ONKOCET
high technology in medical equipment

The temperature in an executive cabin is considered to be the main point, which cryotherapeutical effect is based on. According to the temperature indexes, three classes of treatment using cooled gas are determined. It was shown that being treated in cryogenic installation does not always give a high medical effect.

Temperature gas index determinates the temperature meaning in skin tissues of a patient by the end of treatment. Using an extreme cryotherapy the skin surface is cooled too fast, so the treatment lasts not very long, that's why its result is rather small. Cooling doesn't influence on internal outerskin boundary. In low temperature gaseous hypothermal action, recooling of internal outerskin boundary appears before the temperature skin surface reaches necessary index. Only using gas with suitable cryo-therapeutical temperature synchronizes internal and external cooling processes.

Cryogenic installations being cooled by machines don't provide necessary temperature level in executive cabin.

Refrigeration systems are not able to operate at temperature below - 1200C because of low energetic technological efficiency. According to temperature level these installations should be regarded as low temperature physio-therapeutical equipment.

Cryogenic installation cooling system is to decrease the temperature of air in cabin, up to optimum level and maintain it constant as well. Often required temperature (-1500C - 1300C) is reached only in to empty cryogenic installation and after a patient came in the cabin the temperature increases up to - 900C or higher. Such fluctuations are not permitted, as instead of cryotherapy, patients are influenced by hypothermal action.

Taking into account that the number of cryogenic installation producers is increasing, it is necessary to determine minimum requirements to the cooling power of cryogenic installation. It will help practising doctors to avoid buying low-quality installations.

Cryotherapy is based on skin surface cooling to -20C - +20C temperature region.

In order to low the surface body temperature to this level and to avoid recooling of a body. Cooling should be very intensive. A body looses about 600 kg of heat almost for 2-3 min., that is 3kw of one patient.

Cooling systems using liquid nitrogen are preferable to use in cryogenic installations. These systems compared with others are simpler and possess large latent power.

Fig.1 Changing of a physiotherapy effect and max temperature and min temperature of the outside and inside skin larger of the body depending on gas temperature in the cryogenic camera.

For example, the consumption of 1kg. of liquid nitrogen per minute allows to drain heat flow of 4 kw. power from cryogenic installation. Nitrogen is necessary not only to cool a patient, but for other needs, too. Minimum necessity in liquid nitrogen can be determinated, as 1kg/min. per 5 patients should not consume less than 5 kg. per minute. If producers show less consumptions you should not buy it. Not to admit the increasing of gas temperature when a patient enters the cabin the cooling system of cryogenic installation should be provided with electrodrive. Energetic efficiency of cooling mechanisms at low temperatures is extremely small. (fig.2). figures of coefficient efficiency for refrigeration cycle of cascade refrigeration system and cryogenic gaseous machine working on inverse cycles used in group installations, coefficient efficiency is lowering so fast at –1000C temperature region, that serious doubts about capacity for work of cryogenic installation with these coolants appear.
 

Fig.2 Exergetic coefficient efficiency of coolants (-cryogenic gaseous machine (C.G.M) (- refrigeration gaseous cycle (R.G.C),cascade refrigeration machine (C.R.M)

For cryogenic gaseous machine specific relation required heat to energetic consumption for the work of cooling system in the temperature region (-1500C – 1300C) will be 15-25% (fig. 3).

In order to remove 1kw of heat from executive cabin, cryogenic gaseous machine with consuming electric power of 6kw will be required. Therefore to compensate mean heat emission from body surface of a patient during treatment a machine with electric power not less than 18kw is needed and this is together with using the most effective coolant, which is not used in cryogenic installation because of high cost and small resource. At the same time, installations with cabin per 5 patients which cooling system has only 16kw of power are sold in Russia. With such lack of power the installation is not suitable for treatment.
 

Fig.3 Specific refrigeration capacity of cryogenic gaseous machine at low temperatures.

