ABSTRACT
Dead space to tidal volume ratio (V(D)/V(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(E)/VCO(2)) measured at the lactate threshold that are highly predictive of normality or abnormality of exercise V(D)/V(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(E)/VCO(2) at the lactate threshold was ≤28, 96 % of subjects had normal V(D)/V(T). For V(E)/VCO(2) 29-32, V(D)/V(T) was normal in 83 % of cases. V(E)/VCO(2) of 33-38 provided no useful information; V(D)/V(T) was normal and abnormal in 50 % of cases each. When V(E)/VCO(2) was ≥39, V(D)/V(T) was abnormal in 87 % of cases. For V(E)/VCO(2) ≥ 39, when FEV(1)/VC was <70 %, V(D)/V(T) was abnormal in 95 % of cases. End-tidal PCO(2) was of no help in distinguishing V(D)/V(T) normality in any V(E)/VCO(2) range. Our results reveal that certain values of V(E)/VCO(2) at LT (V (E)/VCO(2) ≤ 28 and V(E)/VCO(2) ≥ 39), but not others (V(E)/VCO(2) 29-32 and especially V(E)/VCO(2) of 33-38), can be helpful in determining normality of V(D)/V(T) during exercise in patients presenting for cardiopulmonary exercise testing.
