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Questions and Answers
Increased SNS activity increases ______, _______, and ______.
Increased SNS activity increases ______, _______, and ______.
Chronotropic, inotropic, and dromotropic activity.
Sympathetic nervous system activation results in mobilization of myocardial -__ _____ and _________ for energy use by the myocardial cells.
Sympathetic nervous system activation results in mobilization of myocardial -__ _____ and _________ for energy use by the myocardial cells.
Fat-free acids and glycogen
Preganglionic SNS fibers originate from the cells in the __________ columns of the _______ _______ segments of the _______ _____.
Preganglionic SNS fibers originate from the cells in the __________ columns of the _______ _______ segments of the _______ _____.
Intermediolateral, higher thoracic, spinal cord
SNS fibers synapse at the ____ through the _______ _______ paravertebral ganglia.
SNS fibers synapse at the ____ through the _______ _______ paravertebral ganglia.
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SNS spinal cord segments are known as __________ ________.
SNS spinal cord segments are known as __________ ________.
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Preganglionic PNS fibers originate in the dorsal motor nucleus of the medulla
Preganglionic PNS fibers originate in the dorsal motor nucleus of the medulla
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Suppression or blockade of thoracic (1st-5th) portion of the spinal cord by regional anesthesia causes hypotension and bradycardia by inhibition of parasympathetic ganglia.
Suppression or blockade of thoracic (1st-5th) portion of the spinal cord by regional anesthesia causes hypotension and bradycardia by inhibition of parasympathetic ganglia.
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Parasympathetic tone decrease _____ _____.
Parasympathetic tone decrease _____ _____.
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Maximum vagal nerve stimulation reduces contractile by ____ %
Maximum vagal nerve stimulation reduces contractile by ____ %
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Maximum stimulation of SNS increases contractility by ____ %
Maximum stimulation of SNS increases contractility by ____ %
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Physiologic effects of PNS stimulation occur because of increased permeability of cardiac muscle cell membranes to which ion? (Resulting in hyperpolarization)
Physiologic effects of PNS stimulation occur because of increased permeability of cardiac muscle cell membranes to which ion? (Resulting in hyperpolarization)
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Hyperpolarization of the cardiac muscle cell membrane makes SA and AV node more excitable.
Hyperpolarization of the cardiac muscle cell membrane makes SA and AV node more excitable.
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_______ is the neurotransmitter of the PNS.
_______ is the neurotransmitter of the PNS.
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Located along the epicardial surface at the junction of the SVC and RA.
Located along the epicardial surface at the junction of the SVC and RA.
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SA node speed of conduction ___ m/sec
SA node speed of conduction ___ m/sec
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Intrinsic rate of SA node ____ to ____ bpm
Intrinsic rate of SA node ____ to ____ bpm
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_______ ________ preferential conduction pathways between the SA and the AV node.
_______ ________ preferential conduction pathways between the SA and the AV node.
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AV node impulse conduction is considerably slower than any other region within the normal cardiac conduction at ____ m/sec.
AV node impulse conduction is considerably slower than any other region within the normal cardiac conduction at ____ m/sec.
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___ _______ is the preferential channel for conduction of the action potential from atria to the ventricles.
___ _______ is the preferential channel for conduction of the action potential from atria to the ventricles.
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Conduction velocity of from the bundle of His into the left and right bundle branches along the intraventricular septum ____ m/sec.
Conduction velocity of from the bundle of His into the left and right bundle branches along the intraventricular septum ____ m/sec.
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Purkinje fibers fire at a rate of ___ to ___bpm
Purkinje fibers fire at a rate of ___ to ___bpm
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SNS stimulation catecholamines are released from the CNS and the _______ ________.
SNS stimulation catecholamines are released from the CNS and the _______ ________.
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When catecholamones interact with Beta-1 receptors, this increases myocardial cell permeability to _______ and ________.
