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Microcirculation is the blood flow through the smallest vessels in the circulatory system, i.e. artioles, venules, shunts and capillaries. Microcirculation exists in all tissues and organs except for the cornea. Its main functions are:
- Transport of blood cells and substances such as oxygen to/from tissues (nutritive flow)
- Aids in blood pressure regulation
- Acts as a thermoregulator (skin)
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Microcirculatory blood flow can exhibit vasomotion, rhythmic oscillations in the vascular tone caused by changes in smooth muscle constriction and dilation. This phenomenon is controlled locally as well as systemically. The variations are usually 4-10 cycles per minute (cpm) and may vary with the temperature. Interestingly, vasomotion is significantly reduced in microneuropathy and problematic flaps. Vasomotion can be studied using the PeriFlux System 5000.
The microcirculation also shows extreme dynamics. Under normal conditions, the blood perfusion can differ several thousand percent between a cold and warm fingertip. It also exhibits large spatial variations and may vary up to 100 percent in forearm skin if the measurement site is moved one millimeter. Blood perfusion measurements using laser Doppler will reflect these extreme dynamics and large spatial variations.
Parameters known to influence the microcirculation are:
- Temperature of the subject
- Systemic blood pressure
- General status (stress, food, medication, smoking, etc)
- Mental activity
- Physical activity
- Age
As a consequence of the large normal variations observed in the microcirculatory blood flow, provocations are often used to facilitate data interpretation. Provocations allows the user to look at the response to a certain provocation rather than just a basal value of micorcirculatory flow. Commonly used provocations include:
- Heat - maximum dilation, tissue reserve capacity
- Occlusion - post-occlusive reactive hyperemia
- Drugs - patch tests, iontophoresis, injections
- Posture - veno-arterial reflex, leg elevation
- Cooling - Raynaud phenomena
- Electrical stimulation - c-fiber stimulation
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