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Biomedical subjects

S Johnsen

Publications and source records attributed to S Johnsen.

At least 19 recordsLinked to original sources
PubMed2006

Investigation into the suitability of a portable psychometric device to be used in the field: an illicit drugs field investigation.

RATIONALE: Driving performance is easily disrupted as a direct consequence of the use of alcohol, licit and illicit drugs. The use of such drugs has a high degree of correlation with increased accident risk. Europe wide research projects into drugged driving have called for the development of a portable objective device capable of screening those impaired through drug use which can be used at the roadside. OBJECTIVE: This study investigated the cognitive and psychomotor performance of a cohort of polydrug drug users in field conditions. Volunteers completed a psychometric test battery on a hand held device in music festival conditions. The test battery comprised a critical tracking task (CTT) and a sustained attention to response task (SART). Volunteers also took a breathanalyser and provided a saliva sample for a DOA screen. RESULTS: On the CTT significance was observed for tracking error following response to a peripheral stimulus in the high alcohol (>80 mg/100 ml) illicit drug group (p=0.0090) and approached significance for the low alcohol (<80 mg/100 ml) illicit drug group (p=0.088). For the SART, incorrect presses to the target stimulus was impaired for volunteers in both the low (<80 mg/100 ml) alcohol illicit drug group (p=0.0080) and the high alcohol (>80 mg/100 ml) illicit drug group (p=0.0415). Discrimination analysis demonstrated that the impairment device was able to discriminate between those individuals who had consumed neither alcohol nor drugs (94.12%), those in the low alcohol drug group (46.67%) and those in the high alcohol drug group (60.00%). CONCLUSION: It is possible to derive an impairment ratio. Further research will demonstrate whether this device could significantly contribute to drug driving detection and road traffic safety.

Adolescent↗
PubMed2005

Treatment of therapy-refractive ulcera cruris of various origins with autologous keratinocytes in fibrin sealant.

BACKGROUND: Evaluation of the effects of cultivated, subconfluent, autologous keratinocytes in fibrin sealant (BioSeed-S) on the healing of therapy-refractive chronic wounds. PATIENTS AND METHODS: Open observational study in 60 patients with chronic leg ulcers and impaired wound healing of various origins. After whole-skin excision and cultivation of the autologous keratinocytes, the suspended cells were applied to the preconditioned wound in fibrin sealant. Wound epithelization and wound size were recorded at defined times. RESULTS: Fifty-two of the 60 participating patients could be evaluated. After 6 weeks, 29 ulcers (55.8%) were healed. The mean epithelization increased between the 8th and 42nd postoperative day from 23% to 62.5%. In 50.0% of the patients, global assessment of the wound showed a high degree of epithelization or healing after 42 days. In 32.6% of treated patients, improvement was observed, while no healing tendency was to be found in 17.4%. CONCLUSION: The present observational study indicates that the transplantation of autologous keratinocytes suspended in fibrin sealant could be of advantage in the treatment of refractive leg ulcers.

Aged↗
PubMed2004

[Oxidative stress in a model for experimental diabetic retinopathy: treatment with antioxidants].

PURPOSE: Diabetic retinopathy is the primary cause of blindness in developed countries, and though strict glycemic control is desirable to prevent complications, this is not always achievable. Thus, adjunctive therapies are needed to help in preventing or delaying the onset of diabetic complications. We have studied the biochemical and functional changes in the retina of diabetic mice, and the ability of ebselen and lutein, two antioxidants, to reverse these effects, using as a comparison the effect of insulin therapy. METHODS: Alloxan injection was used to achieve hyperglycemia. Malondialdehyde (MDA) concentration in blood and glutathione peroxidase (GPx) activity in eye homogenate were measured. Serial electroretinograms (ERG) were recorded. RESULTS: MDA concentration in the blood was high in diabetic animals. GPx activity in eye homogenate decreased in the diabetic conditions. Maximal electroretinogram amplitude decreased in diabetic animals with respect to controls. Ebselen and lutein restored MDA levels, GPx activity and ERG amplitude, and had no effect on glycemia. CONCLUSION: These results call for further studies on ebselen or lutein as adequate adjunctive therapies for diabetes.

Animals↗
PubMed2003

Homogeneous climate variability across East Antarctica over the past three glacial cycles.

Recent ice core studies have raised the disturbing possibility that glacial-interglacial climate changes may be non-uniform across Antarctica. These findings have been confined to records from the Ross Sea sector of the continent, but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from Vostok, East Antarctica, on large spatial scales. Here we present an isotopic profile from a core drilled at Dome Fuji, situated 1,500 km from Vostok in a different sector of East Antarctica. The two records show remarkable similarities over the past three glacial cycles (the extent of the Dome Fuji record) in both large-amplitude changes, such as terminations, interglacials and interstadials and more subtle glacial events, even when the origin of precipitation is accounted for. Our results indicate that Antarctic climate is essentially homogeneous at the scale of the East Antarctic Plateau, possibly as a consequence of the symmetry of the plateau and the adjacent ocean.

