Physical effects of ultrasound:
1- Thermal effects
2- Non-thermal effects
3- Effect of US in tissue repair
First: thermal effect
@ It is due to generation of heat within the tissue due to adsorption of US.
@ Tissue with high amount of protein absorbs US more than other tissues.
@ Generation of heat within the tissue will decrease pain, joint stiffness & increase blood flow.
@ Thermal effect achieved if the temperature of the tissue is raised to 40°c - 45°c for at least 5 minutes, so the treatment time should not be less than 5 minutes.
@ It is important to know:
* Type of injury.
* Nature of the tissue of injured area.
* Which freq to use?!!
* The blood flow in injured area.
* Never apply US over metal prosthesis (mode conversion ( increase temperature ( pain.
Second: non-thermal effect
Non-thermal effect cause@
* Stimulation of tissue repair.
* Increase blood flow in chronically ischemic tissue.
* Protein synthesis.
* Bone repair.
@ This is can be achieved by:
1- Cavitations ( it is formation of very small bubbles in gas containing fluid which leads to changes in cell permeability to various ions as calcium "by low pressure amplitudes".
2- Acoustic streaming ( it is the unidirectional movement of the fluid in the US field which leads to: * Stimulation of cell activities.
* Stimulation of cell permeability & 2nd messenger activities ( acceleration of tissue repair because of: 1- Increase protein synthesis.
2- Increase secretion from mast cell.
3- Changes in fibroblast mobility.
4- Increase the uptake of 2nd messenger calcium.
5- Increase production of growth factors by macrophages.
3- Standing waves ( it is formed by interact of oncoming waves & reflected waves of US. This reflection due to the hits of US waves at the interface between 2 different tissues (e.g. bone & muscle). There are 3 points of this wave, maximum& minimum antinodes "where gas bubbles collected" & fixed nodes "where cells collected"
When standing waves formed, the cells move to collect at suitable pressure points, but in case of fixed cells which are not movable "as endothelial cells which line the blood vessels" they will be damaged.
Important: move the applicator "head" of US continuously & use the lowest intensity required to cause the effects to minimize the standing waves.
Third: effect of US in tissue repair
1- during inflammation phase
@ There is much evidence that US can produce membrane changes in a number of cell types. This range from gross destructive changes to more subtle reversible changes. Gross changes can be achieved if levels of US are high enough. Even when using therapeutic levels of US it is possible to achieve the destruction if a standing wave field is allowed to form because of bad clinical practice (failing to keep the applicator head moving).
@ Effects of US during inflammatory phase:
1- Increase cell permeability.
2- Increase releases of serotonin from cells.
3- Increase production of platelets which contain wound factors. 4- Stimulate mast cells degranulation ( releasing histamine into the surrounding tissue by increase its permeability to calcium which increase synthesis & secretion of wound factors. 5- Change the permeability to potassium.
6- Reduction sodium-potassium pump activity "if it occurs in neural plasma membrane ( inhibits the transduction of noxious stimuli & neural transmission ( pain relief.
@ It has been shown that a single treatment of US if given soon after injury "during the early inflammatory phase" can stimulate mast cell to degranulate & releasing histamine into the surrounding tissue. @ Us at an intensity of 0.5 w/cm² & freq of 0.75 MHz is the most effective in encouraging the immediate release of factors already present in the cell cytoplasm & more potent in their effect on stimulation of fibroblast population...
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