Use of heat packs in physical therapy of patients is common for the treatment of many common conditions, such as treating a variety of muscular problems and inflamed joints. Over the years, a variety of different heat packs have been developed for use in such applications.

The simplest heat packs use hot water bottles wrapped in towels which are then pressed upon the treatment area. However, typical hot water bottles are difficult to use as most of the different body parts treated by the hot pack are not flat. If a rigid hot water bottle is used, such as a cylindrically shaped metal or plastic container, only a small portion of the bottle will contact the skin. Further, due to the effects of gravity, the low viscosity hot fluid will tend to pool in the lowest areas of the bottle. Even if a hot water bottle made of a flexible rubber is used, the water will tend to pool in the lowest areas of the bottle. As a result, the treatment area is heated unevenly, resulting in the portions closest to the heated fluid being heated more than the remoter areas. To overcome some of these difficulties of hot water bottles, a common alternative is a moist heat pack such as the Hydrocollator available from Chattanooga Corporation. The Hydrocollator comprises a flexible container such as a canvas bag containing several compartments filled with a water saturable clay-like medium having a relatively high heat capacity. Before application of the heat pack to the treatment area, the heat pack is heated by, for example,

immersing the pack in a hot water bath at 170° F. Alternatively, the pack may be warmed by a micro-wave oven or by an electric heater. The pack is then placed in towels or in a special cover with the moist heat being wicked through the cover to the treatment area. Such special covers may further include velcro covered straps for securing the heat pack to the body of the patient.

Nonetheless, the clay filled heat packs also have disadvantages. The heat packs cool off over a period of time. Initially the heat pack is at an elevated temperature and eventually it cools to the ambient temperature. The only means typically available for controlling the heat applied to the treatment area is to add or remove towels to retard or accelerate the heat transfer. In addition, the duration of the heat treatment is not readily controlled and depends upon the number of towels used and the amount of heat absorbed from the medium having the high heat capacity. An additional problem for such heat packs is the weight of the high heat capacity medium.

It has also been known that various exothermic reactions may be used for providing controlled heating of foodstuffs such as is evidenced in U.S. Patent No. 5,035,230. However, such food heaters of the prior art generally provide even heating only if positioned on a level surface.

Therefore it is a first object of the invention to provide a hot pack that uniformly heats the treatment area over an extended time period. It is a second object of the invention to precisely control the duration of the heat treatment. It is yet another object of the invention to provide more precise temperature control without the use of toxic chemicals. It is a still further object to provide such heat packs that may be disposed of using conventional disposal methods without any adverse environmental effects.

Summary of the Invention

These and other objects of the invention are achieved through the use of preferably a liquid based polymerizable fuel/water mixture used with a complementary oxidizer. In an embodiment, the fuel/water mixture is stored in an inner bag and the oxidizer is stored in the outer bag. The fuel/water mixture contains excess fuel and the inner bag is of a weaker construction than the outer bag.

When using this embodiment, the inner bag is ruptured and the ingredients are mixed to produce heat. During the reaction, non- water soluble, non-organic acids are preferably formed to polymerize some of the fuel, causing the viscosity of the mixture to increase to that of a gel. The gel keeps the reactants from flowing away from the treatment area when the treatment area is not a level surface.

Preferably, a thin sponge is attached to the outside of the heater. Before initiating the chemical reaction, the sponge is saturated with water to provide moist heat. By controlling the dimensions of the outer bag, the concentrations and amount of the oxidizer and the fuel, total heating time and maximum heat can be carefully controlled.

Description of the Drawings

Figure 1 shows a top plan view of an embodiment of the disclosed invention.

Figure 2 shows a cross sectional view of an embodiment of the invention taken along line 2-2 in Figure 1 .

Figure 3 shows a cross sectional view of a second embodiment of the invention.

