Heart Review

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Heart Review
2012-04-02 17:31:06
Physio Heart

Physio Heart I
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  1. This word deals with the strength or force of contraction
  2. How do myofibers of the heart differ from myofibers of the skeletal muscle in terms of action potential?
    Heart myofibers don't receive potential from individual nerves, and there are no neuromuscular junctinos
  3. Process of HCN channels
    • Spontaneous depolarization causes channels to open at -60, Na+ rushes in, goes to threshshold at -40V, this voltage triggers Ca2+ channels in the plasma of the pacemaker cells to open
    • -Inward flux of calcium results in the spike and thereafter contractions
  4. Diastolic depolarization
    Occurs during diastole, when the spontaneous depolarization occurs as Na+ comes in
  5. Ca+ influx
    Na+ is responsible in other cells for depolarization, Unlike other cells, Ca+ is reponsible for the depolarizat
  6. Ectopic pacemaker
    (or ectopic focus)
    Rhythm set by a pacemaker other than the SA node
  7. Ventricular Cardiac Myocyte Potential
    (Nonpacemaker cell potential)
    • AV node gives potential to a ventricular myocyte
    • This myocyte will now produce it's own potential
    • -Resting potential: -85V (so it's more stable)
    • -Upon being stimulated, they reach threshold, and the Na+ gates open
    • -Na inwardly diffuse through rapid Na+ channels
  8. Comparing a contraction with a ventricular mycardial cell
    Long action potential results in longer refractory period
  9. Action potential of myocardial cell in ventricle vs ECG
    • P wave: spread of depolarization thru atria (when half mass depolarized, v reaches max, when all polarized, it reaches 0 since no dif in polarity in atria)
    • QRS wave: Depolarization into the ventricle
    • T wave Repolarization of the ventricle
  10. Why are QRS and T repolarization of the ventricle going the same direction?
    Depolarization goes from endocardium to epicardium, while repolarization occurs from epicardium to endocardium
  11. Why are the depolarization/repolarization of ventricles go in the same direction?
    Depolarization goes from endocardium to epicardium, while repolarization occurs from epicardium to endocardium
  12. 70% of the blood _____from atria to ventricle
    30% of the blood _____by ______
    • 1. Falls through
    • 2. Squeezed through by tricuspid and bicspic (or atriaventricular valves) because of the contraction
  13. What creates the lub and dub sounds in the heart?
    • QRS is seen at the beginning of systole (contraction)
    • 1st heart sound (lub) produced by the contraction of the ventricle right after the QRS wave, when the intraventricular pressure is high and the atrioventricular valve is shut
    • 2nd sound (dub) is after the T wave begins, when the ventricle is relaxed (beginning of diastole, decrease pressure, causing the semilunar aorta valve to shut
  14. How are infarcted hearts detected?
    Infarctd heart causes slower waves because action potential can't travel through
  15. Detected by the ECG, what do you call the condition where a tissue is not getting enough oxygen supply because of inadequent blood supply?
    This issue is called Ischemic, you can detect a depression of the S-T segment as a result of myocardial ischemia
  16. What is isoproternol?
    • A strong beta agonist, causing the heart rate to sky-rocket;
    • a heart attack may happen- causing an inversion of the T wave
  17. Bardycardia
    A cardiac rate slower than 60 beats per minute
  18. Tachycardia
    A cardiac rate faster than 100 beats per minute
  19. What is a disadvantage of ECG?
    While it's good at tell you what's going on with your heart at the moment, but it doesn't tell you what happens when your heart is under stress, under workload, therefore, stress tests are important
  20. A wave
    • (atrial contraction)
    • pressure low, P wave comes, atrial pressure goes up a little to squeeze 30 percent of the blood into the ventricle
  21. C wave
    Ventricular contraction: comes about from the ventricular contraction-ventricular pressure goes up really high

    • Due to this, the ventricles bulge into the atrial chamber, less
    • Since there is less area in the atria, it causes a higher prssure in the atria as well
  22. V wave
    Slow pressure buildup in the atria: ventrical contraction but atrial relaxation and blood is returning to the atria from venus return, so the slow buildup of pressure in the atria is the V wave
  23. When ventricle relaxes, pressure in it is below atria, what happens?
    The AV valve opens, 70% blood falls back
  24. Ventricular contraction is what kind of contraction
    Isometric, because as the AV nod shuts (lub), the blood is trapped in the ventricle but ventricle is contracting against it
  25. When the ventricles relax (T wave), the pressures is becoming lower, what valve shuts?
    The semilunar valve, it snaps shut in order to trap the blood in the aorta, otherwise there would be back flow into the venetricles

