The aim of this work was to attempt to classify the changes in states of the heart rate (HR) regulation during 24-h monitoring in patients with arterial hypertension and coronary heart disease. A HR regulation state was understood as the complex of HR parameters in a preset period of time (5 min) since it is known that the statistical and spectral characteristics of a cardiointerval time series make it possible to monitor quantitative indices of the tone of the sympathetic and parasympathetic nervous systems, which form the current state of HR regulation [1][2][3][4][5][6][7][8][9][10][11]. The question is whether the sequence of functional states (in terms of the complex of the autonomic regulation characteristics during the 5-min interval) is a nonrepeating continuum of events or there are interchanging "discrete" classes of states. Elucidation of this question might be of importance for constructing models for short-term prediction of states.
METHODSWe tested 30 patients with stage 1 or 2 (according to the Society of Cardiology of the Russian Federation, 2001) hypertension verified by conventional examination. Of them, three patients had coronary heart disease in the form of class II stable angina of effort. The group consisted of 20 men and 10 women. The mean age was 46.4 ± 10.1 years. The mean systolic pressure was 132.3 ± 11.2 mmHg; the mean diastolic pressure, 82.4 ± 9.3 mmHg; and the mean HR, 66.9 ± 9.98 bpm. The patients were treated with hypotensive drugs of the main types. In all patients, cardiointervals were continuously monitored for 24 h using a Cardio Tens-01 instrument (Meditech, Hungary), which allows continuous recording of RR intervals over 24 h and temporal and spectral analyses of the HR for a predetermined time interval. A continuous chain of consecutive nonoverlapping 5-min RR interval segments was analyzed for a 24-h period. Patients with a minimal number of artifacts (no more than five to ten episodes during the observation) and without rhythm disorders were selected. Segments with artifacts were excluded from the analysis. The following parameters were determined for each 5-min interval: the RR interval mode (MoRR, ms), the total spectral power (TP, ms 2 ), the low-frequency component (LF, ms 2 ), the high-frequency component (HF, ms 2 ), and the LF/HF ratio; the technique and the ranges were as recommended in [1]. The number of 5-min intervals analyzed for a patient varied from 239 to 286. Since the above HR parameters reflect the influence of several control systems [1-11], the term functional state of HR regulation in a given segment of time may be used. For example, Fig. 1 shows the chronological sequence of the synchronous HR parameters in a 65-min segment (13 5-min intervals) in patient Kh. The letters a , b , c , and d at the top of vertical lines 7, 8, 9, and 10 designate different functional states of HR regulation. To classify the states changing over 24 h, we used pattern recognition (clustering) methods, including a combination of the hypersphere and potential function metho...