Decreased Exercise Heart Rate and Blood Pressure Response in Diabetic Subjects With Cardiac Autonomic Neuropathy

Abstract

Abnormal hemodynamic responses to exercise have been observed in diabetic subjects, but the pathogenesis and significance remain uncertain. We used maximal treadmill exercise to study 32 subjects with long-term insulin-dependent diabetes without clinical evidence of cardiac disease. Two of the 32 had occult ischemic heart disease revealed by stress electrocardiography and myocardial-perfusion scintigraphy and were excluded from subsequent analysis. In the remaining 30 subjects, we compared the responses to exercise of the 17 subjects with cardiac autonomic neuropathy diagnosed by noninvasive maneuvers (group 1) with the 13 without (group 2). At rest, the pressure-rate product (PRP) was higher in group 1 (114.0 ± 5.7 vs. 95.9 ± 5.3, P < .05). With maximal exercise the increase in heart rate ('44.6 ± 4.8 vs. 79.0 ± 5.4 beats/min, P < .001), systolic blood pressure (36.8 ± 5.9 vs. 55.0 ± 5.8 mmHg, P = .02), and the PRP (102.0 ± 7.3 vs. 182.0 ± 8.2, P < .001) were all lower in group 1 than in group 2, despite similar total treadmill times (631 ± 47 vs. 587 ± 40 s, P > .1). At each stage of exercise, the increase in heart rate and systolic blood pressure was lower in group 1 patients. The severity of cardiac autonomic neuropathy correlated inversely with the maximal increase in heart rate(γ = – .68, P < .001) and the PRP (γ = − .58, P < .005). Age, duration of diabetes, and the presence and severity of microvascular disease did not correlate with any of the hemodynamic parameters. Thus, cardiac autonomic neuropathy is associated with an impairment of the hemodynamic responses to exercise in diabetic subjects without ischemic heart disease.