Having completed this lesson, you will be able to:

• Define the term homeostasis.
• Describe one factor that influences the degree to which the body is affected by a hot or cold application (e.g., the greater the temperature difference between the body and the hydrotherapy application the greater the physiological effect on the body, the length of the hydrotherapy application influences the physiological effect on the body, the larger the body area treated by hydrotherapy the greater the effect on the body, etc.).
• Match these temperatures to written descriptions of their physiological effects: hot, neutral, cold, contrasting temperatures.

Understanding hydrotherapy’s effects on the body begins with the concept of homeostasis. Homeostasis is the relative constancy of the body’s internal environment. The body’s internal environment includes the extracellular fluid that bathes cells. From this fluid cells receive oxygen and nutrients, and into this fluid cells excrete wastes from their metabolic activities. The health of each cell and an organism’s survival depends on the ability of the organism to sustain a relatively constant internal environment. If the internal environment is disturbed to the extent that it can’t adjust, such as by prolonged exposure to cold and hypothermia, death of cells and potential death of the organism result.

Humans are able to maintain internal environmental stability because intricate regulatory mechanisms continually monitor and correct the body’s internal environment by adjusting physiological functions.⁸ The body’s core temperature is relatively constant, even in the face of widely varying external environmental temperatures, because of this ability. For example, the body produces heat when the core becomes too cool, and increases heat loss when the core starts to overheat. Hydrotherapy applications are designed to change the internal environment of the body by applying temperatures above, close to, or below that of the body’s normal temperature (97°F). The physiological effects of hydrotherapy occur as a result of the body’s attempt to return to a constant internal state. For example, a common physiological effect of the application of heat is vasodilatation of blood vessels and increased blood flow to the local area, which moves warm blood out toward the periphery, cooling the core of the body. A common physiological effect of cold is decreased local edema and decreased pain. The edema is reduced through vasoconstriction of blood vessels, which drives warm blood back to the core ensuring the core maintains the proper temperature. As a result, pain is reduced by a decrease in nerve conduction velocity. Three key factors influence the degree to which the body is affected by hydrotherapy applications:

• The greater the temperature difference between the body and the hydrotherapy application, the greater the physiological effect on the body. If a client is placed in a bath at 97°F (close to normal body temperature), neither the therapist nor the client will notice much of a physiological difference (although a mild tonic effects occurs with neutral applications). If the same client is placed in a bath at 110° F, the physiological changes in the body will be readily apparent to both. The pulse rate increases, the skin flushes, body temperature rises, metabolism picks up, the blood becomes more alkaline, and white blood cells increase in number. The client may feel nervous or even agitated by the application and will probably want to get out of the hot water.
• The length of the hydrotherapy application influences the physiological effect on the body. A client placed in very cold water (32-55°F) will have two very different reactions based on the length of the treatment. If the application is brief (less than 1 minute), blood vessels will constrict to prevent heat loss. A short time later, blood vessels will dilate as the body attempts to warm itself and prevent tissue loss at the periphery. Muscle tone is increased, and there is an initial spike in blood pressure and respiratory rate. The client is likely to report feeling refreshed and invigorated. If the application is longer than 1 minute, the client’s blood vessels constrict as the body attempts to move blood to the core to keep the core temperature consistent. After about 20-30 minutes of continuous cold, vasodilation occurs, which increases circulation (Box 16-1), although not above the baseline when the cold was first applied. The physiological processes of the body are depressed, and if the client is not removed from the cold water, death could result.

<box16-1>

• The larger the body area treated, the greater the physiological effect on the body. Hydrotherapy applications can be used over the entire body or locally. If the body is immersed in a bath, as in the examples above, the effect is more profound than if a cold pack is applied to one local area, say the hamstring. If the cold application is a full body immersion, the hunting reaction described in Box 16-1 is potentially deadly because heat from the body’s core is used to delay tissue loss at the periphery. If the cold is applied just to the hamstrings, the hunting reaction acts as a pump to flush out metabolic wastes in tissues and bring fresh oxygen and nutrient-rich blood to the area.

