1) Haemodynamics Equations

Question 1

What is flow?

Answer 1

Flow is the volume transferred per unit time

(A rate)- usually measured in mL/min

Question 2

What is pressure?

Answer 2

Pressure is the force per unit area (when measuring BP use mmHg units)

Question 3

What is Darcy’s law?

Answer 3

Flow=change in pressure/resistance

Question 4

Which factors influence resistance to flow?

Answer 4

Diameter, length of vessel and viscosity

Physiologically diameter is the most important quantitatively (vessel length doesn’t change and viscosity of blood is regulated within narrow range)

Question 5

What is velocity in relation to blood?

Answer 5

The distance blood moves in a given time (cm/s)

Question 6

What equation relates flow and velocity?

Answer 6

Flow= V x A
Where V is velocity
A is the cross-sectional area of vessel

Question 7

What is pulse pressure?

Answer 7

PP is peak systolic pressure- end systolic pressure

PP=SBP-DBP

Question 8

What is the equation for mean arterial pressure?

Answer 8

MAP= DBP+ 1/3PP
Alternatively
MAP= DBP+ (SBP-DBP)/3

Question 9

What equation links MAP, cardiac output and TPR?

Answer 9

MAP= CO x TPR

Question 10

What equation links stroke volume, cardiac output and heart rate?

Answer 10

CO= SV x HR