EP0088704A1 - Insulator for confining and transporting human beings in a sterile atmosphere, especially newly born infants - Google Patents

Abstract

Installation for the containment and transport in a sterile atmosphere of human beings, in particular newborns (2). It comprises a sealed enclosure (1) ventilated by a forced circulation of fresh air set in motion by a first fan (8) through an inlet filter (6) and an outlet filter (7) and , between the fresh air inlet and outlet, a bypass (10) provided with a second fan (11) and a variable temperature heating element (12), automatically limited to a maximum value of order of 120 ° C, so as to create a reheating and a regulation at a set temperature of the internal atmosphere by partial recycling thereof, all of the energy necessary for the operation of the installation being supplied by a autonomous storage battery (14) which may be that of the transport vehicle.

Description

The present invention relates to the field of transport in a sterile atmosphere of human beings who need, for medical reasons, to be confined in a sterile atmosphere and transferred from one place to another inside the same hospital, or even on a journey of several tens or hundreds of kilometers, consequently comprising a transport in an autonomous vehicle (automobile, helicopter, plane) without breaking the seal and the sterility of the environment in which they bathe, nor the possibility to medically intervene on them to carry out certain essential emergency treatments. This is the case in particular of individuals who have temporarily lost at least all or part of their immunological defenses and also of certain premature newborns to whom it is necessary to sometimes travel long distances to provide them with treatment for suitable survival.

In the case of newborns who represent the preferential although not exclusive area of application of the present invention, use is made in a known manner of incubators which must theoretically protect these children from the three factors essentials which are: bacterial contamination, humidity and temperature. Unfortunately, experience shows that the protection actually obtained against these three factors is very illusory for the following reasons.

As regards first of all bacteriology, the confinement offered by an incubator, which is strictly speaking only an enclosure closed by a cover, is not waterproof because any intervention on the newborn supposes the opening of this enclosure. This simple observation therefore implies limiting all intervention during transport to the strict minimum necessary and, on the other hand, considering sterilization of the interior of the vehicle in which transport is carried out, which, in practice, is practically impossi ble and in any case can not be done quickly when you need to perform emergency transport.

Some newborn babies need high humidity levels above normal in the lungs. These same subjects may require an ambient temperature reaching 37 ° C. The combination of these two physical conditions creates a climate particularly favorable to bacterial development.

Finally, with regard to temperature, there are often relatively abrupt variations in incubators, even when they are well thermally conditioned, since the need to open the cover a certain number of times to practice care, leads each time a significant volume of fresh air which causes the temperature to drop suddenly. These variations can in some cases be very annoying for the child (phenomenon of "stress").

Furthermore, in the technique of medical interventions at a fixed station and in a confined atmosphere, isolators are used which make it possible to biologically completely separate a patient from the outside, while communicating with him in both directions (entry and removal of objects or materials) using waterproof transfer devices or also waterproof intervention devices, some of which, such as gloves, diving suits and others, can be at least partially an integral part of the wall of the enclosure. An enclosure of this nature is generally ventilated by an air circuit between an inlet and an outlet, each having an absolute filter which stops the entry or exit of any microbial germ. When the need arises, such an enclosure provided with its filters can be very easily sterilized by a microbicidal agent circulating in the ventilation circuit for a certain time, such as for example peracetic acid.

Such insulators and their intervention devices have been described in particular on p. 121 to 125 of n ° 284 of February 1979 of the Revue Labo Pharma, p. 227 to 230 of volume 3 of 1978 of Science and Techniques of Laboratory Animals, as well as in BF 80 03 067 filed on February 12, 1980 by the plaintiff.

One could obviously think of using such insulators for the transport of human beings in a sterile environment, but one immediately encounters an almost insurmountable difficulty which is that of the heating power of such an insulator operating in open circuit. Indeed, experience shows that to heat and maintain around 37 ° C a human insulator immersed in an atmosphere at 20 ° C and traversed by a fresh air flow of 10m ³ / h, it is necessary to have a electrical power of 680 W and the rise in temperature requires approximately 1 hour 30 minutes. Such use, which can easily be imagined at a fixed station where there is an electrical network, is difficult to put into practice on board a vehicle using a conventional storage battery, even if it is recharged. permanently by the vehicle's alternator. It must be taken into account that such transport is often carried out in an emergency state by ambulance type vehicles which are, by their very nature, large consumers of energy not only for heating, but for headlights , giro-lighthouses and sirens; the accumulator batteries of such ambulances, even when powered by a dynamo or an alternator connected to the engine, tend to discharge quickly and could not therefore ensure transport for several hours by providing such high additional power .

