Lecture #2 Flashcards
Myocardium has ____ ATP content and _____ ATP demand
Low, Very High
What supplementary molecule may help the heart maintain ATP levels?
Creatine Phosphate going btw mitochondria and contractile units
Name of cardiac creatine phosphokinase
CK-MB
What do elevated CK-MB leves imply?
Recent Acute Myocardial Infarction
Biggest contributor of energy to the heart? 2nd place?
Fatty Acids
Carbohydrates (Primarily Glucose)
Using Pressure-Volume Loop, what is stroke work? stroke volume?
Work = Area Enclosed by loop Volume = Area between the two isovolumetric volume stages
What are the four points on the pressure-volume loop. Assume A is the first heart sound.
A = Mitral Valve Closure B = Aortic Semilunar Valve Opens C = Aortic Semilunar Valve Closes D = Mitral Valve Opens
Review Loop on P. 68
Fuck this class. Fuck this school.
What is laplace’s law used to estimate?
Wall Tension and Stress
Wall tension is proportional to….
Vessel Pressure and Radius
Ventricular wall tension required to open semilunar vales is a measure of….
Afterload
Equation for Wall stress
S=Tension/Wall Thickness
(remember Tension = PressureXRadius
Ways to reduce vessel wall stress?
Decrease r, decrease P or increase thickness
Effects of congestive heart failure on ventricles, EDV, EJF
Dilation of ventricles
Increase in EDV
Decreased EJF
Effect of Increased EDV and Decreased EJF on SV?
Initially, nothing.
Eventually, requires hypertrophy and limits are reached
Can’t be maintained
Relationship of Wall Stress, Pressure, and Volume
S is proportional to P and proportional to the cube root of volume.
ex. 100% increase in volume increases stress by 26%
100% increase in pressure increases to 100%.
Causes of Increased Pressure Work of the Heart?
Elevated MAP (hypertension) or outflow resistance (stenosis)
Causes of Increased Volume Work of the Heart?
Elevated Preload (Exercise) or Aortic Insufficiency (regurgitation)
Define Preload.
The degree to which the ventricles are distended after diastolic filling
What is Cardiac Efficiency? (concept)
Fraction of myocardial metabolic energy used as work
What is Cardiac Efficiancy? (equation)
(Cardiac Work) / (Myocardial Oxygen Consumption)
Which is more oxygen demanding, volume or pressure work?
Pressure Work
Four Major Determinants of CO?
Preload
Afterload
HR
Myocardial Contractility
The greater the stretch of the myocardium……
This is reflected by….
the greater the force generated in systole + the SV
Starling’s Law of the Heart
Different ways of expressing preload…
Length of ventricular muscle fibers at systole onset
End Diastolic Volume
Central Venous/Atrial Pressure
Preload alters ______, NOT _________
Why not the second blank?
Force of Contraction, Myocardial Contractility
MC relates to force at a given muscle fiber length
Two ways of manipulating preload.
Blood Volume (diuretics and fluid infusion) Venous Capacity (altered by drugs)
How will a missed beat influence preload?
Extra Time – Bonus Preload – More pumped out on next beat
What allows average CO to be maintained despite individual HR variances?
Starling Law
Relationship between Central Venous Pressure and CO
Inverse
What is mean filling pressure?
Pressure within the cardiovascular system after the heart is removed and the flow ceases.
If a heart is restarted, why will arterial pressure change faster?
Veins are more compliant.
In a cardiac output curve, CO is plotted against…
Central Venous Pressure (Preload)
Increasing Central Venous Pressure will do what to CO
Increase It
Increasing CO will do what to Central Venous Pressure
Decrease It
Why give a shit about cardiac/vascular fxn curves?
The point at which they overlap is a state the heart must stay balanced in.
Describe what would happen if you dropped CO (in the context of the Cardio/Venous Pressure Curves)
Initial Rise in Venous Pressure (Preload)
Rise in CO (Starling)
Drop in Venous Pressure/CO back to operating point
Best definition of afterload
Myocardial wall tension during systole
Three ways to increase ventricular afterload
Inc. Mean Aortic Pressure
Inc. Total Peripheral Resistance
Inc. Aortic/Pulmonary Valve Resistance
Primary cause of HR variance in an individual?
Symp. and PS input at SA node
What is myocardial contractility/cardiac inotropic state?
