Predicting ventilatory function from weight?

The metabolic needs of the body are determined by the metabolic mass. It therefore seems logical to predict various lung function indices, which must somehow relate to the body’s metabolic needs, from body weight. In principle, that is correct. However, body weight may be affected e.g. by disease irrespective of the metabolic needs and without the lung needing to make any size adjustments. Thus, obesity is not associated with a larger lung, nor is cachexia associated with a smaller lung. In both cases standing height is unaffected. In practice it is therefore better to predict lung function indices from standing height than from an individual’s body weight.

In the follow-up of individuals, however, it may be prudent to take changes in weight into account. In adult males reductions in FEV1 have been reported per kg gain in weight of between 13.9 and 23 mL/kg (ref. 1). Also, waist circumference is negatively associated with FEV1 and FVC.

See also:
Sources of variability between subjects

Ref. 1 - Change in body mass and in FEV1

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