<cb16-3> Concept Brief 16-3: Physiological Effects of Hydrotherapy

The effects of hydrotherapy applications can be understood in terms of six primary categories, which overlap and interrelate:

• physiological effects
• psychological effects
• reflexive effects
• mechanical effects
• effects from dissolved substances
• effects from specific temperatures

A combination of different types of effects usually occurs simultaneously during a hydrotherapy application. For example, different temperatures cause physiological effects, and dissolved substances, like herbs, can influence the psychological impact of an application.

Physiological Effects

As mentioned earlier, many of the effects of hydrotherapy occur because the body responds to temperatures above or below normal body temperature in an effort to maintain homeostasis. Hydrotherapy applications have a strong effect on blood circulation, causing vasodilation of blood vessels in some instances and vasoconstriction of blood vessels in others. Certain applications can shift blood from one area of the body to another or cause cycles of vasoconstriction and vasodilation that flush the local tissue of metabolic wastes by bringing fresh nutrient- and oxygen-rich blood into an area, pushing blood back out, and repeating the process. In this way, metabolic wastes are removed from the area, leaving the tissue healthier. Certain types of applications cause an increase in blood pressure and heart rate, while others cause it to decrease.

The skin is also directly impacted by hydrotherapy applications because sensory receptors are responding to all the textures and nuances of feeling created by the application and sending rapid signals to the brain. Overheating the body, as in a sauna treatment or hot immersion bath, stimulates the sweat glands, which helps the skin excrete metabolic wastes from the body. Metabolic wastes that have accumulated in the adipose layers under the skin can be metabolized and released during this process, helping the body to naturally detoxify.

Psychological Effects

While the psychological effects of water and hydrotherapy applications are not always as clearly defined as physiological effects, you have only to contemplate your feelings as you visualize a warm tub full of water, the delights of a swimming hole on a hot summer day, or the feel of warm sea mist on your face to understand water’s psychological impact. People love water. In fact, maps of the world’s population show that most of humanity lives near water. People gather along coastlines, along the course of rivers, and on islands. Popular vacation spots are often located on bodies of water.⁹ Water holds an important place in myth and legend and is often viewed as a transformative power. Artemis in Greek mythology ruled the tides as the goddess of the moon. She also personified the unconscious depths of the human mind, which are associated with water. Rituals of purification often involve water, as it is a substance that washes away dirt from the body and in some religions cleanses the soul. Many cultures believe that life sprang from water and that special waters impart youth and renewed beauty. Water can represent an important passage through difficulties to renewal of the spirit. All of these conscious and subconscious factors can be at play during hydrotherapy sessions and benefit clients through the pleasure they receive through interaction with water.

Reflexive Effects

Hydrotherapy applications can produce reflexive effects (sometimes called a consensual response) that occur because of a nervous system reaction to the treatment. Reflexive effects happen in an area removed from the point of local application, usually between the skin and the viscera, although heat applied to one limb will increase circulation in the other limb. The reflex relationship between the skin and the internal organs is due to a segmental connection. Both receive sensory innervation from the same segment of the spinal cord. For example, heat applied to the abdomen causes the activity of the intestines to decrease. A hot or cold application to the sternum affects the function of the esophagus. A cold application to the head stimulates mental activity, while the application of a cold pack to the sacrum or feet causes dilation of the uterine blood vessels.¹⁰

Mechanical Effects

When water is pressurized in a spray, shower, hydrotherapy jet, or whirlpool, the force of the water on the skin’s surface and on the muscle tissue below manipulates the tissue for a mechanical effect. The body may respond to the sensation of water striking the tissue defensively at first, causing muscle tone to increase. Gradually the body relaxes into the sensation of the pressurized water and muscular tension is reduced, circulation is improved, and overall body function and vital energy are increased.

