Cardiac Continued

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LeahS
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66601
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Cardiac Continued
Updated:
2011-02-15 23:50:02
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Proenza Cardiac
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Muscle Physics/Heart as Pump & Exercise
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  1. How are SV, HR, and CO related?
    CO = SV x HR
  2. How is HR regulated?
    Highly regulated by autonomic nervous system
  3. Normal rest and max HRs? Trend w age?
    • Normal resting: 70 bpm
    • Max HR: 200 bpm
    • Decreases w age (220 - age); active people tend to have less decrease w age
  4. Definition of stroke volume? average?
    • Defined as volume of blood pumped per beat
    • at rest, average SV = 70 ml; increased by exercise training
  5. How is SV controlled?
    • Mostly controlled by regulation of strength of contraction, via 2 types of mechanisms:
    • 1) length-dependent intrinsic mechanisms (Frank-Starling Law of the Heart)
    • 2) length-independent mechs (intropy, typically via sympathetic nervous system)
  6. Normal cardiac output at rest?
    • 4-6 L/min
    • depends on size of person, metabolism, exercise, etc
    • *remember to convert SV mL to L for CO L/min
  7. T/F: CO can be different for Rt and Lft sides of heart.
    • False. CO MUST be the same for left and right sides of heart.
    • Closed loop system, therefore CO MUST equal venous return (VR = volume of blood flowing into right atrium per minute)
  8. Effects of exercise on CO, HR, and SV?
    • CO increases by as much as 8 fold (up to 40 L/min in elite athletes; max normal people is 25 L/min)
    • HR can increase 4 fold
    • SV can increase 2 fold
  9. relationship between arterial pressure, total peripheral resistance, and CO?
    • CO = arterial pressure / total peripheral resistance
    • Q = P/R (think increased resistance, so decreased flow)
  10. Describe the "filling phase" on the Wigger's diagram.
    • First phase.
    • Mitral valve is open.
    • The end of diastole, so left atrium has passively filled w blood returning from pulmonary vein. Electrical signal from SA node triggers contraction of atrium.
    • Left atrium contracts (atrial systole), so pressure increases for both atria and ventricle (filling passively with blood).
  11. Describe Isovolumetric Contraction phase on Wigger's diagram.
    • As wave of electrical excitation arrives at left ventricle, it begins to contract.
    • Aortic valve is closed as left ventricle begins to contract b/c aortic pressure is higher than ventricular pressure.
    • As left ventricle contraction begins, mitral valve closes because ventricular pressure quickly exceeds atrial pressure.
    • As ventricle begins to contract, the blood has no where to go (both valves are closed), so ventricular pressure rises rapidly.
  12. Describe Ejection Phase of Wigger's Diagram.
    As ventricle continues to contract, ventricular pressure increases until it's greater than the aortic pressure; at this point, aortic valve opens and blood flows from ventricle into aorta.
  13. Describe Isovolumetric Relaxation phase of Wigger's Diagram.
    • After ejection phase.
    • As wave of depolarization passes, ventricular myocytes relax, and ventricular pressure falls. Pressure decreases slowly at first.
    • When ventricular pressure drops below aortic pressure, the aortic valve closes.
    • Since the mitral valve is still closed, the ventricular pressure falls rapidly.
  14. Describe the Filling Phase of the Wigger's Diagram.
    • As ventricle continues to relax, the pressure eventually falls below that of the atrium, allowing the mitral valve to open.
    • Blood flows into the ventricle until next cardiac cycle is initiated by depolarization of the SA node.
  15. What term represents the pressure-volume relationship during filling of the heart BEFORE contraction?
    • Diastolic Pressure Volume Relationship (DPVR)
    • *passive tension curve: cardiac muscle is stiff & resists stretch passively; not much change normally in pressure w/ change in volume, except at very high volume where heart is just too full --> shallow slope of DPVR
    • *represents PRELOAD of the heart (EDV): the load to which a muscle is subjected before shortening
    • change in pressure as volume increases during diastole
  16. What term represents the pressure-volume relationship during contraction of the heart?
    • Systolic Pressure Volume Relationship (SPVR)
    • much steeper than DPVR - pressure increases a lot, even at low volume/small volume changes
    • includes the passive + active properties (ie: DPVR)
    • change in pressure as volume increases during systole
  17. What is afterload?
    • Afterload: the load against which a muscle contracts.
