Effect of Body Position on Spirometry in Abdominal Obesity.

Detailed Summary

Objective: Study the effect of body position on spirometry in obese patients as defined by waist to hip ratio (WHR) of greater than 0.85 in women, and 0.9 in men Background: Spirometry is routinely ordered to work up dyspnea in obesity. The most common abnormality is a restrictive disease pattern. The underlying mechanisms of this pattern are not completely understood. One plausible explanation is diaphragmatic weakness or skeletal muscle weakness. The change in forced vital capacity (FVC) from sitting to supine is a very sensitive and specific test for detecting diaphragmatic weakness. The effect of body position on spirometry in obesity has not been extensively studied, and there are no studies that look at this when obesity is measured by waist to hip ratio. Effect of body position has been studied in normal patients, and it is expected the FVC can decrease as much as 10% when changing from sitting to supine. The investigators do not know what would be considered 'the normal' amount for FVC to decrease by in the obese population, and thus would like to test patients with increased WHR both in sitting and supine position. The investigators also want to do muscle strength test by measuring the maximal inspiratory and expiratory pressures (MIPs and MEPs). Anticipated results: the investigators anticipate that our study population will replicate the restrictive disease pattern usually seen in obesity. The investigators also anticipate for the FVC to decrease when in the supine position compared to sitting. The amount by which it decreases will likely fall between 10 -25%. The investigators anticipate to not find any abnormalities in MIPs and MEPs in obesity.

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