title: Absence of diurnal variability of airway reactivity and hypoxic ventilatory drive in adolescents with stable asthma.
abstract: BACKGROUND
  Symptoms from asthma are often prominent at night. In adults significant circadian variation has been shown with reduced peak expiratory flow rates and increased bronchial reactivity to methacholine in the early morning hours. Because adolescence is the age group with the greatest increase in asthma-related deaths in the 1980s, we hypothesized that adolescents might be susceptible to circadian variation of airway reactivity.
  
  
  OBJECTIVE
  We sought to measure circadian variation of reactivity to methacholine (PC20) and hypoxic ventilatory drive (HVD), both of which would accentuate asthma that occurs at night and may predispose to death.
  
  
  METHODS
  Sixteen children with asthma of various severity, aged 9 to 18 years, were studied at 4 PM and again at 4 AM to define circadian variation in FEV1, PC20, and HVD. Eleven children were studied on a second day 4 to 10 weeks after the first study.
  
  
  RESULTS
  There was no systematic variation between 4 PM and 4 AM for FEV1 (P =.69), PC20 (P =.94), or HVD (P =.47). Six of the 16 children had PC20 values that were greater than 2-fold different between 4 PM and 4 AM; 3 of these were more reactive (requiring less methacholine) at 4 PM, and 3 were more reactive at 4 AM. At the second study, results were similar, with no systematic variation. Diurnal variability for PC20 was not consistent over the 2 study days, and at the second study all children with diurnal variability were more reactive at 4 PM.
  
  
  CONCLUSIONS
  These data on airway reactivity, HVD, and other measures modulated by cholinergic neural mechanisms do not identify any systematic diurnal variation that would place an adolescent at risk for nighttime problems with asthma.
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000503:physiopathology*; D016535:Bronchial Hyperreactivity / Q000503:physiopathology*; D001985:Bronchial Provocation Tests; D002648:Child; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D016210:Methacholine Chloride; D012720:Severity of Illness Index; D014630:Vagus Nerve / Q000502:physiology