Hemodynamics

Question 1

Name three types of pressure that drive blood flow through vessels

Answer 1

1. Pressure diff btw arterial and venous blood
2. Transmural- pressure difference across wall of vessel
3. gravitational pressure

Question 2

Which vessels are known as resistance vessels?

Answer 2

Arterioles

Question 3

Which vessels are known as capacitance vessels?

Answer 3

veins- hold largest volume of blood

Question 4

Flow equation and what are the assumptions of this equation

Answer 4

Flow (Q) = ΔP/R
P= pressure
R=resistance
Assumptions: constant pressure, constant resistance, straight rigid tube, laminar flow, non-pulsatile flow

Question 5

Velocity equation

Answer 5

v= Q/A

Where A is cross sectional area, and Q is flow

Question 6

Cardiac output equation and average CO

Answer 6

(mean arterial pressure- venous pressure)/ Total peripheral resistance (TPR)
Avg CO= 5L/min

Question 7

Poiseuilles Equation

Answer 7

Q= ∆P x [(pi r^4)/ (8nl)]
Q=flow
r=radius
l=length
P= pressure
n= viscosity of blood
Note:  only valid for single vessels

Question 8

Describe flow through CV system

Answer 8

Flow is constant b/c CV system is closed loop . Total flow is Cardiac output. Flow in must equal flow out

Question 9

Resistance equation- parallel vessels

Answer 9

1/Rt = 1/R1 + 1/R2 + 1/R3
Rt= total resistance

Question 10

Resistance equation - vessels in series

Answer 10

Rt= R1+ R2+ R3
Rt= total resistance

Question 11

Compare resistance in parallel vs in series vessels

Answer 11

Parallel: Total resistance is lower than the resistance of a single lowest resistance vessel in the system. In each vessel, pressure is the same but flow can be different
In series: Total resistance of a series of vessels is higher than the resistance of any individual vessel. Flow is constant but pressure decreases through the series

Question 12

What is laminar flow

Answer 12

• smooth, streamlined, and most efficient

* velocity slowest at edge of tube, fastest in center

Question 13

What is turbulent flow?

Answer 13

• irregular, with eddies & vortices (less efficient)

* requires more pressure for same average velocity compared to laminar flow

Question 14

What increases turbulent flow?

Answer 14

large diameter, high velocity, low viscosity, abrupt changes in diameter, irregularities on tube walls.

Question 15

What is shearing force?

Answer 15

Turbulent flow causes viscous drag of fluid flowing through tube, which exerts force on the walls. Shear forces can damage vascular endothelium, which promotes formation of thrombi and embolisms

Question 16

What is pulsatile flow?

Answer 16

Heart pumps intermittently, creating pulsatile flow in the aorta — arterial pressure is not constant.

Question 17

What is systolic and diastolic pressure?

Answer 17

• Systolic pressure = peak aortic (~arterial) pressure; Diastolic pressure = minimum aortic pressure
o Systole = contraction phase of cardiac cycle; Diastole = relaxation phase

Question 18

Pulse pressure = ?

Answer 18

systolic – diastolic = 120 – 80 = 40 mmHg

Question 19

Explain how the pulsatile flow of blood produced by the heart is converted to steady flow in the capillary beds.

Answer 19

in capillary beds, no pulse variation, pressure (and thus flow) is continuous. Pulse pressure, mean pressure and velocity all decrease from aorta to capillaries. Compliance of arteries absorbs energy, transforms pulsatile flow to continuous flow

Question 20

Define vascular compliance.

Answer 20

C= ∆V/∆P
V=volume in ml
P= pressure mmHg

Compliance represents the elastic properties of vessels. Determined by relative amounts of elastin vs smooth muscle and collagen

Question 21

What is LaPlace’s law?

Answer 21

T= (∆P r)/ u
T=tension (wall stress)
∆P= transmural pressure
r= radius
u= wall thickness

Question 22

What is Fick’s principle?

Answer 22

How much of a substance is used by a tissue
x(used)= Q([x]i - [x]o)
x(used)= amount used
Q= flow
Xi= initial amount
Xo= final amount

Question 23

What is starlings equation?

Answer 23

Flux = k[(Pc-Pi) – (πc – πi)]	
Flux = net movement across capillary wall
k = constant
Pc = capillary hydrostatic pressure
Pi = interstitial hydrostatic pressure
πc = capillary oncotic pressure
πi = interstitial oncotic pressure

Question 24

What is Mean arterial pressure?

Answer 24

diastolic pressure + 1/3(systolic – diastolic)

-Diastole is longer than systole at rest

Question 25

More compliance in aorta = ______ pulse pressure

Answer 25

Lower

Question 26

Arteriosclerosis = ?

Answer 26

General term for loss of compliance caused by thickening and hardening of arteries. Raises the pulse pressure

Question 27

What is an aneurysm?

Answer 27

weakened vessel wall bulges outward, increasing the radius, thus increasing the tension that cells in the wall have to withstand. Over time cells become weaker, allowing the wall to bulge more so that tension increases further, until the aneurysm ruptures

Question 28

Bulk transport=

Answer 28

x= Q[x]
where x is transport rate, Q is the flow, and [x] is the concentration of x
-Describes how much is delivered

Question 29

Ficks principle for Cardiac output

Answer 29

mVO2= CO ([O2]a - [O2]v)
mVO2 = myocardial oxygen consumption (ml/min)
CO = cardiac output (L/min)
[O2]a = arterial O2 concentration
[O2]v = venous O2 concentration

Question 30

Fick’s principle for Fractional oxygen extraction from blood

Answer 30

EO2 is the amount of oxygen used by a tissue expressed as a fraction of the original (arterial) oxygen concentration
EO2= ([O2]a - [O2]v)/ [O2]a

Question 31

Hydrostatic pressure = ?

Answer 31

fluid pressure as we have been considering so far – blood pressure in this case. tends to be outward

Question 32

Oncotic pressure=?

Answer 32

(colloid osmotic pressure) is the osmotic force created by proteins in the blood and interstitial fluid. α Globulin and albumin are major determinants of oncotic pressure.

Question 33

Is oncotic pressure higher in capillaries or interstitial fluid?

Answer 33

capillaries- promotes REABSORPTION of fluid (movement of fluid into capillaries)

Question 34

Gas diffusion depends on what?

Answer 34

Distance btw capillary and tissue, and amount of gas in blood (free and bound)

Question 35

SMall lipid insoluble molecules diffuse through what?

Answer 35

interendothelial junctions btw capillary endothelial cells

Question 36

Filtration is favored in ____________, absorption favored in ____________

Answer 36

arteries, veins