The hydrostatic pressure of water (as described in Topic 16-1) can be considered to exert a mechanical effect on body tissue. Recall that water exerts more pressure on body areas that are deeper in the water. This effect can be used to squeeze fluid from the lower extremities to the thorax; for example, exercising in water reduces edema in the lower legs. In some types of hydrotherapy applications, fluids are pulled from the upper body to the lower body. A classic example is the use of a hot foot bath to decrease congestion in the sinuses due to a cold. The hot water pulls fluid down toward the feet and out of the head. In folk medicine, migraines are treated with a warm foot bath and an ice pack on the back of the neck. The dilation of blood vessels in one body area reduces the fluid congestion in another area.

Another type of mechanical effect of hydrotherapy applications occurs with classic friction rubs like salt glows, wet skin brushing (like dry skin brushing as described in Chapter 15 except the skin is dampened with water or vinegar), or cold mitt friction. The mechanical action of the rough-textured product, brush, or mitts against the skin causes local circulation to increase as the friction generates heat in the tissue.

Effects from Dissolved Substances

In Topic 16-1 you learned that water is called the universal solvent because it dissolves many other substances such as minerals and plants, creating a therapeutic “soup.” For example, the Dead Sea is an ancient landlocked sea whose water has been slowly evaporating over the centuries, producing a highly concentrated natural salt solution. After bathing in the Dead Sea, people often report a feeling of increased energy and well-being as well as soft skin. The main mineral elements in Dead Sea water are chlorine, magnesium, sodium, calcium, potassium, and bromine.¹¹ Research on the usefulness of bathing in the Dead Sea confirms that it benefits a variety of skin conditions because it improves the barrier function of the skin.¹² It is also used to reduce inflammation from musculoskeletal injuries including back injuries,¹³ improves the function of joints effected by both rheumatoid and osteoarthritis,^{14, 15} and decreases the severity of symptoms associated with fibromyalgia.¹⁶ Additives dissolved in water may have physiological or psychological effects that enhance and support the benefits of the hydrotherapy application. For example:

• Herbs: When herbs are soaked in water, many of their chemical components are transferred to the water along with their therapeutic properties. Red clover, lavender flowers, chamomile flowers, powdered oatmeal, comfrey, elderflower, and calendula petals soothe skin irritation and are used to improve many skin conditions. Juniper berries, ginger root, clove bud, allspice, rosemary, and sage warm the body and support perspiration for detoxification treatments. A wide range of herbs and herbal products are used in combination with hydrotherapy applications. Visit spa and massage supplier websites to research your options.
• Milk: Milk, powdered milk, buttermilk, and cream can be dissolved in water to soften and condition the skin.
• Minerals: Minerals in salts like those from the Dead Sea, regular sea salt, or Bearn salt from the mineral springs of the Pyreness Mountains of Southern France dissolve in water, allowing the minerals to be absorbed by the skin to improve both the texture of the skin and overall body function. Epson salts are inorganic mineral salts that help the body detoxify and increase general circulation. They are well known for use with sprains, strains, and sore, fatigued muscles. They also relax the body and are useful for insomnia.
• Seaweed: Seaweed contains many bioactive compounds that can be absorbed through the skin and used by the body to support overall body function. Seaweeds have high concentrations of vitamins A, B1, B2, B5, B12, C, D, E, and K. They also contain polyphenols and carotenoids, which play a role in protecting the body from oxidative stress. Brown seaweeds such as Laminaria, Sargassum, Fucus, and Ascophylum species stimulate metabolism, raise body temperature, and affect cell membrane transport, facilitating detoxification. All seaweeds contain some amount of iodine, which influences thyroid activity. For this reason do not use seaweed with clients who have iodine, shellfish, or seaweed allergies or who take thyroid medications.
• Essential oils: Essential oils do not dissolve in water, as noted in Chapter 15 (Spa Therapies and Other Approaches), but they are commonly added to baths, saunas, and steam rooms to increase the therapeutic benefits of these applications. Review the aromatherapy section of Chapter 15 for specific information on essential oils to use in such treatments.

