Biomedical subjects

R G Tompkins

Publications and source records attributed to R G Tompkins.

At least 37 records · Page 2Linked to original sources

PubMed1999

Acute hand burns in children: management and long-term outcome based on a 10-year experience with 698 injured hands.

OBJECTIVE: To document long-term results associated with an coordinated plan of care for acutely burned hands in children. SUMMARY AND BACKGROUND DATA: Optimal hand function is a crucial component of a high-quality survival after burn injury. This can be achieved only with a coordinated approach to the injuries. Long-term outcomes associated with such a plan of care have not been previously reported. METHODS: Over a 10-year period, 495 children with 698 acutely burned hands were managed at a regional pediatric burn facility; 219 children with 395 injured hands were followed in the authors' outpatient clinic for at least 1 year and an average of >5 years. The authors' approach to the acutely burned hand emphasizes ranging and splinting throughout the hospital stay, prompt sheet autograft wound closure as soon as practical, and the selective use of axial pin fixation and flaps. Long-term follow-up, hand therapy, and reconstructive surgery are emphasized. RESULTS: Normal functional results were seen in 97% of second-degree and 85% of third-degree injuries; in children with burns involving underlying tendon and bone, 70% could perform activities of daily living and 20% had normal function. Reconstructive hand surgery was required in 4.4% of second-degree burns, 32% of third-degree burns, and 65% of those with injuries involving underlying bone and tendon. CONCLUSIONS: When managed in a coordinated long-term program, the large majority of children with serious hand burns can be expected to have excellent functional results.

Adolescent↗

PubMed1999

Measurement of muscle protein synthesis by positron emission tomography with L-[methyl-11C]methionine: effects of transamination and transmethylation.

BACKGROUND: Positron emission tomography with L-[methyl-11C]methionine provides a measure of regional protein synthesis rate (PSR) in skeletal muscle. However, the validity of the method depends on incorporation of methionine into protein with minimal transamination, transmethylation, or both. To test directly these assumptions, uptake of L-[methyl-14C]methionine in skeletal muscle was measured in control and cycloheximide-treated rats. METHODS: Normal and cycloheximide-treated rats (n = 8/group) were injected with 50 microCi of L-[methyl-14C]methionine and arterial blood sampled over 90 minutes. After killing, thigh muscle was homogenized, centrifuged, and treated with trichloroacetic acid. PSR from circulating methionine was estimated from trichloroacetic acid-precipitable radioactivity, arterial time-activity curves, and plasma methionine concentrations. RESULTS: In normal rats, approximately 70% of the tissue radioactivity was precipitated with trichloroacetic acid. In normal animals, PSR was 0.22 nmoles x min(-1) x g(-1), in excellent agreement with previous results. In the cycloheximide-treated group, PSR was 0.0032 nmoles x min(-1) x g(-1); approximately 98% reduction compared with controls. CONCLUSION: These studies support the hypothesis that L-[methyl-11(14C]methionine accumulates in skeletal muscle as 11(14)C-labeled protein.

Amination↗

PubMed1999

A unique mechanism of desensitization to lipolysis mediated by beta(3)-adrenoceptor in rats with thermal injury.

Thermal injury causes a hypermetabolic state associated with increased levels of catabolic hormones, but the molecular bases for the metabolic abnormalities are poorly understood. We investigated the lipolytic responses after beta(3)-adrenoceptor (beta(3)-AR) agonists and evaluated the associated changes in beta-AR and its downstream signaling molecules in adipocytes isolated from rats with thermal injury. Maximal lipolytic responses to a specific beta(3)-AR agonist, BRL-37344, were significantly attenuated at post burn days (PBD) 3 and 7. Despite significant reduction of the cell surface beta(3)-AR number and its mRNA at PBD 3 and 7, BRL-37344 and forskolin-stimulated cAMP levels were not decreased. Glycerol production in response to dibutyryl cAMP, a direct stimulant of hormone-sensitive lipase (HSL) via protein kinase A (PKA), was significantly attenuated. Although immunoblot analysis indicated no differences in the expression and activity of PKA or in the expression of HSL, HSL activity showed significant reductions. Finally, beta(3)-AR-induced insulin secretion was indeed attenuated in vivo. These studies indicate that the beta(3)-AR system is desensitized after burns, both in the adipocytes and in beta(3)-AR-induced secretion of insulin. Furthermore, these data suggest a complex and unique mechanism underlying the altered signaling of lipolysis at the level of HSL in animals after burns.

