Er:YAG laser skin resurfacing using repetitive long-pulse exposure and cryogen spray cooling: I. Histological study

Er:YAG laser brain surgery with vascular specific coagulation

BACKGROUND AND OBJECTIVE

Erbium:yttrium-aluminum-garnet (Er:YAG) laser ablation can effectively resect water-bearing tissues. Application of Er:YAG resection in neurosurgery is complicated by unpredictable bleeding in surgical field. Recently, an integrated theranostic system combining a dual-wavelength laser surgery system using a thulium (Tm) fiber-laser for coagulation and Er:YAG for resection, combined with optical coherence tomography (OCT) guidance was demonstrated for the in vivo resection of tumor tissue. However, lateral thermal spread in the range of 100 seconds of micrometers is common due to lack of vascular specificity using a Tm fiber-laser for coagulation. In this study, a vascular specific ytterbium (Yb) fiber-laser is utilized for enhanced photocoagulation during in vivo neurosurgery improving the precision of Er:YAG tissue resection with minimal lateral thermal spread.

METHODS

Mice underwent stereotactic laser surgery with the proposed Yb/Er:YAG dual wavelength vascular specific neurosurgery in vivo. An OCT system (wavelength range 1310 ± 70 nm) and OCT derived angiography  images were used to record cortical images to confirm the coagulation of blood vessels and guide subsequent Er:YAG resection steps. After the laser surgery, mice were killed, and histological analysis was carried out using hematoxylin and eosin staining and Nissl staining to compare the lateral thermal spread with our previously reported Tm/Er:YAG neurosurgery where a continuous wave  Tm fiber-laser was used for coagulation.

RESULTS

Coagulation scheme using a Yb fiber-laser allowed stoppage of blood flow in disparately sized blood vessels encountered in the mice brain. Histological analysis of murine brain slices post Yb/Er:YAG laser surgery yielded lower thermal spread compared with Tm/Er:YAG laser surgery, maximizing the efficiency in both hemostasis (blood flow stoppage) and maximizing tissue ablation efficiency with minimal residual thermal damage zone.

CONCLUSION

In this study, a vascular specific coagulation scheme with Yb/Er:YAG dual-wavelength surgery is presented for neurosurgery. Additionally, Yb/Er:YAG study results are compared with that of a tissue coagulation approach in Tm/Er:YAG surgery previously reported to highlight improved coagulation, reduced nonspecific thermal damage and limited lateral thermal spread. Experimental results suggest that the developed dual-wavelength laser system can effectively resect neural tissues with high localization, minimal lateral thermal spread at the micrometer level while maintaining a bloodless surgical field.

Vaginal erbium laser for treatment of stress urinary incontinence: optimization of treatment regimen for a sustained long-term effect

Stress urinary incontinence (SUI) is a common health problem that affects roughly 35% of women in the reproductive period. A prospective uncontrolled study was conducted to assess the long-term efficacy and safety of a non-ablative Er:YAG laser treatment of SUI. Forty-three patients participated in the study. All women underwent three sessions of IncontiLase® procedure, and efficacy of laser treatment was assessed by 1-h pad test, 24-h pad test, 3-day voiding diary, and ICIQ-UI SF questionnaire at multiple follow-ups. Statistical analysis was performed using one-way repeated measures ANOVA. Patients were questioned about discomfort during treatment and any adverse events following the laser procedures. All outcome measures showed a significant change over a period of the entire clinical trial. Eighteen-month follow-up revealed a fading of the effect, which was alleviated by single-session maintenance treatments every 6 months. There were no serious adverse events reported during the study. All reported side effects were mild and transient. The application of non-ablative Er:YAG laser for SUI treatment significantly improves the SUI symptoms. High improvement rates and patient satisfaction can be maintained with single-session maintenance treatments performed every 6 months. Long-term safety profile of multiple non-ablative Er:YAG laser treatment is shown. NCT04348994, 16.04.2020, retrospectively registered.

Characteristics of Non-Ablative Resurfacing of Soft Tissues by Repetitive Er:YAG Laser Pulse Irradiation

Background and Objectives

Recently, several minimally invasive gynecological, ENT and esthetic procedures have been introduced that are based on delivering “smooth” sequences of Er:YAG laser pulses to cutaneous or mucosal tissue at moderate cumulative fluences that are not only below the ablation threshold but typically also do not require local anesthesia.  To explain the observed clinical results using “smooth‐resurfacing,” it has been suggested that in addition to the direct heat injury to deeper‐lying connective tissues, there is an additional mechanism based on indirect triggering of tissue regeneration through short‐exposure, intense heat shocking of epithelia. The goal of this study is to improve understanding of the complex dynamics of the exposure of tissues to a series of short Er:YAG laser pulses, during which the thermal exposure times transition from extremely short to long durations.

Study Design/Materials and Methods

A physical model of laser‐tissue interaction was used to calculate the temperature evolution at the irradiated surface and deeper within the tissue, in combination with a chemical model of tissue response based on the recently introduced variable heat shock (VHS) model, which assumes that the tissue damage represents a combined effect of two limiting Arrhenius′ processes, defining cell viability at extremely long and short exposure times. Superficial tissue temperature evolution was measured during smooth‐resurfacing of cutaneous and mucosal tissue, and compared with the model. Two modalities of non‐ablative resurfacing were explored: a standard “sub‐resurfacing” modality with cumulative fluences near the ablation threshold, and the “smooth‐resurfacing” modality with fluences below the patient′s pain threshold. An exemplary skin tightening clinical situation was explored by measuring pain tolerance threshold fluences for treatments on abdominal skin with and without topical anesthesia. The obtained temperature data and pain thresholds were then used to study the influence of Er:YAG laser sequence parameters on the superficial (triggering) and deep (coagulative) tissue response.

Results

The simulations show that for the sub‐resurfacing modality, the parameter range where no excessive damage to the tissue will occur is very narrow. On the other hand, using pain tolerance as an indicator, the smooth‐resurfacing treatments can be performed more safely and without sacrificing the treatment efficacy. Two preferred smooth‐resurfacing treatment modalities were identified. One involves using optimally long pulse sequence durations (≈1–3 seconds) with an optimal number of pulses (N ≈ 10–30), resulting in a maximal short‐exposure superficial tissue response and moderate coagulation depths. And for deeper coagulation, without significant superficial heat shocking, very long pulse sequences (>5 seconds) with a large number of delivered pulses are to be used in combination with topical anesthesia.

Conclusions

A comparison of the simulations with the established smooth‐resurfacing clinical protocols in gynecology, ENT, and esthetics suggests that, through clinical experience, the clinical protocols have been optimized for the maximal superficial heat shock triggering effect. Further research is needed to gain a better understanding of the proposed role of heat shock triggering in the clinically observed regeneration of cutaneous, vaginal, and oral tissues following Er:YAG laser smooth‐resurfacing. Lasers Surg. Med. © 2021 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC.

Erbium:YAG laser augments the penetration of cryotherapy

Cryotherapy is commonly used during dermatologic practice. Several modifications such as an "add-on" to topicals or intralesional applications have been already defined to enhance efficacy. The aim of this study is to test our hypothesis that ablative laser application before cryotherapy would increase the depth of freezing.Throughout this experiment, target points received either cryotherapy alone or a combination of erbium:yttrium-aluminum garnet (erbium:YAG) laser and cryotherapy. Freezing durations of 10 (C10), 20 (C20), and 30 seconds (C30) were investigated. Erbium:YAG laser groups received equal high energy shots with different pulse durations (100 μs versus 1500 μs) before freezing. The treatment points were arranged on the peripheral side of porcine skin specimens, and dermoscopic images revealing the iceball visible from the lateral side were immediately captured. Repeated experimental results were compared by Wilcoxon's test. The comparison of the vertical length of the iceball between the three different freezing durations of 10 seconds, 20 seconds, and 30 seconds was statistically significant (p<0.05). The vertical length of the iceball was higher in both laser groups receiving 30-second freezing (mean ± SD: 4.32±0.53, 3.9±0.38 for micro-short pulse (MSP) and extra-long pulse (XLP), respectively) when compared with 30-second freezing alone (mean ± SD:3.51±0.44) (p=0.016). The two laser settings did not reveal a difference for the penetration of 30-second freezing (p=0.122). In this study, through visual monitorization of the iceball, erbium:YAG laser is found to augment the penetration of cryotherapy. The defined combination regimen has the potential to ameliorate treatment outcomes of cryotherapy.

Effects of non-ablative Er:YAG laser on the skin and the vaginal wall: systematic review of the clinical and experimental literature

INTRODUCTION AND HYPOTHESIS

Er:YAG laser is frequently used in dermatology and gynecology. Clinical studies document high satisfaction rates; however, hard data on the effects at the structural and molecular levels are limited. The aim of this systematic review was to summarize current knowledge about the objective effects of non-ablative Er:YAG laser on the skin and vaginal wall.

METHODS

We searched MEDLINE, Embase, Cochrane, and the Web of Science. Studies investigating objectively measured effects of non-ablative Er:YAG laser on the skin or vaginal wall were included. Studies of any design were included. Owing to the lack of methodological uniformity, no meta-analysis could be performed and therefore results are presented as a narrative review.

