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David W Chang

Publications and source records attributed to David W Chang.

35 records · Page 2Linked to original sources
PubMed2003

Oligomerization is a general mechanism for the activation of apoptosis initiator and inflammatory procaspases.

Proteolytic activation of initiator procaspases is a crucial step in the cellular commitment to apoptosis. Alternative models have been postulated for the activation mechanism, namely the oligomerization or induced proximity model and the allosteric regulation model. While the former holds that procaspases become activated upon proper oligomerization by an adaptor protein, the latter states that the adaptor is an allosteric regulator for procaspases. The allosteric regulation model has been applied for the activation of procaspase-9 by apoptotic protease-activating factor (Apaf-1) in an oligomeric complex known as the apoptosome. Using approaches that allow for controlled oligomerization, we show here that aggregation of multiple procaspase-9 molecules can induce their activation independent of the apoptosome. Oligomerization-induced procaspase-9 activation, both within the apoptosome and in artificial systems, requires stable homophilic association of the protease domains, raising the possibility that the function of Apaf-1 is not only to oligomerize procaspase-9 but also to maintain the interaction of the caspase-9 protease domain after processing. In addition, we provide biochemical evidence that other apoptosis initiator caspases (caspase-2 and -10) as well as a procaspase involved in inflammation (murine caspase-11) are also activated by oligomerization. Thus, oligomerization of precursor molecules appears to be a general mechanism for the activation of both apoptosis initiator and inflammatory procaspases.

Animals↗
PubMed2003

Activation of procaspases by FK506 binding protein-mediated oligomerization.

Oligomerization is an important biological mechanism for regulating signal transduction. Activation of caspases during apoptosis is triggered by adaptor protein-mediated oligomerization of initiator procaspases. To facilitate the study of initiator caspase activation, a system that allows inducible activation of various caspases both in vitro and in vivo is highly desired. Here we describe such a caspase activation system that is based on FK506 binding protein (FKBP)-mediated oligomerization. The NH(2)-terminal prodomains of initiator procaspases that facilitate the interaction between procaspases and their adaptor proteins are replaced by a derivative of FKBP called Fv. The Fv-caspase fusions can then be dimerized by a synthetic divalent Fv ligand, AP20187, which binds strongly to Fv but weakly to the endogenous FKBPs. This FKBP-based system may be widely applicable to the study of the regulation and functions of caspases.

Caspase 8↗
PubMed2003

Effects of cryogen spray cooling and high radiant exposures on selective vascular injury during laser irradiation of human skin.

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). DESIGN: Observational study. SETTING: Academic hospital and research laboratory. PATIENTS: Twenty women with normal abdominal skin (skin phototypes I-VI). 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/cm2) without and with cryogen spray cooling (50- to 300-millisecond cryogen spurts). 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. 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.

Adult↗
PubMed2003

Thermal response of human skin epidermis to 595-nm laser irradiation at high incident dosages and long pulse durations in conjunction with cryogen spray cooling: an ex-vivo study.

BACKGROUND AND OBJECTIVES: Improved laser treatment of cutaneous hypervascular lesions is expected by utilizing higher incident dosages, longer pulse durations and longer wavelengths than those currently used in clinical settings. However, simply increasing the incident dosage will also increase the risk of nonspecific thermal injury to the epidermis due to light absorption by melanin. In this study, we investigated the thermal response of human skin epidermis to 595-nm wavelength laser irradiation at high incident dosages (up to 20 J/cm(2)) and long pulse durations (up to 40 milliseconds) in conjunction with cryogen spray cooling (CSC) using ex-vivo human skin samples. STUDY DESIGN/MATERIALS AND METHODS: The Candela V-beam trade mark laser (595-nm wavelength) was used in the experiments. Ex-vivo human skin samples (Fitzpatrick types I-VI) were irradiated at the incident dosages D(0) = 4, 6, 10, 15, and 20 J/cm(2), laser pulse durations tau(laser) = 1.5, 10, and 40 milliseconds, without and with CSC (refrigerant-134A, spurt duration tau(CSC) = 100 milliseconds). Thermal injury to the epidermis was evaluated by histological observations. RESULTS: Under the same incident dosage, longer pulse durations led to reduced thermal injury to the epidermis. Without CSC, no demonstrable thermal injury to the epidermis was observed in skin types I-II irradiated at the incident dosage as high as 15 J/cm(2), and in skin types III-IV at 10 J/cm(2). When CSC was applied, no evidence of thermal injury to the epidermis was present in skin types I-II even when irradiated at the maximum available incident dosage of the laser system (20 J/cm(2)). In skin types III-IV, no demonstrable thermal injury to the epidermis was observed when using incident dosage as high as 15 J/cm(2) in conjunction with CSC. In skin type VI, thermal injury to the epidermis could not be avoided even at the setting D(0) = 4 J/cm(2), tau(laser) = 40 milliseconds in conjunction with CSC. CONCLUSIONS: For a given incident dosage, longer pulse durations help reduce thermal injury to the epidermis. When a 100-millisecond cryogen spurt is applied, thermal injury to the epidermis can be prevented in ex-vivo skin types I-IV when irradiated at higher incident dosages (15-20 J/cm(2)) than those currently used in clinical settings. Further studies on optimizing the CSC parameters in conjunction with the laser irradiation parameters are needed to protect skin types V-VI from thermal injury to the epidermis.

