Exam 1 - Cardiac I Flashcards
Define renal clearance?
The volume of plasma cleared of a substance per unit time
What is the free water clearance?
How would ADH levels relate to free water clearance?
- The volume of water removed from the body per unit time
- High levels of ADH = water retention and decreased water excretion = low free water clearance
- Low levels of ADH = low water retention and increased water excretion = high free water clearance
What is a normal MAP and BP?
What is the formula for MAP?
- 100 mmHg and 120/80
- Diastolic + 1/3(Systolic - Diastolic)
What is the normal arteriole and veunle capillary blood pressure (hydrostatic pressure)?
- Arteriole: 30 mmHg
- Venule: 10 mmHg
What is a normal right atrial pressure (RAP)?
0 mmHg
What is normal mean pulmonary arterial pressure (PAP or MPAP)?
What is a normal pulmonary artery blood pressure?
- 16 mmHg
- 25/8
What is normal left atrial pressure (LAP)?
2 mmHg
What is the ▲P of the pulmonary circulation?
PAP - LAP
16mmHg - 2 mmHg = 14 mmHg
What is the ▲P of the systemic circulation?
MAP - RAP
100 mmHg - 0 mmHg = 100 mmHg
How is pulse pressure calculated?
What is normal aortic pulse pressure?
- Systolic - Diastolic
- 120 - 80 = 40 mmHg
Where is there a widening of pulse pressure in the systemic circulation?
Why?
- Large arteries like the femoral arteries
- The large arteries have stiffer walls which require a greater pressure to push the volume of blood through
- It also causes the walls to stay open during diastole, lowering diastolic pressure
Why is pulse pressure lower in the aorta than the large arteries?
What important effect during diastole does this property produce?
- The walls of the aorta are very stretchy allowing a large volume of blood to be accommodated at a lower pressure
- During diastole the aortic walls collapse causing a “secondary heartbeat” that helps push the large volume of blood forward
Explain why pulse pressure is high/widened in stiff arteries and low/narrowed in stretchy arteries?
Stiff arteries: the walls are not elastic so during systole the pressure is very high in order to move the blood through. During diastole the walls do not collapse meaning the vessel diameter is the same size for a small volume of blood which creates a low pressure. (140/60 = pulse pressure of 80)
Stretchy arteries: the walls expand and collapse during systole and diastole accommodating the volume of blood. This requires a lower pressure during systole and a higher pressure during diastole leading to a narrowed pulse pressure. (120/80 = pulse pressure of 40)
What is the expected pulse pressure in the veins?
Why?
- There should not be a pulse pressure
- The veins are extremely stretchy and can accomodate a large volume of blood.
What two factors can infulence pulse pressure?
- Stroke volume
- Vessel elasticity
Why is the pulse pressure low in the pulmonary circulation as shown?
The pulmonary tissues are very elastic which leads to a low resistance and causes a low pulse pressure
What is compliance?
How is it calculated?
- Describes the ability of a container to accept a volume of a substance.
- Compliance = ▲V/▲P
If it takes a small amount of pressure for a container to accept a large volume it is considered to have a high compliance.
If it takes a high pressure for a container to accept a small volume, the container is considered to have a low compliance.
What makes the arterioles high resistance?
They have thick walls comprised of smooth musle and a narrow opening for blood to move through
What makes the veins low reistance?
They have thin walls of smooth muscle making them very elastic and large diameter which can accomodate a large volume of blood
What type of cells make up capillaries?
Where else are these found in the CV system?
- Endothelial cells
- Endothelial cells line the entirety of the cardiovascular system including the chambers of the heart.
What is normal cardiac output, stroke volume, and heart rate per Dr. Schmidt?
How is cardiac output calculated?
CO = 5 L/min
SV = 70 mL
HR = 72 bmp
CO = SV x HR
How is velocity of blood calculated?
v = F/A
velocity = flow (L/min) / area (cm2)
high flow through a small area = high velocity (aorta)
What are some things the capillaries are permeable to?
