Featured Research

from universities, journals, and other organizations

Body's clock may lead to increased risk for fainting during the nighttime

Date:
March 8, 2011
Source:
Brigham and Women's Hospital
Summary:
The circadian system may contribute to the daily pattern of vasovagal syncope via its influences on physiological responses to changes in body posture.

Fainting, or syncope, is quite common. About 50% of people will experience fainting at some point during their lifetime. 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.

Related Articles


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.


Story Source:

The above story is based on materials provided by Brigham and Women's Hospital. Note: Materials may be edited for content and length.


Journal Reference:

  1. K. Hu, F. A. J. L. Scheer, M. Laker, C. Smales, S. A. Shea. Endogenous Circadian Rhythm in Vasovagal Response to Head-Up Tilt. Circulation, 2011; DOI: 10.1161/CIRCULATIONAHA.110.943019

Cite This Page:

Brigham and Women's Hospital. "Body's clock may lead to increased risk for fainting during the nighttime." ScienceDaily. ScienceDaily, 8 March 2011. <www.sciencedaily.com/releases/2011/03/110307161956.htm>.
Brigham and Women's Hospital. (2011, March 8). Body's clock may lead to increased risk for fainting during the nighttime. ScienceDaily. Retrieved November 23, 2014 from www.sciencedaily.com/releases/2011/03/110307161956.htm
Brigham and Women's Hospital. "Body's clock may lead to increased risk for fainting during the nighttime." ScienceDaily. www.sciencedaily.com/releases/2011/03/110307161956.htm (accessed November 23, 2014).

Share This


More From ScienceDaily



More Health & Medicine News

Sunday, November 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

WFP: Ebola Risks Heightened Among Women Throughout Africa

WFP: Ebola Risks Heightened Among Women Throughout Africa

AFP (Nov. 21, 2014) Having children has always been a frightening prospect in Sierra Leone, the world's most dangerous place to give birth, but Ebola has presented an alarming new threat for expectant mothers. Duration: 00:37 Video provided by AFP
Powered by NewsLook.com
Could Your Genes Be The Reason You're Single?

Could Your Genes Be The Reason You're Single?

Newsy (Nov. 21, 2014) Researchers in Beijing discovered a gene called 5-HTA1, and carriers are reportedly 20 percent more likely to be single. Video provided by Newsy
Powered by NewsLook.com
Raw: Paralyzed Marine Walks With Robotic Braces

Raw: Paralyzed Marine Walks With Robotic Braces

AP (Nov. 21, 2014) Marine Corps officials say a special operations officer left paralyzed by a sniper's bullet in Afghanistan walked using robotic leg braces in a ceremony to award him a Bronze Star. (Nov. 21) Video provided by AP
Powered by NewsLook.com
Milestone Birthdays Can Bring Existential Crisis, Study Says

Milestone Birthdays Can Bring Existential Crisis, Study Says

Newsy (Nov. 21, 2014) Researchers find that as people approach new decades in their lives they make bigger life decisions. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins