CARDIOVASCULAR-RESPONSE TO EXERCISE IN DIABETIC-PATIENTS - INFLUENCE OF AUTONOMIC NEUROPATHY OF DIFFERENT SEVERITY

We investigated cardiovascular function and plasma catecholamine respo nse 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 asso ciated parasympathetic and sympathetic (DAN+PH+) damage to the autonom ic nervous system. A group of healthy volunteers was studied as a cont rol group. All the patients and control subjects underwent a submaxima l 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 epinephr ine plasma levels. Haemodynamic parameters and plasma catecholamines w ere computed at rest and at 25, 50, 75 and 100% of the peak VO2(VO2max ). The breath-by-breath relationships among VO2, heart rate and VO2/he art rate against work were assessed during exercise for patients and c ontrol subjects. While VO2max in absolute values was not significantly different among the diabetic groups, VO2max 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 g roups was similar but markedly reduced in respect to that of control s ubjects (p<0.001). The relationship between oxygen pulse (VO2/heart ra te) 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 ex ercise both DAN+PH- and DAN+PH+ exhibit abnormal heart rate, systolic blood pressure and catecholamine responses which, however, appear clea rly distinct between the two groups of DAN+. In DAN+ the VO, 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.