Cardiovascular response to exercise in diabetic patients: influence of autonomic neuropathy of different severity

Abstract

We investigated cardiovascular function and plasma catecholamine response during incremental exercise and recovery in diabetic patients with (DAN+) and without autonomic neuropathy (DAN−). The former group was divided according to the presence of parasympathetic (DAN+PH−) or associated parasympathetic and sympathetic (DAN+PH+) damage to the autonomic nervous system. A group of healthy volunteers was studied as a control group. All the patients and control subjects underwent a submaximal or symptom-limited incremental exercise test using a cycle-ergometer. Air flow and respiratory gas fractions were sampled at the level of the mouth allowing a breath-by-breath analysis of oxygen consumption (VO2). Heart rate and systolic blood pressure were recorded and venous blood samples were obtained from the patients at rest and during each minute of exercise and recovery to measure norepinephrine and epinephrine plasma levels. Haemodynamic parameters and plasma catecholamines were computed at rest and at 25, 50, 75 and 100% of the peak VO2 (VO2 max). The breath-by-breath relationships among VO2, heart rate and VO2/heart rate against work were assessed during exercise for patients and control subjects. While VO2 max in absolute values was not significantly different among the diabetic groups, VO2 max was much less in diabetic patients than in control subjects (p<0.01). During exercise the rate of heart rate, systolic blood pressure, norepinephrine and epinephrine increase was different among the diabetic groups, being significantly blunted in DAN+PH+. The VO2/work relationship of the three diabetic groups was similar but markedly reduced in respect to that of control subjects (p<0.001). The relationship between oxygen pulse (VO2/heart rate) and work showed no differences among the diabetic groups, whereas its slope was significantly steeper in control subjects (p<0.01 vs DAN−; p<0.05 vs DAN+PH− and DAN+PH+). In conclusion during incremental exercise both DAN+PH− and DAN+PH+ exhibit abnormal heart rate, systolic blood pressure and catecholamine responses which, however, appear clearly distinct between the two groups of DAN+. In DAN+ the VO2 increment is reduced during exercise. Since DAN−show the same impairment, this particular finding seems most likely to be influenced by factors (i.e.: diabetic cardiomyopathy) other than overt autonomic neuropathy.