Gases, glucose, electrolytes
What is the effect of gravity on pressure when moving away from a pressure source? (Give the numbers)
For every 13.6 mm (1.36 cm) below a pressure source, the pressure increases by 1 mmHg
What is the isogravimetric point?
Where is it located?
- The “zero point” in the heart where there is no effect on pressure from gravity
- Located in the middle of the tricuspid valve (right heart)
What is the pressure at the umbilicus in the indicated large vein caused by gravity?
+22 mmHg
What is the pressure above the knee in the indicated large vein caused by gravity?
+ 40mmHg
What is the pressure at the base of the foot in the indicated large vein caused by gravity?
+ 90 mmHg
What is the pressure in the in the indicated large veins caused by gravity?
Why?
- 0 mmHg
- These vessels are very large and stretchy, so they accommodate volume very well
- If the internal pressure were negative the vein would collapse due to its very thin walls.
What is the pressure in the sagittal sinus shown below?
Why?
When is this a concern for us in the operating room?
- -10 mmHg
- The sinuses are made of rigid meninges leading to low compliance
- If the sinus is made open to the atmosphere while the patient is upright, it will suck air in and can lead to an air embolisim.
Why is the pressure in the upper arm slightly elevated even though it is almost symmetrical to the isogravimetric point?
The anatomy of the vasculature has a curvature to it, which is a small column of blood that adds to the pressure in the arm while upright
What is the role of valves in the veins?
- Prevent backflow of blood
- Act as a shelf to support the weight of blood and limit some of the effects of gravity
How is blood moved through the venous system and its valves?
Muscle activity compresses the thin walled veins and drives the blood forward.
What is the pathophysiology of varicose veins?
Overtime after years of standing, veins stretch out and the valves can no longer close fully. This leads to pooling of blood that worsens overtime.
What would you expect the pressure to be in the veins if the valves cannot close while standing?
The bottom of the vein would be brunting the full weight of blood and the effects from gravity and be 95 mmHg (90 mmHg from gravity and 5 mmHg from normal venous pressure).
What would be the arterial pressure in the foot while standing, accounting for gravity?
It would be ~190 mmHg (100 mmHg from MAP + 90 mmHg from gravity).
The arteries have no valves like veins so they support the full weight of blood and gravity.
Why do you pass out if standing completely still for too long?
If you are not contracting your leg muscles, then blood is not being pushed back to the heart and pools in the lower extremities. This reduces your cardiac output and leads to fainting.
What concern should you have if your patient is paralyzed and in an upright position?
They cannot contract their muscles so blood will pool very quickly in their legs and drop their cardiac output.
What is vascular distensibility?
How is it calculated?
Can be thought of as “expandibility”. If a container starts off small and can become very large, then it has high distensibility.
Formula is the same as vascular compliance with the addition of the original volume of the container.
What is conductance and resistance?
What is their relationship?
Resistance describes how easy or difficult it is to move something through an area.
Conductance is the inverse of resistance.
Low resistance = high conductance, High resistance = low conductance
What is the relationship between vessel diameter and conductance/resistance?
A small change in vessel diameter has a huge change on conductance/resistance.
What is Ohm’s Law?
How is it changed for the CV system?
V=IR
▲P = Flow x Vascular resistance
How can you calculate vascular resistance?
R = ▲P/F
resistance = 1/conductance
At normal arterial pressure, how much volume is contained in the arterial system?
~700 mL
The arterial system operates at high pressure and low volumes
At normal venous pressure, how much volume is contained in the venous system?
~ 2500 mL
The venous system operates at low pressures and high volumes
In the below diagram, what can be deduced about the compliance of the artertial and venous systems?
- The arterial system slope is very steep, meaning a small increase in volume results in a large increase in pressure. This means the arterial system has a low compliance.
- The venous system slope is very shallow, meaning a large increase in volume results in only a small increase in pressure. This means the venous system has a high compliance.
What is the importance of sympathetic stimulation in the arterial and venous systems?
As shown in the diagram, the pressure in the arteries is highly dependent on the SNS because they are less compliant, whereas in the veins, the SNS has a lesser effect because they are much more compliant.
SNS stimulation of the veins is important in returning more blood to the heart to increase cardiac output.
What is Reynold’s number?
What number is important for us to know?
- A hypothetical number with no units that estimates turbulent flow of air or blood
- > 2000 means there is turbulent flow
What are sequela of turbulent flow?
What is an observable symptom of turbulent flow?
- Hardened arteries from cholesterol and calcium deposits
- The large volume being restricted is usually audible (wheezing)
What is the Reynold’s equation?
(velocity × diameter × density) / viscosity
What factors increase our risk for turbulent flow?
What vessels are at greatest risk for turbulent flow?
- Increased velocity, diameter, and density
- Decreased viscosity
- Large arterties and arteries close to the heart (aorta)
Anything that would increase the Reynold’s number
How does this sensor detect flow?
The device is situated around the vessel and detects the electromagnetic field created by the iron in hemoglobin
How is a right heart pressure volume loop different from a left heart pressure volume loop?
They have the same shape, but the right heart operates at much lower pressures
What is happening during phase I of the cardiac cycle? Include when it starts and ends, and valve positions.
- The ventricles are filling because pressure in the atria is higher than the ventricles
- Begins when atrial valves are open and ends when atrial valves close
- Mitral and tricuspid valves are open
- Aortic and pulmonic valves are closed
Describe how the heart fills during diastole?
- Primarily passive; dependent on preload
- Small amount of volume contibuted by atrial contraction in healthy individuals (10 mL)
- In patients with cardiac pathology, atrial contraction is very important and may provide > 25% of the ventricular volume.
What is happening during phase II of the cardiac cycle? Include when it starts and ends, and valve positions.
- The ventricles are beginning to contract
- Begins when mitral valve closes and ends when aortic valves opens
- Pressure inside the ventricle is higher than the atria closing the mitral and tricuspid valves
- There should be no volume changes (isovolumetric contraction) because all valves are closed
What is happening during phase III of the cardiac cycle? Include when it starts and ends, and valve positions.
- Ejection of blood occurs because ventricular pressure exceeds aortic/pulmonic artery pressures
- Begins when aortic valve opens, end when aortic valve closes
- Aortic and pulmonic valves are open, mitral and tricuspid valves are closed
What are the normal values for ESV and EDV?
At what specific point are these values obtained in the cardiac cycle?
ESV = 50 mL, EDV = 120 mL
- ESV is the measured volume of blood retained in the ventricle immediately prior to diastole (end of phase IV/beginning of phase I)
- EDV is the measured volume of blood in the ventricle immediately prior to systole (end of phase I/beginning of phase II)
How is stroke volume obtained via pressure volume loops?
Volume difference between the beginning and end of phase III
Could also take EDV - ESV
What is happening during phase IV of the cardiac cycle? Include when it starts and ends, and valve positions.
- Pressure in the aorta is greater than the ventricle, closing the aortic valve
- Begins when aortic valve closes, ends when mitral valve opens
- The mitral valve is still closed, so there is no change in ventricular volume (isovolumetric relaxation)
How is blood pressure measured in relation the the cardiac cycle?
- Systole is the peak pressure in arteries while the aortic valve is open
- Diastole is the lowest pressure in the arteries while the aortic valve is open
Does the electrical activity of the heart create instantaneous physical cardiac contraction?
No, there is a short delay. The electrical event happens first shortly followed by the cardiac contraction.
When does phase I occur on an ECG?
Between the end of the T and peak of R
When is diastole during the cardiac cycle per Dr. Schmidt?
Starts when aortic valve closes (end of phase III) and ends when mitral valve closes (beginning of phase II)
When is systole during the cardiac cycle per Dr. Schmidt?
Starts when mitral valve closes (beginning of phase II) and ends at the end when aortic valve closes (end of phase III)
If phase I were divided into thirds, how much filling would occur during each third?
1st third: rapid filling due to build up of blood (pressure) in the atria
2nd third: passive filling done, not much filling happening bc atrial and ventricular pressures are equal
3rd third: small increase in filling due to atrial contraction
What happens to filling in someone with mitral valve stenosis?
What should you avoid in these patients?
The mitral valve doesn’t open normally decreasing the speed of filling, meaning it takes more time for the ventricles to fill properly.
Avoid tachycardia as this reduces filling time even more and drops cardiac output.
What causes the 1st and 2nd heart sounds?
1st: AV valve closing
2nd: Aortic valve closing
What causes the a wave on a CVP waveform?
- Retrograde movement of blood from the atria into the vena cavae during atrial contraction
- There is only one valve in the atria so some of the volume moves backwards
What is another name for the mitral valve?
Bicuspid valve
What is the name of this diagram?
Carl J. Wigger’s diagram
What happens to venous return as RAP increases? (asssuming no other changes)
Venous return decreases because ▲P is smaller which creates a lower flow
Flow = ▲P/vascular resistance
▲P = Psf - RAP
▲P = 7-4 = 3 mmHg
A positive RAP opposes Psf
What happens to venous return when RAP decreases? (assuming no other changes)
Venous return increases because now ▲P is larger which creats a larger flow
Flow = ▲P/vascular resistance
▲P = Psf - RAP
▲P = 7 - (-4) = 11mmHg
What is the plateau volume for venous return if Psf is unchagned but theres max cardiac stimulation?
Why?
- 6 L/min
- Creates a negative RAP that collapses the veins
What is mean systemic filling pressure (Psf)?
What is the normal value?
- Sum of pressures in all vessels at equilibration
- This is the pressure available to fill the right atria
- Normal Psf is +7 mmHg
It is so low because most of the blood remains in the veins where pressures are very low due to high compliance
What is the best way to increase systemic filling pressure?
What does this cause?
What do we do operatively that inhibts this ability?
- Contraction of the veins by the nervous system
- ↑ venous return
- General anesthesia
What is resistance to venous return (RVR)?
- How easy is it for blood to return to the heart
- Easy = ↓ RVR, ↑ venous return, ↑ CO
- Difficult = ↑ RVR, ↓ venous return, ↓ CO
What would you expect venous return to be if RAP were normal but Psf were doubled?
Psf cut in half?
- If Psf were doubled and RAP was normal, venous return should double (larger △P)
- If Psf were halfed and RAP was normal, venous return should half (smaller △P)
What 2 things influence systemic filling pressure
- Venous tone
- Blood volume
What external force influences venous return?
Intrathoracic pressure
If increased (ex. PEEP), veins are compressed and ↓ venous return
Under normal sympathetic stimulation, at what RAP do we reach maximal CO?
If RAP is increased to +4 mmHg, then the heart can reach a maximal CO of 13 L/min
Describe the 3 things that allow cardiac output to increase under increased filling pressures as shown below?
- Frank- Starling Law: myocardium is typically understretched which allows the ventricles to stretch to accommodate a increase in volume and therfore ↑ CO.
- Direct atrial stretch: Atrial stretch by increased volume causes an increase in HR by 10-15% (doesn’t require neural input)
- Bainbridge Reflex: Atrial stretch is sensed by the vagus nerve which causes a decrease in parasympathetic input and increase in sympathetic input and can increase HR by 40-50%.
Describe what happens to RAP under maximum sympathetic stimulation?
What about during strong parasympathetic stimulation?
- Max. Sympathetic: RAP decreases due to the hypereffectiveness of the heart which essentially creates a vacuum that is pulling in more volume from the venous system.
- Parasympathetic: RAP increase bc HR is slowed causing an increase in filling time which increases atrial pressure
Why do we see very high CVPs in patients with heart failure?
Because the heart is dysfunctional and cannot maintain CO by itself. In order to keep CO normal, the body has to greatly increase the filling pressure to ensure adequate CO.
What is the equation for flow according to Poiseuille’s Law?
