Chapter 18 Flashcards
the study of blood moving
through the circulatory system
Hemodynamics
_ indicates the volume of
blood moving during a particular time
Flow (volume flow rate)
_ answers the question: How much?
Flow
Units for flow
voulme/time (L/min)
_ the speed or swiftness of a fluid moving
from one location to another
Velocity
Velocity answer the question:
How fast?
Units for velocity
distance/time (cm/s)
Flow patterns in normal vessels are _ and vary with _
extremely complex
location, time within the heart cycle, and exercise
Pathologic conditions create _
even more diversity in flow patterns
Three basic forms of blood flow:
Pulsatile
Phasic
Steady
_ flow – when blood moves at a variable
velocity. Blood accelerates and decelerates as a
result of cardiac contraction, commonly appears in
arterial circulation
Pulsatile
_ flow – blood moves with a variable velocity.
Blood accelerates and decelerates as a result of
respiration, often appears in venous circulation
Phasic
_ flow – occurs when a fluid moves at a constant
speed or velocity. Present in the venous circulation
when individuals stop breathing for a brief moment.
Steady
_ flow is when the
flow streamlines are
aligned and parallel.
Laminar
_ flow is characterized by layers of
blood that travel at
individual speeds
laminar
Laminar flow is commonly found in _
normal physiologic states
2 forms of laminar flow
Plug
Parabolic
bullet-shaped profile. Velocity is highest in the center of the lumen, and gradually decreases to its minimum at the vessel wall.
Parabolic flow
Plug flow
all of the layers and
blood cells travel at the same
velocity
Plug flow and parabolic flow are both associated with
normal physiology
Silent flow
laminar flow
Turbulent flow is
characterized by
chaotic flow patterns in many different directions at many different speeds. The streamlines are often obliterated.
small,
hurricane-like, swirling,
rotational patterns that
appear in turbulent flow
Eddy/vortex
Turbulent flow is often associated with
cardiovascular pathology
and elevated blood
velocities
_ flow may be seen downstream from a stenosis in a vessel
Turbulent
Turbulent flow converts _ into _
flow energy
other forms such as sound or vibration
sound associated with
turbulence
Murmur or bruit
tissue vibration associated with
turbulence, also described as a palpable
murmur
Thrill
The Reynold’s number is _
a unitless number that
predicts whether flow is laminar or turbulent.
Vessels with comparable Reynold’s numbers
exhibit
similar flow characteristics
Reynold’s numbers above 2000 indicate
turbulent flow
Reynold’s numbers under 1500 will have _ flow
laminar
Blood moves from regions of _ to _
higher energy
lower energy
energy is imparted to blood by _
the contraction of
the heart during systole.
Forms of energy associated with blood:
Kinetic
Pressure
gravitational
_ energy: Associated with a moving object
Kinetic
Kinetic energy is determined by 2 factors:
An object’s mass
The speed at which it moves
Heavy/quickly moving objects have _ kinetic
energy
high
Light/slowly moving objects have _ kinetic
energy
low
Pressure Energy
A form of stored or potential energy. It is a major form of energy for circulating blood and creates flow by overcoming resistance
Potential energy has
he ability to perform work
Gravitational energy
A form of stored or potenetial energy that is associated with any elevated object.
All elevated objects have _
stored energy that can perform work
As blood flows through the circulation, energy is
lost in 3 ways:
Viscous loss
Frictional loss
Inertial loss
Viscosity
the thickness of a fluid
The thicker the fluid the _ viscous it is
more
Viscosity is measured in units of
poise
More energy is lost with movement of _ viscosity fluids
high
Viscous loss is associated wit
blood overcoming its internal
stickiness
Hematocrit
the percentage of blood made up of red
blood cells.
