Charles R. Baxter

The role of oxygen-derived free radicals in burn-induced myocardial contractile depression.

The release of oxygen free radicals from ischemic myocardium has been implicated as a causative factor of cardiac dysfunction after thermal injury. In this study, isolated coronary perfused guinea pig hearts were used to determine if free radical scavengers improve left ventricular (LV) intrinsic contractile response to burn shock. Parameters measured included peak isovolumic LV pressure (LVP) and maximal rate of LVP rise (+dP/dtmax) and fall (-dP/dtmax) at a constant preload. Control animals were immersed in body temperature water and divided into four groups: Group 1, untreated N = 10; Group 2, control animals treated with unbound superoxide dismutase (SOD), N = 5; Group 3, control animals treated with ficoll-SOD, N = 5; and Group 4, control animals treated with PEG-SOD, N = 5. Scald burn equivalent to 45% of total body surface area was produced in 64 animals. Fluid resuscitation was initiated immediately after burn in all animals, and animals were then divided into seven burn experimental groups. In Group 5, 10 animals were treated with fluid alone, lactated Ringers, 4 mL/kg/% burn. Burned animals in Group 6 (N = 10) received a reduced volume of Ringers 2 mL/kg/% burn plus unbound-SOD, 50 mg/kg; 10 animals in Group 7 received this volume of Ringers plus ficoll-SOD, 50 mg/kg. In groups 8, 9, and 10 animals were given fluid, lactated Ringers, 2 mL/kg/% burn plus varying doses of PEG-SOD (Group 8: N = 9, 1,000 U; Group 9: N = 10, 6,000 U; Group 10: N = 5, 12,000 U). In Group 11 (N = 10), animals received SOD-PEG, 6,000 U, plus catalase, CAT-PEG, 6,000 U, given with 4 mL/kg/% burn lactated Ringers solution. Hypotension, hypothermia, and hemoconcentration were similar in all animals after thermal injury, regardless of treatment regimen. Burn hearts showed significantly lower LVP, +dP/dt max, and -dP/dt max than control hearts (P less than 0.05). Compared to controls, coronary pressure and coronary vascular resistance were significantly higher in all treated burn groups. There was no significant difference in heart rate or time to peak pressure or time to maximal contraction or relaxation among the groups. Left ventricular function curves for burned hearts were shifted downward and to the right of curves obtained from control hearts (P less than 0.01), regardless of scavenger treatment. PEG-SOD, 6,000 U, improved left ventricular contractility (+dP/dt) at maximal levels of end-diastolic pressure but deficits in left ventricular pressure and relaxation persisted.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipid mobilization and metabolism after thermal trauma.

Lipid mobilization following thermal injury was studied in 25 patients with burns of between 35 and 95% TBSA for 30 to 50 days postinjury. The concentration of free fatty acids and glycerol in the plasma was elevated. The concentration of plasma triglycerides was elevated, while the concentration of ketone bodies remained normal. Thus it is suggested that the free fatty acids are primarily being re-esterified to triglycerides rather than being utilized for ketone body production. During the first 10 days postinjury, the plasma carnitine level was slightly decreased, while the concentration of carnitine in liver and muscle was elevated. The level of carnitine in burn wound fluid was similar to that in plasma. Therefore, the early decrease in plasma carnitine appeared to result from wound losses, as well as the sustained increased uptake by liver and muscle throughout the burn course.

Research: Lipid Peroxidation Following Thermal Injury

Formation of lipid peroxides in vivo leads to a variety of normal and pathologic consequences. For instance, peroxidation of cell membrane lipids results in altered membrane properties and increased cell destruction. Following severe thermal injury, elevated plasma levels of malondialdehyde, one product of lipid peroxidation, were detected, which suggests that an elevated level of lipid peroxidation was occurring in those patients. In vivo the major mechanisms to protect cells from lipid peroxidation are the presence of vitamin E, the fat-soluble antioxidant, and destruction of peroxides by glutathione peroxidase. In four of five patients investigated, the plasma content of vitamin E was low. The erythrocyte glutathione peroxidase activity was initially low in two patients and, by 15 days postburn, was below normal values in the other three patients. The results suggest that lipid peroxidation was occurring at elevated levels in these severely burned patients. An increased rate of lipid peroxidation could contribute to the decreased levels of phosphatidylethanolamine and essential polyunsaturated fatly acids in plasma and erythrocyte lipids and the shortened erythrocyte lifetimes previously observed in severely burned patients.

