The effects of thermal injury on serum interleukin 1 activity in rats.

Interleukin 1 (IL-1) is present in the blood of burned patients but its pathophysiologic role is not fully understood. Rat models would be useful research tools, if this cytokine could be identified in a complex fluid like blood. We describe a methodology, which revealed IL-1 activity from the serum of burned rats. Serum was collected from 37 rats with 30% total body surface burns and 9 unburned controls. To vary the burn response, the wounds of 17 rats were seeded with nonvirulent Pseudomonas aeruginosa at the time of injury. IL-1 activity was assessed by its capacity to induce IL-2 secretion in murine lymphoma cells (LBRM-33-1A5). Only after the serum had been fractionated, concentrated, and dialyzed, was IL-1 activity uncovered. Sera from burned rats contained five times more IL-1 activity than those from control animals (p < 0.05). There was no difference in serum IL-1 activity between burned and burn-seeded animals. The IL-1 activity was heat labile, and not produced by P. aeruginosa endotoxin, TNF-alpha, or endogenous IL-2 in rat serum. These results confirm that serum IL-1 levels are increased following thermal injury, and that there is no apparent relationship between IL-1 levels and infection. The serum preparation scheme presented in this study offers a reasonable approach to the measurement of serum IL-1 levels in rat models of disease and injury.

Effect of burn wound bacterial colonization on sleep and respiratory pattern.

This study examined the effect of bacterial colonization of a burn wound on the sleep pattern and respiration during sleep. Sleep patterns of adult rats were monitored for one week before and two weeks after a 30 percent total body surface, full skin thickness burn with and without seeding the fresh wound with nonvirulent Pseudomonas aeruginosa. Unseeded rats were euthermic and exhibited a normal sleep pattern during the first-week post burn; however, rapid eye movement (REM) sleep percent was significantly decreased by the second week due to a reduction in the frequency rather than duration of REM periods. Rats with seeded wounds were febrile and had a significantly lower REM sleep percent throughout the two-weeks post burn due to a reduction in frequency but not duration of REM periods. The increase in respiratory rate from the non-REM to REM sleep state observed before injury was abolished in the seeded group post burn. There was an immediate but transient 24 h drop in REM sleep following thermal injury. Bacterial colonization of the burn wound by either immediate, artificial seeding or by delayed, spontaneous means significantly decreased REM sleep with and without fever, respectively. These results indicate that noninvasive bacterial colonization of a burn wound was capable of decreasing REM sleep without causing fever and that REM sleep reduction was a more sensitive indicator of the extent of burn wound bacterial colonization than was colonic temperature.

Wound endotoxin is not a principal mediator of postburn hypermetabolism in rats.

Localized bacterial colonization of a 30% total body surface burn (TBSB) wound raises the resting metabolic rate of rats. To determine whether endotoxin (LPS) released in the burn wound contributes to this response, the metabolic rates and colonic temperatures of male Sprague-Dawley rats were monitored before and for 1 week after thermal injury. Wounds were seeded with non-virulent P. aeruginosa (NVP), or S. epidermidis (SE) or were left unseeded at the time of injury. Non-bacteremic SE-seeded rats were as hypermetabolic as the NVP-seeded animals on postburn days (PBDs) 3-4 and 7-8, indicating that wound LPS is not an obligatory mediator of postburn hypermetabolism. Continuous subcutaneous infusion of NVPlps (2.6 and 12.6 micrograms/100 gm/hr) beneath unseeded burn wounds did not raise metabolic rates above those of burned, unseeded controls. Neither NVP seeding nor LPS infusion resulted in measurable endotoxemia on PBDs 7-8. These results indicate that the LPS released in the colonized burn wound does not serve as either a circulating mediator or the principal inducer of other mediators of postburn hypermetabolism in rats.

Metabolic and thermoregulatory responses to burn wound colonization.

This study was designed to determine whether there is a relationship between bacterial colonization of the burn wound and resting oxygen consumption (VO2) and colonic temperature (Tc) in burned rats. Resting VO2, Tc, and blood, spleen, and wound cultures were monitored for 2 weeks after 30% total body surface full-thickness burns. The wounds of 53 animals were seeded with 10(8) nonvirulent P. aeruginosa (NVP) at the time of injury, while the wounds of 33 rats were allowed to colonize spontaneously. The seeded wounds contained 10(6) colony forming units/gm (CFU/gm) by the fourth postburn day (PBD), while the unseeded wounds did not reach this level of colonization until after the first week postinjury. Wound seeding accelerated the metabolic and thermoregulatory responses to injury. Average VO2 and Tc of the seeded group were above the unseeded group on PBD's 3-4 and 7-8, but there were no significant differences between groups on PBD's 14-15. Although the unseeded animals were hypermetabolic during the first week, they remained afebrile. There was a significant correlation between wound bacterial counts and the increase in resting VO2 of 44 nonbacteremic animals, but variations in the data suggest that factors other than number of viable wound bacteria affect this relationship. Changes in Tc were unrelated to wound bacterial count but were correlated with changes in VO2. Taken together, the data suggest that bacteria in the burn wound contribute to the rise in energy expenditure following thermal injury.

