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Obesity, pregnancy and ethnic differences in lung function

We can divide the body mass in fat free mass and total body fat. An increase in total body fat affects the FEV1, VC, residual volume, and the RV/TLC ratio adversely. The effect on the VC is more pronounced, so that obesity is associated with an increase in the FEV1/FVC ratio. Healthy children, including malnourished ones, with the lowest the body mass index were shorter and had relatively shorter legs, and a proportionally smaller FEV1 and FVC, i.e. a normal FEV1/FVC ratio, indicating growth retardation rather than respiratory impairment.

COPD and cystic fibrosis are often associated with a poor nutritional status. Supplementary diets generally improve physical performance, in particular when combined with physical training, but do not clearly improve pulmonary function. In males fat deposition is predominantly central; the FRC decreases by increased abdominal fat both in the supine and sitting posture. There is therefore a greater chance that airway closure occurs in dependent lung regions during normal tidal breathing. In morbid obesity the TLC is reduced. Adiposity is associated with the metabolic syndrome, which leads to the release of inflammatory mediators which play a role in asthma and COPD. There is evidence that the level of adinopectin, an anti-inflammatory protein produced by fat tissue, may play a role: a low level of adinopectin is associated with lower lung function and appears to play a role in COPD.

Pregnancy has minor effects on spirometric indices. The total lung capacity and the VC remain unchanged, but the FRC decreases by 10-25 %. This may lead to airway closure in the normal tidal breathing range.

Differences between ethnic groups are dealt with elsewhere.

Body weight and lung function

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Pregnancy and lung function

1 Parameswaran K, Todd DC, Soth M. Altered respiratory physiology in obesity. Can Respir J 2006; 13(4): 203–210. Manuscript
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