Flashcards in Lecture 1: Cardiovascular Overview Deck (48):
What is the business end of the CV system?
What parameters are controlled by the CV system?
1. Tissue fluid biochemical composition
2. Local concentration of gases and substrates
3. Transportation and delivery of hormones and immune system
4. Local and total body TEMPERATURE control
5. specialized requirements like renal glomerular filtration and GI absorption
What is the cardiovascular system?
A body fluid transportation system whose purpose is to maintain an optimal biochemical and biophysical environment for all cells
What are the two issues that make diffusion from external milieu inadequate to support human metabolism?
1. The diffusion distances are TOO GREAT
2. metabolism requires high substrate delivery and removal rates, which cannot be accomplished by simple diffusion
What is the significance of the cardiovascular system?
1. Minimize diffusion distances
2. Maximize the concentration gradients for the many substances needed by cells
What is the mission of the CV system?
To circulate blood at an appropriate
Inadequate blood flow = ischemia
Excessive blood flow = hyperemia
What are the 2 circulations? Significance?
1. Pulmonary circulation (low pressure)
2. Systemic circulation (high pressure)
Think of CV system as two separate circulations in series
What are the components of the CV system?
2. Great vessels, e.g. aorta, pulm artery,, vena cavae
3. distributing vessels (arterioles and venules)
4. delivery vessels (capillaries)
5. scavenging vessels (lymphatics)
What is the leading cause of INTRAuterine deaths?
Congenital heart disease
What are the characteristics of fetal circulation?
It must function in the intrauterine environment and then INSTANTANEOUSLY transition to the extrauterine environment at the time
Must function effectively as it grows and develops
What are the requirements of the fetal circulation?
1. Placental circulation should be in “series” with the systemic circulation
2. Pulmonary blood flow should be minimized
3. Oxygenation of the upper body should be optimized
4. Perinatal transition to the extra-uterine life and dependence on the lungs for gas exchange must be immediate
What are the modifications of the circulation for intrauterine life?
1. Ductus venosus (bypass 1)
2. Foramen ovale (bypass 2)
3. Ductus arteriosus (bypass 3)
4. INCreased pulm. Vascular resistance
5. DECreased RIGHT ventricular diastolic compliance (less blood to the lungs)
What are the effects of fetal circulatory modifications?
1. Pulmonary blood flow is minimized
2. Umbilical vein blood via the ductus venosus via the ductus venosus to the IVC is routed preferentially across the foramen ovale to the left atrium and to the cephalad (brain) portion of the circulation
3. Superior vena cava blood is routed preferentially to the right ventricle, the pulm artery, across the ductus arteriosus to the caudal portion of the circulation
-then blood flows back to placenta via umbilical arteries
What are the circulatory changes at birth?
1. RV becomes more COMPLIANT
2. Decrease in pulm vascular resistance
3. Increased venous return from the lungs
4. Closure of the ductus arteriosus
How does pulm vascular resistance decrease at birth?
Begins with lung inflation and progresses over first week of extrauterine life
Allows increased pulm blood flow and decreased flow across the ductus arteriosus
How is there increased venous return from lungs at birth?
Increased left heart filling that opposes the flow of IVC across the foramen ovale
What is responsible for closing the ductus arteriosus?
1. triggered by increasing systemic arterial pO2
2. withdrawal of PGE2
Complete by day 4 of extrauterine life
What are the common parameters used to characterize cardiovascular system performance?
1. Cardiac output
2. Cardiac Index
3. Heart rate
4. Stroke volume
5. Systemic arterial pressure
6. Vascular Resistance
7. Left ventricular ejection fraction
What is cardiac output?
The volume of blood pumped per unit time
CO = HR x SV
What is cardiac index?
The cardiac output normalized to body size by dividing by body SURFACE AREA
Normal = 2.5-3.5 L/min/m^2
What is heart rate?
The number of cardiac cycles per minute
What is stroke volume?
The volume of blood ejected during each beat by the heart
Normal value = 100 ml/beat for an adult
What is systemic arterial pressure?
The pressure in the arterial system (in mmHg)
Recorded as the HIGHEST pressure during systole and the LOWEST pressure during diastole
Normal value = 120/80 mmHg
What is Vascular Resistance?
