Single-breath Co diffusing capacity (transfer factor) (DLCo) in patients with muscle weakness is usually normal or mildly reduced. Reduction is due to inability to achieve full distension of the lungs at TLC and consequent failure to expose all the alveolar surface to carbon monoxide. As with other extra-pulmonary causes of lung volume restriction, the transfer coefficient (Kco) is often supernormal.
The measurement is easily performed and well standardized. Disadvantages
A reduced Dlco is a nonspecific finding (but if accompanied by elevation of Kco it suggests extrapulmonary volume restriction). Any effects of respiratory muscle weakness on the measurements are indirect.
The pattern of normal or mildly reduced Dlco and raised Kco directs attention to extrapulmonary conditions, that is, respiratory muscle weakness, pleural disease or rib cage abnormalities. Otherwise, the main role of measurement of CO uptake is in the recognition or exclusion of coexistent lung disease.
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