Evaluation of Sub-Zero and Residence Times After Continuous Versus Multiple Intermittent Cryogen Spray Cooling Exposure on Human Skin Phantom

Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during various laser dermatologic surgeries. However, as the application of single or multiple cryogen spurts becomes available on some commercial lasers devices, it is necessary to determine the optimal CSC parameters for different laser surgeries. The objective of this study was to measure the time the sprayed surface of a human skin phantom (HSP) remains below water freezing temperature 0°C, referred to as subzero time (t_s), and below the cryogen boiling temperature −26°C, referred to as residence time (t_r), as well as the minimum surface temperature (T_min) and the time at which T_min occurs (t_Tmin) for two HSP-initial temperatures (20 °C and 70 °C) during and after the application of single (SCS) and multiple cryogen spurts (MCS). For this propose, a HSP was used to measure t_s, t_r, T_min, and t_Tmin for nine sequences: one SCS of Δt_T = TCT = 40 ms; four MCS sequences, all adding to a Δt_T of 40 ms but with different TCT up to 110 ms and, finally; four SCS that matched the TCT of the four MCS sequences, but lead to different Δt_T. Our results show that the differences between SCS and MCS sequences with the same TCT are negligible for all variables measured (t_s, t_r, T_min, t_Tmin). Moreover, in this interval (40 ms ≤ TCT ≤ 110 ms), this variables show a remarkable linear dependence with the TCT.