Haemodynamics

Question 1

Define cardiac output

Answer 1

Sum of all local tissue blood flows

Question 2

What is velocity proportional to

Answer 2

Inversley proportional to area. As the area increases the velocity stays the same. Flow is consistent throughout

Question 3

Mean arterial pressure equals

Answer 3

TPR * CO

Question 4

Ohms law

Answer 4

Flow equals the change in pressure/resistance

Question 5

What is the average mean arterial blood pressure

Answer 5

100mmHg

Question 6

Cardiac output formula

Answer 6

CO= (PA-PV)/TPR
But typically venous pressure is ) so:
CO= MAP/TPR

Question 7

What is a typical pathology leading to increased venous pressure (and thus the need to include venous pressure when calculating CO

Answer 7

Heart failure

Question 8

Parallel resistance consequences

Answer 8

Little effect on total flow, big effect on local flow

Question 9

Poiseuille law

Answer 9

Flow depends the driving pressure, tube geometry and the viscosity of the fluid

Question 10

What is the factor that has the biggest influence on flow

Answer 10

The radius of the vessel

Question 11

What are the determinants of blood viscosity

Answer 11

Temperature and haematocrit
Also velocity. Increased velocity results in an apparent decrease in velocity due to RBC accumulating centrally in the vessel.
Velocity also can decrease in very small vessels as less RBC fit in

Question 12

Define heamatocrit

Answer 12

The ratio of red cell volume in a sample of peripheral blood

Question 13

Why is blood flow not directly proportional to pressure

Answer 13

Because resistance is variable

Question 14

The contractile state of vascular smooth muscle is controlled by…

Answer 14

Vascular endothelial cells (release NO)
Sympathetic control (NA)
Circulating hormones (vasopressin, angiotensin II)

Question 15

What induces release of NO

Answer 15

Increased flow increases heamodynamic stress, results in endothelial cells releasing NO

Question 16

Factors that may result in turbulent flow

Answer 16

High fluid densities
Large tube diameters
High flow velocities
Low fluid viscosities
Abrupt variation in tube dimensions
Irregularities in the tube walls

Question 17

What is the use of reynolds number and what variables is it based on

Answer 17

A number we can use to predict wether we will get turbulent flow or not. Based on density of fluid, mean velocity of flow, diameter of the tube, viscosity

Question 18

Describe Bernoulli’s principle

Answer 18

That energy remains constant. Energy in blood flow is derived from pressure energy (heart pumping), gravitational energy, and kinetic energy. If one of these goes up the other/s go down. E.g. in stenosis velocity increases

Question 19

What is transmural pressure

Answer 19

The pressure inside the vessel minus the pressure outside the vessel