Hemodynamics Flashcards
Systemic blood pressure fluxes during the day. How does the eye compensate if
- Blood pressure is low
- Blood pressure is high
- Choroid blood vessels will dilate via parasympathetic
2. Choroid blood vessels will constrict via symatpathic
Where is flow rate fastest in the blood vessel?
Poiseuille’s Flow.
Flow rate is fastest in the center of the blood vessel than it is at the edge. At the edge, formed elements have resistance against the side walls.
This is true in all vessel sizes, but overall, blood flow is greater in larger vessels.
Series circuits
- Where are they found?
- How much branching?
- How to find total resistance?
Series circuits are found in vessels that move a lot of blood quickly- aorta.
There is minimal branching, so resistance is additive.
5+25+100= 130 RU (resistance units)
Parallel circuits
- Where are they found?
- How much branching?
- How to find total resistance?
Found in capillary beds.
Highly branched
Much less resistance, which is important for fluid transference between blood and tissues.
find total resistance by dividing parallel vessels. Ex:
1/5 +1/25 + 1/200= 4 RU (resistance units)
Poiseuille’s Flow.
The concept that blood flow is quickest in the center of a blood vessel and slower on the edges, due to resistance from the vessel wall coming in contact with formed elements of the blood.
Relationship between viscosity and hematocrit
Directly related. As hematocrit levels increase, viscosity increases. A higher viscocity= less water components.
Too high hematocrit
Too low hematocrit
Too high= Polycythemia. High viscosity. (Can also occur due to dehydration)
Too low= Anemia. Low viscosity.
Compliant blood vessels
Allow diameter to change. Ex: a rigid tube cannot allow for changes in blood flow to occur, but a compliant blood vessel can.
Is the venous system more or less compliant than the arterial system?
Venous system is more compliant than the arterial system.
Meaning that arteries are less compliant to change shape than veins are.
Arteries have a lot of smooth muscle and rigid internal membrane compared to veins.
At any given time, most of the blood in the body is on the __ side
Venous
Cardiac output
Stroke volume (amount of blood pumped from the left ventricle in one contraction) x heart rate
Factors that can influence cardiac output
stoke volume and heart rate obvi. But also blood pressure and resistance (due to friction between blood cells and blood vessel walls)
The heart is compliant. It becomes less compliant with age. How does this affect an elderly person?
At a young age, if someone is running, heart will stretch more, fill with more blood and be efficient.
At an old age, the heart can’t expand as much, so it just has to work harder/faster.
As you age, systemic pressure slowly increases. Adding to the heart’s work load.
Resistance
Friction between blood and the walls of the vessels. The blood vessel radius, the bloods viscosity, and the total blood vessel length all play a role in resistance.
R= 1/r^4
Smaller vessels offer more or less resistance to blood flow?
More.
Relationship between blood vessel length and resistance
Direct relationship.
As blood vessel length increases, resistance increases.
How many miles of blood vessels for every 1 pound of fat?
200 miles of blood vessels. Obesity can cause high blood pressure.
Systemic vascular resistance is due to
Blood vessel radius, blood viscosity, and blood vessel length.
Speed of blood flow is measured in
cm/sec
How does blood velocity relate to radius
Inversely.
Large radius= slow speed.
Small radius= quick speed
Blood flows slower through the aorta and quicker through veins. Makes sense why veins are more compliant?
Blood pressure is the pressure exerted ___
what causes blood pressure?
By blood on the walls of a vessel. Caused by the contraction of the ventricles.
Blood pressure is highest where??
The aorta
If heart rate increases cardiac output, __ rises.
Pressure falls steadily in systemic circulation with ___ from the ventricle.
BP
Distance
How to calculate mean arterial blood pressure
MABP = diastolic BP + 1/3 (systolic BP- diastolic BP)
Systolic blood pressure vs diastolic blood pressure
Systolic- blood pressure in arteries during contraction of ventricle. 120 mmHG
Diastolic- blood pressure in arteries when ventricles are relaxed, or being filled. 80mmHg.
Mean arterial blood pressure =
- Cardiac output (heart rate x stroke volume) x systemic vascular resistance
Increase CO= increase MABP
Increase systemic vascular resistance = increase MABP
- = DBP + 1/3 (SBP-DBP)
Venous return
Volume of blood flowing back to the heart from the systemic veins. Depends on pressure differences from venules to the right atrium.
How do valves open
Contraction of muscles. Important to flex calf muscles after being still for a long time to return blood to the heart.
Respiratory pump
When you inhale. Moves blood intro thoracic veins and right atrium. Caused due to an increased abdominal pressure and decreased thoracic pressure.
How does venous chance when you are standing vs walking around
Venous pressure is high when standing- valves are closed and blood pressure builds
When walking around, valves open, increasing blood flow and decreasing blood pressure.
Hypervolemia and hypovolemia
Hyper- too much fluid in the blood. (over hydration)
Hypo- too low fluid in the blood. (dehydration)
How are blood vessels autoregulated at the endothelial layer (local tissue level regulation)
Local blood supply can be diverted, or shunted from one area to another. Happens at the capillary level of each organ in response to signal. Could be due to temperature, pH, oxygen levels, NO..)
All regulatory types play a role in the retina (neural, hormonal, and auto regulation)
3 major types of blood flow regulators
Neural- from the brain. Sympathetic nerves that release NE cause constriction and neurons that release NO cause dilation.
Hormonal
Autoregulation- local control of tissues.
All types affect the retina.
How do parasympathetic fiber amounts change with age in the choroid
Diminish. Therefore, so does the ability to vasodilator.
Precapillary sphinctors
In control of autoregulation in the capillaries. Need blood flow to go straight from arterioles and venules? Shut off sphincters. Ex: Cold weather and want blood to flow directly back to the heart and not lose heat in capillaries.