Thermoregulatory and nonthermoregulatory heat production in burned rat.

Severely burned patients are hypermetabolic within their thermoneutral zone (TNZ), where there are no thermoregulatory demands on heat production. The rat has been used as a model of postburn hypermetabolism without clear evidence that it behaves in a similar way. Male rats (400-500 g; n = 34-39) were placed as a group in a respiration chamber and metabolic rates for the average rat were determined over 3-6 h at ambient temperatures between 9 and 36 degrees C. Colonic temperatures (Tco) and body weights were measured after each run. Animals were studied sequentially as normals (N), after clipping (C) and following 50% total body surface scald burns. Clipping increased the lower critical temperature (LCT) from 27.7 to 29.1 degrees C without affecting resting heat production (N = 42.6 +/- 0.5; C = 42.0 +/- 0.8 W/m2; mean +/- S.E.) or Tco (N = 36.6 +/- 0.1; C = 36.6 +/- 0.1 degrees C) in the TNZ. Injury increased LCT to 32.8 degrees C and the burned animals were hypermetabolic (47.2 +/- 0.6 W/m2; P less than 0.05 vs. N) and febrile (36.9 +/- 0.1 degrees C; P less than 0.05 vs. N) in the elevated TNZ. These metabolic and temperature responses of burned rats are limited in magnitude but are qualitatively similar to those of patients. The extra heat production in the TNZ reflects the basic metabolic cost of injury.

Effects of infection on oxygen consumption and core temperature in experimental thermal injury.

Oxygen consumption (VO2) and colonic temperature (Tc) were measured in groups of rats before and after 30% total body surface, full thickness burns. Some wounds were seeded with Pseudomonas aeruginosa or Staphylococcus epidermidis, and some seeded wounds were treated with Sulfamylon or Silvadene. Three groups became bacteremic (B) during the 2-3 week period of observation. At an ambient temperature (Ta) of 32 C, VO2 of the B group rose from 0.83 +/- 0.01 to 1.20 +/- 0.01 ml/hr/g (mean +/- S.E., p less than 0.001) versus 0.81 +/- 0.01 to 0.99 +/- 0.02 for nine nonbacteremic (NB) groups (p less than 0.001). Tc increased only in the B groups--from 36.8 +/- 0.1 to 37.7 +/- 0.1 C (p less than 0.001). In the second or third week postinjury, VO2 of the NB rats was reduced when Ta was increased to 34 C; Tc followed changes in Ta. Sulfamylon lowered VO2 of P. aeruginosa seeded, NB rats. The metabolic cost of wound contamination appeared to vary with bacterial strain. The metabolic effects of infection appear to be a continuum, beginning with a modest rise in VO2 and progressing to greater increases in VO2 and Tc with wound invasion and systemic infection.

Evaluation of (1-sarcosine, 8-isoleucine) angiotensin II as a therapeutic agent for oleic acid-induced pulmonary edema.

(1-Sarcosine, 8-isoleucine) angiotensin II was assessed as a therapeutic agent for acute respiratory distress syndrome with oleic acid pulmonary edema in sheep used as an experimental model. Under general anesthesia with controlled mechanical ventilation with 100% oxygen, 32 sheep received oleic acid (0.075 ml/kg) intravenously. After oleic acid infusion, 20 animals were treated with continuous intravenous infusion of the angiotensin II analogue; nine received 300 ng/kg/min, six received 600 ng/kg/min, and five received 2000 ng/kg/min. Cardiopulmonary measurements were repeated every 30 minutes for 270 minutes. According to time-integrated PaO2, six of 15 animals of the groups given 300 and 600 ng/kg/min (43%) did not respond to the treatment. All animals responded in the group given 2000 ng/kg/min. Animals in the latter group had lower Qs/Qt, PaCO2, and airway resistance than had the control animals. Elevation of pulmonary vascular resistance was limited and mean arterial blood pressure was well maintained. These results reveal that (1-Sar, 8-Ile) angiotensin II is effective in the treatment of oleic acid-induced pulmonary edema.

A new open and closed respiration chamber.