The pathogenesis of abnormal erythrocyte morphology in burns

The anemia of thermal injury is characterized by a decreased RBC half-life and abnormal RBC morphology (predominantly echinocytes). These changes are reversible in crossover studies with normal recipients, suggesting an extrinsic mechanism unrelated to initial heat or mechanical damage. Since alterations in plasma lipids, which are freely exchangeable with red cell lipids, produce similar changes, plasma and erythrocyte membrane lipid composition in 30 patients (mean 60% TBSA) was determined and related to RBC morphology in vivo and in vitro. Total cholesterol (TC) and phospholipids (PL) were decreased in plasma and plasma lipoproteins (LP) but remained normal in red blood cell membranes. The deficit in TC and LP cholesterol resulted from decreased cholesterol esters. Plasma phospholipids contained increased phosphatidylcholine (PC) and low lysophosphatidylcholine (LPC) and sphingomyelin levels. The essential fatty acid (EFA) composition of total plasma lipids rapidly decreased, with a more gradual decrease in EFA in red cell lipids. The ratio of free fatty acids to albumin in the plasma was greatly increased throughout and may have a primary role in the abnormal erythrocyte morphology and decreased half-life in burned patients.

Research: A Mathematical Model for the Thermal Efficacy of Cooling Therapy for Burns

The finite element technique was used to model the transient thermal field in skin during a burn. The resulting temperature field was substituted into a damage integral equation to determine cumulative injury as a function of time and position in the tissue. Postburn cooling protocols were simulated to predict the thermal efficacy of cooling therapy in manipulating skin temperature to reduce injury. Protocol parameters included delay prior to initiation of cooling, cooling temperature, and duration of therapy. The analysis indicates that it is not possible by postburn water cooling to lower the tissue temperature rapidly enough to reduce the extent of burn injury. Any clinical efficacy of postburn cooling should therefore be attributed to nonthermal effects.

Proteolytic activity in burn wound exudates and comparison of fibrin degradation products and protease inhibitors in exudates and sera

Proteolytic (caseinolytic) activity in burn wound exudates was screened over the range pH 5.3 to 8.4. Although activity was greatest at pH 8.4 in four of seven exudates, individual differences indicated that different proteases predominate in the local environment of the wound. Paired exudate and serum samples were compared with regard to fibrin degradation products and three protease inhibitors: antithrombin III, a1-protease inhibitor, and a2-antiplasmin. Fibrin degradation products concentration was higher in exudates than in paired sera, indicating the wound as the source of circulating fibrin degradation products rather than intravascular coagulation followed by fibrinolysis. In contrast, all three protease inhibitors exhibited higher concentrations in serum than in the paired exudate. The serum/exudate ratio for AT III differed significantly from that for a1-protease inhibitor and a2-antiplasmin, and the ratio of two inhibitors in serum differed from the ratio of the same two inhibitors in the exudate in two of three comparisons. These findings emphasize the importance of exudate examinations as a reflection of events in the wound itself. The importance of microenvironments is invoked to account for the significant exudate fibrin degradation products titers, which are seen despite the presence of antithrombin III, which could inhibit coagulation, and the presence of a2-antiplasmin, which could inhibit fibrin degradation.

Leukotrienes LTB4 and LTC4 in thermally injured patients' plasma and burn blister fluid.

Radioimmunoassays for 5(S), 12(R)-dihydroxyeicosa-6, 14-cis, 8,10-trans-tetraenoic acid (leukotriene B4, LTB4) and 5(S)-hydroxy-6(R)-L-gamma-glutamyl-L-cysteinyl-glycinyleicosa-7,9- trans, 11,14-cis-tetraenoic acid (leukotriene C4, LTC4) have been used to quantify the concentrations of these arachidonic acid metabolites in plasma (12 patients) and blister fluid (6 patients) of burned patients. The results of this study demonstrate that, in general, burn plasma LTB4, and LTC4 were not elevated; however, in individual cases, transient high levels of leukotrienes were observed. Correlation between leukotriene peaks and the clinical course could not be established. High levels of LTB4 and LTC4 in burn blister fluid suggest their participation in local inflammatory reactions.