When catecholamones interact with Beta-1 receptors, this increases myocardial cell permeability to _______ and ________.
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The force of myocardial contraction is dependent on the quantity of _____ present within the cardiac cell.
The force of myocardial contraction is dependent on the quantity of _____ present within the cardiac cell.
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Inhibition of calcium influx into cardiac muscle cells is the proposed mechanism by which _____ anesthetic agents cause depression of myocardial contractility.
Inhibition of calcium influx into cardiac muscle cells is the proposed mechanism by which _____ anesthetic agents cause depression of myocardial contractility.
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The resting cell membrane is relatively permeable to _______ and relatively impermeable to both _______ and _______.
The resting cell membrane is relatively permeable to _______ and relatively impermeable to both _______ and _______.
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During Phase 0, fast sodium channels open between -____ to -____ (threshold potential).
During Phase 0, fast sodium channels open between -____ to -____ (threshold potential).
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______ anesthetics such as ______ have an inhibitory effect on Phase 0 by decreasing the influx of sodium.
______ anesthetics such as ______ have an inhibitory effect on Phase 0 by decreasing the influx of sodium.
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Phase 1 (early rapid repolarization) reaches +____mV to +____mV
Phase 1 (early rapid repolarization) reaches +____mV to +____mV
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Slow calcium channels open at -____mV to -_____mV.
Slow calcium channels open at -____mV to -_____mV.
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Inward influx of calcium flux delays and prolongs the ______ refractory period.
Inward influx of calcium flux delays and prolongs the ______ refractory period.
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Phase 2 (Plateau phase) maintains a membrane potential near ____ mV.
Phase 2 (Plateau phase) maintains a membrane potential near ____ mV.
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Calcium channel blockers exert their pharmacological effect during phase __.
Calcium channel blockers exert their pharmacological effect during phase __.
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Phase 3 slow _____ channels become inactivated and is sustained by accelerated ______ efflux.
Phase 3 slow _____ channels become inactivated and is sustained by accelerated ______ efflux.
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Phase 4 (resting potential/diastolic repolarization phase) resting membrane potential is restored ______ ICF to ECF and ____ and ____ ECF to ICF
Phase 4 (resting potential/diastolic repolarization phase) resting membrane potential is restored ______ ICF to ECF and ____ and ____ ECF to ICF
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______ lenthens the duration of the Phase 4 by decreasing the cardiac cell membrane’s permeability to _____ ion; delaying the onset of the resting membrane potential.
______ lenthens the duration of the Phase 4 by decreasing the cardiac cell membrane’s permeability to _____ ion; delaying the onset of the resting membrane potential.
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Period lasts from Phase 0 to the middle of Phase 3.
Period lasts from Phase 0 to the middle of Phase 3.
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The relative refractory period is the time during which
The relative refractory period is the time during which
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Period lasts from the middle of Phase 3 to the beginning of Phase 4. (Occurs during the T wave)
Period lasts from the middle of Phase 3 to the beginning of Phase 4. (Occurs during the T wave)
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Resting membrane potential of the SA node.
Resting membrane potential of the SA node.
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Phases of diatole (name the 3)
Phases of diatole (name the 3)
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Atrial systole is the final period of rapid filling and is commonly referred to as atrial kick.
Atrial systole is the final period of rapid filling and is commonly referred to as atrial kick.
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In patients with mitral stenosis, atrial kick may be responsible for up to ___% of the ventricular filling.
In patients with mitral stenosis, atrial kick may be responsible for up to ___% of the ventricular filling.
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_______ contraction begins with the closure of the mitral valve and lasts until the opening of the aortic valve.
_______ contraction begins with the closure of the mitral valve and lasts until the opening of the aortic valve.
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The a wave represents the end of ____ systole just before mitral valve closure.
The a wave represents the end of ____ systole just before mitral valve closure.
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The ____ wave represents ______ contraction and is produced by bulging of the mitral valve caused by increasing left ventricular pressure.
