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Biomedical subjects

C K Stone

Publications and source records attributed to C K Stone.

At least 19 recordsLinked to original sources
PubMed1997

A rather intense source of fast neutrons for small scale activation.

A thick beryllium target has been developed for installation onto a small proton cyclotron (CTI RDS 112), providing an intense source of fast neutrons for activation purposes. Careful attention was paid to cooling and irradiation geometry, allowing cubic centimeter scale samples to approach the proton beam strike surface to within 5 mm. This proximity assures approximately equal to 10(11) neutron/s passing through the irradiated sample when 20 microgramsA of 11 MeV protons are incident on the beryllium primary target.

Beryllium↗
PubMed1997

Population density, automated external defibrillator use, and survival in rural cardiac arrest.

OBJECTIVE: To determine whether population density is an independent predictor of survival from out-of-hospital cardiac arrest managed by basic life support (BLS) services using automated external defibrillators (AEDs). METHODS: A retrospective, observational study in Kentucky of 34 BLS services covering 22 counties during the years 1992 to 1994 who used AEDs to treat patients who had out-of-hospital cardiac arrests. RESULTS: Of 311 patients who had out-of-hospital cardiac arrests, 110 (35%) were defibrillated, 46 (15%) were resuscitated to hospital admission, and 19 (6%) survived to hospital discharge. Univariate predictors for survival to hospital discharge were emergency medical services response interval (from call receipt to ambulance arrival) < 8 minutes, defibrillation by the AED, initial rhythm of ventricular fibrillation or ventricular tachycardia (VF/VT), and population density > 100/square mile (sq mi) for the BLS service area (p < 0.001). A forced logistic regression model of survival to hospital discharge, using these 4 factors plus the presence of a witnessed arrest or bystander CPR, demonstrated that population density > 100/sq mi was highly significant (OR 9.4, 95% CI: 1.7 to 51.4, p < 0.01). Stepwise logistic regression models with combinations of these 6 factors found that survival to hospital discharge was best predicted by an initial rhythm of VF/VT (p = 0.004) and population density > 100/sq mi (p = 0.011). CONCLUSIONS: Population density is strongly associated with survival from out-of-hospital cardiac arrest. BLS services within areas with population densities < or = 100/sq mi sustained little benefit from the addition of AEDs to their treatment of patients who had out-of-hospital cardiac arrests.

Aged↗
PubMed1996

Cardiac dysrhythmias in severe verapamil overdose: characterization with a canine model.

Verapamil overdose, because of its frequency and severity, represents a significant problem for the emergency physician. With recent search recommending specific therapies for verapamil toxicity, aids to rapid diagnosis hold promise for decreasing morbidity and mortality from overdose of all calcium channel blockers. At this time, diagnosis of verapamil toxicity depends primarily on patient history and identification of cardiac dysrhythmias. This study attempts to improve the diagnostic armamentarium available for verapamil poisoning by analysing cardiac conduction problems seen in a canine model of verapamil toxicity, with the goal of identifying clinically useful dysrhythmia patterns. In 43 verapamil-toxic animals, junctional rhythm without organized atrial activity was the most frequently identified rhythm (55.6%). The next most commonly seen rhythms were tertiary atrioventricular (AV) block (16.3%) and idioventricular rhythm (11.6%); other animals manifested low grade AV block. Of interest, prominent U waves were noted in 25.6% of animals. While these results are subject to the limitations inherent in the use of an animal model, the data generated provide potentially useful patterns of dysrhythmia which may be encountered in humans with verapamil toxicity.

Animals↗
PubMed1996

Glucagon and phenylephrine combination vs glucagon alone in experimental verapamil overdose.

