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The Sauna – Studies of Sauna Treatment and Physiology

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Compiled by Dr. Douglas Lobay, B.Sc., N.D.
October 2004

INFRARED SAUNA

This paper provides of an overview of the use of the therapeutic benefits of infrared sauna radiation and human health. It provides of brief discussion of the electromagnetic spectrum, the biophysics of heating and heating agents and the use of sauna therapy and specifically infrared radiation saunas.

HEAT
Heat is a form of energy called thermal energy. Heat is transferred from a substance of higher temperature to a substance of lower temperature. Thermal energy can be thought of as molecular vibrations. When thermal energy is transferred to a substance, molecular vibrations excite electrons on the atomic structure. The motion of the molecules and their electrons causes emission of electromagnetic waves to adjacent structures. Waves are emitted in discrete packets called photons. Both the average energy of the photons and their rate of emission increase as the temperature of the source is increased. Photons of a particular energy have a characteristic wavelength and frequency. Absorption of photons by a substance leads to an increase in its thermal energy level.

TEMPERATURE
Temperature is a scale that is used to measure the thermal energy of a substance. The Celsius scale, formerly called the centigrade scale, is used in countries that have adopted the system international or metric scale. The Fahrenheit scale, formerly called the imperial scale, is used in countries such as the United States that have not adopted the metric system. On the Celsius scale, 0 degrees denotes the freezing point of water and 100 degrees denotes the boiling point of water. On the Fahrenheit scale, 32 degrees denotes the freezing point of water and 212 degrees denotes the boiling point of water. The quantity of thermal energy needed to raise the temperature of 1 gram of water by 1 degree Celsius is 1 calorie of energy or 4.2 joules.

FREQUENCIES AND WAVELENGTHS
Vibrations of molecules give rise to photons that have different frequencies and wavelengths. Frequency is the number of waves emitted in a particular time period. Hertz is the unit of measurement of frequency and is defined as the number of wave cycles per second. Wavelength is the horizontal distance between crests of adjacent waves. Wavelengths are measured in nanometres and are abbreviated nm. One nanometre equals on thousand millionth of a metre or 1 x 10 to the minus ninth of a metre.

ELECTROMAGNETIC SPECTRUM
Photons exert electric and magnetic forces and give rise to what is called the electromagnetic spectrum. Photons vary in both frequencies and wavelengths. Examples of electromagnetic waves include television, radar, microwaves, infrared waves, visible light waves, ultraviolet, x-rays, gamma rays and cosmic waves. Different wavelengths delineate different portions of the electromagnetic spectra. Radio waves have a wavelength between 10 to 1000 metres. Microwaves have a wavelength between 1 millimetre to 10 metres. Infrared waves have a wavelength between 700 to 15,000 nanometres. Visible light waves have a wavelength between 390 to 700 nanometres. Ultraviolet waves have a wavelength between 180 to 390 nanometres. X-rays have a wavelength less than 180 nanometres.

SPEED OF LIGHT
All electromagnetic waves travel at the speed of light; 300,000 kilometres per second or 186,000 miles per second. The speed of light is constant and is the product of the frequency of the electromagnetic wave times the wavelength. Therefore, frequency varies inversely with the wavelength. The higher the frequency the shorter the wavelength and conversely the lower the frequency the longer the wavelength. Therefore, radio waves which have a longer wavelength should have a lower frequency. X-rays, which have a shorter wavelength tend to have a higher frequency.

INFRARED WAVES
Infrared waves are a small segment of the electromagnetic spectrum that have a wavelength between 700 to 15,000 nanometres and a frequency between 1 x 10 power of 12 to 1 x 10 power 14.

BODY TEMPERATURE
The term core temperature refers to the interior temperature of the human body. The core temperature is tightly regulated and doesn’t very that much. It is controlled through a variety of neuro-hormonal mechanisms that keep the core temperature equilibrated. Core temperature is regulated at 37 degrees Celsius. The core temperature is regulated accurately and does not normally vary from the mean by more than 0.1 degrees Celsius. Oral temperature is at least 0.6 degrees lower than rectal temperature and is affected by many factors including the ingestion of food, hot and cold beverages, environment, humidity, exercises, stress, infection and changes in heart rate. Skin temperature, unlike core temperature, can vary considerably in responses to different external stimuli and internal stressors. Various parts of the body have slightly different temperatures. The extremities are slightly cooler than the midsection.

