145-168 Flashcards
A patient is standing. When measured at the level of the heart, the patient’s systolic blood pressure is 100 mmHg.
What will the systolic pressure be if a measurement is obtained at the level of the patient’s ankle?
What will the systolic pressure be if a measurement is obtained at the level of the patient’s ear?
ankle-level systolic pressure: 195 mmHg
ear-level systolic pressure: 70 mmHg
Assume you obtain measurements of the venous blood pressure from a standing patient. When measured at the level of the heart, the patient’s venous blood pressure is 12 mmHg.
What will the venous pressure be if a measurement is obtained at the level of the patient’s ear?
0 mmHg
What kind of anatomic structure is the diaphragm?
The diaphragm is a large muscle located below the lungs that plays an important role in breathing. When the diaphragm contracts, it flattens and moves downward. When the diaphragm relaxes, it becomes a dome shaped and moves upward.
Name the two body cavities that are separated by the diaphragm.
thorax
abdomen
what effect does the diaphragm have on the thorax and abdomen when we inhale or take in a breath of air?
When we breathe in, the diaphragm contracts and moves downward, resulting in compression of the abdomen. Simultaneously, the thorax expands and is decompressed.
what effect does the diaphragm have on the thorax and abdomen when we exhale or let out a breath of air?
When we breathe out, the diaphragm contracts and moves upward, resulting in compression of the thorax. At the same time, the abdomen expands and is decompressed.
During inspiration, is venous return to the heart from the upper extremities increased or decreased?
increased
During expiration, is venous return to the heart from the upper extremities increased or decreased?
decreased
During inspiration, is venous flow from the lower extremeties increased or decreased?
decreased
During expiration, is venous flow from the lower extremities increased or decreased?
increased
What is energy?
generally defined as having the capacity to perform work
what is an energy gradient?
when the energy at one location is different than the energy at another location, an energy gradient is said to exist.
with regard to hemodynamics, why is an energy gradient important?
In hemodynamics, an energy gradient is important because it is the reason why blood flows from one region to another.
what is friction?
“the act of rubbing”. When two structures rub against each other, heat or thermal energy is created.
with regard to hemodynamics, why is friction important?
In hemodynamics, friction acts to decrease the total energy of blood as it flows through circulation. As blood flows through a vessel, some of the energy is lost as a result of friction.
what is inertial loss?
When the speed of an object changes, there is a loss of energy. This energy loss is called interial loss
with regard to hemodynamics, why is inertia important?
in hemodynamics, energy is lost as blood speeds up and slows down.
what is viscosity? What are its units?
the thickness of a fluid
units of Poise
What is viscous loss?
refers to the loss of fluid energy from internal friction between molecules of the fluid as the slide by each other
with regard to hemodynamics, why is viscous loss important?
in hemodynamics, viscous loss acts to decrease the total energy of blood as it flows through circulation
What happens to the volume of blood in the veins when venous pressure is very low?
What happens to the shape of the cross section of veins when venous pressure is very low?
When venous pressure is very low, the veins are only partially filled with blood (volume is reduced). Consequently, the veins partially collapse and their shape becomes flattened.
What happens to the volume of blood in the veins when venous pressure increases?
What happens to the shape of the cross section of veins when venous pressure increases?
When venous pressure increases, the veins fill completely with blood (volume is increased) and their shape becomes rounded.
Assume that water is flowing through a tube at a constant velocity. The pressure gradient from one end of the tube to the other end is then doubled. What will happen to the flow of the water?
The flow of water will also double.
Assume that water is flowing through a tube at a constant velocity. The flow is then doubled. What will happen to the pressure gradient?
The pressure gradient will also double.
What is an ultrasonic imaging artifact?
any imaging error
Four possible causes of ultrasonic imaging artifacts
violations of certain assumptions about the physics of ultrasound
equipment malfunction or incorrect design
the inherent physical limitations of ultrasonic imaging
operator error
Image acquisition by ultrasonic imaging systems is based on certain assumptions about the physics of ultrasound. Artifacts occur when one or more of these assumptions are either not correct or are violated.
Identify the 6 basic assumptions incorporated into the design of ultrasound systems to bring about accurate image acquisition
- ultrasound travels in a straight line
- Ultrasound reflections are created only from structures along the main axis of the sound beam
- The strength of a reflection is related to the scattering characteristics of the anatomic structure that produces it.
