Hyperthermia technique

A heat therapy technique by which heat is applied to a limited skin area of a patient to penetrate the tissue and produce hyperthermia in an internal region underlying this area without, however, causing undue discomfort to the patient or damaging surface tissue. Applied to the skin area is heated air in a pulsatory air wave pattern whose relatively brief pulses flow at high velocity and are at a high temperature well above body temperature and whose static intervals between pulses are at a medium temperature somewhat above body temperature. As a consequence, heat transfer from the surface tissue toward the internal region takes place during the intervals, thereby reducing the temperature of the surface tissue and preventing it from reaching an unacceptable level despite the high temperature of the high-velocity pulses applied thereto.

BACKGROUND OF INVENTION 
This invention relates generally to techniques for the hyperthermia 
treatment of living tissue, and more particularly to devices for applying 
hot-air, high-velocity pulses to a limited skin area of the body in a 
manner which acts to significantly raise the temperature of an internal 
region underlying the skin area without excessively heating surface 
tissue. 
The interior of the human body has a normal temperature level which is 
usually said to be 98.6.degree. F. But actually, in the course of each 
24-hour period, the body temperature rises above and falls below this 
nominal value within a 1.8.degree. F. range. Body temperature is 
determined by the relationship existing between the amount of heat 
internally generated, which depends on basal metabolism, and the amount of 
heat escaping from the body. Additional heat is produced as a result of 
muscular activity, this being dissipated by an increase in radiation, 
conduction or evaporation from the skin surface and by more rapid and deep 
breathing. 
Thus the skin is the interface between the internally heated body and the 
atmosphere, and is in heat exchange relationship therewith. If the heat 
produced by a body surpasses heat losses therefrom, this gives rise to 
fever; but if heat losses exceed heat production, then the body 
temperature falls below the nominal value, resulting in shivering and 
hypothermia. 
Medical practitioners since ancient times have known that the application 
of heat to the body is useful in the relief of muscle soreness and various 
aches and pains, as well as in the treatment of certain abnormalities. 
Thus the application of heat for the treatment of arthritis and other 
abnormal conditions is commonplace. Hot water bottles and electrical 
heating pads are in widespread use not merely to provide warmth, but also 
to afford a degree of relief or therapy for various conditions. Heat is 
also used medically in the resolution of infected areas. 
While the present invention is generally applicable to all abnormal 
conditions which can be benefited by the application of heat to the 
surface of the body, it will now be considered in the context of malignant 
tumor treatment. It is recognized that by heating tumors to a higher 
temperature than the surrounding tissue, the tumor may be caused to shrink 
and disappear. As noted in The New York Times of April 14, 1981 (section 
C2) in an article on modern approaches to cancer treatment, the 
effectiveness of heat therapy is based on the fact that cancers have poor 
circulation and a reduced ability to dissipate heat. "Thus a temperature 
of more than 113 degrees Fahrenheit could destory cancer cells while 
sparing normal tissue." 
Patients with tumors in their arms and legs have been treated by a 
perfusion therethrough of hot blood, and tumors in bladders have been 
treated by flushing the organ with hot fluid. It has also been known to 
immerse patients in hot wax, and in some cases, medical practitioners have 
gone so far as to elevate the body temperature of patients by infecting 
them with malaria. 
These known hyperthermia techniques, as well as those based on the use of 
microwave, high-frequency radiation and thermoelectric techniques are 
described in some detail in the U.S. patents to Sterzer, Nos. 4,190,053; 
Gordon, 4,106,488; Whalley, 4,121,592; Doss, 4,016,886; Bender, 4,186,294 
and Ulrich, 3,618,590. 
Difficulty has heretofore been experienced in applying heat to a patient 
which is electrically or otherwise generated. When transferring heat 
through living tissue to a site underlying the skin, if the heat applied 
to the skin surface is within a tolerable temperature range, then not 
enough heat energy is transferred to the site to afford beneficial 
effects. When, however, the skin temperature of the applied heat is such 
as to bring about an adequate heat transfer to the internal site, then the 
skin temperature is usually above an acceptable level, and this may result 
in extreme discomfort to the patient and even to the burning of surface 
tissue. The same problem is encountered when using high-frequency radio 
heating; for, as pointed out in the above-identified Whalley patent, in 
many cases such treatment results in damage to the skin. 