REGULATION OF BODY TEMPERATURE
Body temperature is regulated through a complex of external and internal mechanisms. Heat production is generated through basal metabolic activity of the human body, muscular activity, food intake, the hormones thyroxine and epinephrine and normal cellular activity. Heat loss is caused by radiation, conduction, evaporation of sweat and urination and defecation.

PHYSIOLOGICAL EFFECTS OF HEAT
The parameters that determine the extent of the physiological response of the body to heat include: the size of the area exposed, intensity of radiation, relative depths of absorption of the specific radiation, the integrity of the cardiovascular and the nervous systems, structure of the skin and subcutaneous tissues, age of the patient, the nervous system, the hormonal system, functioning thermoregulatory centre in the hypothalamus of the brain, thermal conductivity of the tissue being irradiated and duration of the radiation applied. The effects of heat on the tissues of the body is often the result of the interplay of local and general factors.

HEATING AGENTS

Warmth is associated with tranquility and relaxation. Heating injured tissue has been used for centuries for pain relief and reduction of muscle spasm. In physical rehabilitation, locally applied heating agents are used not only to promote relaxation, but also to increase blood flow, to facilitate tissue healing and to prepare tight muscle and stiff joints for exercise.

There are numerous thermal agents available for tissue heating. These generally fall within one of two
categories: superficial and deep heating agents. Superficial or surface heat agents such as hot packs, paraffin and infrared penetrate less than 2 centimetres depth. Deep heating agent such as diathermies and ultrasound can penetrate 3 to 15 centimetres depth.

Many physiological reactions occur as a result of temperature increase on parts of the body. The most relevant changes include an increase in metabolic activity, cardiovascular activity, nervous system response, skeletal muscle activity, and collagen connective tissue changes.

METABOLIC REACTIONS
Metabolic rate will increase two to three times normal for every 10 degree Celsius rise in temperature. Energy expenditure will increase with increasing temperature. Cellular oxygen uptake will also increase and will be available for tissue repair. As core temperature reaches a certain point, usually 45 to 50 degrees Celsius, human tissues will burn because of thermally induced protein denaturation.

VASCULAR EFFECTS

Blood flow to an area will increase as a result of vasodilation caused by temperature increase. Blood flow to the skin has an important purpose of regulating core body temperature, much like a radiator system. The flow of blood through the cutaneous blood vessels of the skin is not adjusted primarily to the requirements of the skin for oxygen, but rather to the functional requirements of the body for dissipation or conservation of heat.

If core body temperature begins to rise, there is a corresponding vasodilation of skin blood vessels to dissipate some of the core body heat. There are three mechanisms that control vasodilation of peripheral blood vessels.

One is the sympathetic adrenergic nervous system. That is part of the nervous system that deals with “flight or flight” response to a stressor. Under a stressful circumstance, hormones such as epinephrine and norepinephrine are secreted by the body. These hormones act on peripheral blood vessels, including the skin, and cause vasoconstriction. Suppression of the sympathetic adrenergic nervous system can cause a corresponding relaxation of peripheral blood vessels leading to vasodilation.

The second mechanism controlling vasodilation of peripheral blood vessels is the heat-loss area of the brain located in the hypothalamus. Sensory nerves in the skin and core body supply temperature information to the hypothalamus which works like a thermostat. If the hypothalamus senses an increase in temperature it signals reflex vasodilation of peripheral blood vessels.

The third mechanism of controlling dilation of peripheral blood vessels is a localized reflex mediated by sensory nerves located in the skin. When a temperature increase is sensed by a peripheral nerve a localized reflex causes automatic vasodilation of the affected area. Heat also produces the release of chemicals that cause vasodilation including histamine, prostaglandins, kallikrein and bradykinin. The net effect is that heat causes peripheral vasodilation of skin blood vessels.

