cardio-physio-Cardiac electrophysiology Flashcards
The conduction system of the heart is mainly made up of nerves/ specialized cardiac myocytes.
specialized cardiac myocytes
(SA node, AV node, Bundle of His, right and left branch bundles, left aortic fascicle, left posterior fascicle, Purkinje fibers
Which specialized cardiomyocytes are associated with the right atrium?
The SA node and AV node
Which specialized cardiomyocytes are associated with the left atrium?
Bachmann bundle
What is the intrinsic firing rate of the SA node?
70-80 BPM
What is the intrinsic firing rate of AV node?
40-60 BPM
What is the heart’s natural pacemaker?
SA node, I f (funny) Na+ channels
What is the intrinsic firing rate of the Bundle of His?
40
What is the intrinsic firing rate of Purkinje fibers?
15-20
Which 2 phases of the action potential do not exist in the SA node?
1 and 2
Explain how the SA node membrane potential works in phase 4?
Phase 4 contains a drift in depolarizing membrane potential (Na+ and K+)
-the Na+ channels are funny in that they open up during phase 3, as the cells are repolarizing
What happens at the threshold point and Phase 0 of the SA node action potential?
Mainly the Ca2+ channels are opened up
What happens at the threshold point and Phase 3 of the SA node action potential?
K+ is the driving force of the repolarization phase (phase 3).
There are/are not fast Na+ channels in the SA node?
are not
What are the 2 types of calcium channels in the SA node cells?
T-type (transient- Ca2+ slowly trickles in during phase 4)
and L-type (Ca2+ drives membrane potential to depolarize)
What is the name of the Na+ “funny” channels?
HCN channels - cause slight depolarizing drift in phase 4 of SA node
Does the parasympathetic system have any effect on the contractility of the heart?
No, the vagus nerve does not reach branches that go down to the ventricles
Which specialized cardiomyocytes are innervated by the sympathetic as well as parasympathetic nervous system?
The SA and AV nodes
What three things are needed to determine stroke volume?
What does ionotropic mean?
any effect on the contractility of the heart
positive ionotropic = increase contractility
negative ionotropic = decreased contractililty
What is a dromotropic effect?
Affecting the conduction velocity of the heart, positive or negative
What are chronotropic effects?
Affects the HR
positive = speed up HR
negative = slow down HR
What effect does the sympathetic system have on the chronotropic, dromotropic, and ionotropic effects on the heart?
increase action of all three, acts on the B1 receptor, activates Ca2+ current channels, and phosphorylates phospholamban
What effec does the parasympathetic system have on HR, what receptor does it act upon, and what ions are invovled?
Decreased HR, M2 receptor, and decrease or close Na+ funny channels (current), enhance Ach-K+ current, and decrease movement of Ca2+ into cells
What effect does the parasympathetic system have on conduction velocity (dromotropic effect), what receptor does it act upon, and what ions are invovled?
Decrease conduction velocity, M2 receptor, decrease action of Ca2+ current and increase K+ current
What effec does the parasympathetic system have on heart contractility, what receptor does it act upon, and what ions are invovled?
Decrease contractility (in atria only), M2 receptor, decrease Ca2+ current and increase K+ current
What are the effects of Ach, adenosine, and B-blockers on the HR?
Decrease HR
What effect do catecholomines have on HR?
increases it
Which ANS component causes the following effects on the SA node:
steeper phase 4 - reach membrane potential faster
sympathetic ANS
What happens to the phase 4 curve of the SA node action potential when stimulated parasympathetically?
the slope becomes less steep
What happens to the membrane potential during parasympathetic stimulation?
becomes more negative, hyperpolarization
What causes the hyperpolarazation of the action potential during parasympathetic stimulation (by Ach)?
The stimulation of K-Ach channels on the cell membrane (enhance efflux of K+ from cell)
What is a dipole?
separation of charge, it is also a vector- with direction and magnitude
The ECG shows the electrical activity of what?
the atria and ventricles (mainly the ventricles)
What corresponds to the time it takes for the electrical impulse to travel from SA node, through AV node, to the start of ventricular depolarizaton?
The PR interval
What is the normal range for the PR interval?
0.12-0.20 seconds (3 to 5 small boxes)
What is an example of a pathology with abnormal PR intervals (
First-degree AV block
Which part of the ECG corresponds with venticular depolarization and what is the normal range?
The QRS complex, < or equal to 0.10 sec (around 2.5 sec)
A QRS complex longer than 0.10 sec could indicate what?
Delayed condcution within bundle branches or later branches or delayed conductin outside conduction pathways - ventricular tachycardia
What part of the ECG corresponds to the mechanical contracton of the ventricles?
