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Biomedical subjects

David W Chang

Publications and source records attributed to David W Chang.

At least 19 recordsLinked to original sources
PubMed2006

Reconstruction of the chestwall and thorax.

Chest wall reconstructions can be complex and challenging procedures and may require a multidisciplinary approach. The most common indications for chest wall reconstruction are the repair of defects due to tumor ablation, infection, radiation necrosis, congenital deformities, and trauma. Flap reconstruction by plastic surgery is often required when skin is removed as part of the chest wall resection or when radiation therapy is given pre- or post-operatively. Tissue flaps may be needed to provide vascularized tissue over alloplastic materials used to stabilize the chest wall, to cover vital structures of the chest cavity, to fill dead space, and to improve cosmesis.

Female↗
PubMed2006

Comparison of donor-site complications and functional outcomes in free muscle-sparing TRAM flap and free DIEP flap breast reconstruction.

BACKGROUND: One presumed advantage of the free deep inferior epigastric perforator (DIEP) flap over the free muscle-sparing transverse rectus abdominis myocutaneous (TRAM) flap is decreased donor-site morbidity. The purpose of this study was to compare the donor-site morbidity and functional outcomes in women who underwent free muscle-sparing TRAM flap or free DIEP flap breast reconstruction. METHODS: All patients who underwent breast reconstruction using a free muscle-sparing TRAM flap or a free DIEP flap performed by the two senior authors at the M. D. Anderson Cancer Center between 1999 and 2003 were included in the study. The authors conducted a chart review to obtain demographic data and information regarding flap-related complications and donor-site complications. Each living patient was sent a 12-item questionnaire to elicit her perceptions about donor-site outcomes. RESULTS: One hundred sixty-four patient charts were reviewed (203 flaps). Muscle-sparing TRAM flaps were used in 124 patients (98 unilateral and 26 bilateral). DIEP flaps were used in 35 patients (27 unilateral and eight bilateral). In five bilateral breast reconstructions, a muscle-sparing TRAM flap was used for one side and a DIEP flap was used for the other side. There was no significant difference in flap-related complications or donor-site morbidity between the free muscle-sparing TRAM and free DIEP flaps. Eighty-nine of 159 patients (56 percent) responded to the questionnaire; results showed no significant difference in patient-perceived abdominal function after free muscle-sparing TRAM flaps and free DIEP flaps. CONCLUSIONS: In the authors' experience, there is no significant difference in flap-related complications or donor-site morbidity between the free muscle-sparing TRAM flap and the free DIEP flap. Thus, the authors advocate using the most expeditious and reliable flap based on the vascular anatomy of the DIEP system.

Algorithms↗
PubMed2005

Interdimer processing and linearity of procaspase-3 activation. A unifying mechanism for the activation of initiator and effector caspases.

Caspase activation during apoptosis occurs in a cascade from the initiator caspase(s) (e.g. caspase-8) to the effector caspases (e.g. caspase-3), which ensures the generation of large amounts of active caspases to dismantle cells. However, the mechanism that safeguards against inadvertent caspase activation is not well understood. Previous studies have suggested that the activation of procaspase-8 is mediated by cross-cleavage of precursor dimers, formed upon apoptosis induction, which are not only enzymatically competent but also highly susceptible to cleavage, and that procaspase-8 activation is a linear process without self-amplification. Effector procaspases constitutively exist as dimers and their activation is started by trans-cleavage by an initiator caspase followed by autocleavage of effector caspases. Here we show that the dimerization of caspase-3 molecules through their protease domains is required for their processing by initiator caspases. The subsequent autoprocessing takes place through cleavage between the dimeric intermediates. Moreover, mature caspase-3 fails to process its own precursor. Thus, despite a marked difference in the generation of active intermediates, the activation of initiator and effector caspases shares the features of interdimer cleavage and lack of self-amplification. These features may be important in preventing accidental cell death.

Caspase 3↗
PubMed2005

Comparison of 585 and 595 nm laser-induced vascular response of normal in vivo human skin.

BACKGROUND AND OBJECTIVES: Two wavelengths, 585 and 595 nm, are currently common options for treating vascular malformations such as port-wine stains (PWS). Controversy exists as to which wavelength induces greater photothermal damage to the blood vessels and subsequent resolution of the malformations. STUDY DESIGN/MATERIALS AND METHODS: We irradiated normal, human skin in vivo at 585 and 595 nm wavelengths using fluences of 10-30 J/cm(2) with a 1.5 millisecond laser pulse. The level of purpura, total vascular damage, maximum coagulation depth (MCD), and perivascular damage were quantified by gross observation and histological analysis. RESULTS: Results demonstrated that 585 nm light caused greater purpura, vascular damage, maximum coagulation depth, and perivascular damage than 595 nm. Purpura showed a positive correlation with total vascular damage to a certain extent beyond which the total vascular damage did not change. For equivalent purpura, 585 and 595 nm produced no statistically significant difference in vascular damage. The difference in the laser-induced vascular damage between 585 and 595 nm, although statistically significant, was no more than 50%. CONCLUSIONS: The bathochromic (red) shift and formation of met-hemoglobin, which reduces the 585 nm light absorption and increases that of 595 nm compared to native oxy-hemoglobin, play a considerable role in creating more parity in vascular damage between the two wavelengths than would be expected based on their respective "native" absorption coefficients alone.

