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Biomedical subjects

K A Mitchell

Publications and source records attributed to K A Mitchell.

At least 19 recordsLinked to original sources
PubMed2004

Chaos-induced pulse trains in the ionization of hydrogen.

We predict that a hydrogen atom in parallel electric and magnetic fields, excited by a short laser pulse to an energy above the classical saddle, ionizes via a train of electron pulses. These pulses are a consequence of classical chaos induced by the magnetic field. We connect the structure of this pulse train (e.g., pulse size and spacing) to fractal structure in the classical dynamics. This structure displays a weak self-similarity, which we call "epistrophic self-similarity." We demonstrate how this self-similarity is reflected in the pulse train.

Journal Article↗
PubMed2003

Geometry and topology of escape. I. Epistrophes.

We consider a dynamical system given by an area-preserving map on a two-dimensional phase plane and consider a one-dimensional line of initial conditions within this plane. We record the number of iterates it takes a trajectory to escape from a bounded region of the plane as a function along the line of initial conditions, forming an "escape-time plot." For a chaotic system, this plot is in general not a smooth function, but rather has many singularities at which the escape time is infinite; these singularities form a complicated fractal set. In this article we prove the existence of regular repeated sequences, called "epistrophes," which occur at all levels of resolution within the escape-time plot. (The word "epistrophe" comes from rhetoric and means "a repeated ending following a variable beginning.") The epistrophes give the escape-time plot a certain self-similarity, called "epistrophic" self-similarity, which need not imply either strict or asymptotic self-similarity.

Fractals↗
PubMed2003

Geometry and topology of escape. II. Homotopic lobe dynamics.

We continue our study of the fractal structure of escape-time plots for chaotic maps. In the preceding paper, we showed that the escape-time plot contains regular sequences of successive escape segments, called epistrophes, which converge geometrically upon each end point of every escape segment. In the present paper, we use topological techniques to: (1) show that there exists a minimal required set of escape segments within the escape-time plot; (2) develop an algorithm which computes this minimal set; (3) show that the minimal set eventually displays a recursive structure governed by an "Epistrophe Start Rule:" a new epistrophe is spawned Delta=D+1 iterates after the segment to which it converges, where D is the minimum delay time of the complex.

Algorithms↗
PubMed2001

Flavonoid characters contributing to the taxonomic revision of the Hebe parviflora complex.

Comparative flavonoid chemistry is a key element of a multidisciplinary study aimed at a revision of the genus Hebe, New Zealand's largest genus of flowering plants. One aspect of this study has been an investigation of the Hebe parviflora complex. A recent botanical paper on this topic marshalls generalised flavonoid data and morphological characters to support the recognition of two species in this complex, Hebe stenophylla and Hebe parviflora, which are clearly distinguishable from each other and from the related Hebe traversii and Hebe strictissima. A detailed study of the flavonoid chemistry and the distributional data used to support these conclusions are presented here. Six new compounds have been isolated in this study, including 6-hydroxyapigenin-7-O-beta-[2-O-beta-xyloxyloside] and-7-O-beta-[2-O-beta-xyloglucoside], 6-hydroxyluteolin-7-O-beta-[2-O-beta-xyloxyloside] and, luteolin-, 6-hydroxyluteolin- and 4'-O-methylluteolin-7-O-beta-[6-O-beta-xyloglucoside]. Other flavonoids include apigenin and luteolin 7- and 4'- mono-, di- and possibly tri-O-glycosides, 8-hydroxyluteolin 7- and 8-O-glucosides, and kaempferol and quercetin 3-O-mono- and di-glycosides. New structure assignments are supported with detailed 1H and 13C NMR data, including HMQC and HMBC measurements.

Chromatography, High Pressure Liquid↗
PubMed2001

Epidemic increases in cocaine and opiate use by trauma center patients: documentation with a large clinical toxicology database.

