Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Estrogen linked to more efficient regulation of a woman’s heartbeat

05.11.2002


Age is the ’equalizer,’ according to a study that provides new insights into why women live longer than men



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 October 2002 edition of the American Journal of Physiology--Heart and Circulatory Physiology.

Methodology

The study entailed the participation of 480 volunteers (240 women and 240 men), age 40–79, similar to overall distribution of males and females. They were distributed into eight groupings based on five-year age intervals, with each age stratum containing 30 women and 30 men. Subjects excluded had cardiovascular fluctuations: hypotension, hypertension, diabetic neuropathy, an implanted cardiac pacemaker, frequent occurrence of atrial fibrillation, premature atrial or ventricular contractions, or other forms of arrhythmia. Nonlinear analysis of short-term resting R-R intervals was performed using the correlation dimension (CD), approximate entropy (ApEn), and largest Lyapunov exponent (LLE). Evidence of nonlinear structure was obtained by the surrogate data test. CD, ApEn, and LLE were negatively correlated with age.

Results

The short-term heart rate variability analyses reveal that a woman’s heart rate is characterized by a higher CD, ApEn, and LLE when compared with that of a man in the middle age, indicating a more complex signal broadcasting from a woman’s cardiac pacemaker.

In assessing the brain, a more complex neural signal is always accompanied with a more involved neural network. On the other hand, a very simple firing pattern can only be observed in an isolated neuron. Thus the higher complexity of women’s heart rate dynamics implies that the female heart is modulated more comprehensively by the autonomic nervous system (ANS), especially the rapid vagal influence, although such modulation is not strong enough to produce an evident change in the mean and standard deviation of R-R intervals. With the effect of age, previous studies have revealed that aging is accompanied with a decrease of complexity in either cardiac pacemaker activity or midbrain neural activity. Older subjects, regardless of gender, had a lower CD, ApEn, and LLE, indicating a lower degree of neural modulation to the cardiac pacemaker.

The researchers conclude that this lower complexity in the elderly may be due to a decrease in the ANS potency resulting from the normal aging process. The higher complexity of heart rate dynamics observed in women before the age of menopause may be related to the lower cardiac mortality and longer life expectancy of women. Previous studies regarding the nonlinear analysis of HR dynamics chiefly focused on its capability to discriminate pathological states or senile changes from normal conditions. Because illness and aging may lead to a prominent change in ANS function, which in turn leads to a prominent change in HR dynamics, such alterations can usually be detected by traditional linear methods.

Conclusions

In almost every country, women have a longer life expectancy than men, generally attributed to gender-related differences in cardiovascular function. The exact mechanism underlying these differences remains unclear; however, the data in this study indicate that changes in the nonlinear properties may reflect effects of gender and aging on cardiac parasympathetic regulation. The gender-related difference in autonomic regulation function is key: women before menopause have a lower risk of heart diseases than do men. The "cardioprotective" effect of estrogen has been proposed for this trend but the linkage between the sex hormone and the heart is ambiguous. Because a potentiated vagal function may protect the heart from tachyarrhythmias after ischemic heart disease and decrease the mortality rate, the dominance of vagal function in middle-aged women may produce a protective effect against lethal tachyarrhythmias.

The study revealed 71 percent of women were postmenopausal; the mean age of menopause was 47.7, and only six percent of postmenopausal women received hormone replacement therapy. Thus the loss of gender-related differences in the nonlinear indexes after age 50 supports the hypothesis that estrogen has a facilitating effect on cardiac parasympathetic regulation as revealed by the nonlinear content of heart rate dynamics. Nonlinear analysis techniques may reveal new aspects of HR dynamics. Mechanisms underlying the effects of gender and aging on nonlinear properties of cardiac pacemaker activity and related clinical applications warrant further investigations. Because the algorithms may be directly incorporated into current HRV analysis protocols, CD, ApEn, and LLE have a high potential for studying gender-related differences in cardiac pacemaker activity and related autonomic regulation.


###
Source: October 2002 edition of the American Journal of Physiology--Heart and Circulatory Physiology.

The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.

Donna Krupa | EurekAlert!

More articles from Health and Medicine:

nachricht Usher syndrome: Gene therapy restores hearing and balance
25.09.2017 | Institut Pasteur

nachricht MRI contrast agent locates and distinguishes aggressive from slow-growing breast cancer
25.09.2017 | Case Western Reserve University

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Fraunhofer ISE Pushes World Record for Multicrystalline Silicon Solar Cells to 22.3 Percent

25.09.2017 | Power and Electrical Engineering

Usher syndrome: Gene therapy restores hearing and balance

25.09.2017 | Health and Medicine

An international team of physicists a coherent amplification effect in laser excited dielectrics

25.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>