The most common type of fainting is vasovagal syncope (VVS) that is caused by a sudden drop in blood pressure resulting in reduced blood flow to the brain. VVS can occur in healthy people due to inappropriate cardiovascular responses to certain behavioral or emotional triggers such as fear, needle prick or even standing up. VVS has a daily pattern with more occurrences during the morning. This daily pattern is possibly due to the daily distribution of behavioral and emotional stimuli or perhaps due to influences from the internal circadian system, or 'body clock'. In a new study, researchers at Brigham and Women's Hospital (BWH) provide strong evidence that the circadian system may contribute to the daily pattern of VVS via its influences on physiological responses to changes in body posture. These findings are published on March 8, 2011 in the journal Circulation.
Lead study author Kun Hu, PhD, of the Division of Sleep Medicine at BWH said that "the susceptibility to VVS is probably present in all healthy humans. Fainting can cause an individual to fall which can result in severe trauma, including skull and limb bone fractures. Recurrent VVS can also affect quality of life due to reduced activities and social adjustment. Understanding the causes of VVS is important for diagnosis, prevention and treatment of people with a history of recurrent VVS".
In this study, repeated tilt-table tests were used to determine the susceptibility to VVS across the day and night in twelve healthy participants who stayed in a controlled laboratory environment for almost 2 weeks. To measure the influence of the internal body clock on VVS while controlling for other factors including the sleep/wake cycle, meals and the environment, the researchers scheduled all behaviors of participants while they lived on a recurring 20-hour "day" (with 6.7 hours scheduled for sleep and 13.3 hours for wake). The study was performed in dim light so that the internal body clock still oscillated with an approximate 24-hour period. Core body temperature was measured throughout to indicate the times of the internal body clock. To stop the participants from actually fainting, signs of imminent VVS (presyncope) were closely monitored and tilt-table tests were immediately aborted whenever there were notable symptoms of nausea, dry mouth, dizziness, or low blood pressure or rapidly falling blood pressure.
The researchers found that the vulnerability to presyncope has a strong connection to the internal body clock, with susceptibility nine times higher at the circadian times between 10:30 PM and 10:30 AM compared to between 10:30 AM through 10:30 PM. The highest risk for presyncope occurred at the circadian time corresponding to 4:30 AM. "This vulnerable period may have relevance to individuals who remain awake or wake up frequently during the night, such as shift workers, parents feeding their infants and elderly people with increased nocturia or insomnia. These people may be at higher risk for syncope due to their postural changes during the night" said one of the investigators, Dr. Steven Shea of the Division of Sleep Medicine at BWH.
In addition, this study highlights the importance of performing tilt-table tests at similar circadian times when comparing responses of different individuals or the same person before and after treatments for syncope. The results also suggest that a higher sensitivity may be achieved by performing tilt-table testing during early morning hours or the night.
The research was funded by grants from the National Institutes of Health and the Harvard Catalyst.
Brigham and Women's Hospital (BWH) is a 793-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare, an integrated health care delivery network. BWH is the home of the Carl J. and Ruth Shapiro Cardiovascular Center, the most advanced center of its kind. BWH is committed to excellence in patient care with expertise in virtually every specialty of medicine and surgery. The BWH medical preeminence dates back to 1832, and today that rich history in clinical care is coupled with its national leadership in quality improvement and patient safety initiatives and its dedication to educating and training the next generation of health care professionals. Through investigation and discovery conducted at its Biomedical Research Institute (BRI), BWH is an international leader in basic, clinical and translational research on human diseases, involving more than 900 physician-investigators and renowned biomedical scientists and faculty supported by more than $ 537 M in funding. BWH is also home to major landmark epidemiologic population studies, including the Nurses' and Physicians' Health Studies and the Women's Health Initiative. For more information about BWH, please visit www.brighamandwomens.org.
Holly Brown-Ayers | EurekAlert!
Researchers identify potentially druggable mutant p53 proteins that promote cancer growth
09.12.2016 | Cold Spring Harbor Laboratory
Plant-based substance boosts eyelash growth
09.12.2016 | Fraunhofer-Institut für Angewandte Polymerforschung IAP
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine