8.6 Cardiovascular Physiology (HT) Flashcards
What are some major properties involved in the study of the movement of blood?
- Flow
- Pressure
- Tension
- Compliance
- Resistance
- Energy
What is compliance?
How easy it is to change volume when pressure is applied.
What is flow and what are the units?
- The volume moving past a given point per unit time
- Flow = ΔV/Δt
- Units: L/min
Is flow a rate?
Yes
Give the formula for calculating cardiac output.
Cardiac output = Stroke volume x Heart rate
Give some typical values for:
- Stroke volume
- Heart rate
- Cardiac output
- Stroke volume = 70ml
- Heart rate = 70 bpm
- Cardiac output = 70 x 70 = About 5L/min
What is the normal cardiac output at rest?
5L/min
Do larger compartments of the circulatory system have greater flow?
No, because of conservation of flow.
What are the two divisions of the circulation?
- Systemic circulation
- Pulmonary circulation
Is velocity the same as flow?
No!
Give the equation relating flow to velocity.
Flow (cm3/s) = Velocity (cm/s) x Cross-sectional area (cm2)
Draw graphs to show how cross-sectional area and velocity change throughout the systemic circulation.
When the total cross-sectional area of vessels increases, what happens to the velocity?
- It decreases
- This is because flow is conserved and it is equal to the product of the velocity and cross-sectional area
Is pressure in the aorta constant and is this desirable?
- No, it varies between systole and diastole of the heart
- Theoretically these pressure waves are not desirable, but we have valves, so it is ok
What happens to pressure waves in the heart and why?
- They decay with distance and become less pulsatile
- This is due to the elasticity of the vessels
What are ABP and CVP?
- Arterial blood pressure -> The pressure exerted by the blood in the large arteries
- Central venous pressure -> The blood pressure in the venae cavae, near the right atrium of the heart
Does pulse velocity in vessels measure blood velocity?
No, the pulse wave is much faster (400cm/s) than the blood velocity (20cm/s).
What are the standard units for blood pressure?
mmHg
(cmH2O is also occasionally used)
Explain why the units of blood pressure are mmHg or cmH2O.
How does a failing heart affect CVP?
- Increases the CVP
- Because blood builds up behind the heart
Name some things that can cause a high or low CVP.
High CVP:
- Heart failure
- Decreased contractility
- Valve abnormalities
- Dysrhythmias
- Increased pulmonary arterial pressure
- Increased juxta-cardial pressure (e.g. tension pneumothorax)
Low CVP:
- Hypovolemia
- Venodilation
Describe how you can measure CVP.
- CVP is best estimated indirectly by measuring the JVP (jugular venous pressure) -> This is non-invasive
- The patient is laid down at a 45* angle and their internal jugular vein is located (not to be confused with the carotid artery)
- The highest level above the sternal angle at which the vein pulsates is measured (the vertical measurement is taken, perpendicular to the ground)
- 5cm can be added to this to account for the distance between the right atrium and the sternal angle
- In healthy patients, the value should not exceed 9cmH2O
There are also direct, invasive ways of measuring CVP, such as a central venous catheter placed through either the subclavian or internal jugular veins. An ultrasound may also be used.
What is a normal CVP value?
5mmHg (or 7cmH2O)
Describe the principle on which arterial pressure was first measured.
- An animal’s artery could be cut and the blood that spurted out could be made to rise up a tube
- The higher the pressure, the higher the blood would rise
- The height to which it rose was the ABP in cmH2O