OBJECTIVE: To evaluate glucagon and phenylephrine in combination as a treatment for the hemodynamic effects of verapamil overdose. METHODS: Pentobarbital-anesthetized and instrumented dogs were overdosed using a previously developed verapamil overdose model (15 mg/kg IV over 30 minutes). The animals were maintained and observed for 90 minutes or until death. Cardiac output (CO), heart rate (HR), and mean arterial pressure (MAP) were monitored. Following the 30-minute verapamil infusion (toxicity), the control animals received no treatment; the glucagon animals received a 5-mg glucagon bolus and a drip of 5 mg/90 minutes; and the glucagon/phenylephrine animals received the same glucagon therapy plus a phenylephrine drip titrated to 180 micrograms/min over 15 minutes. The groups were compared using analysis of variance: the experimental variables were group and time; the response variables were changes from toxicity for the hemodynamic parameters. Post-hoc comparisons were done with alpha set at 0.05. RESULTS: A significant change in CO was seen in the glucagon group (delta = 2.6 L/min) and the glucagon/phenylephrine group (delta = 1.9 L/min) compared with the control group (delta = 0.8 L/min). The change in CO was significantly larger for the glucagon animals compared with the glucagon/phenylephrine animals. The change in MAP for the glucagon/phenylephrine group (delta = 24 mm Hg) was significant compared with the control group (delta = 14 mm Hg). The MAP change for the glucagon group (delta = 19 mm Hg) was not significantly different from that of either the control or the glucagon/phenylephrine group. The change in glucagon HR (delta = 6 beats/min) was significant compared with the control group (delta = -4 beats/min) and the glucagon/phenylephrine group (delta = -4 beats/min). CONCLUSION: The glucagon/phenylephrine therapy improved MAP compared with the control, but reduced CO and HR compared with glucagon alone. Glucagon/phenylephrine therapy is not as effective as glucagon alone in reversing the hemodynamic effects of experimental verapamil overdose.

Adrenergic alpha-Agonists↗
PubMed1996

Rate of patient workups by non-emergency medicine residents in an academic emergency department.

OBJECTIVE: To quantify the number of patients seen per hour by non-emergency medicine (non-EM) residents in a university hospital ED. METHODS: This retrospective observational study was performed in a university hospital ED and level I trauma center. The facility had no EM residency, but was staffed with 24-hour EM faculty coverage. A computerized tracking system was searched for the number of patients seen by each of 93 non-EM residents for 12 nonconsecutive months. The ED schedule for each month was used to calculate the number of hours worked by each resident. From these figures, the number of patients seen per hour by each resident was calculated. RESULTS: The postgraduate years of training of the residents were as follows: 78 (84%) were PGY1, ten (11%) were PGY2, and five (5%) were PGY3. All the residents combined saw a mean 0.95 +/- 0.20 patients/hour, with a range from 0.58 to 1.75 patients/hour. There was no significant difference between the numbers of patients seen when compared by specialty using the Tukey-Kramer test (alpha = 0.05). CONCLUSION: The rate at which non-EM residents work up patients is consistent with previously reported rates for EM residents.

Education, Medical, Graduate↗
PubMed1996

Amrinone as an antidote in experimental verapamil overdose.

OBJECTIVE: To evaluate the effect of amrinone as a treatment for the hemodynamic effects of verapamil overdose in a canine model. METHODS: This nonblind interventional study was performed in an established canine model of verapamil toxicity, without concurrent control animals. Pentobarbital-anesthetized and instrumented dogs (n = 8) were maintained and observed for 60 minutes or until death. The animals were overdosed with verapamil, 15 mg/ kg IV, over 30 minutes. Hemodynamic parameters, including cardiac index (CI), heart rate (HR), and mean arterial pressure (MAP), were monitored. Completion of the verapamil infusion represented the defined point of toxicity; at that point, all the animals received an amrinone bolus of 2 mg/kg IV over 2 minutes followed by an amrinone drip at 10 micrograms/kg/min. The hemodynamic values at the defined point of toxicity were compared with those obtained postinitiation of the amrinone infusion. RESULTS: Two animals died before the 60-minute observation period elapsed. Baseline CI was 5.6 L/min/m2. Following verapamil-induced toxicity, mean CI was 2.2 L/min/m2. After administration of amrinone, a significant (p < 0.05) increase in CI was observed at 30 minutes (CI = 3.6 L/min/m2), 45 minutes (CI = 4.2 L/ min/m2), and 60 minutes (CI = 4.2 L/min/m2). There was no statistically significant difference noted for MAP or HR compared with "point of toxicity" values. CONCLUSION: Amrinone appears to reverse the depressed cardiac index associated with verapamil overdose in a canine model while having no significant effect on the hypotension or bradycardia.

