neurologic disorders
Overview of the Autonomic Nervous System
Evaluation of Autonomic Insufficiency
Symptoms suggesting autonomic insufficiency include Orthostatic intolerance (development of autonomic symptoms such as lightheadedness that is relieved by sitting down) due to orthostatic hypotension or postural orthostatic tachycardia syndrome Heat intolerance Loss of bladder and bowel control Erectile dysfunction (an early symptom) Other possible symptoms include dry eyes and dry mouth, but they are less specific. Important parts of the examination include the following: 10 mm Hg in diastolic BP with standing indicates Orthostatic Hypotension . Heart rate change with respiration and standing should be noted; absence of physiologic sinus arrhythmia and failure of heart rate to increase with standing indicate autonomic insufficiency. In contrast, patients with Miosis and mild ptosis ( Horner Syndrome ) suggest a sympathetic lesion. A dilated, unreactive pupil (Adie pupil) suggests a parasympathetic lesion. Genitourinary (GU) and rectal reflexes:Abnormal GU and rectal reflexes may indicate autonomic nervous system deficits. Testing includes the cremasteric reflex (normally, stroking the upper inner thigh results in retraction of the testes), anal wink reflex (normally, stroking perianal skin results in contraction of the anal sphincter), and bulbocavernosus reflex (normally, squeezing the glans penis or clitoris results in contraction of the anal sphincter). In practice, the GU and rectal reflexes are rarely tested because laboratory testing is much more reliable. If patients have symptoms and signs suggesting autonomic insufficiency, sudomotor, cardiovagal, and adrenergic testing is usually done to help determine severity and distribution of the insufficiency. Sudomotor testingincludes the following: Quantitative sudomotor axon-reflex test:This test evaluates integrity of postganglionic fibers. The fibers are activated by iontophoresis using acetylcholine. Standard sites on the leg and wrist are tested, and the volume of sweat is then measured. The test can detect decreased or absent sweat production. Thermoregulatory sweat test:This test evaluates both preganglionic and postganglionic pathways. After a dye is applied to the skin, patients enter a closed compartment that is heated to cause maximal sweating. Sweating causes the dye to change color, so that areas of anhidrosis and hypohidrosis are apparent and can be calculated as a percentage of body surface area (BSA). Cardiovagal testingevaluates heart rate response (via ECG rhythm strip) to deep breathing and to the Valsalva maneuver (forced expiration against a closed glottis). If the autonomic nervous system is intact, heart rate varies with these maneuvers; normal responses to deep breathing and the Valsalva ratio vary by age. The Valsalva ratio is the maximum heart rate during the Valsalva maneuver divided by the heart rate 30 seconds after the maneuver. The lower limit for normal is 1.0. Adrenergic testingevaluates response of beat-to-beat BP to the following: Blood is shifted to dependent parts, causing reflex responses in BP and heart rate. This test helps differentiate Autonomic Neuropathies from postural orthostatic tachycardia syndrome. Valsalva maneuver:This maneuver increases intrathoracic pressure and reduces venous return, causing changes in BP and heart rate that reflect vagal and adrenergic baroreflex function. With the head-up tilt test and Valsalva maneuvers, the pattern of responses is an index of adrenergic function. 5 minutes. Normally, levels increase after standing. If patients have autonomic insufficiency, levels may not increase with standing and may be low in the supine position, particularly in postganglionic disorders (eg, Autonomic Neuropathies , 