The resistance to flow through a vascular system
Applicable to both the systemic and pulm circulations as well as local vascular beds
What is LV ejection fraction?
The percent of the blood volume in the left ventricle at END-DIASTOLE that is ejected during systole
LVEF is a crude measure of left contractile performance
55-70% = normal value
(LVEDV – LVESV)/LVEDV
What are the physical parameters important in characterizing and influencing cardiovascular performance?
What is pressure?
Force per unit exerted by a GAS or FLUID on its container
Expressed as difference between two pressures
e.g. Difference between the pressure in a vessel compared to atmospheric pressure
What are the different types of PRESSURE parameters that define CV performance?
1. Driving pressure
2. Transmural pressure
3. Hydrostatic pressure
4. Osmotic pressure
What is driving pressure?
Axial pressure difference
-one part of the tube vs. another part of the tube
What is transmural pressure?
Radial pressure difference, DISTENTION
difference between what is pushing from inside vs. pushing from outside
What is hydrostatic pressure?
Pressure at two different levels of the body due to gravitational effect
The fact that we are upright
What are the different types of FLOW parameters that define CV performance?
1. Flow rate
2. Flow velocity
3. Flow resistance
What is flow rate?
Volume transferred from one location to another per unit time
L/min or ml/s
What is flow velocity?
The velocity with which fluid moves within a vessel
What is flow resistance?
The resistance to flow provided by a structure
The principal mechanism by which blood pressure and flow are regulated
Related to vessel radius and blood viscosity
Units = dynes*sec*cm^-5…Wood units
What are key characteristics of COMPLIANCE parameters that define CV performance?
The relationship between the pressure distending a structure and its volume
Units = dV/dP
Change in volume due to change in pressure
Rigid stiff structures have LOW compliance
Highly compliant structures distend easily
Compliance is actually more complex because of the LaPlace relationship
What are the 5 physical principles that govern the CV system’s operation?
1. Bernoulli Principle
2. LaPlace Relationship
3. Poiseuille Relationship (spelled wrong on ppt slide)
4. Reynolds’ Relationship
5. Ohm’s Law
What is Bernoulli’s Principle?
Governs relationship between pressure gradient (driving pressure) and flow velocity
P + 1/2v^2 = C
Inverse QUADRATIC relationship between P and velocity
So the higher the velocity the LOWER the pressure
What is the significance of Bernoulli’s?
Critically important in determining pressure drops across obstructions to blood flow
If you measure flow velocity, you can calculate the magnitude of pressure drop required to achieve the flow
Enables you to determine the severity of obstruction caused by a diseased valve or severity of stenosis
What is LaPlace Relationship?
Governs relationship between transmural pressure, radius and wall force
Tension = P x r(adius)
Pressure and radius are INVERSELY related while P and T are directly related
Radius term is most important feature of the relationship
Key effect is that larger radius requires greater wall force to generate a given pressure in chamber cavity
What is the significance of LaPlace Relationship?
Determines the force in blood vessel walls
Risk of rupture for aneurysms
Determines the force that myocardium has to generate in order to generate pressure
Determines contractile performance of diseased hearts
What is Poiseuille’s Relationship?
F = P*r^4/8nl
Pressure and radius are inversely related by factor of 4
P and viscosity; P and length are directly proportional
What is the significance of Poiseuille Relationship?
Defines mechanism by which the circulation’s pressure and flow are regulated
Pressure is regulated by regulating flow resistance through modulation of arteriolar diameter
Implications for disorders affecting blood viscosity
Increased blood viscosity impairs circulatory performance
What is Reynolds Relationship?
Describes the relationship between flow velocity, vessel diameter, blood viscosity and development of flow turbulence
What is the significance of Reynolds?
Determines whether blood flow will be smooth (LAMINAR, efficient, silent) or turbulent (less efficient, noisy)
Important in generation of cardiac murmurs and vascular bruits
What is laminar flow?
What is Ohm’s law? Significance?
I = V/R
DC electrical circuit analogy to the circulatory system (fluid dynamics)
Q(flow) = P/R