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CVT Apex > ANS Reflexes > Flashcards

ANS Reflexes Flashcards

1
Q

The reflexes

A

“3 B’s in the CV…Ouch”

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2
Q

baroreceptor reflex is a (-/+) feedback loop

A

negative

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3
Q

What does the baroceptor reflex cause?

A

bradycardia + hypoTN

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4
Q

What will cause the baroreceptor reflex?
What surgeries especially?

A

mechanical stimulation in the carotid sinus & transverse aortic arch

carotid endarterectomy/stenting
mediastinoscopy

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5
Q

The first line defense against arterial BP changes

A

baroreceptor reflex

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6
Q

The setpoint for baroreceptors can increase or decrease. How long does this take?

A

1-3 days

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7
Q

Why does the baroreceptor function exist?

A
  • keeps arterial BP around a set point
  • preserve CO during hemorrhage/shock
  • maintain BP from supine to standing

(first line defense against arterial BP changes)

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8
Q

CV reflexes are reflex loops between…

A

CV and CNS systems

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9
Q

The 2 mechanisms that control blood volume and BP

A

neural & hormonal

neural: short term (secs-min)
ANS

hormonal: long term (mins-days)
RAAS

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10
Q

ANS reflex receptors

A

mechanoreceptors
(pressure & stretch)

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11
Q

hormonal reflex receptors
(3)

A

RAAS
vasopressin
natriuretic peptides

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12
Q

the baroreceptor reflex is a (low/high) pressure arterial reflex

A

high

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13
Q

How does the baroreceptor reflex respond to increased & decreased BP?

A

(high pressure ART baroreceptor reflex)

increased BP = decreases HR, contractility, SVR

decreased BP = increases HR, contractility, SVR

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14
Q

Why are chronic HTN patients not tolerant of hypoTN?

A

they have a higher BP setpoint, so their BP autoregulates at a higher MAP range

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15
Q

t/f
the baroreceptor reflex can control BP long term

A

true

baroreceptor mechanisms exist on a continuum w/ substantial overlap

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16
Q

another name for baroreceptor reflex

A

carotid sinus reflex

hence manipulating the carotid bifurcation during carotid endarterectomy can cause bradycardia

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17
Q

triggering the baroreceptor reflex during mediastinoscopy

A

pressure from the scope on the transverse aortic arch can cause bradycardia

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18
Q

Negative
vs.
Positive

feedback loop

A

negative: the stimulus/disturbance & response oppose each other

positive: the stimulus/disturbance & response reinforce each other

positive feedback loops are less common

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19
Q

Baroreceptor reflex in action

A
  1. increased MAP stretches baroreceptors (transv. A arch & carotid A bifurcation), altering the rate of AP generation
  2. afferent pathways send APs to the control centers (A.Arch → Vagus nerve; Carotid → carotid sinus n./hering’s →CN IX/glossphryng)
  3. afferent info @ NTS in the medulla (control center)
  4. efferent (via SNS & vagus) → heart & vascular
  5. slows HR & dilates (decreases SVR)
  6. decreased MAP
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20
Q

where are baroreceptors located?

A

transverse aortic arch
&
bifurcation of carotid arteries (carotid sinus)

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21
Q

Where do baroreceptors in the transverse aortic arch & bifurcation of carotid arteries send their afferent signals?

A

“Transverse To Ten”

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22
Q

The glosspharyngeal & vagus nerves are (afferent/efferent) pathways for the baroreceptor reflex

A

afferent

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23
Q
A
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24
Q

Which common drugs can diminish the baroreceptor reflex?

A

Labetalol
Sevo
(decrease BP AND HR)

Prop (usually but not always)

