title: Diurnal Variation in Peak Expiratory Flow and Forced Expiratory Volume.
abstract: BACKGROUND
  Diurnal variability in airways has most commonly been reported using peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1). Characteristics of variability in small, mid and large airways caliber are expected to be different but have not been studied.
  
  
  OBJECTIVE
  The aim of the study was to assess diurnal variation in small mid and large airways caliber using FEF25, FEF50, FEF75 and FEF25-75 along with PEF and FEV1 in healthy subjects.
  
  
  METHODS
  Spirometry was performed in 161 healthy subjects twice in a day. Diurnal variability in FEF25, FEF50, FEF75, FEF25-75, PEF and FEV1 were determined and compared.
  
  
  RESULTS
  It revealed that all parameters exhibit significant diurnal variability. Diurnal variability is highest in large airways and lowest in smaller airways.
  
  
  CONCLUSIONS
  Proximal airways show greater diurnal variation in their caliber than distal airways as reflected by greater variability in PEF as compared to FEV1.
authors.affiliation: Assistant Professor, Department of Physiology, All India Institute of Medical Science , Rishikesh, Uttarakhand, India .
authors.forename: Arun
authors.initials: A
authors.lastname: Goel
authors.affiliation: Assistant Professor, Department of Physiology, All India Institute of Medical Science , Bhubaneswar, Odisha, India .
authors.forename: Manish
authors.initials: M
authors.lastname: Goyal
authors.affiliation: Assistant Professor, Department of Physiology, All India Institute of Medical Science , Bhopal, MP, India .
authors.forename: Ruchi
authors.initials: R
authors.lastname: Singh
authors.affiliation: Professor, Department of Physiology, King George's Medical University , Lucknow, UP, India .
authors.forename: Narsingh
authors.initials: N
authors.lastname: Verma
authors.affiliation: Professor & Head, Department of Physiology, King George's Medical University , Lucknow, UP, India .
authors.forename: Sunita
authors.initials: S
authors.lastname: Tiwari
keywords: Airways; Diurnal variability; FEV; FEV1; PEF