Adult↗
PubMed2003

Use of the free fibula flap for restoration of orbital support and midfacial projection following maxillectomy.

A total maxillectomy defect, if left unreconstructed or if poorly reconstructed, can lead to enophthalmos, orbital dystopia, feeding and speech problems, and loss of midfacial projection and vertical facial height. When the eye is preserved, despite resection of the supporting infraorbital bone during maxillectomy, bone reconstruction needs to be considered, using a vascularized bone flap. The authors have used the free fibula flap to simultaneously provide orbital support and restore midfacial projection in three patients, following total maxillectomy without orbital exenteration. For large maxillectomy defects with insufficient bony support, a free fibula flap should be considered as a reconstructive method, to adequately restore contour and the necessary structural support, and to provide optimal aesthetic and functional results.

Carcinoma↗
PubMed2003

Breast reconstruction in older women: advantages of autogenous tissue.

As the population ages, the treatment of breast cancer among elderly women is becoming increasingly common. Decisions with regard to breast reconstruction require not only consideration of patient age and comorbidities but also a need to balance life expectancy with quality of life. Although it is often assumed that implant-based breast reconstruction is the least disruptive method, especially among patients who may be facing limited survival times, it was hypothesized that autogenous tissue breast reconstruction is a well-tolerated and perhaps preferable means of reconstruction for older women who choose to undergo reconstruction following mastectomy. No large series of autogenous tissue reconstructions in this age group has been presented. A retrospective study of 84 postmastectomy reconstructions (66 unilateral and 18 bilateral; 78.6 percent immediate) performed at the authors' institution for 81 women 65 years of age or older, between April of 1987 and December of 2000, was undertaken. Reconstructions were implant-based ( = 26), latissimus dorsi flap-based ( = 24), or transverse rectus abdominis myocutaneous (TRAM) flap-based ( = 34). Of the 34 TRAM flaps, 21 were free or supercharged. Breast complications were more frequent ( < 0.05) among recipients of implant-based reconstructions (76.9 percent) than among recipients of latissimus dorsi flap (41.7 percent) or TRAM flap (35.3 percent) reconstructions. In multivariate logistic regression analyses, comorbidities, smoking, radiotherapy, and body mass index had no effect. Medical complications without long-term sequelae were observed for two patients who underwent latissimus dorsi flap reconstructions and two patients who underwent free TRAM flap reconstructions; the difference in the rates of medical complications was not significant. At the mean follow-up time of 4.2 years, 92.8 percent of all study patients exhibited no evidence of disease. Notably, despite being free of disease, seven of the 26 patients (27 percent) who underwent implant-based reconstructions abandoned further reconstructive efforts after complications necessitated implant removal. It was concluded that age alone should not determine the type of breast reconstruction and that autogenous tissue breast reconstruction can be a safe successful alternative for women 65 years of age or older.

Age Factors↗
PubMed2003

Cavernous nerve reconstruction to preserve erectile function following non-nerve-sparing radical retropubic prostatectomy: a prospective study.

