title: A deep breath bronchoconstricts obese asthmatics.
abstract: BACKGROUND
  Asthma is characterized by the loss of a deep breath (DB)-induced bronchodilation and bronchoprotection. Obesity causes lung restriction and increases airway resistance, which may further worsen the capacity of a DB to induce bronchodilation; however, whether increasing BMI impairs the bronchodilatory response to a DB in asthmatics is unknown.
  
  
  METHODS
  The population consisted of 99 subjects, 87 with moderate to severe persistent asthma and 12 obese control subjects. Using transfer impedance we derived airway resistance (Raw). Participants breathed for 1 minute and took a slow DB followed by passive exhalation to functional residual capacity (FRC) and tidal breathing for another minute.
  
  
  RESULTS
  After a DB, obese asthmatics had the largest percent increase in Raw (median 9.8% interquartile range [IQR] 3.1-15.1), compared with overweight (6.5% IQR -1.3, 12.1) and lean (0.7% IQR -3, 7.9) asthmatics and obese controls (2.5% IQR -.6, 11) (p for trend = 0.008). The association between the percent increase in Raw after a DB and BMI as a continuous variable was significant (p = 0.02).
  
  
  CONCLUSIONS
  In obese, moderate to severe and poorly controlled asthmatics, a DB results in increased Raw. This phenomenon was not observed in leaner asthmatics of similar severity or in obese control subjects.
authors.affiliation: Asthma Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA. holguinf@upmc.edu
authors.forename: Fernando
authors.initials: F
authors.lastname: Holguin
authors.forename: Sushma
authors.initials: S
authors.lastname: Cribbs
authors.forename: Anne M
authors.initials: AM
authors.lastname: Fitzpatrick
authors.forename: Roland H
authors.initials: RH
authors.lastname: Ingram
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Jackson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000403:Airway Resistance / Q000502:physiology*; D001249:Asthma / Q000150:complications* / Q000503:physiopathology* / Q000628:therapy; D015992:Body Mass Index; D016084:Bronchoconstriction / Q000502:physiology*; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D005652:Functional Residual Capacity / Q000502:physiology; D006801:Humans; D001239:Inhalation / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications* / Q000503:physiopathology*; D050177:Overweight / Q000150:complications / Q000503:physiopathology; D015656:Respiratory Mechanics / Q000502:physiology*; D014797:Vital Capacity / Q000502:physiology; D055815:Young Adult