BACKGROUND: Although reports have documented alcohol and other drug use by trauma patients, no studies of long-term trends have been published. We assessed substance use trends in a large cohort of patients admitted to a regional Level I adult trauma center between July 1984 and June 2000. METHODS: Positive toxicology results, collected via retrospective database review, were analyzed for patients admitted directly to the center. Data were abstracted from a clinical toxicology database for 53,338 patients. Results were analyzed for alcohol, cocaine, and opiates relative to sex, age (< 40/> or = 40 years), and injury type (nonviolence/violence). Positive toxicology test result trends were assessed for the 3 years at the beginning and end of the period (chi2). Testing biases were assessed for sex, race, and injury type. RESULTS: The patient profile was as follows: men, 72%; age < 40 years, 69%; nonviolence victims, 77%. Alcohol-positive results decreased 37%, but cocaine-positive and opiate-positive results increased 212% and 543%, respectively (all p < 0.001). Cocaine-positive/opiate-positive results increased 152%/640% for nonviolence and 226%/258% for violence victims, respectively (all p < 0.001). In fiscal year 2000, cocaine-positive and opiate-positive results were highest among violence victims (27.4% for both drugs). Cocaine-positive and opiate-positive results among nonviolence victims were 9.4% and 17.6%, respectively. Patients who were minorities or victims of violence were not tested more frequently than other patients. CONCLUSION: Epidemic increases in cocaine and opiate use were documented in all groups of trauma patients, with the greatest increases being in violence victims. Alcohol use decreased for all groups.

Adult↗
PubMed2001

A longitudinal study of former trauma center patients: the association between toxicology status and subsequent injury mortality.

BACKGROUND: Despite the current emphasis on injury prevention, little has been done to incorporate alcohol intervention programs into the care of the injured patient. The purpose of this study was to determine whether patients admitted to a trauma center with positive toxicology findings (TOX+) have a higher subsequent injury mortality than those without such findings (TOX-). METHODS: We followed a cohort of 27,399 trauma patients discharged alive between 1983 and 1995 to determine subsequent mortality. Death certificates were obtained to identify the cause of death. RESULTS: TOX+ patients had an injury mortality rate approximately twice that of the TOX- group (1.9% vs. 1.0%, p < 0.001). Overall, 22.7% of the deaths were due to injury; the TOX+ rate was 34.7% versus 15.4% for the TOX-. CONCLUSION: These data add strength to the premise that untreated substance abuse-related injury remains an untapped injury prevention opportunity.

Adolescent↗
PubMed2000

Anthocyanic vacuolar inclusions--their nature and significance in flower colouration.

The petals of a number of flowers are shown to contain similar intensely coloured intravacuolar bodies referred to herein as anthocyanic vacuolar inclusions (AVIs). The AVIs in a blue-grey carnation and in purple lisianthus have been studied in detail. AVIs occur predominantly in the adaxial epidermal cells and their presence is shown to have a major influence on flower colour by enhancing both intensity and blueness. The latter effect is especially dramatic in the carnation where the normally pink pelargonidin pigments produce a blue-grey colouration. In lisianthus, the presence of large AVIs produces marked colour intensification in the inner zone of the petal by concentrating anthocyanins above levels that would be possible in vacuolar solution. Electron microscopy studies on lisianthus epidermal tissue failed to detect a membrane boundary in AVI bodies. AVIs isolated from lisianthus cells are shown to have a protein matrix. Bound to this matrix are four cyanidin and delphinidin acylated 3,5-diglycosides (three, new to lisianthus), which are relatively minor anthocyanins in whole petal extracts where acylated delphinidin triglycosides predominate. Flavonol glycosides were not bound. A high level of anthocyanin structural specificity in this association is thus implied. The specificity and effectiveness of this anthocyanin "trapping" is confirmed by the presence in the surrounding vacuolar solution of only delphinidin triglycosides, accompanied by the full range of flavonol glycosides. "Trapped" anthocyanins are shown to differ from solution anthocyanins only in that they lack a terminal rhamnose on the 3-linked galactose. The results of this study define for the first time the substantial effect AVIs have on flower colour, and provide insights into their nature and their specificity as vacuolar anthocyanin traps.