The QT interval
What pathology is associated with an abnormal QT interval?
Long QT syndrome -inherited or acquired
Which type of pathology is indicated in the following:
progressive prolongation of the PR interval and eventual failure of P wave to conduct to ventricle
What is the pathology? Several P waves for every QRS
What is the pathology? QRS complexes unrelated to P waves
Which ECG leads are bipolar?
I,II,III
Which leads are precordial unipolar?
V1-V6
Which bipolar lead is described below?
• left arm (+) to right arm (−) = (angle of view 0°);
Lead I
Which bipolar lead is described below?
left leg (+) to right arm (−) = (angle of view +60°);
Lead II
Which lead is described below?
• left leg (+) to left arm (−) = angle of view +120°
lead III
What are the uniploar limb leads?
aVL, aVF, aVR
Study the diagram
What is the direction of the QRS complex in lead I?
Up
What does the T wave represent on the ECG?
ventricular repolarization
Study this diagram
What are the heart rate intervals with the 300 rule?
3 types of capillaries?
- Continuous
- Fenestrated
- Discontinuos
This is the most common form of capillary, with interendothelial junctions 10 to 15 nm wide (e.g., skeletal muscle). However, these clefts are absent in the bloodbrain barrier, whose capillaries have narrow tight junctions
Continuous capillary
In these capillaries, the endothelial cells are thin and perforated with fenestrations. These capillaries most often surround epithelia (e.g., small intestine, exocrine glands).
Fenestrated
In addition to fenestrae, these capillaries have large gaps. Discontinuous capillaries are found in sinusoids (e.g., liver)
. Discontinuous capillary.
Which type of flow tends to fluctuate: increase and decrease every ~ 15 sec (vasomotion)?
Capillary
Vasomotion (fluctuating capillary flow), can for a while in “closed” capillaries.
stop
Which 3 criteria allow for sufficient surface area and enough time for efficient exchange of gases, water, nutrients, and waste products.
- Decreased blood pressure
- Increased exchange surface area
- Decreased blood velocity
Although diastolic and mean arterial pressures are relatively constant, systolic pressure may be up to mmHg higher in the brachial artery than in the aorta
40 mmHg
What phenomonen arises principally because of an increase in arterial stiffness moving away from the heart?
Systolic pressure amplification
The peripheral resistance is increased by vasodilation/vasoconstriction?
vasoconstriction
What are the mechanisms promoting an increase in peripheral resistance?
Endocrine and neuronal
What endocrine system hormones are released to increase peripheral resistance?
epinephrine
norepinephrine
angiotensin-II
renin
What endocrine system process occurs to decrease peripheral resistance?
decreased renin secretion
Describe neural controlled differences that occur during vasoconstricion and vasodilation to increase or decrease peripheral resistance?
- Increased sympathetic activity for increased peripheral resistance
- increased parasympathetic and decreased sympathetic activity to promote vasodilation to decrease peripheral resistance
What are the two main families of receptors of the sympathetic nervous system?
α and β
Two main families of receptors of the sympathetic nervous system, designated α and β, are classified based on response to the adrenergic agonists epinephrine, norepinephrine, and .
isoproterenol
Alterations in the structure of the receptors influence their affinity for various agents.
primary
What are the major effects mediated by a1 adrenoreceptors?
What are the major effects mediated by a2 adrenoreceptors?
What are the major effects mediated by B1 adrenoreceptors?
What are the major effects mediated by B2 adrenoreceptors?
is a medication used for the treatment of bradycardia (slow heart rate), heart block, and rarely for asthma.
isoproterenol
Isoproterenol is a β adrenoreceptor agonist that is the isopropylamine analog of epinephrine (adrenaline).
non-selective
Vasoconstriction evoked by the sympathetic nerve activity is caused by the local release of .
Norepinephrine
Intra-arterially injected elicits only vasoconstriction (α1-adrenergic receptor).
norepinephrine
Low doses of epinephrine produce (β2- adrenergic receptor), whereas large doses cause .
vasodilation; vasoconstriction
What is the distending force that tends to increase the circumference of the vessel?
The transmural pressure (ΔP)
Which law describes how tension in the vessel wall increases with transmural pressure?
Laplace’s law
According to LaPlace’s law, for a given internal fluid pressure, the wall tension will be to the radius of the vessel.
proportional
It is convenient to express this wall tension (T) as the force that must be applied to bring together the two edges of an imaginary , of unit length L, cut in the wall along the longitudinal axis of the vessel.
slit
Larger/smaller arteries must have stronger walls since an artery of twice the radius must be able to withstand twice the wall tension
Larger
The tiny capillaries rely on their size to protect them from wall tension.
small
vesicles form when the plasma membrane invaginates and pinches off to capture and internalize an extracellular fluid sample. The vesicles then migrate across the vessel wall and release their contents on the opposite side.