RESULTS

We identified in vitro or ex vivo studies on human cells or tissues, studies in rats, and clinical studies. Most studies were on the skin (n = 11); the rest were on the vagina (n = 4). The quality of studies is limited and the settings of the laser were very diverse. Although the methods used were not comparable, there were demonstrable effects in all studies. Immediately after application the increase in superficial temperature, partial preservation of epithelium and subepithelial extracellular matrix coagulation were documented. Later, an increase in epithelial thickness, inflammatory response, fibroblast proliferation, an increase in the amount of collagen, and vascularization were described.

CONCLUSIONS

Er:YAG laser energy may induce changes in the deeper skin or vaginal wall, without causing unwanted epithelial ablation. Laser energy initiates a process of cell activation, production of extracellular matrix, and tissue remodeling.

Histological findings after argon plasma coagulation: an ex-vivo study revealing a possible role in superficial ablative treatment of the skin

Argon plasma coagulation (APC) is an electrosurgical technique which can be used to ablate skin lesions with limited invasion depth into dermal tissue. Hence, APC might be well suited for the removal of epithelial tumours. However, there are no data on the effects of APC on human skin tissue. Thus, the aim of this study was to determine the extent of epidermal and dermal damage after APC of human skin. We performed APC ex-vivo on 91 freshly resected human skin samples, which were obtained after reconstructive surgical closures in actinically damaged areas. Tissue effects were evaluated histologically and compared across different power settings. Using 15, 30, and 45 W, median (interquartile range; IQR) coagulation depths were 110.0 µm (91.7-130.0), 113.3 µm (85.8-135.0), and 130.0 µm (100.0-153.3.0), respectively. Median (IQR) thickness of necrosis zone was 30.0 µm (23.3-40.0) at 15 W, 26.7 µm (20.0-41.6) at 30 W, and 43.3 µm (30.8-57.5) at 45 W. The Kruskal-Wallis test showed significant differences between 15 and 30 W versus 45 W for coagulation depth (P = 0.0414), necrosis zone (P = 0.0017), and necrosis according to overlaying epidermal thickness (P = 0.0467). In summary, APC is a simple and controllable electrosurgical technique to remove epidermal tissue with limited penetration to the dermis. Thus, APC is particularly suited for the ablation of epithelial skin lesions and, therefore, may serve as possible treatment approach for intraepithelial neoplasms such as actinic keratosis.

Treatment of lichen pilaris with a Q-switched Nd:YAG laser in quasi long-pulsed mode: A case report (a secondary publication)

BACKGROUND AND AIMS

Lichen pilaris is a very common disease typically seen among young adults on their upper arms as a manifestation of hyperkeratotic lesions occurring in the pores. Only a few treatments have been reported as significantly effective, so often natural resolution over time is the only option. The present study examined the use of a 1064 nm Q-switched Nd:YAG laser (QSNY) in quasi long-pulsed mode, in an attempt to treat a case of lichen pilaris.

SUBJECT AND METHODS

A 33-year-old male presented with light-brown aggregated papules observed on both sides of the upper arms. The affected areas were treated every other week (QSNY, pulse width 300 µs, pulse energy 3.0 J/cm(2), spot size 6 mm and repetition rate 10 Hz). Clinical photography was taken of the lesions at baseline and three months after the final treatment in addition to macrophotography and 3-D photography, biopsies being taken at both time points for histological comparison.

RESULTS

The clinical photography and objective image evaluation demonstrated shrinkage of pores and improvement of the unevenness of the skin. Histological examination suggested that the effect of the micropulsed QSNY on the horny layer, epidermal keratinocytes and dermal collagen resulted in a peeling effect and increased dermal collagen density, which eventually led to the shrinkage of the pores and improvement of the skin condition.

CONCLUSIONS

The results of this single patient case report suggest that the micropulsed QSNY could be an effective treatment option for lichen pilaris, improvement of which is often difficult. Further studies with an appropriately-sized population are merited to confirm these preliminary results.

Multiple minimally invasive Erbium: Yttrium Aluminum Garnet laser mini-peels for skin rejuvenation: an objective assessment

BACKGROUND

As the demand for minimally invasive rejuvenation is increasing, micropeel resurfacing using Erbium:Yttrium Aluminum Garnet (Er:YAG) laser 2940 nm has been reported for the treatment of photoaged skin without ablation of the epidermis. However, little is known about the efficacy and underlying histologic changes associated with this type of treatment.

AIMS

The aims of this study are to evaluate the clinical effect and objectively quantify the histological changes in response to multiple sessions of Er:YAG laser 2940 nm mini-peels.

PATIENTS AND METHODS

Six female volunteers of Fitzpatrick skin type III-IV and Glogau's class I-III wrinkles were subjected to six microresurfacing peels at 2-week intervals using Er:YAG 2940 nm laser at subablative fluences of 2-3 J/cm(2) to treat periorbital rhytides. Quantitative evaluation of collagen types I, III, and VII, newly synthesized collagen, total elastin, and tropoelastin was performed by histochemistry and immunohistochemistry coupled with computerized morphometric analysis at base line, end of treatment, and 3 months post-treatment.

