Assessment of peak oxygen consumption, lactate and ventilatory thresholds and correlation with resting and exercise...

To determine the clinical value of respiratory gas analysis during exercise, oxygen consumption (VO2) at peak exercise and at lactate and ventilatory threshold was assessed in 34 patients with chronic heart failure who underwent maximal exercise testing with expiratory gas monitoring and serial determinations of mixed venous lactate and hemodynamics by Swan-Ganz catheterization. A lactate threshold, defined as the point of abrupt increment of blood lactate, could be identified in every patient; the ventilatory threshold, detected on the basis of the respiratory changes, was found in 26 patients (77%). Lactate and ventilatory thresholds were significantly related to each other (r = 0.94; p less than 0.001) and to peak VO2 (r = 0.89; p less than 0.001 in both). Among the resting hemodynamic measurements, peak VO2 was significantly related only to total pulmonary resistances (r = -0.35). Among the parameters at maximal exercise, it was positively related to cardiac index, stroke work, stroke volume index and mean arterial pressure (r = 0.89, 0.74, 0.74 and 0.56, respectively) and inversely related to systemic vascular and total pulmonary resistances (r = -0.74 and -0.63). Using multivariate stepwise regression analysis only maximal cardiac index and, to a lesser degree, total pulmonary resistance were related to peak VO2. Similar correlations were found between the hemodynamics and the lactate and ventilatory threshold. Thus, peak VO2, lactate and ventilatory thresholds can be detected in most patients with chronic heart failure. These parameters are highly correlated to each other and bear similar relations to the hemodynamic response to exercise. The cardiac index is the main central hemodynamic determinant of exercise capacity.