What Are the Uses of Ultrasound for Pain Management?

The method of applying ultrasound to the human body to achieve therapeutic purposes is called ultrasound therapy. The use of ultrasound therapy is becoming wider and wider, and has far exceeded the original general therapies in physical therapy departments, such as ultrasound treatment of cancer, urinary lithotripsy and application of stomatology. Therefore, the concept of ultrasound therapy should be broad (including various special ultrasound Therapy) and narrow (referring to the non-invasive dose therapy commonly used in physical therapy).

Pan Yu	(Deputy Chief Physician)	Beijing Rehabilitation Center Rehabilitation Department
She Shuyan	(Deputy Chief Physician)	Beijing Rehabilitation Center Rehabilitation Department
Wang Luyi	(Resident)	Beijing Rehabilitation Center Rehabilitation Department

Introduction to Ultrasound Therapy

Sound waves above 20kHz are called ultrasound. The method of applying ultrasound to the human body to achieve therapeutic purposes is called ultrasound therapy. Ultrasound is a sound wave that exceeds the hearing limits of the human ear. The mechanical vibration of the sound source can cause the vibration of the surrounding elastic medium. The vibration propagates along the medium from near and far away, forming a mechanical wave-a sound wave.

Ultrasound with a frequency of 500 to 2500 kHz has a certain therapeutic effect. Frequently used in physical therapy is generally 800-1000 kHz. The use of ultrasound therapy is becoming wider and wider, and has far exceeded the original general therapies in physical therapy departments, such as ultrasound treatment of cancer, urinary lithotripsy and application of stomatology. Therefore, the concept of ultrasound therapy should be broad (including various special ultrasound Therapy) and narrow (referring to the non-invasive dose therapy commonly used in physical therapy). At the same time, with the advancement of modern science and technology, ultrasound is not only used for treatment, but also widely used in diagnostic, basic and experimental medicine, so it has been called "ultrasonic medicine" ^[1] .

Physical characteristics of ultrasound therapy

Ultrasound and sound waves are essentially the same. They are all mechanical vibration waves formed by the propagation of mechanical vibrations of an object in an elastic medium.

Ultrasound treatment of ultrasound transmission

1. Because sound waves are a form of material propagation energy, their propagation must depend on the medium, but they cannot propagate in a vacuum. This is different from light waves and electromagnetic waves.

2. When the ultrasonic wave propagates to the surrounding medium, it produces a dense and dense waveform. The elastic waves formed by this continuous compression layer and sparse layer alternately coincide with the direction of the sound source oscillation, which is an elastic longitudinal wave). Because the ultrasonic wave has a very short wavelength, it can be gathered into a narrow emission line beam and spread straight in a beam shape, so the propagation has a certain directivity.

3. Propagation speed The propagation speed of sound waves is related to the characteristics of the medium, and has nothing to do with the frequency of sound waves. The propagation speed of sound waves increases with the temperature of the medium.

4. Ultrasound absorption and penetration: When ultrasound propagates in a medium, its intensity decreases with its propagation distance, which indicates that the ultrasonic energy is absorbed, the absorption of ultrasound and the density, viscosity, thermal conductivity, and frequency of ultrasound, etc. related. Ultrasound is absorbed most in gas, less absorbed in liquid, and smallest absorbed in solid. The absorption coefficient in air is about one thousand times larger than that in water. And the absorption coefficient of the medium is directly proportional to the square of the ultrasonic frequency, so the attenuation of high-frequency ultrasound in the air is extremely severe. Therefore, although there is a very small air bubble under the acoustic head during treatment, it should also be avoided.

In practice, a half-valence layer or a half-absorptive layer is often used to indicate the ability of a medium to absorb ultrasonic waves. The semi-absorbing layer refers to the thickness when the ultrasonic wave is attenuated to half the original energy in a certain medium. The thickness of the semi-absorptive layer is large, indicating that the absorption capacity is weak. Different tissues have different half-absorptive layer values for the same frequency of ultrasound. For example, at 300 kHz, the semi-absorptive layer of muscle is 3.6 cm, the fat is 6.8 cm. It is 4.9 cm. The same tissue also absorbs different frequencies of ultrasound. The higher the ultrasound frequency, the more it absorbs and the shallower it penetrates. For example, 90 thousand cycles of ultrasound can penetrate 10 cm of soft tissue, and 1 trillion cycles of ultrasound will penetrate 5 cm. Megacycle ultrasound only penetrates a depth of 1 cm. Therefore, the ultrasound commonly used in physiotherapy is selected at 8000 kilocycles / second, and the penetration depth is about 5 cm.