Taking into account the essential distinctions in principle of operating, size and construction of compared installations, to evaluate its work capacity we can determine the power of electrodrive of cooling system for carrying out cryotherapy with patient.

For example, if coolant power consumption of cryogenic installation per 5 patients is 16kw., so about 3kw of electric power per one patient. Will be it is possible to calculate electrodrive power of a perfect coolant which is able to drain the same quantity of heat as a nitrogen coolant with 1kg of cryogenic liquid consumption per minute. As it was mentioned above such coolant can drain from a cabin about 4kw of heat, that is equal to refrigeration installation work with 25kw electric power consumption.

Cryogenic installation cooled by liquid nitrogen gives every patient some energetic influence, where power is eight times higher than in installations with refrigeration machines.

To illustrate negative power lack results of cooling systems by mathematical model of cryogenic installation a numerical experiment was made to investigate the line of treatment with different indexes of cooling installation power. To increase visuals of analisis results some simplifying assumptions were made. The temperature is supposed to be –130C by the beginning of treatment and the patient is the only source of heat.

In simulating of cooling system work the dependence of cooling coefficient efficiency on the temperature in cabin was taken into account. (fig.3). the simulating processes results in executive cabin are shown in figure 4.
 

Fig.4 The changing of gas temperature in executive cabin with different indexes of cooling system power.

If a patient gets no more than 5kw of a cryogenic system power, just after the beginning of treatment the temperature in cabin increases fast. Heatemitting from a patient body surface exceeds the refrigerating capacity of cooling system. Gas in an executive cabin is getting hot at 40C/C velocity, till the refrigeration capacity of cooling system will balance heatemitting from a patient. In case of 5kw power the balance is reached only at –300C.

The real gas temperature increase coordinates well with the practice of using the same systems. For the lack of cooling system power some large intervals are supposed to be. During one hour only four treatments which last for 16 min. can be done. So, an interval lasts about 10 min. Only for this period of time a low power cryogenic system is able to recover the temperature in empty executive cabin. As we can see from figure 4, in order to stabilize temperature conditions in cryogenic installation is necessary to increase power up to 25kw per patient. By using mathematical model of cryogenic installation, the experiment in determining the physiotherapeutical effect of treatment was made with using cooling system of different electric power. Two possible indexes of gas temperature in executive cabin (-1200C and –1300C) are regarded.

The works of cryogenic installations with cooling power from 5 till 30kw per patient are also investigated. The dependence of physiotherapeutical effect on cooling power index is shown in figure 5. This figure shows that being not in dependence on temperature index maintained in empty cabin by small index of treatment effect. In all cases, with the power less than 50u.d.a/m 2 .*(u.d.a. – unit of disturbing action).

So the lack of power leads to the fact that cryogenic installations with the inside temperature no more than –1300C give the patient hypothermic influence.

The increasing of power up to 25kw leads to some essential changes in the effectiveness of compared variants of cryotherapeutical organization. The rated effect in cryogenic installation with the temperature of –1200C increases up to, 110 u.d.a/m2 it remains on hypothermic level. The lowering of temperature up to –1300C allows the installation of 25kw power to increase the effect to 335u.d.a/m2

Fig.5 The dependence of physiotherapeutical effect of cryotherapy on expended power cooling system per one patient.

Taking into account the fact that the coolant of 25kw power corresponds to liquid coolant with nitrogen consumption of 0.6kg/min (15kw) give the patient a hypothermic influence.

Only when liquid nitrogen consumption is more than 1kg/min and temperature level is no more than –1300C, cryogenic installation provides effective cryotherapy. Nitrogen consumption in individual cryogenic installations made in Russia corresponds to these requirements. And group cryogenic installations (per 5 patients) have a power lack equals to 100kw. Today’s cost of these installation is rather high (250.000 Euro). Together with the increasing of refrigeration machine power which is necessary for effective cryotherapeutical level, the price is also increasing (about 5-6 times).

Besides, placing of such installations of 125 kw power in medical organizations is connected with a complex of additional problems.