Biopsy, Needle↗
PubMed2005

Epidermal and vascular damage analysis of in vivo human skin in response to 595 nm pulsed laser irradiation.

BACKGROUND AND OBJECTIVES: Laser irradiation is the current modality for treatment of cutaneous hypervascular malformations such as port wine stains and telangiectasia. Although cryogen spray cooling (CSC) is used to protect the epidermis from non-specific laser-induced thermal damage in moderately-pigmented skin types, individuals with high melanin content are still at risk for epidermal damage using the current laser irradiation and CSC parameters. The objective of this study was to investigate the influence of the spray Weber number (1,100 or 5,100) on epidermal protection and examine vascular coagulation in response to pulsed dye laser irradiation. STUDY DESIGN/MATERIALS AND METHODS: Normal, in vivo human skin from eight subjects of Fitzpatrick skin types I-V were precooled with either low or high Weber number cryogen sprays and subsequently irradiated with a pulsed dye laser at 595 nm. Analysis of gross purpura, morphological vascular damage, and apoptosis of the vascular walls were performed. RESULTS: Results demonstrated a high Weber number spray of 5,100 decreased the level of epidermal damage in darker and moderate pigmented individuals compared to a Weber number spray of 1,100. This study also established a positive correlation between gross purpura and the level of vessel wall apoptosis. CONCLUSIONS: This study has demonstrated that CSC with a high Weber number spray can decrease nonspecific thermal damage to the epidermis in response to laser irradiation in vivo. We have also established a positive correlation between gross purpura and the level of vessel wall apoptosis. Lasers Surg. Med. (c) 2005 Wiley-Liss, Inc.

Aerosol Propellants↗
PubMed2005

Strategies and options for free TRAM flap breast reconstruction in patients with midline abdominal scars.

BACKGROUND: Patients who have a midline abdominal scar from previous abdominal surgery often present a challenge when use of a transverse rectus abdominis myocutaneous (TRAM) flap is desired for breast reconstruction. In this study, the authors reviewed their experience with the TRAM flap for breast reconstruction in patients with midline abdominal scars to evaluate the various strategies used to optimize reconstructive outcomes. METHODS: Between January of 1994 and December of 2001, 43 patients with a midline abdominal scar underwent unilateral autologous tissue breast reconstruction with a TRAM flap at The University of Texas, M. D. Anderson Cancer Center. RESULTS: The mean age of the midline abdominal scar was 13 years (range, 4 to 45 years). In 26 patients, only free hemi-TRAM flaps were used for breast reconstruction. Free TRAM flaps were used in nine patients in whom zone II across the midline scar had an adequate blood supply and was able to be incorporated into the flap for breast reconstruction. In five patients, blood supplies from both sides of the TRAM flap were used to augment perfusion to the tissue across the midline scar. In three patients with infraumbilical midline scars, a free TRAM flap was designed higher in the abdomen so that the superior half of the flap was scar-free. CONCLUSIONS: Various strategies are available for autologous tissue breast reconstruction using a free TRAM flap in patients with a previous midline abdominal surgical scar. In some cases, the TRAM flap tissue across the midline scar can be used reliably for breast reconstruction.

Abdomen↗
PubMed2005

Use of a vascularized fibula bone flap and intercalary allograft for diaphyseal reconstruction after resection of primary extremity bone sarcomas.

