Cryogen spray cooling in laser dermatology: effects of ambient humidity and frost formation.
OBJECTIVE
Dynamics of cryogen spray deposition, water condensation and frost formation is studied in relationship to cooling rate and efficiency of cryogen spray cooling (CSC) in combination with laser dermatologic surgery.


METHODS
A high-speed video camera was used to image the surface of human skin during and after CSC using a commercial device. The influence of ambient humidity on heat extraction dynamics was measured in an atmosphere-controlled chamber using an epoxy block with embedded thermocouples.


RESULTS
A layer of liquid cryogen may remain on the skin after the spurt termination and prolong the cooling time well beyond that selected by the user. A layer of frost starts forming only after the liquid cryogen retracts. Condensation of ambient water vapor and subsequent frost formation deposit latent heat to the target site and may significantly impair the CSC cooling rate.


CONCLUSIONS
Frost formation following CSC does not usually affect laser dosage delivered for therapy of subsurface targets. Moreover, frost formation may reduce the risk of cryo-injury associated with prolonged cooling. The epidermal protection during CSC assisted laser dermatologic surgery can be further improved by eliminating the adverse influence of ambient humidity.
Majaron
B
B
Beckman Laser Institute and Medical Clinic, University of California, Irvine, CA 92612, USA. boris.majaron@ijs.si
Kimel
S
S
Verkruysse
W
W
Aguilar
G
G
Pope
K
K
Svaasand
L O
LO
Lavernia
E J
EJ
Nelson
J S
JS
D000335:Aerosol Propellants / Q000494:pharmacology*; D062109:Dermatologic Surgical Procedures; D006801:Humans; D006813:Humidity; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology*; D053685:Laser Therapy; D012867:Skin / Q000187:drug effects*; D013696:Temperature; D004980:Ethane / Q000031:analogs & derivatives; D005466:Fluorocarbons
D000335:Aerosol Propellants; D006845:Hydrocarbons, Fluorinated; C063006:norflurane; D004980:Ethane; D005466:Fluorocarbons