5. Refraction, reflection and focusing: When ultrasonic waves propagate from one medium to another, part of the ultrasonic wave will be reflected back to the first medium (reflection) at the interface, and the rest will enter the second medium through the interface, but the transmission will occur. Directional deflection (refraction). The degree to which sound waves are reflected at the interface depends on the difference in sound resistance and the angle of incidence of the two media. The smaller the incident angle, the smaller the reflection angle, the less the ultrasonic energy reflection, and the higher the efficiency. The greater the difference in sound resistance, the greater the degree of reflection, (the product of the density of the medium and the speed of sound is called the sound resistance of the medium).

The reflection between the acoustic head and the air is nearly 100%, so paraffin oil is used as a contact agent during ultrasound treatment to reduce the reflection. Experiments have shown that only 35 to 40% of the ultrasonic energy entering the tissue from the acoustic head is reflected, while 60 to 65% is reflected. Due to the reflection between air and tissue, a large amount of ultrasonic energy is lost, so the ultrasound cannot pass through the lungs and the inflated stomach.

Based on the principle of reflection and refraction propagated by ultrasound, the lens and the arc reflection are used to focus the sound beam on the focal point to generate powerful energy, and to treat certain diseases, such as destroying brain tumors with beam ultrasound

Ultrasound treatment of ultrasound sound field

The spatial range in which ultrasonic waves propagate in a medium, that is, the area where the medium is subjected to ultrasonic vibration energy, is called an ultrasonic sound field. Because of its high frequency, ultrasound has similar beam emission characteristics. The section near the acoustic head is an almost parallel beam, which is called the near-field region. The beam then spreads and is called the far-field region. Due to this characteristic of the ultrasound field, in order to overcome the uneven energy distribution, the acoustic head should be moved slowly at the treatment site during treatment.

Ultrasonic sound field

The main physical quantities describing the ultrasonic sound field are sound pressure and sound intensity.

1. Sound pressure: When ultrasonic waves propagate through the medium, the particles of the medium reciprocate near its equilibrium position, which causes a dense and dense change in the medium. This dense change forms a pressure change, that is, sound pressure. Represents the intensity of ultrasound. Sound pressure is directly proportional to the frequency and amplitude of the ultrasonic wave, and inversely proportional to the sound resistance.

2. Sound intensity: The intensity of sound energy per unit of time, that is, the sound energy that passes through each square centimeter of area vertically per second. A common measurement unit is Watt / cm2 (W / cm2). The commonly used clinical treatment dose is below 3W / cm2.

Ultrasound treatment of the occurrence of ultrasound

There are various methods for generating ultrasonic waves, mainly using a piezoelectric ultrasonic generator, which is made according to the principle of piezoelectric effect. When a crystal with piezoelectric effect is compressed or stretched, an equal amount of charges with opposite signs will be generated on its force surface. This physical phenomenon is called piezoelectric effect ^[2] .

Biophysical characteristics of ultrasound in treating ultrasound

Mechanical effects of ultrasound treatment

When ultrasonic waves propagate in the medium, the particles of the medium reciprocate near its equilibrium position, which causes a sparse and dense change of the rhythm inside the medium. This sparse change forms a pressure change and can produce a fine massage effect on human tissue cells. Micro-massage is the most basic mechanism for ultrasound to treat diseases. This fine massage effect on cells can change the volume of tissue cells, reduce swelling, change the permeability of membranes, promote the exchange of metabolites, change the function of cells, and improve the regeneration capacity of tissue cells. Therefore, the treatment of certain local circulation disorders, such as malnutrition ulcers, works well. Some people have observed that under the mechanical effect of ultrasound, the amplitude of spinal cord reflection is reduced, the transmission of reflection is inhibited, and the bioelectrical activity of nerve tissue is reduced, so ultrasound has a significant analgesic effect. The mechanical effect of ultrasound can also lengthen and soften the hard connective tissue, which is used to treat scars, adhesions and scleroderma.

