Load compensation in obese patients during quiet tidal breathing

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Abstract
Seventeen eucapnic massively obese patients and 8 normal subjects had their respiratory cycle parameters studied while breathing room air at rest. Despite large variations in the degree of obesity, the patients demonstrated normal mean inspiratory and expiratory flow rates, duty cycles and minute ventilation. Maintenance of normal mean inspiratory flow rates was dependent on an augmentation of neuromuscular drive (P0.1); a strong positive correlation between percentage ideal body weight (i.e, the degree of obesity) and P0.1 was present. The obese partitioned their tidal volume preferentially to their rib cage compartment, choosing to leave the abdominal compartment relatively immobile. Analysis of the diaphragmatic electromyogram revealed a persistence of activity into early expiration, the length of which also depended on the degree of obesity. Apparently, the diaphragm''s volume-generating function in the obese is reduced and the persistence of its activity in expiration serves to attenuate the rate of expiratory flow. No significant difference in any respiratory cycle parameter was found between simple obesity patients and formerly hypercapnic obese patients.