Dysautonomia

Dysautonomia is impaired function of the autonomic nervous system, which regulates involuntary processes such as heart rate, blood pressure, digestion, and temperature control. It can arise from many different disorders and causes.

Autonomic nervous system: The nervous system division that regulates involuntary functions, including heart rate, digestion, and glandular activity. Dysautonomia is impaired function of this regulatory system.
Postural orthostatic tachycardia syndrome: A syndrome marked by excessive heart-rate increase on standing, with chronic orthostatic symptoms. It is a common, specifically defined form of orthostatic autonomic dysfunction.
Tilt table test: A test that monitors cardiovascular responses while a person is moved from lying down to an upright tilt. It can reveal abnormal heart-rate or blood-pressure responses to upright posture.
Vasovagal syncope: A transient faint caused by a reflex that lowers heart rate or blood pressure, reducing blood flow to the brain. It can resemble dysautonomia but is typically defined by episodic reflex fainting.
Orthostatic intolerance: Difficulty tolerating an upright posture, often involving symptoms such as dizziness, weakness, or palpitations. Impaired autonomic adjustment to standing can cause these symptoms.
Multiple system atrophy: A progressive neurodegenerative disease combining autonomic failure with parkinsonian or cerebellar features. It illustrates severe autonomic dysfunction arising within a neurological disease.
Valsalva maneuver: A forced exhalation against a closed airway that produces measurable changes in heart rate and blood pressure. Its cardiovascular responses help assess autonomic reflex function.
Dehydration: A state in which the body has lost more water than it has taken in. It can mimic or worsen orthostatic symptoms without being autonomic nerve disease.
Baroreflex: A reflex that uses pressure sensors to adjust heart rate and blood vessel tone as blood pressure changes. Dysfunction can impair rapid blood-pressure regulation when posture changes.
Pure autonomic failure: A neurodegenerative disorder causing autonomic failure without prominent motor or cognitive symptoms. It is a disorder in which autonomic impairment is the principal feature.

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