It can be seen that the mechanical effect of ultrasound can soften tissues, enhance penetration, improve metabolism, promote blood circulation, stimulate the nervous system and cell functions, so it has important therapeutic significance and occupies an important position in the mechanism of ultrasound therapy.

Ultrasound Therapy for Warming Effects

Ultrasound can generate heat when it acts on the body. The formation of heat in the body is mainly the result of the tissue absorbing sound energy. Its heat production has the following characteristics:

1. Because the amount of sound energy absorbed by each tissue of the human body is different, the heat production is also different. Generally, the heat effect of ultrasound is significant in bone and connective tissue, and fat and blood are the least. For example, when the ultrasound is applied at 5 W / cm2 for 1.5 minutes, the temperature rise is 1.1 ° C in the muscle and 5.9 ° C in the bone.

2. The unique feature of ultrasonic heat effect is that it can selectively heat in addition to general stool absorption. It is mainly generated at the interface of two different media, especially localized high fever on the periosteum. This has great significance in the treatment of sports injuries such as joints and ligaments. Therefore, the thermal effect (uniform heating) of ultrasonic waves is different from the diffuse thermal effect (uniform heating) of high frequency and other physical factors.

3. 79-82% of the heat generated by ultrasound will be taken away by blood circulation, and 18-21% will be dissipated by heat conduction from nearby tissues. Therefore, when ultrasound acts on tissues that lack blood circulation, such as the cornea, crystals, vitreous body, and testicles Should be very careful to generate overheating to avoid damage ^[3] .

Ultrasound treatment of cavitation

Ultrasonic waves generate sound pressure as they propagate in a liquid medium. When the negative sound pressure generated exceeds the cohesive force of the liquid, fine cavities appear in the liquid, that is, cavitation. There are two types of cavities, namely stable cavities and temporary cavities.

The stable cavity vibrates back and forth under the effect of sound pressure, and a local unidirectional liquid flow is generated around the cavity. This very small fluid flow is called microflow and plays an important role in ultrasound treatment. Microfluidics can change the permeability of cell membranes and the distribution of potassium and calcium ions on both sides of the membrane, thus speeding up the process of tissue repair, changing the electrical activity of nerves, and alleviating pain. The temporary cavity breaks down when the sound pressure changes, resulting in phenomena such as high heat, high pressure, light emission, and discharge, which have a damaging effect on the body.

Ultrasound therapy treatment principle

Ultrasound acts on human tissues to produce mechanical, thermal and cavitation effects, leading to accelerated blood flow in local tissues, improved blood circulation, increased peristalsis of blood vessels, enhanced cell membrane permeability, redistribution of ions, strong metabolism, and hydrogen ions in tissue Decreased concentration, increased PH value, increased enzyme activity, enhanced tissue regeneration and repair capacity, muscle relaxation, decreased muscle tone, pain relief or relief.

Local tissue changes in ultrasound treatment can affect a certain stage of the body or the whole body through the neurohumoral pathway, playing a therapeutic role.

The role of ultrasound therapy

Effects of ultrasound treatment on the nervous system

Low-dose ultrasound can increase nerve excitability, speed up the conduction speed, reduce the inflammatory response of nerves, promote the healing of nerve damage, increase the pain threshold, and reduce pain. Therefore, it has obvious analgesic effect on peripheral nerve diseases such as neuritis and neuralgia. High-dose ultrasound on peripheral nerves can cause vascular paralysis, tissue cells hypoxia, and then necrosis.

The central nervous system shows high sensitivity to ultrasound. Within a certain dose, the effect of ultrasound on the central nerve is as follows: acting on the brain can stimulate cell energy metabolism, cerebral vasodilation, accelerated blood flow, accelerate the establishment of collateral circulation, and accelerate the brain Recovery of cell function; action on the interbrain can speed up heartbeat and increase blood pressure; action on the spinal cord can change sensory and motor nerve conduction.

