airflow obstruction (forced expiratory volume in 1 s (FEV1): 40±18% pred) and lung hyperinflation. Regardless of the position, patients had lower inspiratory capacity (IC) and higher IND for a given tidal volume (VT) (i.e. greater neuromechanical dissociation (NMD)), higher intensity of breathing discomfort, higher minute ventilation (V′E) and higher breathing frequency (fB) compared with controls (all p<0.05). For controls in a supine position, IC increased by 0.48 L versus sitting erect, with a small drop in V′E, mainly due to reduced fB (all p<0.05). By contrast, IC remained unaltered in patients with COPD, but dynamic lung compliance (CLdyn) decreased (p<0.05) in the supine position. Breathing discomfort, inspiratory work of breathing (WOB), inspiratory effort, IND, NMD and neuroventilatory uncoupling all increased in COPD patients in the supine position (p<0.05), but not in the healthy controls. Orthopnoea was associated with acute changes in IND (r=0.65, p=0.01), neuroventilatory uncoupling (r=0.76, p=0.001) and NMD (r=0.73, p=0.002).
In COPD, onset of orthopnoea coincided with an abrupt increase in elastic loading of the inspiratory muscles in recumbency, in association with increased IND and greater NMD of the respiratory system.
Abstract
Orthopnoea, a troublesome symptom in patients with severe COPD, is associated with increased neural drive to the diaphragm and heightened respiratory effort to compensate for abrupt augmentation of load–capacity imbalance of the inspiratory muscles https://bit.ly/2ZLvyiI
Footnotes
This article has an editorial commentary: https://doi.org/10.1183/13993003.04415-2020
This article has supplementary material available from erj.ersjournals.com
Author contributions: All authors played a role in developing the content and writing the manuscript. D.E. O'Donnell was the principal investigator and provided the original idea for the study. D.E. O'Donnell and A.F. Elbehairy had input into the study design and the conduct of the study. A.F. Elbehairy and H. McIsaac collected the data. A.F. Elbehairy and A. Faisal performed the data analysis and prepared it for presentation.
Parts of the data presented herein were presented as a poster presentation at the European Respiratory Society International Congress in Madrid, 2019 (https://doi.org/10.1183/13993003.congress-2019.PA879).
Conflict of interest: A.F. Elbehairy has nothing to disclose.
Conflict of interest: A. Faisal has nothing to disclose.
Conflict of interest: H. McIsaac has nothing to disclose.
Conflict of interest: N.J. Domnik has nothing to disclose.
Conflict of interest: K.M. Milne has nothing to disclose.
Conflict of interest: M.D. James has nothing to disclose.
Conflict of interest: J.A. Neder has nothing to disclose.
Conflict of interest: D.E. O'Donnell has nothing to disclose.
Support statement: The Canadian Respiratory Research Network (CRRN) is supported by grants from the Canadian Institutes of Health Research (CIHR) – Institute of Circulatory and Respiratory Health, the Canadian Lung Association (CLA)/Canadian Thoracic Society (CTS), the British Columbia Lung Association and the industry partners Boehringer Ingelheim Canada Ltd, AstraZeneca Canada Inc. and Novartis Canada Ltd. A.F. Elbehairy acknowledges the support of the European Respiratory Society (Fellowship LTRF 2019). The funders had no role in study design, data collection and analysis, or preparation of the manuscript. Funding information for this article has been deposited with the Crossref Funder Registry.
- Received March 18, 2020.
- Accepted September 15, 2020.
- Copyright ©ERS 2021.