The present invention specifically relates to an isolator for the containment and transport in sterile atmosphere of human deterrents which allows to resolve the above difficulties, using an insulator or sealed enclosures of the type mentioned above, using exclusively a storage battery to ensure the operation of the assembly.

This insulator, of the type which includes, in a known manner, a sealed enclosure, ventilated by a forced circulation of fresh air set in motion by a first fan through an absolute inlet filter and a filter absolute output, rapid and leaktight transfer devices with the outside, also watertight intervention devices, some of which are an integral part of the wall of the enclosure, is characterized in that it comprises, between the inlet and the fresh air outlet, a bypass fitted with a second fan and a variable temperature heating element, automatically limited to a maximum value of around 120 ° C, so as to create reheating and regulation at a set temperature of the internal atmosphere by partial recycling thereof, all of the energy necessary for the operation of the installation being supplied by an autonomous storage battery which may be that of the transport vehicle.

The fact of providing, in accordance with the invention, on a sealed insulator or enclosure of known type, two ventilation circuits in parallel, namely a fresh air circuit for breathing of the patient and a heating recycling circuit, makes it possible to limit the heat losses to their strict minimum and thus limit the electrical power sufficient to ensure the operation of the installation to about one hundred watts. Furthermore, the use of a sealed enclosure provided with inlet and outlet filters makes it possible to keep all the advantages of this type of insulator mentioned above, at the same time, in particular the transfer from one treatment center to another, long-distance transport, entry and exit of various objects and direct intervention through the wall of the enclosure.

Furthermore, the automatic limitation to a maximum value of the order of 120 ° C but frequently of 80 ° C or 90 ° C of the variable temperature heating element avoids carrying elements to red in the circuit. recycling of the internal atmosphere of the enclosure, which is fundamental in particular when, for biological reasons, the internal atmosphere is enriched with oxygen and could lead to significant risks of ignition in the event of leakage. The sealed enclosure thus equipped with its two ventilation and recycling circuits can be moved at will on a simple cart having an autonomous accumulator battery which ensures its independence during different transfers within the same hospital for example . As soon as a transport by vehicle is necessary, one can at will either keep the same accumulator battery which will be asked for an additional contribution of the order of 100W, or resort to the battery of this vehicle.

The isolator ₃ according to the invention has the great advantage of allowing the transfer and transport from one sterile chamber to another, located several hundred kilometers away, without ever breaking the seal and the biological sterility of the the atmosphere in which the patient is confined, while continuing to administer the medication and care he may need on an ongoing basis.

According to another characteristic of the insulator which is the subject of the invention, the rotational speeds of the first and second fans are maintained at preset pre-selected values, and the set temperature of the enclosure atmosphere is obtained by adjusting the simul heating element temperature temporarily using a part of a basic command taking into account the difference between the external and set temperature and the operating or quiescent state of the first fan and; on the other hand, a complementary fine servo loop whose error signal is generated from the difference between the internal and set temperature.

The choice to keep the two fans of fresh air and recycling atmosphere at constant rotation speeds results from a desire for simplicity because, on board a vehicle, it is more tacit to modulate the heating to the using a servo system. Furthermore, these fans of a type known per se require only a very low power of the order of 8 W for example, for a flow rate of a few cubic meters per hour.

As for the design of the heating and the temperature regulation of the sealed enclosure, it results from the fact that for an installation of this type, the heat loss is approximately at least, proportional to the difference between the set temperature and the temperature. outdoor ambient. This is why we choose to carry out, using a basic command, heating to a temperature close to the desired setpoint and to supplement it with a complementary fine servo loop whose action depends on the difference at all times between the set temperature and the actual temperature inside the enclosure; under these conditions, this complementary loop only has to provide the additional overheating or underheating necessary to obtain the exact set temperature from the approximate temperature obtained by the basic control.

According to another advantageous characteristic of the present invention, the heating element located in the recycling bypass consists of power transistors traversed by a current regulated by the basic control and the control loop and whose cooling fins are immersed in the air recirculation bypass.

According to the invention, the heating element is further equipped with thermistors which vary with temperature and which, if necessary, automatically reduce the current in the power transistors so as to limit the temperature of the heating element to a maximum value of the order of 120 ° C.

