Lecture 10

Question 1

Types of Blood Flow

Answer 1

1) Laminar Flow–> Arteries/veins
- Silent/unobstructed
- Parabolic shape
- Layers blood in concentric rings = less energy to move blood

2) Turbulent Flow–> Ventricles, stenosis
- Noisy
- Laminar flow disrupted
- Movement chaotic

3) Single line/margin flow –> Capillaries
- RBC diameter > capillary diameter

Question 2

Reynold’s number

Answer 2

-Predicts whether blood flow is laminar or turbulent

Re = v D ρ / η

Re>2000 = laminar becomes turbulent

Question 3

What increases/decreases turbulence

Answer 3

Increases:

• High flow velocity (MOST important)
• Large vessel diameter
• High blood density

Decrease:
-Increase viscosity

Question 4

Clinical conditions that will cause turbulence?

Answer 4

1) Stenosis
2) Defective valves in heart
3) Narrowed blood vessel

Question 5

Sickle cell

Answer 5

• RBC rigid/sickle shape

- Do not pass easily through capillary –> tissue ischemia and painful “sickling crisis”

Question 6

La Place’s Law

Answer 6

Calc:
(Transmural pressure) ∆P = 2T/r

Key:

• T = Wall TENSION in vessels to counteract pressure
• R= Radius
• Transmural Pressure (∆P) = Pi - Pt

Effects:

• Greater radius = greater tension
• Thickness/hypertrophy = decreases tension

-Think tight rope explanation

Question 7

Aneurysm

Answer 7

-Aorta radius large – requires more tension to offset given blood pressure

• Vessel cannot generate more wall tension
• -> rupture

Question 8

Compare Vein and artery compliance

Answer 8

Def:
-Compliance describes how the volume of a
compartment changes (∆V) in response to a given change in the pressure within (∆ P).

Calc:
Compliance = ∆ V/∆ P

Comparison:

• Veins need a small change in pressure to accommodate a large change in volume of blood
• More distensible (measure of compliance)

-Arteries need a large change in pressure to accommodate a small change in volume of blood

Question 9

Sympathetics and Compliance

Answer 9

• Sympathetics reduce compliance

- Force blood to

Question 10

Venous Pooling

Answer 10

• Person standing for long periods of time
• On standing, the pressure (distending) in the veins of the foot increases, and since the veins are so compliant these veins will accommodate a large volume of blood

Question 11

Effects of venoconstriction and venodilation?

Answer 11

Venoconstriction

• “squeezes” blood out of the veins – and shifts it towards the heart.
• ↑Sympathetic → Venoconstriction

Venodilation

• allows more blood to pool in the veins
• ↓Sympathetic → Venodilation

Question 12

Compare Veins and arteries elasticity

Answer 12

Arteries more elastic than veins

Question 13

Arterial compliance and age

Answer 13

-Vessels become stiffer w age = decreased compliance –> generate more systolic pressures to move blood into circulation

Clinical Correlation:

1) Systolic hypertension (Elderly) –> 160/80
- Changes in artery
- Cannot hold same volume of blood as a younger person

Question 14

Effects of Altered Ventricular Compliance

Answer 14

↓ ventricular compliance → ↑ LVEDPr and vice versa

LV hypertrophy –> Reduced Ventricular compliance

• ↓ compliance
• ↑LVEDPr
• ↓ Stroke volume
• ↓ Cardiac output

Dilated cardiomyopathies

• ↑ compliance
• ↓LVEDPr

Question 15

Pulse pressure calculation and factors that effect it

Answer 15

Systolic BP - Diastolic BP (Diff between two)
120-80 = 40mmHG

-Gives idea of stroke volume

Factors that Effect it:
-Arterial compliance

Question 16

Mean Arterial Pressure (MAP)

Answer 16

• Pressure in the aorta during single cardiac cycle
• Average effective pressure that drives blood around the circulation
• Gives idea of cardiac output

Calcs:
-MAP = Pdiastolic +⅓ (Psystolic – Pdiastolic)
~95mmHg

Question 17

Arterial Pressure (Pulse) Wave

Answer 17

• When blood is ejected at high pressure into the aorta – a pressure wave is set up which is transmitted along the walls of the arteries
• Pressure wave velocity is faster in stiffer (older) arteries

Question 18

Artierosclerosis

Answer 18

Stiffening of the arteries

Usually in older ppl

Question 19

Atherosclerosis

Answer 19

Plaque formation –> Narrowed vessels

Question 20

Why can you maintain venous return from supine to standing?

Answer 20

-There is still pressure diff between arteries
and veins – blood will flow

??

Question 21

Factors that Affect Venous return

Answer 21

Increase:

1) Inspiration (breathing in)
2) Skeletal muscle pump contraction (Decreasing Venous PR)?

Decrease
2) Expiration (breathing out)

Question 22

Define Venous Pressure and Central venous pressure

Answer 22

1) Venous Pressure
- Pressure in venous compartment

2) Central venous pressure
-pressure in thoracic vena cava near RA
(Determines filling pressure of RA)

Question 23

Factors that affect RAP and CVP

Answer 23

RAP
-Depends on ability to pump blood/tendency of blood to flow back into heart

1) Inverse relationship w contraction
(Decrease= strong, Increase = weak)

2) Cardiac failure
(increase RAP, CVP, and hydrostatic pressure)

Question 24

Factors that affect venous return and central venous pressure

Answer 24

Increase VR and CVP:
↑ Blood volume
↑ Venomotor tone
(Increase RAP)

Decrease VR and CVP
-Hemorrhage
-Venodilation
(Decrease RAP)

-Cardiac failure can also increase RAP, CVP, and hydrostatic pressure

Question 25

Measuring blood flow – Fick principle

Answer 25

-Calcs rate of cardiac output

Q (Flow) = O2 consumption/arterialO2 - venousO2