NEUROMUSCULAR EFFECTS
Heat is used therapeutically to provide pain relief, analgesia and relax muscle spasms. Although the mechanisms of action has not been completely elucidated, heat has the ability to elevate the pain threshold through a variety of different mechanisms. Heat can alter nerve conduction velocity, neuro-hormonal reflexes and change muscle tone. The net effect is that pain decreases and muscles relax.

CONNECTIVE TISSUE EFFECTS
Temperature can alter the visco-elastic qualities of connective tissue. Heat applied to connective can increase the viscosity of connective tissue which leads to elongation, particularly after a stretch is applied. Joint stiffness is a common complaint of osteoarthritis, rheumatoid arthritis and other degenerative diseases. Joint stiffness is believed to be caused by in-elasticity of joint structure, particularly the connective tissue components. Localized heating applied to a joint can decrease pain, improve joint stiffness and increase the extensibility of the joint by increasing connective tissue viscosity. The net effect is reduced pain and improved mobility of the affected joint.

EFFECTS OF HEAT ON TISSUES
The local effects of heat lead to vasodilation of blood vessels of the skin up to 42 degrees Celsius. Blood flow to the skin can increase four to five times resting levels. There is ample evidence to prove the blood flow to muscles is not increased by the local application of heat. The rate of metabolism of skin or muscle depends in part on temperature. Metabolism can increase two to three times that of resting level from thermal stimuli. The speed of cellular oxidation can increase with temperature. Within the electromagnetic spectrum , the band of wavelengths that produce thermal sensation is between 700 to 100,000 nanometres. Heat produces definite sedative effects in the body. Skin temperature above 45 degrees Celsius can evoke pain sensation. Local heating promptly opens the arteriovenous shunts in the skin

DEPTH OF HEATING

Different heating modalities can have different depths of penetration depending the thermal modality used and the part of the body to which is applied. High water content tissues such as the skin, muscle liver, kidney, blood and heart absorb heat quickly . Low water content tissues such as bone and fat poorly absorb heat. Subcutaneous fat tends to a thermal barrier and does not conduct heat effectively.

BLOOD FLOW
In the resting skin the blood volume is 0.25 litres per square metre of body surface area. This amount of blood is twenty times as much as is needed to supply oxygen to the tissues. On maximum heating the blood volume is increase 7.5 times the resting level. A large portion of this high volume flows through the arteriovenous channels by-passing the usual capillary routes and thus blood , as it perfuses all the veins, conducts heat to the outside. The arteriovenous plexuses act as a storage depot for blood.

LYMPHATIC SYSTEM
The skin is rich in lymphatic vessels. There are three layers of lymphatic connections in the dermis. The purpose of lymphatic vessels is to collect lymph fluid. Lymph fluid is a composite of extracellular fluid that contains waste products that are not collected by the arteriovenous system.

SENSORY RECEPTORS
There are many types of sensory nerves found throughout the skin. Each sensory nerves transmits only one modality of sensation. These include pressure, movement, pain, stretch, balance and thermal receptors.

THE SKIN
The skin is primarily made up of two distinct layers: the epidermis and the dermis.

THE EPIDERMIS
The epidermis is the outermost part of the skin. The thickness of the epidermis varies from 0.07 to 12 millimetres over most of the body except for the palms and the soles of the feet there it reaches a thickness from 0.8 to 1.4 millimetres. The epidermis has no blood vessels. There are only two types of cells in the epidermis. The malpighian cells make up the bulk of the epidermis. The malpighian cells produce keratin; a mostly insoluble protein that forms the glue that holds the skin together. The second type of cells are melanocytes and are the pigmentary cells that are responsible for the production of melanin. Melanin is the protein that is responsible in part for the colour of our skin.

THE DERMIS
The dermis is below the epidermis and is a tough, flexible and highly elastic tissue. The average thickness of the dermis is one to two millimetres and about 3 millimetres on the palms and soles of our feet. The outer surface of the dermis is in contact with the epidermis and consists of a vast network of elastic fibres and collagen. The dermis has a vast network of blood vessels including arteries, arterioles, veins, venules and capillaries. The skin is the only part of the body that has a network of arterieoles directly connecting to venules, bypassing capillaries. This is done to help the skin respond to thermal changes quickly and effectively.

HAIR FOLLICLES
Hairs are slender keratinous filaments that are found in the dermis and epidermis. Modified dermis cells produce hair and push the filaments through the skin surface. Hair follicles are nourished and lubricated by oil producing cells called sebaceous cells. The oil or sebum also helps to lubricate the skin surface and has some antibacterial properties.

SWEAT GLANDS
Sweat gland are found in almost every part of the skin. The usual consist of a tube coiled up in the form of a ball. They originate in the dermis and have a tube that reaches through the epidermis to the skin surface. Sweat glands occur throughout the skin but are more concentrated on the head, armpit, groin, hands and feet. Sweating is under neuro-hormonal control and is meant to help the body dissipate heat quickly and effectively. Sweat glands can be stimulated by a variety of physical and emotional stressors.

SWEAT
The composition of sweat is 99% water, with salt or sodium chloride and other compounds such as lactic acid and urea. The density of sweat is 1.04 g/ml. The pH of sweat reflects the internal pH and is sometimes acidic and is sometimes alkaline. In abnormal internal states the sweat may contain compounds not usually present such as bile pigment,, sugar, albumin and blood. The amount of water lost through the glands is 0.5 to 2.5 litres per day. Insensible water loss, that is unnoticeable water evaporation from the skin amounts to 50 millimetres per hour. During physical exercise this amount can increase to 1200 millimetres per hour. Water is lost through the skin primarily through sweat glands, but can also be lost by osmosis through connective tissue. Sweating is primarily controlled through the sympathetic nervous system; which controls the “flight or flight” response to stressors. The core ball of the sweat gland found in the dermis secretes a fluid very similar to plasma in the blood, except that it does not contain plasma proteins such as albumin and globulin. The primary secretion than travels the sweat tube to the surface. When stress glands are relaxed sodium and chloride ions are resorbed through the sweat gland tube walls. As a result of the change in ionic pressure water follows through and is also resorbed. When sweat glands are stimulated by the sympathetic nervous system there is increased production of the sweat precursor solution and inhibition of sodium resorption. The net effect is a large amount of sweat solution is pushed from the primary coil through the tube to the surface of the skin.

INFRARED RADIATION
Most radiant heat sources such as sunshine, open fires, heated stones, irons and steam saunas emit varying degrees of infrared radiations. Infrared radiations occupy a small segment of the electromagnetic spectrum having wavelengths from 700 to 15,000 nanometres. Infrared radiations are further classified according to their distance from the visible spectrum. The visible spectrum has wavelengths from 390 to 770 nanometres. Near or short infrared rays have wavelengths from 770 to 4000 nanometres. Far or long infrared waves have wavelengths from 4000 to 15,000 nanometres.

CONVECTION, CONDUCTION AND RADIATION
There are three methods of transferring electromagnetic energy from one substance to another: convection, conduction and radiation. Convection transfers electromagnetic energy through an intermediate substance such as ambient air. A distant energy source heats up ambient air particles. The air particles move around and come in contact with another substance, such as the person. The air particles transfer their thermal energy to the substance. Conduction conducts electromagnetic energy through direct contact of one substance to another. When one substance having higher thermal energy comes in contact with another substance of lower thermal energy and thermal gradient is created. Thermal energy is transferred from one substance to another of lower energy by direct contact. Radiant transfer of electromagnetic energy does not depend on a conductive medium nor by direct contact. Radiant energy transfers energy by electromagnetic waves. Infrared red radiation depends less on conduction and convection and utilizes radiant energy. One of the main advantages of infrared radiation is that you don’t have to heat up the source of thermal energy, nor the ambient air to the same degree as a conductive or convective method of heat transfer. You can still transfer thermal energy to a substance by radiation without using a higher temperature that you would otherwise use with conductive and convective methods.

