title: Distal airway dysfunction in obese subjects corrects after bariatric surgery.
abstract: BACKGROUND
  Obesity is frequently associated with respiratory symptoms despite normal large airway function as assessed by spirometry. However, reduced functional residual capacity and expiratory reserve volume are common and might reflect distal airway dysfunction. Impulse oscillometry (IOS) might identify distal airway abnormalities not detected using routine spirometry screening. Our objective was to test the hypothesis that excess body weight will result in distal airway dysfunction detected by IOS that reverses after bariatric surgery. The setting was a university hospital.
  
  
  METHODS
  A total of 342 subjects underwent spirometry, plethysmography, and IOS before bariatric surgery. Of these patients, 75 repeated the testing after the loss of 20% of the total body weight. The data from 47 subjects with normal baseline spirometry and complete pre- and postoperative data were analyzed.
  
  
  RESULTS
  IOS detected preoperative distal airway dysfunction despite normal spirometry findings by an abnormal airway resistance at an oscillation frequency of 20 Hz (4.75 ± 1.2 cm H2O/L/s), frequency dependence of resistance from 5 to 20 Hz (2.20 ± 1.6 cm H2O/L/s), and reactance at 5 Hz (-3.47 ± 2.1 cm H2O/L/s). Postoperatively, the subjects demonstrated 57% ± 15% excess weight loss. The body mass index decreased (from 44 ± 6 to 32 ± 5 kg/m2, P < .001). Improvements in functional residual capacity (from 59% ± 11% to 75% ± 20% predicted, P < .001) and expiratory reserve volume (from 41% ± 20% to 75% ± 20% predicted, P < .001) were demonstrated. Distal airway function also improved: airway resistance at an oscillation frequency of 20 Hz (3.91 ± .9, P < .001), frequency dependence of resistance from 5 to 20 Hz (1.17 ± .9, P < .001), and reactance at 5 Hz (-1.85 ± .9, P < .001).
  
  
  CONCLUSIONS
  The present study detected significant distal airway dysfunction despite normal preoperative spirometry findings. The effect of increased body weight was likely the main mechanism for these abnormalities. However, the inflammatory state of obesity or associated respiratory disease could also be invoked. These abnormalities improved significantly toward normal after weight loss. The results of the present study highlight the importance of bariatric surgery as an effective intervention in reversing these respiratory abnormalities.
authors.affiliation: André Cournand Pulmonary Physiology Laboratory, Division of Pulmonary, Critical Care and Sleep, Department of Medicine, Bellevue Hospital/New York University School of Medicine, New York, New York 10016, USA. beno.oppenheimer@nyumc.org
authors.forename: Beno W
authors.initials: BW
authors.lastname: Oppenheimer
authors.forename: Ryan
authors.initials: R
authors.lastname: Macht
authors.forename: Roberta M
authors.initials: RM
authors.lastname: Goldring
authors.forename: Alexandra
authors.initials: A
authors.lastname: Stabile
authors.forename: Kenneth I
authors.initials: KI
authors.lastname: Berger
authors.forename: Manish
authors.initials: M
authors.lastname: Parikh
mesh_terms: D000328:Adult; D050110:Bariatric Surgery / Q000379:methods*; D015992:Body Mass Index; D001982:Bronchial Diseases / Q000209:etiology* / Q000503:physiopathology / Q000601:surgery; D005260:Female; D006801:Humans; D010535:Laparoscopy / Q000379:methods*; D008297:Male; D009767:Obesity, Morbid / Q000150:complications / Q000503:physiopathology / Q000601:surgery*; D009991:Oscillometry; D011182:Postoperative Care; D011300:Preoperative Care; D012120:Respiration Disorders / Q000209:etiology* / Q000503:physiopathology / Q000601:surgery; D012129:Respiratory Function Tests; D012189:Retrospective Studies; D013147:Spirometry; D015431:Weight Loss