The ability of the myocardium to develop contractile force for a given muscle fiber length
How to distinguish between myocardial contractility changes and Starling Law Effect?
Starling Law is all about increases in fiber length
Myo. cont. is about the ability to generate force at a given length
Maximum change in pressure over time can be determined from intraventricular pressure curves at what stage?
Isovolumetric Contraction
What is strain rate?
Shortening Velocity per Fiber Length
How are myocardial contractility and end systolic volume related?
More MyoCont means that ESV is decreased
If EDV remains the same the increase in stroke volume will reflect the new ESV
Ways to influence myocardial contractility via Ca
More extracellular Ca Increased HR Pos Inotrophic Agents (Cate. and Digitalis) Neg Inotropic Agents Myocardial Ischemia
Influence of Heart Failure on SV, Contractility, and Preload
Decreased contractility
Elevated Preload
Decreased SV
Two major NTs of autonomic system
Acetylcholine
Norepinephrine
Most sympathetic postganglionic neurons are….
Adrenergic
Most parasympathetic postganglionic neurons are…
Cholinergic
Neurosecretory cells of the adrenal medulla? What do they release?
Chromaffin cells
80% Epinephrine
20% Norepinephrine
Enzyme that breaks down norepinephrine.
Monamine Oxidase
Acetylcholine binds what two receptor types
Nicotinic Receptors
Muscarinic Receptors
Where are muscarinic receptors found?
Membranes of cells that receive innervation form postganglionic neurons of the PS division
Norepinephrine and epinephrine both can bind what two receptors.
alpha and beta adrenergic recepters
Where are alpha receptors found?
What do they do?
BV walls
Alpha-1 –> Vasoconstriction
Alpha-2 –> Inhibition of Norepinephrine Release from Symp.
Where are beta adrenergic receptors found?
What do they do?
Pacemaker Cells/Myocardium
Beta-1 –> increase HR and Contraction Force
Beta-2 –> In certain blood vessels to help with dilation
Which nucleus gets the info from the pressure/chemical sensors?
Solitary Nucleus
Main control center for autonomics?
Hypothalamus
Stimulating certain parts of thalamus can produce….
Tachycardia
Specifically – What part of the heart gets PS input –
The SA and AV nodes
Stimulation of beta-1 adrenergic receptors in the heart causes…
Increased Contractility
Accelerated Pacemaker Firing
Accelerated AV conduction
Increased Myocardial relaxation in diastole
What does chronotropic mean?
Affecting the rate
What does dromotropic mean?
Relating to Conductivity of a fiber
What does lusitropy relate to?
Relaxation of the heart
How do you inhibit sympathetic response?
beta-blockers (propranolol)
They block Beta-1 and Beta-2 adrenergic receptors
Describe molecular process following norepinephrine release
Binding to beta-1 adren. on the heart Activate G-stim Activates Ad Cyc cAMP generated ---> PKA Phos. L-type voltage gated calcium channels, ryanodine, and phospholamban
Describe the molecular process following muscarinic receptor activation.
Activate G-inhib
Decrease in cAMP
Major effect of PS release of acetylcholine?
Slow the Heart and Reduce AV conduction rate
How do you inhibit parasympathetics on the heart?
Atropine
Arteries, Arterioles, Muscular Venules, and Veins get main innervation from….
Sympathetics
Generally speaking…what will symp. stim at vessels do?
Activate alpha-adrenergic vasoconstriction
T or F. Sympathetic nerves are only active in fight or flight.
F. There is continuous vasoconstriction of all innervated blood vessels.
Overall sympathetic effect on heart.
Increased HR, Contractility, Lusitropy, Dromotropy
beta-adrenergic receptors
Sympathetic effects on non-heart CV system.
Vasoconstriction (alpha-adrenergics)
Renin Release
How does hemorrhage turn on sympathetic support?
Baroreceptor Reflex
Sympathetic responses to hemorrhage?
Inc. myocardial contractility
Inc HR + pos. lusitropic effect
Vasoconstriction
benefit of systemic vasoconstriction in hemorrhage?
Increased preload, leading to increased CO
Three places on heart innervated by vagus
SA
AV
Atrial Myocardium
Molecular effect of PS stim.
Altered properties of K channels
Equation for compliance
(Change in V) / (Change in P)
Equation for Elastance
1/Compliance
