TABLE 166 Syncope and Similar Disorders



Precipitating Factors

Vasodepressor Syncope

(the common faint)

Sudden peripheral vasodilatation, especially in the skeletal muscles, without a compensatory rise in cardiac output. Blood pressure falls.

A strong emotion such as fear or pain

Postural (orthostatic) Hypotension

Inadequate vasoconstrictor reflexes in both arterioles and veins, with resultant venous pooling, decreased cardiac output, and low blood pressure

Standing up

Cough Syncope Micturition Syncope

Cardiovascular Disorders


Aortic Stenosis and Hypertrophic Cardiomyopathy

Myocardial Infarction

Massive Pulmonary Embolism

Disorders Resembling Syncope

Hypocapnia (decreased carbon dioxide) Due to Hyperventilation

■ Hypovolemia, a diminished blood volume insufficient to maintain cardiac output and blood pressure, especially in the upright position

Several possible mechanisms associated with increased intrathoracic pressure


Decreased cardiac output secondary to rhythms that are too fast (usually more than 180) or too slow (less than 35-40)

Vascular resistance falls with exercise, but cardiac output cannot rise.

Sudden arrhythmia or decreased cardiac output

Sudden hypoxia or decreased cardiac output

Constriction of cerebral blood vessels secondary to hypocapnia that is induced by hyperventilation

■ Standing up after hemorrhage or dehydration

Severe paroxysm of coughing

Emptying the bladder after getting out of bed to void

A sudden change in rhythm


Variable Variable

Possibly a stressful situation


Insufficient glucose to maintain cerebral metabolism; secretion of epinephrine contributes to symptoms.

Variable, including fasting

Hysterical Fainting Due to a Conversion Reaction*

The symbolic expression of an unacceptable idea through body language

Stressful situation

* Important diagnostic observations in hysterical fainting include normal skin color and normal vital signs, sometimes bizarre and purposive movements, and occurrence in the presence of other people.

TABLE 16-6 ■ Syncope and Similar Disorders

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