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Introduction

Ischemic heart disease (IHD) is rapidly becoming the leading cause of death in developing countries around the world. Psychosocial factors are now recognized as playing a significant and independent role in the development of IHD and its complications. Mental stress has been implicated as a trigger of myocardial infarction (MI) and sudden death in patients with coronary artery disease [1]. Therefore it is important to research the psychosocial risk factors reducing methods, particularly in the setting of cardiac rehabilitation.

Chronic imbalance of the autonomic nervous system is a prevalent and potent risk factor for adverse cardiovascular events, including mortality. Transient variations in HRV have recently been validated as a measure of short-term changes in autonomic tone [2, 3].

There are many exercises and techniques for achieving relaxation. Progressive muscle relaxation (PMR) is a primary method that is easily learned. Previous studies have shown that PMR has beneficial physiologic and psychological effects for various populations. Research has demonstrated that PMR significantly lowers patients’ perception of stress, and it enhances their perception of health. PMR is beneficial for patients with essential hypertension [4]. Resent research findings also show that progressive muscular relaxation training may be an effective therapy for improving psychological health and quality of life in anxious heart patients [5].

The studies of meditations therapeutic effects show the benefits ranging from reduced cardiovascular risk factors to improved psychological status [6]. The Mindfulness-Based Stress Reduction (MBSR) program is a meditation training course developed by Dr. Kabat-Zinn and colleagues at the University of Massachusetts Medical School [7]. "Mindfulness" is defined as moment- to-moment nonjudgmental attention and awareness actively cultivated and developed through meditation. In America the use of mindfulness training in treating specific pain conditions, hypertension, myocardial ischemia, weight control, irritable bowel syndrome, insomnia, human immunodeficiency virus (HIV), and substance abuse is presently under investigation in research supported by the National Institutes of Health [7].

While long-term relaxation therapies improve psychological well-being in heart diseases, there is little information regarding the short-term effects of relaxation techniques on beat-to-beat heart rate dynamics. The focus of our work was on whether PMR and MBSM produce any reliable changes of HRV and whether these changes are any different from those produced by a period of just lying quietly. So the main purpose of our work was to reveal the peculiarities of heart rate variability during two relaxation techniques.