ASSESSMENT OF CARDIAC AUTONOMIC BALANCE BY MEANS OF A NEW TIME DOMAIN METHOD (TONE-ENTROPY ANALYSIS)

Abstract

ECG R-R interval power spectral analysis of heart rate variability allows some degree of separation of the sympathetic and vagal contributions. In this analysis, subjects need to breath in synchrony with a metronome at 15 times/min to ensure the respiratory-linked vagal component from other sources. The purpose of the present study was to evaluate our newly developed Tone-Entropy analysis to determine cardiac autonomic activity without any troublesome restrictions. Passive tilting tests (0°, 40°, 80°) were performed in fourteen healthy subjects. During the test, ECG was continuously displayed on a computer screen and stored sequentially on a disk for later analysis. Successive R-R interval variation was evaluated by the percentage index (PI), i.e., beat-to-beat changes in cardiac acceleration-deceleration. Based upon our pharmacological blockade experiments, two indices were defined on PI distribution: Tone representing vagal activity and Entropy representative of over-all cardiac autonomic activity during exercise (Oida et al., JAP,1997) and diabetic alterations (Oida et al., Acta Physiol. Scand., 1999). Results indicated that there were significant increases in Tone at 40° and 80° than those at 0° [-0.19 ± 0.04 (0°) vs. −0.08 ± 0.04 (40°) and −0.39 ± 0.01 (80°), p < 0.01]. On the other hand, the values of Entropy were significantly increased at 40° and at 80° [4.21 ± 0.19 (0°) vs. 3.54 ± 0.14 (40°) and 3.36 ± 0.13 bit (80°), p < 0.01]. Our results are consistent with previous findings employing R-R interval power spectral analysis; the sympathetic activity was increased and/or the parasympathetic activity was withdrawn according to the degree of tilt. These results suggested that the cardiac autonomic balance could be evaluated by our newly developed time domain method, Tone-Entropy analysis.