physical & physiological effects of ultrasound 3rd lect

8/4/2019 Physical & Physiological Effects of Ultrasound 3RD LECT

http://slidepdf.com/reader/full/physical-physiological-effects-of-ultrasound-3rd-lect 1/22

Physical & Physiological Effects of

Ultrasound:

• If heat generated ≠ heat dissipated ; whichaccounts for thermal effects [less vascular tissue-dense connective tissue-tendon or

ligament].• If heat dissipation = heat generation; which

accounts for non-thermal effects [highly vascular tissues-muscle] . Using low intensities or pulsing the output achievesnon-thermal effects.



Thermal Effects:

– preferential heating of collagen tissue and

effective penetration of this energy to deeply

placed structures.

– may cause a temporary increase in their extensibility, and hence a decrease in joint

stiffness.

•

effect of reducing pain and muscle spasm and promoting healing processes.



• Non-Thermal Effects:

1) Cavitation:

2) Acoustic Streaming:3) Standing Waves:

4) Micromassage:



1) Cavitation: -Formation of tiny gas bubbles in the

tissues. These bubbles, generally of a micron (10 -6 m)or so in diameter.

– This can be of two types

a) Stable cavitation occurs when the bubbles oscillate toand fro within the ultrasound pressure waves but remainintact.

b) Transient (or collapse) cavitation occurs when the volume

of the bubble changes rapidly and then collapses(implodes) causing high pressure and temperaturechanges and resulting in gross damage to tissues, whichis only likely to occur at high intensities.



2) Acoustic Streaming:

• Acoustic streaming is a steady fluid flow due toradiation torque.

• These very small fluid movements also occur around cells, tissue fibres, and other boundaries,

which is known as microstreaming which exertsviscous stress on the cell membrane and thusmay increase membrane permeability.

• Increased rate of ion diffusion increased

calcium uptake, increased secretion from mast cells, and greater growth factor production by macrophages.



3) Standing Waves:• Standing waves are due to reflected waves

being superimposed on the incident waves.

• There is also the possibility of marked local heating where the amplitude of the

combined waves is high. Which is known as

“hotspots”.



4) Micromassage:

• The micromassage effect of ultrasound occurs at a cellular level where the cells are

alternately compressed and then pulled

further apart.• Reduce oedema.



Effect of US on inflammation and

tissue repair:

Acute Stage:• increased calcium ion diffusion across the cell membrane

•Increased production and release of wound-healing

factors

• Release of histamine from mast cells and growth factors

released from macrophages.

• In this way, ultrasound has the potential to accelerate

normal resolution of inflammation.

• Thus, ultrasound has a pro-inflammatory, not an anti-

inflammatory action.



Proliferative (Granulation) Stage: [ 3 days after ]

1. During repair, fibroblasts may be stimulated

to produce more collagen; by increasing cell

membrane permeability.

2. The enhanced release of growth factors

from macrophages following exposure to US

may cause proliferation of fibroblasts.

3. Not only is more collagen formed but it is

also of greater tensile strength after

ultrasound treatment.



Remodeling Stage(maturation phase):

• This stage lasts months or years until the new

tissue is as near in structure as possible to theoriginal tissue.

• Ultrasound is considered to improve the

extensibility of mature collagen such as is found in scar tissue, which occur by

promoting the reorientation of the fibres

(remodelling), which leads to greater elasticity without loss of strength.



Therapeutic Uses of Ultrasound:Ulcers:

• Ultrasound promotes healing of varicose ulcersand pressure sores (decubital ulcer).

Pain relief: tender point

• Ultrasound is used in herpes zoster, low

backache, prolapsed intervertebral disc (PIVD)and many other conditions like and plantar

fasciitis..

• Scar tissue: Ultrasound improves quality of scar

tissue and excessive fibrous tissue likeDupuytren’s contracture.



Acute tissue injury:

• Perineal post-natal scar pain.

• Muscle strain

• Ligament sprain

• Tendon injuries.

Chronic Indurated Oedema:• The mechanical effect of ultrasound has an effect

on chronic oedema and helps in its treatment. Italso breaks down adhesions formed between

adjacent structures.



Dangers of Ultrasound:

– Burns could occur if the heat generated exceeded

the physiological ability to dissipate it.

– Tissue destruction would result from transient

cavitation. – Blood cell stasis and endothelial damage may

occur if there is standing wave formation.

These dangers would be more likely with high-intensity continuous output with a stationary

head or over bony prominences.



Contraindications of Ultrasound:

Rapid dividing tissues:

• it might encourage neoplastic growth and provoke metastases. Therefore, treatment

over tumours or over tissue in precancerousstates should be avoided.

Tuberculosis:

•Due to the possible risk of reactivatingencapsulated lesions tuberculous regionsshould not be treated.



Pregnant Uterus: To the rapidly dividing anddifferentiating cells of the embryo and fetus

should be avoided by not applying treatmentover the pregnant uterus.

Epiphyseal Plates: Avoid giving ultrasound oncartilaginous epiphyseal plates because growth of

the bone is impeded.Radiotherapy: Areas that have received

radiotherapy in the last few months should notbe treated because of the risk of encouraging

pre-cancerous changes.



Spread of Infection:

• Bacterial or viral infection could be spread by

ultrasound, presumably by facilitating

microorganism movement across membranes

and through the tissues. The low-grade

infections of venous ulcers, or similar, would

seem to be safe to treat.



Vascular Problems:

•haemarthrosis or haematoma or uncontrollable haemophilia.

• Severely ischaemic tissues should be avoided

because of the poor heat transfer.• Venous thrombosis might extend the thrombus

or disrupt its attachment to the vein wall

forming an embolus. Areas of atherosclerosisare best avoided for the same reason.



Specialized Tissue:

• The fluid-filled eye offers exceptionally good

ultrasound transmission and retinal damage

could occur.

• Treatment over the gonads is not recommended.



Implants:

• Smaller and superficial implants, like metal bone-fixingpins subcutaneously placed; as a precaution, low dosesshould be used in these circumstances.

• Plastics used in replacement surgery, such as high-density polyethylene and acrylic should be avoided.

• Treatment over implanted cardiac pacemakers should not be given because the sonic vibration may interfere with the pacemaker’s stimulating frequency.



Relative C/I

Anaesthetic areas:

• High doses should not be given over

anaesthetic areas.

Nervous System:

• Treatment over the cervical ganglia or vagus

nerve might be dangerous in cardiac disease.



Pulsed Ultrasound:

• A circuit in the ultrasonic generator is arranged toturn the ultrasound on in short bursts or pulses.

• Many therapeutic ultrasound generators produce2 ms pulses and vary the intervals betweenpulses. This can be expressed either as:

• The mark : space ratio, which is the ratio of thepulse length to the interval

• The duty cycle, which is the ratio of the pulselength to the total length of the pulse plusinterval, expressed as percentage.

• This reduces the time averaged intensity.



Thank You

physical & physiological effects of ultrasound 3rd lect

Documents