The ____ wave represents ______ contraction and is produced by bulging of the mitral valve caused by increasing left ventricular pressure.
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The ___ wave represents increased pressure in the LA caused by blood return from the pulmonary veins before mitral valve opening.
The ___ wave represents increased pressure in the LA caused by blood return from the pulmonary veins before mitral valve opening.
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During systole, blood flow ceases to the __________ from compression due to myocardial muscle fiber tendon.
During systole, blood flow ceases to the __________ from compression due to myocardial muscle fiber tendon.
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Flow through the _______ vessels is NOT affected during systole.
Flow through the _______ vessels is NOT affected during systole.
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Myocardial oxygen demand is determined by: (4)
Myocardial oxygen demand is determined by: (4)
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Myocardial oxygen supply is determined by: (5)
Myocardial oxygen supply is determined by: (5)
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Increased _____ _____ is the most important factor that negatively affects myocardial oxygen consumption.
Increased _____ _____ is the most important factor that negatively affects myocardial oxygen consumption.
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80-90% of coronary filling and myocardial perfusion occurs during
80-90% of coronary filling and myocardial perfusion occurs during
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Beta blockers increase _____ and decrease _____, protecting the heart from ischemia.
Beta blockers increase _____ and decrease _____, protecting the heart from ischemia.
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Myocardium extracts 65%-70% of the available oxygen from hemoglobin.
Myocardium extracts 65%-70% of the available oxygen from hemoglobin.
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Coronary artery vasodilation can increase coronary blood flow by ____ to _____ times.
Coronary artery vasodilation can increase coronary blood flow by ____ to _____ times.
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List the vasodilators substances released by the endocardium in response to decreased oxygen delivery or concentration. (7)
List the vasodilators substances released by the endocardium in response to decreased oxygen delivery or concentration. (7)
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Coronary blood flow is maintained at a constant flow rate through a MAP range of ____ to _____ mmHg.
Coronary blood flow is maintained at a constant flow rate through a MAP range of ____ to _____ mmHg.
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Major determinant of coronary perfusion pressure is _____ blood pressure.
Major determinant of coronary perfusion pressure is _____ blood pressure.
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Normal EF:
Normal EF:
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Match each definition with the term.
Match each definition with the term.
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Chemoreceptor response is elicited from ______, ______, and _______.
Chemoreceptor response is elicited from ______, ______, and _______.
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Chemoreceptor reflex stimulates the SNS to
Chemoreceptor reflex stimulates the SNS to
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Threshold potential of the SA node
Threshold potential of the SA node
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Cardioaccelerator fibers originate in the higher thoracic segment of
Cardioaccelerator fibers originate in the higher thoracic segment of
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Local anesthetics
Local anesthetics
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Opioids
Opioids
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Volatile anesthetics
Volatile anesthetics
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Study Notes
Sympathetic and Parasympathetic Nervous Systems
- Increased sympathetic nervous system (SNS) activity enhances heart rate, contractility, and conduction velocity.
- SNS activation mobilizes myocardial free fatty acids and glucose for energy use.
- Preganglionic SNS fibers originate from the intermediolateral columns of thoracic spinal cord segments.
- SNS fibers synapse at the sympathetic trunk through paravertebral ganglia.
- SNS spinal cord segments are known as thoracolumbar outflow.
- Preganglionic parasympathetic nervous system (PNS) fibers arise from the dorsal motor nucleus of the medulla.
Effects of Spinal Cord Anesthesia
- Blockade of thoracic spine (T1-T5) by regional anesthesia results in hypotension and bradycardia by inhibiting PNS ganglia.
- Decreased parasympathetic tone can lead to increased heart rate.
- Maximum vagal nerve stimulation can reduce contractility by approximately 25%.
- Maximum SNS stimulation increases contractility by up to 100%.
Cardiac Conduction System
- Increased permeability of cardiac muscle cell membranes to potassium results in hyperpolarization.
