3. Haemodynamics Flashcards
What is serum?
Plasma without clotting factors
What are the 2 types of blood flow?
Laminar flow - smooth and silent Turbulent flow (vessel lumen smaller at a point) - disorganised and noisy
How does blood flow?
Form high pressure to low pressure
What is flow?
Volume transferred per unit time (L/min)
What is pressure?
Force per unit area (mmHg but SI unit is Pa)
What is the flow equation using K (conductance)?
Flow = K(delta P)
What is K?
Conductance
Measure of ease of flow
What is R?
Resistance
Measure of difficulty of flow
Reciprocal of K
What is the equation for flow using R?
Flow = delta P/R
What has to happen to change blood supply to an organ?
Change in resistance
What does R = delta P/flow represent?
The difference in mean pressure needed to move one unit of flow in steady state
mmHg min/L
What happens if resistance increases and flow is maintained?
Pressure difference has to rise
What are the primary factors in resistance to flow?
Diameter
Length of vessel
Viscosity
However vessel length doesn’t change and viscosity of blood is regulated so diameter is the most important
Small change in diameter has large change in flow
Which has lower resistance, pulmonary circulation or systemic system?
Pulmonary system - shorter and wider vessels
What is velocity?
Distance fluid moves in a given time (cm/s)
What is flow proportional to?
V x r^2
Why is there a lower velocity in capillaries than in large arteries?
Allows more time for diffusion to occur
How do you work out pulse pressure?
Systolic blood pressure - diastolic blood pressure
How do you work out mean arterial pressure?
Diastolic blood pressure + 1/3 pulse pressure
How do you work out delta P?
Mean aortic pressure - central venous pressure
How do you work out R (resistance)?
Systemic resistance - total peripheral resistance
How do you work out total peripheral resistance?
Mean aortic pressure/cardiac output
How do you work out mean arterial pressure?
CO x TPR (total peripheral resistance)
What is pulse pressure?
Volume of blood ejected and the compliance of the arterial system govern pulse pressure
What can increase pulse pressure?
Heart block - bradycardia
Vasodilation
Elite athletes - systolic increased and diastolic decreases
What do the principles of indirect BP measurement rely on?
Changes in type of flow - laminar and turbulent
What is thrill and bruit?
Thrill can be felt
Bruit can be heard
