Chapter 18 Flashcards
Hemodynamics
is the study of blood moving through the circulatory system
Flow, also called volume flow rate
-indicates the volume of blood moving during a particular time
-Answers the question how much?
-Units are liters/min, ml/s or any volume over time
Velocity
-indicates the speed or swiftness of a fluid
-Answers the question how fast and in what direction
-Units are cm/s, m/min or any distance over time
Flow, there are 3 forms
Pulsatile
Phasic
Steady
Pulsatile flow
-occurs when blood moves with a variable velocity
-Blood accelerates and decelerates from cardiac contraction
- typically in arterial circulation
Phasic flow
-occurs when blood moves with a variable velocity
-Blood accelerates and decelerates from respiration
-often in venous circulation
Steady flow
-occurs when a fluid moves at a constant speed or velocity
-present in the venous circulation when individuals stop breathing for a moment
Laminar flow
-flow streamlines are aligned and parallel
-Characterized by layers of blood that travel at individual speeds
Plug flow
all of the layers travel at the same velocity
Parabolic
velocity is highest in the center and gradually decreases to its minimum at the vessel wall
-flow has a bullet-shaped profile
Turbulent flow
chaotic flow patterns in many different directions at many speeds
Eddy currents (vortex)
may appear as small swirling, rotational patterns
a murmur or a bruit
Sound associated with turbulent flow
- can be heard on auscultation with a stethoscope
critical Reynolds Number
number of > 2000
Energy Gradient
from high energy to low energy
pressure gradient
blood moving from high to low pressure
Kinetic energy
objects with greater mass and speed move more swiftly
Gravitational energy
objects move more swiftly from high to low gravitation
As blood flows through the circulation, energy is lost in 3 ways
Viscous loss
Frictional loss
Inertial loss
Viscous loss
Viscosity describes the thickness of a fluid, and more energy is lost with the movement of high viscosity fluids
-units of Poise [pwahz]
Frictional Energy Loss
occur when flow energy is converted to heat as one object rubs against another
Inertial Energy Loss
Refers to the tendency of a fluid to resist changes in its velocity
In the circulatory system inertial energy loss happens during 3 events:
Pulsatile flow
Phasic flow
Velocity changes
Stenosis
Is a narrowing in the lumen of a vessel and has these effects on blood flow
Resistance increases with
Increase in tube length
Increase in viscosity
Decrease in tube diameter
Ohms Law
The movement of fluid through a tube and the movement of electricity through a wire are similar
Venous Hemodynamics
Veins are thin and collapsible, low resistance vessels
Hydrostatic Pressure
Pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level
-Measured in mmHg
Hydrostatic Pressure and Blood Pressure
Blood pressure is only accurate if taken at heart level as it is not affected by hydrostatic pressure
Hydrostatic pressure in the standing person is estimated at:
100 mmHg at the ankle
75 mmHg at the knee
50 mmHg at the waist
-30 mmHg at the top of the head
Respiration has a profound effect on venous flow for 2 reasons
- Venous system is low pressure
- Muscles responsible for respiration alter pressures in the thorax and abdomen
Inspiration
-The diaphragm moves downward, and thoracic cavity expands, abdominal cavity compresses
-Thoracic pressure decreases, abdominal pressure increases
-Flow into the thoracic cavity and to the heart increases
-Flow from the legs into the abdominal cavity decreases
