Comparison Between Spectral Analysis and Symbolic Dynamics for Heart Rate Variability Analysis in the Rat

Abstract

Although spectral analysis has been widely used to assess the autonomic control of the heart, several issues are still in debate about its interpretation, especially in experimental animals such as rats and mice. A nonlinear alternative method, namely symbolic dynamics, was proposed and has been reported to be very useful to represent sympathetic and parasympathetic modulation to the heart. However, studies evaluating the validity of symbolic dynamics in experimental models still lack. Conscious male Wistar rats, under continuous recording of electrocardiogram (ECG) or arterial pressure (AP), were subjected to autonomic imbalance by two protocols: pharmacological blockade of adrenergic or cholinergic muscarinic receptors administration (atenolol 4 mg/kg or methylatropine 2 mg/kg, iv, N=9 in each group) and reflex changes in sympatho‐vagal balance by AP changes elicited by phenylephrine (PHE, N=9) or sodium nitroprusside (NPS, N=9). Beat by beat series of cardiac interval (CI) were generated from ECG or AP recordings and both spectral analysis and symbolic dynamics were calculated for each animal. Spectra of CI series were calculated by FFT and integrated in low‐ (LF: 0.2–0.8Hz) and high‐frequency bands (HF: 0.8–3Hz). For symbolic analysis, symbols were attributed to CI values and sequences of 3 symbols were classified as 0, 1 or 2V according to the number of variations showed. Percentage of 0V and 2V are associated to sympathetic and vagal cardiac modulation, respectively. Hypertensive response caused by PHE (33 ± 3 mmHg) led to a reflex bradycardia (−45 ± 3 bpm) while hypotension due to NPS (−15 ± 1 mmHg) was accompanied by tachycardia (46 ± 6 bpm). The administration of atenolol and atropine led to a reduction and an increase in HR, respectively (−19 ± 6 and 70 ± 8 bpm). All drugs used reduced the total variability (standard deviation) of the CI series. The results of the spectral and symbolic analysis are showed in the table at the end. The symbolic dynamics proved to be more robust than the spectral analysis for the evaluation of the autonomic control in rats. The 1V family patterns, hitherto unknown, have been shown to be linked to sympathetic modulation in the rat and should be considered in future studies.Support or Funding InformationFapesp basal atenolol basal atropine basal NPS basal PHE LF (nu) 35±2 23±4* 40±4 28±4* 9.8±2.1 14±4 11±2 9.3±2.0 HF (ms2) 6.0±0.8 2.7±0.9* 4.3±0.4 0.2±0.03* 10±2 6.3±1.5* 4.2±1.0 25±6* 0V (%) 27±2 16±3* 27±3 29±4 7.7±1.4 9.1±1.7 9.0±1.4 5.6±1.2 1V (%) 44±1 38±2* 42±1 46±2 35±2 40±1* 45±2 33±2* 2UV (%) 25±2 37±4* 26±2 19±1* 50±3 43±2* 39±3 51±4* P<0.05 compared to basal.