Adipocytes↗

PubMed1999

Low-dose inhaled nitric oxide in acutely burned children with profound respiratory failure.

BACKGROUND: Inhaled nitric oxide (NO) is a rapidly acting selective pulmonary vasodilator that partially reverses the pathophysiology of acute respiratory distress syndrome (ARDS). METHODS: After human studies approval, we studied 11 burned children with severe ARDS in a trial of inhaled NO therapy, assessing its effect on intrapulmonary shunt as measured by the PaO2/FiO2 ratio (PFR). There were 12 episodes of administration; 1 child was treated twice. RESULTS: The children had an average age of 8.3 +/- 4.8 years (mean +/- SEM, range 11 months to 14 years) and average burn size of 64% +/- 22%. At the time of enrollment, the PFR averaged 95 +/- 50 and Murray lung score 3.1 +/- 0.5. Inhaled NO was begun an average of 6.3 +/- 5.5 days after injury and was administered for an average of 7.8 +/- 7.2 days at an average dose of 6.7 +/- 2.4 parts per million. PFR improved an average of 162% +/- 214%. Eight of the 11 children (73%) survived. The 3 nonsurvivors had similar admission PFR values (100 +/- 75 versus 93 +/- 44, P = .089) but a significantly less favorable initial response to inhaled NO, with a percentage of improvement in PFR at 1 hour after enrollment of 7.3% +/- 6.4% versus 213% +/- 226% (P = .026). There were no complications related to NO administration. CONCLUSIONS: Inhaled NO can be safely administered to treat ARDS in children with acute burns and appears to improve their ventilatory management. An immediate improvement in PFR with inhaled NO may correlate with survival.

Acute Disease↗

PubMed1999

Laser ablation of burns: initial clinical trial.

BACKGROUND: Scanning, high-powered carbon dioxide laser ablation of eschar may facilitate blood conservation in patients with burns. METHODS: Twenty-one children with full-thickness burns that required serial excisions were enrolled in a Human Studies Committee approved protocol in which a full-thickness wound was ablated with a rapidly scanned continuous wave carbon dioxide laser system. A control wound was sharply excised, and both wounds were immediately autografted. End points were engraftment at 7 days and serial Vancouver scar scores. RESULTS: The children had an average age of 8.3 +/- 1.2 years, weight of 36.3 +/- 4.9 kg, and burn size of 40% +/- 5.1%. The study wounds were ablated with an average energy of 99.2 +/- 5.7 W; there was no bleeding from 19 successfully ablated wounds. Initial engraftment averaged 94.7% +/- 3.5% in the control sites and 94.7% +/- 3.3% in the study sites (P = 1.0). There was no significant difference in Vancouver scar scores at an average follow-up of 32.0 +/- 5.2 weeks. CONCLUSIONS: This pilot study follows a successful trial of this concept in a porcine model and demonstrates the technical feasibility of laser vaporization of burn eschar in humans with immediate autografting. Further refinement of the technique is required before it can be generally recommended.

Adolescent↗

PubMed1998

Muscle protein synthesis by positron-emission tomography with L-[methyl-11C]methionine in adult humans.

