16, 17 In this method, a short cryogen spurt (on the order of tens of milliseconds) is sprayed onto the skin surface immediately before laser exposure. As heat diffuses out of the dermal blood vessels into the adjacent tissue, perivascular collagen damage can also occur, especially near the lesion's surface, where fluence levels are much higher than at deeper depths.Ĭryogen spray cooling (CSC) has recently been developed to selectively cool the skin during laser treatment of cutaneous vascular lesions. 13, 14 The epidermis offers a competing site for light absorption by melanin, 15 resulting in nonspecific heating therein and subsequent blistering and dyspigmentation. 8 - 10Īlthough motivation exists to increase radiant exposures, the degree of vascular damage selectivity decreases as higher radiant exposures increase the risk of damage to the epidermis 8, 9, 11, 12 and perivascular tissues. Second, there is a need to use higher radiant exposures in dark-skinned patients due to decreased dermal fluence levels. In addition, raised temperatures within blood vessels will facilitate clearing of the ectatic vessels at all depths of the dermis. First, increased radiant exposures will raise the fluence level deep within the dermis, enabling a deeper depth of vascular injury per treatment session, ultimately leading to a decreased number of treatments required for successful clinical outcome. Increasing the radiant exposure potentially provides a method for a more successful treatment of PWSs. 7 Incomplete clearing of the lesion may be due to insufficient heat generation within the targeted vasculature, which is affected by pulse duration (τ p), wavelength (λ), and radiant exposure (D 0). These therapies have proven effective 2 - 6 however, multiple treatments are often required, and complete clearing of the lesion is not always achieved, 6 especially in patients with large-diameter vessels and extensive vasculature that extends deep within the dermis. By proper selection of pulse duration (τ p) and wavelength (λ), thermal energy remains confined to the targeted vasculature. 1 Ideally, during this process, laser light is used to selectively heat and subsequently destroy the vascular lesion. LASER-MEDIATED treatments of cutaneous hypervascular malformations, such as port-wine stain (PWS) birthmarks, are based on the principle of selective photothermolysis. Additional studies are necessary to prove clinical safety of these protocols. In addition, long cryogen spurt durations (>200 milliseconds) prevented perivascular collagen coagulation in all skin types.Ĭonclusions 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. 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). 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/cm 2) however, epidermal protection could not be achieved in dark-skinned individuals (skin phototypes V-VI) even at the lowest radiant exposure (8 J/cm 2). Main Outcome Measure 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. Interventions 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/cm 2) without and with cryogen spray cooling (50- to 300-millisecond cryogen spurts). Patients Twenty women with normal abdominal skin (skin phototypes I-VI). Setting Academic hospital and research laboratory. 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/cm 2).
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