In my above-identified U.S. Pat. No. 4,307,286, apparatus is disclosed 
whereby cold, pre-cooked packaged meals may be rapidly heated to a service 
temperature level without causing destructive re-cooking of the meals. To 
this end, applied to the package is a stream of heated air in a pulsatory 
thermal wave pattern whose pulses are at a temperature well above the 
service temperature level and whose intervals between pulses are at a 
lower temperature. As a result of this thermal wave pattern, heat is 
transferred from the surface of the food body to the interior thereof 
during the lower temperature intervals, thereby preventing the surface 
temperature from rising above the service temperature level despite the 
fact that it is subjected to high temperature pulses. 
In the present invention, this pulsatory thermal wave pattern is exploited 
to carry out heat therapy on patients without injury to surface tissue. 
While the invention will be described mainly in connection with therapy 
produced by hyperthermia, the same principles are applicable to 
hypothermia treatment, in which therapeutic effects are produced by 
cooling an internal body site. 
SUMMARY OF INVENTION 
In view of the foregoing, the main object of this invention is to provide a 
method and apparatus which makes effective high temperature heat therapy 
feasible without inflicting injury to the surface tissue in the area where 
the heat is applied and without causing undue discomfort to the patient. 
It must be borne in mind that when heat is applied to a skin area at a 
temperature which is significantly greater than body temperature, some 
unavoidable degree of discomfort will be experienced, and that the concern 
of the present invention is to keep such discomfort within a tolerable 
range and to avoid any damage to surface tissue. 
More particularly, an object of this invention is to provide a technique 
which applies a stream of heated air to a limited skin area to effect heat 
transfer to an internal region underlying this area to cause the 
temperature of the region to rise to a level appropriate to hyperthermia 
treatment without giving rise to an excessive temperature damaging to the 
surface tissue. 
Yet another object of this invention is to provide an apparatus which 
includes an applicator in the form of a flexible heating pad which is 
adapted to conform to a body area to be heated. 
Also an object of the invention is to provide an efficient and reliable 
heat therapy instrument which is easy and safe to operate and which may be 
manufactured at relatively low cost. 
Briefly stated, these objects are attained in a heat therapy technique by 
which heat is applied to a limited skin area of a patient to penetrate the 
tissue to produce hyperthermia in an internal region underlying this area 
without, however, causing undue discomfort to the patient or damaging 
surface tissue. Applied to the skin area is heated air in a pulsatory air 
wave pattern whose relatively brief pulses flow at high velocity and are 
at a high temperature well above body temperature and whose static 
intervals between pulses are at a medium temperature. 
As a consequence, heat transferred from the surface tissue toward the 
internal region takes place during the intervals, thereby reducing the 
temperature of the surface tissue and preventing it from reaching an 
unacceptable level despite the high temperature of the high-velocity 
pulses applied thereto.

DESCRIPTION OF INVENTION 
First Embodiment 
Referring now to FIG. 1, there is shown a heat therapy device for applying 
heat to the skin surface 10 of a patient in order to subject an internal 
tumor 11 to hyperthermia treatment, the tumor lying in a region underlying 
the area of the skin subjected to the heat generated in the device. 
The device includes an applicator, generally designated by numeral 12, 
which is constituted by a rectangular pad 13 formed of synthetic flexible 
foam material such as polyurethane or PVC whose outer face is molded to 
define a staggered array of projecting fingers 14 and an array of outlets 
15 interspersed between the fingers in the troughs formed thereby. The 
inner face of the pad is indented to define a shallow well closed by a 
cover plate 16 to form an internal chamber 17. 
When in use, the projecting fingers 14 rest on the skin while heated air is 
emitted from outlets 15 at high velocity, to uniformly heat the underlying 
skin area. The application of heat is confined to this skin area by a 
thermal blanket 18 having an opening to accommodate the applicator. In 
practice, the skin area being treated may be protectively coated with 
Vaseline, silicone oil or other preparation having protective properties. 
