ANS Disorders Flashcards
clinical assessments of autonomic function: easy to? but difficult to? purpose?
easy to perform, difficult to interpret. to decide if dysfunction is visceral sensory, central reflex, or efferent autonomic
orthostatic test/tilt-table: how to test
90 degree head up passive tilt, blood goes to leg veins
orthostatic test/tilt-table: what happens in normal subject?
increased heart rate, little change in blood pressure, but heart rate increase not always seen in trained athletes
orthostatic test/tilt-table: normal subjects - reason for response?
baroreceptor reflex: vagally mediated increase in HR, followed by sympathetically mediated further HR increase. vasoconstriction in splanchnic, renal, skeletal muscle vascular beds
orthostatic test/tilt-table: with mild autonomic impairment?
dramatic tachycardia, but no fall in blood pressure. so baroreceptors functional, increased HR accounts for mild peripheral denervation
orthostatic test/tilt-table: moderate autonomic neuropathy?
tachycardia, orthostatic hypotension may occur. the worse the neuropathy, the worse the hypotension
orthostatic test/tilt-table: severe autonomic neuropathy?
BP can fall to less than 100 mmHg with no change in heart rate
valsalva maneuver: what? result?
exhale against a closed glottis = increased intrathoracic pressure
valsalva maneuver: see what two things in pressure?
initial increase in aortic pressure (mechanical). followed by cardiac output + BP fall, because of decreased venous input
valsalva: what happens to heart rate?
initial decrease in HR, but later reflex tachycardia (+ peripheral vasoconstriction)
valsalva: after exhaling what happens?
BP overshoots normal values b/c of persisting vasoconstriction. parasymp effects then cause reflex bradycardia.
cold pressor test?
hands in ice water = vasoconstriction, increase in BP, reflex bradycardia
mental arithmetic test: what? doesn’t depend on?
stress of doing math in noisy surroundings = increase in pulse rate + BP. response doesn’t depend on activation of afferent limb of a symp reflex arc.
skin temp: sympathetic vs. parasymp temp?
sympathetic = cool. parasymp = warm.
skin conductance
lie detector: increased sweating = increased skin conductance. but questionable reliability
QSART: stands for? what?
quantitative sudomotor axon reflex test. apply ACh to skin, normally causes increased sweating because it evokes an axon reflex from symp cholinergic axons
paroxysmal autonomic syncope: what?
fainting: transient decreased perfusion of reticular activating system of brainstem
3 causes of paroxysmal autonomic syncope
orthostatic hypothension. acute decrease in cardiac output (from baroreceptor sensitization, or activation of cardiac mechaonoreceptors after prolonged tachycardia). acute increase in cerebrovascular reistance.
orthostatic hypotension: drugs?
blockade of sympathetic tone to blood vessels
orthostatic hypothension: neurally mediated?
neurally mediate syncope, aka vasovagal attack: sudden change in ANS activity = acute hemodynamic reaction = reverse the normal pattern of outflow that maintains BP
orthostatic hypotension: what do the paras/symp do?
increase parasymp outflow = bradycardia. decreased symp = vasodilation
orthostatic hypotension: triggered by? (4) pathway of signals?
pain, fear, anxiety, embarassment: descending signals from cortical, limbic or hypothalamic structures to autonomic centers in medulla
orthostatic hypotension: peripheral mechs? (2)
compression of carotid barorecetpors. rapid emptying of distended bladder.
acute rise in cerebrovascular resistance: causes?
increased intracranial pressure, panic attacks (hyperventilation = decreased CO2 in blood = cerebral vasoconstriction = decreased perfusion of RAS).