Existing methods for assessing protein synthetic rates (PSRs) in human skeletal muscle are invasive and do not readily provide information about individual muscle groups. Recent studies in canine skeletal muscle yielded PSRs similar to results of simultaneous stable isotope measurements using L-[1-13C, methyl-2H3]methionine, suggesting that positron-emission tomography (PET) with L-[methyl-11C]methionine could be used along with blood sampling and a kinetic model to provide a less invasive, regional assessment of PSR. We have extended and refined this method in an investigation with healthy volunteers studied in the postabsorptive state. They received approximately 25 mCi of L-[methyl-11C]methionine with serial PET imaging of the thighs and arterial blood sampling for a period of 90 min. Tissue and metabolite-corrected arterial blood time activity curves were fitted to a three-compartment model. PSR (nmol methionine.min-1.g muscle tissue-1) was calculated from the fitted parameter values and the plasma methionine concentrations, assuming equal rates of protein synthesis and degradation. Pooled mean PSR for the anterior and posterior sites was 0.50 +/- 0.040. When converted to a fractional synthesis rate for mixed proteins in muscle, assuming a protein-bound methionine content of muscle tissue, the value of 0.125 +/- 0.01%.h-1 compares well with estimates from direct tracer incorporation studies, which generally range from approximately 0.05 to 0.09%.h-1. We conclude that PET can be used to estimate skeletal muscle PSR in healthy human subjects and that it holds promise for future in vivo, noninvasive studies of the influences of physiological factors, pharmacological manipulations, and disease states on this important component of muscle protein turnover and balance.

Adult↗

PubMed1998

Genetically modified human keratinocytes overexpressing PDGF-A enhance the performance of a composite skin graft.

Skin loss due to burns and ulcers is a major medical problem. Bioengineered skin substitutes that use cultured keratinocytes as an epidermal layer with or without analogues of the dermis are one strategy for skin repair. However, none can achieve definitive wound closure, function, or cosmesis comparable to split-thickness autografts. Moreover, autograft donor sites, which require time to heal, may be limited or have attendant problems such as infection or functional/cosmetic deficiencies. To determine if the performance of composite skin grafts of keratinocytes on a dermal analogue could be enhanced, human keratinocytes were genetically modified to overexpress platelet-derived growth factor A chain (PDGF-A). Composite grafts of modified keratinocytes seeded onto acellular dermis, prepared from cryopreserved cadaver skin, secreted PDGF-AA protein in vitro [90 ng/graft (1.5 x 1.5 cm)/24 hr]. To test their performance in a wound healing model, composite grafts were transplanted to full-thickness excisional wounds on the back of athymic mice. PDGF-A grafts formed a stratified differentiated epidermis similar to control grafts. The acellular dermis was repopulated with host fibrovascular cells and by day 7, the PDGF-A grafts had significantly more cells in the dermis and increased staining for murine collagen types I and IV. At this early time point, wound contraction was also significantly inhibited in PDGF-A grafts versus control grafts. Thus, PDGF-A overexpression improves graft performance during the first critical week after transplantation.

3T3 Cells↗

PubMed1998

Objective estimates of the probability of death from burn injuries.

BACKGROUND: Over the past 20 years, there has been remarkable improvement in the chances of survival of patients treated in burn centers. A simple, accurate system for objectively estimating the probability of death would be useful in counseling patients and making medical decisions. METHODS: We conducted a retrospective review of all 1665 patients with acute burn injuries admitted from 1990 to 1994 to Massachusetts General Hospital and the Shriners Burns Institute in Boston. Using logistic-regression analysis, we developed probability estimates for the prediction of mortality based on a minimal set of well-defined variables. The resulting mortality formula was used to determine whether changes in mortality have occurred since 1984, and it was tested prospectively on all 530 patients with acute burn injuries admitted in 1995 or 1996. RESULTS: Of the 1665 patients (mean [+/-SD] age, 21+/-20 years; mean burn size, 14+/-20 percent of body-surface area), 1598 (96 percent) lived to discharge. The mean length of stay was 21+/-29 days. Three risk factors for death were identified: age greater than 60 years, more than 40 percent of body-surface area burned, and inhalation injury. The mortality formula we developed predicts 0.3 percent, 3 percent, 33 percent, or approximately 90 percent mortality, depending on whether zero, one, two, or three risk factors are present. The results of the prospective test of the formula were similar. A large increase in the proportion of patients who chose not to be resuscitated complicated comparisons of mortality over time. CONCLUSIONS: The probability of mortality after burns is low and can be predicted soon after injury on the basis of simple, objective clinical criteria.

Adolescent↗

PubMed1998

A rabbit model for metabolic studies after burn injury.

