Pulmonary gas exchange in the morbidly obese

Obes Rev. 2008 Jul;9(4):326-39. doi: 10.1111/j.1467-789X.2008.00471.x. Epub 2008 Mar 4.


The literature on pulmonary gas exchange at rest, during exercise, and with weight loss in the morbidly obese (body mass index or BMI > or = 40 kg m(-2)) is reviewed. Forty-one studies were found (768 subjects weighted mean = 40 years old, BMI = 48 kg m(-2)). The alveolar-to-arterial oxygen partial pressure difference (AaDO2) was large at rest in upright subjects at sea level (23, range 5-38 mmHg) while the arterial pressure of oxygen (PaO2) was low (81, range 50-95 mmHg). Arterial pressure of carbon dioxide (PaCO2) was normal. At peak exercise (162 W), gas exchange improves. Weight loss of 45 kg (BMI = -13 kg m(-2)) over 18 months is associated with an improvement in PaO2 (by 10 mmHg, range 1-23 mmHg), a reduction in AaDO2 (by 8 mmHg, range -3 to -16 mmHg), and PaCO2 (by -3 mmHg, range 3 to -14 mmHg) at rest. Every 5-6 kg reduction in weight increases PaO2 by 1 and reduces AaDO2 by 1 mmHg, respectively. Morbidly obese women have better gas exchange at rest compared with morbidly obese men which is likely due to lower waist-to-hip ratios in women than from differences in weight or BMI.

Publication types

  • Review

MeSH terms

  • Blood Gas Analysis
  • Body Mass Index
  • Carbon Dioxide / analysis
  • Carbon Dioxide / blood
  • Exercise / physiology*
  • Humans
  • Obesity, Morbid / blood
  • Obesity, Morbid / physiopathology*
  • Oxygen / analysis
  • Oxygen / blood
  • Partial Pressure
  • Pulmonary Gas Exchange / physiology*
  • Weight Loss / physiology*


  • Carbon Dioxide
  • Oxygen