Neural respiratory drive in healthy subjects and in chronic obstructive pulmonary disease

¹ King's College London School of Medicine, King's College Hospital
² Guangzhou Institute of Respiratory Diseases, Guangzhou Medical College, State Key Laboratory of Respiratory Disease, Guangzhou, China
³ Royal Brompton Hospital, London, UK

^* To whom correspondence should be addressed. E-mail: caroline.jolley{at}kcl.ac.uk.

	Abstract

We aimed to use the diaphragm electromyogram (EMG_di) to compare levels of neural respiratory drive (NRD) in a cohort of healthy subjects and COPD patients, and to investigate the relationship between NRD and pulmonary function in COPD.

EMG_di was recorded at rest and normalised to peak EMG_di recorded during maximum inspiratory manoeuvres (EMG_di%max) in 100 healthy subjects and 30 patients with COPD, using a multipair oesophageal electrode. EMG_di was normalised to the amplitude of the diaphragm compound muscle action potential (CMAP_diMS) in 64 healthy subjects.

EMG_di%max was 9.0 (3.4)% in healthy subjects and 27.9 (9.9)% in COPD (p<0.001), and correlated with %predicted FEV₁ (r²=0.40, p<0.001), VC (r²=0.61, p<0.001), and inspiratory capacity (r²=0.28, p=0.02) in patients. EMG_di%max was higher in healthy 51–80 year olds than 18–50 year olds (11.4 (3.4) vs 8.2 (2.9) %, p<0.001). Observations in the healthy group were similar when peak EMG_di or CMAP_diMS were used to normalise EMG_di.

Levels of NRD were higher in COPD than healthy subjects, and related to disease severity. CMAP_diMS could be used to normalise EMG_di if volitional inspiratory manoeuvres cannot be performed, allowing translation of the technique to critically-ill and ventilated patients.