RESULTS

Compared to the base line, evaluation of volunteers revealed obvious clinical improvement in response to Er:YAG mini-peels. Collagen types I, III, and VII, as well as newly synthesized collagen, together with tropoelastin showed a statistically significant increase in response to treatment, while the mean level of total elastin was significantly decreased in response to treatment. However, this was followed by regression of improvement at 3 months post-treatment but was still better than baseline.

CONCLUSIONS

This study revealed that multiple Er:YAG mini-peels is a promising treatment option for photoaging as it reverses the signs of photoaged skin with little downtime and side effects. However, to maintain the short-term improvement achieved after treatment, continued Er:YAG 2940 nm laser mini-peels is required.

Fractional versus ablative erbium:yttrium-aluminum-garnet laser resurfacing for facial rejuvenation: an objective evaluation

BACKGROUND

Laser is one of the main tools for skin resurfacing. Erbium:yttrium-aluminum-garnet (Er:YAG) was the second ablative laser, after carbon dioxide, emitting wavelength of 2940 nm. Fractional laser resurfacing has been developed to overcome the drawbacks of ablative lasers.

OBJECTIVE

We aimed to objectively evaluate the histopathological and immunohistochemical effects of Er:YAG 2940-nm laser for facial rejuvenation (multiple sessions of fractional vs single session of ablative Er:YAG laser).

METHODS

Facial resurfacing with single-session ablative Er:YAG laser was performed on 6 volunteers. Another 6 were resurfaced using fractional Er:YAG laser (4 sessions). Histopathological (hematoxylin-eosin, orcein, Masson trichrome, and picrosirius red stains) and immunohistochemical assessment for skin biopsy specimens were done before laser resurfacing and after 1 and 6 months. Histometry for epidermal thickness and quantitative assessment for neocollagen formation; collagen I, III, and VII; elastin; and tropoelastin were done for all skin biopsy specimens.

RESULTS

Both lasers resulted in increased epidermal thickness. Dermal collagen showed increased neocollagen formation with increased concentration of collagen types I, III, and VII. Dermal elastic tissue studies revealed decreased elastin whereas tropoelastin concentration increased after laser resurfacing. Neither laser showed significant difference between their effects clinically and on dermal collagen. Changes in epidermal thickness, elastin, and tropoelastin were significantly more marked after ablative laser.

LIMITATIONS

The small number of patients is a limitation, yet the results show significant improvement.

CONCLUSION

Multiple sessions of fractional laser have comparable effects to a single session of ablative Er:YAG laser on dermal collagen but ablative laser has more effect on elastic tissue and epidermis.

Investigation of irradiation by different nonablative lasers on primary cultured skin fibroblasts

BACKGROUND

A variety of lasers with different wavelengths and biological effects are widely used for nonablative skin rejuvenation, but the underlying mechanisms have not been fully investigated.

AIM

To investigate the effects of irradiation by different nonablative lasers on collagen synthesis and the antioxidant status of cultured fibroblasts to identify a possible mechanism for laser photorejuvenation.

METHODS

Cultured skin fibroblasts were irradiated with three different lasers: 532 nm potassium-titanyl phosphate (KTP), 1064 nm Q-switched neodymium:yttrium-aluminium-garnet (Nd:Yag) and 1064 nm long-pulse Nd:YAG, and production of collagen and changes in lactate dehydrogenase (LDH), malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were assayed.

RESULTS

Irradiation by all three lasers led to a marked increase in collagen production. Two major antioxidant enzymes, SOD and GSH, were significantly increased, whereas MDA was markedly reduced after laser irradiation. No change in LDH activity was found between nonirradiated and irradiated fibroblasts.

CONCLUSION

This study indicates that the increased collagen synthesis by fibroblasts after laser treatment may be partly due to improved antioxidant capacity, which reduces oxidative stress and thus stimulates new collagen production.

Selective creation of thermal injury zones in the superficial musculoaponeurotic system using intense ultrasound therapy: a new target for noninvasive facial rejuvenation

OBJECTIVES

To transcutaneously deliver intense ultrasound (IUS) energy to target the facial superficial musculoaponeurotic system (SMAS), to produce discrete thermal injury zones (TIZs) in the SMAS, and to demonstrate the relative sparing of adjacent nontargeted layers superficial and deep to the SMAS layer.

METHODS

In 6 unfixed human cadaveric specimens, the SMAS layer was visualized and targeted using the ultrasound imaging component of the IUS device. Using 2 IUS handpieces, 202 exposure lines were delivered bilaterally in multiple facial regions by varying combinations of power and exposure time (0.5-8.0 J). Tissue was then excised and examined grossly and histologically for evidence of thermal injury using nitroblue tetrazolium chloride viability stain.

