Exam 1 Flashcards
What is clearance, and what is it a function of?
Volume of plasma cleared of a certain component per unit time.
Function of how the kidney handles a compound (filterability)
What does clearance of free water (or free water clearance) refer to?
Volume of water removed from the body per unit time.
Is our free water clearance high or low if we have an abundance of ADH?
Low - body holds on to free water.
Is our free water clearance high or low if we have an absence of ADH?
High - lack the ability to hang on to free water in the absence of ADH.
Does free water clearance tell us the quantity of electrolytes removed from the body?
No - free water clearance tells us how much water is removed from the body WITHOUT taking into account electrolytes.
What is a ballpark normal MAP at the beginning of systemic circulation (aorta)?
100mmHg
What is a normal systolic/diastolic BP pressure?
120/80
What is the formula for MAP?
Diastolic BP + 1/3(systolic - diastolic)
i.e.
BP 120/80
80 + 1/3(120-80)
80+1/3(40)
80+13ish = 93mmHg
^Note that this is not a MAP of 100mmHg. 100mmHg is a ballpark, but the formula will give us an accurate MAP.
What is the area of highest resistance in all circulation?
Arterioles
Pressure downstream of arterioles will be ___ due to high resistance at the arterioles.
Low
Pressure upstream from arterioles will be ___ due to high resistance at the arterioles.
High
Within the systemic capillary, what is the pressure at the arteriolar end?
What about the venous end?
What is ΔP?
30mmHg
10mmHg
ΔP = 20mmHg (difference between pressures)
As we move further from the aorta, what happens to the BP? Why?
Lower and lower BP due to moving from areas with high resistance to low resistance.
What is the BP at the start of a venule?
10mmHg
Where is the start of systemic circulation, and what is the BP?
Aorta; 100mmHg
Where is the end of systemic circulation, and what is the BP?
Right atrium; 0mmHg (in a healthy adult).
The normal pressure inside of the right atrium is 0mmHg. How does this change in someone in the ICU with heart failure?
The pressure of the right atrium will likely be elevated.
What is ΔP of systemic circulation in a healthy adult?
100mmHg
Where is the start of pulmonary circulation?
Pulmonary arteries
What is the normal pulmonary arterial pressure (PAP)?
What is another name for this?
16mmHg
Sometimes referred to as mPAP (mean pulmonary arterial pressure).
What is the normal systolic/diastolic pressure of the pulmonary circuit?
25/8 in a healthy adult.
^Note: If we use the formula given for MAP, we won’t get 16mmHg for the mPAP. Daddy said just use 16mmHg for a healthy adult.
Where is the end of the pulmonary circuit?
Left atrium
What is the pressure within the left atrium in a perfectly healthy person?
2mmHg
What is ΔP of the pulmonary circuit?
16mmHg - 2mmHg = 14mmHg
What is pulse pressure?
Difference between systolic and diastolic. (i.e. 120/80 has a pulse pressure of 40mmHg)
Ideal pulse pressure is 40mmHg.
Is pulse pressure greater in the arteries or the veins? Why?
Arteries. Arteries are more stiff, so they have more change in pressure when volume is introduced vs. veins stretch out and accommodate extra fluid.
Is pulse pressure greater in the aorta or the large arteries? Why?
The large arteries have a slightly greater pulse pressure than the aorta. This is because the large arteries are much less stretchy than the aorta. (fluid fed into a stiff container will have a greater pressure variance).
When it comes to stretchiness, how does the aorta work through the cardiac cycle?
The aorta is pretty stretchy if it’s healthy.
Systole - walls of the aorta are stretched.
Diastole - walls come closer together and act like a second heart pump, which helps pump blood downstream during diastole.
If someone had severe arterial stenosis, what would their pulse pressure be like and why?
They would have a very wide pulse pressure. Systolic would be very high, and diastolic pressures would be very low.
When fluid is put into a container with no give, it takes a lot of pressure which elevates systolic pressure.
When fluid is not being put into a stiff container, the pressures are very low.
If someone is given 1L of fluid, does it impact pressure within the veins?
Not really.. veins are very stretchy and accommodate lots of extra blood/fluid. Veins don’t really have a pulse pressure.
How does stroke volume (SV) impact pulse pressure?
Tight walls + High SV = wide pulse pressure.
In general, increasing SV increases pulse pressure, vice versa.
Why does the pulmonary circuit have a low pulse pressure?
1 reason for low pulmonary pressure is that the vascular resistance is low.
It is stretchy, like Nacho Libres pants.
What term are we using this semester for stretchiness, and where does it apply?
Compliance.
Can use the term in blood vessels within the heart and lungs, as well as the airway.