    • For left ventricle, afterload = aortic pressure.
    • range of afterload values lie along SPVR curve
  18. What is "active tension"?
    • Active tension is difference between DPVR and SPVR = tension developed by the contraction (independent of passive properties/preload)
    • *plot of active tension = "Starling Curve" or "Ventricular Function Curve": ascending and descending limbs (if you stretch it too far, the pressure decreases)
  19. What are 3 ways to state the Frank Starling Law of the Heart?
    • 1) Heart always functions on the ascending limb of the venticular function curve.
    • 2) Heart responds to an increase in EDV by increasing the force of contraction.
    • 3) What goes in, must come out. Cardiac output must = VR.
  20. Is Frank-Starling Law an intrinsic or extrinsic mechanism by which the heart adapts to changing load?
    Intrinsic
  21. What is the molecular basis for Starling's Law?
    • 1) cardiac titin isoform is very stiff, resists stretch
    • 2) Ca2+ sensitivity of myofilaments increases as sarcomeres are stretched. Same Ca2+ = greater force of contraction.
    • 3) closer lattice spacing- stretched sarcomeres have altered spacing between actin & myosin, which results in more force generated per crossbridge
  22. Is Starling's Law dependent on the autonomic nervous system? To what is this law analogous?
    • Independent of autonomic nervous system regulation
    • Analogous to, and dependent on, sarcomere length-tension relationship
  23. What is the Bainbridge Reflex?
    • If you stretch the sinus node = increase HR
    • via increased sympathetic tone (sensory afferents and brainstem); also intrinsic mechs in SA node
    • another way in which increased venous return causes increased cardiac output
  24. Describe Filling Phase in PV loop diagram.
    • Start at beginning of diastole, when mitral valve opens.
    • Ventricular volume and pressure at their minimum values.
    • Volume is ESV (note: not 0; heart doesn't pump out all blood)
    • During diastole, the ventricular volume increases as blood flows into the left ventricle from the left atrium.
    • Little pressure change, except slight hump that corresponds to atrial contraction.
  25. Describe Isovolumetric Contraction Phase in PV loop diagram.
    • At point C, ventricle begins to contract
    • Almost immediately, the pressure in the ventricle exceeds that in the atrium and the mitral valve is pushed close.
    • Volume is EDV
  26. Describe Ejection Phase of PV Loop Diagram.
    • When left ventricular pressure exceeds the aortic pressure, the aortic valve is pushed open (point D) and the ejection phase begins.
    • As blood leaves the ventricle, the volume decreases.
    • At first the pressure continues to increase, as blood cannot leave the aorta fast enough.
  27. Describe Isovolumetric Relaxation Phase in PV Loop diagram.
    • When ventricular pressure again falls below the aortic pressure, the aortic valve closes (point F).
    • Again, both valves are closed, so no change in volume but pressure drops dramatically as ventricle continues to relax.
  28. How do you calculate blood pressure from a PV Loop Diagram?
    • Diastolic Pressure - Point D (where aortic valve opens)
    • Systolic Pressure - Point E (highest pressure)
    • Difference between systolic pressure and diastolic pressure = pulse pressure
  29. What's the equation for SV?
    SV = EDV- ESV
  30. What's the Ejection Fraction equation?
    • EF = SV/ EDV
    • normal ejection fraction is 50-70%
    • <55% may indicate damage (previous heart attack)
    • 35-40% may confirm diagnosis of systolic heart failure or cardiomyopathy
    • <35% patient may be at risk for sudden heart attack, transplant indicated
    • often measured by ECG
  31. What is "stroke work"? How is it measured?
    • Stoke work = amount of energy as work per beat
    • area inside a PV loop diagram
    • units = Joules
    • NOT the same for right and left heart, as systemic circulation has higher pressure so left heart does more work
