Autonomic Nervous System Disorders

Autonomic Nervous System Disorders is a topic covered in the Harrison's Manual of Medicine.

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The autonomic nervous system (ANS) (Fig. 186-1) innervates the entire neuraxis and permeates all organ systems. It regulates bp, heart rate, sleep, and bladder and bowel function. It operates automatically, so that its full importance becomes recognized only when ANS function is compromised, resulting in dysautonomia.

Key features of the ANS are summarized in Table 186-1. Responses to sympathetic or parasympathetic activation often have opposite effects; partial activation of both systems allows for simultaneous integration of multiple body functions.

TABLE 186-1: FUNCTIONAL CONSEQUENCES OF NORMAL ANS ACTIVATION
 SympatheticParasympathetic
Heart rateIncreasedDecreased
Blood pressureIncreasedMildly decreased
BladderIncreased sphincter toneVoiding (decreased tone)
Bowel motilityDecreased motilityIncreased
LungBronchodilationBronchoconstriction
Sweat glandsSweating
PupilsDilationConstriction
Adrenal glandsCatecholamine release
Sexual functionEjaculation, orgasmErection
Lacrimal glandsTearing
Parotid glandsSalivation
Abbreviation: ANS, autonomic nervous system.

Consider disorders of autonomic function in the differential diagnosis of pts with unexplained orthostatic hypotension (OH), sleep dysfunction, impotence, bladder dysfunction (urinary frequency, hesitancy, or incontinence), diarrhea, constipation, upper gastrointestinal symptoms (bloating, nausea, vomiting of old food), impaired lacrimation, or altered sweating (hyperhidrosis or hypohidrosis).

OH is often the most disabling feature of autonomic dysfunction. Syncope results when the drop in bp impairs cerebral perfusion (Chap. 50). Other manifestations of impaired baroreflexes are supine hypertension, a fixed heart rate regardless of posture, postprandial hypotension, and a high nocturnal bp. Many pts with OH have a preceding diagnosis of hypertension. Most causes of OH are not neurologic in origin; these must be distinguished from neurogenic causes.

FIGURE 186-1

Schematic representation of the autonomic nervous system. (From M. Moskowitz: Clin Endocrinol Metab 6:745, 1977.)

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TY - ELEC T1 - Autonomic Nervous System Disorders ID - 623110 Y1 - 2017 PB - Harrison's Manual of Medicine UR - https://harrisons.unboundmedicine.com/harrisons/view/Harrisons-Manual-of-Medicine/623110/all/Autonomic_Nervous_System_Disorders ER -