Measurement and validity of the ventilatory threshold in patients with congenital heart disease.

The purpose of the present study was to measure oxygen uptake (VO2) at the ventilatory threshold (VT) in patients with congenital heart disease using a progressive exercise protocol on a treadmill and to evaluate the validity and feasibility of this procedure. Eight control subjects and seventeen patients performed a maximal exercise test with breath-by-breath measurement of ventilation and gas exchange variables. VT(VE) was determined by the change in the ventilatory equivalent for VO2 and carbon dioxide output, VT(V-sl) by the V-slope method, and the lactate threshold (LT) by the change in blood lactate concentration; these parameters were determined in 100%, 88%, and 96% of subjects, respectively. The interobserver error among three evaluators was not significant, and LT was correlated with each VT (r = 0.97, 0.92; p = 0.0001) and with peak VO2 (r = 0.91; p = 0.0001). The VTs were correlated with each other when expressed as milliliter per minute and milliliters per kilogram per minute. It was concluded that a progressive exercise protocol on a treadmill was a feasible procedure for determining the VTs in most individuals and that VTs were valid, useful parameters for evaluating submaximal exercise tolerance in patients with congenital heart disease.