Physiology Midterm 2

Front 1

Hemodynamics

Back 1

Blood flow is driven by a constant pressure along varying resistances

Front 2

Elements of CV system

Back 2

Pump, vessels, blood

Front 3

Blood pressure

Back 3

Measured as pressure difference between two points

Front 4

Blood flow

Back 4

Blood flow = cardiac output = stroke volume x heart rate

Front 5

Types of pressure difference

Back 5

Axial, radial, hydrostatic

Front 6

Circulation evolutionary consequence of:

Back 6

body size

Front 7

Circulatory system integrates three organs:

Back 7

heart, blood vessels, blood

Front 8

The heart is a dual pump that drives the blood that drives blood in two serial circuits of blood vessels:

Back 8

systemic and pulmonary circulations

Front 9

Driving pressure difference

Back 9

= Flow x Resistance (viscous)

Front 10

Flow

Back 10

= delta(V) / delta(t)
= Av (cross section x velocity)

Front 11

Blood flow is driven by constant pressure head across variable resistances

Back 11

Left and right heart each maintain a constant pressure head that drives blood flow across a branched system of blood vessels acting as resistors

Front 12

Total peripheral resistance to blood flow is result of combination of blood vessels in parallel and in series

Back 12

Parallel:
1/R_total = 1/R_1+1/R_2+1/R_3+...

Series:
R_total=R_1+R_2+R_3+...

Front 13

Three types of pressure difference in blood vessel:

Back 13

Driving pressure between arterial and venous ends of the circulation:
(between 2 points along x axis)

Transmural pressure between intravascular and tissue space (between two points along r axis)

Hydrostatic pressure between two points in a vertical column of blood (between two points along h axis)

Front 14

Total flow of blood delivered by the heart (total mean flow in the circulation) is called the cardiac output

Back 14

Total flow of blood = Cardiac output = Heart Rate x Stroke volume.

Example:
4.9 L/min = 70 beats/min x 70 mL/beat

Front 15

Flow in idealized vessel increases with the fourth power of radius:

Back 15

Hagen-Poiseuille Equation

F = delta(P) * pi*r^4 / (8*nu*l)

Front 16

Viscous resistance to flow is proportional to the viscosity of blood, but does not depend on properties of the blood-vessel walls

Back 16

R = 8*nu*l/ (pi*r^4)

Front 17

Viscosity of blood

Back 17

Measure of the lack of "internal slipperiness" between layers of fluid

viscosity = nu = shear stress / shear rate
=(Force/A)/(delta(v)/delta(x))

Front 18

Blood flow is laminar

Back 18

Distinction between laminar and turbulent flow is clinically very important

Front 19

Critical quantity concerned in the generation of turbulence

Back 19

Reynolds number (dimensionless)

Re = v_bar * 2r*rho / nu

v_bar = mean linear velocity
r = vessel radius
pho = density of fluid
nu = viscosity of fluid

Front 20

Pressure and flow oscillate with each heartbeat

Back 20

Maximum: systolic
Minimum: diastolic

Front 21

Gravity

Back 21

When there is a difference in height, there will be a hydrostatic pressure difference

Front 22

Low compliance of vessel

Back 22

Causes transmural pressure to increase when the vessel blood volume is increased

Front 23

Viscous resistance of blood

Back 23

Causes axial pressure difference when there is flow

Front 24

Inertia of blood and vessels

Back 24

Causes pressure to decrease when velocity of blood flow increases

Front 25

Whole blood

Back 25

Whole blood has an anomalous viscosity. Although the viscosity of water and blood plasma are Newtonian, whole blood is non-Newtonian (viscosity varies with rate of shear or flow)

Front 26

Influence on blood viscosity:

Back 26

i) Increases with fibrinogen concentration

ii) Increases with hematocrit

iii) Decreases as vessel radius falls belows a certain threshold

iv) Increases at low flows

v) Increases at low temperatures

Front 27

With progressive branching of vascular tree, several parameters change at each arborization:

Back 27

i) Number of vessels

ii) Vessel radius

iii) Aggregate cross-sectional area of vessels

iv) mean linear velocity

v) flow through a vessel

vi) relative blood volume

vii) circulation (or transit) time

viii) pressure profile

Front 28

Physical properties of vessels

Back 28

Closely follow level of branching in the circuit

Front 29

Blood volume

Back 29

Mostly resides in systemic veins

Front 30

Intravascular pressures

Back 30

Intravascular pressures along the systemic circuit are higher than those along the pulmonary circuit

Front 31

Steepest drop in systemic circulation

Back 31

Under normal conditions, occurs in arterioles, the site of greatest vascular resistance.
Vasoconstriction and vasodilation can steepen or flatten the pressure profile

Front 32

Local intravascular pressure

Back 32

Depends on distribution of vascular resistance. Midpoint capillary pressure

Pc = [(Rpost/Rpre)Pa+Pv] / [1+(Rpost/Rpre)]

Front 33

Blood vessels are elastic tubes

Back 33

Distensible elastic materials in blood vessels (elastin and collagen) allow blood vessels to distend with increasing pressure, thereby decreasing resistance