RESULTS

Reproducible TIZs were produced selectively in the SMAS at depths of up to 7.8 mm, and sparing of surrounding tissue including the epidermis. Higher energy settings and high-density exposure line pattern produced a greater degree of tissue shrinkage.

CONCLUSIONS

In human cadaveric facial tissue, IUS can noninvasively target and selectively produce TIZs of reproducible location, size, and geometry in the SMAS layer. The ability to produce focused thermal collagen denaturation in the SMAS to induce shrinkage and tissue tightening has not been previously reported and has significant implications for aesthetic facial rejuvenation.

Traumatic Tattoo: Use of the Variable Pulsed Erbium:YAG Laser

OBJECTIVE

The aim of this study was to evaluate the efficacy and safety of removing traumatic tattoos in the skin by laser. The objective was to achieve selective dermabrasion on the tattoo site without injuries to the surrounding skin, as in the classical mechanical dermabrasion.

METHODS

Four patients with traumatic tattoos in the face were treated by a variable pulsed erbium:YAG laser. The fluence of the ablative pulses was 5 J/cm(2). The end-point for the treatment was the macroscopic removal of the foreign bodies. Postoperatively, silver sulphadiazine or polyvinylpyrrolidone was applied daily until wound closure occured. Use of a total sun block was mandatory for a period of 6 months. Pre- and post-operative photographs were taken of all cases. The results were evaluated by a panel of four independent observers, who were asked to judge the percentage of tattoo clearance as well as any evidence of pigmentation problems or scarring.

RESULTS

All results were rated from good to excellent. In all patients, a nearly complete clearance of the traumatic tattoo was achieved in one laser session. No scarring, skin atrophy, or hypo- or hyperpigmentation was observed. Furthermore, a high patient satisfaction rate was achieved.

CONCLUSION

The selective ablation of scar/foreign body tissue is a safe procedure. Compared to results reported with 1064-nm laser treatments, where several laser procedures are necessary, better clearance and scar quality was observed. Compared to mechanical dermabrasion, the procedure is more reliable and causes fewer side effects.

Electro-optical synergy (ELOS?) technology for nonablative skin rejuvenation: a preliminary prospective study

BACKGROUND AND OBJECTIVES

In this preliminary prospective study, we evaluated the efficacy and safety of nonablative wrinkle treatment using combined radiofrequency (RF) and optical energy (Polaris). The dual energy technology of Polaris, called ELOS, which stands for electro-optical synergy, uses synchronous pulses of bipolar RF current and pulsed visible light (diode laser) delivered in the same pulse.

MATERIALS AND METHODS

Twenty-four subjects with periorbital and perioral wrinkles received six treatments at 4-week intervals with the Polaris WR (Syneron, Inc., Israel, 900 nm, max. RF energy 100 J/cm(3), max. laser energy 50 J/cm(2)). Each treatment consisted of two passes over the treatment area using pulsed optical and RF parameters that were determined by the patient's skin phenotype and distribution of target chromophores. The follow-up period was 3 months after the last treatment.

RESULTS

Independent scoring of blinded photographs showed a wrinkle score improvement of at least 1 (0 = no improvement, 1 = medium, 2 = good, 3 = excellent improvement) 3 months after the last of six treatment sessions. There was no difference between periorbital and perioral wrinkle reduction. Fifty-eight per cent (14/24) of the subjects reported a notable wrinkle reduction; 16% noted mild to moderate oedema and erythema lasting for no more than 1 day. Scarring or pigmentary changes were not detected. The average pain score was 0.6 (0 = no pain, 5 = intolerable pain).

CONCLUSION

Multiple treatments with the Polaris WR produced objective and subjective reduction of periorbital and perioral wrinkles. The occurrence of side-effects and pain was very low. The clinical effect may be caused by matrix coagulation of the deep dermis by the RF and selective thermolysis of blood vessels with the 900 nm diode laser.

Nonablative lasers

The trend toward minimally invasive rejuvenation techniques has led to the widespread use of nonablative lasers. Nonablative lasers can be classified in two groups based on their wavelengths: lasers emitting light in the visible range, and those emitting in the infrared range. In this review, different laser and intense pulsed light (IPL) systems are presented and critically discussed along with findings of the studies in the literature.

Comparison of biophysical properties of skin measured by using non-invasive techniques in the KM mice following 595 nm pulsed dye, 1064 nm Q-Switched Nd:YAG and 1320 nm Nd:YAG laser non-ablative rejuvenation

BACKGROUNDS/AIMS

The aim of the study was to compare the changes of the biophysical properties and to objectify the effects of 595 nm pulsed dye, 1064 nm Q-switched Nd:YAG and 1320 nm Nd:YAG lasers non-ablative rejuvenation by non-invasive techniques.