BACKGROUND: The standard treatment for primary bone sarcomas of the extremities has become chemotherapy and limb salvage surgery. However, the difficulties in achieving reliable long-term healing with allograft reconstruction have led us to use vascularized fibula transfer to enhance healing. METHODS: From 1992 to 2003, 14 vascularized fibula transfers were performed at our institution for bone reconstruction in 12 patients with bone sarcoma. Free vascularized fibula transfers were performed in 13 cases, and a pedicled vascularized fibula transfer in one case. The mean age was 25 years (range, 6 to 71 years). Locations included the femur (n = 10), humerus (n = 1), and tibia (n = 3). The mean length of the vascularized fibula transfer was 17.4 cm (range, 10 to 24 cm). Indications for use of a vascularized fibula transfer included allograft nonunion (n = 8), and primary diaphyseal bone defect reconstruction combined with an intercalary allograft (n = 6). For all allograft nonunions, a vascularized fibula transfer was used with an onlay technique. For segmental bone defects, an intramedullary technique was used in three cases and an onlay technique in two cases. RESULTS: The overall mean time for bone union after a vascularized fibula transfer was 8.6 months (range, 3 to 24 months): 10 months (range, 5 to 24 months) for patients with allograft nonunions, and 6 months (range, 3 to 8 months) for patients who underwent immediate segmental bone reconstruction. All but one patient had successful bone union. One patient with persistent nonunion required a second vascularized fibula transfer. The mean time from initial limb salvage surgery to full use of the reconstructed limb without restrictions was 28 months (range, 13 to 45 months) for patients treated with a delayed vascularized fibula transfer for an allograft nonunion and 6 months (range, 3 to 8 months) for patients who underwent immediate reconstruction with a vascularized fibula transfer combined with an allograft. CONCLUSIONS: The use of a vascularized fibula transfer combined with an intercalary allograft to reconstruct bone defects after tumor resection can prevent allograft nonunion and result in decreased time to bone healing, leading to earlier patient recovery and return of function.

Adolescent↗
PubMed2005

Extending the limits of fingertip composite grafting with moist-exposed dressing.

We introduced the concept of moist wound healing to extend the limits of fingertip composite grafting. In this retrospective study, we assessed the success of fingertip composite grafting with moist-exposed ointment dressing, which has been shown to maintain adequate moisture for optimal healing by frequent ointment application without the need for a secondary overlying dressing. We reviewed the outcome of composite graft replacement of 60 amputated fingertips in 56 consecutive patients over a period of 3 years and 3 months. Forty-two fingertips had survived completely and 18 had failed. Twelve of 15 fingers among patients younger than 15 years of age and 30 of 45 fingers among those 16 years of age and older had survived completely. We believe that our use of antibiotic ointment to maintain a moist environment was an important factor in improving the survival of composite grafts.

Administration, Topical↗
PubMed2004

A new approach to carotid angioplasty and stenting with transcervical occlusion and protective shunting: Why it may be a better carotid artery intervention.

OBJECTIVE: The purpose of this study was to evaluate the effectiveness and demonstrate the advantages of a new technique for carotid angioplasty and stenting (CAS) with proximal cerebral protection through a direct transcervical approach, as compared with a percutaneous transfemoral approach. METHODS: CAS procedures were carried out in 25 consecutive patients, 4 with the femoral approach and 21 through a 2-cm incision at the base of the neck, with the patient under local anesthesia. For transcervical occlusion and protective shunting (TOPS), a short 9F sheath was inserted directly into the common carotid artery and connected to a 6F sheath placed percutaneously in the ipsilateral internal jugular vein. After clamping the common carotid artery proximal to the 9F sheath, internal carotid artery blood flow reversal was confirmed or an occluding external carotid balloon was placed. A filter interposed between the arterial and venous sheaths collected embolic debris from transcarotid manipulations. The arterial puncture was directly repaired with suture. Neurologic status was assessed with the National Institutes of Health stroke scale by an independent neurology consultant before and after the procedure. RESULTS: One of the four percutaneous femoral approaches that failed because of tortuous anatomy was successfully treated with TOPS. Angiographic confirmation demonstrating resolution of asymptomatic (>80%; n = 12) stenosis or symptomatic (>60%; n = 12) stenosis was achieved in all patients with stents. A 0% technical failure rate and 0% combined 30-day stroke or mortality rate were achieved in all CAS attempted with TOPS. There were no hematomas in the cervical group, despite pretreatment with clopidogrel bisulfate and heparin, and one hematoma in the femoral group after failure of a Perclose arterial closure device. In one of the patients in the femoral group bilateral cholesterol emboli to the toes developed. CONCLUSION: TOPS solves problems of access, embolization into the cerebral and peripheral circulation, and specialized cerebral protection devices, and enables secure closure of the access vessel in patients given anticoagulation therapy. TOPS may provide a safer, more effective, economical means for performing CAS.

Aged↗
PubMed2004

Segmental femur reconstruction using an intercalary allograft with an intramedullary vascularized fibula bone flap.

The use of intercalary allografts has been an important innovation for use in limb-salvage surgery. However, the principal disadvantage of intercalary allografts is a high incidence of nonunion, fracture, and infection. With a recent trend toward higher doses of chemotherapy, an increased incidence of nonunion and healing problems can be anticipated with the use of allografts. In this article, the authors report two cases in which a vascularized fibula bone flap was used with an intercalary allograft, utilising an intramedullary approach, for immediate femur reconstruction following sarcoma resection. The rationale for this approach is to combine the mechanical strength of an allograft with the biologic activity of a vascularized bone flap. The allograft provides bone stock and early stability, while the addition of the vascularized bone flap substantially facilitates the host-allograft union.

