Estrogen linked to more efficient regulation of a woman's heartbeat.

2002 DEC 19 - (NewsRx.com & NewsRx.net) -- Men die earlier than women. This fact leads scientists and medical researchers to conclude that gender and age are two basic factors continuously affecting body functions, disease categories and even life expectancy.

Previous research has determined that gender influences brain structure and functions; however, in considering the cardiac pacemaker, there is still debate as to whether heart rate dynamics differ between women and men.

Electrocardiogram (ECG) findings offer interesting arguments for both sides of the issue. There is a similarity in the sexes regarding the mean and standard deviation of the R-R interval portion of electrocardiogram (intervals between positive deflection of the QRS complex, which involves the depolarization of ventricular cardiac cells).

On the other hand, women have been reported to have lower, similar, and higher high-frequency power (HF) and similar low-frequency power (LF) of heart rate variability (HRV). (HRV is a strong predictor of mortality adversely affected by such problems as anxiety, depression, and trauma.)

A team of researchers has speculated whether confusing findings in heart activity of the sexes could be attributed to the nonlinear characteristics of pacemaker activity, which may cause large variations when analyzed by traditional linear methods. Such variations might lead to severe interference if there are gender differences in the discharge from the heart's natural pacemaker, the sinus (SA) node. Accordingly, they set out to determine whether the complexity or chaos of cardiac pacemaker activity differs between women and men.

Because aging may be a major determinate of heart rate dynamics, the researchers systemically studied the effect of aging on nonlinear properties and on gender-related differences. The results were then compared with standard frequency-domain methods to measure the nervous system's parasympathetic and sympathetic regulation of heart rate.

The authors of "Sexual dimorphism in the complexity of cardiac pacemaker activity," are Terry B.J. Kuo from Tzu Chi University and Tzu Chi Buddhist General Hospital, Hualien, Taiwan, and Cheryl C.H. Yang, also from Tzu Chi University. Their findings appeared in the American Journal of Physiology-Heart and Circulatory Physiology (2002;283(4):H1695-702).