What is compliance?
Some change in volume over change in pressure.
(ΔV/ΔP) = Compliance
If a container doesn’t have much give, lots of pressure is needed to fill said container. Does this container have high or low compliance?
Low
If the volume is small and pressure is high, the container will have ___ compliance.
Low
If the volume is high, and the pressure is low, the container will have ____ compliance.
High
In the equation ΔV/ΔP, what does a high number mean? How about a low number?
High number = more compliant
Low number = less compliant
Within the CV system, what is the unit of pressure we use?
mmHg
Within the pulmonary system (airway), what is the unit of pressure that we use?
cmH20
How do you solve for vascular resistance?
ΔP/F
ΔP is the change in pressure
F is blood flow
example:
(100-0mmHg)/(5L/min) = vascular resistance, or SVR if we use a conversion factor
What is a normal SVR?
Between 800-1600 (he didn’t say units, may or may not need this, it was in passing)
What must venous return equal?
Cardiac output
Does a block in perfusion have to do more with cardiac output, or venous return?
Venous return
Can’t pump what isn’t there
What has a wider pulse pressure - left ventricle, or aorta?
Left ventricle.
Diastolic pressure of the left ventricle is low. What does this permit?
Filling
Systolic pressures of the left ventricle are high. What does the permit?
Pressure slightly exceeds aortic pressure. This allows blood to flow into the aorta during systole.
Which has a wider pulse pressure - the right ventricle, or the pulmonary artery?
Right ventricle - allows for the same mechanics as the left ventricle/aorta.
What is the peak systolic pressure within the right ventricle?
25mmHg
Arterioles have ____ walls and ____ openings. Why?
Thick walls with small openings.
This is due to high resistance from vascular smooth muscle within the arterioles.
Veins are more compliant than arteries. Why?
Wider internal diameter, stretchy, accommodates lots of volume.
There is a small smooth muscle layer, but much thinner than what is seen in arterioles.
Capillaries have ___ walls.
Thin
What is continuous with the chambers of the heart, and all blood vessels within circulation?
Thin endothelial cells that make up capillaries.
The aorta has a ___ opening, and ____ wall.
Wide opening; thick wall
Is the aorta stretchy? When might it not be?
In a healthy adult, yes.
As we age, the aorta becomes less stretchy and more rigid.
A person with a rigid aorta will have a ____ pulse pressure.
Wider
What is a normal cardiac output for a healthy adult, and where does it flow?
5L/min
Flows through the entire system.. aorta, capillaries, vena cava, etc. All areas get 5L/min output.
What is the formula for cardiac output?
CO = SV x HR
What is a normal heart rate (HR)?
72BPM
What is a normal Stroke Volume (SV)?
70mL
What is blood flow (velocity) determined by?
Cross sectional area
i.e., we have one aorta, but have two vena cava.. thus a larger cross sectional area in the vena cava, resulting in a slower blood flow/velocity within the vena cava.
What is the formula for velocity of blood? What do the symbols stand for?
V = F/A
V = velocity
F = flow
A = cross sectional area
An increase in cardiac output will do what to velocity of flow?
Increase velocity
A reduction of cross sectional area will do what to velocity of flow?
Increase velocity
Where in the capillary is filtration preferred?
Arterial end
Where in the capillary is reabsorption preferred?
Venous end
How do nutrients move through capillaries?
Capillaries generally are permeable to electrolytes, glucose, nutrients, gasses etc.
Fluid that is not reabsorbed by the venous side of a capillary is reabsorbed by what?
The lymphatic system.
How far below a pressure source will the pressure be 1mmHg higher?
13.6mm
Why does pressure increase as you go below a pressure source?
Blood and water are heavy in a column.
If a column of water is 13.6mm tall, what will be the pressure at the bottom?
1mmHg
What is the Isogravimetric point? Where is it?
It is the point in the body that there is no effect on pressure from gravity.
It is located in the middle of the tricuspid valve.
What name did we give the Isogravimetric point while we worked bedside?
Phlebostatic axis
In a standing adult, how much higher will the pressure be at the umbilicus compared to the Isogravimetric point?
+22mmHg
If an adult is standing, but not moving around.. what would the venous pressure be in the large foot veins compared to the isogravimetric point?
+90mmHg
Will pressure be higher or lower if measured above the isogravimetric point while standing?
Lower
Why is the pressure is the sagittal sinus subatmospheric when standing?
Is this a concern if exposed to open air? Why?
These vessels are rigid, have meninges/connective tissue supporting them. They are not very compliant.
Yes; if exposed to open air, air would be sucked into the CV system and cause an air embolism.
