Biomedical subjects
Publications and source records attributed to T K Hunt.
The time line of wound healing is altered by various local conditions, such as inflammation and neuropathy; however, the most important factor regulating the regional time line of healing is blood flow. Factors that can increase oxygen delivery to the regional tissue, such as supplemental oxygen, warmth, and sympathetic blockade, can accelerate the time line of healing.
BACKGROUND: "Respiratory burst" activity, ie, O2- production, is dependent on PO2, temperature, pH, and glucose concentrations within the physiologic range. OBJECTIVES: To determine whether environmental conditions characteristic of wounds may limit human neutrophil respiratory burst metabolism and to clarify the degree to which bactericidal oxidant production depends on local PO2. METHODS: Human blood and wound neutrophils were stimulated with phorbol myristate acetate. Oxygen consumption and superoxide production were measured over a range of 30 to 300 mm Hg PO2, 0 to 40 mmol/L glucose, pH 6.0 to 8.0, and 30 degrees C to 37 degrees C. The apparent Michaelis Menten constant for oxidant production with respect to PO2 was calculated. RESULTS: Oxygen consumption and O2- production were dependent on PO2 throughout the range tested. Half-maximal oxidant production occurred in the range of 45 to 80 mm Hg PO2 and maximal at PO2 higher than 300 mm Hg. These data agree with the highest previous estimates. Oxidant generation was also dependent on pH, temperature, and glucose concentration, but to a lesser extent. CONCLUSIONS: Leukocyte bacterial killing capacity as measured by oxygen consumption and superoxide production are substantially impaired at the low oxygen tensions often found in wounds. Changes in pH, temperature, and glucose concentration have lesser but nonetheless significant consequences. The data provide a plausible mechanism for the vulnerability of some wounds to infection and for the previous finding that increasing oxygen tension at wound sites enhances bactericidal function. Thus, the data serve as a basis for future studies on prevention of wound infection.
OBJECTIVE: To test the hypothesis that subcutaneous wound oxygen tension (PsqO2) has a predictive relation to the development of wound infection in surgical patients. DESIGN: A noninterventional, prospective study. SETTING: A university department of surgery. PATIENTS: One hundred thirty operative general surgical patients at notable risk of infection as predicted by an anticipated Study on the Effect of Nosocomial Infection Control (SENIC) score of 1 or greater. OUTCOME MEASURES: PsqO2 was measured perioperatively. Its relation to the subsequent incidence of surgical wound infection was then determined and compared with the SENIC score as a criterion standard. RESULTS: Although the SENIC score and PsqO2 are inversely correlated, PsqO2 is the stronger predictor of infection. Low PsqO2 identified patients at risk and concentrated them in a cohort that was about half the size of that identified by the SENIC score. CONCLUSIONS: Subcutaneous perfusion and oxygenation are important components of immunity to wound infections. The SENIC score identifies systemic physiological variables that are important to the development of wound infection. Nevertheless, PsqO2 is the more powerful predictor of wound infection. Moreover, PsqO2 can be manipulated by available clinical means, and thus may direct interventions to prevent infection.
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Wound healing can be enhanced and wound infections prevented, often by simple, inexpensive, readily available means. Preoperative evaluation for impediments to healing, such as malnutrition, vasoconstriction, hyperglycemia, and steroid use, allows correction prior to operation. Intraoperatively, the surgeon should concentrate on surgical technique, appropriate antibiotic use, and prevention of vasoconstriction (volume, warming). Postoperatively, the focus should be on prevention of vasoconstriction through pain relief, warming, and adequate volume resuscitation and on maintaining nutrition and normoglycemia. These approaches apply as well to chronic wounds. Additionally, maintenance of a moist environment, correction of local vasospasm with sympathetic blockade or warming, and stimulation of angiogenesis through aggressive debridement or hyperbaric oxygen therapy enhance healing of chronic wounds.
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High levels of contamination are associated with delayed healing of pressure ulcers, and problems occur when surface contaminants invade the tissues and produce infection. This article addresses differentiating contamination from infection, identifying infection when it is present, and treating the patient with a contaminated or infected pressure ulcer. Systemic support for healing is discussed with a focus on oxygenation and nutrition. A comprehensive plan for the concomitant treatment of all factors contributing to pressure ulcer infection is recommended.