INFRARED RAYS
Infrared rays are produced when an object is heated above absolute zero. All incandescent bodies found in light bulbs, such as tungsten and carbon filament lamps produced some infrared radiations. All objects that generate infrared rays along with some visible light are called luminous sources of infrared rays. An electric current passed through a copper wire generates some heat primarily in the form of infrared rays. All objects that generate infrared rays without visible light are called non-luminous sources of infrared rays.

REFLECTION, ABSORPTION AND TRANSMISSION
All radiations that strike the body must be reflected, absorbed or transmitted. For therapeutic benefit most rays must be absorbed by the body. There are many factors that can influence infrared ray absorption, including the frequency or wavelength of the rays, the thermal conductivity of the tissues, the density of the tissue, specific heat of each tissue, angle of the incidence rays, distance from the source of the infrared rays, patency of the circulation and the source of the infrared rays. It is important to note that maximal absorption of infrared rays occurs when the rays are perpendicular to the absorptive surface. As the angle of incidence increases, so does the refection of the rays.

DEPTH OF PENETRATION
Depth of penetration is a relative term. Short or near infrared waves of wavelengths from 770 to 440 nanometres penetrate about 3 millimetres below the surface of the skin. Long or far infrared waves penetrate less than 1 millimetre depth below the skin surface. The relative thickness of the layers of skin, the patency of skin circulation, and the quantity of underlying fat will affect penetration of infrared rays. The density of the connective tissue and fat below the skin surface will affect the absorption of the rays. Generally fat and connective tissue impede thermal conductivity. The intensity of the rays varies inversely with the depth of absorption. This means that even though some rays may penetrate deeper their relative intensity may be poor, not strong enough to illicit a physiological reaction.

LUMINOUS VERSUS NON-LUMINOUS
Infrared generators are classified as luminous or non-luminous, depending if they produce some light in the visible spectrum. They are all generally light weight and portable. They come in various sizes and shapes, have different levels of energy output from 250 to 1000 watts.

Non-luminous generators consist of a resistance wire coiled on a cylinder of insulating material such as clay or porcelain or a plate of resistance metal. The resistance wire serves as the heater and the cylinder or plate becomes the radiant source. Infrared rays are emitted from the heat from the resistance wire. Infrared waves are transferred to the cylinder or plate and is heated by conduction. Generally, non-luminous infrared generator emit wavelengths between 770 nanometres and 15,000 nanometres. Maximum emission is between 3500 and 4000 nanometres. There is a minimal emission of waves in the short infrared spectrum.

Luminous generators consist of gases and hot bodies that emit visible rays in the spectrum of 392 to 800 nanometres. Incandescent lamps containing tungsten or carbon filaments emit these visible rays plus a large proportion of infrared rays. Lamps generally come in different sizes and shapes. The power output varies from 100 to 1500 watts. The luminous generators emits up to 70% short infrared waves and less than 30% long infrared waves.

PHYSIOLOGICAL RESPONSES OF INFRARED
Infrared rays have the immediate effect of producing heat wherever they are absorbed. The amount of temperature rise is dependent on different factors including the source of infrared rays, the distance to the patient, the tissue being irradiated and the circulatory response. The main effects of infrared rays are due to the moderate temperature rise at superficial levels. It is a slow rise with a minimal thermal gradient. The temperature rise at deeper dermis levels is not more than 2 degrees Celsius and about 1 to 2 degrees in the superficial dermis.

NERVE STIMULATION
Both the long and the short infrared rays stimulate the sensory nerves, and can thus reduce pain and spasm. The underlying physiological mechanism of this is not fully known. Perhaps the raised temperature decreases gamma fibre activity. Usually a fast warming of the muscle spindle causes a temporary inhibition of its activity.

VASODILATION
If skin temperature is raised above core temperature, cutaneous vasodilation occurs to help distribute the heat more evenly. There is some conduction of heat to the deeper levels, but unless muscle is very superficially places, there is no vasodilation in muscles. Circulation in superficial joints may be increased refexly. Heat causes the liberation of histamine-like substances which act on the capillaries to dilate them. The heat regulating centre in the brain send signals to the capillaries to dilate them.

