ANS Reflexes Flashcards
Key points of integrations between the ANS and endocrine system
Renin-angiotensin-aldosterone system (RAAS)
Vasopressin
Glucocorticoids
Insulin
Five components of the biological feedback loop (arc)
Sensor
Afferent pathway
Control center
Efferent pathway
Effector organ or tissue
Component of the biological feedback loop that monitors the environment
Sensor
Component of the biological feedback loop that detects and change in a variable
Sensor
Component of the biological feedback loop that conducts the action potential towards the control center
Afferent pathway
Most common location of control center
CNS
Component of the biological feedback loop that links the sensor and control center
Afferent pathway
Component of the biological feedback loop that modifies output to effector
Control center
Component of the biological feedback loop that maintains a set point
Control center
Component of the biological feedback loop that links the control center to the effector organ/ tissue
Efferent pathway
Pathway that is almost alway a 2- neuron pathway (pre- and post- ganglionic)
Efferent pathway
Component of the biological feedback loop that elicits a physiologic change to restor homeostasis
Effector
Effector tissues/ organs in autonomic (visceral) reflex arcs
Smooth muscle
Cardiac muscle
Glands
Fast- acting reflex loops between the cardiovascular system and CNS
Cardiovascular reflexes
Short term BP control takes place via what mechanism?
Neural (ANS reflexes–> mechanoreceptors)
Longer term BP control takes place via what mechanism
Hormonal (RAAS, vasopressin, natriuretic peptides)
List the cardiac reflexes
Baroreceptor
Bainbridge
Bezold- Jarisch
Chemoreceptor
Vasovagal
Oculocardiac
Reflex that aims at maintaining BP around a setpoint
Baroreceptor reflex
Reflex that is responsible for maintaining BP during position changes
Baroreceptor reflex
Why do patients with chronic hypertension not tolerate hypotension well?
Baroreceptors have adapted to the higher BP and increased the set point for autoregulation
Location of high-pressure baroreceptors
Transverse aortic arch
Bifurcations of the carotid arteries
Afferent pathway of baroreceptor reflex
Transverse aortic arch > Vagus n (CN 10)
Carotid bifurcation > carotid sinus n (Hering’s n) > glossopharyngeal n (CN 9)
Where is the control center for the baroreceptor reflex?
Nucleus tractus solitarius (NTS) in the medulla
The spinal cord origin of cardioaccelerator fibers
T1-T4
Effect on baroreceptor reflex: volatile anesthetics
Impair in a dose-dependent fashion
Volatile anesthetic associated with the least impairment of the baroreceptor reflex
Isoflurane (has mild B1 agonist properties)
Effect on baroreceptor reflex: Propofol
Usually impairs
Effect on baroreceptor reflex: Ketamine
Activates SNS = increased HR with minimal change in SVR
Effect on baroreceptor reflex: Etomidate
Usually unchanged HR with small decrease in SVR
Effect on baroreceptor reflex: Thiopental
Preserves reflex
Decrease SVR with compensatory increase in HR
Effect on baroreceptor reflex: hydralazine
Preserves reflex
Decrease SVR d/t vasodilation and increase HR
Effect on baroreceptor reflex: nitroglycerine and nitroprusside
Preserved reflex
Effect on baroreceptor reflex: beta blockers
Impair reflex
Prevent compensatory increase in HR depending on extent of B1 blockade
Labetolol also blocks alpha-1 receptor and may increase the risk of orthostatic hypotension
Effect on baroreceptor reflex: phenylephrine
Preserves
Effect on baroreceptor reflex: norepinephrine
Lower doses = B1 chronotropic effects prevail
As dose increases, alpha-1 vasoconstriciton overshadows and reflex is preserved
Reflex that slows HR in the setting of profound hypovolemia
Bezold-Jarisch reflex
Bezold-Jarisch triad
Bradycardia
Hypotension
Coronary artery dilation
Reflex that prevents sludging of the blood in the veins, atria, and pulmonary circulation
Bainbridge reflex
Reflex that increases HR and inotropy in the setting of persistent hypoxemia