Amrinone↗
PubMed1996

Sherpa brain glucose metabolism and defense adaptations against chronic hypoxia.

The brain of hypoxia-tolerant vertebrates is known to survive extreme oxygen limitation at least in part because of very low rats of ATP utilization and ATP production. To asses whether similar adaptations are involved in healthy humans during hypoxia adaptation over generational time, we initially used positron-emission tomography measurements of glucose metabolic rates in the brain of Quechuas, whose ancestors have been indigenous to the Andes at altitudes between approximately 3,300 and 4,500 m for several hundred years. Workers in this field generally believe that the lineage of Sherpas has been indigenous to the Himalayas for even longer and that Sherpas and other peoples indigenous to the Tibetan plateau are perhaps the most exquisitely hypoxia adapted of all humans. For this reason, in this study we extended our database to include Sherpas. With the use of the same protocol as before, two metabolic states were analyzed: 1) the presumed normal (hypoxia-adapted) state, monitored as soon as possible after subjects left the Himalayas and 2) the deacclimated state, monitored after 3 wk at low altitudes. Positron-emission tomography measurements of 2-[18F]deoxy-2-fluoro-D-glucose metabolic rates, quantified in 26 regions of the brain, indicated that the Sherpas' brain metabolism differed significantly from that of Quechuas but was essentially identical to that of lowlanders. Region-by-region patterns were similar in all three groups, indicating that the regional organization of glucose metabolism in the brain is a conservative, relatively constant characteristic.

Adaptation, Physiological↗
PubMed1995

Myocardial kinetics of a putative hypoxic tissue marker, 99mTc-labeled nitroimidazole (BMS-181321), after regional ischemia and reperfusion.

BACKGROUND: A new nitroimidazole complex, 99mTc-propylene amine oxime-1,2-nitroimidazole (BMS-181321), has been developed to allow the positive imaging of hypoxic myocardium by standard gamma camera techniques. METHODS AND RESULTS: To determine the myocardial kinetics of BMS-181321 during myocardial ischemia and reperfusion, seven open-chest swine were prepared according to a model of extracorporeal coronary perfusion in which left ventricular wall thickening (percent end-diastolic thickness) and substrate use in the left anterior descending (LAD) region ([14C]palmitate and [3H]glucose infusions) were determined. Measurements were obtained at baseline, during 40 minutes of ischemia produced by reducing flow in the LAD distribution by 60%, and during 70 minutes of reperfusion. Three aerobic control hearts were also studied in which LAD blood flow was not reduced. Regional coronary circulation was further assessed in all hearts by use of radiolabeled microspheres injected during ischemia. BMS-181321 (20 to 30 mCi) was injected after 30 minutes of ischemia, and its myocardial uptake was assessed by dynamic planar gamma imaging. Ischemia was associated with declines in fatty acid metabolism (15 +/- 11 mumol.h-1.g dry wt-1, mean +/- SEM), systolic wall thickening (20 +/- 6%), and myocardial oxygen consumption (3 +/- 1 mL.min-1.100 g-1) and an increase in exogenous glucose utilization (75 +/- 13 mumol.h-1.g dry wt-1). Systolic wall thickening recovered by only 8 +/- 3% with reperfusion. Initial distribution of BMS-181321 in the aerobic hearts appeared homogeneous. Washout from the ischemic and reperfused LAD bed was slower than the aerobically perfused LAD bed in the control group (t1/2 = 136 +/- 1 versus 80 +/- 1 minutes, P < .05), allowing visualization of the LAD region during reperfusion. Tissue activity of BMS-181321 was inversely related to LAD blood flow during ischemia (r = -.68 +/- .05), and the ratio of BMS-181321 in the LAD region versus normal myocardium was 1.7 +/- 0.2. Control swine lacked regional deposition of the tracer in the normally perfused LAD distribution. CONCLUSIONS: Thus, acute regional ischemia in these studies was visualized as an increase in retention of BMS-181321, suggesting its applicability in the imaging of clinical conditions of myocardial hypoperfusion.

