Ventilation/Perfusion Distribution Abnormalities In Morbidly Obese Subjects Before and After Bariatric Surgery

BACKGROUND: Obesity is a global and growing public health problem. Bariatric surgery (BS) is indicated in patients with morbid obesity. To our knowledge, the effects of morbid obesity and BS on ventilation/perfusion ((V) over dot(A)/(Q) over dot) ratio distributions using the multiple inert gas elimination technique have never before been explored. METHODS: We compared respiratory and inert gas ((V) over dot(A)/(Q) over dot ratio distributions) pulmonary gas exchange, breathing both ambient air and 100% oxygen, in 19 morbidly obese women (BMI, 45 kg/m(2)), both before and 1 year after BS, and in eight normal-weight, never smoker, age-matched, healthy women. RESULTS: Before BS, morbidly obese individuals had reduced arterial Po-2 (76 +/- 2 mm Hg) and an increased alveolar-arterial Po-2 difference (27 +/- 2 mm Hg) caused by small amounts of shunt (4.3% +/- 1.1% of cardiac output), along with abnormally broadly unimodal blood flow dispersion (0.83 +/- 0.06). During 100% oxygen breathing, shunt increased twofold in parallel with a reduction of blood flow to low (V) over dot(A)/(Q) over dot units, suggesting the development of reabsorption atelectasis without reversion of hypoxic pulmonary vasoconstriction. After BS, body weight was reduced significantly (BMI, 31 kg/m(2)), and pulmonary gas exchange abnormalities were decreased. CONCLUSIONS: Morbid obesity is associated with mild to moderate shunt and (V) over dot(A)/(Q) over dot imbalance. These abnormalities are reduced after BS.