## 3 Results  
Remarkably, while the orthostatic hypotension patients (Group 1) were characterized by a smaller number of reduced autonomic tests results (\(5.0\pm 1.2\) vs. \(2.5\pm 1.1\)) suggesting rather moderate autonomic dysfunction particularly less severe than that one in the diabetes patients (Group 2), they were characterized by considerably more pronounced blood pressure reduction during tilt test (\(34\pm 13\) vs. \(17\pm 14\) for systolic and \(17\pm 7\) vs. \(2\pm 16\) for dyastolic blood pressure, respectively). Analysis of both the entire tilt test records as well as each of its phases revealed that, as expected, the BRS differs significantly between healthy individuals and both patient groups, according to the non-parametric Mann-Whitney U-test (\(p<0.05\) for the first group with orthostatic hypotension and \(p<0.001\) for the second group of diabetes patients with autonomic neuropathy). Remarkably, in addition to the well-established BRS index, nearly all studied mutual information indices exhibited significant differences between the patients' groups and the healthy volunteers (\(p<0.05\)). In marked contrast, when  
Figure 3: Typical dynamics of blood pressure and pulse intervals during a head-up tilt test, vertical red lines denote the test phases. it comes to differential diagnostics, only a few studied metrics have shown significant discrepancies between the first and the second patients' groups. In particular, besides the well established BRS index (\(p<0.05\)), also Sync (\(p<0.05\)) and TDS (\(p<0.005\)) mutual information metrics have shown significant differences (see also Figures 4-6 for visual illustration). Figure 4: The overall average of the six studied mutual information metrics: (**a**) Sync, (**b**) TDS, (**c**) _TAU,_ (**d**) _CE,_ (**e**) _Coher_ and (**f**) BRS averaged for the overall duration of the tilt test records. The horizontal axis denotes group number (also denoted by color): 1 (blue)—orthostatic hypotension; 2 (red)—diabetes mellitus with autonomic neuropathy; 3 (green)—healthy volunteers (control group). Figure 5: The values of the six studied mutual information metrics: (**a**) Sync, (**b**) TDS, (**c**) _TAU,_ (**d**) _CE,_ (**e**) _Coher_ and (**f**) BRS obtained during the supine phase of the tilt test. The horizontal axis denotes group number (also denoted by color): 1 (blue)—orthostatic hypotension; 2 (red)—diabetes mellitus with autonomic neuropathy; 3 (green)—healthy volunteers (control group). For a better representation of the overall response patterns quantified simultaneously by several indicators, Figure 7 also depicts the star-style diagrams summarizing our results after appropriate normalization. Those indices that were not normalized by definition have been rescaled by dividing all values by the corresponding observed maxima. Significant changes between the supine and the orthostatic phases of the tilt test could be observed for nearly all studied metrics except CE in the diabetes patients' group (\(p<0.05\)). However, only BRS and Coher metrics (\(p<0.01\)) significantly differed between the supine and the orthostatic test phases both in the control group and in the first patient group with orthostatic hypotension, while no significant differences between the test phases could be observed in other studied indices. In particular, although BRS reduced significantly in the orthostatic position for the patients with non-diabetic orthostatic hypotension (Group 1), given that their initial \(BRS\) values (\(9.59\pm 4.65\)) (medians \(\pm\) interquartile ranges are given here and below) in the supine position were only slightly below those in the control group (see Figure 5), they appeared only moderately reduced also in the orthostatic position (\(5.16\pm 4.12\), see also Figure 6).