This design of the realization of the heating element makes it possible both to avoid the presence of red dots or sparks, which could occur with ordinary electrical resistances and would lead to very significant risks in the event that a oxygen therapy is necessary for the transported patient, In any case, the presence of thermistors which allow the temperature to be limited to a maximum value of the order of 80 ° C to 120 ° C also constitutes safety both with regard to the risks risk of overheating the enclosure.

Finally, the isolator according to the invention may also include, inside the sealed enclosure, a breathing helmet supplied from the outside and which covers the head of the patient in a non-sealed manner, to condition the nature and / or the hygrometric degree of the atmosphere which it breathes, the consumed part of this atmosphere being, at least in part, discharged directly into the enclosure.

This respiratory helmet allows, with the aid of its autonomous supply passing in leaktight manner through the walls of the enclosure, a respiratory supply of the assisted patient almost independently; it is very useful for all cases where it is desired to provide the patient with a particular respiratory mixture, and in particular for oxygen therapy sessions. It also makes it possible to solve in a simple and elegant way the problem of the hygrometry of the gaseous atmosphere breathed by newborns; this helmet being simply fitted without any particular seal. lière on the head of the patient, the latter rejects, directly into the sealed enclosure itself, part of the gases or moisture thus brought, which does not offer serious drawbacks in terms of hygromerism because the portion of the gaseous atmosphere discharged into the enclosure always remains very small and becomes diluted in the course of the whole.

• - la figure 1 est une vue schématique générale en élévation d'un isolateur conforme à l'invention munie de certains de ces accessoires de fonctionnement ;
• - la figure 2 représente le détail d'implantation du casque respiratoire d'un patient transporté ;
• - la figure 3 représente un schéma de principe du système de commandeet d'asservissement de l'élément de chauffe de l' isolateur
• - la figure 4 représente le système des transistors de puissance utilisés pour constituer l'élément de chauffe de 1' isolateur.

In any case, the invention will be better understood by referring to the following description of an exemplary embodiment of the isolator for the transport of humans in a sterile atmosphere; this description, which is given mainly by way of explanation and without limitation, will be made with reference to Figures 1 to 3 attached, in which:

• - Figure 1 is a general schematic view in elevation of an insulator according to the invention provided with some of these operating accessories;
• - Figure 2 shows the detail of implantation of the respiratory helmet of a transported patient;
• - Figure 3 shows a block diagram of the control and servo system of the insulator heating element
• - Figure 4 shows the system of power transistors used to form the heating element of one isolator.

In Figure 1, we see a sealed enclosure or isolator 1 of a type known per se and intended for the transport of a newborn 2. In the example described, the enclosure 1 has a volume of 120 liters. The newborn 2 rests, in the particular case, on a vacuum mattress 3 of a kind known per se and constituted by a number of small diameter plastic balls enclosed in a flexible and waterproof envelope in which there is empties. Such a mattress 3 is very useful for molding the shape of the body of the patient 2 by ensuring its support and its maintenance in position during variations in acceleration which arise due to transport.

The sealed enclosure 1 comprises, in a known manner, a fresh air inlet 4 and waste air outlet pipe 5 on which the absolute filters 6 and 7 are located respectively, the pore size of which is chosen so that they are likely to stop any bacterial transfer. In the pipe 4, is located before the filter 6, the fin of the first fan 8 whose motor and electrical control are not shown and which ensures the circulation of fresh air for the breathing of the newborn 2 in the enclosure 1. This fan has a power of the order of 8 W and it ensures inside the enclosure 1, a circulation of fresh air at constant flow rate of the order of 3 m ³ / h. A sealed double door transfer system 9, of a type known per se, in particular by BF 69/10571 of April 4, 1969, allows the rapid introduction and exit into enclosure 1 of all the necessary accessories and materials. to the patient without breaking the tightness of the installation.

According to the invention, a recycling bypass 10, placed between the inlet 4 and fresh air outlet 5 pipes, comprises a second fan 11 and a heating element 12 which make it possible to recycle a constant flow of the order of 9 m ³ / h of the atmosphere contained in the enclosure 1 by heating it in contact with the heating fins 13 of the heating element 12.

The whole of the insulator described in FIG. 1 is made autonomous from an energy point of view thanks to the conventional storage battery 14 which supplies all the fans 8 and 11 and the heating element 12 to the through an electric general control 15, certain details of which will be described and shown below with reference to FIG. 3.