METHODS

KM mice were used for the study. The 595 nm pulsed dye, 1064 nm Q-switched Nd:YAG and 1320 nm Nd:YAG laser treatments were evaluated with biophysical parameter measurements including skin elasticity, skin color, skin trans-epidermal water loss (TEWL) and skin hydration.

RESULTS

All three lasers improved the biophysical properties in the skin of KM mice. In skin elasticity measurements, the 1064 nm laser treatment showed the lowest ratio (0.61+/-0.09) while the 1320 nm laser showed the highest one (0.76+/-0.07) on day 60. For erythema values, a significant increase was observed immediately after the 1064 nm laser treatment (196.67+/-19.17), but the lowest values occurred with the 1320 nm laser treatment (189.83+/-16.54). None of the three lasers resulted in obvious changes of skin melanin. TEWL increased immediately after laser irradiation, then began to recover and decreased 60 days after the 595 and 1064 nm laser treatments. With the 1320 nm laser treatment the TEWL began to decrease from day 7 and obtained the lowest mean values (5.23+/-1.13). The water-holding capacity increased initially for the 595 and 1320 nm laser irradiation, while decreased for the 1064 nm laser. At day 60 of the experiment, skin hydration values in all animals were superior to those of the controls. The 1320 nm laser treatment caused the highest ratio (1.29+/-0.26). Both the values of TEWL and skin hydration for the 1320 nm laser treated areas differed significantly from the other two lasers.

CONCLUSIONS

Our data showed the 1064 nm Q-switched Nd:YAG laser treatment was most effective in improving the skins' mechanical properties, while the 1320 nm Nd:YAG laser can enhance greatly the skin barrier function and the water-holding capacity. Moreover, we demonstrated the biophysical properties differed considerably between different areas.

Comparison of histologic, biochemical, and mechanical properties of murine skin treated with the 1064-nm and 1320-nm Nd:YAG lasers

The goal of this study was to compare the effects of the Q-switched 1064-nm Nd:YAG laser and the 1320-nm Nd:YAG laser non-ablative treatments on mouse skin in vivo. Skin elasticity measurements were carried out with a Reviscometer, and skin samples were taken for histological study, hydroxyproline content assay and estimation of collagen type I and III. By the second month after non-ablative treatments, the 1064-nm laser treatment resulted in an average of 25% greater improvement of skin elasticity, 6% more increase of dermal thickness, and 11% higher synthesis of hydroxyproline than the 1320-nm laser. Collagen type III increased markedly after the 1064-nm laser treatment whereas more collagen type I was elicited by the 1320-nm laser. Our results demonstrated that the 1064-nm laser was more effective than the 1320-nm Nd:YAG laser in non-ablative treatments, but the results needed to be confirmed in humans. It appeared that photo-mechanic reaction could cause more collagen type III synthesis whereas the photo-thermal effect was in favor of the formation of collagen type I.

Biophysical, histological and biochemical changes after non-ablative treatments with the 595 and 1320 nm lasers: a comparative study

BACKGROUND/PURPOSE

The objective was to compare the efficiencies of the 595 nm pulsed dye and the 1320 nm Nd : YAG laser non-ablative rejuvenation.

METHODS

KM mice were irradiated with the 595 nm pulsed dye and the 1320 nm Nd : YAG lasers. Histological changes were evaluated immediately, 1, 7, 21, 30 and 60 days after the two laser treatments. Skin hydration and hydroxyproline content were measured to quantify the degree of improvement of the skin's water-holding capacity and the rate of hydroxyproline synthesis.

RESULTS

Although not statistically significant, the 1320 nm Nd : YAG laser treatment induced 9.7% greater improvement of skin hydration than the 595 nm laser while the 595 nm pulsed dye laser treatment led to a thicker dermis and 8.7% greater increase of hydroxyproline than the 1320 nm laser. More than 50% increase of collagen type I was observed in 75% of 595 nm laser-treated sites and 42% of 1320 nm laser-treated sites, and more than 25% increase of collagen type III was observed in 75% of 595 nm laser-treated sites and 50% of 1320 nm laser-treated sites. The 595 nm laser treatment was better in increasing the amount of collagen fibers, especially collagen type I (P < 0.05).

CONCLUSION

Our results demonstrated that the 595 nm laser appeared to be more effective in increasing new collagen formation, while the 1320 nm laser was superior to the 595 nm laser in improving the skin's water-holding capacity.

Repetitive Er:YAG laser irradiation of human skin: a histological evaluation

BACKGROUND AND OBJECTIVE

Deep coagulation of skin collagen by Er:YAG laser repetitive pulses has been predicted by previous theoretical models and later demonstrated on animal skin. The goal of this study was to determine the effect of repetitive Er:YAG laser pulses on human skin and its response to this treatment.