Effects from Specific Temperatures

Different reflexive and physiological effects depend on the temperature of the water applied to the body. Table 16-1 provides an overview of common water temperatures used in hydrotherapy, while Table 16-2 summarizes the effects of hot and cold temperatures. Hot, cold, neutral, and contrasting temperatures are used in hydrotherapy applications.

<tab16-1> <tab16-2>

Effects of Heat

The physiological responses of the body to heat result from the body’s attempt to prevent a rise in body temperature. Brief applications stimulate the body, while applications of longer duration sedate the body. The use of external applications of heat for therapeutic purposes is sometimes referred to as thermotherapy.

When heat is applied to a client with a full immersion bath, steam bath, sauna, hot pack, or partial bath such as a foot bath, the peripheral blood vessels dilate and the client begins to perspire. The blood flow to the area where hydrotherapy is applied increases significantly and flushes the tissue. The heart rate, pulse rate, respiratory rate, and overall rate of metabolism rise, which increases the consumption of oxygen in the tissues. The rise in core body temperature creates an artificial fever which in turn stimulates the immune system and causes the body’s white blood cell count to increase, inhibiting the growth of some bacteria and viruses. The higher blood flow to the area relaxes muscles, reduces muscular spasm, increases the extensibility of collagen, “melts” the superficial fascia, increases the range of motion in joints, reduces pain, and is generally relaxing.

Effects of Cold

The physiological responses of the body in reaction to cold result from the body’s attempt to prevent a decrease in body temperature. Like heat, brief applications stimulate the body, while applications of longer duration sedate the body. The use of external applications of cold for therapeutic purposes is sometimes referred to as cryotherapy.

Cold penetrates more deeply into the tissues than heat as vasoconstriction causes a decrease in local circulation and tissue metabolism. There is also a decrease in leukocytic migration through the capillary walls, which aids in the reduction of edema and pain. Initially there is an increase in respiratory rate, heart rate, blood pressure, and muscle tone. These gradually drop if the application of cold is prolonged. The reduction of nerve conduction velocity leads to a numbing effect that significantly reduces pain. If the cold persists, vasodilatation and circulation are briefly stimulated.

Clients often have difficulty with cold applications and pass through distinct stages that might feel uncomfortable. The first stage is a sensation of cold, which progresses to a feeling of itchiness or tingling. As the cold continues, the tissue feels as if it is aching and burning. Eventually numbness replaces the uncomfortable feelings and the client relaxes towards the later stages of the treatment.

Effects of Neutral Temperatures

Neutral applications are administered at or close to normal body temperature and produce a tonic and balancing effect in most clients. These types of applications are used to soothe the nervous system and can be an effective treatment for insomnia, nervous irritability, anxiety, or depression. Neutral applications are sometimes used at the beginning or end of a hot or cold application to help the body ease into or out of more extreme temperatures. The use of external applications for therapeutic purposes at temperatures close to the body’s normal temperature is sometimes called neutrotherapy.

Effects of Contrasting Temperatures

Contrasting applications involve applying a heat application and then a cold application to the same body area in an alternating sequence. This creates a vascular flush in which the tissues are “pumped” free of metabolic waste build-up due to the alternating vasoconstriction and vasodilatation of the peripheral blood vessels. Often the treatment uses a pattern of 3 minutes of heat to 1 minute of cold for 3 rounds. The treatment always ends with a cold application to prevent congestion in the local tissue. Sometimes a longer rotation is used with a ratio of 10-15 minutes for the hot application followed by 10-15 minutes of a cold application. Again, the treatment ends with a cold application. When using packs to apply heat and cold, it works well to place a cold pack on the area of injury and a hot pack proximal to the injury site close to the cold pack. This relaxes the client and makes it easier to tolerate the cold pack. Contrasting applications are used with immersion baths, partial baths, showers, and packs.