The assembly is carried on a mobile trolley 16 and can either move independently within the same hospital for example, or be placed on board a transport ambulance which it is then by no means need to prepare by disinfecting it beforehand.

The walls of the sealed enclosure 1 also include intervention devices forming part of this wall such as gloves 17 and 18; various other useful medical accessories can also be provided on the transport cart 16, such as for example feeding probes and the oxygen cylinder 19 which is used to supply the breathing helmet 20 covering the head of the transported newborn 2.

All these accessories can be, in a conventional and known manner, handled and used thanks to the double door system 9 and to the handling gloves 17 and 18 without at any time the confinement of the sealed enclosure 1 being broken.

Energy savings can still be made complete on _{1 insulator} object of the invention, by providing, in places where it is not necessary to see what happens in the chamber 1, to carry it with a double wall into which glass wool is introduced, which is an excellent thermal insulator. In addition, you can also, during transport, place a hull on the installation, wrapping everything and itself constructed with a double plastic envelope containing glass wool. This makes it possible to further strengthen the thermal insulation and to reduce losses, either during the heating of the enclosure before the patient's introduction, or during transport when the doctors do not need to intervene. This shell (not shown) can also be provided with viewing windows, which nevertheless makes it possible to monitor the child.

• - avant l'introduction du patient, on commence d'abord par stériliser l'enceinte. Ceci est réalisé de façon connue, comme l'indique par exemple le BF 80 03067 de la demanderesse, à l'aide d'une circulation d'acide peracétique qui détruit tous les germes vivants, non seulement dans l'enceinte 1, mais dans les canalisations qui l'alimentent et dans les filtres absolus 6 et 7. Cette circulation ainsi que le balayage d'air frais consécutif sont réalisés à l'aide du ventilateur 8 et des canalisations 4 et 5.

The operation of 1 ¹ insulator as shown in Figure 1, generally includes the following steps:

• - before the patient is introduced, we first sterilize the enclosure. This is carried out in a known manner, as indicated for example by the applicant's BF 80 03067, using a circulation of peracetic acid which destroys all living germs, not only in enclosure 1, but in the pipes which supply it and in the absolute filters 6 and 7. This circulation as well as the subsequent fresh air sweep are carried out using the fan 8 and the pipes 4 and 5.

This first operation having been carried out, preheating of the enclosure 1 is carried out preferably using the sector if there is one available, or the battery 14 otherwise. To carry out this preheating, only the fan 11 and the recycling circulation are started in the duct 10. The fan 11 which, for reasons of simplicity already explained, has only one speed of rotation, delivers about 9m ³ / h for an enclosure 1 of 120 liters of capacity approximately. This flow rate of 9 m ³ / h results from a choice which results from an optimization to ensure both a minimum transfer of heat energy. From the heating element 12 to the enclosure 1 and to avoid at the same time too much air mixing in the enclosure 1 which would lead to too high heat losses.

When the heating is thus carried out, the patient 2 can be introduced by the double sealed door 9 of course. From this moment, it is essential to start the ventilator 8 located on the air duct 9 to propel the fresh respiratory air to the patient 2 (arrows F). The fan 8 also rotates at constant speed and ensures, in the particular case described, an hourly flow rate of approximately 3 m ³ / h. This figure was retained as a result of an optimization based on three essential criteria which are on the one hand to allow a normal breathing, on the other hand to preserve the homogenization of the atmosphere of enclosure 1 and finally to ensure a sufficient dilution of the surplus oxygen present in this atmosphere: in fact, when the patient receives through his helmet 20 a respiratory mixture enriched with oxygen, the latter must never exceed, for safety reasons with regard to the risk of explosions, the proportion of 28% of oxygen by volume.

An isolator of the type described in FIG. 1 operates in total autonomy on a battery 14 to which a total power of the order of 100 w is required. This means that it allows long distance transport (several hundred kilometers) in ambulances or vehicles that do not need to be specialized or prepared in advance. With this type of equipment, a temperature difference of 30 ° C can be obtained if necessary between the temperature of the sealed enclosure 1 and the outside temperature, which is of great interest in countries where winter is very cold, like Canada or the USSR and where until now, such remote transport independently was practically very delicate. Of course; the biological protection of patient 2 remains during all transport thanks to the action of filters 5 and 6.