Erectile dysfunction following radical prostatectomy for treatment of clinically localized prostate cancer remains a problem that deters many men from seeking surgical treatment. Sparing the cavernous nerves has been popularized as a method of preserving potency, but men with locally advanced disease may be at increased risk for positive margins with this technique. In this study, sural nerve grafting of the cavernous nerve bundles, to preserve postoperative potency while potentially maximizing cancer control, was examined. Thirty men were enrolled in this prospective phase I study and underwent non-nerve-sparing radical prostatectomy performed by one of two protocol surgeons. Preoperative erectile function was assessed both objectively, using a RigiScan (Timm Medical Technologies, Inc., Eden Prairie, Minn.), and subjectively. The cavernous nerves were identified and resected during the operation with the use of an intraoperative mapping device (CaverMap; Alliant Medical Technologies, Norwood, Mass.). Bilateral autologous sural nerve grafting to the cavernous nerve stumps was performed by one of two protocol plastic surgeons. Postoperative erectile dysfunction therapy, using intracorporeal injection, a vacuum pump, and/or oral sildenafil therapy, was instituted 6 weeks after the operation. Spontaneous erectile activity was subjectively and objectively measured every 3 months after the operation. Follow-up periods ranged from 13 to 33 months (mean, 23 months). Overall, 18 of 30 patients (60 percent) demonstrated both objective and subjective evidence of spontaneous erectile activity. Of those 18 men, 13 (72 percent) were able to have intercourse (seven unassisted and six with the aid of sildenafil). No disease or biochemical recurrences have been noted in this group of patients with locally advanced disease. In conclusion, autologous sural nerve grafting after non-nerve-sparing radical prostatectomy is an effective means of preserving spontaneous erectile activity after the operation while maximizing cancer control potential.

Aged↗
PubMed2002

Autologous breast reconstruction with the extended latissimus dorsi flap.

The extended latissimus dorsi myocutaneous flap can provide autogenous tissue replacement of breast volume without an implant. Nevertheless, experience with the extended latissimus dorsi flap for breast reconstruction is relatively limited. In this study, the authors evaluated their experience with the extended latissimus dorsi flap for breast reconstruction to better understand its indications, limitations, complications, and clinical outcomes. All patients who underwent breast reconstruction with extended latissimus dorsi flaps at the authors' institution between January of 1990 and December of 2000 were reviewed. During the study period, 75 extended latissimus dorsi flap breast reconstructions were performed in 67 patients. Bilateral breast reconstructions were performed in eight patients, and 59 patients underwent unilateral breast reconstruction. There were 45 immediate and 30 delayed reconstructions. Mean patient age was 51.5 years. Mean body mass index was 31.8 kg/m2. Flap complications developed in 21 of 75 flaps (28.0 percent), and donor-site complications developed in 29 of 75 donor sites (38.7 percent). Mastectomy skin flap necrosis (17.3 percent) and donor-site seroma (25.3 percent) were found to be the most common complications. There were no flap losses. Patients aged 65 years or older had higher odds of developing flap complications compared with those 45 years or younger (p = 0.03). Patients with size D reconstructed breasts had significantly higher odds of flap complications compared with those with size A or B reconstructed breasts (p = 0.05). Obesity (body mass index greater than or equal to 30 kg/m2) was associated with a 2.15-fold increase in the odds of developing donor-site complications compared with patients with a body mass index less than 30 kg/m2 (p = 0.01). No other studied factors had a significant relationship with flap or donor-site complications. In most patients, the extended latissimus dorsi flap alone, without an implant, can provide good to excellent autologous reconstruction of small to medium sized breasts. In selected patients, larger breasts may be reconstructed with the extended latissimus dorsi flap alone. This flap's main disadvantage is donor-site morbidity with prolonged drainage and risk of seroma. Patients who are obese are at higher risk of developing these donor-site complications. In conclusion, the extended latissimus dorsi flap is a reliable method for total autologous breast reconstruction in most patients and should be considered more often as a primary choice for breast reconstruction.

Body Mass Index↗
PubMed2002

c-FLIP(L) is a dual function regulator for caspase-8 activation and CD95-mediated apoptosis.

