Fainting

FAINTING

Fainting is a common symptom in the elderly, generally referred to in the medical literature as syncope. Fainting is defined as transient loss of consciousness accompanied by loss of postural tone, with spontaneous recovery, not requiring resuscitation. Fainting has multiple underlying causes. This common symptom has potential adverse consequences, such as falls, fractures, brain injury, soft tissue injuries, and anxiety, which particularly in the elderly may lead to loss of independent function. When the reason for fainting is an underlying heart disease, an increased risk of sudden death is suggested; but when fainting is unexplained after thorough initial evaluation and recurrent then there is no such increased risk.

A person who faints may have some convulsions but recovers quickly and is not confused for more than a few minutes, whereas a person with epilepsy will usually have more prolonged convulsions and be confused for a longer time. In coma the heart beats and the person breathes but consciousness is not regained as quickly.

Basic mechanisms and predisposition in elderly people

Fainting results from inadequate energy substrate delivery to the brain. The major energy substrates are oxygen and glucose. Significant lowering of blood sugar tends to result in coma rather than fainting, and a prolonged cessation of oxygen delivery results in death. Thus transient loss of delivery of oxygen to the brain due to decreased blood flow to the brain is the final common pathway in most causes of fainting. Generalized lowering of oxygen in the blood from heart or lung disease or reduced oxygen-carrying capacity of the blood from anemia are risk factors for fainting, particularly in the elderly, but rarely the sole cause.

Blood pressure lowered enough to decrease blood flow to the brain may cause fainting, and the causes of fainting can be deduced from the blood pressure formula. Blood pressure is the product of cardiac output and total peripheral resistance of the arteries. Cardiac output is the product of stroke volume and heart rate per minute. Stroke volume is the amount of blood that the heart ejects in one beat. Total peripheral resistance is a measure of how constricted the arterial blood vessels are. Thus anything that will reduce the volume of blood that is ejected, impair heart rate, or cause dilatation of the arteries may lead to a fainting spell.

Elderly people are predisposed to fainting by the presence of multiple abnormalities, both age- and disease related. These conditions add up to threaten cerebral blood flow or reduce oxygen content in the blood. A situational stress that further reduces blood pressure, such as standing up from a lying position or straining at stools or voiding, may reduce cerebral oxygen delivery below the critical threshold and result in fainting. Several homeostatic mechanisms that normally preserve blood pressure and cerebral oxygen delivery in the face of stress become impaired with age. These mechanisms include cerebral blood flow autoregulation, blood pressure sensors in the carotid artery (baroreflexes), relaxation of the heart muscle, and sodium conservation by the kidneys.

Causes

Multiple studies have shown that 20 to 30 percent of fainting episodes have cardiac causes, 10 to 20 percent have other causes, and 30 to 50 percent remain unexplained in spite of extensive evaluation.

Several cardiac diseases may cause fainting, such as those that cause mechanical obstruction to blood flow such as narrowing of heart valves or abnormal thickening of the heart muscle, called cardiomyopathy. Blood clots from veins of the body, most often the legs, may also present with fainting due to obstruction of blood flow through the lungs and heart. Both slow heart rate (less than 40 beats per minute) and rapid heart rate (more than 140 beats per minute) may cause fainting. The rapid heart rate causes fainting by not giving the heart enough time to fill with blood before ejection into the circulation. The causes of these heart rate abnormalities include heart attacks, disease of the conduction system of the heart, and disease—most often seen in the elderly—of the sinus node of the heart, where the origin of the heart beat occurs normally.

Orthostatic hypotension is a term for blood pressure that drops more than 20 mm of mercury on position change, such as standing up from a lying or sitting position. This may cause dizziness when in mild stages but frequently causes elderly people to faint. It is either due to volume depletion or inability to constrict blood vessels under this type of stress. Volume depletion may be caused by fluid loss or blood loss or by too little fluid intake, or by medications such as diuretics, which increase excretion of fluid through the kidneys. Dilatation of the blood vessels may be caused by prolonged inactivity, such as bed rest, or by medications such as blood pressure– lowering medications and the older types of medications prescribed for depression. By only giving the lowest effective dose of medications to the elderly person, these types of adverse effects may be avoided or corrected. Disturbed autonomic function may cause dilatation of the blood vessels and cause fainting. Examples of these are central nervous system diseases—such as Multiple System Atrophy, Parkinson's disease, or Dementia with Lewy Bodies—and peripheral autonomic neuropathies caused by diseases such as diabetes mellitus or amyloidosis. Digestion of food may lead to hypotension and fainting in the elderly person due to inability to compensate for blood pooling in the gut during digestion, so-called postprandial hypotension. Finally, reflexes may cause dilatation of blood vessels, triggered by straining at stools, urination, swallowing, or coughing or by hypersensitivity of the carotid sinus, which is located in the neck.

Evaluation and treatment

The patient's history is the most important part of the evaluation, and the physical examination focuses on blood pressure and heart evaluation to exclude the life-threatening causes of fainting. Therapy should be directed toward minimizing multiple risks of fainting, avoiding toxic interventions, and treating specific symptomatic diseases (for example, with pacemakers for certain conduction diseases in the heart), while basing treatment on the underlying disease, rather than on age per se.

PÁlmi V. JÓnsson

See also Balance and Mobility; Dementia with Lewy Bodies; Dizziness; Epilepsy; Heart Disease; Multiple Systems Atrophy; Parkinsonism.

BIBLIOGRAPHY

JÓnsson, P. V., and Lipsitz, L. A. "Dizziness and Syncope." In Principles of Geriatric Medicine and Gerontology, 3d ed. Edited by William R. Hazzard, Edwin L. Bierman, John P. Blass, Walter H. Ettinger, Jr., and Jeffrey B. Halter. McGraw-Hill Inc., 1994. Pages 1165–1181.

Linzer, M.; Yang, E. H.; Estes, N. A., III; Wang, P.; Vorperian, V. R.; and Kapoor, W. N. "Diagnosing Syncope. Part 2: Unexplained Syncope. Clinical Efficacy Assessment Project of the American College of Physicians." Annals of Internal Medicine 127, no. 1 (1997): 76–86.

Shaw, F. E., and Kenny, R. A. "The Overlap between Syncope and Falls in the Elderly." Postgraduate Medical Journal 73, no. 864 (1997): 635–639.

FALLS

See Balance and mobility