FIG. 2 shows the detail of use of a respiratory helmet 20 on the head of patient 2 when the need arises. To this end, two inlet 21 and outlet 22 pipes for respiratory gas pass through the wall 1 of the enclosure in leaktight fashion and penetrate in the case that 20 which is simply placed without any sealing on the head of the patient 2, who can thus reject part of the atmosphere breathed into the internal atmosphere of the enclosure 1. This helmet 20 allows, as already explained previously, both to choose a respiratory atmosphere of particular composition desired and to adjust the humidity of that same atmosphere.

FIG. 3 schematically represents the control and the control of the heating of the enclosure 1. In this FIG. 3, we see the internal temperature sensors 25 and the external temperature 26. The desired set temperature for the interior of the enclosure 1 is displayed on the temperature control 27. The internal temperature 25 is displayed on an external thermometer 28 which in any case allows the doctor supervising the patient to be informed at any time about the value of this temperature.

A first summer S ₁ constitutes the temperature error signal between the set temperature displayed at 27 and the external temperature 26. It delivers a first signal which, after passing through the corrector 30, feeds one of the three inputs 31 of the summator S ₃ . The corrector 30 has two positions depending on the state of rest or rotation of the fresh air circulation fan 8. When this fan 8 is stopped, the error signal present at 29 is transmitted in the state at 31 to the adder S ₃ ; when, on the contrary, the fan 8 is operating at its nominal speed, the signal present at 29 is multiplied before being transmitted on the line 31 by a fixed factor which takes account of the constant cooling introduced into the enclosure 1 by the fresh air flow. The circuit 29, 30, 31 thus carries out the basic control which ensures through the summator S ₃ and its output 32 towards the heating element 12 a basic adjustment of this element 12 which makes it possible to approach the temperature prevailing in enclosure 1 of the setpoint displayed at 26.

In accordance with the invention, a complementary fine control loop makes it possible to complete the adjustment of the heating element 12 as follows: a second error signal constructed from the difference between the indications of the internal sensor 25 and temperature control 27 is developed in the adder S ₂ and transmitted on line 33 through a correction network 34 at input 35 of the summator S ₃ . Finally, a thermal safety device 36 consisting of variable thermistors and connected to the heating element 12 transmits on line 37 to the sammator S ₃ indications concerning a possible overshoot of the admissible limit temperature for heating element 12 and which is located most often in the vicinity of 80 ° C to 120 ° C - These indications present on line 37, are subtracted in the summator S ₃ from the signals present at inputs 31 and 35 so as to reduce the command 32 of the element of heats 12 and lower its temperature. The summator S ₃ therefore receives on its three inputs 31, 35 and 37 control signals originating respectively from the basic control, from the additional servo control and from thermal safety 36 in order to finally develop on its output 32 the control of the current serving when heating the heating element 12.

To illustrate the interest and the operation of the control device of FIG. 3, a numerical example will be given below which will make it possible to better understand the respective actions of the basic control and of the control loop.

In an installation like that of FIG. 1, natural losses of energy of 5 W / ° C. of temperature difference between the inside and the outside of the sealed enclosure 1 can be allowed.

If an internal setpoint temperature of 38 ° C is therefore accepted for an ambient temperature of 20 ° C, the difference between the latter two temperatures is 18 ° C, which means that a power of 5 is required. 18 = 90 W to maintain temperatures at their previous value.

Suppose first that the control loop 3 is the only one involved. Its control gain in the example described is of the order of 50 W / ° C, that is to say that for each degree of difference observed between the sensor 25 and the set temperature control 27, it generates by the summator S ₃ a signal which develops 50 W of heating in the element 12. To then develop under these conditions the 90 W required to heat the enclosure, an error signal should be
90: 50 = 1.8 ° C

This means that the actual temperature in enclosure 1 would then be 18 - 1.8 = 16.2 ° C

If we then add the control loop 29, 30, 31, the gain of which is around 4 W / ° C, this loop will control the power of:
4. 18 = 72 W

In these conditions. the control loop will only work for the command of:
90 - 72 = 18 W and the temperature difference between the setpoint and the interior will only be:
18: 50 = 0.36 ° C which leads to internal regulation at the value of:
38 - 0.36 = 37.64 ° C and the temperature difference between the internal temperature and the set temperature has therefore increased from
1.8 ° C to 0.36 ° C.

This example allows us to understand that the more efficient and precise the control loop 29, 30, 31 in temperature-power correspondence, the better the regulation of the whole.

de base de la boucle d'asservissement.

