American Review of Respiratory Disease

The hypothesis that exercise limitation of respiratory origin can be predicted accurately from the lung function impairment has been tested using maximal oxygen uptake (O2max) as the dependent variable in a multiple regression analysis. The subjects were 157 men who met objective criteria for exercise being limited by respiratory impairment. O2max (mean value, 1.38 L min−1) was described by FEV1 and single-breath lung transfer factor (diffusing capacity) for carbon monoxide (Tl′) singly or in combination, but the accuracy was poor (at best, standard error of the estimate, 0.36 L min−1; r2, 29.1%). FEV1 could be replaced by FVC and FEV1/FVC. Description of O2max was improved by also including in the equation the variables age, fat-free mass, and submaximal exercise ventilation (e). Transfer factor did not then contribute significantly. O2max as percent of predicted (mean value of 60%) was described by %FVC or %FEV1, but the accuracy was poor (SEE, 16.0%; r2, 14%). Prediction was improved somewhat by the alternative use of inspiratory vital capacity and FEV1/FVC. Transfer factor did not contribute additional information; however, inclusion of e materially improved the accuracy (SEE, 12.9%; r2, 44%). Among a subgroup of 35 men whose lung disease was due to asbestos, %Tl′ or transfer factor measured using a multibreath estimate of residual volume (%TlCO) made a small contribution to the explained variance, e.g.: %O2max = 0.440/0 FEV1 −0.78 e + 0.16% TlCO + 52.3 SEE 7.27%. This equation also described the %O2max of all subjects (SEE, 13%). It was concluded that in patients whose exercise capacity was limited by respiratory factors, the limitation could not be assessed accurately in terms of FEV1, FVC, and transfer factor. These indices were not independent, and their predictive power was poor. for the accuracy to be acceptable, additional indices were needed; for example, ventilation at a standard oxygen uptake during submaximal exercise.


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