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, 4, 5, 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, 5, 6, 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/m3. At a temperature level of 170 K, a refrigerator with such a power has a heat-removing capacity of not more than 400 W/m3, which is comparable with the physiological heat release of a patient under thermal comfort conditions (150 W) .
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. [10, 11].
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.