DIAGNOSIS OF CARDIOVASCULAR AUTONOMIC NEUROPATHY IN DIABETES

The utility of standard cardiovascular tests for diagnosis of cardiac autonomic neuropathy in diabetes has been well documented. Attention m ust be paid to standardizing the procedure with regard to time of day metabolic status, distance from meal and insulin, coffee and smoking a voidance, and patient's collaboration. In the presence of cardiovascul ar disease or drugs affecting the cardiovascular or autonomic nervous system, some caution is needed in interpreting the results. More recen t reflex tests, which evaluate mainly sympathetic or baroreflex activi ty, despite their ability to detect early autonomic involvement, lack sufficient standardization and still need to be proved as valid altern atives. Of the different methods of measuring heart rate variability, spectral analysis has a greater ability to differentiate vagal and sym pathetic modulation of heart rate than do time-domain methods. However , since these latter methods are easier and more widely available, the y can be used as a screening approach. Twenty-four-hour evaluation of heart rate variability provides data on the circadian rhythm of sympat hovagal activity, which can be affected earlier than and differently f rom cardiovascular reflex tests. Information obtained could have progn ostic implications in terms of cardiovascular morbidity and mortality and offer therapeutic opportunities. However, a wide consensus on many technical aspects of both time-domain and frequency-domain methods is needed. Furthermore, large prospective studies in the diabetic popula tion to assess the prognostic value of 24-h heart rate variability par ameters on cardiovascular morbidity and mortality are lacking. Recentl y, I-123 meta-iodobenzylguanidine (MIBG) scintigraphy has documented a bnormalities of sympathetic myocardial innervation also in newly diagn osed IDDM. The meaning of this finding, whether it is an expression of functional or structural defects, needs to be clarified. Preliminary data point to a possible pathogenetic meaning of the known association between autonomic neuropathy and other diabetic complications. This a rea of investigation could provide useful insights into the complex an d multifactorial pathogenesis of diabetic complications.