Syncope ( from the Greek ‘I interrupt', or 'I cut')) is defined as a temporary loss of consciousness, that generally occurs in the upright posture and leads to falling. Caused by a reduction in blood volume to the brain, it is a symptom that occurs as a result of some underlying disease, rather than being a disease itself. Each year, over one million people in the United States are evaluated for syncope. For some individuals, testing may reveal a definitive cause for their fainting (e.g. heart problems, dehydration), but for the majority of individuals impacted by recurrent syncope, the physician will identify it as being a problem in the autonomic nervous system (neurally-mediated).
For the physician, syncope can often be a difficult symptom to assess. To determine which of the many underlying mechanisms that might be causing the syncope, multiple diagnostic exams are often needed. Furthermore, most patients are not symptomatic when they visit their doctor, adding to the diagnostic dilemma. This process can be frustrating for both the patient as well as the treating physician. It is also not unusual for patients to see multiple physicians in an effort to determine the cause of their syncope.
(Neurally-mediated syncope refers to a reflex response where some triggering mechanism leads to a sudden drop in heart rate (bradycardia) and/or a vasodilatation (an expansion of blood vessels). While a specific trigger can sometimes be identified (e.g. coughing, the sight of blood), most patients have no clear triggering mechanism that can be identified Other terminology that is often used to describe this type of syncope include neurocardiogenic and vasovagal syncope. Generally, most research in autonomic labs separates the patients who experience syncope as a symptom of a broader disorder (e.g. POTS) from those who have sudden fainting episodes that are not associated with other symptoms.
Below you will find links to full text articles that are available for download or for viewing. Keep in mind that this research is intended for a medical professional audience, and may not be easily understood without consultation with your physician. Also, there are numerous medical journals that publish medical research, each with its own set of standards of review and acceptance. What one journal will accept may have been rejected by several other journals as not meeting peer scrutiny.
As you read the journal articles that are available here, please keep in mind that research findings often may point to conflicting results. A single study's results may not be able to be duplicated, or may be contradicted by results from another study.
You should speak to your physician before making any judgments based upon this information.
Below are links to full text review articles that discuss the autonomic nervous system and orthostatic intolerance. Click on the hyperlink to open up a PDF file. You will need to have Adobe's free Reader program installed in order to view these files.
Neurocardiogenic syncope and related disorders of orthostatic intolerance.
Circulation. 2005 Jun 7;111(22):2997-3006. Review.
Guidelines on management (diagnosis and treatment) of syncope--update 2004.
Europace. 2004 Nov;6(6):467-537
Dysautonomias: clinical disorders of the autonomic nervous system.
Ann Intern Med. 2002 Nov 5;137(9):753-63. Review.
Clinical disorders of the autonomic nervous system associated with orthostatic intolerance: an overview of classification, clinical evaluation, and management.
Pacing Clin Electrophysiol. 1999 May;22(5):798-810. Review
The following links provide access to journal articles on NMS from the National Library of Medicine's PubMed database of medical research. By clicking on the hyperlink, you will be directed to the NLM web site where you can access the abstract. Use the "Full Text" link to open the full article in your browser window. Most articles have a PDF version available for downloading, saving or printing. If you are looking for additional information or articles that provide abstracts only, please visit the NLM web site.