title: An analysis of heat removal during cryogen spray cooling and effects of simultaneous airflow application.
abstract: OBJECTIVE
  Cryogen spray cooling (CSC) is a method used to protect the epidermis from non-specific thermal injury that may occur as a result of various dermatological laser procedures. However, better understanding of cryogen deposition and skin thermal response to CSC is needed to optimize the technique.
  
  
  METHODS
  Temperature measurements and video imaging were carried out on an epoxy phantom as well as human skin during CSC with and without simultaneous application of airflow which was intended to accelerate cryogen evaporation from the substrate surface. An inverse thermal conduction model was used to estimate heat flux and total heat removed.
  
  
  RESULTS
  Lifetime of the cryogen film deposited on the surface of skin and epoxy phantom lasted several hundred milliseconds beyond the spurt, but could be reduced to the spurt duration by application of airflow. Values over 100 J/cm(3) were estimated for volumetric heat removed from the epidermis using CSC.
  
  
  CONCLUSIONS
  "Film cooling" instead of "evaporative cooling" appears to be the dominant mode of CSC on skin. Estimated values of heat removed from the epidermis suggest that a cryogen spurt as long as 200 milliseconds is required to counteract heat generated by high laser fluences (e.g., in treatment of port wine stains) in patients with high concentration of epidermal melanin. Additional cooling beyond spurt termination can be avoided by simultaneous application of airflow, although it is unclear at the moment if avoiding the additional cooling would be beneficial in the actual clinical situation.
authors: Department of Bioengineering, Rice University, Houston, Texas 77005, USA. jhtorres@ruf.rice.edu
authors: J H
authors: JH
authors: Torres
authors: J W
authors: JW
authors: Tunnell
authors: B M
authors: BM
authors: Pikkula
authors: B
authors: B
authors: Anvari
mesh_terms: D000335:Aerosol Propellants / Q000494:pharmacology*; D000392:Air Movements; D004853:Epoxy Resins; D006801:Humans; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology*; D053685:Laser Therapy; D008954:Models, Biological; D012867:Skin / Q000187:drug effects*; D012879:Skin Physiological Phenomena; D012881:Skin Temperature / Q000187:drug effects / Q000528:radiation effects; D014741:Video Recording; D004980:Ethane / Q000031:analogs & derivatives; D005466:Fluorocarbons
chemical_list: D000335:Aerosol Propellants; D004853:Epoxy Resins; D006845:Hydrocarbons, Fluorinated; C063006:norflurane; D004980:Ethane; D005466:Fluorocarbons