Effects of ultrasound treatment on the circulatory system

The atrioventricular beam is sensitive to the effects of ultrasound. Ultrasound mainly affects the heart's ability to move and its rhythm. High-dose ultrasound can slow the heart rhythm, induce angina pectoris, and cause heart rhythm disturbance in severe cases, eventually leading to cardiac arrest; low-dose ultrasound congests the heart capillaries, which has the effect of expanding the arterial lumen and relieving vasospasm in patients with coronary heart disease. Patients with insufficient arterial blood supply have a certain effect.

Therapeutic dose ultrasound has no damaging effect on blood vessels, usually dilated blood vessels and accelerated blood circulation. Under the action of low-intensity ultrasound, the vascular organs dilate; under the action of larger doses, it can cause vasoconstriction. Higher doses of ultrasound paralyze vascular motor nerves, causing blood flow to stop. The use of high-dose ultrasound can directly cause vascular endothelial swelling and blood circulation disorders.

Impact of ultrasound treatment on eyes

Because the anatomical structure of the eye is characterized by the shape of the sphere, there are many layers, and the factors such as liquid composition and blood circulation characteristics are prone to heat accumulation and cause damage. High-dose ultrasound can cause conjunctival congestion, corneal edema, and even fundus changes, which can cause thermal cataracts to the lens. It can also cause sympathetic ophthalmia. However, a small dose can promote absorption, improve circulation, and have better effects on vitreous opacity, intraocular hemorrhage, retinitis, and traumatic cataract.

Effects of ultrasound treatment on the reproductive system

The reproductive organs are more sensitive to ultrasound. An appropriate amount of ultrasound can increase the number of sperm, increase sperm motility, and increase the conception rate. High-dose ultrasound can shrink sperm. Appropriate amount of ultrasound can promote follicular follicle formation, and high-dose ultrasound can degenerate follicles. Ultrasound can deform embryos and cause abortion.

Effects of ultrasound treatment on bones

Low-dose ultrasound multiple projections can promote bone growth and epiphyseal formation; high-dose ultrasound acts on non-ossified bones, which can cause bone hypoplasia. Therefore, ultrasound is disabled in the epiphysis of young children.

Effect of ultrasound treatment on connective tissue

Connective tissue is less sensitive to ultrasound, and has the effect of stimulating the growth of connective tissue in wounds with tissue damage. When the connective tissue grows excessively, ultrasound has the effect of softening and dissipating, especially for concentrated fibrous tissue. Therefore, ultrasound has the effect of "separating fibers" on scarring connective tissue, and it also has the effect of turning "gel into sol". It is also seen clinically that ultrasound has a more obvious softening effect on scars.

The effect of ultrasound on the skin

Ultrasound on the skin can increase the permeability of skin blood vessels and make the skin slightly congested, but without erythema. Ultrasound can enhance the secretion of sweat glands in the skin, promote skin excretion, and enhance dermal regeneration. High-dose ultrasound can cause nociceptive inflammatory reactions in the skin.

Ultrasound Therapy

Direct ultrasonic treatment

The ultrasound head is directly contacted with the skin of the treatment site for treatment. At this time, a contact agent should be added between the skin and the acoustic head.

(1) Moving method: This method is most commonly used. During treatment, the acoustic head gently presses the skin, and it moves slowly at the treatment site, and the speed of movement is preferably 1-2 cm per second.

(2) Fixed method: rarely used. The ultrasonic head is fixed to the treatment site with appropriate pressure. This method is prone to overheating and "periosteal pain response". Therefore, the treatment dose should be small.

Ultrasound treatment indirect contact

(1) Underwater method: During the treatment, the ultrasonic acoustic head and the treatment limb are immersed in warm boiling water at 36-38 ° C. The distance between the acoustic head and the skin is 1-5 cm.

This method is often used on irregular body surfaces, areas with local pain sensitivity or inaccessible areas such as fingers, toes, ankles, elbows, ulcers, etc.

(2) Auxiliary treatment method: Water funnel method, water pillow or water bag method are commonly used. The latter is a bag made of a thin rubber film, filled with boiled warm water, and then coated with a contact agent for treatment, which is used for unevenness on the face, neck, joints, prostate, teeth, eyes, etc.

