Pulmonary gas exchange and severe obesity: bariatric surgery effects
[eng] 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 mòrbid obesity and BS on ventilation/perfusion (VA/Q) ratio distributions using the multiple inert gas elimination technique...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2016 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/105454 |
| Acceso en línea: | https://hdl.handle.net/2445/105454 http://hdl.handle.net/10803/398948 |
| Access Level: | acceso abierto |
| Palabra clave: | Obesitat Cirurgia de l'obesitat Obesity Obesity surgery |
| Sumario: | [eng] 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 mòrbid obesity and BS on ventilation/perfusion (VA/Q) ratio distributions using the multiple inert gas elimination technique have never before been explored. Methods: We compared respiratory and inert gas (VA/Q ratio distributions) pulmonary gas exchange, breathing both ambient air and 100% oxygen, in 19 morbidly obese women (BMI, 45 ± 1 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 PO2 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 VA/Q units, suggesting the development of reabsorption atelectasis without reversion of hypoxic pulmonary vasoconstriction. After BS, body weight was reduced significantly (BMI, 31 ± 1 kg/m2), and pulmonary gas exchange abnormalities were decreased. Conclusions: Morbid obesity is associated with mild to moderate shunt and VA/Q imbalance. These abnormalities are reduced after BS. Manuscript 2. Postural effects on pulmonary gas exchange abnormalities in severe obesity before and after bariatric surgery Background: We hypothesized that in morbid obesity, pulmonary gas Exchange abnormalities will worsen when supine and that bariatric surgery (BS) will mitigate this effect. Methods: Gas exchange was investigated in 19 morbidly obese and 8 non-obese, age-matched control females, spontaneously breathing ambient air, both upright and supine, before and one year after BS. Results: In control non-obese individuals, no postural changes in arterial blood gases (ABGs) were observed. While obese subjects had more altered PaO2, SaO2 and AaPO2 values than controls (p<0.05 each) when upright, the values unexpectedly remained unchanged when supine. This was also the case in the subset of 6 normoxemic obese but the remaining 13 hypoxemic individuals actually improved ABGs when supine: AaPO2 (by –3.4 ± 1.4 mmHg), SaO2 (by +1.5 ± 0.6 %), pH (by +0.01 ± 0.01); and cardiac output increased (by +0.4 ± 0.2 L·min-1) (p<0.05 each). After BS, PaO2 (from 75.5 ± 2.4 to 89.4 ± 2.4 mmHg) and AaPO2 (from 27.0 ± 2.0 to 15.4 ± 2.1 mmHg) (p<0.05 each) and pulmonary gas exchange were improved compared to before BS when upright, but ABGs worsened when supine (PaO2, by –4.6 ± 1.7 mmHg; AaPO2, by +4.2 ± 1.6 mmHg) (p<0.05 each). Conclusions: Before BS, ABGs are not altered in normoxemic obese subjects moving from upright to supine, even improving in those with hypoxemia when supine. After successful BS, pulmonary gas exchange improved when upright in all subjects but ABGs deteriorated when supine. However, the important clinical observation is the lack of gas Exchange deterioration when supine, which may have implications for critical care and anesthesia settings. Manuscript 3. Lung tissue volume is elevated in obesity and reduced by bariatric surgery Background: Bariatric surgery (BS) in severely obese subjects causes a significant reduction of body weight and improvement in lung function. We have shown previously that abnormalities in pulmonary gas exchange in morbidly obese are substantially improved with BS. These abnormalities were thought to be related to reduced lung volumes as well as to abnormal endothelial function induced by low-grade chronic inflammation linked to perivascular adipose tissue (PVAT). In this study we used computed tomography (CT) to assess whether BS also caused measurable structural changes in the lung. We focused in lung tissue volume (Vtiss) and cross-sectional vessel analysis hypothesizing that these measures could be related to the previously reported lung functional changes. Methods: Pulmonary vessels and lung volumes, including Vtiss, were quantified in thoracic CT scans. We compared findings in 12 obese women before and after BS and in 8 healthy lean women. Results: Vtiss was significantly elevated in obese subjects before BS compared to control subjects and systematically reduced after BS (by 8%); other CT lung volumes or vascular areas were not affected in a consistent manner. No relationship was observed between BS-induced individual changes in Vtiss and pulmonary vessel area. Conclusions: Vtiss is elevated in morbidly obese, compared to lean individuals of similar body height, and is systematically reduced by BS. These effects do not appear related to vascular changes but may be caused by elevated extra-vascular lung water, due to low-grade inflammation, and/or hypertrophic PVAT in severe obesity. |
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