**1. Introduction**

Equipment for whole-body cryotherapy (WBC) has been used in clinics around the world for over 40 years [1, 2]. Despite this, until today there is no universally accepted concept describing the mechanism for achieving the healthcare effect of this physiotherapeutic procedure, and the physical conditions of safety and effectiveness of cryogenic cooling of the patient's skin surface have not been determined [3–6]. Temperature of the cooling gas and the duration of its contact with the patient's skin, being the most important technological parameters of WBC, vary over a wide range. The requirements for the power supply capacity of equipment for the implementation of WBC technology are not defined. In such conditions, manufacturers of devices for WBC procedures gradually increase the value of the minimum gas temperature in the WBC cab. Over 40 years of cryotherapeutic system production, the gas temperature declared by manufacturers of devices for WBC has doubled from 98 K in 1978 [1, 2] to 192 K [4–7]. By increasing the operating temperature of the equipment, manufacturers significantly reduce the cost of its production. For 40 years, the cost of devices for group WBC has

decreased by 30 times. Low prices for equipment provide a high level of sales, so the trend of increasing operating temperature of WBC devices persists. An increase in the temperature level is accompanied by a decrease in the power of systems for cryostatting the WBC zone. The newest installations are equipped with refrigerators with a specific power of the electric driver of not more than 1 kW/m<sup>3</sup> . At a temperature level of 170 K, a refrigerator with such a power has a heat-removing capacity of not more than 400 W/m<sup>3</sup> , which is comparable with the physiological heat release of a patient under thermal comfort conditions (150 W) [7].

Unreasonable changes in WBC technology affect the effectiveness of the procedures. Recently, more and more articles appear, the authors of which express doubt that cryotherapy can provide the healthcare effects described in papers published before 1990 [7, 8]. The reason that many modern WBC systems are not able to provide the conditions for obtaining the healthcare effects described in the last century [1, 2] is the increase in gas temperature in the working zone of new installations. This can be seen even from the titles of the articles [1, 8]. The temperature increase from 170°C (102 K) to 110°C (163 K) changes the absolute value of the temperature by 1.6 times, which cannot but affect the intensity of heat removal, the degree of supercooling of the patient's body surface, etc. From a thermophysical point of view, it is obvious that from 1978 to 2018 the technology, which is commonly referred to as WBC, has qualitatively changed. And, judging by contemporary publications, this qualitative change had a negative impact on the healthcare effectiveness of the procedures, which until recently were successfully used to treat a number of severe diseases: rheumatoid arthritis, bronchial asthma, psoriasis, etc. [9, 10].

In such conditions, the determination of cause–effect relationships between the WBC technological parameters and the magnitude of the healthcare effect acquires high scientific and social significance. Formation of the thermophysical theory of WBC creates a scientific basis for restoring the production of effective cryotherapeutic installations at the modern technical level.

determined by the requirement of the inadmissibility of air condensation on the surface of a heat exchanger. The temperature of the outer surface of the heat exchanger *THC* must be higher than the condensation temperature T<sup>00</sup>

*THC*>*T*″

by natural convection.

**Figure 1.**

**135**

*Multi-seat cab for WBC.*

and the heat-removing surface is 20 K:

Minimum possible air temperature in the cab:

*Technique and Technology of Whole-Body Cryotherapy (WBC)*

*DOI: http://dx.doi.org/10.5772/intechopen.83680*

*TA* ¼ *T*″

The removal of heat from air to the surface of the heat exchanger was carried out

With natural convection, the calculated temperature gradient between the gas

*<sup>A</sup>* <sup>þ</sup> *<sup>Δ</sup>TA*�*HC*≈101 K �172°

Thus, the "Сryotium" design determined the WBC technology. Perhaps, that is why the author of the method did not give any reason for the WBC temperature regime in his works. The ratios of the boiling points of nitrogen and air, as well as the design features of the device in which the procedures were performed, have randomly created the conditions for a safe and highly efficient procedure.

The value of the air temperature during the WBC sessions specified by the method's author [1] is the lowest possible temperature that could be achieved in this

cab design. It is important to note that in "Сryotium" the temperature was maintained by choosing the pressure of liquid nitrogen (LN) vapor in the heat exchanger tubes (**Figure 2**). The boiling point of LN depends on pressure; by increasing the vapor pressure to a level of *P* ≥ 0.2 MPa, it is possible to ensure the fulfillment of condition (1) without using the temperature control systems. The lack of a temperature control system has provided "Сryotium" with unique operational advantages over modern WBC devices. Heat exchangers filled with liquid nitrogen successfully dealt with an increase in heat load when patients entered, and the

correct choice of operating pressure prevented air condensation.

A:

C *:* (3)

*<sup>A</sup>* ¼ 81 *K:* (1)

*TA*�*HC* ¼ *TA* � *THC*≈20 K*:* (2)