Pinocytosis
Which transportation mechanism is not a major pathway for exchange, but it does provide for transit of large, charged molecules such as antibodies?
Pinocytosis
Blood entering capillaries is pressurized, so pathways allow water and anything dissolved in it (e.g. electrolytes) to be driven out of the vasculature and into the interstitium. This of fluid is not completely unregulated, however. Intercellular junctions typically contain a proteinaceous barrier that both cements cells together and filters fluid as it leaves the blood. Proteins are too large to escape via junctions or pores and remain trapped within the vasculature.
bulk flow
What type of transportation mechanism is from the capillary via junctions and fenestrations and is driven by blood pressure (P)?
Bulk flow
The same pathways that allow for bulk flow also provide pathways for of water and other small molecules via fenestrations and pores.
simple diffusion - Movement is driven by chemical concentration gradients between blood, interstitium, and cells.
Lipid-soluble materials cross between blood and interstitium by simple diffusion across cells and their plasma membranes. This is the primary means by which O2 and CO2 are exchanged.
endothelial
Which of the following mechanisms is most important quantitatively for the exchange of electrolytes across capillaries?
A) Bulk flow B) Diffusion C) Osmosis D) Vesicular transport
The correct answer is “a” because this is the mechanism by which fluid and accompanying electrolytes move through capillary intercellular junctions. Choice “b” is incorrect because diffusion, although an important mechanism of exchange, is quantitatively less important than bulk flow. Furthermore, electrolytes are charged ions and therefore do not diffuse through membrane lipid bilayers. Choice “c” is incorrect because osmosis concerns the movement of water. Choice “d” is incorrect because vesicular transport is primarily for the transport of large macromolecules.
Since virtually the entire capillary surface is available for diffusion, the permeability is extremely high/low.
high
Respiratory gases, general anaesthetics and the blood flow tracer xenon are examples of what type of solute?
lipophlic
Describe simple diffusion as it relates to lipid soluble molecules and gases, water soluble molecules, and proteins:
Fluid movement between the blood vessels and tissues depends on two driving forces:
- Hydrostatic (blood) pressure
- Osmotic (oncotic) pressure
The Starling forces (hydrostatic and oncotic pressures) allow for of fluid and nutrients across the capillary wall.
bulk flow
Hydrostatic vs osmotic pressures
Hydrostatic “pushes” fluid across boundary while osmotic pressure “pulls” fluid across boundary
Fluid transfer across capillaries is convective and depends on hydrostatic and osmotic forces (i.e., Starling forces).
net
The net driving force formula?
Blood enters capillaries at a pressure of ~35 mm Hg. Blood exits capillaries and enters veins at a pressure of ~15 mm Hg. Mean capillary hydrostatic pressure (Pc) is typically closer/farther to venous pressure than it is to arteriolar pressure but still is usually a positive pressure that drives fluid out of the capillary and into the interstitium.
Also, what type of force is being described here?
closer; Capillary hydrostatic pressure
The main force opposing capillary hydrostatic pressure (Pc) is the ?
osmotic pressure created by plasma proteins. Values for πc typically average ~25 mm Hg.
What happens if fluid filters from the vasculature faster than it can be removed?
Tissue swells
Tissues that are enclosed within skin, bone, or another physical boundary have limited opportunity for expansion, so interstitial (Pi) climbs and can become a significant force driving fluid back into the .
capillary
As part of an immune response to foreign pathogens, is produced by basophils and by mast cells found in nearby connective tissues.
histamine
Histamine increases/decreases the permeability of the capillaries to white blood cells and some proteins.
increases
What is the principle that water permeability of the capillary wall – depends on capillary type.
Kf - hydraulic conductance
Kf - hydraulic conductance is not influenced by such factors as changes in arteriolar resistance, hypoxia, or buildup of metabolites but can be influenced by .
Histamine
What is the formula for fluid movement (Jv) acros the capillary wall?
Maintaining a balance between the forces governing fluid and from the vasculature is vital for continued health.
filtration; reabsorption
Excess fluid filtration causes ?
edema
What happens if there is an inability to recover filtered fluid?
Compromise LV preload and MAP
Review diagram
What arises in the interstitium as small, thin-walled channels of endothelial cells that then join together to form increasingly larger vessels?
Lymphatics
What are similar to capillaries but with many interendothelial junctions that behave like one-way microvalves?