Animals↗
PubMed1995

Utilization of a pressure-sensing monitor to improve in-flight chest compressions.

Previous research at the Division of Air Medical Services at East Carolina University School of Medicine has demonstrated impairment of chest compression efficacy in the setting of an airborne BO-105 helicopter. This study was undertaken to determine whether in-flight compression efficacy could be improved with utilization of a pressure-sensing monitor providing real-time feedback during cardiopulmonary resuscitation (CPR). Ten flight nurses each performed two minutes of in-flight chest compressions on a mannequin that electronically assessed compression depth and hand placement. The session was then repeated using the pressure-sensing device. The mean proportion of correct compressions (95.7 +/- 3.2%) achieved with utilization of the pressure-sensing monitor was significantly higher (P < .01) than the corresponding proportion for the control group (33.4 +/- 12.1%). This study demonstrated that the difficulties of performing effective in-flight chest compressions are largely overcome with utilization of a pressure-sensing device providing real-time feedback on compression efficacy.

Aerospace Medicine↗
PubMed1995

Exacerbation of verapamil-induced hyperglycemia with glucagon.

To evaluate the effects of verapamil intoxication and glucagon treatment on blood glucose levels in an intact canine model, 15 mg/kg verapamil was administered intravenously over a 30-minute period to mongrel dogs under pentobarbital anesthesia. Animals in the experimental group subsequently were administered 2.5 mg glucagon followed by an infusion of 2.5 mg per hour; control group animals were administered an equal volume of saline. Blood glucose was assessed before verapamil administration (baseline), and at 10 minutes (time 10) and 60 minutes (time 60) after completion of the verapamil infusion. Glucose values were compared between control and experimental groups using Dunnett's method (P = .05). At baseline, no animals were hyperglycemic and there was no difference in glucose levels. Animals in both groups became hyperglycemic after verapamil infusion. At time 10, the experimental group had significantly higher glucose levels (265 +/- 17.1 mg/dL) than the control group (209 +/- 18.3 mg/dL). By time 60, there was no significant difference between glucose values in the control (262 +/- 31.4) and experimental (246 +/- 24.8) groups. It was concluded that verapamil intoxication consistently resulted in hyperglycemia in this model. Glucagon therapy was associated with an early but nonsustained exacerbation of verapamil-induced hyperglycemia.

Animals↗
PubMed1995

Decay in quality of closed-chest compressions over time.