    Then blood drops from the atria, next contraction happens, valve opens
  26. Systolic pressure/Diastolic pressure
  27. Aortic pressure curve
    (When the valve opens)
    • When pressure in the ventricle goes above aortic, the aortic valve opens up, now increased pressure from the continued systole of the ventricles squeezse the blood into aorta to 120mmHg
    • -Ventricle at this point, starts to relax (T wave), pressure drops
    • -When the pressure in ventricle is dropped to lower than prssure in atria, the AV valves passively open
  28. Aoertic pressure curve
    (when the valve closes)
    Since the ventricular pressure dropped, the AV valve closes, blood starts to flow back from the aorta into the ventricle, that's when the aortic valve snaps shut (dub)

    • Now we are going from the HIGH pressure in the aorta to the systemic circulation, and immediately before the next systole
    • (Diastolic pressure (80 mmHg)
  29. Aortic pressure curve (Incisera or dichrotic notch)
    That's when you know the aortic valve shut
  30. What's the systolic and diastolic pressure on the right side?
    25/8 mmHg
  31. Ejection fraction
    Cardiac output (amount pushed out of left ventricle into aorta and circulation)
  32. Which wave represents depolarization of the ventricles?
    QRS wave
  33. Which wave represents the repolarization of the ventricles?
    T wave
  34. QRS and T waves happen at what point of systole and diastole?
    • QRS happens at the beginning of systole
    • T waves happens at the beginning of diastole
  35. The effect of autonomic nerves on pacemaker potential of the SA node
    • Sympathetic nerve stimulation: increase the rate of spontaneous depolarization
    • Parasympathetic: Decrease
  36. Is the heart going to go faster or slower if you cut all the nerves in the body?
    It will go up, because you're removing the parasympathetic tone which dominates under resting conditions
  37. What do you call the regulation of rate by the autonomic nervous system?
    Chronotropic effect, when sym and parasym acts in antagonistically
  38. How does parasym slow the heart rate?
    • Ach promotes opening of K channels, which affects action potentials in pacemaker region
    • Increase K permeability, results in lower and longer hypopolarization threshold whichslows heart rate
  39. Difference between para and sym on the nature of contraction
    • Parasympathetic predominates on the SA node,
    • It doesn't decrease the force,
    • -Slower rate--->weaker contractions

    Sympathetic, sends fiber directly to the ventricular muscle mass--> affects force of contraction
  40. How does sym increase the heart rate?
    • 1. Norepi and Epi stimuate opneing of HCN channels (hyperpolarization channels)
    • Opens the HCN (Na and Ca channels more, causing sharter slope (meaning more cardiac cycles per minute)
  41. 4 ways of Extrinsit regulation of the heart
    • 1. Neurally controlled
    • 2. Major center in CNS is located in medulla
    • 3. Endocrine
    • 4. Frank Starling Law
  42. Draw the graph for Frank-Starling Law
    • On x-axis, ventricular end-diastolic volume (ml)
    • On y-axis, stroke volume (ml)

    Frank-Starling: increased contractibility caused by sympathetic nerve stimulation (the steeper curve)
  43. Stroke volume
    • =End-diastolic volume-systolic volume
    • 135ml-65ml=70ml
  44. Define diastolic volume
    • Volume of blood in ventricle at the end of diastole, before the next ventricular contraction
    • -135 ml
    • Increase diastolic volume with a higher venus return
  45. Ways to increase venus return?
    • 1. Lay on the floor, no more gravity to fight, this also allows the stroke volume to go up
    • 2
  46. End systolic volume

    Why is there still blood left?
    • After contraction volume
    • 65ml in heart after contraction
    • -This blood is left because when the ventricle starts to relax, even if it squeezed out all the blood from it into the aorta, the aortic pressure is higher than the ventricle and some of the blood flow back in before the semilunar valve snaps shut
  47. Ejection fraction
    The PERCENT you actually pump out

    Start with 135ml and pump out 70 you get about 55% ejection fraction
  48. Contraction force of the heart is simiilar to skeletal muscle in the principle of length and tension relationship
    How is that?
    • If you increase end diastolic volume, you stretch th cradaic muscle myofibers, and they reach a more optimum overlap, by doing so, contract more forcefully
    • Although we don't have resting length in cardiac muscle, but we have some length where there is an optimum OVERLAP
  49. Basically, when you add epinephrine, not only you open up the HCN channel, you allow a little more Ca in with each contraction? What happens?
    • Increases contractility which shifts curve to th left in the Frank-Starling law effect graph
    • Causing it to be hypereffective
    • It INCREASES the stroke volume
    • but end-diastolic volume STAYS the same
  50. 3 Variebles that affect venous return and thuse end-diastolic volume
    • 1. Blood volume (Urine volume and tissue-fluid volume both contribute indirectly)
    • 2. Negative intrathoracic pressure (Caused by breathing)
    • 3. Venous pressure (Venoconstriction, caused by sympathetic nerve stimulation, and skeletal muscle pump)