Both dry and moist heats are applied locally. Through local application of heat there occurs localized increase of temperature, local blood supply improves, metabolites taken out quickly, and dissolution or absorption of the hoematoma takes place.
Purpose for heat therapy are:
(i) To relieve pain and discomfort by local action of counter-irritation (Counter irritation is the production of superficial skin irritation to counter act other deeper inflammation);
(ii) To increase the absorption of inflammatory products;
(iii) To relieve stress on the blood circulation;
(iv) To improve nutrition of the part;
(v) To reduce distension and congestion;
(vi) To promote suppuration (oozing of the pus to come out); and Dry heat is applied for drying casts, moist wounds or burns.
Dry heat is applied when the part is dry or to be kept dry, and is provided through (a) hot water bottle (b) hot brick bats wrapped in a towel, (c) hot sand bags, (d) hot salt bags (e) hot cotton pads, (f) electrical appliances etc.
Among the electrical appliances are : infra-red or ultra-violet rays, ordinary bulbs, electrical pads, electrical stimulators or vibrators, shortwave diathermy and micro-wave diathermy, ultra-sonic apparatus, Ionizers etc.
(vii) To give warmth to the body.
Moist heat is administered through (a) hot saline water, (partial immersion, full immersion or fuming vapor) (b) hot whirlpool flow, (c) hot water packs, (d) paraffin wax bath (for the mobility of the joints).
Effect of dry heat is superficial, heats the surroundings only, and does not penetrate. This is applied only when the injury is at the upper layer i.e., superficial. Dry heat is given for half an hour at bed.
No heat is applied on the day of the injury. After application of dry heat, the part is not immediately exposed to cold unless advised by the physician. While applying moist or wet heat, heat is applied through hot water or steam. In steam application. Vapour comes in direct contact with the injured part. When application is through hot water, the particular part is dipped wholly (full immersion) or partly (partial immersion). Temperature of hot water should not be so hot that it burns.
Moist heat may be given for half an hour. It also does not go too deep, but it is somewhat better than dry heat. Sometimes salt is added with water as it appears to help in reducing pain and swelling.
While applying heat through paraffin bags, paraffin bags are melted into liquid. This melted paraffin tries to freeze the part which is dipped into it. Some flexion and extension exercises are done at this point, particularly in finger injuries. Paraffin wax bath is repeated for 10 minutes or so.
Application of heat through electrical appliances results in chemical, thermal, excitable effects along with physiological effects.
Infra-red lamp gives light beyond spectrum red, and has penetrating effect up to the soft tissue. But it heats a comparatively large area. Its power decreases as it goes deep. It is not effective in joint injuries. Infra-red ray is applied after one week of injury, for three weeks, once in a day for 20-30 minutes daily. The lamp is placed 1-2 ft away from the part, according to injury and adaptability of the person.
It is given by a diathermy machine, to which are attached two pads or coils showing positive and negative ends. Its heat goes more deep than infra-red ray. When applied, pads are placed at the part. It is given 20 minutes daily for 2-3 weeks. Because it goes deeper, it is helpful in joint injuries and some chronic type of injuries.
Physiologic effects in shortwave diathermy – increased blood supply through augmented blood circulation, increased metabolism, increased activity of sweat glands, sedative effect, reducing effects on inflammation.
Shortwave diathermy is not to be given when there is hoemorrhage, when there is defective arterial blood supply or any arterial disease. It should not be given to abdomen or pelvis during pregnancy or during menstruation. Also it is not to be given to persons having mental defects, and not to small children.
In microwave diathermy, energy is generated by a magnetron tube which directs its current through a co-axial cable directed to a specific area. Its physiological effects are: increase in capillary circulation, increase in local metabolism, phagocytes (destruction of the damaged injured cells).
Penetrating power of microwaves is 2″ deep.
It raises temperature up to 104°F.
Its dosage should be 15-20 minutes daily for 2-3 weeks.
Heat should better be applied from a little distance.
Inflammatory condition of joints, muscle tissue conditions in sub-acute and chronic inflammatory stages.
Should not be applied over adhesive tape, recent injury, over metal plants, anesthetic area, clothing’s, high swelling (except in chronic conditions) and moist skin.
Advantages of micro-wave over shortwave:
(i) Easy to operate, (ii) Accurate measurement of dosage, (iii) More effective deep tissue heating without any effect on the epidermis, (iv) Related comfort afforded to the patient, (v) Absorption through microwave heating is greater in tissues of high water content i.e., muscles and lesser in tissues of low water content i.e., bones.
(a) Only one side can be radiated (b) Superficial burns likely by higher doses.
The unit of ultrasonic therapy consists of three parts: (a) generator of radiofrequency electrical energy, (b) ultrasonic applicator coupled to the generator by a flexible cable, and (c) a transducer to convert electrical energy into mechanical vibration. The sounds of the waves are not audible.
Operation of the applicator:
(i) moving technique – for diffused treatment and underwater treatment.
(ii) Stationary technique – Used in case of localized injury.
The part to be heated is lubricated with paraffin or some oil. The applicator head of the machine is then moved around. Given for 15-20 minutes, once in a day for two weeks.
Raises muscle temperature at a level 2″ below the surface 7-8 degrees Fahrenheit; micro massage action due to sound waves; localised heating at the region; permeability of cell membrane is facilitated; increased metabolism and detoxification.
Effective in certain conditions of muscles and tendons; improves the sub-acute and chronic conditions of pain due to bursitis, arthritis, fibrositis etc; also in certain neural conditions, and to treat adherent scars.
Avoidance of over exposure to anoesthetised areas; in conditions of haemorrhaging and infection; at nerve plexuses and brain; at spinal cord, eyes, ears, nasal sinuses, heat, and reproductive organs.
It is an apparatus in which NaCI is split into ions -»Na+ + Cl-; and in case of KI -»K* + I-; and as a result, heat is produced. The negative pole is kept over the area to be heated and then current is passed. Generally KI is used. Iodine has the characteristic that it heats up the tissue in increasing vascular supplies. Generally used in case of painful wounds, particularly for deeper needs.