PHAGOCYTOSIS
An increase in temperature creates superficial inflammation on just below the skin surface. Heating activates white blood cells to eat up or phagocytize inflammatory residue such as bacteria, dead cells, or pus fluid. The white blood cells can help to drain carbuncles or furuncles around the skin.

REFLEX HEATING
Infrared rays can be applied to one area of the body can cause reflex heating in another distant area of the body. For instance, infrared heat applied to the abdomen can increase peripheral circulation in the legs. The physiological basis of is that heating of the large spanchnic vessels in the abdomen stimulates the heat centre in the brain, which then reflexly open peripheral vessels in an effort to regulate body temperature quickly.

PIGMENTATION AND ERYTHEMA
Infrared rays cause a reddening of the skin, which is a gentle erythema that disappears one the heat is dissipated.

SWEATNG
There is an increase in sweat gland activity both locally to the applied heat and reflexly by stimulation by the heat regulating centre in the brain. Infrared, unlike ultraviolet light, does not cause tanning or burning of the skin.

BLOOD PRESSURE
If heating is given to a large area of the body for a prolonged period, as in the use of an infrared sauna, there is a fall in blood pressure, due to generalized vasodilation and reduction of peripheral resistance in the arterioles.

HEALTH INDICATIONS
There five main indications for the use of infrared sauna: pain and muscle spasm, edema and swelling, healing of wound and chronic suppurative areas, detoxification and socialization.

The use of infrared radiation will cause a reduction of pain and muscle spasm in superficial areas. It should not be used in acute trauma in the first 24 hours, but can be used later. The luminous lamp is more effective than the non-luminous lamp. Increased vasodilation will improve circulation, remove pain and inflammation metabolites and break the cycle of pain and muscle spasm.

In cases of chronic edema or swelling of the hand, arm. foot and leg, if the exudate is mild and not tenacious, infrared radiation along with elevation of the affected part will result in capillary vasodilation.

Infrared radiation also aids in the healing of indolent wounds by its vasodilatory effects. For cases of slow healing post-operative wounds, infrared rays can be used to improve healing time.

CONTRAINDICATIONS
Caution must be used in individuals with impaired nerve sensation on the skin. Care must be taken of applying infrared rays to areas of poor circulation and thrombi. Care must be taken in applying heat to individuals with dermatological conditions such as fungal infections. No metal, such as jewellery or necklaces should be in the field of the infrared radiations. Caution must be used in individuals with surgically implanted metal screws and plates. Caution should be used in applying intense infrared radiations over the eyes. Caution should be used with elderly patients in general, especially the weak and infirm with compromised cardiovascular function. If individuals are on prescription narcotics and pain killers caution should be used when applying infrared heat. Caution should be used in individuals who have received radiation therapy in the last three months. They may have impaired thermoregulatory sensation. Most topical creams and ointments should be removed prior to applying infrared radiation. Individuals with skin tumours, such as carcinoma and melanoma should not receive strong doses of infrared radiation. Caution should be used in individuals with acute infections, whether respiratory or skin. Individuals on blood pressure medicines should be monitored for unusual blood pressure changes. And finally, caution should be used in individuals with compromised cardiac function, such as congestive heart failure.

SAUNA THERAPY
The temperature of the skin increases to over 40 degrees Celcsus, but after the sweating has started, usually in three to five minutes, the temperature declines and starts to rise slowly again. The temperature in deeper parts of the body increases much less; in the rectum and esophagus the temperature is around 37.5 to 38 degrees after a twenty minute sauna.

CARDIAC OUTPUT
The increased temperature dilates cutaneous capillary blood vessels and to maintain sufficient cardiac output increases two to three times normal. Considerable redistribution of cardiac output take place. Normally the skin blood flow is 5 to 10% of cardiac output, but can increases to 50 to 70% in a sauna. Correspondingly, the blood flow to inner organs and muscles decreases. The changes of blood pressure are moderate. Most often a small decrease of systolic and diastolic blood pressure takes place. During the cooling perid, especially if it happens vigorously in a cold shower or by swimming in ice cold water, blood pressure rapidly increases. The increase of cardiac load in the sauna is similar to that seen during brisk walking exercise.

