Decreases w age (220 - age); active people tend to have less decrease w age
Definition of stroke volume? average?
Defined as volume of blood pumped per beat
at rest, average SV = 70 ml; increased by exercise training
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)
Normal cardiac output at rest?
depends on size of person, metabolism, exercise, etc
*remember to convert SV mL to L for CO L/min
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)
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
relationship between arterial pressure, total peripheral resistance, and CO?
CO = arterial pressure / total peripheral resistance
Q = P/R (think increased resistance, so decreased flow)
Describe the "filling phase" on the Wigger's diagram.
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).
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.
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.
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.
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.
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
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
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
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)
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.
Is Frank-Starling Law an intrinsic or extrinsic mechanism by which the heart adapts to changing load?
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
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
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
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.
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
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.
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.
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
What's the equation for SV?
SV = EDV- ESV
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
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
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
Upon what does EDV depend?
ventricular compliance - important property in determining cardiac function
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.
Subsequent beat: the increased ESV with constant venous return means increased preload, so increased SV
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)
If you increase inotropy while preload and afterload remain constant, what happens to SV, ESV, EF, and SV?
Subsequent beat: SV remains elevated as long as inotropy is high
What are some uncontrollable and controllable risk factors of Cardiac Disease?
*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)
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.
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)
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)
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)
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)
What is angina pectoris?
Type of Ischemic Heart Disease.
episodes of chest pain/tightness/heaviness (poorly localized, difficult to describe)
- 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
Which disease is the underlying cause of death of 90% of patients who suffer from it?
50% die from heart disease or heart failure
5% renal failure
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
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)
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.
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)
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)
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
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)
What is the primary response to exercise?
Huge increase in CO
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
What is VO2-max?
Maximum rate of O2 consumption during strenuous exercise