Transcript Blood Pumps - cardiac anesthesia basics

Blood Pumps
Pressure/Flow/Resistance
Brian Schwartz, CCP
Perfusion I
September 16, 2003
Blood Pumps
Purpose of Blood Pumps
Ideal Blood Pump
Types of Blood Pumps
Most Commonly Used Pumps
Types of Blood Flow
Other Blood Pumps Used
Development of Blood
Pumps
To replace the beating heart
during heart surgery
They propel blood and other
physiologic fluids throughout
the extracorporeal circuit;
which includes the patient’s
natural circulation as well as
the artificial one
The Ideal Blood Pump

Move volumes of blood up to 5.0 L/Min
 Must be able to pump blood at low
velocities of flow
 All parts in contact with blood should
have smooth surface
 Must be possible to dismantle, clean and
sterilize the pump with ease, and the
blood handling components must be
disposable
The Ideal Blood Pump
(continued)

Calibration should be easy, reliable, and
reproducible
 Pump should be automatically controlled;
however, option for manual operation in
case of power failure
 Must have adjustable stroke volume and
pulse rate
FYI

The average human heart can pump up to
30 liters of blood per minute under
extreme conditions.
 In the operating room setting this is not
necessary due to may reasons:
– patient is asleep
– patient is given muscle relaxants
– patient metabolic rate is greatly reduced
– patient is cooled during CPB
Types of Blood Pumps

Kinetic Pumps
– Centrifugal pumps

Positive Displacement Pumps:
– Rotary Pumps
– Reciprocating Pumps
Centrifugal Pumps

The pumping action is performed by the
addition of kinetic energy to the fluid
through the forced rotation of an impeller
Centrifugal Pumps

Designed with impellers arranged with
vanes or cones
 Centrifugal pumps are magnetically driven
and produce a pressure differential as
they rotate
 It is the pressure differential between the
inlet and outlet that causes blood to be
propelled
Positive Displacement
Pumps

This type of pump moves blood forward
by displacing the liquid progressively,
from the suction, to the discharge opening
of the unit
Positive Displacement
Pumps (continued)

Rotary Pumps
– Roller Pumps
– Screw Pumps
 Reciprocating Pumps
– Pistons
– Bar Compression
– Diaphragm
Rotary Pumps

Rotary Pumps
– use rollers along flexible tubing to provide
the pumping stroke and give direction to
the flow
 Archimedean Screw Pumps
– a solid helical rotor revolving within a stator
with different pitches so the blood is drawn
along the threads
Rotary Pumps (continued)

Multiple Fingers
– the direction of flow is produced by a series
of keys that press in sequence against the
tubing
Reciprocating Pumps

Pistons
– this pump uses motor driven syringes that
are equipped with suitable valves,
delivering pulsatile flow
– limited to low output capacity
 Bar Compression
– blood moves from the alternate
compression and expansion of the tube or
bulb between a moving bar and a solid
back-plate
Reciprocating Pumps
(continued)

Diaphragm Pumps
– with a flat diaphragm or finger shaped
membrane made of rubber, plastic, or
metal, blood is propelled forward
 Ventricle Pumps
– a compressible chamber mounted in a
casing and are activated by displacement
of liquid or gas in the casing
Two Most Common Pumps
Today

Roller Pump
– Advantages


Occlusive, therefore if power goes out the
arterial line won’t act as a venous line
Out put is accurate because it is not
dependent of the circuits resistance
(including the patients resistance)
– Disadvantages

Can cause large amounts of damage to
blood (hemolysis) if over-occluded
Two Most Common Pumps
Today (continued)

Centrifugal Pump
– Advantages





Reduced hemolysis
No cavitation
No dangerous inflow/outflow pressures
Air gets trapped in pump
No need to calibrate
Two Most Common Pumps
Today (continued)

Centrifugal Pump
– Disadvantages




Causes over-heating
Over heating promotes clotting
Difficult to de-air
If power goes out, arterial line acts like a
venous line
Roller Pump
Two Types of Perfusion

Pulsatile Flow (simulates the human heart)
– Decreases peripheral resistance
– Increases urinary flow
– Better lymph formation
– Increases myocardial blood flow
– Need 2.3 times more energy to deliver
blood in a pulsatile manner than with nonpulsatile flow
Two Types of Perfusion
(continued)

Non-Pulsatile Flow
– Simply means continuous flow
Various Opinions on
Pulsatile Flow

Advocates
– It simulates the beating heart, aiding in
preserving capillary perfusion and cell
function
– With the extra energy produced with
pulsatile flow, we can avoid the closing
down of the capillary beds.
Various Opinions on
Pulsatile Flow (continued)

Opponents
– Pulsatile flow is a more complex procedure
for minimal benefits
– Capillary Critical Closing Pressure:
(although never seen under microscope)
The belief that when the pressure in the
capillary system goes below a certain point
the capillaries will close…reducing the gas
exchange between the blood and the
tissues
Flow, Pressure and
Resistance

Blood Flow: defined as the movement of
blood flow through the body, or in our
case, the extracorporeal circuit

Pressure: defined as the force vector that
is exerted at a 90 degree to that of blood
flow

Resistance: the force vector opposite to
that of pressure
The Relationship Between Pressure,
Flow and Resistance

Flow = Pressure / Resistance

Resistance = Pressure / Flow

Pressure = Flow X Resistance
Laminar Flow

Definition: Referring to blood flow, where
all the layers run parallel to the walls of
the blood vessels or tube
Reynold’s Number





An equation that enables us to determine
whether blood flow is laminar or turbulent
R.N = 2 (fluid density)( average velocity)(r)
(fluid viscosity)
If R.N. < 2000 flow is laminar
If R.N. > 3000 flow is turbulent
If R.N. between 2000 and 3000 flow
unstable
Reynold’s Number
(continued)

Blood acts as a Newtonian fluid, one that
has a constant viscosity at all velocities

A thixotropic fluid : the viscosity is altered
by changing velocities
Viscosity

Another important factor that effects the
flow of blood

Viscosity = Shear Stress / Shear Rate
Poiseuille’s Law

Expresses how different variables effect
flow. The most notable variable is radius
of the vessel or tube.

Flow = (Pressure gradient)(3.14)(radius 4)
8 (viscosity)(length)
Resistance


The main source of resistance is the
arterioles. This resistance comes after the
pressure source (the heart) giving up
peripheral resistance
TPR = MAP/F
 TPR= Sum of all factors effecting the
resistance to flow
Resistance (continued)
• SVR= PA - PV / Q
•
•
•
PA= MAP
PV= RAP
Q= Flow Rate
• SVR= (MAP-CVP/C.O.) X 80
Pressure
• When the heart contracts and the pressure
rises, the highest point is called systolic
pressure
• When the heart relaxes and the aortic
pressure reaches the lowest point.. this is
called diastolic pressure
• Mean arterial pressure = SP/DP
Pressure (continued)
• Because vessels aren’t normally rigid,
rather they are flexible, you will see a nice
rise in the arterial wave form.
• If the aorta, the most flexible vessel, is
rigid, the systolic pressure would rise
sharply. (A good diagnostic indicator)
Resistance

The main source of resistance is the
arterioles

Viscosity = Shear Stress / Shear Rate

F= (P1-P2) X 3.14 X r4/8L X Viscosity