SWEAT LOSS
The average fluid loss during a sauna bath is 500 millilitres or 500 mg of sweat. It corresponds to less than 1.0% of total body weight. Sweat contains less salt than blood and thus mild sauna can increase blood levels of sodium and potassium. The concentration of hemoglobin can increase temporarily. Taken together, fluid loss during an ordinary sauna bath is relatively small and it can easily be compensated by drinking a couple of glasses of water. Sauna therapy does not induce significant changes in blood coagulation.

ENDOCRINE SYSTEM
Sauna affects the endocrine system in many ways. According to most sauna studies, sauna stimulates the production of the hormones, noradrenaline, prolactin, growth hormone, cardiac natriuretic peptide and activates the renin-angiotensin,-aldosterone system. The findings on ACTH or adrenocorticotrophic hormone and cortisol in inconsistent and not changes seem to take place in adrenaline, FSH, LH, testosterone or thyroid hormones.

LONGEVITY
The scientific literature is inconclusive with respect to longevity and sauna. Regular sauna therapy has been widely touted by peoples of Finland for many health benefits. The people of Finland are among the longest lived people in the world. Many people in Finland are regular sauna bathers. How much of their longevity is due to regular sauna baths remains to be proven.

PREGNANCY
High temperatures for prolonged periods can induce congenital malformations in some pregnant experimental animals including spina bifida and anencephaly. Caution should be exercises in pregnant females who engage in sauna therapy. Limitations in both the frequency, intensity and duration of sauna therapy may be employed. One study in Finland showed no connection between sauna and congenital malformation in pregnant females.

LUNG PROBLEMS
There were some earlier concerns about the incidence of sauna therapy and the development of lung cancer. Some individuals proposed the breathing dust from sauna baths could be carcinogenic. A Finnish study showed that there was no association between sauna therapy and the development of lung cancer.

HEART ATTACK AND CONGESTIVE HEART FAILURE
There were some concerns about the use of sauna of individuals with heart attack and/or congestive heart failure. No strong association was found in some studies between the use of sauna and the development of heart attacks. Caution should be used in individuals with congestive heart failure who have particularly decompensated hearts and the duration and intensity of sauna treatment.

COLD PREVENTION
Some regular sauna users contend that regular sauna use prevents the common cold. In one small, controlled study regular sauna bathing twice per week for six months lead to a 30% reduction in the incidence of cold episodes. In the study, 22 kindergarten children who took a weekly sauna for 18 months had reduced incidence of colds, flu and ear infection. Obviously further studies would be necessary to prove this benefit.

HEAVY METAL DETOXIFICATION
Numerous scientific studies show that sweat can contain significant levels of heavy or toxic metals. Minerals such as sodium, chloride, iron, copper, lead, manganese, mercury, nickel, cadmium and zinc have been quantified in sweat. When compared to urine, sweat contained higher concentrations of nickel and cadmium and the same concentration for lead. Negligible effects on calcium, magnesium and potassium were observed. The content of sweat mimics the serum in the blood minus the plasma proteins. Therefore, it can be assumed that other factors in the blood can be found in sweat. Higher levels of urea and uric acid have been detected in sweat. Negligible amounts of cholesterol and triglycerides have been observed

ENDOTHELIAL FUNCTION
Sauna improves blood vessel tone, otherwise known as vascular endothelial function. Upregulation of vascular endothelial nitric oxide has been observed. Nitric oxide is a potent vasodilator. As thermal energy promotes cutaneous vasodilation based on a number of different mechanisms, there is a probably and an increased sensitivity to nitric oxide. As a result, less nitric oxide may be required to cause vasodilation than before.

