Cardiovascular System, Lecture 6

Question 1

Hemodynamics - factors affect blood flow

Answer 1

• blood flow (F): blood volume moved per unit time (mL/min)
• F = △P/R
• △P (change in pressure) = P1 - P2 (pressure at one point and pressure at next point)
• blood pressure (P): force per unit time area exerted by blood on blood vessel wall (mmHg)
• blood resistance (R): friction as blood flows through blood vessel
• it is not about pressure rather the change

Question 2

Hemodynamics - factors affecting resistance

Answer 2

• R (resistance) = 8Lη/πr*4
  ◦ η = blood viscosity
  ◦ L = blood vessel length
  ◦ r = blood vessel radius
  poisueille’s equation:
• combine F = △P/R and R = 8Lη/πr*4:
• F = △Pπr*4/8Lη
• radius is very important because it will have a big influence if we change things (to the power of 4)
  ◦ one we have control over, one of the key things we can manipulate
• double the pressure, double the blood flow
• double the viscosity, it will be half blood flow (on the bottom)
  ◦ change things by factor of 1
• radius has a larger effect on resistance (or flow) than viscosity or length
• manipulate radius of blood vessel:
  - vasoconstriction: decrease radius
  - vasodilation: increase radius

Question 3

Hemodynamics - distribution of cardiac output

Answer 3

addition to Q̇ (HR and SV) adding 2 variables effecting distribution of Q̇ in blood vessels:
-> Q̇ = MAP/TPR or rearranged as MAP = Q̇ * TPR
- total peripheral resistance (TPR; sum of all resistance in systemic circulation)
- mean arterial pressure (MAP; pressure driving blood into tissues averaged over entire cardiac cycle)
- systolic pressure (SBP): maximal arterial pressure
- diastolic pressure (DBP): minimum arterial pressure
- MAP = DBP + (1/3 * (SBP - DBP))
- Example: 80 + (1/3 * (120 - 80) = 93mmHg)

Question 4

Arteries

Answer 4

blood pressure
* MAP - little change
total cross sectional area
- measure of resistance
- large vessels - minimal branching - minimal area - minimal resistance
- results in high velocity of blood flow

Question 5

Arteries - 2 types

Answer 5

elastic arteries:
- heart (large) to medium sized arteries
- form a “pressure reservoir”
-> ventricular systole generates pressure to maintain blood flow into arteries and arterioles
-> during ventricular diastole - ventricular relaxing, exit valve from ventricle closed - what is maintaining blood flow?
-> portion of ventricular systole pressure stretching elastic arteries walls
-> stretch acts as pressure reservoir; recoil during ventricular diastole to maintain blood flow
muscular arteries:
- medium sized to smaller arteries
- more smooth muscle, less elastic tissue
- distribution arteries to organs

Question 6

Arteries - MAP - regulation

Answer 6

strongly related:
- short term regulation: seconds by altering TPR in blood vessels and/or Q̇ from heart:
- altering Q̇ via HR - SA node firing, AV node delay
- altering Q̇ via SV - preload, atrial and ventricular contractility, afterload
- altering TPR via vasoconstriction/vasodilation
- long term regulation: minutes to days by altering blood volume in kidneys:
- altering BV

Question 7

Arteries - arterial baroreceptors - regulation

Answer 7

• pressure sensors
• key receptor monitoring MAP (control condition)
• locations:
  ◦ carotid sinus - monitor MAP to brain
  ◦ aortic arch - monitor MAP to systemic circulation
• input to CV center to medulla oblongata:
  ◦ includes centers already mentioned:
  ‣ cardioacceleratory center - sympathetic - cardiac accelerator nerves
  ‣ cardioinhibitory center - parasympathetic - vagus nerves
  * effector responses in HR and SV leading to responses in Q
• also includes not mentioned yet:
  ◦ vasomotor center - sympathetic - vasomotor nerves
  ‣ effector responses in blood vessel vasoconstriction and vasodilation leading to responses in TPR