Applicator 12 is coupled to a pulsatory heat generator, generally 
designated by numeral 19, by means of a flexible pipe 20, one end of which 
communicates with the inlet port 21 of the applicator, the other end 
communicating with the outlet port 22 of the heat generator. 
Heat generator 19 is supported by means of a suitable stand 23, such as one 
having suction cups 23 C on its base, on a table 24. Generator 19 is 
provided with a cylindrical casing 25 having a motor 26 mounted therein at 
one end, the motor driving a fan 27. The fan acts to draw ambient air into 
the casing through an adjustable shutter composed of a fixed disc 28 
having a circular series of slots therein and a rotatable disc 29 having a 
similar slotted formation, the maximum opening being when the slots in the 
two discs are in exact registration and the minimum when the slots are 
altogether out of registration. 
Ambient air drawn into casing 25 by fan 27 is blown through an electrical 
heater element 30, the hot air being forced through a fibrous or 
sponge-like replaceable air filter 31 into a cylindrical valve 32. In 
practice, filter 31 may be continuously saturated with a liquid medicant 
fed thereto at a controlled rate from a supply 33. 
Valve 32 is provided with a port 32P and is oscillated about its axis by a 
reciprocating motor 34, such that port 32P is alternately in registration 
with outlet 22 coupled to applicator pipe 20 or with an outlet 35 whose 
position is diametrically opposed to outlet 22, the heated air being 
discharged into the atmosphere through outlet 35. 
The temperature of air passing out of air filter 31 is sensed by a 
thermistor or other form of detector 36, while the temperature of the air 
in applicator chamber 17 is sensed by a similar detector 37. The detected 
signals are applied to an electronic timing and control center 38 which 
acts to adjust and control the parameters of the heat generator 19 to 
provide and maintain the desired pulsatory wave pattern. 
Control center 38 includes a manually-settable timer to activate the heat 
generator for a desired period, such as a half hour, or any other 
appropriate period. The relative durations of the pulses and intervals are 
also adjustable so that, for example, each pulse may last 4 seconds and 
each interval 7 seconds. Detector 36, which senses the temperature of the 
air fed into valve 32, acts in conjunction with the control center to 
thermostatically regulate heater 30 to maintain a desired temperature 
level. Detector 36, which senses the heat within casing 25, acts in 
conjunction with the control center to regulate shutter 29 to adjust the 
air input opening thereof to provide the desired air temperature for the 
skin. 
In practice, the control may be manual, in which case means are provided to 
indicate the applicator temperature, and the operator then turns the 
shutter to provide incoming air resulting in a diresed temperature level 
and turns a potentiometer coupled to the heater to adjust the heater 
temperature. 
In order to render the generator useful for hypothermia, element 30 may be 
of the thermoelectric type capable of selectively providing either a 
reduced temperature or an elevated temperature. Such thermoelectric 
elements make use of dissimilar metals and replace the mechanics of 
conventional refrigeration when operating in the cold mode. Thus when the 
generator is operative in the hyperthermia mode, air drawn into the casing 
is heated and blown at high velocity into valve 32 which alternately feeds 
the air into the applicator and into the atmosphere; and when the 
generator is operative in the hypothermia mode, the air drawn into the 
casing is cooled and blown at high velocity into valve 32 to produce in 
the applicator pulses of cold air. 
Operation 
Normal body temperature is 98.6.degree. F., this level being indicated in 
FIG. 5 by horizontal line N. The pulsatory thermal wave pattern is above 
line N and is constituted by periodic pulses P at a high temperature of, 
say, 150.degree. F. and higher, and no-flow or static intervals between 
pulses at a medium temperature somewhat above body temperature, such as 
110.0.degree. to 120.degree. F. Because the high temperature air flows 
over the skin area at high velocity during the pulses, this forced 
convection results in a rapid heat exchange. And while the small volume of 
air in the confined skin area during the static intervals has a very low 
thermal capacity, its temperature because of residual heat in the 
applicator is somewhat above skin temperature. 