Anthocyanins↗
PubMed2000

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) suppresses the humoral and cell-mediated immune responses to influenza A virus without affecting cytolytic activity in the lung.

The immune response to influenza virus is exquisitely sensitive to suppression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD); however, the cellular mechanisms underlying the suppressive effects of TCDD are unknown. Mice exposed to TCDD exhibited a dose-responsive increase in mortality following an otherwise non-lethal influenza virus infection. Given that cytotoxic T lymphocytes (CTL) are generally thought to resolve primary infections in the lung, we tested the hypothesis that exposure to TCDD suppresses T-cell responsiveness, leading to decreased CTL in the lung. After infection with influenza virus, naive CD8+ lymphocytes are activated and differentiate in the mediastinal lymph node (MLN). In mice exposed to TCDD and infected with influenza virus, the number of CD8+ MLN cells was reduced 60% compared to vehicle-treated mice. Moreover, MLN cells from TCDD-treated mice failed to develop cytolytic activity, and the production of interleukin (IL)-2 and interferon (IFN)-gamma was suppressed. Exposure to TCDD also altered the production of virus-specific antibodies, decreased the recruitment of CD8+ cells to the lung, reduced the percentage and number of bronchoalveolar lavage cells bearing a CTL phenotype (CD8+CD44hiCD62L(l) degrees ), and suppressed IL-12 levels in the lung. Despite our findings that exposure to TCDD suppressed T cell-dependent functions, the cytolytic activity of lung lavage cells from TCDD and vehicle treated mice was equivalent, and IFN gamma levels in the lungs of mice treated with TCDD were enhanced 10-fold. Thus, while exposure to TCDD suppressed a number of responses associated with the development of adaptive immunity to influenza virus, a direct link between these effects and enhanced susceptibility to influenza remains unclear.

Animals↗
PubMed2000

External fixation as a bridge to intramedullary nailing for patients with multiple injuries and with femur fractures: damage control orthopedics.

BACKGROUND: The advantages of early fracture fixation in patients with multiple injuries have been challenged recently, particularly in patients with head injury. External fixation (EF) has been used to stabilize pelvic fractures after multiple injury. It potentially offers similar benefits to intramedullary nail (IMN) in long-bone fractures and may obviate some of the risks. We report on the use of EF as a temporary fracture fixation in a group of patients with multiple injuries and with femoral shaft fractures. METHODS: Retrospective review of charts and registry data of patients admitted to our Level 1 trauma center July of 1995 to June of 1998. Forty-three patients initially treated with EF of the femur were compared to 284 patients treated with primary IMN of the femur. RESULTS: Patients treated with EF had more severe injuries with significantly higher Injury Severity Scores (26.8 vs. 16.8) and required significantly more fluid (11.9 vs. 6.2 liters) and blood (1.5 vs. 1.0 liters) in the initial 24 hours. Glasgow Coma Scale score was lower (p < 0.01) in those treated with EF (11 vs. 14.2). Twelve patients (28%) had head injuries severe enough to require intracranial pressure monitoring. All 12 required therapy for intracranial pressure control with mannitol (100%), barbiturates (75%), and/or hyperventilation (75%). Most patients had more than one contraindication to IMN, including head injury in 46% of cases, hemodynamic instability in 65%, thoracoabdominal injuries in 51%, and/or other serious injuries in 46%, most often multiple orthopedic injuries. Median operating room time for EF was 35 minutes with estimated blood loss of 90 mL. IMN was performed in 35 of 43 patients at a mean of 4.8 days after EF. Median operating room time for IMN was 135 minutes with an estimated blood loss of 400 mL. One patient died before IMN. One other patient with a mangled extremity was treated with amputation after EF. There was one complication of EF, i.e., bleeding around a pin site, which was self-limited. Four patients in the EF group died, three from head injuries and one from acute organ failure. No death was secondary to the fracture treatment selected. One patient who had EF followed by IMN had bone infection and another had acute hardware failure. CONCLUSION: EF is a viable alternative to attain temporary rigid stabilization in patients with multiple injuries. It is rapid, causes negligible blood loss, and can be followed by IMN when the patient is stabilized. There were minimal orthopedic complications.

