Cardio physiology Guyton/Nagelhout
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Cardio physiology Guyton/Nagelhout

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Questions and Answers

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.

Fat-free acids and glycogen

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.

<p>First, fifth thoracic</p> Signup and view all the answers

SNS spinal cord segments are known as __________ ________.

<p>Cardioaccelerator fibers</p> Signup and view all the answers

Preganglionic PNS fibers originate in the dorsal motor nucleus of the medulla

<p>True</p> Signup and view all the answers

Suppression or blockade of thoracic (1st-5th) portion of the spinal cord by regional anesthesia causes hypotension and bradycardia by inhibition of parasympathetic ganglia.

<p>False</p> Signup and view all the answers

Parasympathetic tone decrease _____ _____.

<p>Heart rate</p> Signup and view all the answers

Maximum vagal nerve stimulation reduces contractile by ____ %

<p>30</p> Signup and view all the answers

Maximum stimulation of SNS increases contractility by ____ %

<p>100</p> Signup and view all the answers

Physiologic effects of PNS stimulation occur because of increased permeability of cardiac muscle cell membranes to which ion? (Resulting in hyperpolarization)

<p>Potassium</p> Signup and view all the answers

Hyperpolarization of the cardiac muscle cell membrane makes SA and AV node more excitable.

<p>False</p> Signup and view all the answers

_______ is the neurotransmitter of the PNS.

<p>Acetylcholine</p> Signup and view all the answers

Located along the epicardial surface at the junction of the SVC and RA.

<p>SA node</p> Signup and view all the answers

SA node speed of conduction ___ m/sec

<p>0.5</p> Signup and view all the answers

Intrinsic rate of SA node ____ to ____ bpm

<p>60-100</p> Signup and view all the answers

_______ ________ preferential conduction pathways between the SA and the AV node.

<p>Internodal tracts</p> Signup and view all the answers

AV node impulse conduction is considerably slower than any other region within the normal cardiac conduction at ____ m/sec.

<p>0.05</p> Signup and view all the answers

___ _______ is the preferential channel for conduction of the action potential from atria to the ventricles.

<p>AV bundle</p> Signup and view all the answers

Conduction velocity of from the bundle of His into the left and right bundle branches along the intraventricular septum ____ m/sec.

<p>2</p> Signup and view all the answers

Purkinje fibers fire at a rate of ___ to ___bpm

<p>20 to 40</p> Signup and view all the answers

SNS stimulation catecholamines are released from the CNS and the _______ ________.

<p>Adrenal medulla</p> Signup and view all the answers

When catecholamones interact with Beta-1 receptors, this increases myocardial cell permeability to _______ and ________.

<p>Calcium and sodium</p> Signup and view all the answers

The force of myocardial contraction is dependent on the quantity of _____ present within the cardiac cell.

<p>Calcium</p> Signup and view all the answers

Inhibition of calcium influx into cardiac muscle cells is the proposed mechanism by which _____ anesthetic agents cause depression of myocardial contractility.

<p>Inhaled</p> Signup and view all the answers

The resting cell membrane is relatively permeable to _______ and relatively impermeable to both _______ and _______.

<p>Potassium, calcium and sodium</p> Signup and view all the answers

During Phase 0, fast sodium channels open between -____ to -____ (threshold potential).

<p>-70 to -65mV</p> Signup and view all the answers

______ anesthetics such as ______ have an inhibitory effect on Phase 0 by decreasing the influx of sodium.

<p>Local, lidocaine</p> Signup and view all the answers

Phase 1 (early rapid repolarization) reaches +____mV to +____mV

<p>2 to 30</p> Signup and view all the answers

Slow calcium channels open at -____mV to -_____mV.

<p>-30 to -40</p> Signup and view all the answers

Inward influx of calcium flux delays and prolongs the ______ refractory period.

<p>Absolute</p> Signup and view all the answers

Phase 2 (Plateau phase) maintains a membrane potential near ____ mV.

<p>0</p> Signup and view all the answers

Calcium channel blockers exert their pharmacological effect during phase __.

<p>2</p> Signup and view all the answers

Phase 3 slow _____ channels become inactivated and is sustained by accelerated ______ efflux.

<p>Calcium, potassium</p> Signup and view all the answers

Phase 4 (resting potential/diastolic repolarization phase) resting membrane potential is restored ______ ICF to ECF and ____ and ____ ECF to ICF

<p>Potassium, sodium and calcium</p> Signup and view all the answers

______ 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.

<p>Lidocaine, potassium</p> Signup and view all the answers

Period lasts from Phase 0 to the middle of Phase 3.

<p>Absolute refractory period</p> Signup and view all the answers

The relative refractory period is the time during which

<p>A second stimulus can result in an action potential.</p> Signup and view all the answers

Period lasts from the middle of Phase 3 to the beginning of Phase 4. (Occurs during the T wave)

<p>Relative refractory period</p> Signup and view all the answers

Resting membrane potential of the SA node.

