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 Researchers release the brakes on the immune system
18.10.2017 | Rheinische Friedrich-Wilhelms-Universität Bonn

nachricht Norovirus evades immune system by hiding out in rare gut cells
12.10.2017 | University of Pennsylvania School of Medicine

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: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>