(3) Concentrated irradiation method: Use a concave mirror and an acoustic lens to focus the ultrasound on a certain position to obtain the effect of high-energy ultrasound for special treatment. Such as when treating tumors.

Ultrasound treatment dose

1. The treatment intensity: 0.4-1.5W / cm2 is appropriate. The intensity of the underwater method and the water pillow method can be slightly larger. Clinically, low and medium intensity are used.

2. Treatment time: The total time is generally no more than 15 minutes, and more choices are 5-10 minutes. The fixed method is shorter than the mobile method.

3. Course of treatment: 5-10 times for general treatment, 15-20 times for chronic disease or more. Daily or every other day. The treatment interval is 1-2 weeks.

Indications for ultrasound therapy

1. Surgical diseases: soft tissue contusion, mastitis, cervical spondylosis, traumatic diseases of sports support organs, low back pain, myalgia, periarthritis of the shoulder, proliferative spondylitis, temporomandibular arthritis, tenosynovitis, degenerative osteoarthritis, etc.

2. Dermatological diseases: urticaria, pruritus, scleroderma, neurodermatitis, psoriasis, shingles, eczema, etc.

3. Neurological diseases: cerebral thrombosis, cerebral infarction, cerebral hemorrhage, traumatic brain injury, neuritis, neuralgia, phantom limb pain, sciatica, etc.

4. Other cerebrovascular diseases, hemiplegia, insufficient coronary blood supply, retinal inflammation, vitreous opacity, malnutrition, peptic ulcers, bronchial asthma, and gastrointestinal disorders.

Contraindications to ultrasound treatment

Where malignant tumors, acute systemic infections, high fever, active tuberculosis, heart regions and stellate ganglia of severe heart disease, bleeding tendency, abnormal parts of sensory nerves, pregnant women's abdomen, etc.

Examples of clinical applications of ultrasound therapy

1. Organized hematomas are mostly blunt forces acting on body tissues, causing local subcutaneous blood vessels to rupture, blood penetrating the local tissue space, and signs that appear because blood cannot be completely absorbed. Clinically, drug treatment is not effective.

Human body with soft tissues after closed trauma has a large amount of bleeding that cannot be absorbed, which can easily cause subcutaneous hematomas. Mechanization of hematomas can adhere to subcutaneous tissues and compress the surrounding tissues to produce symptoms. Ultrasound has biological effects such as thermal effects, mechanical effects, and cavitation effects. The mechanical action of ultrasonic waves can disperse the hard connective tissue collagen fiber bundles, and then separate from the connective tissue cements, make the dense and hard connective tissues extend, soften, and make the adhesion group

Weaving gets loose. Ultrasound can not only increase blood circulation, improve the local nutrition of hematoma, promote metabolism, and facilitate the absorption of hematoma; it also has the effect of sound pressure and forms a fine massage effect on tissues and cells. It is an effective method to treat mechanized hematoma.

2. Temporomandibular joint disorder, also known as temporomandibular joint dysfunction syndrome, is a common and frequently-occurring disease of the oral and maxillofacial region. The main symptoms are soreness or pain when chewing and mouth opening, popping and restricted mouth opening. The disease has a long course and is prone to recurrent attacks, which seriously affects the patient's working life. Application of acupuncture, specific electromagnetic wave therapy (TDP) irradiation, and ultrasonic therapy to comprehensively treat temporomandibular joint disorders to achieve satisfactory results. TDP irradiation is also known as specific electromagnetic wave radiation therapy. Using its warming effect, it can improve blood circulation, eliminate painful chemical transmitters, reduce local swelling, promote tissue tension decline, and restore strained muscles and joints. The ultrasonic therapy instrument uses the heat penetration effect of ultrasound to have deep hyperthermia and drug penetration effects. At the same time, it uses diclofenac diethylamine latex as a transmitter, which has analgesic, antispasmodic, and anti-inflammatory effects, and can relieve local adhesion and eliminate The purpose of edema is three-pronged, so it can achieve satisfactory results.