  32. If you increase preload while afterload and inotropy remain constant, what happens to ESV, EDV, EF, and SV?
    • Increased EDV (same thing as preload)
    • Increase SV (in NEXT BEAT), via Starling's Law
    • No change in ESV
    • Slightly increased EF
    • In next beat, SV back to normal b/c ESV is unchanged and contractility is unchanged
  33. Upon what does EDV depend?
    • filling pressure
    • filling time
    • ventricular compliance - important property in determining cardiac function
  34. If you increase afterload while preload and inotropy remain constant, what happens to SV, EDV, ESV, and VF?
    • Afterload is tension against which muscle must contract. For cardiac muscle, this is Aortic Pressure (~ mean systemic arterial pressure)
    • Decrease SV (in NEXT BEAT) because ventricle has to work harder against increased aortic pressure, so less blood is ejected. Also, aortic P is higher, so aortic valve closes at higher P.
    • EDV unchanged
    • EF decreased
    • ESV increases
    • Subsequent beat: the increased ESV with constant venous return means increased preload, so increased SV
  35. Inotropy is force of contraction. What is contractility controlled by? What is inotropy regulated by?
    • Contractility controlled by amt of Ca2+ available to contractile proteins.
    • Regulated by autonomic nervous system (sympathetic stimulation)
  36. If you increase inotropy while preload and afterload remain constant, what happens to SV, ESV, EF, and SV?
    • Increase SV
    • ESV decreases
    • EF increases
    • Subsequent beat: SV remains elevated as long as inotropy is high
  37. What are some uncontrollable and controllable risk factors of Cardiac Disease?
    • Uncontrollable: age, male gender, heredity & race
    • Controllable: physical inactivity, overweight/obesity, high cholesterol, hypertension, diabetes, smoking (atherogenic = irritates vascular endothelial cells & increase platelet adhesion, increases BP, increases LDL and decreases HDL)
  38. Definition of "Ischemic Heart Disease"?
    • Oxygen consumption of the heart exceeds supply.
    • *Most common type of heart disease (6.8% of Americans)
    • Most often caused by atherosclerosis in coronary arteries (atherosclerosis in cerebral arteries is leading cause of stroke)
  39. Definition and details of atherosclerosis.
    • Def: an inflammatory response to damage of the vascular epithelium.
    • hardening and thickening of arteries due to "plaques": deposits of fatty substances, cholesterol, and fibrin
    • CVD risk factors cause endothelial damage. Once endothelium is damaged, plaques begin to form.
  40. Describe atherosclerotic plaques.
    • "Crunchy on outside, greasy & thrombogenic on inside"
    • Consist of fibrous cap (collagen + other ECM molecules secreted by ectopic smooth muscle cells) that overlays a lipid core (lipid core is intensely thrombogenic, with cellular debris and cholesterol)
    • plaques form at branches and curves of arteries (areas with increased hemodynamic forces on walls, with turbulent instead of laminar flow)
  41. What's a "stenotic plaque"?
    Plaques themselves aren't usually the cause of acute problems. Stable plaques can be "stenotic" - that is, cause narrowing of arteries - but those occlusions tend to be relatively benign (at worst, cause angina)
  42. What does a plaque rupture cause?
    Plaque rupture causes thrombosis, as the fibrous cap is destabilized over time and lipid core escapes. This can cause sudden and dramatic occlusion of artery = myocardial infarcation or ischemic stroke (80% of strokes)
  43. List the steps in plaque formation
    • Damaged endothelium is leaky (leaky endothelium allows LDL cholesterol to enter intima)
    • Leukocyte adhesion and migration (oxidized LDL promotes adhesion of leukocytes, which enter the intima and differentiate)
    • Foam cells form (High cholesterol diet down-regulates normal LDL receptors. Differentiated leukocytes take up LOADS of cholesterol, forming "foam cells")
    • Proliferative response in vessel wall (vascular smooth muscle cells (VSMCs) produce collagen = formation of fibrous cap which temporarily stabilizes the plaque)
    • Plaque rupture and thrombosis (VSMCs de-differentiate and release cytokines that decrease collagen production and promote collagen degradation)
  44. What is angina pectoris?
    • Type of Ischemic Heart Disease.