STUDY OBJECTIVE: To characterize fatigue-induced deterioration in the adequacy of closed-chest compressions performed over a period of 5 minutes and to determine whether CPR providers can recognize the effects of fatigue on compression adequacy. DESIGN: Prospective evaluation of study subjects performing closed-chest compressions on an electronic mannequin that assesses compression placement and depth. SETTING: Major resuscitation room in rural university hospital emergency department. PARTICIPANTS: Eleven experienced nursing assistants who regularly provide CPR in the ED. RESULTS: Each study participant performed 5 minutes of closed-chest compressions. Compression adequacy (for placement and depth) was assessed with the mannequin and reported on an attached monitor out of view of the study subjects. Subjects were asked to verbally indicate the point during their 5-minute compression period at which they felt too fatigued to provide effective compressions (arbitrarily defined as a minimum of 90% of all compressions being judged correct by the mannequin). We used one-way repeated-measures ANOVA and regression analysis to determine whether compression adequacy diminished over time. ANOVA was also used to determine whether the total compressions performed per minute diminished over time. The percentage of correct chest compressions decreased significantly after 1 minute of compressions (P = .0001). We found 92.9% of compressions performed during minute 1 to be correct. The percentages for minutes 2 through 5 were as follows: 67.1%, 39.2%, 31.2%, and 18.0%. Regression analysis revealed a decrement in compression adequacy of 18.6% per minute after the first minute of compressions. The number of total compressions attempted per minute did not decrease (P = .98). Study subjects did not accurately identify the point during their 5-minute sessions at which their fatigue caused compressions to become impaired. Whereas mean compression adequacy declined below 90% after only 1 minute, the time of indicated fatigue was 253 +/- 40 seconds (mean +/- SD). CONCLUSION: Although compression rate was maintained over time, chest compression quality declined significantly over the study period. Because CPR providers could not recognize their inability to provide proper compressions, cardiac arrest team leaders should carefully monitor compression adequacy during CPR to assure maximally effective care for patients receiving CPR.

Analysis of Variance↗
PubMed1995

Does a sodium-free buffer affect QRS width in experimental amitriptyline overdose?

STUDY OBJECTIVES: We carried out this study to determine the effects of pH alteration on QRS width with administration of tromethamine, a non-sodium-containing buffering agent, in experimental amitriptyline overdose. DESIGN: Prospective, nonblinded trial. PARTICIPANTS: Adult mongrel dogs. INTERVENTIONS: Pentobarbital-anesthetized dogs were overdosed with amitriptyline 5 mg/kg followed by infusion at 1.0 mg/kg/minute until the QRS width doubled, then decreased to .5 mg/kg/minute until the end of the experiment. At two defined points of toxicity, the dose of tromethamine required to raise the pH to 7.50 +/- 4 was given. pH and QRS width at a speed of 100 mm/second were measured over a 30-minute period after each tromethamine dose. Data were analyzed with non-linear-regression analysis. RESULTS: At toxicity 1 the mean pH was 7.32, with a QRS width of 11.6 mm. Two minutes after the tromethamine dose the pH rose to 7.51, with narrowing of the QRS width to 8.4 mm. At toxicity 2 the pH was 7.40, with QRS width of 10.6 mm. Two minutes after tromethamine, the pH rose to 7.49 and the QRS width decreased to 9.7 mm. Regression analysis showed a correlation between pH and QRS width; as pH increased, QRS width decreased (P = .0001). CONCLUSION: Cardiac toxicity of amitriptyline overdose, as manifested by QRS widening, is reversible by pH changes alone.

Amitriptyline↗
PubMed1995

Treatment of verapamil overdose with glucagon in dogs.

STUDY OBJECTIVE: The purpose of this study was to evaluate the effectiveness of glucagon as a treatment for the hemodynamic effects of verapamil overdose in a canine model. DESIGN: The study was performed in a nonblinded, controlled animal model. INTERVENTIONS: Pentobarbital-anesthetized and instrumented dogs were maintained and observed for 60 minutes or until death. All animals were overdosed with 15 mg/kg i.v. verapamil over 30 minutes. Mean arterial pressure, heart rate, ECG, and cardiac output were monitored. The experimental group received a 2.5 mg glucagon i.v. bolus followed by a glucagon drip at 2.5 mg/hr. The control group received an equal volume of i.v. normal saline solution in the same fashion. Analysis was performed with the Dunnett and Tukey-Kramer methods, with alpha set at .05. RESULTS: There were eight experimental and seven control animals, with mortality rates of 0% and 29%, respectively. The experimental group had increases in cardiac output and heart rate that were statistically significant at 45 and 60 minutes compared with those of the control group. In addition, there was a significant difference in heart rate at 30 minutes. No difference was noted between the groups for mean arterial pressure. CONCLUSION: Glucagon appears to reverse both the bradycardia and the depressed cardiac output associated with verapamil overdose in a canine model.