STUDY DESIGN/MATERIALS AND METHODS

Lid skin of six female volunteers with blepharochalasis has been treated with laser at day 0, 7, and 21 before elective surgery-blepharoplasty. The treated skin was excised as part of the procedure and prepared for further histological examination. We used a 2,940 nm Er:YAG laser (Fidelis M320A by Fotona) with 'smooth' mode parameters: fluence from 0.50 to 2.00 J/cm2; six pulses per packet; 550 microsecond/pulse, 250 millisecond/packet; single pass, no overlapping; spot size 5 mm; repetition rate 20 Hz.

RESULTS

We observed deep collagen denaturation at laser fluences of 1.25 J/cm2 and over; epidermal damage was proportional to fluence with total coagulation of the epidermal layer at fluences of 1.75 J/cm2 and over. At day 7 after laser treatment we observed a complete regeneration of the epidermal layer and a regeneration zone within the dermis with prominent infiltration of CD68+ monocytes/macrophages. At day 21 after laser treatment we observed collagen remodeling and (myo-)fibroblast proliferation at tissue depths of up to 240 microm.

CONCLUSIONS

Repetitive Er:YAG laser irradiation is effective in deep denaturation and remodeling of human skin collagen in vivo, with less epidermal damage compared to standard Er:YAG laser skin resurfacing.

Clinical, histologic, and ultrastructural changes after nonablative treatment with a 595-nm flashlamp-pumped pulsed dye laser: comparison of varying settings

BACKGROUND

The flashlamp-pulsed dye laser has been used for nonablative dermal remodeling.

OBJECTIVE

We conducted a study analyzing the clinical, histologic, and electron microscopic findings after treatment with different flashlamp-pulsed dye laser settingss in the same subject.

RESULTS

Most subjects showed mild to moderate improvement after flashlamp-pulsed dye laser laser treatment. There was no statistical difference in the clinical, histologic, or electron microscopic findings with a variety of laser treatment settings.

CONCLUSION

Nonablative dermal remodeling can be accomplished with not only a variety of different technologies, but also with the same laser using markedly different settings.

Nonablative laser and light treatments: histology and tissue effects--a review

BACKGROUND AND OBJECTIVES

Nonablative laser and light treatments have largely replaced ablative laser therapy in clinical use for the improvement of the visible signs of cutaneous photoaging, including rhytides, vascular lesions, and pigmentation. However, the mechanisms underlying the reported clinical efficacy of nonablative treatments are not well-understood. The purpose of this analysis is to critically evaluate what is known about histologic and tissue effects of nonablative laser therapy and suggest future directions for research.

STUDY DESIGN/MATERIALS AND METHODS

This is a review of the English language literature pertaining to nonablative laser and light treatments available through MEDline (1995-2002), and unpublished reports presented at major national meetings. Only studies that included harvesting and analysis of tissue samples are included.

RESULTS AND CONCLUSIONS

(a) Thermal injury to the dermis in association with epidermal cooling most likely affects the dermal vasculature, which initiates a cascade of inflammatory events that includes fibroblastic proliferation and apparent up-regulation of collagen expression; (b) There is no indication that nonablative treatments are harmful or able to induce skin cancer; (c) It is possible that the horizontally distributed collagen reported after nonablative treatments is a "microscar," an enlarged Grenz sone associated with repetitive photo-induced trauma; (d) Further research is needed to elucidate the biophysical mechanisms underlying nonablative treatment, as well as to distinguish the utility of different wavelengths on epidermal and dermal improvement.

Facial rhytides--subsurfacing or resurfacing? A review

STUDY DESIGN/BACKGROUND AND OBJECTIVES: Currently, ablative laser therapy (with CO2/Er:YAG lasers) is considered an effective and promising method of skin rejuvenation. The induction of collagen synthesis was observed after treatments with the CO2 laser and with the long-pulsed Er:Yag laser. In past years, the undesirable side effects and risks of these methods have led to intensified research efforts in the fields of non-ablative facial rejuvenation as well as subsurfacing by means of non-ablative laser systems and intense pulsed light systems. The objective is to achieve selective, heat-induced denaturalization of dermal collagen that leads to subsequent reactive synthesis of neocollagen but does not damage the epidermis. This article reviews the use of different types of lasers and intense pulsed light sources for the non-ablative treatment of facial rhytides.

RESULTS

The results of numerous clinical and histological investigations have recently indicated that these new technologies are successful. Some studies demonstrated remarkable effects with non-ablative systems; others, however, showed only limited cosmetic improvement or none at all.

CONCLUSIONS

After critical review and assessment of current literature on the treatment of rhytides, we have found that non-ablative methods do not appear to be a comparable alternative to ablative skin resurfacing in terms of their efficacy and side effects.