A new, fully automated, open and closed respiration chamber has been constructed, which is large enough to accommodate man or comparable sized animals. Metabolic rate is calculated from measured changes in respiratory gas volumes while the system is hermetically sealed. When CO2 concentration reaches a prescribed level, large ports are opened and the chamber is ventilated. By repeating this process, a series of metabolic determinations can be conducted over an extended period. Temperature, humidity and air velocity are fixed, but chamber volume and pressure vary with changes in the respiratory exchange of the animal and/or barometric pressure. Small, rapid changes in gas volumes are monitored by a low-resistance spirometer and large changes accommodated in a second, high-volume, motorized spirometer. Chamber operations, data acquisition and metabolic calculations are performed by a small computer. System calibration with methanol combustion indicates that estimates of respiratory gas exchange are highly accurate over a temperature range from 10-40 degrees C.

Depressed reflex vasomotor control of the burn wound.

Total leg blood flow was measured by venous occlusion plethysmography in five normals and 14 burned patients before and after 30 min of external heating. Leg surface temperatures were held constant, but rectal temperatures increased on the average of 0.4 to 0.5 degrees C in all subjects following this heat load. Leg blood flow increased by 56.0% in the controls, 63.2% in five patients with essentially no leg burn (mean burn size = 1.5% leg surface), and 9.6% in nine patients with major leg injuries (mean burn size 55% leg surface). Failure of reflex vasodilatation in the burned leg was evident up to 107 days postinjury even when the wound was well-healed. All subjects sweated freely from the unburned skin. In two patients, where arm and leg blood flows were measured simultaneously, flow to the uninjured arm increased while that to the injured leg remained unchanged. This lack of reflex vasodilatation in the burned limbs suggests either that wound vessels are denervated or that they are so dilated in the basal state that further dilatation is limited. The bulk of this and other data would support the denervation concept. This physical or chemical denervation could occur at the time of injury, be localised to the area of the wound, and result in loss of both neurogenic vasoconstrictor tone and active reflex vasodilatation.

Arm and leg intravascular temperatures of men during submaximal exercise.

Rectal (Tre) and blood temperatures in the femoral artery (Tfa), femoral vein (Tfv), axillary artery (Taa), and axillary vein (Tav) were determined in three men over a range of steady-state treadmill exercise (173-401 W/m2) in a 24 degree C db, 15 degree C wb environment. When the men were standing quietly before the walks Tre greater than Tfa greater than Taa greater than Tfv greater than Tav, indicating that under these resting conditions both the arms and the legs served as avenues for arterial heat dissipation. By the end of all 1-h walks, Tre, Tfa, Tasa, and Tfv had increased in a linear fashion with work load, Tav had dropped, and Tre greater than Tfv greater than or equal to Tfa greater than or equal to Taa greater than Tav. The maintenance or expansion of axillary arteriovenous temperature differences during exercise indicated that the less active arms continued to serve as routes for arterial heat loss. The lack of femoral arteriovenous temperature differences demonstrated that under these steady-state exercise conditions there was little or no net vascular heat transfer between the active legs and the central circulation. Rectal-femoral intravascular temperature differences at rest and over the full range of submaximal work employed favor heat transfer from the rectum to the circulation. Consequently the rise in Tre during leg work was considered the result of a reduction in local heat dissipation and some possible heat gained from nearby intrapelvic muscles.

Visceral blood flow following thermal injury.

To determine if visceral blood flow was altered by thermal injury, effective renal blood flow (ERBF) was measured by para-aminohippurate clearance in five control subjects and 13 nonbacteremic burn patients (mean burn size: 50% total body surface, range: 24.5-83.5) 6-25 days after burn injury. Splanchnic blood flow (SBF) and cardiac output were determined in a matched group of ten patients by indocyanine green clearance and dilution techniques, respectively. Renal and splanchnic oxygen consumptions (VO2) were calculated from regional arteriovenous O2 differences and blood flows. ERBF was not significantly elevated in these patients (780 +/- 68 ml/min x m2, mean +/- SE, versus 552 +/- 37 in controls). SBF, at 1463 +/- 96 ml/min x m2, was twice normal and 19% of the cardiac index (7764 +/- 393 ml/min x m2). Individual variations in ERBF and SBF were unrelated to burn size or the time after injury, but ERBF varied with 24-hour sodium excretion. Renal and splanchnic VO2 were twice normal levels at 33 +/- 6 and 66 +/- 4 ml/min, respectively. These results indicate that an increase in ERBF is not an obligatory response to burn injury, but is dependent on sodium load and/or vascular volume. Conversely, SBF is consistently increased by thermal injury and contributes to the rise in cardiac output after injury. While the increase of SBF is appropriate for the rise in local VO2, the cause of the apparent splanchnic vasodilation is unknown.

Increased renal perfusion and kidney size in convalescent burn patients.

Renal blood flow was elevated in convalescent burn patients shortly before discharge (992 +/- 112 mL/min/sq m in burn patients vs 551 +/- 37 mL/min/sq m in normal subjects; mean +/- SE). Autopsy studies demonstrated that renal enlargement was a constant feature of patients after a prolonged hospital course; the kidneys of 28 patients who died after 60 days of hospitalization weighed 241 +/- 10 g vs 153 +/- 8 g in control subjects. The increase in renal weight was primarily related to cellular hypertrophy and hyperplasia. These physiological and morphological findings in thermally injured patients may be a form of renal work hypertrophy following increased protein catabolism accompanying severe injury.

