Key words: autonomic nervous system, cardiovascular disease risk, diabetes mellitus, heart rate variability, vagus nerve.
IntroductionAutonomic diabetic neuropathy (ADN) is a frequent and serious complication of diabetes mellitus. A clinical and subclinical disease, it can affect all organ systems, including the gastrointestinal tract, the urogenital tract and the cardiovascular system. 1 ADN with multiple organ involvement occurs only rarely, however. The clinical presentation is most often a heterogeneous pattern of symptoms in different organ systems, which can lead to misdiagnosis.2,3 Since they coincide in approximately 50% of cases, in a patient with ADN evidence of sensorimotor diabetic neuropathy should be sought. 4 There are also connections to other long-term diabetic complications, such as nephropathy and retinopathy.
5Cardiac autonomic diabetic neuropathy (CADN) Cardiac autonomic diabetic neuropathy (CADN) is the primary disease of ADN and is one of the most frequently researched complications of diabetes. 6 The earliest sign of CADN is a reduction in heart rate variability (HRV), which is detectable at the subclinical stage 5,7,8 and can, for instance, be clearly verified during deep respiration (figure 1).Further symptoms become apparent at advanced stages. Primarily the vagus (pneumogastric) nerve is damaged: this results in a resting tachycardia since sympathetic influences become predominant. After about five years of latency, regression of tachycardia occurs due to damage to the sympathetic nerve fibres; 9 however, the heart rate remains higher than in healthy patients.10 Additional symptoms such as exercise intolerance, orthostatic hypotension and an increasing limitation in heart rate variability are the manifestations of progressive damage to the autonomic balance.5 Often cardiac pain perception is impaired due to the additional damage to sensory nerve fibres, so that warning signs of myocardial ischaemia are not recognised in time to be adequately treated. A meta-analysis of 12 studies by Vinik et al. 2 found that patients with CADN had DIABETES AND VASCULAR DISEASE RESEARCH
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Cardiac autonomic diabetic neuropathy MARTIN SCHÖNAUER, ANDREAS THOMAS, STEPHAN MORBACH, JOSEF NIEBAUER, ULRIKE SCHÖNAUER, HOLGER THIELE