BACKGROUND: A rabbit burn model was developed and characterized, which will allow conduct of repeated, noninvasive and more sophisticated in vivo metabolic studies to explore the pathophysiology of burn injury, owing to its larger blood volume and tissue mass than the rat. MATERIALS AND METHODS: A 20% body surface, full thickness burn was applied to the backs of six anesthetized rabbits by immersion into a boiling-water bath for 10 s, followed by resuscitation with saline. Resting energy expenditure (REE) was measured daily in pre- and postburn periods. Whole body protein kinetics were evaluated using L-[1(-13)C]leucine tracer, on the preburn and the third postburn day. Fasting plasma glucose was also measured. RESULTS: A significant elevation of REE began on the second postburn day and reached 34 +/- 8% above the preburn level (P < 0.05, paired t test) on the third postburn day. The fasting plasma leucine flux and oxidation were significantly elevated from their preburn levels (both P < 0.05), indicating an accelerated proteolysis and a more negative body protein balance (P < 0.05); however, the rate of whole body protein synthesis did not differ significantly pre- and postburn injury. Fasting plasma glucose also increased (P < 0.001). on the third postburn day. The burn scar remained intact during the study, without any sign of infection. CONCLUSIONS: The metabolic changes observed in this animal model can be attributed to burn injury per se and they mimic those for flow phase in burn patients. This rabbit burn model should be suitable for exploring mechanistic aspects of the burn-induced changes in metabolism and nutrient balance.

Animals↗

PubMed1998

Death in the burn unit: sterile multiple organ failure.

It has been our impression over the years that the most common cause of death in our burn patients is multiple organ failure, despite the clinical absence of uncontrolled infection at the time of death. A six year review of all deaths in our unit confirmed this impression, revealing that multiorgan failure is indeed the most common cause of death (48 patients, 67 per cent), followed rather distantly by early withdrawal of support (15 patients, 21 per cent), resuscitation failure (4 patients, 6 per cent) and isolated pulmonary failure (4 patients, 6 per cent). Finally, we found that our patients dying of multiorgan failure, although often having had multiple small infections during their course, were indeed clinically uninfected at the time of death. These findings are consistent with the supposition that uncontrolled systemic inflammation, initially triggered by tissue injury and isolated infection, persists despite control of these infections and leads to multiple organ failure and death.

Adolescent↗

PubMed1998

Characterization of a composite tissue model that supports clonal growth of human melanocytes in vitro and in vivo.

To aid in the investigation of factors that control the proliferation and function of melanocytes, we have characterized a skin equivalent model that supports melanocyte growth and function in vitro and in vivo. Passenger melanocytes survive and proliferate at low numbers when keratinocytes of the epidermis are cultured in serum-containing medium using a fibroblast feeder layer. When the surface of de-epidermalized acellular dermis was seeded with these cultured cells, the keratinocytes formed a stratified epithelium in vitro containing rete ridges, and the melanocytes were preferentially located in the bottom of these rete ridges. Melanocyte cell number was much less than in normal skin, but in some areas the melanocytes were in clusters, consistent with clonal growth of the cells. When transplanted to athymic mice, the grafts formed foci of pigmentation at 3 wk that expanded and repigmented the entire graft by 8 wk. Histologic examination of these foci revealed that they corresponded to clusters of melanocytes that proliferated and migrated to eventually repopulate the entire graft. In grafts of mixed cells from light and dark skin donors, distinct foci of pigmentation were obvious at 3 wk and, instead of progressing to complete repigmentation, these foci remained stable for over 6 wk. Histologic examination confirmed that these grafts of mixed cells were entirely repopulated with melanocytes and that the grafts contained distinct zones of melanocytes that were of exclusively dark or light skin origin. This model should be valuable for studying the clonal growth of melanocytes in the context of the epidermis.

Animals↗

PubMed1998

Both C3a and C3a(desArg) regulate interleukin-6 synthesis in human peripheral blood mononuclear cells.