Control of blood flow in a large surface wound.

To study the factors which control the increased blood flow to a large granulating wound, Doppler flow probes were implanted around the external iliac arteries bilaterally in 20-40 kg goats. Following operative recovery and basal measurements, skin was excised from one hind limb. Blood flow in the injured leg of five awake, resting goats rose above that of the uninjured leg by the fourth postoperative day and plateaued at 70-90% above uninjured leg flows for the next two weeks. The increase in injured leg blood flow was associated in time with the formation of a highly vascularized wound. This increased blood flow to the injured leg persisted in 11 anesthetized goats studied 9-12 days postinjury (186 +/- 27 ml/minute versus 107 +/- 19, p < 0.01, mean +/- SEM). Substrate turnover revealed that elevated blood flow to the injured leg was not the result of increased oxygen consumption, but was associated with increased glucose uptake (7.8 +/- 1.1 mg/minute versus 2.7 +/- 0.6, p < 0.001) and lactate release (3.6 +/- 1.3 mg/minute versus 1.1 +/- 0.7, p < 0.05). Limitations in oxygen delivery failed to explain the increased blood flow to the injured leg, since raising arterial PO(2) or exposing the leg to a high oxygen environment had no effect on limb perfusion. Although lactate and potassium, both potential vasodilators, were elevated in the femoral vein blood from the injured leg, a series of cross perfusion studies failed to reduce vascular resistance in another leg on the same or a second uninjured animal. Additional studies revealed that changes in leg vascular resistance were markedly diminished in the injured leg following hemorrhage, spinal anesthesia, or intravenous infusion of epinephrine or norepinephrine. These studies of large granulating wounds reveal: 1) elevated injured leg flow is not the result of local hypoxia; 2) any wound vasodilators have no impact on systemic circulation; 3) the wound vasculature appears relatively insensitive to circulating and neurogenic vasomotor drives.

Effect of injury and infection on visceral metabolism and circulation.

To characterize the role of the liver and kidney in the metabolic response to injury and infection, selective catheterization of the hepatic (42 veins) and renal veins (21 veins) was performed in 31 burn patients (mean burn size: 51% TBS), studied 4-129 days postinjury. Blood flow was determined by standard clearance techniques (ICG and PAH), and simultaneous arterial and hepatic and/or renal vein blood was obtained for oxygen, glucose, lactate, pyruvate, and amino acids. Patients studied in the first to third weeks postinjury were classified as noninfected (8 studies), bacteremic (8 studies), or bacteremic with complications (5 studies). There was no difference in age, weight, mean burn size, pulse rate, blood pressure, rectal temperature, total body oxygen consumption, or cardiac index among these groups. Estimated hepatic blood flow (EHBF) and hepatic substrate balance of these patients were compared with postabsorptive normal subjects in the literature (mean +/- SEM or range). :Formula: (See Text) Thermal injury alone resulted in marked increases in EHBF, hepatic oxygen uptake, and glucogenesis. The added insult of bacteremia significantly increased hepatic glucose output; as clinical sepsis progressed, glucose output decreased sharply. The kidney consistently demonstrated a net uptake of glucose in all studies. The changes in hepatic glucose output in bacteremic patients occurred without significant differences in EHBF, oxygen utilization or lactate uptake, but were associated with marked alterations in amino acid uptake.

Increased peripheral amino acid release following burn injury.

Turnover rates of 10 amino acids were determined in four normal subjects and 18 burned patients (mean burn size, 41% of total body surface) by measuring leg blood flow by venous occlusion plethysmography and arterial (A) and femoral venous (FV) amino acid concentrations. Patient arterial plasma amino acid concentrations generally were low or normal, although phenylalanine was elevated. Only alanine demonstrated significant A-FV concentration difference (-9 +/- 2 mumole/100 ml in patients vs -5 +/- 1in controls, mean +/- SEM). Leg blood flow was 6.26 +/- 0.57 ml/100 ml of leg volume . min in the patients and 2.62 +/- 0.57 in controls. While the net peripheral release of the 10 amino acids was accelerated following injury, only alanine release was consistently greater in the patients (0.27 plus or minus 0.05 mumole/100 ml in leg volume . min) as compared with that of controls (0.08 +/- 0.02). The increased alanine release from legs of patients generally was related to the extent of total body surface injury and oxygen consumption of the patient, but was unrelated to size of limb burn or leg blood flow. The accelerated rate of alanine release from limbs of burn patients relates to the generalized catabolic effects of injury rather than to local inflammatory or metabolic events which may occur in the injured extremity.