Impairments in the neural control of the respiratory muscles in breathing and swallowing have been a key discovery of these projects. This will enable the application of existing- and new- treatments to improve respiratory motor impairments including dyspnoea, to mitigate the burden of disease for people with COPD. For example, inefficient and dis-coordinated control of the respiratory muscles for ventilation in COPD could be targeted with physiotherapy or biofeedback to restore the usual pattern of respiratory muscle activity and function.
Respiratory muscle coordination. A proof-of concept study showed that in healthy participants, voluntary changes in the pattern of breathing can increase muscle activity for some respiratory muscles, but without a corresponding increase in ventilation. This suggests that there can be dis-coordinated and inefficient muscle activity (i.e. muscle activity that is not translated to an increase in ventilation) which will be explored in COPD.
Coupling between respiratory muscle mechanics and activity. A validation study was conducted using computed tomography (CT) images and a novel algorithm to track rib movement during changes in lung volume. Rib motion over large changes in lung volume was less in participants with COPD, but when differences in respiratory function (i.e. lung capacity) were accounted for, rib motion was comparable to participants without COPD. These findings can be used to validate measures of respiratory muscle mechanics in COPD using ultrasound, a technique under development to assess respiratory muscle mechanics. Ultrasound was used to assess changes in muscle length of the intercostal muscles in 10 young healthy adults and these measures will be performed in COPD. A non-invasive method to determine how the muscle activity in the different regions of the intercostal muscles changes in COPD is also being developed and will be correlated with measures of muscle mechanics.
Abnormal cortical contribution to quiet breathing in COPD. Using measures of brain activity (electroencephalography; EEG), it was determined that age, rather than COPD, was the factor associated with an abnormal cortical contribution in the control of quiet breathing. When breathing was made harder with an added external load to breathing, an abnormal cortical contribution was associated with higher ratings of dyspnoea (the sensation of breathlessness) in all participants. These data suggest that impaired neural control of breathing in older participants with COPD has implications for dyspnoea during quiet breathing and when breathing becomes loaded (e.g. during exercise).
Respiratory sensation in COPD. This large study on altered respiratory sensation in COPD is still underway as it was delayed due to covid-19. To date, data has been collected from 16 participants with COPD and 11 healthy age-matched control participants for the assessment of dyspnoea using load magnitude estimation. To assess abnormal central processing of respiratory sensations using EEG, data were collected from 11 participants with COPD, 3 healthy age-matched controls and 15 healthy young controls.
Reflex control of respiratory muscles and swallowing impairment in COPD. When the airway is blocked briefly during inspiration, there is inhibition of on-going muscle activity that is thought to protect the airway against aspiration. It was found that this inhibition is longer in COPD and older adults compared to younger controls. There was no differential tongue weakness in COPD compared to elderly controls, but in COPD, signs of airway invasion during swallowing of liquids were observed, which were associated with a delayed inhibitory reflex in inspiratory muscles.