Group mean values for resting and exercise arterial plasma lactate concentration, and for parameters a and b are shown in Table 3. Resting lactate concentrations were similar in normal subjects and patients. Although lactate concentration increased significantly with exercise for each subgroup, the peak lactate concentration achieved was progressively smaller as the functional status worsened. Within each functional class of patients, no significant relationship was found between peak exercise minute ventilaton (Ve) and plasma lactate concentration. As indicated by parameter b, the La/VO2 relationship became gradually steeper with the reduction in exercise capacity. To appreciate the modification of the La/VO2 relationship that accompanied the deterioration in functional status, average La/VO2 relationships were constructed for normal subjects and the three classes of patients (Figure 2). This was done using all individual values for lactate concentration and VO2 obtained at each exercise step. For a given VO2, the lactate concentration increased progressively as the functional status deteriorated.
Table 3. Lactate kinetics parameters in relation to the functional class
|Class D (n=8)||Class C (n=31)||Class B (n=15)||Normal subjects (n=10)|
All values mean ± SD. *P<0.05 versus any other group; TP<0.001 versus any other group; TP<0.001 versus classsC and P<0.05 versus class b or normal subjects