Chemoreceptor reflex
Bainbridge reflex: stimulus
Increased blood volume
Bainbridge reflex: sensor
Increased firing of low-pressure stretch receptors during atrial firing
Bainbridge reflex: afferent pathway
Vagus (CN 10) to the nucleus tractus solitarius
Location of low-pressure baroreceptors
Atria
Lung vasculature
Bainbridge reflex: control center
Nucleus tractus soltarius and its projections to CV centers in medulla
Bainbridge reflex: efferent pathway
PNS and SNS pathways to SA node
Bainbridge reflex: effector and response
SA node > increase HR
Bainbridge reflex: effects on contractility and stroke volume
Insignificant
Counterbalances the baroreceptor reflex
Bainbridge reflex
Cardio-inhibitory reflex that may play a prominent role in cardioprotective reflexes in response to noxious stimuli
Bezold-Jarisch
Chemical triggers for the Bezold-Jarisch reflex
Veratrum alkaloids, nicotine, capsaicin, histamine, sertonin, snake/ insect venoms
Bezold-Jarisch reflex: stimulus
Noxious ventricular stimuli (MI, low venous return, thrombolysis)
Bezold-Jarisch reflex: sensor
Chemo- and mechanoreceptors in the LV wall
Bezold-Jarisch reflex: afferent pathway
Nonmyelinated C fibers in the vagus (CN 10) to the nucleus tractus solarius
Bezold-Jarisch reflex: control center
Nucleus tractus solarius and medullary cardiovascular nuclei and centers
Bezold-Jarisch reflex: efferent pathway
Vagus (CN 10)
Bezold-Jarisch reflex: effector and response
SA node > decrease HR/ AV node > decrease dromotropy
Strongest stimulus at peripheral chemoreceptors
Hypoxia
Afferent pathway of peripheral chemoreceptors
Hypoxia> afferent impulse from carotid and aortic bodies > hering n (branch of CN 9) > vagus (CN 10) > nucleus tractus soliatrius
Effector response to hypoxia
Increased RR
Increased Vt
= Increased minute ventilation
Acute cardiovascular response to hypoxemia
Activation of PNS > decreased HR and decreased inotropy
Cardiovascular response to persistent hypoxemia
SNS activation > increased HR and increased inotropy = increased cardiac output
What drugs blunt the chemoreceptor reflex?
Subanesthetic concentrations of most volatile anesthetics (<0.1 MAC)
Opioids
Nitrous oxide
Vasovagal reflex triggers
Psychological stress
Periotoneal stretching or distension
When is fainting more likely to occur due to vasovagal reflex?
In a warm room
After a volume loss
Upon standing up
Afferent limb of oculocardiac reflex
Long and short ciliary nerves > ciliary ganglion > ophthalmic division (V1) of trigeminal (CN 5) > trigeminal ganglion
Efferent limb of oculocardiac reflex
Vagus (CN 10)
Oculocardiac reflex: stimulus
Traction on the extraocular muscles (especially the medial rectus)
Strabismus surgery
Pressure on the globe
Pressure on the conjunctiva
Ocular trauma
Pressure on the orbital tissue following enucleation
Retrobulbar block (can cause or prevent)
Oculocardiac reflex: Sensor
Mechanoreceptors in the ocular tissues
Oculocardiac reflex: Control center
Nucleus soltarius tractus and medullary cardiovascular nuclei and centers
Oculocardiac reflex: effector and response
Decreased activity of the SA and AV nodes
Oculocardiac reflex: clinical presentation
Bradycardia
Hypotension
Junctional rhythm
AV block
Asystole
Oculocardiac reflex: factors that worsen the severity
Hypoxemia
Hypercarbia
Light anesthesia
Oculocardiac reflex: treatment options
Remove stimulus
Administer 100% O2, ensure adequate ventilation, and deepen anesthetic
Administer anticholinergic (atropine, glycopyrrolate)
Massive SNS activation due to profound decrease in medullary vasomotor centers
CNS ischemic reflex
Result of CNS ischemic reflex trigger
Immense vasoconstriction
Profound increase in BP, often as high as the heart can create
Type of CNS ischemic response that results from increased intracranial pressure
Cushing Reflex
Cushing’s Triad
Hypertension
Bradycardia
Irregular respirations
Control center for temperature maintenance
Preoptic area of the hypothalamus