Normal hematocrirt
aprrox. 45%
Viscous energy loss is determined b
Hematocrit
Frictional losses occur when
low energy is
converted to heat as one object rubs against
another
exxample of frictional loss:
Blood sliding across vessel walls creates heat
Inertial Energy Loss: Energy is lost when
the speed of a fluid changes, regardless
of whether the fluid accelerates or decelerates
tendency of a fluid to resist changes in velocity
Inertia
Inertial energy loss occurs during three events:
Pulsatile flow
Phasic flow
Velocity changes at a stenosis (maximum velocity exists where
the vessel is narrowest and decreases as the blood flows out of
the stenosis into a vessel segment of normal diameter)
a narrowing in the lumen of a vessel
Stenosis
Stenosis may have these effects on blood flow:
[] Changes in direction as blood flows into and out of the narrow portion of the vessel
Increased velocity within the stenosis (Velocity is the highest where the vessel is the narrowest)
Turbulence downstream from the stenosis (post-stenotic turbulance)
Eddy currents, vortices, may have bruit, murmur or thrill
Pressure gradient across the stenosis (pressure downstream is lower than the pressure upstream)
Conversion of pulsatile flow patterns to steady flow
Effects of a stenosis
- change in flow direction
- increased velocity as vessel narrows
- turbulence downstream from the stenosis
- pressure gradient across the stenosis
- loss of pulsatility
Describes the relationship between velocity and
pressure in a moving fluid
Bernoullis principle
Bernoullis principle s derived from
the principle of conservation of energy
With steady flow, the sum of all forms of energy is _
the same everywhere
Bernouliis principle: the sum of _ energy and _ energy remains constant
kinetic and pressure
Bernoulli’s Principle: Where kinetic energy is the highest,
pressure energy will be _
the lowest and vise versa
Pressure gradient =
flow x resistance
Study of blood flow is complex due to
the elastic nature of
blood vessels, composition of blood, and pulsatile nature of
heart pumping
Pressure gradient increases with _
an increase in flow or resistance
Flow increases with
an increase in pressure gradient or a
decrease in resistance
Ohms law
Voltage = current x resistance
Electrical resistance is reported
ohms
Resistance vessels are called
arterioles
Fluids: pressure
Electricity:
voltage
Fluids: flow
Electricity:
current
Fluids: resistance
Electricity:
resistance (ohms)
_ are thin-walled and
collapsible
veins
During normal function,
veins have a _ pressure
and are _
expanded (_ shaped)
low
only partly
hourglass
Veins are _ resistance vessels
low
When venous flow increases
with exercise, the cross-
sectional shape of a vein
changes from_, to _, and then to _
hourglass
oval
round
As veins become more round,
the resistance to flow_ which increases _
decreases
outflow toward the heart
Hydrostatic pressure
Pressure related to the weight of blood pressing
on a vessel measured at a height above or
below heart level
Units for hydrostatic pressure
mmHg
Hydrostatic pressure is important when _
measuring blood pressure
Pressures are accurately assessed when the
measurement is made at
heart level
Measurement is too _ if measurement is made
below heart
high
Measurement is too _ if measurement is made
above heart
low
When a person is _, all
parts of the body are at the
same level as the heart
supine
When a person is supine hydrostatic pressure is _
zero everywhere
A pressure measured
anywhere on a supine patient
accurately represents_
true circulatory pressure
Hydrostatic Pressure- standing: At heart level, the hydrostatic pressure is _
zero
Hydrostatic pressure- standing: At locations below heart level, hydrostatic
pressure is _. The measured pressure will be _
positive
higher than true circulatory pressure
Hydrostatic pressure- standing: At locations above the heart, hydrostatic pressure
is _. The measured pressure will be _
negative
lower than the true circulatory pressure
Hydrostatic pressure- standing: measured pressure=
circulatory pressure + hydrostatic pressure
hydrostatic pressure @ ankle
100 mmHg
hydrostatic pressure @ knee
75 mmHg
hydrostatic pressure @ waist
50 mmHg
hydrostatic pressure @ mid chest
0 mmHg
hydrostatic pressure @ top of head
-30 mmHg
n normal individuals, respiration affects venous
flow for two reasons:
The venous system is low pressure
Muscles responsible for respiration alter pressures in the thorax and the abdomen
Breathing affects two venous flows:
Venous flow in the legs
Venous return to the heart (compromises venous flow from the head, arms, and flow from the IVC to the heart)
_ is the
muscle responsible for
breathing
the diaphragm
the diaphragm is located between _ and _
thorax and abdomen
During inspiration, the
diaphragm moves
downward
During inspiration, the chest cavity _, creating _ in the chest
expands
negative pressure
Negative thoracic pressure
creates
suction that increases
venous return to the heart
Venous flow from the head,
arms, and vena cava _
during inspiration
increases
During inspiration, the
diaphragm also
presses into the abdomen
inspiration: Abdominal compression
increases _
abdominal pressure
Inspiration: venous flow in the legs _
decreases
During expiration, the
diaphragm moves _, _pressure in the chest
upward
increasing
Expiration: Increased thoracic pressure
__(increases or reduces) venous return to the
heart.
reduces
Venous flow from the head,
arms, and vena cava all
_ during expiration.
decrease
During expiration, the
diaphragm _
the abdomen.
decompresses
Expiration: _ in abdominal pressure
decrease
Expiration: _ in venous flow from the legs
increase
Inspiration: Diaphragm moves _ Thoracic pressure _ Abdominal pressure _ Venous return to the heart _ Venous flow in legs _
downward toward the abdomen decreases increases increases decreases
Expiration: Diaphragm moves _ Thoracic pressure _ Abdominal pressure _ Venous return to the heart _ Venous flow in legs _
upward into the thorax increases decreases decreases increases
Venous flow in the legs correlates with
movement of the diaphragm.
Downward movement of diaphragm =
decreases
venous flow in the legs
Upward movement of diaphragm =
ncreases
venous flow in the legs
Changes in venous return to the heart are _ to those of venous flow in the legs
opposite
Valsalva _ (increases or decreases_ pressure in the thorax and reduces all venous flows
increases
