Background: Several methods are used to study heart rate variability, but they have limitations, which might be overcome by the use of a three-dimensional return map.
Objectives: To evaluate the performance of three-dimensional return map-derived indices to detect (1) sympathetic and parasympathetic modulation to the sinus node and (2) autonomic dysfunction in diabetic patients.
Methods: Six healthy subjects underwent partial and total pharmacological autonomic blockade in a protocol that incorporated vagal and sympathetic predominance. Twenty-two patients with type 2 diabetes mellitus and 12 normal controls participated in the subsequent validation experiment. Three-dimensional return maps were constructed by plotting RRn intervals versus the difference between adjacent RR intervals [(RRn+1)-(RRn)] versus the number of counts, and four derived indices (P1, P2, P3, MN) were created for quantification.
Results: Both indices P1 and MN were significantly increased after sympathetic blockade with propranolol, while all indices except P1 were modified after parasympathetic blockade (P < 0.05). During the validation experiments, P1 and MN detected differences between normal controls, and diabetic patients with and without autonomic neuropathy. The overall accuracy of most three-dimensional indices to detect autonomic dysfunction, estimated by the area under the ROC curve, was significantly better than traditional time domain indices. Three-dimensional return map-derived indices also showed adequate reproducibility on two different recording days (intra-class correlation coefficients of 0.69 to 0.82; P < 0.001).
Conclusions: Three-dimensional return map-derived indices are reproducible, quantify parasympathetic as well as sympathetic modulation to the sinus node, and are capable of detecting autonomic dysfunction in diabetic patients.