title: The effects of body mass index on lung volumes.
abstract: BACKGROUND
  Obesity is a major health issue in North America, and the trend is for obesity to be a more important medical issue in the future. Since obesity can cause respiratory symptoms, many obese people are referred for pulmonary function tests (PFTs). It is well known that obesity causes decreases in lung volumes, but there has never been a large study showing the correlation between body mass index (BMI) and the various lung volumes.
  
  
  METHODS
  We collected PFT results from 373 patients sent for lung function testing who had normal values for airway function but a wide range of BMIs.
  
  
  METHODS
  The PFTs were done in two accredited outpatient laboratories.
  
  
  RESULTS
  There were significant linear relationships between BMI and vital capacity and total lung capacity, but the group mean values remained within the normal ranges even for morbidly obese patients. However, functional residual capacity (FRC) and expiratory reserve volume (ERV) decreased exponentially with increasing BMI, such that morbid obesity resulted in patients breathing near their residual volume. An important finding was that the greatest rates of change in FRC and ERV occurred in the overweight condition and in mild obesity. At a BMI of 30 kg/m2, FRC and ERV were only 75% and 47%, respectively, of the values for a lean person with a BMI of 20 kg/m2.
  
  
  CONCLUSIONS
  We showed that BMI has significant effects on all of the lung volumes, and the greatest effects were on FRC and ERV, which occurred at BMI values < 30 kg/m2. Our results will assist clinicians when interpreting PFT results in patients with normal airway function.
authors.affiliation: Pulmonary Division, University of Alberta, Edmonton, AB, Canada T6G 2B7. rjones@cha.ab.ca
authors.forename: Richard L
authors.initials: RL
authors.lastname: Jones
authors.forename: Mary-Magdalene U
authors.initials: MM
authors.lastname: Nzekwu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D005105:Expiratory Reserve Volume / Q000502:physiology; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D005652:Functional Residual Capacity / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008168:Lung / Q000473:pathology* / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D012016:Reference Values; D012129:Respiratory Function Tests; D012131:Respiratory Insufficiency / Q000209:etiology / Q000503:physiopathology; D012189:Retrospective Studies; D014797:Vital Capacity / Q000502:physiology