Thrombin's actions on platelets, macrophages, fibroblasts, and endothelial cells have prompted the hypothesis that thrombin may be important for inflammatory and fibroproliferative processes in wound healing. Protease-activated receptor 1 (PAR1) is a G-protein-coupled receptor that mediates many of the cellular activities of thrombin. To test the role of this receptor in vivo, we generated PAR1-deficient mice. Despite the observation that fibroblasts cultured from these mice lacked responsiveness to thrombin in vitro, we now report that there was no difference detected between wild-type and PAR1-deficient mice in skin wound healing assays including time to closure of open wounds, tensile strength of healed incisional wounds, wound histology, and hydroxyproline/DNA content of wound implants. We conclude that PAR1 is not necessary for normal skin wound healing in mice.
Lymphoid tissues from asymptomatic HIV-infected individuals, as compared with symptomatic HIV-infected subjects, show limited histopathological changes and lower levels of HIV expression. In this report we correlate the control of HIV replication in lymph nodes to the non-cytolytic anti-HIV activity of lymphoid tissue CD8+ cells. Five subjects at different stages of HIV-related disease were studied and the ability of their CD8+ cells, isolated from both lymphoid tissue and peripheral blood, to inhibit HIV replication was compared. CD8+ cells from lymphoid tissue and peripheral blood of two HIV-infected long-term survivors suppressed HIV replication at a low CD8+:CD4+ cell ratio of 0.1. The CD8+ cells from the lymphoid tissue of a third asymptomatic subject suppressed HIV replication at a CD8+:CD4+ cell ratio of 0.25; the subject's peripheral blood CD8+ cells showed this antiviral response at a lower ratio of 0.05. The lymphoid tissue CD8+ cells from two AIDS patients were not able to suppress HIV replication, and the peripheral blood CD8+ cells of only one of them suppressed HIV replication. The plasma viremia, cellular HIV load as well as the extent of pathology and virus expression in the lymphoid tissue of the two long-term survivors, were reduced compared with these parameters in the three other subjects. The data suggest that the extent of anti-HIV activity by CD8+ cells from lymphoid tissue relative to peripheral blood correlates best with the clinical state measured by lymphoid tissue pathology and HIV burden in lymphoid tissues and blood. The results add further emphasis to the importance of this cellular immune response in controlling HIV pathogenesis.
OBJECTIVE: To compare the lateral transabdominal and posterior retroperitoneal laparoscopic methods for performing adrenalectomy. DESIGN: Nonrandomized. SETTING: Hospitals affiliated with the University of California, San Francisco. PATIENTS: Thirty-six patients (15 men and 21 women), aged 5 to 78 years (mean age, 49 years), were treated for the following conditions: aldosteronoma, 18 patients; pheochromocytoma, 4 patients; Cushing syndrome, 6 patients; androgen-secreting tumor, 1 patient; nonfunctioning adenoma, 3 patients; adrenal hemorrhage, 1 patient; metastatic neoplasm, 2 patients; and myelolipoma, 1 patient. INTERVENTIONS: Twenty-three lateral and 14 posterior laparoscopic adrenalectomies. MAIN OUTCOME MEASURES: Success rate, operating time, complications, and length of hospital stay. RESULTS: The tumors, which ranged in size from 1 to 13 cm (mean, 4.2 cm; median, 2.5 cm), were all successfully resected laparoscopically. All 8 tumors larger than 6 cm were resected by the lateral approach. One critically ill patient died. No patient required blood transfusions or conversion to laparotomy. Mean operating time was 3.8 hours vs 3.4 hours (median, 3.5 hours vs 3 hours) and mean hospital stay was 2.2 days vs 1.5 days (median, 2 days vs 1 day) for the lateral and posterior approaches, respectively. All patients without concomitant procedures were ready to be discharged within 48 hours. CONCLUSIONS: Both approaches were effective and safe. We prefer the lateral approach for tumors larger than 6 cm and the posterior approach for bilateral tumors.