<p>-55mV to -60mV</p> Signup and view all the answers

Phases of diatole (name the 3)

<ol> <li>rapid inflow 2) reduced inflow (diastasis) 3) atrial systole</li> </ol> Signup and view all the answers

Atrial systole is the final period of rapid filling and is commonly referred to as atrial kick.

<p>True</p> Signup and view all the answers

In patients with mitral stenosis, atrial kick may be responsible for up to ___% of the ventricular filling.

<p>40</p> Signup and view all the answers

_______ contraction begins with the closure of the mitral valve and lasts until the opening of the aortic valve.

<p>Isovolumetric</p> Signup and view all the answers

The a wave represents the end of ____ systole just before mitral valve closure.

<p>Atrial</p> Signup and view all the answers

The ____ wave represents ______ contraction and is produced by bulging of the mitral valve caused by increasing left ventricular pressure.

<p>C, ventricular</p> Signup and view all the answers

The ___ wave represents increased pressure in the LA caused by blood return from the pulmonary veins before mitral valve opening.

<p>V</p> Signup and view all the answers

During systole, blood flow ceases to the __________ from compression due to myocardial muscle fiber tendon.

<p>Subendocardium</p> Signup and view all the answers

Flow through the _______ vessels is NOT affected during systole.

<p>Epicardial</p> Signup and view all the answers

Myocardial oxygen demand is determined by: (4)

<ol> <li>preload 2) afterload 3) contractility 4) HR</li> </ol> Signup and view all the answers

Myocardial oxygen supply is determined by: (5)

<ol> <li>arterial blood content 2) DBP 3) diastolic time (HR) 4) oxygen extraction by the tissues 5) coronary blood flow</li> </ol> Signup and view all the answers

Increased _____ _____ is the most important factor that negatively affects myocardial oxygen consumption.

<p>Heart rate</p> Signup and view all the answers

80-90% of coronary filling and myocardial perfusion occurs during

<p>Diastole</p> Signup and view all the answers

Beta blockers increase _____ and decrease _____, protecting the heart from ischemia.

<p>Supply, demand</p> Signup and view all the answers

Myocardium extracts 65%-70% of the available oxygen from hemoglobin.

<p>True</p> Signup and view all the answers

Coronary artery vasodilation can increase coronary blood flow by ____ to _____ times.

<p>Three to four</p> Signup and view all the answers

List the vasodilators substances released by the endocardium in response to decreased oxygen delivery or concentration. (7)

<ol> <li>adenosine 2) adenosine phosphate compounds 3) potassium ions 4) hydrogen ions 5) CO2 6) Bradykinin 7) prostaglandin</li> </ol> Signup and view all the answers

Coronary blood flow is maintained at a constant flow rate through a MAP range of ____ to _____ mmHg.

<p>60 to 140</p> Signup and view all the answers

Major determinant of coronary perfusion pressure is _____ blood pressure.

<p>Diastolic</p> Signup and view all the answers

Normal EF:

<p>50-70%</p> Signup and view all the answers

Match each definition with the term.

<p>Occurs as a result of forced expiration against a closed glottis; inhibits (SNS) the vasomotor center in the medulla = Valsalva maneuver Decreases in arterial blood pressure causing increased sympathetic tone and acute hypertension causes opposite response to occur. = Baroreceptor Reflex Traction on the extraocular muscles, conjunctiva or orbital structures can cause hypotension and a reflex bradycardia. = Oculocardiac reflex An increased volume of blood in the heart causes SNS system stimulation. SA node increases HR by 10 to 15%. ADH secretion is decreased from the posterior pituitary gland is decreased. ANP is increased which promotes diuresis = Bainbridge reflex</p> Signup and view all the answers

Chemoreceptor response is elicited from ______, ______, and _______.

<p>Hypoxia, hypercarbia, and acidosis</p> Signup and view all the answers

Chemoreceptor reflex stimulates the SNS to

<p>Increase minute ventilation, blood pressure, and heart rate</p> Signup and view all the answers

Threshold potential of the SA node

<p>-40mV</p> Signup and view all the answers

Cardioaccelerator fibers originate in the higher thoracic segment of

<p>t1-t4</p> Signup and view all the answers

Local anesthetics

<p>Concentrations decrease conduction by binding to fast sodium channels, decrease SA node conduction</p> Signup and view all the answers

Opioids

<ol> <li>depress cardiac conduction 2) increase AV conduction time 3) increase refractory period 4) prolong duration of purkinje fiber action potential</li> </ol> Signup and view all the answers

Volatile anesthetics

<p>Depress SA node automaticity, moderate effect on AV node, junctions tachycardia under general anesthesia with anticholinergics</p> Signup and view all the answers

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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