Ultraviolet
Ultraviolet radiation ranges from 150 A° to 3.900 A° units, to be
absorbed by the body at a depth of 1 mm. The main effect of ultraviolet is
chemical in nature, which causes changes in the various chemical
processes in the body. Furthermore, ultraviolet is required for various
metabolic processes, healing and general health maintenance.
Physics:
Mercury vapor has been the accepted source of ultraviolet radiation
in therapeutic lamps for many years. High-voltage generators provide the
energy necessary to vaporize droplets of mercury, housed in special
quartz-glass tubing. These droplets are placed within reflecting surfaces,
designed to project the radiation outward in a prescribed field.
Penetration:
According to the wavelength, Ultraviolet is classified into two
different bands:
* Near band:
It ranges from 3.900 A° to 2.900 A° units, which are close to the
visible spectrum. They are absorbed in the deep epidermis and the blood
of the superficial capillary loops in the dermis, to be generally utilized for
its anti-rachitic effect.
* Far band:
It ranges from 2.900 A° to 1.800 A° units, which are removed from
the visible spectrum. They are absorbed in the superficial epidermis, to be
utilized most for erythemal dosages.
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Physiological effects:
The physiological effects vary with different wavelengths but most
ultraviolet lamps emit multiple wavelengths.
* General effects:
It has beneficial effects, which appear in the treatment of patients
suffering from debility and children who are under-weight. It has a tonic
effect as it improves appetite, nervousness, irritability and sleeplessness.
* Local effects:
a) Erythema reaction:
When ultraviolet is absorbed in the skin, it causes chemical
reactions, which result in irritation and destruction of cells. This causes
liberation of the “H” substance (similar to histamine), which produces:
- Dilatation of the capillaries, due to the direct effect of “H” substance.
- Dilatation of the arterioles.
- Exudation of fluid into the tissues, due to the increased permeability of
the capillary wall.
These effects are similar to the changes, observed in inflammation,
so erythema is regarded as an inflammatory reaction. The intensity of the
reaction varies according to the strength of the irradiation.
1. First-degree erythema: It is a slight redness of the skin, with no
irritation or soreness. It fades within 24 hours.
2. Second-degree erythema: It is a more marked redness, with slight
soreness. It fades in two or three days.
3. Third-degree erythema: It is marked redness of the skin, which is hot,
sore and edematous. The reaction lasts for a week nearly.
4. Fourth-degree erythema: It is similar to the third degree, except that
formation of blisters.
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b) Thickening of the epidermis:
It is a process of protection against the rays and replacement for the
damaged cells.
c) Desquamation:
There is casting of dead cells from the surface of the body. The
amount of peeling varies with the strength of irradiation. After firstdegree erythema, there is no peeling, while after the second degree, there
is fine powdery peeling. Moreover, after the third or the fourth degree
erythema, there is free peeling.
d) Pigmentation:
Ultraviolet rays of wavelengths between 2.900 and 3.100 A° are
absorbed in the deep epidermis. This initiates a chemical reaction, which
results in conversion of amino acid “tyrosine” into pigment “melanin”.
e) Abiotic effect:
Ultraviolet rays of wavelengths less than 2.900 A° inhibit the
growth of bacteria.
f) Vitamin D formation:
Ultraviolet rays of wavelengths between 2.700 and 3.100 A° cause
chemical reaction, which results in conversion of 7-dehydrocholesterole
into vitamin D.
Therapeutic effects:
- Increased blood supply to the skin.
- Stimulation of growth of epidermis.
- Destruction of bacteria.
- Desquamation.
- Counter-irritation.
- Dermatologic conditions: Alopecia, herpes zoster, lupus valgaris,
ulcerations and psoriasis.
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Contraindications:
* Photosensitive individuals:
Those are patients who have sensitive skin, which reacts strongly
to irritation. These individuals may develop headache, nausea, vomiting
and rise of temperature.
* Photosensitive treatments:
Ultraviolet should not be applied to an area, which has been
recently subjected to X-ray therapy. A period of six months should elapse
after X-ray therapy before application of ultraviolet to the same area.
* Certain diseases:
- Pulmonary tuberculosis.
- Severe cardiac disturbances.
- Severe diabetes.
- Acute dermatitis or acute eczema.
- Nephritis.
- Addison’s disease (light sensitive).
Dangers and precautions:
- Conjunctivitis:
Exposure of the eyes to ultraviolet rays causes conjunctivitis. So,
special glasses should protect the eyes of both the patients and the
physical therapist.
- Overdose:
The skin becomes red, painful and sore and there may be nausea
and vomiting. In this case, infrared should be applied immediately to the
area over-irradiated by ultraviolet. This is because infrared erythema
reduces the effect of ultraviolet erythema. Cold cream or calamine lotion
should be applied later, if the case is not relieved.
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- Burns:
They result from directly touching the lamp. So, the patient should
be instructed not to move before removal of the lamp.
Treatment procedures:
1. Determination of minimal erythema dosage (MED):
In contrast to the transient hyperemia that accompanies infrared,
erythema that accompanies ultraviolet has generalized and systemic
effects, such as:
- Pro-vitamin D production with low dosages.
- Germicidal effects with increased dosages.
- With extremely high dosages, ultraviolet has a destructive erythemal
effect, to be used in treatment of open arthritis.
Determination of minimal erythema dosage should precede all
ultraviolet treatment. There are many factors, which determine the
degree of erythema such as:
- Individual patient’s sensitivity.
- Intensity of radiation.
- Distance of lamp-to-target.
- Angle of incidence of radiation at skin.
- Duration of exposure.
- Skin texture.
Determination of MED is a must to obtain the desired goal of
ultraviolet on the exposed skin (slight pinking). This is accomplished by:
- A large piece of cardboard is needed.
- A hole, 2-inches in diameter, is cut for the tested area.
- The rest of the patient’s skin should be covered to limit the exposure to
ultraviolet to the hole, made in such cardboard.
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- Utilizing the volar surface of the patient’s forearm, change the position
of the cardboard hole to examine other areas, with increments of 15
seconds each.
- Reexamine the skin in 4 - 8 hours for comparison to detect the MED.
2. Determination of dosage of treatment:
- Once MED is known, treatment may be started with increments of 15
seconds each session until the maximum is reached (2 minutes usually).
- Peeling and sunburn should not be evident; otherwise the radiation
should be reduced.
- Tanning of the patient should occur gradually throughout treatment.
3. Determination of the distance:
- The usual distance between the lamp and the skin is ranging between 24
and 30 inches at an angle of 90°.
- Further angulation at the same distance requires increased dosage of
about 10%.
- Less distance necessitates reduced dosages and vice versa.
4. Determination of the duration:
As the minimal exposure time needed to produce first-degree
erythema is determined, time needed to produce other degrees can be
calculated as follows:
- Second-degree erythema: Requires 2 ½ times the exposure duration,
necessary to produce the first-degree erythema.
- Third-degree erythema: Requires 5 times the exposure duration,
necessary to produce the first-degree erythema.
- Fourth-degree erythema: Requires 10 times the exposure duration,
necessary to produce the first-degree erythema.
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