Cardiac Output and Contractility Flashcards

1
Q
  • What is the effect of a positive inotropic agent?
A

Increase in contractility

  • Increase in EDV
  • Increase in CO
  • Increase in SV
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2
Q
  • What is the effect of a positive chonotropic agent?
A
  • Increase in HR
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3
Q
  • What is the effect of a negative inotropic agent?
A
  • Decrease contractility
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4
Q
  • What is the effect of a negative chonotropic agent?
A
  • Decrease HR
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5
Q
  • What is preload? (General sense)
A
  • End Diastolic Volume
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6
Q
  • What is preload in a more detailed sense?
A
  • Amount of wall tension in RV or LV just before contraction is initiated
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7
Q
  • What is afterload (in a general sense)?
A
  • Aortic diastolic pressure
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8
Q
  • What is afterload in a more detailed sense?
A
  • The amount of diastolic pressure in the aorta/pulmonary arteries that must be exceeded for semilunar valves to open
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9
Q
  • How are afterload and velocity related?
A
  • They are inversely related
  • Increase in afterload leads to a decrease in velocity of contraction/shortening of muscle fibers
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10
Q
  • How do you calculate stroke volume ?
A
  • SV=EDV-ESV
  • Note that in normal conditions, this is approx 70 mL
  • Represents volume of blood ejected by ventricle with each beat
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11
Q
  • How do you calculate ejection fraction?
A
  • EF%=SV/EDV
  • Usually around 55%
  • Represents the fraction of EDV that is ejected in each stroke volume
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12
Q
  • How do you calculate cardiac output?
A
  • CO=HR x SV
  • Volume of blood ejected by the ventricle per minute
  • Normal=5 L/min
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13
Q
  • What does the Frank Starling relationship tell us?
A
  • The volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastole (EDV)
  • Note that EDV relates to venous return (more venous return, larger EDV)
  • In a steady state CO=venous return
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14
Q
  • Will a chonotropic effect have an inotropic effect?
A
  • Yes
  • Positive chonotropic effect will have positive effect on inotropy and vice versa
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15
Q

What is represented by points 1-2 in the following pressure volume curve?

A
  • Isovolumetric contraction
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16
Q
  • What is represented by points 2-3 in the pressure volume loop?
A
  • Ejection of blood
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17
Q
  • What is represented from points 3-4 in the pressure volume loop?
A
  • Isometric relaxation
18
Q
  • What is represented by points 4-1 in the pressure volume loop?
A
  • Ventricular filling
19
Q
  • Which point on the curve represents preload?
A
  • 1
  • Remember preload=EDV
20
Q
  • Which point on the loop represents afterload?
A
  • 2
  • Remember that afterload is the aortic pressure that must be exceeded in order for the aortic valve to open and blood to be ejected from the ventricle
21
Q
  • On which points of the loop are the AV valves opening and closing?
  • On which points of the loop are the semilunar valves opening and closing?
A
  • AV valves open during 4
  • AV valves close during 1
  • Semilunar valves open at 2
  • Semilunar valves close during 3
22
Q
  • What are the effects of increased pre-load on the pressure volume loop?
A
  • Increase in EDV
  • Afterload and contractility remain constant
  • Increased stroke volume
23
Q
  • What are the effects of increased afterload on the pressure volume loop?
A
  • Greater pressure in aorta
  • Reduced SV
  • Reduced EF%
24
Q
  • What are the effects of increased contractility on pressure volume loop?
A
  • Increased SV
  • Increased aortic pressure
  • Decreased ESV
25
* What type of effect does sympathetic stimulation have on CO? * Via what receptors does this act? * Via what NTX does this act? * What are the biochemical effects that occur as a result of sympathetic stimulation?
* **Positive inotropic effect** * **Beta 1 adrenergic receptors** * **NE** * **Phosphorylation of sarcolemma Ca2+ channels (leads to increased intracellular Ca2+ concentrations)** * **Phosphorylation of phospholamban (increased sequestering of Ca2+ in the SR; important for subsequent contractions)** * **Phosphorylation of Troponin I (Inhibits troponin i so that troponin c can bind to Ca2+ and help enable cross bridge formation)**
26
* What type of effect does the parasympathetic nervous system have on cardiac output? * Through which receptor does it work? * What biochemical events occur as a result?
* **Negative inotropic effect in ATRIA ONLY** * **Muscarinic receptor activation** * **​**Decreases inward Ca2+ current during plateau * AcH increases outward K+ current via K+-ACh channel (hyperpolarizes membrane)
27
* How does increasing HR affect contractility?
* Positive chonotropic effect increases HR and increased HR increases contractility (positive inotropic effect) * **Positive staircase effect (Bowditch staircase)** * **​More Ca2+ enters into cell and taken up into SR** * **Postextrasystolic potentiation (arrythmia, extra beat)**
28
* What is volume work equivalent to? * What is pressure work equal to? * Which is greater?
* Cardiac output * Aortic pressure * Pressure work
29
* **What is minute work?**
**Minute work=CO x aortic pressure (pressure work)**
30
* **What is stroke work?**
* **Performed by the LV** * **Stroke Work=SV X aortic pressure** * **Represents the area within the pressure volume loop**
31
* What is the **Fick principle?**
* **Cardiac output=O2 consumption/([O2]pulmonary vein-[O2]pulmonary artery)**
32
* What is the relationship between CO and venous return at a steady state?
* **At a steady state, the volume of blood ejected by Lv (CO)=venous return**
33
* Changing what factor will shift which part of the cardiac curve ONLY?
Inotropy
34
* Changes in what parameter will change the vascular function curve only?
* **Changes in blood volume**
35
* **What parameter affects both Cardiac and Vascular function curves?**
**TPR**
36
What is represented by the blue dot in the following figure?
Equilibrium-where CO=venous return
37
What is represented by the arrows in the following diagram?
* 1st arrow=equilibrium where CO=venous return * 2nd arrow=Mean systemic pressure; proportional to blood volume and preload\*\*
38
* What parameter is causing the changes in the cardiac function curve?
* Left represents a **positive inotropic effect (increased inotropy, increased HR, increased afterload)** * Left represents a **negative inotropic effect (decreased inotropy, decreaed heart rarte, increased afterload)**
39
* **Changing what parameter has caused the shifts in the following figures?**
* Right * Increasing blood volume * Decreasing systemic vascular resistance (SVR) * Decreasing mean circulatory filling pressure/mean systemic pressure * Left * Decreasing blood volume * Increasing systemic vascular resistance * Increasing mean circulatory filling pressure/mean systemic pressure
40
* **_What parameter has been changed to cause the shifts in the diagrams below?_**
* TPR * **Left diagram shows an increase in TPR** **which leads to a right shift of the cardiac function curve and a left shift of the vascular function curve** * **Right diagram shows a decrease in TPR which leads to a left shift of the cardiac function curve and a right shift of the vascular function curve**
41
* What is the relationship between CO and venous return in an individual with heart failure?
* Decreased inotropy * Decreased vascular complaince * Increased blood volume * Increased SVR