Cardiac Pharmacology Flashcards
Where are the high pressure baroreceptors located?
Carotid sinus
Aortic arch
Where are the low pressure baroreceptors located?
Right atrium: at junction of SVC & IVC
Left atrium: junction of 4 pulmonary veins
What does stimulation of Vagal C fibers cause?
Bradycardia, hypotension, brief apnea
What is the Bezold-Jarisch reflex?
Fibers in endocardium touching each other (due to too much contraction) can increase vagal tone and try and decrease contractility
Are baroreceptors more sensitive to rates of change or magnitude of change?
Rate of change
What occurs when you have increased baroreceptor discharge?
Inhibit sympathetic discharge
Excite vagal innervation
Sympathetic innervation to arterioles causes ______ and innervation to veins causes ______
Vasoconstriction, mild vasconstriction
Sympathetic innervation to skeletal muscle arterioles causes ______
Cholinergic vasodilation
Parasympathetic innervation to vasculature causes ______
Trick question! Nothing. There is no parasympathetic innervation to the vasculature
How does vasodilation occur?
Withdrawal of sympathetic tone (dimmer switch)
What are the clinical effects of increased baroreceptor discharge?
Vasodilation
Decreased blood pressure
Decreased heart rate
Decreased cardiac output
What occurs to vessels with sympathetic withdrawal?
Decreased venous tone (Increased venous capacity)
Decreased arterial tone
Decrease in CO
What occurs to vessels with increased sympathetic tone?
Increased mean arterial pressure
Increased venous tone
Increase in CO
What occurs to the heart with sympathetic stimulation?
Chronotropy (heart rate increases)
Dromotropy (rate of conduction increases)
Inotropy (force of contraction increases)
Lusotropy (rate of relaxation increases)
What occurs to the heart with parasympathetic stimulation?
Heart rate slowed
Decreased force of contraction
Describe the pressor response?
Fall in MAP is sensed by arterial baroreceptors
Pressor response: sympathetic tone increases, causing increased CO and TPR and therefore increased MAP
What is the effect of sympathetic increase in exercise on heart, veins, and arteries?
Heart - increased HR, increased SV
Veins - increased venous tone
Arteries - vasoconstriction except in muscle (vasodilation)
What occurs in phase 1 of valsalva?
BP increase
HR decrease
Blood pressure rises at onset of straining due to increase in intrathoracic pressure
Baroreceptors fire, decreasing sympathetic tone and decreasing heart rate
What occurs in phase 2 of valsalva?
BP decrease
HR increase
High intrathoracic pressure compresses veins, decreasing venous return to heart and decreasing cardiac output, causing blood pressure to drop
Decrease in pressure inhibits the baroreceptors, causing tachycardia and a rise in peripheral resistance
What occurs in phase 3 of valsalva?
Glottis is opened
Transient decrease in BP
Intrathoracic pressure had decreased the amount of blood in peripheral vasculature
Once you release the strain, still have decreased amount of blood, therefore BP decreases transiently
What occurs in phase 4 of valsalva?
BP increases
HR decreases
Intrathoracic pressure returns to normal and cardiac output is restored, but peripheral vessels are still constricted so BP rises above normal
BP increase stimulates baroreceptors, causing bradycardia
HR stays decreased for prolonged period
Is syncope during physical activity benign?
NO
What are the 3 presentations of neurocardiogenic syncope aka vasovagal syncope?
Cardioinhibitory - increased parasympathetic tone –> bradycardia
Vasodepresspr - decreased sympathetic tone –> hypotension
Mixed response of cardioinhibitory and vasodepressor
What it the theory of how neurocardiogenic syncope occurs?
Sensory input via vagal afferents to Nucleus Tractus Solitarius
Causes sympathetic withdrawal - vasodepressor
Causes parasymapthetic tone - cardioinhibitory
Describe a typical neurocardiogenic syncope episode?
Prolonged standing = venous pooling and decreased BP
Baroreceptors are inhibited by decreased BP and sympathetic tone increases
HR increases, contractility increases
Pressure receptors in heart are stimulated by excessive contractility, causing vagal efferent influence on heart and sympathetic withdrawal