BLOOD PRESSURE AND HEART RATE
Sauna treatment can lower blood pressure. Changes in both systolic and diastolic blood pressures have been observed with sauna therapy. While more pronounced during and shortly after sauna treatment a generalized trend of lowering blood pressure has been observed. One study showed that systolic pressure decreased an average of 6 percent. Diastolic pressure decreased an average of 4%. Heart rate increased an average of 32% above resting heart rate. Resting heart rate returned to normal after sauna treatment was finished. No arrhythmias or EKG changes were detected. Myocardial ischemia or decreased blood flow to the heart, was observed on nuclear scintigraphic imaging. The myocardial ischemia induced while undergoing sauna treatment was equivalent to exercise-induced ischemia. No clinical symptoms, such as angina, were observed with the myocardial ischemia. The implications of this study are that sauna therapy will increase heart rate temporarily, decrease blood pressure temporarily while causing a temporary reduction of blood flow to the heart muscle. In individuals with stable coronary angina sauna therapy was generally well tolerated with no significant side effects. However, caution should be exercised in individuals with unstable coronary angina who might otherwise undergo sauna treatments. Another study shows that cardiac function can actually improve with repetitive sauna treatments in individuals with class II and class III congestive heart failure.

DETOXIFICATION
Sauna has been widely touted as an effective means of detoxification. The skin is the largest organ in the body. It is responsible in part for detoxification. In several studies, significant increases in the heavy metal concentration of sweat has been observed in individuals undergoing sauna treatment. Sauna is usually recommended as part of detoxification procedure in individuals with heavy metal toxicity. There are many other toxins in the environment that can pollute the human body. Numerous pesticides and pesticides have been found in tissue samples of the human body. Toxic chemicals such as DDT, DDE and PCB’s have also been found in tissue samples. While many of these toxins are water soluble some are lipophyllic or fat soluble. Many of the exposed toxins have accumulated in fat tissue throughout the body. Theoretically mobilizing these toxins through sauna induced sweating creates a concentration gradient that allows the migration of these toxins through the excretory organs such as the skin. Many anecdotal reports of individuals and health practitioners about sauna-induced detoxification are rife in the media and internet. However, good scientific data about non-heavy metal toxins such as herbicides, pesticides and the like is lacking. Further scientific studies evaluating the fat-soluble concentration of these toxins is necessary to determine the effectiveness of sauna therapy as an agent for detoxification.

PAIN AND INFLAMMATION RELIEF
Sauna therapy provides some level of pain relief and reduction in inflammation. The exact degree of pain relief and reduction in inflammation is highly variable, depending on the person, the nature of the problem, the location and other physical factors. Infrared radiation has been utilized in some form since the early 1900’s. Treatment of post-acute trauma responds well to heat and infrared therapy. Transient decrease in pain and inflammation has been observed in individuals in chronic pain such as osteoarthritis. Improvement and relief of chronic muscular problems has been observed with infrared treatment. Other improvement in soft tissue, such as ligaments and tendons has been observed with infrared treatment.

SOCIAL
Then there is the social and stress-reduction benefits of sauna therapy. Sauna therapy, whether infrared or not, can be a good social outing. The use of sauna therapy as a means of community socialization has been engrained in many cultures throughout the world. It can also help to relax from the demands of our busy secular lifestyles. It can help tense muscles to relax and offer a meditative environment removed the busy world outside.

SUMMARY
Infrared Sauna therapy isolates a specific range of the electromagnetic spectrum just below the visible spectrum. Infrared uses radiant energy to heat up the body. One major advantage of infrared sauna therapy over the traditional heat sauna is that the temperature need not be that high to achieve therapeutic benefit. While many steam saunas require a temperature of over 60 degrees Celsius, infrared sauna temperatures range from 38 to 60 degrees. Infrared sauna therapy can be easily tolerated by individuals who are heat sensitive or who suffer from heart disease or general debility. The main therapeutic uses of infrared sauna are for reduction of pain and inflammation, detoxification and socialization. Benefits to the cardiovascular system, lymphatic, endocrine and immune system have been observed. Additional benefits include an improvement in general health and well being.

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