Figure 4 shows a plot of a typical temperature profile of the embodiment of the invention shown in Figure 1 . Description of the Preferred Embodiments

Figure 1 shows a cross-sectional view of a first embodiment 10 of the invention. The embodiment 10 comprises an inner fuel bag 20 (Figure 2) placed within an outer bag 30 containing a complementary oxidizer. Although shown to have a rectangular shape, other embodiment may have other shapes to conform better to the treatment area such as a ring (not shown), which may be used for treating limbs of the patient. The inner bag is preferably made of a flexible material such as a plastic film like polyethylene or mylar and preferably has one or more weakened seams 22. The inner bag 20 acts as barrier to prevent the fuel from mixing with the oxidizer until the desired time and is of a weaker construction than the outer bag 30. By applying a few pounds per square inch of pressure to the inner bag through squeezing the outer bag 30, the inner bag 20 ruptures. Alternatively, other structures may be used to separate the oxidizer from the fuel by a barrier (not shown) and then rupturing the barrier to combine the fuel with the oxidizer such as those shown in U.S. Patent No. 5,035,230. Still further, the fuel may be placed in the outer bag 30 and the oxidizer may be placed in the inner bag 20. After rupturing the barrier separating the oxidizer and the fuel, the user should preferably knead the heat pack to provide a more uniform reaction.

In the embodiment 10, the inner bag 10 is preferably filled to the maximum capacity with a fuel/water mixture 24 such as a glycerine/water mixture. In one embodiment, the glycerine/water mixture is 90% by volume glycerine and 10% by volume water. However, alternative fuels may be used such as a fuel/water mixture with the fuel component being glycerine, sugar or corn syrup, molasses, sorghum syrup or ethylene glycol. Any other water soluble substance that undergoes an exothermic reaction when oxidized and is polymerized by the resultant products of the reaction may be used. In particular, the polymerization should provide an increase of at least three orders of magnitude of the viscosity of the combined fuel/oxidizer mixture, resulting in a desired viscosity in the range of 10 ⁶ to 10 ⁹ centipoise. The increased viscosity of the fluids is desirable as it inhibits the flow of the combined fuel/oxidizer mixture due to gravity and thus permits more even heating of the treatment area.

The outer bag 30 is preferably made of polyethelyene, polypropylene or mylar film. The film of the outer bag 30 may be coated with a thin layer of a non-toxic heat conductive metal. The outer bag 30 typically contains the oxidizer, preferably a potassium permanganate based oxidizer mixed with water. The oxidizer is preferably only partially soluble in water (about 6.6 in 100 parts is preferable) so that the outer bag contains a mixture of a weak solution and particles of the oxidizer. In one embodiment of the invention for use with the glycerine/water mixture, the oxidizer may be bound within a binding agent for better control of the reaction rate. For example, 1 5.5 grams of potassium permanganate (KMnO ₄ ) may be bound with 4.5 grams of a sodium silicate/water binding agent slurry. The sodium silicate/water slurry is preferably 85 % sodium silicate (Na ₂ SiO ₃ ) by volume and 15 % water by volume and may be obtained from J.T.

Baker Co. As an alternative to water, other polar inorganic solvents may be used. The potassium permanganate/sodium silicate/water mixture may then be diluted by partially dissolving the oxidizer in 200 cubic centimeters of water. Inorganic binders such as sodium silicate should be used if the fuel is mixed with an inorganic solvent such as water while an organic binder should be used if the solvent for the fuel is an organic chemical.

Once the fuel and the oxidizer are combined, an exothermic reaction starts, quickly heating the heat pack up to a maximum temperature that is preferably less than 85°C. Preferably the reaction produces non-water soluble, inorganic, non-toxic acids or other chemicals that polymerize some of the remaining fuel at the temperature of interest.

It is also important that there is excess fuel in the inner bag. An end product of the reaction may include non-water soluble, inorganic acids, which polymerize the excess fuel at the temperatures of interest, about 35°C to 85°C. The polymerized excess fuel increases the viscosity of the mixture by several orders of magnitude, from, for example, about 1 ,000 centipoise for a glycerine fuel mixture to greater than 10 ⁶ , and preferably greater than 10 ⁹ centipoise. The typical desired increase in viscosity should result in a gel or jelly-like substance.

