By Thomas Mulvey M.S., P.T., M.B.A.
There is much controversy as to when you should use the topical applications of heat or cold. Heating Pads, Microwave Packs, and Ice Packs, have become a staple in every household.
The treatment effects and the physiological effects are different for both.
Heat
1) Increased metabolism in heated tissues.
2) Increased perspiration in area of absorption.
3) Local vasodilatation, with hyperemia, and subsequent erythema (Increased cellular demand for nutrients, oxygen, or from stimulation of cells that release a histamine-like substance.)
4) In the short-term, decreased fast nerve fiber sensation (touch)
5) In the long term, decreased slow twitch fiber sensation (sedation to pain)
6)Muscle relaxation because of effects on muscle spindles and golgi tendon organs.
7)Increased capillary pressure and cell permeability, which can promote local swelling.
8)The electrical resistance of the skin decreases.
- Precaution: With repeated use of strong doses, undesirable mottled pigmentation may become evident. This results from destruction of red blood cells or paralysis of arterioles in a dilated state.
Cold
1) In the short- term, intense local vasoconstriction
2) In the long –term, decreased fast nerve fiber ( touch ) and slow nerve fiber ( pain ) sensation.
3) Increased pain threshold. Analgesia.
4) Local metabolism is decreased. This results in a lower demand for oxygen and decreased response to acute injury or inflammation.
5) Long-term exposure to cold ( greater than 30 minutes ) can lower intra-articular temperature, reducing joint metabolism, and decreasing activity of cartilage degrading enzymes.
6) Endorphins may be released.
7) Muscle spindle activity is decreased.
8) The ability to perform rapid movements is diminished, resulting from increased muscle viscosity or prolonged muscle contraction and relaxation times.
9) Connective tissue becomes stiffer and is not as plastic following treatment. Tensile strength decreases.
10) Muscular Force generation (concentric and eccentric) is diminished.
How it works
Cold , as part of PRICE ( prevention, rest, ice, compression, and elevation ), is an effective way of controlling post traumatic injury to an injured area of the body.
Theoretically, Cold will prevent further exudation from the injured capillary beds while the compression will maintain a higher interstitial pressure. PROLONGED CONTINUED USE OF COLD, will allow the proteins released into the interstitial spaces to coagulate. This coagulation will allow distension of the interstitial spaces.
It is important to remember that the term used is Heat, not Hot. The modalities of Heat and Cold themselves may cause bodily injury. Electrical Heating Pads, when left on long enough, can burn ( different than a warm bath that can lose its heat ). Even when left on a low setting. Therefore, DO NOT SLEEP WITH A HEATING PAD. Even cold, when applied without some type of barrier can cause frost bite. Some persons also have neurovascular conditions ( Raynaud’s Phenomenon ) that make exposure to cold painful and dangerous.
The sensation of temperature is transmitted via unencapsulated nerve endings in the skin to the spinal cord from unmyelinated nerve fibers for warmth receptors and mylinated nerve fibers for cold receptors. The temperature sensation is then transmitted (the Lateral Spinothalamic Tract) to higher centers for thermoregulation in the brain.
Two parts of the Hypothalamus (Brain) are used for thermoregulation. The Anterior Hypothalamus initiates sweating and vasodilatation of cutaneous vessels, when an increased temperature is noted. Decreased temperature causes the posterior hypothalamus to initiate vasoconstriction of peripheral vessels, producing shivering and increased visceral activities. Shivering helps the body generate heat.
Indications
Indications for the use of Heat include Subacute and Chronic conditions such as Osteoarthritis, Muscle Injury, and /or Muscle tightening/ stiffness/ or spasm.
Indications for the use of Cold include Early, Acute injury ( sprains, strains, contusions, or post surgery ); resulting in Acute Inflammation, or Acute/ Chronic pain.
Contraindications
Contraindications for Heat include:
1) ACUTE inflammatory conditions such as sprains and strains may be aggravated by heating.
2) Previously existing fever may be further elevated by systemic heating of the patient.
3) Malignancies may metastasize as a result of increased blood flow produced by heating.
4) Active bleeding, such as that which occurs with acute trauma, may be prolonged.
5) Patients with cardiac insufficiency may not be able to tolerate the additional stress on the heart produced by generalized heating.
6) Older adults and children less than 4 yrs. of age have unreliable thermoregulatory systems and may develop fever quite easily as a result of generalized heat treatments.
7) Patients with peripheral vascular disease have diminished capacity to meet the increased metabolic demands if tissues in the affected extremities are heated directly.
8) Tissues that are devitalized by x-ray therapy or age , should not be treated.
Contraindications for Cold
1) Patients with angina pectoris or other cardiac dysfunction should not be treated by general cold. Relatively minor problems , distant from the thorax, may be treated with local cold applications safely.
2) Because of the vasoconstriction produced by cold, open wounds should not be treated by cold after 48 to 72 hours.
3) Patients with arterial insufficiency are at risk of tissue damage from the vasoconstriction with cold exposures.
Sources
1) Klein, Milton, D.O., M.B.A.: Superficial Heat and Cold, Medscape.com
2) Lee, Douglas H.K.: Heat and Cold Effects and Control; Public Health Monograph; 79: 5, May 1964
3) Sonna, Larry A. et. al.; Molecular Biology of Thermoregulation: Effects of heat and Cold stress on mammalian gene expression; Journal of Applied Physiology, 92: 1723-1742, 2002.
4) Hayes, Karen W. ; Manual for Physical Agents, fifth edition; Prentice Hall.
5) Santiesteban, A. Joseph; James Gould and George Davies, editors; Orthopedic and Sports Physical Therapy; C.V. Mosby Company , St. Louis, Mo., 1985.