title: Nocturnal asthma monitoring by chest wall electromyography.
abstract: BACKGROUND
  Patients with suboptimal asthma control often have nocturnal symptoms which wake them, causing sleep fragmentation.
  
  
  OBJECTIVE
  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 (EMG(para)) 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/m(2), 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/m(2), 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, EMG(para)%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 EMG(para) inversely reflect changes in pulmonary function tests. Measuring the EMG(para) offers a method to monitor asthma breath-by-breath while subjects are asleep, which could be adapted for home use.
authors.affiliation: King's College London School of Medicine, Chest Unit, 2nd floor Cheyne Wing, Denmark Hill, London SE5 9RS, UK. joerg.steier@kcl.ac.uk
authors.forename: Joerg
authors.initials: J
authors.lastname: Steier
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Jolley
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
authors.forename: John
authors.initials: J
authors.lastname: Moxham
mesh_terms: D000293:Adolescent; D000328:Adult; D001249:Asthma / Q000150:complications / Q000503:physiopathology*; D002940:Circadian Rhythm / Q000502:physiology; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D007366:Intercostal Muscles / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D010366:Peak Expiratory Flow Rate / Q000502:physiology; D017286:Polysomnography / Q000379:methods; D012129:Respiratory Function Tests; D012890:Sleep / Q000502:physiology*; D012893:Sleep Wake Disorders / Q000209:etiology / Q000503:physiopathology; D055815:Young Adult