The rate of pulsing is a crucial aspect of the invention, for the body 
region containing tumor 11 is formed of living tissue having relatively 
poor heat conductivity and is composed effectively of a succession of 
layers, beginning with the surface or skin layer L.sub.1 and going through 
layers L.sub.2 etc. into the tumor. The tumor can be heated to a 
hyperthermia level above body temperature, say, to 115.degree. F. and 
above, only by transmitting heat through the successive layers of poor 
thermal conductivity. 
As noted in the article "Heat Therapy for Cancer" in Discover, June 1981, 
published by Time, Inc., because the circulation in tumors is poor, the 
blood moves sluggishly therein and does not carry away heat as rapidly as 
it does in ordinary tissue. Thus a tumor can be heated to a lethal 
temperature of over 110.degree. F. while the tissue in the region between 
the tumor and skin remains at a safe, lower temperature. Tumor cells are 
apparently more sensitive to heat than normal cells and seem to have a 
higher metabolism; hence tumor cells are more easily overstressed by heat. 
While the question of whether cancerous cells have a greater sensitivity 
than normal cells remains controversial, there is little argument about 
the lethal effect of heat on tumors. 
Outer layer L.sub.1 is initially at 98.6.degree. F. Assuming that each high 
temperature pulse period lasts 3 seconds followed by a five-second lower 
temperature interval, and that the first 180.degree. F. pulse flowing past 
the skin area at high velocity for three seconds acts to raise the 
temperature of the first layer L.sub.1 to 104.degree. F., then during the 
110.degree. F. interval which follows, heat from outer layer L.sub.1 will 
be transferred inwardly to second layer L.sub.2 which is thereby raised in 
temperature to, say, 100.degree. F. with a resultant reduction in the 
temperature of the outer layer to, say, 102.degree. F. 
Thus the interval between the hot air pulses represents a relaxation period 
during which heat transfer takes place from the outside in, but not from 
the inside out; for the temperature outside the skin is always above the 
body temperature. When outer layer L.sub.1, now at 102.degree. F., is 
again subjected to the next hot air high velocity pulse at 180.degree. F., 
this will raise the temperature of the outer layer another notch, and the 
temperature of this layer will again be somewhat reduced during the 
interval which follows when heat is transferred from outer layer L.sub.1 
to the next layer L.sub.2. 
It is important to bear in mind that a small volume of air has a low 
thermal capacity, and that because of the high velocity of the pulses, a 
larger volume of air is brought into heat exchange relationship with the 
skin during the pulse period, whereas in the interval, it is only a small 
volume of air. 
Similar heat transfer actions take place concurrently between the second 
and third layers L.sub.2 and L.sub.3 and between the third and fourth 
layers L.sub.3 and L.sub.4 and so on toward the tumor region, very much in 
the fashion of an electronic cascade counter in which when an input signal 
(heat pulse) is received, the state of each stage (layer) in the cascade 
is advanced in an ordered sequence. 
Thus the intervals between hot air pulses applied to the surface layer of 
the body allows time for transfer of heat to take place from layer to 
layer; and because outer layer L.sub.1 is permitted to cool down during 
these intervals, the temperature of the outer layer is never permitted to 
rise to an execessive level, even when the tumor is heated to an effective 
hyperthermia temperature of above 115.degree. F. And while the tissue 
between the tumor and the skin is also caused to rise in temperature, the 
cooling effect of the circulatory system prevents this tissue from being 
overheated. 
The heating applicator may be used in those medical applications which 
benefit from the use of conventional heating hot water bottles or heater 
pads, the advantage of the present pad being that it is possible to 
transfer more heat into the body without, however, undue discomfort to the 
patient or damage to his skin. 
While there have been shown and described preferred embodiments of a 
hyperthermia technique in accordance with the invention, it will be 
appreciated that many changes and modifications may be made therein 
without, however, departing from the essential spirit thereof. Thus while 
a particular form of heat or cold generator has been disclosed herein 
operating in conjunction with a particular form of applicator, in practice 
any of the pulsed wave sources disclosed in the above-identified copending 
application may be used for the generator. And the applicator may take 
other forms and need not be constituted by a foam plastic pad.