HEART RATE VARIABILITY AS A NON-INVASIVE MARKER OF AUTONOMIC CARDIOVASCULAR REGULATION: PHYSIOLOGICAL MECHANISMS, ASSESSMENT METHODS, AND RESEARCH PERSPECTIVES

Heart rate variability (HRV) represents the physiological variation in consecutive cardiac cycles and is widely used as a non-invasive indicator of autonomic cardiovascular regulation. This review summarizes the physiological mechanisms underlying HRV, including sinoatrial node modulation, respiratory sinus arrhythmia, baroreflex activity, and sympathetic–parasympathetic interactions. Current approaches to HRV assessment, including time-domain, frequency-domain, and non-linear indices, are considered with emphasis on methodological standardization and physiological interpretation. The influence of physical activity, age, respiration, posture, circadian rhythms, and cardiovascular dysfunction on HRV is also discussed. HRV provides an accessible window into autonomic regulation, but its interpretation requires careful control of confounding factors and should be integrated with clinical and physiological data.