INTRODUCTION
A woman spends 1/3 of her life in the postmenopausal state. Health management during this period could be considered important because it affects the entire quality of life.
1) Menopause starts when menstruation is terminated permanently due to loss of ovary function, and its onset age is almost constant.
2) In Korea, the mean age of menopause is 48 years, and it occurs within 5-10 years around the age of 48 years. The menopausal state could be broadly divided into 3 stages: premenopause, perimenopause, and postmenopause. Based on the last menstrual period, if the period of amenorrhea is longer than 12 months, it is considered postmenopause. First 3 months of amenorrhea is considered premenopause. Perimenopause is amenorrhea of 3-12 months, and the volume or frequency of menstruation becomes irregular due to estrogen deficiency during perimenopause.
3) Many women present with diverse physical as well as psychological symptoms during perimenopause and postmenopause. They are referred to as climacteric symptoms or menopausal symptoms.
According to the survey conducted by the Korean Society of Menopause, of 707 women who underwent natural menopause, 89% answered that they experienced menopausal symptoms or have symptoms currently.
1) Such menopausal symptoms include hot flashes, irregular heart beats, insomnia, and fatigue, in addition to myalgia and arthralgia, decreased desire, mood changes, hypersensitivity, anxiety, depression, memory impairment, etc., and urogenital symptoms, such as dry vagina, dyspareusia, cystitis, urodynia, and urinary urgency.
To estimate such climacteric symptoms, questionnaire survey methods, such as the Greene
4) menopause index, Kupperman index, and the menopause rating scale (MRS), etc. have been used.
5) Questionnaire survey methods have advantages in that they could be simply and readily used for assessment of menopausal symptoms.
The basic cause of menopausal symptoms is the complex relationship of estrogen metabolism and the autonomic nervous system. Therefore, imbalance of the autonomic nervous system may correlate with menopausal symptoms. Disharmony of the autonomic nervous system could be evaluated by measurement of heart rate variability (HRV).
6) Heart rate variability is cyclic interval changes of the heart rate.
7) This is the value that measures changes from one cardiac cycle to the next cycle or change of the RR interval with electrocardiogram. The activity level of the autonomic nervous system could be quantified by analysis of heart rate variability using power spectral analysis (time and frequency domain analysis).
8)
Until now, study of the correlation of such menopausal symptoms with heart rate variability has not been adequate. In this study, the relationship of menopausal symptoms with heart rate variability was examined using a questionnaire survey method.
DISCUSSION
Heart rate is determined by the proprietary autonomy of the sinoatrial node and the autonomic nervous system. The autonomic nervous system, which controls the sinoatrial node, is constantly influenced by diverse changes of environment, and the cyclic interval change of heart rate that appears at that time is referred to as HRV.
12) Analysis of such HRV, which could be used in assessing the activity level of the autonomic nervous system, could be performed relatively inexpensively; it is non-invasive and quantitative; thus, numerous studies have been conducted. Consequently, the task force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology standardized the method for measurement of HRV and its physiological and clinical uses in 1996.
13) Clinical application of LF is controversial; nonetheless, LF has been used as the index of control of the sinoatrial node of the heart by the sympathetic nerve, and HF as the index of control of the sinoatrial by the vagus nerve. And the LF/HF ratio, which reflects activity of sympathetic nerves, has been used as the index of the balance state of the autonomic nervous system.
14) It has been reported that the general characteristic of HRV is shown in general by time domain analysis; nonetheless, frequency domain analysis better shows the balance state of the sympathetic nerve and the parasympathetic nerve.
12)
In this study, the relationship of menopausal symptoms and HRV was examined. In the menopausal group, the LF/HF ratio was found to be significantly elevated in comparison with the group without menopausal symptoms. Until now, studies comparing the HRV of young premenopausal women with that of postmenopausal women have reported that the LF/HF ratio was elevated in postmenopausal women.
14) However, studies comparing HRV of the group with menopausal symptoms and the group without menopausal symptoms in perimenopausal and postmenopausal woman, such as our research, have not been conducted. Results of this study have shown that the group with menopausal symptoms showed a greater increase in sympathetic nerve activity.
No significant differences of HRV index were observed according to severity of postmenopausal symptoms. Results of this study do not concur with results of a study reported by Ahn et al. in 2005,
15) which applied HRV as a standard of climacteric symptoms. They reported that in the group with severe menopausal symptoms, the SDNN and the RMSSD were reduced. Nevertheless, the study by Ahn et al.
15) has a limitation in that the number of subjects was small (n = 16). Our study also has a small number of subjects; thus, it is difficult to draw a concrete conclusion in regard to the association of the level of menopausal symptoms with HRV. Studies with larger number of subjects will be required in the future.
According to our results that show the association of the 11 subcategories of the MRS and the index of HRV, the LF/HF ratio was found to increase in the group whose levels of hot flashes and sleep disorders were higher than moderate. The results concur with results reported by Hoikkala et al.
16) in 2009 that showed the normalized LF and normalized HF value were different by the level of hot flashes. In addition, although direct comparison is difficult, the findings are similar to those of the study by Rebecca et al. in 2009, which was on hot flashes and control of the heart by the vagus nerve and showed that HF decreased when hot flashes were severe. Other studies and ours found that, according to hot flash symptoms, one of which is menopausal symptoms, imbalance of the autonomic nervous system such as reduction of the activity level of the parasympathetic nerve may be present. The mechanism of postmenopausal sleep disorders has not been elucidated. However, several studies speculate that hot flashes induce wakefulness during sleep, resulting in chronic sleep deprivation and fatigue.
17) Consequently, deterioration of the sleep quality lowers the level of activity of the parasympathetic nerves.
12) When the autonomic nervous system, which maintains the electrical stability of heart, is impaired, arrhythmia or consequent death may increase.
12) Therefore, our study found that the level of imbalance of the autonomic nervous system was different by the severity of hot flashes or sleep disorder symptoms.
The group with menopausal symptoms had higher anxiety traits with statistical significance that the group without menopausal symptoms. When postmenopausal physical symptoms manifest, anyone experiences negative self-esteem such as hurt pride, uselessness, lack of self-confidence, etc.; thus, a state of emotional crisis, such as anxiety, depression, etc. may be induced.
18)
This study has several limitations. First, although 5-minute measurement of HRV has been applied as a useful tool for evaluation of the autonomic nervous system function, which controls the heart, the area of very LF, which directly shows the level of activity of the sympathetic nervous system, could be measured with accuracy using 24-hour measurement.
13) So, our study measured SDNN and the LF area among measurements of 5-minute HRV; then attempted indirect analysis. For more accurate studies, measurement of 24-hour HRV is required. Second, the number of subjects was not sufficient; thus, the association of the level of menopausal symptoms with HRV was analyzed using a non-parametric testing method. It is suggested that studies on a larger number of subjects should be conducted.
Despite such limitations, our study observed that the presence or absence of menopausal symptoms was associated with HRV. The LH/HF ratio became different depending on the severity of hot flashes and sleep disorders, and the elevation of anxiety trait and other emotional disorders were observed in the group with menopausal symptoms. The association of menopausal symptoms with cardiovascular disease could not be directly compared only by HRV; nonetheless, in cases experiencing a higher-than-moderate level of hot flashes and sleep disorders, based on the increase of the LF/HF ratio, the increased level of activity of the sympathetic nervous system could be confirmed in our study.