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Obes Surg. 2008 Mar;18(3):256-63. doi: 10.1007/s11695-007-9294-9. Epub 2008 Jan 12.

Alveolar-membrane diffusing capacity improves in the morbidly obese after bariatric surgery.

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Department of Obstetrics, Gynecology and Women's Health, School of Medicine, Saint Mary's Health Center, Saint Louis University, 6420 Clayton Road, Suite 290, Saint Louis, MO 63117, USA.



Morbidly obese individuals may have impaired alveolar-membrane diffusing capacity (DmCO). The purpose of this study was to measure pulmonary diffusing capacity for NO (DLNO) as an index of DmCO pre- and postbariatric surgery in the morbidly obese.


Twenty-one patients [age = 40 +/- 9 years, body mass index (BMI) = 48.5 +/- 7.2 kg/m2] with an excess weight of 72 +/- 17 kg scheduled for bariatric surgery were recruited. Pulmonary function and arterial blood-gases were measured pre- and postsurgery.


DmCO was 88 +/- 23% of predicted before surgery (p < 0.05). There was loss in BMI and excess weight of 7.7 +/- 2.0 kg/m2 and 31 +/- 8%, respectively. Because DmCO = DLNO/2.42, the increase in DLNO postsurgery resulted in a normalization of the predicted DmCO to 97 +/- 29% predicted, or an improvement of DLNO by 11 +/- 18 (95% CI = 3.5, 19.1; p = 0.01) milliliters per minute per millimeter of mercury without any improvement in DLCO. The DLNO/DLCO ratio and alveolar volume both increased, respectively (p < 0.05), and pulmonary capillary blood volume to DmCO ratio decreased postsurgery (p < 0.01). Multiple linear regression revealed that the change in DLNO was most strongly associated with changes in alveolar volume and the waist-to-hip ratio (adjusted r2 = 0.76; p < 0.001) and was not related to the reduction in the alveolar-to-arterial PO2 difference.


Alveolar-membrane diffusion normalizes within 10 weeks after bariatric surgery. This is likely due to the increase in alveolar volume from the reduction in the waist-to-hip ratio.

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