title: Skin model surface temperatures during single and multiple cryogen spurts used in laser dermatologic surgery.
abstract: BACKGROUND
  Although cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery, concern has been expressed that CSC may induce cryo-injury. In order to address this concern, it is necessary to evaluate the effects of prolonged exposure of human skin phantoms (HSP) to CSC.
  
  
  OBJECTIVE
  To measure the minimum surface temperature (T(min)) and the time at which it occurs (t(Tmin)) as well as determine the time the sprayed HSP surface remains below 0 degrees C (sub-zero time, Deltat(s)) and -26 degrees C (residence time, Deltat(r)) during the application of single (SCS) and multiple (MCS) cryogen spurts. Two initial HSP substrate temperatures were studied, T(i): 23 and 70 degrees C.
  
  
  METHODS
  An epoxy-based HSP was constructed to measure T(min), t(Tmin), Deltat(s), and Deltat(r), for 17 spray patterns: 1 SCS with a total cryo-delivery time (Deltat(c)) of 40 milliseconds; 8 MCS patterns with identical Deltat(c), but with a total cooling time (Deltat(total)) varying from 50 to 280 milliseconds; and 8 SCS patterns that matched the Deltat(total) of the MCS patterns.
  
  
  RESULTS
  For both T(i), our results show that it is possible to distinguish between two different cooling regimes. For Deltat(total) </= 110 milliseconds, the differences between SCS and MCS patterns with the same Deltat(total) for all variables (T(min), t(Tmin), Deltat(s), Deltat(r)) are negligible. Most importantly, all these variables show a remarkable linear dependence with Deltat(total). In the interval 110 milliseconds < Deltat(total) < 280 milliseconds, T(min) and t(Tmin) are similar for SCS and MCS, while Deltat(s) and Deltat(r) show more pronounced differences between the two spray patterns. In this interval, the values of T(min) and Deltat(s) for MCS remain invariant and similar to the corresponding values for Deltat(total) = 110 milliseconds.
  
  
  CONCLUSIONS
  These results suggest that: (1) similar epidermal protection may be attained with SCS and MCS for Deltat(total) </= 110 milliseconds; and (2) for 110 milliseconds < Deltat(total) </= 280 milliseconds, MCS help to maintain Deltat(s) similar to that of SCS at Deltat(total) = 100 milliseconds, which may be beneficial to prevent cryo-injury.
authors.affiliation: Beckman Laser Institute and Medical Clinic, University of California, Irvine, California 92612, USA.
authors.forename: Julio C
authors.initials: JC
authors.lastname: Ramirez-San-Juan
authors.forename: Guillermo
authors.initials: G
authors.lastname: Aguilar
authors.forename: Alia T
authors.initials: AT
authors.lastname: Tuqan
authors.forename: Kristen M
authors.initials: KM
authors.lastname: Kelly
authors.forename: J Stuart
authors.initials: JS
authors.lastname: Nelson
mesh_terms: D000336:Aerosols; D003080:Cold Temperature; D017679:Cryotherapy / Q000295:instrumentation*; D062109:Dermatologic Surgical Procedures; D006801:Humans; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D053685:Laser Therapy / Q000379:methods*; D008953:Models, Anatomic; D012680:Sensitivity and Specificity; D012867:Skin / Q000473:pathology; D012881:Skin Temperature; D013817:Thermography / Q000379:methods*; D013997:Time Factors
chemical_list: D000336:Aerosols; D006845:Hydrocarbons, Fluorinated