- Hyperpolarization makes the SA and AV nodes more excitable; acetylcholine is the chief PNS neurotransmitter.
- SA node conduction speed is approximately 0.8 m/sec.
- The intrinsic firing rate of the SA node is between 60 to 100 beats per minute.
- Specialized conduction pathways exist between the SA and AV nodes for efficient impulse transmission.
- AV node conduction is notably slower at 0.05 m/sec.
- The His-Purkinje system allows rapid conduction from the atria to the ventricles.
Cardiac Muscle Ion Dynamics
- Conduction velocity from the bundle of His into the left and right bundle branches is about 2-4 m/sec.
- Purkinje fibers can fire at a rate of 20 to 40 beats per minute.
- SNS stimulation leads to catecholamine release from the CNS and adrenal medulla, increasing myocardial cell permeability to calcium and sodium.
- Cellular contractility depends heavily on calcium levels; certain anesthetics inhibit calcium influx, diminishing myocardial contractility.
Action Potential Phases
- Resting cell membrane has high permeability to potassium, low permeability to sodium and calcium.
- Phase 0 (depolarization) involves fast sodium channels opening between -70 mV to -50 mV.
- Local anesthetics can inhibit Phase 0 by blocking sodium influx.
- Phase 1 (early rapid repolarization) peaks at +20 to +30 mV.
- Slow calcium channels open at -40 mV to -25 mV, prolonging the refractory period.
- Phase 2 (plateau) maintains a membrane potential near 0 mV.
- Pharmacological effects of calcium channel blockers take effect during Phase 2.
- Phase 3 involves inactivation of slow calcium channels and sustained potassium efflux.
- Phase 4 restores the resting membrane potential, with ion exchange occurring between intracellular fluid (ICF) and extracellular fluid (ECF).
Cardiac Cycle and Function
- Atrial systole is the final rapid filling period, often referred to as the atrial kick, which may account for up to 30% of ventricular filling in mitral stenosis patients.
- Ventricular contraction commences with mitral valve closure and ends with aortic valve opening.
- The "a" wave indicates the end of atrial systole before mitral valve closure.
- The "c" wave is associated with ventricular contraction pressure affecting the mitral valve.
- The "v" wave occurs after blood return from pulmonary veins, indicating increased left atrial pressure before mitral valve opening.
Myocardial Oxygen Dynamics
- Systolic compression of the coronary vessels reduces blood flow, while flow to other vessels remains unaffected.
- Myocardial oxygen demand is influenced by heart rate, contractility, wall tension, and afterload.
- Oxygen supply depends on coronary blood flow, hemoglobin levels, oxygen extraction efficiency, and vascular resistance factors.
- Elevated myocardial oxygen demand is a critical factor negatively impacting consumption.
- 80-90% of coronary blood flow occurs during diastole.
Pharmacological Influences
- Beta blockers can increase oxygen supply while decreasing demand, providing protection from ischemia.
- The myocardium extracts approximately 65-70% of available oxygen.
- Coronary artery vasodilation may boost blood flow by 3 to 5 times in response to stimuli.
- Vasodilators released in response to reduced oxygen delivery include nitric oxide, adenosine, prostaglandins, and others.
Coronary Blood Flow Regulation
- Coronary blood flow is maintained between a mean arterial pressure (MAP) range of 60 to 120 mmHg.
- Coronary perfusion pressure is primarily determined by diastolic blood pressure.
Reflex Responses and Thresholds
- Chemoreceptor responses involve peripheral chemoreceptors, central chemoreceptors, and mechanoreceptors, stimulating the SNS.
- SA node threshold potential is a critical determinant for rhythm initiation.
- Cardioaccelerator fibers originate from higher thoracic segments in spinal cord.
Anesthetic Effects
- Local anesthetics and opioids can influence cardiac conduction and contractility, with volatile anesthetics also providing similar effects.
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