The amount of excess fuel needed depends upon the particular fuel and oxidizer chemistry, the amount of diluting materials such as water and any binders, the desired resulting viscosity of the polymerized fuel, and the desired time for heat treatment of the patient. However, typically more than 50% of the total fuel originally contained within the inner bag will not be oxidized during the heating period. The amount and type of fuel, oxidizer, binder and diluent are also important to control the reaction rate, which affects the peak

temperature, viscosity, and the temperature of the heat pack over time (the temperature time profile). Typically, the greater the viscosity of the resultant fluid, the slower the reaction rate. Also, for example, by altering the diluent strength of the binder, one can control the rate at which heat is output as explained in Table 1 below. Table 1 shows the heat output for the ratio of a sodium silicate binder to water diluent binding potassium permanganate when used with an ethylene glycol fuel.

TABLE I

Bond Strength Surface Recession Heat Output Rate

(Ratio of Binder (inches/min) (BTU/in ² -min.) to Dilution Water)

75% 62% 50%

Other heat output rates may be experimentally determined by

altering the ratios of the chemicals. Also, the dimensions of the

outer bag 20 will effect the temperature and may be experimentally

determined by varying the size of the bag along with the ratios and

quantities of the various constituent chemicals.

Figure 4 shows a temperature profile for a heater made

according to the present invention. The reaction was conducted

using inner and outer bags made of polyethylene. Twenty grams of

an oxidizer/binder mixture was diluted with 200 cubic centimeters of

water and placed in an outer bag of 2 mil thick polyethylene

dimensioned approximately 8 inches by 7 inches by 3/4 inches high.

The inner bag was filled to capacity with a fuel comprised of 40

cubic centimeters of a 90% glycerine/10% water solution. A

temperature/time profile 1 for a thermocouple placed approximately

at the center of an exterior surface of the outer bag and a

temperature/time profile 2 for a thermocouple positioned about 1 .5

inches from the first thermocouple on the exterior of the outer bag

are shown in Figure 3. As can be seen from Figure 3, the

temperature over the surface of the outer bag is uniform so that the

patient will experience uniform heating.

In an alternative embodiment of the invention shown in Figure

2, a sponge 40 is attached to at least one surface of the outer bag

to provide moist heat. The sponge 40 may be formed of celluose or

preferably a disposable, cloth-like material comprised of a scrim

coated with a superabsorbent material having one or more

nonwoven fibrous webs bonded to the scrim. Such cloth-like

materials are available from Wigert International of Lake Forest,

Illinois under the brand name of Wipex.

Before or immediately after starting the exothermic chemical

reaction, the sponge is saturated with water or a liquid ointment.

Due to the high heat capacity of a liquid such as water, the

saturated sponge may act as a heat sink initially, lowering the peak

temperature of the heat pack.

Lowering the peak temperature through the use of a water

saturated sponge also results in a more extended elevated

temperature of the heater. The polymers formed with most of the

fuels and oxidizers are more stable at lower temperatures and these

polymers also inhibit to some degree the reaction rate. As a result

of having the polymers initially formed at a lower temperature, the

reaction rate is slowed so that the reaction takes longer to complete.

For even better control of the temperature and temperature/

time profile of the heat pack, the sponge 40 may be preloaded

before packaging of the heater in a sealed container with a specific

amount of water. This will allow the manufacturer to more

accurately set the maximum temperature and the duration that the

heater is at the desired temperature level.

For treatment of a patient, the heat pack may after activation

be wrapped in towels or inserted in a conventional heat pack cover

for treatment of the desired area according to conventional physical

therapy techniques. The increased viscosity to a gel or jelly-like

viscosity provides fo improved heat transfer as the reactant mixture

does not readily pool at the lowest point as do liquids such as water.

However, compared to conventional heat packs such as

water/sand heated heat packs, the disclosed heat packs are lighter

and do not require hot water baths. Further, the instant

embodiments exhibit more uniform temperature/time profiles as the

temperature/time profile may be carefully controlled by controlling

the amount of water in the sponge, by the selection of the binder,

oxidizer, diluents and fuel and by the relative ratios of the

constituent chemicals. Also, the resultant products appear to be

non-toxic and may be disposed without any special procedures.

Although a specific embodiment 10 is shown, it would be

understood by those of ordinary skill that the same principles may

be applied to other embodiments. Resort to the true scope of the

invention should be had by resort to the claims.