AMONG VARIOUS PHYSICAL changes accompanying psychological disturbances, autonomic symptoms are frequently encountered in clinical practice, including palpitation, sweating, diarrhea and so on, and are incorporated in the diagnosis of mental disorders.1 It is, therefore, reasonable to assume that autonomic measurement can become a useful tool for biologically assessing the psychological states. In the field of cardiac function, in addition to conventional heart rate (HR) measurement, heart rate variability (HRV) is utilized as a convenient and informative way to evaluate autonomic activity by recording electrocardiogram or pulse wave, and has been used frequently in psychiatric research.2 It is clinically applicable because the patients experience little distress on measurement.
HRV was first utilized in the field of fetal health check, and the relationship to intra-uterine condition has been discussed.3 A number of studies were then conducted with regard to ischemic heart disease, and it was found that HRV change was an important risk factor.4 In the field of psychiatry, complication of depression in ischemic heart disease has been noted,5 and HRV was used to analyze this relationship.6,7 Furthermore, a reduction of HRV was observed in depressed patients without cardiac dysfunction.8 Changes in HRV indices were also reported in other psychiatric disorders including post-traumatic stress disorder (PTSD), panic disorder and schizophrenia.9–13
Considering the presence of HRV abnormalities in various mental disorders, it is interesting to examine whether HRV indices can be utilized to assess the psychological state of normal individuals for early detection of mental changes and prevention of the psychiatric disturbances. It has been reported that social isolation, anger and high emotional stress were accompanied with changes in HRV.14,15 Subjects with low HRV reported high anxiety when confronting fearful stimuli.16 HRV is also different depending on pain sensitivity.17 Thus, it is known that HRV is related to various aspects of temperament and behavior.18
The aim of the present study was to further promote the usefulness of HRV in evaluating mental health by focusing on its responsiveness to behavioral or environmental changes, because HRV is profoundly influenced by concurrent physical activity.19 The HRV components respond to the environmental stimuli differently depending on emotional context.20,21 Previous reports have also shown that anxiety and depressed mood are related to low levels of HRV parasympathetic components during exposure to stressors.22–24 Accumulation of data, however, is still necessary to apply HRV responsiveness in evaluating the mental state of normal individuals. Based on this background, we used task application in the present study as a form of stress, and evaluated the responsiveness of HRV to the task in relation to psychological conditions.