    • episodes of chest pain/tightness/heaviness (poorly localized, difficult to describe)
    • transient decrease in blood flow (so cardiac demand transiently exceeds supply)
  45. Define "demand angina", "supply angina", "stable angina" and "unstable angina".
    • Demand angina: provoked by exertion and stress; relieved within minutes at rest
    • Supply angina: provoked by sudden decrease in supply (ex: occlusion from clot)
    • Stable angina: usually demand angina; fairly good prognosis
    • Unstable angina: usually worsening of stable angina, medical emergency with poor prognosis, caused by dynamic plaques
  46. What is myocardial infarction?
    • Type of ischemic heart disease.
    • death of cardiac myocytes caused by lack of blood supply
    • most often in left ventricle
    • myocardial cell death begins 15-40 minutes after occlusion of artery; very few cells left after 6 hours
    • leaves scar tissue (collagen) - permanent damage, compromised cardiac function
  47. What are some symptoms of myocardial infarction?
    • sudden onset (50% have warning signs)
    • severe chest pain
    • shortness of breath (dyspnea)
    • autonomic symptoms: sweating, weakness, nausea, vomiting
    • loss of heart function
    • arrhythmias
    • >30% silent/ no symptoms (esp in elderly and diabetic patients)
  48. How do we diagnose myocardial infarction?
    • damaged cells leak proteins into blood = markers for infarction (creatine kinase; troponin T)
    • medical hx indicates ischemic chest pain >20 min
    • ECG changes (ST segment shifts, abnormal Q waves)
  49. What is hypertension? What values indicate the various stages?
    • BP> 140/90 (normal is LESS THAN 120/80)
    • Normal: < 120/80
    • Prehypertension: 120/80 to 139/89
    • Stage I: 140/90 to 159/99
    • Stage II: >160/100
  50. Fun fact about linear relationship between degree of hypertension and risk?
    After 115/75, each increase of 20/10 DOUBLES risk of CVD incidents.
  51. Why is hypertension considered to be so bad?
    • - "Silent killer": assymptomatic until permanent damage has occurred
    • - irreversible
    • - increased afterload can lead to Left Ventricular Hypertrophy - eventual cause of heart failure
    • - damages vascular endothelium - causes atherosclerosis
    • - can cause aneurysms (bulges) in vessels - weak, chance of rupture; rupture in cerebral arteries = hemorrhagic stroke
    • - usually results in arteriosclerosis - hypertrophy in vessels: reduced compliance - normal increase in BP w aging
  52. Which disease is the underlying cause of death of 90% of patients who suffer from it?
    • Hypertension
    • 50% die from heart disease or heart failure
    • 33% stroke
    • 5% renal failure
  53. Definition of arrhythmia.
    • Disorders of cardiac rate and rhythm
    • Can be benign or life-threatening
    • a) Rate disorders (bradycardia = too slow, tachycardia = too fast). Caused by sinus node dysfunction and/or ectopic pacemakers
    • b) Conduction abnormalities: Conduction block (AVN or block in His-Perkinje system or damaged myocardium)
    • c) Disordered beating: premature beats caused by after depolarizations during EADs or soon after DADs normal repolarization, atrial fib (rapid irregular arrhythmia), ventricular fib (no pumping). Only hope is AED system.
    • d) Cardiac arrest: heart stops; due to infarction or rhythm disorders
  54. Definition of heart failure.
    Progressive syndrome in which the heart cannot pump enough blood to meet demand and/or it cannot pump enough blood to prevent fluid backup in lungs and periphery (thus "congestive" heart failure)
  55. Is heart failure a disease itself?
    No. Heart failure is not a disease. It is the end stage for other CV diseases, especially hypertension and coronary artery disease.
  56. What's the annual death rate for heart failure?
    • 10% death rate annually (50% dead in 5 years)
    • 5 million people in US currently diagnosed (1-2% of population; 25% of people over 85)
  57. What happens in Heart Failure?
    • Progressive deterioration of myocardium
    • Molecular changes in cardiac myocytes
    • Premature myocyte cell death
    • Pathological hypertrophy – heart grows but in a maladaptive way.