Adolescent↗
PubMed1999

Early fracture fixation may be "just fine" after head injury: no difference in central nervous system outcomes.

BACKGROUND: Recent reports suggest that early fracture fixation worsens central nervous system (CNS) outcomes. We compared discharge Glasgow Coma Scale (GCS) scores, CNS complications, and mortality of severely injured adults with head injuries and pelvic/lower extremity fractures treated with early versus delayed fixation. METHODS: Using trauma registry data, records meeting preselected inclusion criteria from the years 1991 to 1995 were examined. We identified 171 patients aged 14 to 65 years (mean age, 32.7 years) with head injuries and fractures who underwent early fixation (< or = 24 hours after admission) (n = 147) versus delayed fixation (> 24 hours after admission) (n = 24). RESULTS: Patients were severely injured, with a mean admission GCS score of 9.1, Revised Trauma Score of 6.2, Injury Severity Score of 38, median intensive care unit length of stay of 16.5 days, and hospital length of stay of 23 days. No differences between groups were found by age, admission GCS score, Injury Severity Score, Revised Trauma Score, intensive care unit length of stay, hospital length of stay, shock, vasopressors, major nonorthopedic operative procedures, total intravenous fluids or blood products, or mortality rates. In survivors, no differences in discharge GCS scores or CNS complications were found. CONCLUSION: We found no evidence to suggest that early fracture fixation negatively influences CNS outcomes or mortality.

Adolescent↗
PubMed1994

Evaluation of minor head injury in children.

The authors' goal was to determine criteria for hospitalization for children with minor head injuries. A retrospective review was performed of the hospital records of 401 children with isolated minor head injuries who were admitted to a level I pediatric trauma center between July 1988 and December 1990. Specific information regarding each patient was documented, including demographic data, pertinent physical findings, diagnostic studies, criteria for admission, and hospitalization costs. Fifty-one patients with a mechanism of injury compatible with minor head injury, a brief or no loss of consciousness, a Glasgow coma score of 15, and no abnormalities on radiographic examination did not have neurological complications. The authors believe that these 51 patients could have been discharged from the hospital to responsible parents, thereby decreasing the costs of hospitalization. Prospective studies to substantiate these data and determine which patients should be hospitalized are warranted.

Child↗
PubMed1994

Flail chest as a marker for significant injuries.

The records of 92 patients with flail chest injury treated at a Level I trauma center were analyzed retrospectively. Associated intrathoracic injuries included pulmonary contusion (46 percent) and pneumothorax or hemothorax, or both (70 percent). The incidence of great vessel, tracheobronchial and diaphragmatic injuries was no different from that of a control population with simple rib fractures. Adult respiratory distress syndrome developed in 27 percent of patients with flail chest; 69 percent of all patients required ventilation (mean duration, 22 days). Mean length of hospital stay was 24 days. The mortality rate was 33 percent. We conclude that flail chest serves as a marker of significant intrathoracic injury, highly associated with pulmonary contusion, but even more so with pneumothorax or hemothorax. Flail chest does not seem to be a marker for great vessel, tracheobronchial, or diaphragmatic injuries. The majority of patients (more than two-thirds) will require mechanical ventilation for prolonged periods. Of paramount importance is the recognition of flail chest as a marker of high kinetic energy absorption, resulting in life-threatening thoracic as well as nonthoracic injuries.

Adult↗
PubMed1992

Surgical complications and procedures in neonates on extracorporeal membrane oxygenation.

