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.a/ Q.) ratio distributions using the multiple inert gas elimination technique have never before been explored. METHODS:We compared respiratory and inert gas ( V.a/ Q.ratio distributions) pulmonary gas exchange, breathing both ambient air and 100% oxygen, in 19 morbidly obese women (BMI, 45 kg/m2), 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 Po2(76 ± 2 mm Hg) and an increased alveolar-arterial Po2difference (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.a/ Q.units, suggesting the development of reabsorption atelectasis without reversion of hypoxic pulmonary vasoconstriction. After BS, body weight was reduced significantly (BMI, 31 kg/m2), and pulmonary gas exchange abnormalities were decreased. CONCLUSIONS:Morbid obesity is associated with mild to moderate shunt and V.a/ Q.imbalance. These abnormalities are reduced after BS.