Therapeutic Heat: Physiological & Therapeutic Effects

Physiological & Therapeutic Effects of heat therapy for UG physiotherapy students.

1. THERPEUTIC HEAT PHYSIOLOGICAL EFFECTS Dr. Sreeraj S R, PhD.

2. 2 Therapeutic Heat Superficial Heat Convective agents Conductive agents Conversive agents Fluidotherapy Hydrotherapy Hot packs Heating pads Paraffin wax bath IR/UVR/LASER Deep heat Ultrasound SWD MWD Contrast Bath

3. Therapeutic Heat The greatest temperature elevation with superficial heating modalities occurs in the skin and the subcutaneous tissues within 0.5 to 2 cm of the skin surface. Deep heating agents, such as continuous TUS and continuous SWD, can increase the temperature of tissues at depths of 3 to 5 cm. Muscle temperature will require a longer duration of exposure of 15 to 30 minutes to reach peak values. 3

4. Therapeutic Heat Degrees of heat sensation can be categorized as follows; 4 MINIMAL WARMTH Threshold value, Gentle comforting warmth. MEDIUM WARMTH Distinct feeling of agreeable warmth. MAXIMUM WARMTH Intense feeling of heat, close to tolerance. DANGER LEVEL Intolerable heat, Burning sensation.

5. Therapeutic Heat Therapeutic levels of heating are categorized as Mild, less than 40°C and Vigorous 40°C to 45°C Hyperemia or Erythema or redness of the skin is noted, caused by an increase in the blood flow in the capillaries in the lower layers of the skin. Temperature greater than 45° results in thermal pain and irreversible tissue damage. 5

6. Physiological Effects of Heat Physiological changes depend on several factors: Extent of the temperature increase Rate at which energy is being added to the tissue Volume of tissue exposed Composition of the absorbing tissue Capacity of the tissue to dissipate heat (largely a factor of blood supply) 6

7. Physiological Effects of Heat Hemodynamic effect Neuromuscular effect Metabolic effect Connective Tissue Effects / Tissue extensibility Pulse Rate & Blood Pressure Rate of Breathing 7

8. Hemodynamic effect 8 ↑ Temparature Inflammation ↑ Vasodilator (Histamine & Prostaglandin) release Vasodilatiation Cutaneous thermoreceptors Spinal cord dorsal root ganglion Smooth muscle relaxation Direct Reflex Activation Indirect Activation

9. Hemodynamic effect: Inflammation The stimulation of cutaneous thermoreceptors causes the release of nitrous oxide, causing relaxation of the smooth muscles of the vessel walls > vasodilation at the area. Temperature elevation causes the release of enzyme kallikrein from sweat glands leads to increase in vascular permeability. 9

10. Hemodynamic effect: Cutaneous Thermoreceptors 10 The sympathetic innervation of the blood vessels regulates vasomotor tone. These nerve fibers leave the spinal cord through thoracolumbar spinal nerves. Cutaneous thermoreceptors also synapse with sympathetic neurons in the lateral gray horn of the thoracolumbar segments in the spinal cord. When there is local heating, the firing of cutaneous thermoreceptors inhibits this firing and thus decreasing sympathetic output. This reduces vasomotor tone , resulting in vasodilation at the site of heat application and in the cutaneous vessels of the distal extremities.

11. Neuromuscular Effects: Pain The increased firing rate of thermoreceptors in cutaneous tissue may block input from the primary nociceptive afferent to the dorsal horn (the “thermal gate theory”) . Heat is used therapeutically to provide analgesia and to help resolve pain and muscle-guarding spasms. Heat can cause a conduction block on demyelinated peripheral nerves because it can shorten the duration of sodium channel opening during neuronal depolarization. 11

12. Neuromuscular Effects: Spasm Muscle-guarding spasms can result from the injury and overuse of a muscle. Pain can be a trigger beginning the pain-spasm-pain cycle. Elevating muscle temperature to 42°C has been shown to Decreasing the firing rate of muscle spindles (alpha and gamma motor neurons) but Increase the firing rate from GTOs. These changes in nerve firing rates are thought to contribute to a reduction in muscle spasm. 12

13. Neuromuscular Effects: Muscle Strength Muscle strength and endurance have been found to decrease during the initial 30 minutes after applying either deep or superficial heating agents. This is because of heat on Decreasing the firing rate of muscle spindles (alpha and gamma motor neurons) but Increasing the firing rate from GTOs. Beyond 30 minutes and for the next 2 hours after the heat is applied, muscle strength gradually recovers. Heat is not used prior to strengthening or strength measurement. 13

