Intro to CVS physiology & hemodynamics Flashcards
What is the main function of the cardiovascular system?
1) Delivering oxygen and nutrients
2) Removing CO2 and waste products
What are the other functions of the CVS?
1) Delivering hormones
2) Regulates body temperature
3) Maintains adequate blood supply
The cardiac output is equal to what?
In healthy individuals, it is equal to the venous return (about 5L/min)
Describe the normal blood distribution to the body
1) 25% GI
2) 25% Skeletal Muscles
3) 25% Renal
4) 15% Cerebral
5) 5% Skin
6) 5% Coronary (Heart)
In which part of the body the blood has the highest amount of pressure?
Aorta 120/80mmHg
What makes blood move?
The difference in pressure (PRESSURE GRADIENT)
Compare the pulmonary and systemic circulations
The Systemic circulation has a higher pressure compared to the pulmonary circulation with a pressure gradient of 93mmHg compared to 10mmHg in the pulmonary circulation
What helps to keep the valves open?
1) Papillary Muscles
2) Chordae Tendineae
Which artery carries deoxygenated blood?
Pulmonary Artery
Which vein carries oxygenated blood?
Pulmonary vein
Which part of the vascular system has the smallest internal radius?
The true capillaries
Which part of the vascular system has the smallest wall thickness?
Veins
Which part of the vascular system Has the most elastic fibers and the thickest wall?
Aorta
Which part of the vascular system has the most collagen fibers and the biggest radius?
Vena cava
What is the function of the arteries?
Carries blood from point A to B under high pressure
What is the function of the arterioles?
They are the smallest branch of the arteries and have the highest resistance (AKA resistors)
What is the function of the capillaries?
Exchange of fluid, nutrients, and gasses, facilitated by its tiny internal radius and wall thickness (the smallest of all)
What is the function of the venules?
Collects blood from the capillaries merging into larger veins
What is the function of the veins?
They transport blood back to the heart under low pressure, and thy hold most of the blood reserve (about 60%)
What is meant by compliance?
How easily a blood vessel can stretch (veins can stretch more than arteries)
What is meant by capacitance?
The amount of blood a vessel can hold (Veins have a higher capacitance when compared to arteries)
How to calculate compliance?
Compliance (C) = Change in volume / Change in pressure
Describe the relationship between the venous and arterial systems when the volume is changed
In the arterial system, a small change in volume will largely increase the pressure, on the contrary, veins are exactly the opposite
Describe the effect of age and sympathetic stimulation on the volume/pressure curves
With increased age and sympathetic stimulation, the smooth muscle will increase in tone increasing the pressure at each volume in the artery
Describe the relationship between the blood flow, Resistance & pressure
Blood flow (Q) = Change in pressure (P) / Vascular resistance (R)
- Blood flow is inversely related to resistance and directly related to the change in pressure (the greater the more)
What are the types of blood flow?
1) Laminar flow
2) Turbulent flow
Describe the laminar flow
1) Fluid molecules flow in layers
2) It is Silent (you can’t hear it with a stethoscope)
3) The velocity is maximum in the center and minimum at the periphery due to the resistance by the BV
Describe the turbulent flow
1) It is when fluid molecules bounce around (due to an obstruction) like Vascular aneurysm, Stenosis & arteriovenous fistula (abnormal connections between arteries and veins), Anemia
2) It is noisy
3) It has a low velocity
What is meant by Reynold’s Number (NR)?
It is a number that is calculated to determine whether the flow is laminar or turbulent
How to calculate the Reynold’s Number?
NR= (Velocity * Diameter * Density) / Viscosity
- NR > 2000 = Turbulent Flow
- NR <2000 = Laminar flow
What is the unit of blood flow?
Volume per unit time (ml/s)
Describe the relationship between velocity and the cross-sectional area of the blood vessel
Velocity and the cross-sectional area are inversely proportional meaning that the higher the cross-sectional area of the blood vessel the lower the velocity
Compare the Aorta to the Capillaries
The capillaries have a lower velocity due to the higher cross-sectional area of 2500cm^2 being the largest making it most suitable for exchange
Which BV has the highest velocity?
The Aorta and thus it has the lowest cross-sectional area
Compare the flow of blood (amount of blood) through the pulmonary circulation & Systemic Circulation
It is the same (CO = VR)
What happens to the pressure in a vein when it losses blood?
The pressure will decrease, as the volume decreases (though minimal since vein have high compliance)
What remains constant in the cardiovascular system?
The mean arterial pressure
Compare the volume of blood pumped by the right and left ventricles
It is the same volume (Cardiac output “CO” = Venous Return “VR”)
How is the resistance to blood flow calculated?
Resistance (R) = change in pressure (P) / Blood Flow ml/sec
What are the units of resistance?
mmHg/ml/min or PRU (peripheral resistance unit
Describe the different variables when calculating the resistance
1) Resistance in the systematic circulation is about 1PRU & in the pulmonary circulation is about 0.14PRU (less resistance)
2) Blood flow is about 5L/min or 100ml/sec
3) The change in pressure in the systematic arteries is about 100mmHg
What is poiseulle’s law?
