Cardiovascular Techniques II Flashcards
Describe the setup for the technique of pressure myography.
- For small vessels including arterioles > 50μm
- Segments mounted on two glass microcannulae and pressurised to an appropriate transmural pressure
- Kept in a chamber with physiological salt solution at 37 degrees with oxygen
What is the vascular myogenic response?
- As pressure increases, a threshold is reached
- Beyond the threshold, contraction increases to counteract the increased pressure
- Stretch of smooth muscle causes vasoconstriction
- This is an example of autoregulation
What is the role of the myogenic response?
- Intrinsic property of vessels - autoregulation
- Stabilises blood flow despite increases in pressure (between 40-100mmHg)
- Contributes to basal vascular tone
A larger shear stress on endothelial cells produces what autoregulated response?
Large flow-induced vasodilatation (relaxation)
Flow-induced vasodilation is impaired under what circumstances?
In cardiovascular diseases such as atherosclerosis and ageing
Describe 5 advantages of isobaric diameter recording (pressure myography)
- Examine functional properties of small vessels, inc. myogenic contraction and flow-induced dilation
- Freshly prepared vessels are viable for many hours
- Detail investigation into mechanisms of action
- Compare vascular functions in control vs disease states
- Can be combined with other techniques
Describe 3 disadvantages of isobaric diameter recording.
- Dissection and mounting of vessels requires skills and suitable apparatus
- Isolation of vessels might remove influences from surrounding tissues
- Difficult to study longer-term changes in vascular function using the same vessels
How are isolated vascular beds used?
- Cannulate supply artery to a vascular bed
- E.g. measure perfusion pressure under constant flow rate
- Flow = perfusion pressure/vascular resistance
What is the Langendorff heart preparation?
- Cannulate the ascending aorta (retrograde perfusion)
- Measure coronary perfusion pressure under constant flow rate
- Viable for a few hours
- Can also examine left ventricular contractions and heart rate
What is Doppler shift?
Change in frequency of a wave (light or sound) due to motion of the source or the reciever.
What is Doppler flowmetry?
- For measurement of blood flow in vivo
- With a stationary source and receiver, measure Doppler shift due to reflection by red blood cells
- Doppler signal indicates amount of red blood cells that flow through a unit area per unit time
- Blood or tissue perfusion units (ml x min-1 x 100-1 g tissue)
- The larger the Doppler signal, the greater the blood flow
What is Ultrasound Doppler flowmetry?
- For blood flow in arteries
- High-frequency sound waves (ultrasound) for higher velocity blood flow
- Allows measurement of higher velocity blood flow
How can ultrasound scanning be used in humans to test in vivo for endothelial function?
- Flow-induced dilation is tested using ultrasound Dopper flowmetry
- A pressure cuff is used to stop and reintroduce flow, before measuring the response
- A reduced FID response may indicate disease - e.g. hypertension, diabetes
Name 4 advantages of using Dopper flowmetry.
- Examine changes in blood flow in vivo
- Compare vascular functions in control vs disease states
- Used for non-invasive measurements
- Allows long-term measurement of blood flow in the same vessels
Name 4 disadvantages of using Doppler flowmetry
- Relative rather than absolute measurements of blood flow - not precise
- Signal to noise ratio depends on tissues and machines - may be low
- Invasive procedures and anaesthesia may be necessary
- Expertise required for experimentation, data analysis and interpretation
