Peripheral resistance and blood pressure/flow

Question 1

Mean Arterial Pressure - BP

Answer 1

Cardiac Output x Total Peripheral Resistance

Question 2

Cardiac output

Answer 2

Heart rate (HR) x Stroke volume (SV)

Question 3

Poiseuille’s Law (1846)

Answer 3

describes the factors that determine the flow through a tube in terms of pressure, flow and resistance

Question 4

Flow (Q)

Answer 4

is directly proportional to the pressure gradient (P ) vessel and the radius4 (r4) of the tube and inversely proportional to the length (L) of the vessel and to the viscosity (η) of the fluid.

Question 5

The cardiovascular system can be equated to Poiseuilles Law

Answer 5

Flow (Q) is proportional to the pressure gradient (ΔP ) and inversely proportional to the resistance (R)

Q = ΔP / R
Flow (Q) = cardiac output (L/min)
Pressure gradient (ΔP ) = Blood pressure (mmHg)
Resistance (R) = Peripheral resistance

Question 6

Flow is inversely proportional to the length and viscosity

Answer 6

Length (L)
Longer the tube = more resistance = less flow
remains constant and therefore does NOT control blood flow

Viscosity (η)
Higher the viscosity (i.e. treacle) = more resistance = less flow
Viscosity is related to the hematocrit (red blood cells/erythrocytes)
Dehydration
High altitude
Erythropoietin (EPO) – stimulate production RBC
Remains constant under physiological conditions and therefore does NOT control blood flow

Question 7

what is the most important factor in determining resistance (flow)

Answer 7

Radius (r)
Caused by the friction of the fluid against the vessel wall
The effect of changes in the radius is raised to the power of 4
reducing radius by two fold from 2 to 1 reduces flow by sixteen fold (i.e. resistance increased sixteen fold)
Possible to regulate the radius of
blood vessels using smooth muscle

Question 8

Total peripheral resistance

Answer 8

is the sum of the resistance of all the blood vessels and determines blood pressure

Question 9

Resistance (radius) in the arterioles also determines

Answer 9

the blood flow to individual organs

Question 10

Blood pressure is influenced by height

Answer 10

P = h  g

P = pressure (mmHg)
h = height
(rho) = density
g = gravity

Question 11

Standing

Answer 11

Standing
Increased pressure of mean arterial blood pressure in legs (from 90 to 195 mmHg) leads to pooling of blood in the veins
feet swelling on flights
fainting in stationary soldiers
However, since arterial and venous blood are at the same height
Blood gradient P = constant = blood flow continues