Noninvasive assessment of normality of V sub(D)/V sub(T) in clinical cardiopulmonary exercise testing utilizing incremental cycle ergometry

Dead space to tidal volume ratio (V sub(D)/V sub(T)), a measure of pulmonary gas exchange efficiency, cannot be accurately calculated without arterial blood sampling. We sought to determine, in patients presenting for diagnostic cardiopulmonary exercise tests, whether there are ranges of the ratio of exhaled ventilation to carbon dioxide output (V sub(E)/VCO sub(2)) measured at the lactate threshold that are highly predictive of normality or abnormality of exercise V sub(D)/V sub(T) (below or above 0.3) and whether other demographic or physiologic variables aid in this prediction. We reviewed 691 incremental cycle ergometer cardiopulmonary exercise tests featuring breath-by-breath gas exchange measurement and serial arterial blood sampling that were performed for patients with a range of disorders. When V sub(E)/VCO sub(2) at the lactate threshold was less than or equal to 28, 96 % of subjects had normal V sub(D)/V sub(T). For V sub(E)/VCO sub(2) 29-32, V sub(D)/V sub(T) was normal in 83 % of cases. V sub(E)/VCO sub(2) of 33-38 provided no useful information; V sub(D)/V sub(T) was normal and abnormal in 50 % of cases each. When V sub(E)/VCO sub(2) was greater than or equal to 39, V sub(D)/V sub(T) was abnormal in 87 % of cases. For V sub(E)/VCO sub(2) greater than or equal to 39, when FEV sub(1)/VC was