Therefore, stress is reasonably suspected to function as an important co-factor for the genesis and maintenance of a large number of acute and chronic diseases of almost each physiological system of the organism, such as cardiovascular, respiratory, gastroenterological, autoimmune and inflammatory, metabolic, neurological, mental and psychiatric diseases 3, 4, 5, 6, 7. If the stressor’s influence exceeds the individual coping capacity due to intensity or duration, psychological stress can have harmful physiological effects. Psychological stress can be defined as a psychological state that occurs when “an individual perceives that environmental demands tax or exceed its adaptive capacity” 1, 2. Methods based on RR interval differences like binary symbolic dynamics should be preferred to overcome issues related to nonstationarities. Pattern categories derived from binary symbolic dynamics clearly identified acute stress and accompanying alterations of cardiac autonomic regulation. Neither low frequency oscillations (LF), high frequency oscillations (HF) nor LF/HF could unambiguously reflect changes during acute stress in comparison to rest.
During acute stress the average RR interval and SDNN decreased compared to rest before and after the stress test.
Nonstationarities in RR interval series were present in all periods. An electrocardiogram was recorded throughout the procedure and HRV parameters were calculated for nine 5-min periods. 24 healthy subjects (12 female, 20–35 years) completed the following procedure: waiting period, Trier Social Stress Test to induce acute psychological stress, recovery period. We address the requirement of stationary RR interval series to calculate frequency domain parameters of heart rate variability (HRV) and use binary symbolic dynamics derived from RR interval differences to overcome this obstacle. Acute psychological stress acts also on cardiac autonomic regulation and may lead to nonstationarities in the interbeat interval series. Psychological stress may have harmful physiological effects and result in deteriorating health.
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