Question

1. Consider Poiseuille’s Law. Which factor has the most potential to alter the rate of blood flow? Is this factor directly or indirectly related to flow?

2. For each of the 11 phases of the cardiac cycle, give the state of both the mitral and aortic semilunar valves as either open or closed. This should be in the form of a list with NO further explanation.

3. Why is left-ventricular afterload increased by aortic valve stenosis? How and why is blood flow altered? What mechanism of compensation might follow this condition?

Answer 1

Answer 1:

Poiseuille's Law:

V = π p r4 / 8 η l   

where

V = Volume of blood flow

p = pressure difference between the ends of the vessels

r = internal radius of vessel

l = length of vessel

η = viscosity of blood

Blood viscosity has the most potential to alter the rate of blood flow. When the blood viscosity increases the rate of blood flow decreases because there is more resistance (Peripheral resistance) offered by the wall of vessels to the flow of blood. (Resistance (R) is directly proportional to the length (L) of the blood vessel and the viscosity (η) of the blood and Resistance is inversely proportional to the radius to the power of four (r​​​​​​​​​​​4). Resistance is directly proportional to blood viscosity. Peripheral resistance will increase when blood viscosity will increase).

Blood viscosity is indirectly proportional to the rate of blood flow.