à l'intérieur de chacun des boîtiers qu le reni ment, les transistors 40 peuvent, en certai s points, s'échauffer à l'intérieur jusqu'à une température de l'ordre de 200°C, mais les boîtiers correspondants ne dépasseent pas 120°C, car des thermistances de protection on s sur des transistors 40 empêchent la température externe de ces boîtiers de dépasse 120°C ainsi qu'il a été expliqué à propos du schéma de la figure 3. L'avantage au mode de réalisation de la figure 4 réside dans le fait que les plaquettes 41 munies de leur transistor de puissance 40 et des ailettes de refroidissement 42 sont des éléments que l'on trouve dans le commerce et qui s'adaptent sur une canalisation 10 pour constituer l'élément de chauffe 12 à puissance voulue.In FIG. 4, one finally shows one of the possible diagrams of embodiment of the heating element 12 in the pipe 10 for recycling air from the sealed enclosure. In this embodiment, a certain number of power transistors such as 40, mounted on wafers 41 are provided with their cooling fins 42. Each transistor 40 is supplied through its bias resistor 43. The wafers quilles 41 are mounted two by two face to face in the pipe 10 of which they constitute a part of the walls and the fins 42, licked by the recycling air which circulates in this pipe 1 serve to dissipate the heat produced by the passage in the transistors 40 of the determined current

of the servo loop.

inside each of the housings that the denial, the transistors 40 can, in certain points, heat up inside to a temperature of the order of 200 ° C., but the corresponding housings do not exceed not 120 ° C, because protective thermistors on s on transistors 40 prevent the external temperature of these boxes from exceeding 120 ° C as was explained in connection with the diagram in FIG. 3. The advantage in the mode of embodiment of FIG. 4 resides in the fact that the wafers 41 provided with their power transistor 40 and the cooling fins 42 are elements which are found on the market and which adapt on a pipe 10 to constitute the heating element 12 at desired power.

The heating element 12 thus perfectly meets all the criteria for dissipation of energy at low temperature and the absence of red dots which can cause fires imposed by the safety-use of installations in accordance with the invention.

The figures given above make it possible to see that the 90 W necessary for the operation of this installation makes it possible to use, during transport on a road vehicle, the battery of this vehicle without any particular problem as soon as it is subjected to a permanent recharge from of energy taken from the rotation of the vehicle engine.

Claims (5)

1. Insulator for the confinement and transport in a sterile atmosphere of human beings, and in particular of newborns (2), comprising a bacteriologically sealed enclosure (1), ventilated by a forced circulation of fresh air set in motion by a first fan (8) through an absolute inlet filter (6) and an absolute outlet filter (7), rapid and sealed transfer devices with the outside (9), intervention devices also watertight (17-18), some of which are an integral part of the wall of the enclosure (1), characterized in that it comprises, between the inlet and the outlet of fresh air, a bypass (10) provided a second fan (11) and a variable temperature heating element (12), automatically limited to a maximum value of the order of 120 ° C, so as to create reheating and regulation at a temperature of setpoint of the internal atmosphere by partial recycling thereof, all of the energy necessary for the operation of the installation being provided by an autonomous storage battery (14) which may be that of the transport vehicle. 2. Insulator according to claim 1, characterized in that the rotational speeds of the first (8) and the second (9) fans are maintained at constant pre-selected values and in that the set temperature of the atmosphere of the enclosure (1) is obtained by regulating the temperature of the heating element (12) simultaneously using on the one hand a basic control (29,30,31) taking into account the difference between the temperatures external and setpoint and the operating or quiescent state of the first fan (8) and, on the other hand, of a complementary fine servo loop (33,35) whose error signal is generated at from the difference between the internal and target temperatures. 3. Insulator according to claim 2, characterized in that the heating element (12) consists of power transistors (40) traversed by a current adjusted by the basic control (29,30,31) and the control loop (33

) and including the cooling fins (42)

in the air recycling branch (10). 4. An insulator according to claim, characterized in that the heating element (12) is equipped with thermistors which vary with the temperature and which, if necessary, automatically reduce the current in the power transistors (40) so as to limit the temperature of the heating element to a maximum value of the order of 80 ° C to 120 ° C. 5. An insulator according to claim 1, characterized in that it further comprises a helmet (20) supplied from outside the sealed enclosure (1) and which is covered, in a non-sealed manner, the head of a patient (2), to condition the nature and / or the hygrometric degree of the atmosphere which he breathes, the consumed part of this atmosphere being, at least in part, discharged directly into the enclosure (1).

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