Resistance (R) = (Viscosity of BV * Length of BV (L)) / Radius (r) of BV ^ 4 * (8/PIE)
Describe the relationship between the different factors in poiseulle’s law
1) Resistance is directly related to the viscosity of the BV and its length
2) Resistance in inversely proportional to the radius of the BV
3) If the radius decreases by half the resistance will increase by 16 folds, and if it doubles then vice versa
What stimulates the vasoconstriction of the BV?
1) Increased myogenic activity (depending on the pressure “myogenic activity”)
2) Increased Oxygen
3) Decreased CO2 and other metabolites
4) Increased Endothelin
5) Increased sympathetic stimulation
6) Vasopressin
7) Angiotensin
8) Cold temperatures
What stimulates the vasodilation of the BV?
1) Decreased myogenic activity (depending on the pressure “myogenic activity”)
2) Decreased Oxygen
3) Increased CO2 and other metabolites
4) Increased Nitric oxide
5) Decreased sympathetic stimulation
6) Histamine
7) Hot temperatures
What are the characteristics of the series resistors?
1) The total resistance is calculated by adding all individual resistance together
2) Total resistance is always greater than any individual resistance
3) Adding a resistor in series increases the resistance of the system
4) Flow is equal in all points around the circulation (arteries, arterioles, capillaries, venules and veins)
5) Pressure decreases according to the resistance it has to overcome (the greatest being in the arterioles)
What are the characteristics of the parallel resistors?
1) The total resistance is the sum of all the reciprocals of the individual resistance
2) The total resistance is always smaller than any individual resistance
3) Adding a resistor in parallel decreases the total resistance of the system
4) Increasing the resistance of an individual resistor will increase the total resistance
5) Vessels are arranged in parallel in various organs (coronary, cerebral and renal)
6) Flow in individual resistance can be adjusted independently
What is meant by the hematocrit?
It is the percentage of RBC in the blood
1) Men usually 42 (42 percent of the blood volume is RBC), woman 38
What is blood pressure and how can we calculate it?
It is the force exerted by the blood against any unit area of the vessel wall
- Pressure = Force / area
What is a systolic pressure?
It is the maximum pressure exerted in the aorta (usually during cardiac contraction)
What is the diastolic pressure?
It is the minimum aortic pressure (usually during the relaxation of the heart)
What is the pulse pressure?
It is the difference between systolic and diastolic pressure (systolic - diastolic) it gives us an idea about the compliance of the vessel (as we get old the compliance decreases (hence the pulse pressure increases), an indication of stiffness)
What is meant by the mean arterial pressure (MAP)?
It is the (Mean/Average of systolic and diastolic BP) but given the heart spends more time in diastole we calculate it as (2/3 Diastolic pressure + 1/2 systolic pressure) or (Diastolic pressure + 1/3 pulse pressure)
How is the MAP regulated? what is the equation regulating it?
- MAP (mmHg) = CO (ml/min) * TPR (mmHg/ml/min)
If the CO goes up the TPR goes down and vice versa, and thus the MAP does not fluctuate and it is always maintained within a narrow range
During exercise will the MAP increase?
No, yes the CO will increase but the TPR will decrease as the BV will dilate
By how many folds does our CO increase during vigorous exercise?
from 5-6L/min to 35L/min so about 6 folds
What is the Dicrotic notch (incisura)?
It is the slight change in pressure that occurs when the aortic valve closes
What is the BP in various parts of the circulation?
Systemic Circulation:
- Aorta & large arteries = 100 mmHg
- Capillaries = 17mmHg
- Veins = 0 mmHg
Pulmonary circulation:
- Pulmonary arteries: 16mmHg
- Pulmonary capillaries: 7mmHg
What are the major factors that regulate arterial systolic pressure?
1) Stroke volume (volume of blood pumped out of the heart’s left ventricle during each systolic cardiac contraction)
2) Compliance of the arterial vessels
What are the major factors that regulate the arterial diastolic pressure?
The total peripheral resistance
What are the major factors that regulate the pulse pressure?
1) Stroke volume (volume of blood pumped out of the heart’s left ventricle during each systolic cardiac contraction)
2) Compliance of the arteries
3) TPR
What is meant by the damping of the pressure pulses?
It is the progressive diminishment of the pulse pressure in the peripheral circulation due to the blood movement in the vessels and the compliance of the vessels
- Resistance * compliance
What type of blood flow can we hear in the stethoscope?
The turbulent
What are the two main control mechanisms that change with age in regard to controlling BP?
1) The kidneys: As it regulates BP
2) The decrease in the elasticity of the arteries which increases the systolic blood pressure
Where is the flow velocity the highest and where is it the lowest?
1) Arteries
2) Capillaries
Where is the blood volume the highest and where is it the lowest?
1) Veins and venules
2) Arterioles
Where is the BP the highest and where is it the lowest?
1) Arteries
2) Veins and venules
Where is the vascular resistance the highest and where is it the lowest?
It is the highest in the arterioles
