title: Time constant of inspiratory muscle relaxation in cystic fibrosis.
abstract: BACKGROUND
  Patients with cystic fibrosis (CF) are at increased risk of inspiratory muscle fatigue and respiratory failure. The time constant (τ) of the inspiratory muscle relaxation is a simple bedside test of muscle fatigue. We have compared patients with CF and healthy controls regarding τ and hypothesized that it is negatively associated with severity of lower airway obstruction.
  
  
  METHODS
  For this cross-sectional study, τ after maximal inspiration and spirometric indices (forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC)) were measured.
  
  
  RESULTS
  Fifty-three CF patients (median age 14 y (interquartile range: 11-19.5)) and 53 age- and sex-matched healthy control subjects (14 y (11-19.5)) were recruited. Application of a general linear model revealed that health status (CF vs. non-CF) had a significant effect on τ (P < 0.001), but age group and the interaction of age group with health status did not have significant effects on τ (P = 0.10 and P = 0.71, respectively). Participants with CF had significantly higher τ (253 (188-406)) than control subjects (117 (81-185)) (P < 0.001) and τ was negatively related to FEV1 (r = -0.205; P = 0.031) and FVC (r = -0.294; P = 0.002).
  
  
  CONCLUSIONS
  Patients with CF have higher τ than healthy controls but the correlation of τ with expiratory flow function is modest.
authors: Department of Pediatrics, University of Patras School of Medicine, Patras, Greece.
authors: Theodore
authors: T
authors: Dassios
authors: First Department of Pediatrics, University of Athens School of Medicine, Athens, Greece.
authors: Athanasios
authors: A
authors: Kaditis
authors: Cystic Fibrosis Center, Aghia Sophia Children's Hospital, Athens, Greece.
authors: Anna
authors: A
authors: Katelari
authors: First Department of Pediatrics, University of Athens School of Medicine, Athens, Greece.
authors: George
authors: G
authors: Chrousos
authors: Cystic Fibrosis Center, Aghia Sophia Children's Hospital, Athens, Greece.
authors: Stavros
authors: S
authors: Doudounakis
authors: Department of Pediatrics, University of Patras School of Medicine, Patras, Greece.
authors: Gabriel
authors: G
authors: Dimitriou
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D003430:Cross-Sectional Studies; D003550:Cystic Fibrosis / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D009126:Muscle Relaxation / Q000502:physiology*; D012132:Respiratory Muscles / Q000503:physiopathology; D013147:Spirometry; D013997:Time Factors; D014797:Vital Capacity; D055815:Young Adult