Activation of the caspase cascade is a pivotal step in apoptosis and can occur via death adaptor-mediated homo-oligomerization of initiator procaspases. Here we show that c-FLIP(L), a protease-deficient caspase homolog widely regarded as an apoptosis inhibitor, is enriched in the CD95 death-inducing signaling complex (DISC) and potently promotes procaspase-8 activation through hetero-dimerization. c-FLIP(L) exerts its effect through its protease-like domain, which associates efficiently with the procaspase-8 protease domain and induces the enzymatic activity of the zymogen. Ectopic expression of c-FLIP(L) at physiologically relevant levels enhances procaspase-8 processing in the CD95 DISC and promotes apoptosis, while a decrease of c-FLIP(L) expression results in inhibition of apoptosis. c-FLIP(L) acts as an apoptosis inhibitor only at high ectopic expression levels. Thus, c-FLIP(L) defines a novel type of caspase regulator, distinct from the death adaptors, that can either promote or inhibit apoptosis.

Apoptosis↗
PubMed2002

Analysis of pharyngocutaneous fistula following free jejunal transfer for total laryngopharyngectomy.

The development of a pharyngocutaneous fistula is the most common and troublesome complication in the early postoperative period following free jejunal transfer for total laryngopharyngectomy. However, many aspects of this complication remain unclear. In this study, the authors analyzed their experience with the pharyngocutaneous fistula formation following free jejunal transfers to evaluate its clinical behavior, determine the significance of the anastomotic technique used, and evaluate the role of preoperative radiation therapy on its formation and management. Of 168 patients who underwent free jejunal transfers following total laryngopharyngectomy at the authors' institution between July of 1988 and March of 2000, 23 patients (13.7 percent) with postoperative fistulas were identified. The mean onset of fistula formation was 16 days. Of the 23 fistulas, 13 (56.5 percent) occurred at the proximal and 10 (43.5 percent) at the distal anastomoses. Whereas the majority of the proximal fistulas (69.2 percent) developed near the mesenteric side of the jejunal flap, most of the distal fistulas (90 percent) were located anteriorly. The incidence of proximal fistula formation was higher in patients with a single-layer repair than in patients with a two-layer repair of a proximal anastomosis (80 percent versus 38.5 percent, p = 0.09). The incidence of fistula formation was greater in patients who received preoperative radiation therapy than in those who did not (16.3 percent versus 11.4 percent, p = 0.36). In addition, whereas a majority of fistulas (80 percent) occurred at the proximal anastomosis in patients who did not receive preoperative radiation therapy, most fistulas (61.5 percent) occurred at the distal anastomosis in patients who did receive radiation therapy (p = 0.09). The fistulas closed spontaneously in 15 patients (65 percent). On average, spontaneous closure occurred in 7.4 weeks. Proximal fistulas had a significantly higher rate of spontaneous closure compared with distal fistulas (85 percent versus 40 percent, p = 0.04). The rate of spontaneous fistula closure was higher in patients who had not received preoperative radiation therapy than in those who had (90 percent versus 46 percent, p = 0.07). Surgical closure of the fistula was required in five patients. The fistulas were not repaired in three patients because of recurrent tumor. Twenty patients (87 percent) resumed oral feeding after the closure of the fistula, with 17 (85 percent) of 20 patients tolerating a regular diet and three (15 percent) of 20 a liquid diet only.In conclusion, most fistulas occur at the proximal anastomosis and near the mesenteric side of the jejunal flap, and the use of a two-layer anastomotic technique seems to be associated with a lower incidence of fistula formation at the proximal suture line. Most fistulas close spontaneously, especially ones that occur proximally. Preoperative radiotherapy does seem to increase the risk of fistula formation, especially at the distal anastomotic site and make subsequent resolution of the fistulas more difficult. Most patients are able to resume oral feeding once the fistula is closed.

Cutaneous Fistula↗
PubMed2002

Minimal incision technique for sural nerve graft harvest: experience with 61 patients.

Many different methods for harvesting the sural nerve have been described, including a single, long, longitudinal incision, multiple stair-step incisions, or use of a tendon stripper and endoscopic approach. Drawbacks of these methods may include unsightly donor-site scars, inadvertent transection of the nerve, prolonged operative time, and the need for special equipment. A new minimal incision technique of sural nerve harvesting that is simple and quick, causes minimal donor site morbidity, and preserves the integrity of the nerve is described.

