Autonomic Nervous System Testing
I. Anatomy and Physiology
Preganglionic sympathetic neurons are located in the intermediolateral cell column in the spinal cord from T2 to L1.
Preganglionic parasympathetics are present in the nuclei of cranial nerves III, VII, IX, X and in the spinal cord from S2 to S4.
Primary postganglionic neurotransmitter for sympathetic neurons is norepinephrine.
Primary postganglionic neurotransmitter for parasympathetic neurons is muscarinic acetylcholine.
Primary postganglionic neurotransmitter for sweat glands is acetylcholine.
Denervation hypersensitivity is a sign of a postganglionic lesion.
II. Valsalva Maneuver
Pressure of approximately 40 mm Hg for 15 seconds produces the ideal stimulus.
The valsalva maneuver has four phases
Phase I—increased blood pressure secondary to increased intrathoracic pressure
Phase II early—reduced blood pressure and cardiac output secondary to decreased venous return
Phase II late—4 to 5 seconds later, blood pressure increases because of increased sympathetic tone
Phase III—begins with a sudden release of intrathoracic pressure causing a decrease in blood pressure for 1 to 2 seconds
Phase IV—overshoot of blood pressure lasting less than 10 seconds caused by increased venous return during persistent vasoconstriction
Valsalva maneuver should not be performed in patients with proliferative retinopathy.
Valsalva maneuver may induce syncope, angina or arrhythmia.
Longest R-R interval during phase IV compared with the shortest R-R interval during phase II should be <1.51. This is may be decreased in normal older patients.
Exagerated decrease in phase II suggests sympathetic vasomotor dysfunction.Related posts:
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