- Ultrasound always travels through soft tissue with an exact speed of 1,540 meters per second
- The ultrasonic imaging plane is extremely thin
- Ultrasound pulses travel directly to a reflector and then back to the transducer
Do all artifacts hinder the diagnostic accuracy of clinical ultrasound?
No
Describe the appearance of a reverberation artifact.
Reverberation artifact appears as multiple, equally spaced echoes displayed on the image at ever-increasing depths
What causes reverberation artifact?
Occur when two or more strong reflectors are alrigned with the main axis of the ultrasound pulse.
What can a sonographer do to eliminate reverberations?
May be able to eliminate these artifacts by changing the orientation of the transducer. When the reflectors are no longer in the path of the sound pulse, the reverberations may vanish.
What is refraction?
a change or bending in the direction of an acoustic pulse as it travels from one medium to another
what causes refraction artifact?
occurs at the boundary between two media when two conditions occur. First, the incidence of the sound beam must be oblique to the boundary. Second, the propagation speeds of the two media on either side of the boundary must be different.
what is the effect on an image when refraction occurs?
When refraction occurs, the US system does not recognize that the sound beam has changed direction, and assumes that the pulse has traveled in a straight line. The result is that a copy or duplicate of the anatomic structure is displayed on the image.
With regard to ultrasonic images, what does hypoechoic mean?
used when describing a structure that produces echoes that are less bright than echoes from surrounding tissues or structures
what does hyperechoic mean?
used when describing a structure that produces echoes that are brighter than echoes from surrounding tissues or structures
what does anechoic mean?
refers to the complete absence of echoes
what does isoechoic mean?
used when describing a structure that produces echoes having a brightness that is equal to that of echoes from surrounding tissues or structures
what term would be used to describe a region of tissue displayed on an ultrasound image that appears to have uniform brightness?
homogeneous
what term would be used to describe a region of tissue displayed on an ultrasound image that appears to show variations in brightness?
heterogeneous
Describe a shadowing artifact
characterized by either the absence or a severe reduction in the strength of echoes, extending beyond a highly reflective structure.
What produces shadowing artifact?
when an ultrasound pulse travels through a structure that is highly reflective or absorbent, the sound beam becomes weakened. The amount of attenuation that occurs is considerably greater than normal. Consequently, structures that lie behind the highly attenuating structure will produce weak or faint echoes on the image, and sometimes no echoes at all. This results in a “shadow” on the image.
How can the sonographer offset some of the effects of shadowing artifact?
changing views
describe an enhancement artifact
characterized by the appearance of abnormally bright reflections that begin just beneath a weakly attenuating structure and extend beyond it
what produces enhancement artifact?
when an ultrasound pulse travels through an anatomical structure that has abnormally low attenuation, the sound beam retains atypical strength or intensity. Consequently, the strength of echoes from deeper structures is excessive, and they are displayed on the image with an abnormal degree of brightness.
how can the sonographer offset some of the effects of enhancement artifacts?
changing views
Describe a focal banding artifact
characterized by the appearance of a horizontal band of abnormally bright echoes from structures located at the depth of the focus
what produces a focal banding artifact?
the focal zone of a sound beam has the greatest intensity and, as a result, may produce reflections of unusually large magnitude. Consequently, these high intensity reflections from the focal zone may be displayed on the image with an abnormal degree of brightness
how can the sonographer offset some of the effects of focal banding artifacts?
attempt to decrease the amount of beam focusing
Describes a mirror image artifact
the appearance of a second copy of a single anatomical structure in a different location
What produces mirror image artifact?
A strong smooth boundary is struck by a pulse at an oblique angle and the pulse then reflects off the boundary. The pulse then strikes a structure, reflects back to the boundary, and finally back to the transducer
how can the sonographer eliminate a mirror image artifact?
change the orientation of the ultrasound beam
Assume that two anatomic structures are located 0.5 mm apart from one another and that one of the structures is in front of the other and are oriented parallel to the beam’s main axis. Only a single, long reflection is displayed on the image, however. What is this error in imaging called?
What is the cause of this artifact?
Pulse length artifact
occurs because an acoustic pulse has a finite length.
