Autonomic dysfunction in diabetes: a consequence of cardiovascular damage

In 1976, D.J. Ewing showed a clear survival disadvantage for diabetic patients that had 'diabetic autonomic neuropathy', as assessed by heart rate and blood pressure variations during a battery of bedside tests. However, these variations do not solely depend on autonomic nervous system function, but also and possibly to a more important extent on the integrity of cardiovascular autonomic reflex loops. Increased intima media thickness at the site of the baroreceptors, reduced vascular distensibility, endothelial dysfunction and impaired cardiac function contribute to the cardiovascular autonomic dysfunction. Interestingly, these abnormalities are closely associated with the presence of (micro-) albuminuria that is regarded as a reflection of endothelial dysfunction or vascular damage in diabetes mellitus. Modern techniques to assess cardiovascular autonomic, vascular and cardiac function have improved the ability to detect early abnormalities. Analysis of heart rate variability, baroreflex sensitivity, muscle sympathetic nervous activity, LNMAinfusions and advanced echocardiography have shown that it is the interplay between autonomic control and cardiac and vascular properties that determines cardiovascular autonomic function. Moreover, these modern techniques have improved power to predict survival in diabetic patients in comparison with the classical Ewing's bedside tests. In conclusion, cardiovascular damage may be more important in cardiovascular autonomic dysfunction than neural function.