Synthesis of complement components is part of the acute-phase response. Interleukin-6 (IL-6) is a critical mediator of the acute-phase response during infections and injuries. Plasma levels of C3a and IL-6 have been proposed as prognostic indicators in sepsis and trauma. The effects of C3a and C3a(des)Arg on IL-6 gene expression and protein production in human peripheral blood mononuclear cells (PBMC) were investigated. Neither C3a nor C3a(des)Arg alone induced detectable IL-6 protein or mRNA levels. However, C3a and C3a(des)Arg affected endotoxin-induced IL-6 synthesis in a dose-dependent manner. In nonadherent PBMC, C3a or C3a(des)Arg suppressed, while in adherent PBMC, C3a or C3a(des)Arg enhanced IL-6 protein and mRNA levels. These results suggest that C3a and C3a(des)Arg may provide a control mechanism of acute-phase responses by enhancing IL-6 synthesis in adherent monocytes at local inflammatory sites and by inhibiting IL-6 synthesis in circulating monocytes.

Cell Adhesion↗

PubMed1997

Use of model plant hosts to identify Pseudomonas aeruginosa virulence factors.

We used plants as an in vivo pathogenesis model for the identification of virulence factors of the human opportunistic pathogen Pseudomonas aeruginosa. Nine of nine TnphoA mutant derivatives of P. aeruginosa strain UCBPP-PA14 that were identified in a plant leaf assay for less pathogenic mutants also exhibited significantly reduced pathogenicity in a burned mouse pathogenicity model, suggesting that P. aeruginosa utilizes common strategies to infect both hosts. Seven of these nine mutants contain TnphoA insertions in previously unknown genes. These results demonstrate that an alternative nonvertebrate host of a human bacterial pathogen can be used in an in vivo high throughput screen to identify novel bacterial virulence factors involved in mammalian pathogenesis.

Animals↗

PubMed1997

Analysis of thermal injury-induced insulin resistance in rodents. Implication of postreceptor mechanisms.

Burn injury is associated with insulin resistance. The molecular basis of this resistance was investigated by examining insulin receptor signaling in rats after thermal injury. The impaired insulin-stimulated transport of [3H]2-deoxyglucose into soleus muscle strips confirmed the insulin resistance following burns. In vivo insulin-stimulated phosphoinositide 3-kinase activity, pivotal in translocation of GLUT4, was decreased in burns when assessed by its insulin receptor substrate-1 (IRS-1)-associated activity. Insulin-induced tyrosine kinase activity of insulin receptor (IR) and tyrosine phosphorylation of IRS-1 were also attenuated. Immunoprecipitated IR, however, appeared to have normal insulin-responsive kinase activity. Finally, immunoprecipitated IRS-1 was tested for its effect on partially purified recombinant IR and was found to inhibit its kinase activity. This inhibitory effect of IRS-1 was abolished by prior treatment of IRS-1 with alkaline phosphatase, indicating that burn injury-related hyperphosphorylation of IRS-1 is similar to that observed in TNFalpha-induced inhibition of IR signaling. All of these changes were observed in the absence of quantitative changes in IR, IRS-1, and phosphoinositide 3-kinase. Alterations in postreceptor insulin signaling, therefore, may be responsible for the insulin resistance after thermal injury.

Alkaline Phosphatase↗

PubMed1997

Differences in dermal analogs influence subsequent pigmentation, epidermal differentiation, basement membrane, and rete ridge formation of transplanted composite skin grafts.

This study evaluated the in vitro and in vivo function of composite skin equivalents based on two different dermal analogs. Keratinocytes derived from the same dark-skinned neonatal foreskins were seeded onto both acellular human dermis and fibroblast-contracted collagen gels. Each type of composite graft readily formed an epithelium in vitro. However, the undulating surface of the acellular dermis acted as a template and organized the seeded keratinocytes into a rete ridge-like pattern, whereas the smooth surface of the fibroblast-contracted collagen gels generated an epithelium with a linear basal layer. Moreover, when acellular dermis was used, the composite grafts demonstrated enhanced melanocyte proliferation. When transplanted to athymic mice, both composite grafts formed a fully differentiated human epidermis, but repigmentation of the grafts when acellular dermis was used was more extensive and only the epidermis on the fibroblast-contracted collagen gels showed signs of hyperproliferation at 6 weeks after grafting. These results demonstrate that the type of dermal analog incorporated into a composite skin graft can influence the subsequent functionality of the skin substitute.

