Vascular Science Flashcards
(45 cards)
Types of conditions a vascular scientist encounters?
- Claudication/ limb ischaemia (Peripheral vascular disease)
- TIA/ stroke (cerebrovascular disease)
- Aneurysm
- Deep vein thrombosis
- Varicose veins
What are the 3 vascular beds in the body?
- Peripheral : PVD is a disorder of the blood vessels outside of the heart and brain
- Cerebral: Cerebrovascular is a disorder of the blood vessels leading to and in the brain
Coronary: Coronary disease is a disorder of the blood vessels feeding the heart
What can vascular disease do to blood vessels?
Can cause blood vessels to:
- widen (aneurysm)
- narrow (atherosclerosis/thrombosis)
- spasm (arteritis)
This can occur in arteries or veins
What are the 5 types of blood vessels? What are their functions?
Arteries: Transport high pressure blood from the heart to smaller arteries and arterioles
Arterioles: Connect arteries and capillaries
Capillaries: Allow gas exchange, nutrient transfer and waste removal between blood and tissue fluid
Venules: Connect capillaries and veins
Veins: Act as a reservoir of blood and transport low-pressure blood from venues to heart
Properties of arteries, capillaries and veins?
Arteries: blood away from heart, thicker walls, withstand high pressure
Capillaries: Walls 1-cell thick, exchange gases between blood and tissue cells
Veins: Blood back to heart, thinner walls, low pressure, large lumen, valves prevent back flow of blood, skeletal muscles enhance venous return
What are the layers of arteries and venous vessels?
- Tunica intima
- Endothelium
- Subendothelial layer
- Internal elastic lamina (arteries)
- Tunica media (smooth muscle and elastic fibres)
- External elastic lamina (arteries) - Tunica externa (collagen fibres)
Constituent’s of capillaries?
simple squamous epithelial (endothelial) cells forming a basement membrane (tunica intima)
Risk factors of vascular disease, CVD and coronary artery disease?
Raised cholesterol
Diabetes
Smoking
High blood pressure
Genetics
Gender
Age
Obesity
Vascular disease assessments
- Clinical signs & symptoms
- Physiological measurements (ABPI, toe pressures)
- Ultrasound/Doppler
Diagnostic tests performed for vascular disease?
Duplex (Doppler ultrasound)
ABPI
Is ultrasound safe?
British Medical Ultrasound Society (BMUS)
Ultrasound should only be used:
For medical diagnosis
By trained professional
For the shortest time achievable
With the lowest power output achievable
Generally considered safe as it doesn’t use ionising radiation to create images, only high frequency sound waves. It has been used in medical imagery for decades, and is a painless procedure. Ultrasound machines display mechanical and thermal indexes as a way to reduce ultrasound-induced bioeffects. Thermal index: ultrasound induced bioeffect in which sound waves absorbed by the skin could heat tissue. Mechanical: ultrasound beam can cause non-thermal effects such as cavitation (when a liquid is exposed to high frequency ultrasound, gas pockets form then collapse violently - can cause tissue damage.
What is ultrasound?
Used for diagnostic observation for over 50 years
Continued research
US government relaxed regulations in 1992 to allow power output x8 times prev level
This allowed better image quality but long term effects unknown
What are the risks associated with ultrasound?
1.Thermal effects
(some u/s machines are capable of causing a 6 degree increase) potential risk to foetus/eye
2.Mechanical effects (cavitation)
Pulsation of air bubbles can cause increase movement of cell, cell
damage, increase in platelets
How else can ultrasound be used?
Lithotripsy to break up kidney stones
How do we reduce risks of ultrasound?
‘ALARA’ principle:
As
Low
As
Reasonably
Achievable
Reduce the power output
Only use B mode where possible keeping colour and spectral to a minimum
Reduce exposure time
Keep the probe moving
Change probe frequency
Move focal zone
When should care especially be taken?
Imaging tissue with low blood supply -The eye
Imaging air filled areas – lungs/bowel
Using focused beam
Using spectral/colour Doppler
Areas near bone – Foetus
Using contrast agents (microbubbles)
How does the ultrasound machine ensure safety?
U/S equipment now has to display 2 figures which warn the operator of these risks
These are; Thermal Index (TI) and Mechanical Index (MI)
TI – Gives the indication of the relative potential for a tissue temperature rise
MI – gives the indication of the relative potential for ultrasound to induce an adverse bio effect by anon thermal mechanism such as cavitation
For Vascular Studies, what should TI and MI be?
TI should be kept below 1.0 (BMUS)
MI should be kept below 0.7 (BMUS)
Limitations of Doppler ultrasound?
- Operator dependant skill
- Calculation error (5% angle error can result in measurement error)
- Calcification
- Bowel gas
Are there any side effects to ABPI?
No known adverse effects of continuous wave Doppler
However;
Should not perform an ABPI on a patient with a fistula, had a mastectomy or a distal bypass graft
Be aware of any existing heart or breathing problems in patients who are to perform an exercise test
Limitations fo ABPI?
May give inaccurate readings if vessel calcified, large dressings or oedematous leg
How do you ensure equipment error/safety?
Ensure equipment serviced
Ensure regular equipment QA
What is ultrasound?
Sound is a form of mechanical energy
Sound is a vibration that is transmitted through an elastic solid, liquid or gas
Sound is measured in frequency - Hertz (Hz – cycles per second)
Audible frequency is in range 20 – 20,000Hz
Ultrasound is all sound above audible range so >20KHz but typically 2 – 12MHz for medical applications.
Infrasound is <20Hz.
Ultrasound is a noninvasive imaging test that shows structures inside your body using high-intensity sound waves. An ultrasound picture is called a sonogram.
A device called a transducer, or probe, emits high-frequency sound waves into the body.
These sound waves travel through the body and are reflected back to the transducer when they encounter different tissues and organs.
The transducer contains piezoelectric crystals that convert electrical energy into sound waves and vice versa.
The transducer detects the returning sound waves (echoes) and converts them into electrical signals.
A computer analyzes the electrical signals, taking into account the speed of sound and the time it takes for the echoes to return, to create a two-dimensional image of the internal structures.
Different tissues and organs reflect sound waves differently, allowing the ultrasound machine to distinguish between them.
Real-time Imaging:
Ultrasound imaging can provide real-time images, allowing doctors to see the movement of organs and blood flow.
A special type of ultrasound, called Doppler ultrasound, can show the movement of blood flow and other moving structures.
Ultrasound imaging is considered safe because it does not use ionizing radiation
How is U/S generated?
Piezoelectric effect
Deforming some materials will produce a voltage, and conversely applying a voltage will cause deformity.
Applying an alternating voltage to the transducer causes the piezoelectric material to deform/oscillate which produces ultrasound.
Frequency of oscillation is proportional to frequency of ultrasound produced.
Typical material is lead zirconate titanate – made piezoelectric by placing in a strong electric field at high temp during manufacture.
Combining piezoelectric ceramic with non-piezoelectric polymers improves performance of the performance of the transducer.