Guidelines for preventing 'dilution false negatives' in in vitro laboratory testing of the donor population

In this article we develop a calculation or formula for use in determining the potential dilution effect of fluids administered during patient treatment on serologic testing parameters. The formula uses basic principles of (a) fluid distribution over time from administration; (b) ratios of plasma and extravascular fluid volumes to body weight; and (c) common practices of fluid resuscitation. A dilution threshold of 50% was set using data from enzymelinked immunosorbent assay human immunodeficiency virus antibody determinations performed on in vitro diluted seropositive serum samples. These data respond to issues raised by guidelines from the Centers for Disease Control and the U.S. Food and Drug Administration to achieve recipient safety without unnecessarily restricting the potential donor pool.

Elastase and alpha 1-protease inhibitor in burn wound exudates.

By degrading antithrombin III, polymorphonuclear neutrophil (PMN) elastase can become a procoagulant. Because intravascular coagulation may accompany severe burn injury, this study examined burn wound exudates for PMN elastase and its physiologic inhibitor, plasma alpha 1-protease inhibitor (alpha 1-PI), as a step in evaluating their contributions to coagulopathy in patients with burns. Each of the nine exudates examined were inhibitory for PMN elastase. Chromatographic characterization of the inhibitor indicated that it was alpha 1-PI; its elution volume for four exudates was identical to that of pure alpha 1-PI. Confirmation of the inhibitors identity was achieved by reaction of anti-alpha 1-PI antibody with each exudate and with inhibitory chromatographic fractions of exudates with the most inhibitory activity. Inhibitor potency, determined from dose-response curves against a standard PMN elastase activity, varied twentyfold among exudates. Only one exudate had catalytic activity with the PMN elastase substrate. Although this enzyme had elastase-like properties, it appeared to differ from PMN elastase. The presence of alpha 1-PI in the wound exudate suggests that this inhibitor may act to diminish fibrin formation from the level that might otherwise have been seen if excess elastase were free to degrade antithrombin III.

Effects of ω-3 and ω-6 fatty acid-rich oils on the cardiovascular system of thermally injured rabbits: changes in plasma triglycerides, plasma cholesterol, relative blood viscosity, platelet count, and bleeding time

New Zealand white male rabbits were studied to determine how supplements of soybean oil, soybean + MaxEPA oil, or MaxEPA oil affected their cardiovascular status when they were burned. Plasma triglyceride concentrations increased at 2 hours after burn injury (28 days after supplement administration) and declined by the end of the study in all three experimental groups of rabbits. These same animals showed no noticeable differences in the plasma concentrations of total cholesterol or in the high-density lipoprotein cholesterol subfractions. Plasma low-density/very-low-density lipoprotein cholesterol levels remained unchanged at 2 hours after burn injury/sham treatment but increased by the end of the study in all three experimental groups of rabbits. The mean platelet number was significantly higher in burned/sham treated rabbits given soybean oil supplement as compared with numbers in those given either soybean oil + MaxEPA oil or MaxEPA oil supplement. Plasma relative viscosity was highest in the soybean oil-supplemented rabbits, decreased in animals fed soybean oil + MaxEPA, and lowest in MaxEPA oil-supplemented rabbits. Mean bleeding time was lowest in soybean oil-fed rabbits. The bleeding time was higher in rabbits fed soybean oil+MaxEPA oil and highest in MaxEPA oil-supplemented animals. Platelet number and plasma viscosity were highest in the soybean oil-supplemented rabbits and lowest in the MaxEPA oil-supplemented group. The reverse pattern occurred when bleeding time was established. Overall results obtained suggest that supplementation with oils rich in omega-3 and omega-6 fatty acids may have significant effects on the cardiovascular health of burned male New Zealand white rabbits.