21. Dysautonomia Flashcards
What are the two limbs of ANS signal loop?
- Sensors sense changes in internal environ.
- Afferent neuron from sensing apparatus transmits signal to some sort of processing center (ganglion in SNS or higher processing center like medulla)
- Processing center decides what response is required of the body (PNS or SNS response)
- Efferent neuron from processing center to stimulate/effect effector systems
When does dysautonomia occur?
Dysfxn of sensing app, afferent or efferent nerve, processing center
What is most common example of primary ANS dysfxn?
Parkinson’s syndrome w autonomic failure
What is secondary ANS dysfxn?
Disease not directly affecting ANS but has ANS impacts
- Guillain Barre - body’s immune system attacks PNS initially resulting in weakness + tingling in upper body and may eventually lead to paralysis
- Myasthenia Gravis - breakdown in communication between nerves + muscle
- Rheumatoid Arhtritis - autoimmune disorder –> can cause peripheral neuropathy
- Diabetes Mellitus - common’y causes diabetic neuropathy –> numbness, tingling, pain, and altered pain sensation
Sx of dysautonomia?
- Orthostatic hypotension = dizziness or near blacking up when moving from lying or seated to standing
- Inability to increase heart rate w exercise or stress
- Sweating abnormalities
- Slow digestion –> loss of appetite, bloating, diarrhea, constipation, hard to swallow
- Sexual probs
- Erectile dysfunction
- Diff ejactulation
- Urinary probs
- Incontinence
- Recurring UTI’s due to bladder not emptying
- Diff start urination
- Vision probs
- Failure of pupils to react to changes in light
What causes orthostatic hypotension?
- When going from supine/sitting to standing –> drop in venous return of blood to heart –> decreased CO –> drop BP
- 500-1000mL blood pool in feet
- NORM: Baroreceptors (carotid arteries + aorta) sense BP drop –> effector stimulation –> sympathetic resp + catechol surge –> maintain cerebral perfusion
ORTHO HYPO: cerebral hypoperfusion –> faint to restore supine position + sympathetic surge
How to test to orthostatic hypotension?
- Ask pt to move from sitting/supine to standing position (best to check starting from supine)
- Measure BP
- SBP decrease > 20mmHg
- DBP decrease > 10mmHg
- HOWEVER, BP drop not definitive, could also be due to hypovolemia, anemia…
Increase in ___ can compensate for orthostatic hypotension, despite no changes in BP.
HR.
POTS = postural orthostatic tachycardia syndrome –> good prognosis
What’s supposed to happen when moving from supine to standing position?
- Stand up quickly
- Drop in BP
- Aortic arch + carotid sinus baroreceptors sends sympathetic signal to medulla oblongata
- Sends sympathetic signals to veins, arteries, heart + SA node
- Increased F of contraction
- Increased HR
- Decreased venous pooling
- Increased tone + vascular resistance
- Overall increase in BP to maintain perfusion
What are three types of orthostatic conditions?
- Orthostatic hypotension - ineffective CV reflex –> hypotension –> bad prognosis
- Postural tachycardia - no changes in BP but abnorm increase in HR –> good prognosis
- Reflex syncope - passing out as reflex to some other physiologic signal (e.g. standing urination, exaggerated response to pain) –> sudden decrease in BP + HR
(T/F) Hypotension is sure sign of dysautonomia.
False
What happens during denervation hypersensitivity?
- Denervation/nerve dysfxn –> denervation hypersensitivity
- NORM: innervation = baseline tone/regulation
- When remove nerve stim., muscle responds by gen. more receptors to try to regain baseline tone–> exagg. responses when giving meds
- Careful when giving pressors to hypoT pt
What should be considered during preop eval in pt suspected of dysautonomia?
- Check for orthostasis
- Specialized evals
- Table tilt test: pt placed on a table that can go head + feet down –> measure sp BP responses
- Valsalva test: forced baring down to see CV resp
- Cold pressor test: hand in cold water doesn’t cause increased BP/HR for pt w/ ANS probs
- Deep breathing: looks at HR modulation or sinus arrhymthia during inhalation
- Hyperventilation: drop in CO2 –> systemic vasodilation, but SIG. fall in BP = ANS failure
(T/F) Some HR variability is normal in healthy pt
True.
Variability = sign of good parasympathetic tone. This is low frequency variability.
(T/F) High frequency variability tests over longer period of time.
True.
Show balances b/w sympathetic + parasympathetic reflexes
Describe Bainbridge study.
- Infused fluids directly into dog hearts –> saw increase in CVP + end diastolic P
- When denervated heart from sympathetic + parasympathetic nerves –> stopped this reflex
- Postulated increased HR due to downregulation of PNS as opposed to upregulation of SNS
- Not applicable in humans
What is Bezold-Jarish Reflex?
- Abnormal resp to changes in BP as move from supine to sitting
- Stimulus leads to initial sympathetic response (very forceful contractions) followed by vagal response thinking heart is overloaded
- Results in bradycardia + hypotension + vasodilation–> inadequate perfusion –> syncopal episode
Bezold-Jarish Reflex most commonly seen in pt w…
- AMI
- Spinal anesthetics that accidentally take out cardiac accel. nerves (SNS output) –> cardiac arrest if not treated w catecholamines
- Interscalene/brachial plexus block
What is autonomic dysreflexia?
- Occurs in high spinal cord injuries (above T6), includes both normal + abnormal responses
- Sympathetic response can be activated below injury but parasympathetic response can’t –> causes strong sympathetic outflow
- Usually stimuli = distended bladder or colon
- Brain detects hypertensive crisis –> sends parasympathetic response, but can’t get thru injury
- Continued sympathetic response w/o parasympathetic balance
- Vagus nerve intact to heart –> brady but HTN remains
How to prevent autonomic dysreflexia?
- During surgery still need anesthesia for procedures below spinal cord injury (ANS still sensing the stimulus)
- Remove inciting stimulus (e.g. distended bladder/rectum)