The initial lymphatics
What tethers the initial lymphatics to surrounding connective tissue?
Anchoring filaments
The walls of the larger/smaller collecting lymphatics are similar to those of small veins, consisting of endothelium and sparse smooth muscle.
larger
The large lymphatic vessels, like the veins, have lymph valves that restrict retrograde movement of lymph.
secondary
The large lymphatics ultimately drain into the left and right veins.
subclavian
Although initial lymphatics may appear collapsed and show no contractile activity, a pressure gradient from the interstitial fluid to the lymphatic lumen deforms the endothelial cells so that the microvalves open and fluid enters the initial lymphatic during the phase.
expansion
During this time of initial lymphatics called expansion phase, the secondary lymph valves are open/closed?
closed
Movement of fluid from the interstitium into the lymphatic capillaries is driven by the pressure gradient between the interstitial space and the lymph.
hydrostatic
The edges of lymphatic capillary cells overlap, acting as one-way valves; one-way flow of lymph is also maintained in lymphatic vessels.
endothelial; larger
Flow is augmented by smooth muscle filaments of the lymphatics that contract when stretched.
collecting
Intermittent compression and relaxation of lymphatics occur during what three processes?
espiration, walking, and intestinal peristalsis
Explain lymphatic flow during the compression phase?
Extracellular fluid moves in three convective loops:
- cardiovascular loop
- transvascular loop
- lymphatic loop
What is the transvascular loop?
fluid moves out of the capillaries at their arteriolar end and into the capillaries at their venular end.
Each segment of the lymph vessel between successive valves functions as a separate automatic .
pump- . That is, even slight filling of a segment causes it to contract, and the fluid is pumped through the next valve into the next lymphatic segment.
What refers to the presence of excess fluid in the body tissues?
Edema
In most instances, edema occurs mainly in the extracellular/intracellular fluid compartment.
extracellular
What three conditions are especially prone to cause intracellular swelling:
1) hyponatremia (Hyponatremia is decrease in serum sodium concentration < 136 mEq/L caused by an excess of water relative to solute);
2) depression of the metabolic systems of the tissues;
3) lack of adequate nutrition to the cells.
Extracellular fluid edema occurs when excess fluid accumulates in the extracellular spaces. There are two general causes of extracellular edema:
1) abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries,
2) failure of the lymphatics to return fluid from the interstitium back into the blood, often called lymphedema.
What is the most common clinical cause of interstitial fluid accumulation?
excessive capillary fluid filtration.
Fluid buildup in the body cavities is called?
Effusions
What pathology describes one or both of his heart’s lower chambers lose their ability to pump blood effectively. As a result, blood can back up in their legs, ankles and feet, causing edema. Can also cause swelling in abdomen area. Sometimes, this condition can cause fluid to accumulate in lungs (pulmonary edema), which can lead to shortness of breath.
CHF
Severe disease (such as cirrhosis) causes you to retain fluid. Cirrhosis also leads to high/low levels of albumin and other proteins in your blood. Fluid leaks into the abdomen and can also cause leg edema.
liver; low
When you have disease, extra fluid and sodium in your circulation may cause edema.
kidney;
The edema associated with kidney disease usually occurs where?
In your legs and around your eyes.
Protein malnutrition called is mostly found in people living in geographical areas that have limited food resources. It’s most commonly seen in children whose diets are low in and . Delayed growth in children, a swollen belly, and frequent infections are symptoms.
kwashiorkor; protein; calories
Edema can also be caused by and increase/decrease in hydraulic conductance or capillary permeability
increase
From possible burns, infection, toxins, that result from release of histamine and cytokines
Which drugs work on lowering insulin resistance, which is the underlying problem for many people with type 2 diabetes?
Thiazolidinediones—sometimes shortened to TZDs or glitazones
What is a potent diuretic which, if given in excessive amounts, can lead to a profound diuresis with water and electrolyte depletion. Therefore, careful medical supervision is required and dose and dose schedule must be adjusted to the individual patient’s needs.
LASIX® (furosemide)
What do these drugs have in common:
Drugs that may cause edema
What is a common type of drug used to treat edema?
Diuretics
The correct answer is “c” because increased postcapillary/precapillary resistance ratio caused by arterial (precapillary) vasodilation increases capillary hydrostatic pressure and fluid filtration. Choice “a” is incorrect because a decreased capillary hydrostatic pressure decreases fluid filtration. Choice “b” is incorrect because a decreased capillary filtration constant decreases net filtration. Choice “d” is incorrect because a reduced venous pressure decreases capillary pressure and filtration.
