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29 Cards in this Set
- Front
- Back
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What are the Determinants of cardiac output?
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the factors that contributes to the generation of the cardiac output.
→ the two determinants are: HR and SV |
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Define Inotropy
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the term applied to the changes in the heart muscle performance, independent of changes in preload and afterload. An inotropic drug, is a drug that increases the hearts contractility thus increasing the CO.
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What is a cardiac cycle?
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Cardiac cycle: the events that occur from the beginning of one heart beat to the beginning of another
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Define the term excitation-contraction coupling.
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Excitation-contraction coupling: the mechanism by which the action potential in the cardiac myocyte causes the myofibrils to contract
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What is the optimum sarcomere length in the myocyte for the development of the maximal contractile force?
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2-2.2 µm, because at this length, there is optimal overlap between thin and thick filaments
--> hence maximum number of crossbridge attachments |
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How is the CO controlled in the body?
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Regulation/adjustments of the CO by the body is via two mechanisms:
1-the intrinsic cardiac regulation of pumping in resoponse to changes in volume of blood flowing into the heart 2-control of the heart by the ANS |
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Define the Frank-Starling mechanism.
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Definition: this law is about the intrinsic regulartory mechanism of the heart:
it states that the force of the myocardial contraction is proportional to the initial fiber lengh, up to a point. In effect, it means that the heart is able to pump all the blood that comes to it form the peripheral tissues as the increase inflow of blood into the heart results in increase in the force of contraction in the heart. |
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Why is the Frank-Starling mechanism important?
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As the heart can pump all of the blood that flows into it (even in cases where there is increase flow of blood), this prevents damming/pooling of blood in the heart.
(blood flow is adjusted locally in the peripheral tissues--> increase flow there leads to 'increase flow' in the heart!) |
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What is the optimal end-diastolic filling pressure for the generation of maximal contraction force?
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12 mmHg
at this filling pressure, sarcomere length is 2.2 µm. |
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What is the maximum sarcomere length in the heart?
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2.6 µm, due to the resistance to stretch of the myocardium (at high filling pressures)
--> because of the 'non-contractile' constituents in the heart -->acts as a safety mechanism against over-loading the heart in very high filling pressures. |
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What is the normal 'ventricular' diastolic pressure?
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0-7 mmHg
this leads to an average sarcomere length of 2.2 µm. |
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Write down LaPlace law for the heart.
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T=Pr/w
T: tension in the wall of the ventricle P:transmural pressure r:radius of the ventricle w: wall thickness of the ventricle |
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Why does contractility increases as the fiber length increases?
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1- more optimum sarcomere length
2-increase sensitivity of troponin C to Ca++ |
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What is trigger Ca++?
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Trigger Ca++: is the small amount of Ca++ that enters the cell from the interstial fluid compartment during phase 2 of the cardiac action potential
-->it trigers the release of the intra-cellular Ca++ stores form the sarcoplasmic reticulum |
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What is ryanodine?
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Ryanodine: s a poisonous alkaloid found in the South American plant Ryania speciosa (Flacourtiaceae). It was originally used as an insecticide. The compound has extremely high affinity to the ryanodine receptor, a group of calcium channels found in skeletal and heart muscle cells. It binds with such high affinity to the receptor that it was used as a label for the first purification of that class of ion channels and gave its name to it
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How does chatecholamines increase force of contraction in the heart?
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they cause phosphorylation of the Ca++ channels via a cAMP-dependent protein kinase, thus increasing the intracellular concentration of Ca++
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How does cardiac glycosides incresae force of contraction?
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inhibit Na/K ATPase
-->increase intracellular Na+ -->less Ca++ is removed via the Na/Ca pump |
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How is cardiac relaxation increased by catecholamines?
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1. ↑cAMP
-->phosphorylation of phospholamban -->↑uptake of Ca++ by the SR 2. also phosphorylation of troponin I -->inhibits troponin C - Ca++ binding |
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Define preload.
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Pre-load: the degree of stretch of the heart ventricular chamber due to venous return.
-->is the end-diastolic ventricular wall tension. Usually inferred from ventricular end-diastolic pressure, itself approximating to pulmonary capillary wedge pressure (left) or CVP (right). |
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Define myocardial contractility.
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Myocardial contractility: is the force with which the myocardium contracts.
-->a major determinant of SV, CO and myocardial O2 demand |
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Define cardiac output.
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Cardiac output: is the ‘quantity’ of blood pumped in the aorta each mintue (i.e. it is the flow of blood in the aorta per minute)
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Define veouns return.
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Venous return: is the quantity of blood flowing from the veins into the right atrium each minute.
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What is the normal value for CO?
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normal value for CO is ~5 L/min. This number depends on:
1. Basic level of body metabolism 2. Exercise level 3. Age 4. Body size 5. Sex |
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Define Cardiac Index
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is the cardiac output per square meter of body surface area
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What is the normal CI?
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For a person who is 70 kgs in weight
--> surface area is 1.7 square meters --> thus cardiac index =5/1.7= 3 L/min/square meter |
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What is Bainbridge reflex?
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Bainbridge reflex: reflex tachycardia following an increase in venous return (e.g. following rapid infusion of fluid). Does not occur in transplanted hearts, suggesting true reflex pathways.
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What are Cardiac output curves?
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a quantative expression of the pumping ability of the heart
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What is the Mean sytemic filling pressure?
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a measure of the degree of filling of the systemic circulation; measured everywhere in the systemic circulation when all flow of blood is stopped)
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List the factors that determines venous return.
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Right atrial pressure
Mean systemic filling pressure (Psf) Resistance to blood flow between periphral vessels and RA VR= Psf –P(RA) /RVR Venous tone Blood volume Gravity Posture Muscular activity and venous valves Intra-thoracic pressure Intra-abdominal pressure Repiratory activity Artifical ventilation Vasodilator/vasopressor durg therapy Right and left ventricular function |
