Comparison of metabolic, ventilatory, and neurohumoral responses during light forearm isometric exercise and isotonic exercise in congestive heart failure

Maximal treadmill exercise responses were compared with light forearm isometric exercise responses in patients with chronic, stable heart failure (n = 14), and normal sedentary controls (n = 11). Isometric exercise was performed to exhaustion with 25% of maximal voluntary contraction. Gas-exchange analysis was used to determine oxygen consumption (VO2), carbon dioxide production (VCO2), and minute ventilation (VE) during exercise. Significant correlations were observed in normal controls, but not in patients with heart failure, between peak isotonic exercise and peak isometric exercise for VO2 (r = 0.75, p = 0.001) and VCO2 (r = 0.67, p < 0.03), and between submaximal isotonic exercise (50% of peak) and peak isometric exercise for VO2 (r = 0.75, p = 0.007), VCO2 (r = 0.67, p = 0.02), and VE (r = 0.71, p = 0.01). At 90 seconds after isometric exercise in both groups, significant correlations t < 0.05) were observed with peak isotonic exercise VE (r = 0.62 normals, and r = 0.63 heart failure). Plasma norepinephrine increased significantly (p < 0.01) after both isotonic and isometric exercise in patients with heart failure, although peak values were greater with isotonic than with isometric exercise (p = 0.01). Plasma atrial natriuretic peptide and renin activity did not change with either isotonic or isometric exercise. In conclusion, maximal isotonic exercise responses are not predictive of peak isometric VO2 or VCO2 in patients with heart failure. However, VE during maximal isotonic exercise predicts postisometric exercise ventilation in both normals and patients with heart failure; this may determine the extent of dyspnea that patients with heart failure experience with isometric activities of daily living.