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The usual initial life-threatening effect of injury is hypovolemic shock. In the hierarchical physiologic response to hypovolemia, perfusion of peripheral tissues is sacrificed early and restored late. But the usual hemodynamic and metabolic measurements of blood pressure, urine output, and base deficit are not reliable indices of peripheral perfusion. Although the Clark electrode can quantitate tissue oxygen pressure and thereby serve as an index of perfusion, its use is compromised by several technical deficiencies. Recently, an optical method (optode) using fluorescent technology has been developed for measurement of oxygen tension in subcutaneous tissue (P sgO2). Our studies compared this device with the Clark electrode in the laboratory and tested its value in both animal and clinical studies of hypovolemic shock. The results of these several studies demonstrated that: (1) the new oximeter tracked a rapid fall or rapid rise of oxygen tension between room air (150 mm Hg) and 0 mm Hg ( a glucose oxidase/catalase solution) as well as the Clark electrode without encountering its technical problems; (2) with an acute hemorrhage to 20% of base line, the PsgO2 was found to decline rapidly in parallel with the decline of mean arterial pressure (MAP). Although the MAP rapidly returned to normal after immediate complete return of all shed blood, the PsgO2 did not reach normal levels for at least 2 hours, suggesting persistent peripheral vasoconstriction. (3) Studies in progress suggest that between 35 and 78% of trauma patients (n = 18) adequately resuscitated for hypovolemia b customary criteria have a decreased level of PsgO2 for as long as 60 hours after resuscitation for injury. If care is taken to prevent other causes of catecholamine induced vasoconstriction such as pain, fear, cold, and arterial hypoxia, these several results suggest that a certain number of injured patients are inadequately resuscitated despite the return to normal of conventional hemodynamic measurements. The serial analysis of PsgO2 may assist in managing patients and promote better understanding of the responses to injury.
The influence of inhibiting the nitric oxide (NO) synthetase on tissue perfusion as indicated by tissue oxygen tensions was determined. Tissue oxygen probes were placed subcutaneously and on serosal and mucosal surfaces of colon of anesthetized adult rats. After a control period, the inhibitor of NO formation, N(G)-nitro-L-arginine methyl ester (L-NMMA), was given intravenously and followed 20 min later by infusion of substrate for NO synthetase, L-arginine. Mean arterial blood pressure (MAP), subcutaneous tissue oxygen tension (P(SQ)O2), serosal tissue oxygen tension (P SO(2)), and mucosal tissue oxygen tension (P(M)O2) were simultaneously measured. Baseline values for the measured parameters were MAP = 95 + or - 9 mmHg, P(SQ)O2 = 61 + or - 7 mmHg, P(S)O2 65 + or - 7 mmHg, and P(M)02 = 9 + or - 2 mmHg. The infusion of L-NMMA induced a significant increase in MAP to 123 + or - 7 mmHg (p < .001) and P(SQ)O2 to 72 + or - 7 mmHg (p < .001). P(S)O2 did not change significantly from baseline after L-NMMA infusion. A significant decrease in P(M)O2 to 4 + or - 2 mmHg was noted after L-NMMA infusion (p < .001). The administration of L-arginine promptly returned all measured parameters to baseline levels within 10 min of infusion. A transmural P(O2) gradient exists across the colon with P(M)O2 far lower than P(S)O2. P(SQ)O2 approximates P(S)O2 at baseline and P(S)O2 is not altered by inhibition of the NO synthetase. The 45% reduction in mucosal PO2 after L-NMMA, which was reversed by L-arginine infusion, suggests that nitric oxide participates in splanchnic vasomotor control with a preferential effect in the mucosal vasculature. The observed decrease in mucosal PO2 observed after inhibition of NO production is similar to the worsened hypoxia previously measured during hemorrhagic shock. Further work clarifying the local control mechanisms of gut tissue P02 can direct therapies to increase gut tissue oxygenation.
Injury and inflammation lead to hypoxia and elevated lactate in wounds. This redox environment establishes cells in a reparative phenotype and leads macrophages to release angiogenic substances by unclear mechanisms. We investigated compounds known to modulate polyadenosine diphophoribose (pADP-R) levels in their effect on macrophage-derived angiogenic activity. Macrophages cultured from rabbit bone marrow were exposed to lactate, nicotinamide, and/or beta-nicotinamide adenine dinucleotide (NAD+). Supernatants were assayed for angiogenesis, and macrophages were analyzed for NAD+ content, poly(ADP-ribose) synthetase activity, and total (ADP-ribose)n synthesis. Lactate-, nicotinamide-, and lactate and nicotinamide-treated macrophages elicited significantly increased angiogenic activity compared with control or NAD+-treated cells. Lactate treatment decreased NAD+ content by 42 +/- 4% and (ADP-ribose)n synthesis by 37 +/- 5%. Nicotinamide reduced poly(ADP-ribose) synthetase activity and poly(ADP-ribose) synthesis. Thus, macrophage-derived angiogenic activity may be mediated by the redox environment involving NAD+ metabolites.