Measurements of laser light attenuation following cryogen spray cooling spurt termination

BACKGROUND AND OBJECTIVES

Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatological surgery. However, while CSC can protect the epidermis from non-specific thermal damage, the cryogen film on the skin surface may pose a potential problem of laser light attenuation due to optical scattering.

STUDY DESIGN/MATERIALS AND METHODS

This study is focused on measuring the light transmittance changes that occur following cryogen spurt termination. The wavelengths studied were chosen for their clinical relevance to treatment of hypervascular skin lesions (594 nm) and laser-assisted hair removal (785 nm). Following delivery of cryogen spurts to the surface of an epoxy skin phantom, continuous records of light transmittance for 594 and 785 nm were obtained using an integrating sphere-based light collection apparatus.

RESULTS

Shortly after spurt termination, there was negligible light attenuation by the cryogen film at the two wavelengths studied.

CONCLUSIONS

For the typical clinical use of a 30 milliseconds spurt duration and 30 milliseconds delay between spurt termination and delivery of the laser pulse, a minimum average transmittance value of approximately 97% was measured.

Novel model for evaluation of epidermal preservation and dermal collagen remodeling following photorejuvenation of human skin

BACKGROUND AND OBJECTIVES

In order to optimize photorejuvenation of human skin, a method must be developed to reliably compare the potential for epidermal preservation and dermal fibroblast stimulation of different laser devices and irradiation parameters. We describe a novel human skin tissue culture model developed for this purpose.

MATERIALS AND METHODS

An artificial skin model, consisting of human keratinocytes in the epidermis and human fibroblasts and rat-tail collagen in the dermis, was cultured using the floating collagen gel (RAFT) method. Repetitive low-fluence Er:YAG laser irradiation was applied to test the applicability of our RAFT model for characterization of epidermal preservation and dermal fibroblast stimulation post-laser treatment.

RESULTS

Histopathologic evaluation revealed a thin layer of epidermal keratinocyte preservation immediately after low fluence sub-ablative Er:YAG laser irradiation. One-week post-laser irradiation, the average increase in number of dermal fibroblasts as compared to control was statistically significant (P < 0.01).

CONCLUSIONS

The RAFT model can be used to assess the potential for epidermal preservation and dermal fibroblast stimulation of different photorejuvenation devices and irradiation parameters and offers several advantages over traditional animal and human skin models.

Update on non-ablative light therapy for rejuvenation: a review

BACKGROUND AND OBJECTIVES

Non-ablative technologies are playing an increasing role in the management of photoaging. Newer radiofrequency technologies have added to this therapeutic armamentarium. Shorter wavelength technologies are more effective in targeting pilosebaceous vascular and pigmentary alterations while longer wavelength technologies are most effective in wrinkle reduction mediated through dermal remodeling. An overview of the various technologies available to the practicing laser surgeon are outlined in the present review.

Biophysics of nonablative dermal remodeling

This article explores the physics of nonablative skin remodeling as well as the histologic sequelae. Although there have been several studies of nonablative skin remodeling, the exact mechanisms of action and thus the optimum device-specific parameters are not yet known. The article is divided into a discussion of the physics of laser-tissue interactions, followed by a review of the types of devices used for nonablative skin remodeling, and the histologic findings that follow treatment.

Nonablative laser skin remodeling

Nonablative skin remodeling has become an attractive option for patients whose lifestyles demand a noninvasive approach to skin rejuvenation. This review addresses the rationales for therapy, specific devices, and study outcomes.

Er:YAG laser skin resurfacing using repetitive long-pulse exposure and cryogen spray cooling: II. Theoretical analysis

BACKGROUND AND OBJECTIVE

To analyze the effects of laser pulse duration and cryogen spray cooling (CSC) on epidermal damage and depth of collagen coagulation in skin resurfacing with repetitive Er:YAG laser irradiation.

STUDY DESIGN/MATERIALS AND METHODS

Evolution of temperature field in skin is calculated using a simple one-dimensional model of sub-ablative pulsed laser exposure and CSC. The model is solved numerically for laser pulse durations of 150 and 600 microsec, and 6 msec cryogen spurts delivered just prior to ("pre-cooling"), or during and after ("post-cooling") the 600 microsec laser pulse.

RESULTS

The model indicates a minimal influence of pulse duration on the extent of thermal effect in dermis, but less epidermal damage with 600 microsec pulses as compared to 150 microsec at the same pulse fluence. Application of pre- or post-cooling reduces the peak surface temperature after laser exposure and accelerates its relaxation toward the base temperature to a different degree. However, the temperature profile in skin after 50 msec is in either example very similar to that after a lower-energy laser pulse without CSC.

CONCLUSIONS

When applied in combination with repetitive Er:YAG laser exposure, CSC strongly affects the amount of heat available for dermal coagulation. As a result, CSC may not provide spatially selective epidermal protection in Er:YAG laser skin resurfacing.