Adult↗
PubMed2002

Limb salvage for soft-tissue malignancies of the foot: an evaluation of free-tissue transfer.

Free flaps may safely allow meaningful ambulation, durable limb preservation, and better quality of life in patients undergoing resections of soft-tissue cancers of the foot. To prove this, the records of a series of patients at The University of Texas M. D. Anderson Cancer Center (n = 67) who underwent limb salvage following tumor-related resection (n = 71 procedures) from 1989 to 1999 were retrospectively reviewed. Eighteen patients who were not candidates for local flaps or skin grafts received a total of 20 free flaps to preserve their limbs. Most defects (mean size, 78 cm2; range, 20 to 150 cm2) were on a weight-bearing surface of the foot (nine on a weight-bearing heel, three on a plantar foot); the remainder were on a non-weight-bearing surface (six on dorsum, two on a non-weight-bearing heel). Melanoma was diagnosed in nine cases (50 percent); soft-tissue sarcoma, in seven (39 percent); and squamous cell carcinoma, in two (11 percent). Fasciocutaneous and skin-grafted muscle flaps were used on both weight-bearing and non-weight-bearing surfaces. Free-tissue transfer was successful in 17 of 20 cases (85 percent); the three flap losses occurred in two patients. Minor complications (i.e., small hematoma, partial skin graft loss, and delayed wound healing) occurred in five patients. In all cases of successful free-tissue transfer, patients began partial weight bearing at a mean of 7.4 weeks (range, 2 to 12 weeks), and all ultimately achieved full weight bearing. Sixty-seven percent still required special footwear. In one patient, an ulceration on the weight-bearing portion of the flap resolved after a footwear adjustment. Only one patient was lost to follow-up (mean, 23 months). In the 17 remaining patients, limb salvage succeeded in 15 (88 percent). Of these, nine (60 percent) were alive without evidence of disease, three (20 percent) were alive with disease, and three (20 percent) had died of disease. Local recurrence developed in two patients but was successfully treated by excision and closure. No late amputations were required for local control. Thus, it seems that free flaps help facilitate limb salvage and that they may preserve meaningful limb function in patients who undergo resection of soft-tissue malignancies of the foot.

Adult↗
PubMed2002

Implications of axillary sentinel lymph node biopsy in immediate autologous breast reconstruction.

For patients with invasive breast cancer, if the results of an axillary sentinel node biopsy are determined to be positive after permanent pathologic examination, the current recommendation is to perform a complete axillary node dissection. Subsequent axillary surgery may compromise the blood supply to an immediate autologous breast reconstruction. The purpose of this study was to determine which clinicopathologic factors in clinically node-negative breast cancer patients may be associated with an increased risk of positive axillary nodes. Identification of these factors will allow surgeons to modify their approach to immediate autologous breast reconstruction in these high-risk patients. The relationship between presenting clinicopathologic characteristics and the incidence of axillary metastases was analyzed by chi-square test and multivariate analysis in 167 patients with invasive breast cancer and a clinically negative axilla who underwent modified radical mastectomy with an immediate free transverse rectus abdominis musculocutaneous (TRAM) flap reconstruction. Axillary nodal metastases were found in 35 percent of clinically node-negative breast cancer patients. Multivariate analysis showed that patient age of 50 years or younger (p = 0.019), T2 tumor stage or greater (p = 0.031), and presence of lymphovascular invasion on the initial biopsy specimen (p < 0.001) were independent predictors of axillary metastases in clinically node-negative patients. Based on these results, the authors propose an algorithm for decision making in clinically node-negative breast cancer patients who desire autologous breast reconstruction and sentinel lymph node biopsy. Options for immediate autologous breast reconstruction in patients undergoing mastectomy and axillary sentinel lymph node biopsy that may minimize the risk of vascular damage on reoperation include the use of the internal mammary artery and vein as recipient vessels for a free TRAM flap or a pedicled TRAM flap. If an axillary-based blood supply is used, the authors are considering the use of cadaveric dermis to isolate the pedicle of the flap away from the remaining axillary contents. New developments in breast cancer diagnosis and treatment necessitate a team approach, with increased communication between the breast surgeon and the plastic surgeon in planning surgery for these patients.

Adult↗
PubMedDate not supplied

Breast cancer in reduction mammaplasty specimens: case reports and guidelines.