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OBJECTIVES: To develop a reproducible model to measure transmural gut tissue PO2, to determine the gradient from serosa to mucosa during normovolemia and hypovolemia, and to determine the effect of resuscitation with heparan sulfate (danaparoid sodium) on this gradient. DESIGN: Fluorescent tissue oxygen sensors were placed onto serosal and mucosal surfaces of rat colon. Hemorrhagic shock was induced using a fixed pressure (mean arterial pressure, 40 mm Hg) model and resuscitated with either saline solution or heparan. RESULTS: Control animals had stable mean (+/- SD) serosal and mucosal tissue oxygen tensions (PO2) of 64 +/- 4 and 10 +/- 2 mm Hg, respectively. In shocked animals, baseline serosal PO2 decreased to 37 +/- 2 mm Hg at a mean (+/- SD) of 19 +/- 7 minutes after the initiation of hemorrhage. Mucosal values decreased to a minimum of 4 +/- 2 mm Hg at 45 +/- 15 minutes after the initiation of hemorrhage. Serosal PO2 returned to baseline during resuscitation in both control and heparan-resuscitated animals. Mucosal PO2 did not return to baseline in the shock/no heparan group. In the heparan-resuscitated animals, however, mucosal PO2 increased above baseline (13 +/- 3 mm Hg at 3 hours after completion of hemorrhage). CONCLUSIONS: A transmural gradient of PO2 exists across the colon with mucosal PO2 far lower than serosal PO2. Both serosal and mucosal PO2 decrease during hypovolemia. During hypovolemia, the PO2 of the entire gut wall is in a range in which phagocytic killing is impaired by hypoxia. Heparan improved mucosal PO2 and it may restore and/or protect gut function by oxygen-related mechanisms.
Complications of irradiated tissue include infections and impaired healing. Although fibrosis and hypovascularity contribute, a cellular mechanism has not been identified. This study examines the effect of radiation (10 to 30 Gy) on neutrophil function in a rabbit wound cylinder model. At 3 to 12 weeks after radiation, subcutaneous wound cylinders were implanted in both irradiated and control fields in 19 rabbits. Wound neutrophils were subsequently assayed for phagocytosis (3H-labeled Staphylococcus aureus assay), superoxide production (cytochrome c reduction assay), and surface Mac-1 expression (flow cytometric assay using MHM 23 monoclonal antibody). Phagocytosis of 3H-labeled S. aureus was significantly lower in neutrophils from irradiated fields compared with controls at 6 and 12 weeks after radiation (6.5 versus 18.9 bacteria per neutrophil at 12 weeks; p = 0.027). Stimulated neutrophils from irradiated tissue could not increase superoxide production or Mac-1 expression as much as controls, with differences increasing as postirradiation time increased. The diminished phagocytosis, superoxide production, and Mac-1 expression provide a cellular mechanism that may account for susceptibility to infection and poor healing in irradiated tissues.
Macrophages are a source of cytokines driving repair. Wound macrophages are derived from circulating monocytes. Monocyte chemotactic protein-1 (MCP-1) is a potent specific monocyte chemoattractant. Treatment of serum stimulated dermal fibroblasts with dexamethasone led to a dose dependent down-regulation of MCP-1 mRNA levels. Such an anti-inflammatory effect may partially explain the negative influence of glucocorticoid treatment on wound repair. Topical or parenteral of fibroblasts cultured in serum free media with TGF-beta increased MCP-1 mRNA levels. TGF-beta treatment of fibroblasts cultured in serum also partially overcame the dexamethasone mediated decrease in MCP-1 mRNA levels. In glucocorticoid treated animals TGF-beta may stimulate repair by an indirect pro-inflammatory action following transcriptional up-regulation of MCP-1.