title: Effects of cryogen spray cooling and high radiant exposures on selective vascular injury during laser irradiation of human skin.
abstract: BACKGROUND
  Increasing radiant exposure offers a means to increase treatment efficacy during laser-mediated treatment of vascular lesions, such as port-wine stains; however, excessive radiant exposure decreases selective vascular injury due to increased heat generation within the epidermis and collateral damage to perivascular collagen.
  
  
  OBJECTIVE
  To determine if cryogen spray cooling could be used to maintain selective vascular injury (ie, prevent epidermal and perivascular collagen damage) when using high radiant exposures (16-30 J/cm2).
  
  
  METHODS
  Observational study.
  
  
  METHODS
  Academic hospital and research laboratory.
  
  
  METHODS
  Twenty women with normal abdominal skin (skin phototypes I-VI).
  
  
  METHODS
  Skin was irradiated with a pulsed dye laser (wavelength = 585 nm; pulse duration = 1.5 milliseconds; 5-mm-diameter spot) using various radiant exposures (8-30 J/cm2) without and with cryogen spray cooling (50- to 300-millisecond cryogen spurts).
  
  
  METHODS
  Hematoxylin-eosin-stained histologic sections from each irradiated site were examined for the degree of epidermal damage, maximum depth of red blood cell coagulation, and percentage of vessels containing perivascular collagen coagulation.
  
  
  RESULTS
  Long cryogen spurt durations (>200 milliseconds) protected the epidermis in light-skinned individuals (skin phototypes I-IV) at the highest radiant exposure (30 J/cm2); however, epidermal protection could not be achieved in dark-skinned individuals (skin phototypes V-VI) even at the lowest radiant exposure (8 J/cm2). The red blood cell coagulation depth increased with increasing radiant exposure (to >2.5 mm for skin phototypes I-IV and to approximately 1.2 mm for skin phototypes V-VI). In addition, long cryogen spurt durations (>200 milliseconds) prevented perivascular collagen coagulation in all skin types.
  
  
  CONCLUSIONS
  Cryogen spurt durations much longer than those currently used in therapy (>200 milliseconds) may be clinically useful for protecting the epidermis and perivascular tissues when using high radiant exposures during cutaneous laser therapies. Additional studies are necessary to prove clinical safety of these protocols.
authors.affiliation: Department of Bioengineering, Rice University, Houston, TX 77251, USA.
authors.forename: James W
authors.initials: JW
authors.lastname: Tunnell
authors.forename: David W
authors.initials: DW
authors.lastname: Chang
authors.forename: Carol
authors.initials: C
authors.lastname: Johnston
authors.forename: Jorge H
authors.initials: JH
authors.lastname: Torres
authors.forename: Charles W
authors.initials: CW
authors.lastname: Patrick
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Miller
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Thomsen
authors.forename: Bahman
authors.initials: B
authors.lastname: Anvari
mesh_terms: D000328:Adult; D000368:Aged; D001777:Blood Coagulation / Q000528:radiation effects; D003452:Cryosurgery; D004817:Epidermis / Q000473:pathology / Q000528:radiation effects; D005260:Female; D006801:Humans; D017075:Laser Coagulation; D008875:Middle Aged; D011829:Radiation Dosage; D017445:Skin Diseases, Vascular / Q000473:pathology / Q000601:surgery*; D012880:Skin Pigmentation / Q000528:radiation effects; D013997:Time Factors