**5. Heart rate variability and hormonal therapy**

The aging process causes changes in the autonomic modulation of the cardiovascular system, and particularly in HR. The literature reports that parasympathetic activity in the sinus node decreases with age, leading to a reduction in HRV and a greater risk for cardiovascular events (Lipsitz et al., 1990). Structural and functional changes in the blood vessels, in the cardiac conduction system and in the sensitivity of baroreceptors, as well as increased myocardial stiffness, leading to greater force of contraction and reduced ventricular filling, contribute to reduce the functional capacity of the cardiovascular and hemodynamic system (Walsh, 1987). In addition, with increasing age, submaximal physical activity and decline in functional capacity lead to increased physiological stress (Perini et al., 2002).

The incidence of cardiovascular diseases among premenopausal women is low when compared to that of men in the same age group, but increases significantly after this period (Gensini et al., 1996). In several countries, cardiovascular diseases are the major cause of morbidity and mortality among postmenopausal women, representing an important public health problem (Mosca et al., 1997). The increase in the incidence of cardiovascular events among middle-aged women has been associated with the hypoestrogenism typical of this period of women's lives (Greendale et al., 1999).

With regard to autonomic heart function, some studies have demonstrated the harmful effects of hypoestrogenism on HRV. Mercuro et al. (2000) found a reduction in HRV indices, analyzed in the time and frequency domains, after bilateral oophorectomy, i.e., through the interruption of estrogen production, as occurs in menopause. Liu et al. (2003) demonstrated higher values of HRV, analyzed in the time domain, in premenopausal

Spectral Analysis of Heart Rate Variability in Women 177

In the supine position, it was found that the YG presented significantly higher values of the HF index in absolute units (ms2) and lower LF values (ms2) and ratio than the PostMG. In addition, the YG and PostMG showed a statistical difference in all the evaluated indices (p<0.05), while no difference was found between the PreMG and PostMG groups (p>0.05). In a comparison of the YG vs. PreMG and YG vs. PostMG groups in the sitting position, the

With regard to the effect of postural adjustment on the autonomic HR modulation, a comparison of the indices obtained in the supine and sitting positions revealed significant differences (p<0.05) in all the indices. On the other hand, the PreMG groups showed a difference in the LF/HF index (p<0.05), while the PostMG group showed no significant

Having calculated the regression coefficients, it was found that the straight line of the adjusted regression indicates that, as the age of the subjects increases, it is possible to estimate the reduction of the HF index (ms2). The parameters indicate mainly a reduction of the postural change in parasympathetic modulation. With aging, the adjustment capacity

This chapter discussed the measurement and analysis of HRV, as well as results of data for women and the relationship between aging, hormonal changes (oral contraceptives and hormone replacement therapy) which contribute to modifications in the autonomic control

This chapter was financed by the Brazilian research funding agencies CNPq (National Council for Scientific and Technological Development – Process no. 370448/2007-3) and

Akselrod, S. (1995). Components of heart rate variability: Basic Studies. In: *Heart Rate* 

Arangino, S. et al. (1998). Effect of desogestrel-containing oral contraceptives on vascular

Boettger, M. K. et al. (2010). Influence of Age on Linear and Nonlinear Measures of

Brockbank, C. L. et al. (2000). Heart rate and its variability change after the menopause. *Experimental Physiology*, Vol. 85, No. 3, pp. 327-330, ISSN 1469-445X (Electronic).

*Variability* Malik, M & Camm, AJ, (Ed.), pp. 147-163, Futura Publishing Company,

reactivity and catecholamine levels. *Contraception*, Vol. 58, pp. 289 – 93, ISSN 1879-

Autonomic Cardiovascular Modulation. *Annals Noninvasive Electrocardiology*, Vol.

diminishes, as indicated by the delta between the supine and sitting positions.

FAPESP (São Paulo Research Foundation – Process no. 2006/56788-1).

15, No. 2, pp. 165–174., ISSN 1542-474X (Electronic).

YG presented significantly higher values for the ratio (p<0.05).

difference (p<0.05).

**7. Conclusions** 

of heart rate.

**9. References** 

**8. Acknowledgments** 

New York.

0518 (Electronic).

women than in postmenopausal women and men in the same age group, illustrating the importance of estrogens in the autonomic differences brought about by menopause. Similar findings, also analyzed in the time domain, were reported by Brockbank et al. (2000) for premenopausal women compared to women after more than one year of menopause. Davy et al. (1998) reported that young women have higher HRV than menopausal women, and that HRV in both active and sedentary women tends to decline with advancing age. In earlier studies conducted in our laboratory (Ribeiro et al., 2001; Neves et al., 2007), lower levels of HRV in menopausal women compared to young women were also recorded.

To ascertain if a physical training program could promote physiological adaptations and improved sympathovagal balance of the heart, attenuating the deleterious effects of menopause on the cardiovascular system, Sakabe (2007) evaluated 18 sedentary women divided into two groups: Control Group – 10 postmenopausal women (50 to 60 years old) without hormone therapy (HT); and HT Group – 8 postmenopausal women (50 to 60 years old) undergoing HT (estradiol plus levonorgestrel). Both groups were assessed at two different times: before (assessment) and after (reassessment) a 3-month physical training program (PTP). Protocol 1 – to evaluate the autonomic modulation of the HR, the HR was recorded under resting conditions, supine and sitting positions, for 15 minutes in each position. The indices evaluated in Protocol 1 were: mean HR and R-R intervals (RRI), RMSSD index of the RRI, low (LF) and high (HF) frequency bands of the spectral analysis, in normalized units, and LF/HF ratio. It was concluded that hormone replacement therapy did not have a significant effect on HRV.
