Nocturnal asthma monitoring by chest wall electromyography
- 1King's College London School of Medicine, King's Health Partners, London, UK
- 2NIHR Biomedical Research Unit at the Royal Brompton Hospital and Imperial College London, UK
- Correspondence to Joerg S Steier, King's College London School of Medicine, Chest Unit, 2nd floor Cheyne Wing, Denmark Hill, London SE5 9RS, UK;
- Received 30 September 2010
- Accepted 11 March 2011
- Published Online First 17 April 2011
Rationale Patients with suboptimal asthma control often have nocturnal symptoms which wake them, causing sleep fragmentation.
Objectives It was hypothesised that symptomatic patients were more accurately identified by measuring respiratory effort using chest wall electromyography than by pulmonary function testing.
Methods Nocturnal electrical activity of the parasternal intercostal muscles (EMGpara) in the second intercostal space was measured in subjects with controlled (diurnal peak expiratory flow (PEF) variability <20%, n=12) and uncontrolled (diurnal PEF variability >20%, n=12) asthma, and it was compared with that in normal subjects (n=12).
Results Subjects with controlled and uncontrolled asthma did not differ significantly in age (mean (SD) 42 (17) vs 46 (17) years, p=0.64), body mass index (BMI; 26.6 (2.9) vs 27.5 (3.5) kg/m2, p=0.48) or gender distribution (males:females, 6:6 vs 7:5, p=0.68); the normal subject group was younger (27 (11) years, p=0.011) and slimmer (BMI 21.1 (2.9) kg/m2, p<0.001). An elevated respiratory disturbance index (RDI) was associated with poor asthma control (RDI in normals 0.5 (0.9), in controlled asthma 4.0 (1.9), p<0.001, and in poorly controlled asthma 7.4 (4.3) h−1; p<0.021). Similarly, EMGpara%max (normals 4.9 (3.2)%max evening, 4.9 (3.5)%max morning) was higher in controlled asthma (7.2 (2.3)%max evening, 8.1 (4.0)%max morning, p=0.049) and higher still in uncontrolled asthma (16.8 (14.2)%max in the evening, 18.4 (11.6)%max in the morning, p<0.008).
Conclusions Nocturnal respiratory effort is increased in those with asthma and neural respiratory drive is more variable in patients with poorly controlled asthma. Changes in the EMGpara inversely reflect changes in pulmonary function tests. Measuring the EMGpara offers a method to monitor asthma breath-by-breath while subjects are asleep, which could be adapted for home use.
Funding The study was sponsored by Guy's & St Thomas' Hospital Charity, London, UK. MIP's salary is part funded by the NIHR Respiratory Biomedical research unit of the Royal Brompton and Harefield NHS trust and the National Heart & Lung Institute, Imperial College.
Competing interests None.
Ethics approval This study was conducted with the approval of the King's College Hospital Local Research Ethics Committee.
Provenance and peer review Not commissioned; externally peer reviewed.