    • Affects right or left ventricle (or both... eventually)
  58. Contrast systolic heart failure with diastolic heart failure.
    • Systolic Heart Failure: decreased ability to pump (decreased ejection fraction)
    • - most common cause = myocardial damage from infarction --> therefore underlying cause is atherosclerosis
    • Diastolic Heart Failure: impaired ability to fill due to decreased compliance (cardiac hypertrophy from increased afterload reduces compliance)
    • - most common cause = hypertension (often w diabetes and/or obesity); EF can be preserved
  59. What are some Heart Failure Symptoms?
    • Dypsnea (shortness of breath) - cardinal symptom
    • ○orthopnea: SOB when lying down
    • ·Fatigue (weakness, fainting from lack of O2)
    • ·Peripheral edema (swelling feet and ankles)
    • ·Pulmonary edema (fluid backup into pulm. vein -> increased hydrostatic pressure = net filtration, fluid into air spaces of lungs)
  60. What is the primary response to exercise?
    Huge increase in CO
  61. What are some vascular effects of exercising?
    • blood flow regulation in exercising muscle - local metabolites decrease vascular resistance by increasing vasodilation in arterioles in exercising muscle
    • capillary recruitment in exercising muscle
    • vasoconstriction in inactive tissues - via sympathetic stimulation
  62. What is VO2-max?
    • Maximum rate of O2 consumption during strenuous exercise
    • range: 30 ml/kg/min = couch potato to >80 ml/kg/min = elite athletes
  63. What are some factors that control VO2 max?
    • ○cardiac output (dominant factor) --> determined by HR & SV
    • ○O2 carrying capacity of blood -> determined by hematocrit & O2 uptake in pulmonary capillaries
    • ○blood flow through vessels in exercising muscle-> determined by resistance in arterioles
    • ○muscle O2 uptake -> determined by mitochondrial oxygen consumption
  64. What is the Fisk Equation for Oxygen?
    • VO2 = CO (CaO2-CvO2)
    • VO2 = oxygen consumption (L/min)
    • CO = cardiac output (L/min)
    • CaO2 = oxygen content of arterial blood
    • CvO2 = oxygen content of venous blood

    • (CaO2-CvO2) describes the contributions of O2
    • carrying capacity, blood flow, and O2 uptake
    • *NOTE: CO is main determinant of VO2max
  65. Exercise training increases VO2max and CO. What are some interrelated changes?
    • Decreased heart rate
    • oat rest and at all submaximal levels
    • opartly due to increased stroke volume (lower
    • HR for any given CO)
    • opartly due to decreased sympathetic and
    • increased parasympathetic tone
    • olow HR increases filling time (= increased
    • EDV = increase SV via Starling’s law)

    • · Physiological hypertrophy
    • ○ increased chamber volume & mass
    • ○ different from pathological hypertrophy in heart failure
    • · Increased blood volume
    • ○ 10-15% increase
    • ○ increases EDV, so SV increased via Starling’s law
    • · Decreased blood pressure
    • ○ decreases afterload; can increase cardiac performance
    • Increased contractility
    • ○ increased RATE of Left Ventricular pressure development
    • ○ increased ejection fraction
  66. To what percent does exercise training reduce CVD risk?
    • Up to 50%
    • ○ Directly reduces CVD risk, independent
    • of other risk factors (~40% of benefit).
    • ○ Reduces other CVD risk factors (~60% of
    • benefit). Decreases blood
    • pressure, cholesterol, weight, diabetes, stress
    • - Mostly via decreases in "inflammatory factors" (eg: cytokines & vascular adhesion molecules, which are atherogenic)
  67. What are the minimum exercise guidelines?
    • ○Minimum of 30 min 5 days a week of moderate-intensity aerobic exercise (eg: walking)
    • OR
    • 20 min 3 days a week of vigorous-intensity (eg: running)
    • AND
    • ○Minimum 2 days a week of muscle-strengthening activity (eg: weight-lifting, calisthenics/yoga, etc)
  68. What does it mean when they say "more exercise is better"?
    • Risk of CVD events decreases linearly with increased levels of activity.
    • ○<200 kcal/week exercise = used as baseline
    • ○200-600 kcal/week exercise = 27% decreased risk of CVD events in 10 years
    • ○600-1500 kcal/week = 32% decrease
    • ○>1500 kcal/week = 41% decrease

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