The neck veins are 0mmHg in pressure, even when measured above the isogravimetric point. Why aren’t they below 0mmHg?
If they were below 0mmHg, they would collapse. They are very wide, and also very thin walled. They are very compliant.
There is a column of blood within the veins that run from the upper arm to the vena cava. This results in a pressure difference of what? Why is this important?
+6-8mmHg in the upper arms both in the veins and arteries while standing.
Important because supine BP in the arm will be slightly higher than true BP.
What is the pressure in the large foot veins as compared to the isogravimetric point while supine?
0mmHg - no gravity effects in a supine patient, no pressure difference
How do the veins combat retrograde blood flow?
One way valves; act as shelves to limit effect of gravity on pressure.
Skeletal muscle contraction also helps move blood to the heart.
As we age, what happens to our venous valves? What does this result in, and what is the risk?
They wear down and don’t function properly over time. This results in varicose veins, which is mostly aesthetic. However, it can increase the risk of blood clots.
What is another name for supine? (other than flat)
Recumbent
If someone is in a recumbent, what is the effect of gravity on their veins?
Not very much effect - will see normal pressures. (i.e. foot would not be +90mmHg from isogravimetric point)
What do we rely on to keep veins narrow enough to allow valves to work?
Compression, AKA skeletal muscle contraction
What effect does gravity have on arterial pressure in a standing position?
There are no valves in arteries, so the pressure of a given artery is the following:
Pressure of what is coming from the heart + effects from gravity = significantly elevated BP
i.e., in the foot there would be 100mmHg + 90mmHg = 190mmHg pressure.
A beaker is 1.5 meters tall. What is the pressure at the bottom of the beaker?
90mmHg (remember, 1mmHg increase per 13.6mm below the isogravimetric point).
If you stand still and do nothing, what happens to cardiac output? Why?
There is a decrease in cardiac output due to less venous return. Blood pools in the legs.
If you strap some poor bloke to a piece of plywood, paralyze them, and move the plywood around and different angles, what would happen to the person?
They would quickly pass out because there is no muscle activity to move the blood around. This is what happens in surgery.
What is the formula for vascular compliance? Aside from the circulatory system, where can this formula be used?
ΔV/ΔP
Lungs
What is the difference between compliance and distensibility?
Distensibility takes into account the original volume of a container.
A large container that does not accept volume easily (i.e., uses a lot of pressure to get fluid in it) is said to have ___ distensibility.
Low
If something is distensible, it is said to be _____.
Expandable
If something has a small start volume with a high compliance, it is said to have ____ distensibility.
High
What is resistance?
Descriptor of how difficult it is to move something from one point to another.
What is inverse to conductance?
Resistance
All blood vessels control blood flow due to changes of what?
Tissue metabolism to replenish what is being used by the cells.
Resistance is changed, this impacts flow. Resistance is the single most important variable.
Changes in resistance occur as vessels constrict and relax. This changes diameter, which helps determine flow. What is the formula for this?
F = (πΔPr4)/(8n1)
Note: the 4 is supposed to be an exponent but I can’t type it.
Therefore, resistance and flow are related to diameter to the 4th power.
A small change in diameter of a vessel has what change on resistance?
A huge change
What is the formula for ohms law, and what does it stand for?
V=IR
Voltage = current x resistance
What is the formula for ohms law, but for the CV system? What does it stand for?
ΔP = F x R
Change in pressure = Blood flow x Vascular resistance
If there is a larger ΔP, there is ____ opportunity for blood flow.
More
The ____ system has much higher pressure, but much less volume.
Arterial
The _____ system has much lower pressure, but much more volume.
Venous
In an artery, if you add a little volume what happens to pressure?
It goes way up (less compliant).
In a vein, if you add a lot of volume, what happens to pressure?
It hardly goes up at all (more compliant).
In a graph with volume on the X axis, and pressure on the Y axis, what would a horizontal line (or low slope) represent?
Venous system; highly compliant
In a graph with volume on the X axis, and pressure on the Y axis, what would a vertical line (or high slope) represent?
Arterial system; lower compliance
In the arterial system, ____ is more likely to change. In the venous system, ____ is more likely to change.
Pressure; Volume
Someone with sympathetic inhibition with the normal amount of arterial volume will have a ____ pressure. Why?
Significantly lower; Arterial pressure is highly dependent on SNS tone.
Venous pressure also drops with sympathetic inhibition.
Someone with sympathetic stimulation with a normal amount of blood in the arterial system will have a ____ blood pressure.
Sky high
With sympathetic stimulation, venous pressure rises slightly. What can the body do with this?
Use expanded venous pressure to help return blood to the heart, which then gets pumped by the heart and can help raise pressure.
