**7. Selecting the optimal duration of the WBC procedure**

The author of the WBC method, Yamauchi, limited the exposure of the body contact with a cryogenic gas to a period of 180 sec [1, 2]. The minimum air temperature in the Japanese installation was �175°C. According to the contemporary idea that WBC technology is based on metered supercooling of the body shell, the choice of the cooling exposure should be related to the temperature of the gas in the WBC zone. Using the assumption of the constancy of the gas temperature in the WBC zone, it is possible to determine the maximum duration of cooling at different gas temperatures. Computational experiments on the mathematical model of the human BS showed that with an increase in the heat carrier temperature from 90 to 190 K, the safe duration of a patient's stay in the WBC zone increases from 54 to

*Technique and Technology of Whole-Body Cryotherapy (WBC) DOI: http://dx.doi.org/10.5772/intechopen.83680*

237 sec [3]. At a temperature of 140 K, the safe exposure time for cooling is 161 sec. The practice of using WBC has shown that, along with the maximum duration of cooling, it is necessary to limit the minimum duration of stay of patients in a cryotherapeutic installation [7].

The reasons for this limitation are explained by the graph of dependence *ET = f*(τ) (**Figure 8**). The graph shows that there is a fairly long period in the WBC procedure when a positive effect is not formed. At a gas temperature of 140 K, this phase of the procedure accounts for almost 80%, but 93% of the positive effect is formed after its completion. The reason for the low efficiency of WBC at the beginning of the procedure is the relatively high skin temperature (*TS*) (**Figure 8**), which drops to 275 K (2°C) only by the end of the first phase of the procedure. As it can be seen from the graph of dependence *ISA = f*(*TS*) (**Figure 5**), at a skin temperature of *TS >* 275 K, the intensity of the WBC stimulating effect is negligible *ISA* < 60. The first phase of the WBC procedure reduces the surface temperature of the skin to a temperature of *TS* = 275 K, so it is called the cooling time (τcool) (**Figure 9**). It is obvious that the duration of the WBC procedure must be longer than the duration of the cooling time but less than the time of the violation of safety conditions τcool *<* τ *<* τmax*.* The second, effective, phase of the procedure ensures the formation of the main positive result, the longer the duration of the effective phase, the greater the effect of the procedure.

$$
\tau\_{EP} = \tau\_{\text{max}} - \tau\_{cool} \tag{24}
$$

The calculated dependences of the WBC safe exposure (τmax) and the duration of the cooling time (τcool) on the gas temperature (*Tg*) (**Figure 10**) show that increasing the gas temperature from 90 to 150 K increases the effective phase of the procedure. A further increase in temperature increases the duration of the cooling time. At temperatures above 160 K, the estimated duration of the cooling time exceeds the safe WBC exposure. Even with isothermal cooling, it is impossible to provide an effective WBC when using gas with a temperature *Tg* > 150 K; in real conditions the gas temperature should be no higher than 140 K.

Numerical experiments on a mathematical model of the human body shell allowed to formulate general ideas about the technological foundations of effective WBC. When developing technological recommendations on the design of installations for the implementation of GWBC or IWBC methods, it is necessary to take into account the algorithm for changing the temperature of the gas in contact with the patient's body surface.

#### **Figure 9.**

*The change of the body temperature surface* Ts *and the value of* ET *during the WBC procedure with gas temperature of 140 K.*

When the gas temperature is above 150 K, the danger of supercooling of the body core (*Tf* ! 309 K) occurs before the surface of the body shell is supercooled. The reason for the termination of the WBC procedures becomes a violation of the condition *Tf* ≥ 309 K. At the same time, the temperature of the body shell surface remains at a sufficiently high level of *Ts* ≥ 275 K (2°C), due to which the cold receptors of the skin do not experience significant irritation and the accumulation of a positive WBC effect is extremely slow. The picture described is identical to what is observed at the time of completion of the water hypothermia procedure. Under conditions of isothermal cooling of the body with gas with a temperature of 160 K (�110°C), the estimated duration of the WBC procedure is 207 sec. During this time, the BS surface temperature drops only to 275 K. At this BS surface temperature, the ISA value is 80 times less than the maximum value (**Figure 5**). Under actual conditions, the WBC procedures in installations with a minimum temperature of 160 K (�110°C) do not ensure the constancy of the gas temperature, so the BS surface temperature after the procedure is much higher than the calculated one and is 15–20°C [24]. Such a temperature on the surface of the skin can be obtained using water baths with a temperature of 8°C; therefore, the doubts of some authors [11, 18, 25] on the advisability of using cryogenic technologies are

*The estimated duration of the effect of WBC at different gas temperature.*

According to the results of simulating the process of cooling the BS surface with a cryogenic gas, it can be argued that for effective procedures the gas temperature

The author of the WBC method, Yamauchi, limited the exposure of the body

contact with a cryogenic gas to a period of 180 sec [1, 2]. The minimum air temperature in the Japanese installation was �175°C. According to the contemporary idea that WBC technology is based on metered supercooling of the body shell, the choice of the cooling exposure should be related to the temperature of the gas in the WBC zone. Using the assumption of the constancy of the gas temperature in the WBC zone, it is possible to determine the maximum duration of cooling at different gas temperatures. Computational experiments on the mathematical model of the human BS showed that with an increase in the heat carrier temperature from 90 to 190 K, the safe duration of a patient's stay in the WBC zone increases from 54 to

in the WBC zone should be not lower than 140 K.

**7. Selecting the optimal duration of the WBC procedure**

fully justified.

**146**

**Figure 8.**

*Low-temperature Technologies*

**Figure 10.** *The dependence of the cooling phase duration and safe exposure WBC on the gas temperature.*
