Measurement characteristics of finite heart rate plots
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MEDICAL AND BIOLOGICAL MEASUREMENTS MEASUREMENT CHARACTERISTICS OF FINITE HEART RATE PLOTS
A. A. Kuznetsov
UDC 534.6+612.172.4:57.02
We present a comparative analysis of the measurement characteristics of finite real and virtual heart rate plots based on data from 176 serial electrocardiogram recordings, with the aim of comparing data obtained from digital series of R–R intervals of different lengths using the parameters: mean-square value of the standard deviation, quantity of information, and information entropy. We describe a procedure for normalization of the heart rate plots and we explain the role of the excess entropy production parameter. Keywords: heart rate plot, real and virtual heart rates, normalization, information entropy.
Background. Study of heart rate variability (HRV) by cardiologists all over the world has led to the need for standardization of terminology, development of optimal methods for measuring variability, describing its parameters and their characteristics under normal and pathological conditions. With this goal, in May 1994 the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology prepared a report describing standards of measurement, physiological interpretation, and clinical use of heart rate variability [1]. The parameter introduced as the standard was the normal-to-normal (NN) interval, which is defined as all R–R intervals between successive normal QRS complexes resulting from sinus node depolarization in the heart. HRV analysis is done based on processing the R–R interval file in parametric time and frequency domains of the analysis. In [1], as yet unsolved problems are also indicated such as: insufficient number of long electrocardiogram (ECG) recordings, lack of ECG data for healthy individuals, the impossibility of adequate comparison of data for short and long ECG recordings [1, 2]. The aim of this work was to research the feasibility of adequate comparison of data obtained from digital series of R–R intervals of different recording lengths using the parameters: mean-square value of the standard deviation σ, the quantity of information IΣ , and the information entropy I *. Experimental Section. Twenty-minute ECG recordings were made using the Holter monitor of the AnnA Flash 3000 system for ambulatory ECG signal recording [3], using electrocardiography skin electrodes. In recording the biopotentials, Nehb bipolar leads were used: the first electrode was placed in the second intercostal space at the right sternal border (corresponding to V52); the second electrode was placed in the region of the apex of the heart. Such an electrode placement lets us record the anterior chest lead (A-anterior) corresponding to the standard lead II with maximum amplitude of the waves on the ECG. The data from each electrocardiogram were digitized within the EScreen program [4] with sampling step 1 msec, converted to tachograms in the form of a sequence of R–R interval values, and saved as digital series in text files in the database.
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