We report our experience from May 1985 to January 1991 with surgical complications and procedures performed in neonates on extracorporeal membrane oxygenation (ECMO) (218 venoarterial and 7 venovenous bypass). Eleven children older than 1 month were excluded. Total complications were 96 in 67 patients and included: bleeding (37), problems with initial cannula placement (17), thrombus formation (15), hemothorax, pneumothorax, or effusions (11), mechanical problems (11), and miscellaneous (5). Forty-eight procedures were performed in 37 patients while on ECMO. These were recannulation or reposition of cannulas (14), tube thoracostomy (11), cardiac surgery (6), cardiac catheterization (4), repair of congenital diaphragmatic hernia (5), thoracotomy (4), and others. Twenty-eight complications occurred in 15 of the 27 patients who died. Mortality rate was 12% for the entire group. Primary causes of death were hypoplastic lung (11), cardiac (8), sepsis (4), intraventricular hemorrhage (2), and pulmonary hypertension (2). No deaths were due solely to complications except for the two patients with intraventricular hemorrhage. Mortality in neonates who had complications while on ECMO was significantly higher (P less than .005) than in patients without complications. Hemorrhagic and thoracic complications were associated with higher mortality (P less than .001). Mortality was not affected by mechanical problems, thrombus formation, or catheter-related problems. While on ECMO cardiac defects, diaphragmatic hernia, lobar emphysema, and other conditions can be safely corrected. The use of echocardiography to position the cannulas, better control of coagulation factors and improvement in equipment may ultimately decrease complications.

Evaluation Studies as Topic↗
PubMed1992

Pre-existing disease in trauma patients: a predictor of fate independent of age and injury severity score.

Improvement in trauma management requires a better understanding of the effect of a patient's preinjury health status on outcome. Specific historical findings and laboratory criteria were used to define pre-existing disease (PED) states and determine if they were independent predictors of fate in trauma victims. Of 7,798 adult patients admitted to a level I trauma center from July 1986 through June 1990, 16.0% (1,246) had greater than or equal to 1 PED. The PED+ and PED- patients had no significant difference in Injury Severity Scores (ISSs) (15.7 versus 15.6) and admission Glasgow Coma Scale (GCS) scores (13.9 versus 13.8). The PED+ patients were older (49.2 versus 30.6 years) (p less than 0.001) and had a higher mortality rate (9.2% versus 3.2%) (p less than 0.001) than PED- patients. Mortality rates were also elevated for patients with greater than or equal to 2 PEDs (18%) and for those with renal disease (38%), malignancy (20%), and cardiac disease (18%) (p less than 0.001) compared with PED- patients. Controlling for age and ISS, there was an association between PED and mortality (Mantel-Haenszel p less than 0.03). Multivariate regression showed that PED is an independent predictor of mortality (R2 = 0.1918; p less than 0.0001). The greatest increases in mortality were found among patients less than 55 years and with ISS less than 20. Changes in prehospital triage criteria and outcome scoring are needed. Improvements in the management of trauma victims with chronic disease may decrease their mortality rate.

Adult↗
PubMed1991

The characterisation of thrombus development in an improved model of arterio-venous shunt thrombosis in the rat and the effects of recombinant desulphatohirudin (CGP 39393), heparin, and iloprost.

An existing arterio-venous shunt thrombosis model in the rat has been modified to increase its usefulness for the testing of anti-thrombotic agents and characterised using morphological and radiometric techniques. The thrombus formed on the cotton thread held in the shunt was found to be composed of platelet aggregates surrounded by red thrombus. After 30 min of blood flow there was a 15-fold increase in the platelet content of the thrombus and a 4-fold increase in the fibrin(ogen) content compared with an equivalent weight of whole blood. Use of the anticoagulants recombinant desulphatohirudin (CGP 39393, 4 mg/kg, s.c.) and unfractionated heparin (800 IU/kg, s.c.) showed that approx. 90% inhibition of thrombus weight and approx. 80% inhibition of fibrin(ogen) content could be achieved without significant effect on the platelet content. Conversely, using the platelet inhibitor Iloprost (1 microgram kg-1 min-1), a reduction in thrombus weight of 50% was associated with 75% inhibition of platelet content and only 20% inhibition of fibrin(ogen). These observations suggest that the growth of this type of thrombus is largely the result of continued fibrin formation rather than continued platelet recruitment and activation.

Animals↗