Adolescent↗
PubMed2004

Upper extremity limb salvage with microvascular reconstruction in patients with advanced sarcoma.

Limb salvage is a viable alternative to amputation in many cases of advanced sarcoma. The authors examined their experience with microvascular reconstruction of upper extremity defects after sarcoma resection, focusing on oncologic and functional outcomes. A retrospective analysis yielded 17 patients who underwent 18 free flap procedures and met the inclusion criteria. Most patients (71 percent, n = 12) had recurrent sarcoma at presentation to the authors' institution. Malignant fibrous histiocytoma was the most common pathologic subtype (n = 6). High-grade tumors were present in 94 percent of patients (n = 16). The free flap survival rate was 100 percent. The rectus abdominis flap was the most common free flap used (39 percent; n = 7). Local recurrence occurred in nine flaps (50 percent), and five patients ultimately required amputations. Six patients (35 percent) had distant recurrence. The mean Enneking score for limb function was 73 percent of the maximum (21.9 of 30). The 5-year disease-specific survival rate was 61.3 percent. In select patients with advanced upper extremity sarcoma undergoing limb salvage, microvascular flap reconstruction can provide reliable, safe coverage with reasonable preservation of function.

Adult↗
PubMed2004

Effects of droplet velocity, diameter, and film height on heat removal during cryogen spray cooling.

Cryogen spray cooling (CSC) is an effective method to reduce or eliminate epidermal damage during laser treatment of various dermatoses. This study sought to determine the effects of specific cryogen properties on heat removal. Heat removal was quantified using an algorithm that solved an inverse heat conduction problem from internal temperature measurements made within a skin phantom. A nondimensional parameter, the Weber number, characterized the combined effects of droplet velocity, diameter, and surface tension. CSC experiments with laser irradiation were conducted on ex vivo human skin samples to assess the effect of Weber number on epidermal protection. An empirical relationship between heat removal and the difference in droplet temperature and the substrate, droplet velocity, and diameter was obtained. Histological sections of irradiated ex vivo human skin demonstrated that sprays with higher Weber numbers increased epidermal protection. Results indicate that the cryogen film acts as an impediment to heat transfer between the impinging droplets and the substrate. This study offers the importance of Weber number in heat removal and epidermal protection.

Administration, Topical↗
PubMed2004

Upper extremity reconstruction following resection of soft tissue sarcomas: a functional outcomes analysis.

BACKGROUND: Treatment for soft tissue sarcoma of the upper extremity has evolved to include limb salvage techniques. We reviewed our experience with limb salvage therapy for upper extremity sarcomas with an emphasis on functional outcomes following the reconstructive surgery. METHODS: A retrospective analysis was performed of 81 consecutive patients with soft tissue sarcoma of the upper extremity who had limb salvage therapy with reconstruction by a plastic surgeon. Univariate and multivariate regression analyses of relevant outcome variables were performed. Enneking functional scores were obtained from 43 patients. RESULTS: The study included 16 microvascular reconstructions and 67 non-microvascular reconstructions for a total of 83 reconstructions in 81 patients. The mean defect size was 129 cm(2) (standard deviation: 106 cm(2)). The mean total functional score was 23.1 (range, 9 to 30). Any reconstruction-related complication and preoperative chemotherapy use were associated with a 7.3 point (P = .03) and 4.7 point (P = .01) decrease in total functional score, respectively. Kaplan-Meier product-limit analysis showed 82% 5-year overall survival and 67% 5-year disease-free survival rates. CONCLUSIONS: For soft tissue sarcoma of the upper extremity, limb salvage with good functional outcome is possible with a judicious approach to reconstruction.

Adult↗
PubMed2003

Interdimer processing mechanism of procaspase-8 activation.

The execution of apoptosis depends on the hierarchical activation of caspases. The initiator procaspases become autoproteolytically activated through a less understood process that is triggered by oligomerization. Procaspase-8, an initiator caspase recruited to death receptors, is activated through two cleavage events that proceed in a defined order to generate the large and small subunits of the mature protease. Here we show that dimerization of procaspase-8 produces enzymatically competent precursors through the stable homophilic interaction of the procaspase-8 protease domain. These dimers are also more susceptible to processing than individual procaspase-8 molecules, which leads to their cross-cleavage. The order of the two interdimer cleavage events is maintained by a sequential accessibility mechanism: the separation of the large and small subunits renders the region between the large subunit and prodomain susceptible to further cleavage. In addition, the activation process involves an alteration in the enzymatic properties of caspase-8; while procaspase-8 molecules specifically process one another, mature caspases only cleave effector caspases. These results reveal the key steps leading to the activation of procaspase-8 by oligomerization.

Apoptosis↗