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25
Drugs with which effects will preserve the BRR?
those that: ↓HR + ↑BP (norepi) or ↑HR + ↓BP (hydralazine, thiopental) cannot decrease both
26
Preservation of the BRR means that HR will ___ when the BP ___
HR adjusts as needed when BP changes
27
What shows the the BRR is impaired?
a BP change does NOT produce the expected compensatory change in HR!
28
What agents/classes will impair the BRR?
29
how do the VAs affect the BRR?
30
How do induction agents affect BRR?
31
Which vasodilators preserve the BRR?
hydralazine NTG nipride
32
how does hydralazine preserve the BRR?
potent vasodilation drops SVR BUT BRR produces an increase in HR
33
How do beta blockers affect the BRR?
* may impair it * depends on extent of beta blockade (may produce compenastory ↑HR if hypoTN) * Labetalol also antagonizes A1 = risk of ortho hypoTN
34
How does NE affect HR?
35
These catecholamines increase HR regardless of dose
## Footnote NOT norepi
36
T/F: Phenylephrine is a catecholamine
False!
37
T/F: Phenylephrine preserves the BRR
True increases BP but bradycardia is common
38
How do antihypertensives affect the BRR? (not including B-blkrs)
CCBs and PDEs impair it ACEI alone will not, but if used with another arterial dilator OR hypovolemia, it reduces CV response to increased BP
39
The Bezold Jarisch reflex will cause (3)
1. bradycardia 1. hypoTN 1. coronary artery dilation
40
When does the Bezold-Jarisch reflex occur?
profound hypovolemia slows HR to allow filling time
41
T/F: The Bezold-Jarisch reflex is a cardio-inhibitory reflex
True
42
the five and dime reflex
oculocardiac afferent: trigmeninal CN V efferent: Vagus CN X
43
Bainbridge reflex function
prevents damming or sludging or blood in veins, artia and pulmonary circulation
44
How does persistent hypoxemia trigger reflexes?
causes SNS activation: increased HR & inotropy to increase the CO
45
Persistent hypoxemia triggers SNS activation. Its effects are part of the ____ reflex.
chemoreceptor
46
Bainbridge reflex
tachycardia due to increased venous return LOW pressure cardiopulm baroreceptor reflex
47
The bainbridge reflex sensor
low pressure stretch receptors firing more frequently during atrial filling ## Footnote bainbridge: tachycardia during increased venous return
48
Low pressure baroreceptors
volume detectors found in atria and lung vasculature
49
Bainbridge reflex start to finish
1. stimulus: increased blood vol 1. sensor: low pressure stretch receptors in atria increase their firing 1. afferent: Vagus to NTS 1. control center: NTS + its projections to medulla's CV centers 1. efferent: PNS and SNS to SA node 1. effector & response: SA node changes HR
50
Can you saturate the bainbridge reflex? What happens?
yes those with lower baseline HR experience greatest increase in HR
51
T/F: Tachycardia cause by the Bainbridge reflex has significant effects on contractility and stroke volume.
False insignificant
52
counterbalances the baroreceptor reflex
bainbridge
53
The biphasic effect of venous return & blood volume on heart rate
* volume loading AND depletion cause graded increases in heart rate * volume loading: bainbridge reflex prevails * volume depletion: high pressure baroreceptor reflex dominates
54
When is heart rate change from the bainbridge reflex minimal?
when the effective circulating volume is normal
55
cardiac congestion leads to...
56
Bezold-Jarisch Reflex (BJR)
* cardio**respiratory** reponse to IV Veratrum alkaloids * bradycardia, hypoTN **apnea** * classic triad: bradycardia, hypoTN, dilated coronaries
57
triggers the BJR
* noxious ventricular stimuli (MI, low venous return, thrombolysis) * veratrum alkaloids * nicotine * capsaicin * histamine * serotonin * snake/insect venoms
58
the BJR is a cardio-inhibitory reflex that may play a prominent role in...
cardioprotective reflexes in response to noxious stimuli
59
BJR Feedback Loop
## Footnote Dromotropic: effect on the conduction speed of electrical impulses
60
your pt becomes bradycardic and hypotensive after their spinal/epidural. which reflex is this?
BJR
61
Procedures likely to elicit BJR
* spinal/epidural * shoulder shurgery w/ regional in sitting position
62
These cardiac conditions make the BJR less pronounced
hypertrophy & AFIB
63
Bainbridge vs BJR (preload)
64
these reflexes tend to override the baroreceptor reflex
bainbridge and BJR
65
Bainbridge vs BJR overall
66
What do chemoreceptor typically control?
ventilation some facets include CV responses
67
T/F: the strongest drive/stimulus at peripheral chemoreceptors is hypercarbia
FALSE hypoxia
68
hypoxia's feedback loop
* ilicits afferents from carotid & aortic bodies via Hering nerve (of CN 9) & vagus, respectively → NTS * effector reponses: increase RR, Vt, MV * CV responses depend on acuity * acute: activate PNS (↓HR & ionotropy) * persistent: activate SNS (↑HR & ionotropy & CO)
69
How much volatile is needed to blunt the chemoreceptor response?
subanesthetic concentrations! <0.1 MAC ## Footnote nitrous will attentuate it as well in a dose dependent fashion
70
How do opioids affect the chemoreceptor response?
dose dependent attenuation
71
Vasovagal reflex triggers ## Footnote "vasovagal syncope" "neurocardiogenic syncope"
* stress (blood draws, seeing blood, acute pain) * peritoneal stretch/distention (esp rapid insufflation)
72
What makes you more likely to faint from the vasovagal reflex?
* warm room * volume loss * upon standing
73
Why can you faint from the vasovagal reflex?
transiet drop in perfusion pressure to the brain
74
# Vasovagal reflex Feedback loop
1. vagal afferents → higher CNS (hypothalamus) 1. acts thru ANS nuclei to massively stimulate the PNS & abolish SNS 1. massive vasodilation but NO baroreceptor activation 1. ↓HR + ↓SV = ↓CO 1. the sudden drop in SVR & CO profoundly decrease MAP 1. global cerebral ischemia (dizziness or fainting)
75
# vasovagal reflex At what point does a drop in CBF cause LOC?
if CBF is decreased for ~10 secs (only a few seconds = dizzy or feeling faint)
76
77
# vasovagal reflex after regaining consciouness, oliguria can occur due to ....
high plasma levels of vasopression (ADH)
78
# vasovagal reflex How serious can rapid insufflation be?
a profound vasovagal reaction can cause acute CV collapse and cardiac arrest
79
Oculocardiac reflex stimuli/triggers
80
Oculocardiac reflex feedback loop
81
82
83
How to treat Oculocardiac reflex
84

CVT Apex (12 decks)

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