Animals↗

PubMed1997

Control of hypertrophic scar growth using selective photothermolysis.

BACKGROUND AND OBJECTIVE: Previous studies have shown a clinical improvement of hypertrophic scars (HS) after treatment with a pulsed dye laser. The objective of this study was to investigate the effects of variations in pulse wavelength and energy density on HS tissue using human HS implanted in athymic mice. STUDY DESIGN/MATERIALS AND METHODS: Small pieces (approximately 1 mm3) of HS tissue were implanted into athymic mice and allowed to grow for 5 days. The implant site was then exposed to a single 450 microseconds pulse, and implant growth and histology were monitored for an additional 12 days. Laser wavelength and energy density ranges tested were 585-600 nm and 2-10 J/cm2, respectively. RESULTS: Using a wavelength of 585 nm, laser treatment inhibited implant growth by 70% at 6 J/cm2 and 92% at 10 J/cm2, respectively. The inhibitory effect decreased as the laser wavelength was increased from 585 to 600 nm. A widespread destruction of the implant microvasculature with a minor effect on surrounding extracellular matrix at the highest light dose were observed. CONCLUSION: Pulsed laser treatment inhibits HS implant growth in nude mice. This effect is likely mediated by selective photo-thermolysis of the implant microvasculature.

Animals↗

PubMed1997

Urinary urea nitrogen is imprecise as a predictor of protein balance in burned children.

OBJECTIVE: To compare estimates of protein balance using the urinary urea nitrogen method to predict total urinary nitrogen with isotopically derived estimates of metabolic protein balance as defined by the difference between rates of protein synthesis and breakdown. DESIGN: Prospective, descriptive, repeated measures analysis. Urinary urea nitrogen collections were obtained for 8 to 24 hours before infusion of L-[1-13C] leucine during fed and fasted states. SUBJECTS/SETTING: Eight acutely burned pediatric patients consecutively admitted to Shriners Burns Institute, Boston Unit, for medical and surgical care of their injuries. MAIN OUTCOME MEASURES: The difference between isotopically measured rates of protein synthesis and breakdown was used as an index of protein balance and compared with estimates of protein balance determined using the urinary urea nitrogen method. STATISTICAL ANALYSIS: Least squares regression analysis was used to assess the value of urinary urea nitrogen as a predictor of metabolic protein balance. Limits of agreements were used to determine bias and precision between the two methods. RESULTS: Urinary urea nitrogen was a significant predictor of metabolic protein balance (r2 = .77, P < .001). The direction of protein balance was the same in 14 of 16 measurements; however, there was significant lack of agreement between the two methods as demonstrated by large quantitative differences in protein balance. CONCLUSION: Although the urinary-urea-nitrogen-based estimates of protein balance correlate well with isotopically derived protein balance, they are not precise in determining protein balance in seriously burned children.

Adolescent↗

PubMed1997

Metabolic alterations in muscle of thermally injured rabbits, measured by positron emission tomography.

The hypermetabolic inflammatory state that occurs after major trauma has been extensively studied at the whole body level, however, there is only limited information on metabolic changes in individual tissues. In this study, the effect of thermal injury on metabolic function of uninjured hind limb muscle of rabbits was measured noninvasively by positron emission tomography (PET). Rabbits were subjected to full thickness burn on 25% of their body surface area. Two to three weeks after injury, PET and arterial blood sampling was performed during inhalation of 15O2, C15O2 and 11CO and after injection of 18FDG. The tissue and blood data were analyzed by standard kinetic models for blood flow, oxygen extraction fraction (OEF), oxygen utilization and glucose metabolism. A total of seven injured and five sham animals were studied. Total body oxygen consumption was measured by indirect calorimetry and plasma concentrations of glucose, insulin and IGF-1 were measured with standard assays. Compared to sham rabbits, blood flow to muscle of injured animals was unchanged. However, OEF, oxygen utilization and glucose metabolism were significantly reduced (p<0.01) in uninjured muscle of burned rabbits. These data demonstrate that thermal injury is associated with alterations in muscle metabolism, which are not related to change in blood flow.

Animals↗