Increasing numbers of women of all ages are electing to have reduction mammaplasty for very large breasts. Breast cancer can be an incidental finding in reduction mammaplasty specimens. We report here the discovery of breast cancer in specimens from four patients who underwent elective breast reduction, three of whom had not had recent mammograms. All four patients underwent modified radical mastectomy. The role of mammography, surgical options, specimen evaluation, and practical guidelines are discussed.

Adult↗
PubMedDate not supplied

Ovine model for engineering bone segments.

We propose a large animal model for bone tissue engineering that yields quantitative data and simulates clinical methods and tissue needs. Skeletally mature domestic sheep (n = 20) were each implanted with three rectangular (1 x 1 x 4 cm), hollow tissue-molding chambers that were empty (control) or filled with equal weights (6.71-6.78 g) of particulate autologous bone graft (MBG) or bone graft that was autoclaved to denature stored growth factors (DeMBG). MBG provided scaffold and bioactive factors, and DeMBG provided only scaffold. The chambers were enclosed on five sides and securely implanted so that the open face was apposed to the osteogenic (i.e., cambium) layer of the rib periosteum for 3, 6, 9, 12, or 24 weeks, after which the chambers were harvested and the contents analyzed. Each chamber contained osseous and fibrovascular tissue. MBG-containing chambers had the best maintenance of tissue volume compared with DeMBG-containing or empty chambers, but it still decreased steadily over time. Despite this, the MBG-containing chambers showed continuous active bone formation. There was increasing calcified tissue with penetration of osteogenesis up to a mean of 0.75 +/- 0.15 cm from the periosteum by 9 weeks, and the osteogenic area peaked at 0.59 +/- 0.13 cm2 by 12 weeks. Using quantitative measures that reflect clinical needs (i.e., tissue volume, shape, and quality), it was possible to distinguish differences in performance associated with manipulation of implanted scaffold and bioactive factors. This ovine model may serve as a useful tool to develop clinical osseous tissue-engineering strategies.

Absorbable Implants↗
PubMedDate not supplied

Comparative study of cryogen spray cooling with R-134a and R-404a: implications for laser treatment of dark human skin.

Cutaneous laser treatment in dark skin patients is challenging due to significant light absorption by the melanin at the basal layer of epidermis, which can result in irreversible nonspecific thermal injury to the epidermis. Cryogen spray cooling (CSC) with R-134a (boiling point approximately -26.2 degrees C at 1 atm), which is currently used during cutaneous laser treatment, has shown poor efficacy in protecting dark human skin. We investigated the potential of CSC with R-404a (boiling point approximately -46.5 degrees C at 1 atm), which has a lower boiling point than R-134a, for improved therapeutic outcome in dark human skin at three levels: in vitro (epoxy resin skin phantom), ex vivo (normal dark human skin sample), and in vivo (skin of the rabbit external ear). The skin phantom was used to acquire the surface and internal temperature profiles in response to CSC with R-134a or R-404a at various spurt durations, based upon which CSC-induced heat removal from the skin phantom was estimated using an algorithm that solved a one-dimensional inverse heat conduction problem. CSC with R-404a increased the temperature reductions within the phantom and subsequently the amount of heat removal from the phantom in comparison to that with R-134a. Normal ex vivo Fitzpatrick types V-VI human skin samples were used to investigate the thermal response of dark human skin epidermis to CSC (R-134a or R-404a) at various spurt durations in conjunction with 595-nm pulsed dye laser irradiation at various radiant exposures. Cryogen R-404a increased the threshold radiant exposures for irreversible thermal injury to the epidermis in dark pigmentation skin. No obvious CSC-induced morphological changes to human skin was observed when sprayed with R404-a spurts using durations up to 300 ms. In vivo rabbit ear vasculature was used as a model of cutaneous anomalies to assess the influences of CSC (with R-134a or R-404a) on the photothermolysis of dermal blood vessels. CSC (R-134a or R-404a) with the spurt durations of 100 to 300 ms increased the most superficial depth of thermally damaged dermal blood vessel compared with the sites without CSC, implying possible nonspecific cooling of superficial dermal blood vessels by the cryogen spurts with the settings applied.

Aerosol Propellants↗