14. Tissue Extensibility Temperature elevation in combination with a stretch can alter the viscoelastic properties of connective tissues. The effects of heat on connective tissue include: Elasticity Viscosity Joint stiffness Muscle flexibility A maximum increase in residual length is achieved when the tissue is maintained at 40°C to 45°C for 5 to 10 minutes. 14

15. Metabolic Effects Metabolic rate will increase 2 to 3-fold for each 10°C rise in temperature. With every rise in tissue temperature, the oxygen-hemoglobin dissociation curve shifts to the right, making more oxygen available for tissue repair. The effects of heat on metabolism increases; Enzymatic activity Cellular biochemical reactions Oxygen uptake and speed up healing Energy expenditure will increase with increasing temperature. 15

16. Metabolic Effects Heat is not advised in arthritic conditions like rheumatoid arthritis, where heat can increase the activity of collagenase and thus speed up the destruction of articular cartilage. Therefore, thermotherapy should be used with caution in patients with acute inflammatory disorders. 16

17. Pulse Rate & Blood Pressure The blood vessel dilation lowers the blood pressure because the blood distribution has increased to new areas. The body now must compensate by increasing the cardiac output by increasing the heart rate. Because of the change in pressure, less blood is pumped to the vital organs of the body. Lowering of blood pressure also due to decrease in sodium concentration, loss of urea & other nitrogenous substance due to increased metabolism because of heating. 17

18. Rate of Breathing As the temperature increases, there is an increase in metabolism and more oxyhemoglobin dissociation. Metabolically active cells require more O 2 . Because of these changes in O 2 demand, the rate of respiration too increases to meet the demand. 18

19. Therapeutic Effects Encouragement of healing Relief of Pain Reduction of Muscle Spasm Increase in Range of Joint Motion Prophylaxis (Prevention) of Pressure Sores Reduction of Oedema in Extremities Resolution of Some Skin Diseases 19

20. Contraindications Ischemia—e.g., arterial insufficiency Haemorrhage—there is an increased arterial and capillary blood flow with heat Impaired sensation—e.g., spinal cord injury (SCI) may predispose to burns Inability to communicate or respond to pain—e.g., dementia Malignancy—May increase tumour growth Acute trauma or inflammation—Diffusion across membranes is increased Scar tissue—Elevation of temperature increases the metabolic demand of the tissue. Scar tissue has inadequate vascular supply, and cannot provide an adequate vascular response when heated, which can lead to ischemic necrosis. 20

21. Hot packs Hydrocollator: canvas bags filled with silicon dioxide immersed in tanks of heated water 75° C Applied over several layers of insulating towels Heat treatment lasts 10 to 30 minutes Advantages: low cost, minimal maintenance, long life, patient acceptance, ease of use Disadvantages: Prolonged superficial heat can produce telangiectasia. 21

22. Paraffin wax bath Paraffin wax and mineral oil in a 7:1 or 6:1 ratio heated to 40 to 45° C Commonly used in irregular surfaces such as distal extremities Patients have good compliance, and home units are available 22

23. Hydrotherapy External use of water to treat a physical condition. Water can produce convective heating or cooling, massage, and gentle debridement. Unit size, water temperature, and agitation intensity can be adjusted to meet treatment goals Whirlpool baths for partial body immersion Hubbard tanks used for total body immersion 23

24. Contrast Bath Distal limbs receive alternating heat and cold in a whirlpool tank to produce reflex hyperemia. Temperatures range from hot 35–45° C and cold 15–20° C Technique: Begin with warm soaks to the extremity, then follow with four cycles of alternating 1–4 minute cold soaks and 4–6 minutes warm soaks 24 35–45° C 15–20° C

25. Heating pads Available as electric pads and pads with circulating heated fluid such as water. Peak temperature is 52° C The temperature is maintained at a constant level. If used with moist towels there is a potential risk for electrical shock If the patient lies on the pad there is a potential for burns. This is common in patients with decreased adipose tissue Generally used for periods of 20 minutes 25

26. Fluidotherapy Hot air is blown through a container holding fine cellulose particles (bed of beads or corn husks), which produces a warm air-fluid mixture with properties similar to liquid Advantages: massage action of the turbulent solid-gas mixture; freedom to perform ROM activities Good for hands and feet The typical temperature range is 45 to 50° C 26