Animals↗
PubMed1995

Enhanced cardiac metabolism of plasma glucose in high-altitude natives: adaptation against chronic hypoxia.

The metabolism of glucose in mammalian heart is 25-50% more O2 efficient than the metabolism of free fatty acids. To assess the role of substrate preference in adaptations to chronic hypoxia, positron emission tomographic measurements of heart regional glucose uptake rates after an overnight fast were made in volunteer Quechua subjects and in Sherpa subjects, both indigenous to altitudes of over 3,000 m, and in a group of lowlander volunteers. Highest uptake rates were found in the Quechuas on arrival and in the Sherpas after a 3-wk period at low altitude, intermediate rates in Quechuas after a 3-wk period at low altitude and in the lowlanders, and lowest rates in Sherpas on arrival. These low values were probably related to the stress of travel to the site of the experiments. Measured plasma catecholamines, hormones, and substrates indicated that glucose concentrations correlated best with observed variations in glucose uptake, with a negative correlation for the control subjects and a positive correlation for the Quechuas and Sherpas. Uptake values in Quechuas declined significantly after a 3-wk period at low altitude, but the positive correlation with glucose levels persisted. We conclude that an elevated glucose preference in heart is a true metabolic adaptation in humans adapted over generations to chronic hypoxia.

Adaptation, Physiological↗
PubMed1995

Further evidence of a dose-response threshold for haloperidol in psychosis.

OBJECTIVE: The authors' goal was to determine whether higher doses of haloperidol improve antipsychotic response. METHOD: During a 2-week, double-blind, randomized fixed-dose study, 24 psychotic patients were given 4, 10, or 40 mg/day of haloperidol. RESULTS: No clinically relevant difference between groups in favor of the higher antipsychotic doses could be detected. CONCLUSIONS: Doses of 4 mg/day of haloperidol appear to be as effective as higher doses in the treatment of psychosis.

Adult↗
PubMed1995

Effect of nicotinic acid on exogenous myocardial glucose utilization.

UNLABELLED: Clinical assessment of myocardial glucose uptake with 18F-fluorodeoxyglucose (18F-FDG) and PET requires the control of circulating substrates to achieve acceptable image quality. METHODS: To determine the efficacy of the hypolipemic effect of oral niacin upon myocardial 18F-FDG uptake, five volunteers were studied with 18F-FDG and PET in the fasting state, with and without treatment with niacin. Levels of glucose, fatty acids, insulin and catecholamines were measured at baseline and before and after 18F-FDG administration by programmed infusion. RESULTS: No significant changes in glucose or insulin levels occurred with niacin. A significant decrease in fatty acid levels with niacin treatment was associated with a two- to three-fold increase in myocardial glucose utilization rates relative to the fasting state. Furthermore, regional variation in tracer distribution with greater uptake in the lateral wall than the septum or anterior wall in the fasting studies was not present after niacin treatment. CONCLUSION: As determined by programmed infusion of 18F-FDG and PET imaging, niacin treatment in normal volunteers was associated with an increase in exogenous glucose utilization by the heart and a decrease in the cardiac regional variation of 18F-FDG. Further studies are needed to compare the relative value of niacin therapy and oral glucose loading for determination of myocardial exogenous glucose utilization rates.

Adult↗
PubMed1994

Bilateral epidural empyemas in an adolescent.

Epidural empyema is an unusual cause of headache that may be encountered in the emergency department. The collection of suppurative fluid usually results from local spread of sinusitis, although many other predisposing factors have also been described. Patients with epidural empyema usually present with nonspecific cephalalgia that may be accompanied by fever and leukocytosis but is unlikely to be associated with focal neurological findings. The case of an adolescent who presented to our emergency department twice in 6 days with persistent headache is reported; cranial computed tomography performed on the second visit demonstrated bilateral epidural empyema. This entity is uncommon, but may certainly be encountered by the emergency physician.

Adolescent↗