Journal Article↗
PubMed2003

A placebo controlled investigation into the effects of paroxetine and mirtazapine on measures related to car driving performance.

OBJECTIVE: To assess the effects of paroxetine and mirtazapine on psychometric performance related to car driving, including an on-the-road test of BRT. METHOD: In a 4-way, double blind randomised crossover study, 12 healthy volunteers received paroxetine 20mg mane, mirtazapine 15mg/30mg nocte (comparator), mirtazapine 15mg mane/15 mg b.i.d.(verum) and placebo over a 5 day period with a washout period of 7 days between treatments. Psychometric assessments included 'on-the-road' BRT (BRT), CFF (CFF), CRT (CRT) and subjective measures of sedation and sleep parameters. RESULTS: Paroxetine had no significant effect on BRT compared with placebo. Although subjective ratings of sleep quality and sedation were impaired, there were significant improvements in both CFF and the recognition reaction component of CRT with paroxetine. Mirtazapine 15mg/30mg nocte impaired laboratory performance and some subjective tests. Mirtazapine 15mg mane/15mg b.i.d. improved sleep, but significantly impaired all other measures. CONCLUSION: Paroxetine 20 mg/day has no psychomotor or behavioural toxicity and has no negative impact on BRT. Further research into the chronic and sub-chronic effects of mirtazapine is needed to establish the clinical significance of these results.

Adrenergic alpha-Antagonists↗
PubMed2001

An oceanic cold reversal during the last deglaciation.

A detailed deuterium excess profile measured along the Dome C EPICA (European Project for Ice Coring in Antarctica) core reveals the timing and strength of the sea surface temperature changes at the source regions for Dome C precipitation. We infer that an Oceanic Cold Reversal took place in the southern Indian Ocean, 800 years after the Antarctic Cold Reversal. The temperature gradient between the oceanic moisture source and Antarctica is similar to the Dome C sodium profile during the deglaciation, illustrating the strong link between this gradient and the strength of the atmospheric circulation.

Journal Article↗
PubMed2001

Incident thromboembolism in the aorta and the renal, mesenteric, pelvic, and extremity arteries after discharge from the hospital with a diagnosis of atrial fibrillation.

BACKGROUND: The impact of atrial fibrillation (AF) on risk of peripheral arterial thromboembolism is unknown. METHODS: We analyzed the risk of thromboembolism (embolus and/or thrombosis) in the aorta and the renal, mesenteric, pelvic, and extremity arteries in a cohort of patients discharged from the hospital with an incident diagnosis of AF relative to the risk of thromboembolism in these vessels in the Danish population. In a random sample of half of the Danish population, 14 917 men and 14 945 women aged 50 to 89 years were identified in the Danish National Hospital Discharge Register with a diagnosis of AF from January 1, 1980, through December 31, 1993. Patients were followed up from diagnosis of AF in the Danish National Hospital Discharge Register and the Causes of Death Register until the first diagnosis of a thromboembolic event, death, or the end of 1993. Risk of a thromboembolic event relative to the risk in the Danish population was analyzed by means of Poisson regression modeling. RESULTS: Patients with a hospital diagnosis of AF had an increased risk of thromboembolic events in the aorta and the renal, mesenteric, pelvic, and extremity arteries (relative risk, 4.0 [95% confidence interval, 3.5-4.6] in men; and relative risk, 5.7 [95% confidence interval, 5.1-6.3] in women) compared with the Danish population. CONCLUSION: A hospital diagnosis of AF is an important risk factor for peripheral arterial thromboembolic complications.

Aged↗
PubMed2001

Hidden in plain sight: the ecology and physiology of organismal transparency.

Despite the prevalence and importance of transparency in organisms, particularly pelagic species, it is a poorly understood characteristic. This article reviews the current state of knowledge on the distribution, ecology, and physical basis of biological transparency. Particular attention is paid to the distribution of transparent species relative to their optical environment, the relationship between transparency and visual predation, the physics of transparency, and what is known about the anatomical and ultrastructural modifications required to achieve this condition. Transparency is shown to be primarily a pelagic trait, uncommon in other aquatic habitats and extremely rare on land. Experimental and theoretical studies in terrestrial, freshwater, and marine ecosystems have shown that transparency is a successful form of camouflage, and that several visual adaptations seem to counter it. The physical basis of transparency is still poorly understood, but anatomical observations and mathematical models show that there are various routes to transparency. Future avenues for research include examination of the ultrastructure and optical properties of transparent tissue, exploring the link between transparent species and special visual modifications in the species they interact with, and analysis of the evolution of transparency using comparative methods.

Animals↗
PubMed2000

Incident stroke after discharge from the hospital with a diagnosis of atrial fibrillation.

PURPOSE: Atrial fibrillation is an important risk factor for stroke. We analyzed stroke risk over time in patients discharged from the hospital with a diagnosis of incident atrial fibrillation as compared with the risk of stroke in the Danish population. SUBJECTS AND METHODS: In a random sample of half of the Danish population, we identified 13,625 men and 13,577 women, aged 50 to 89 years, with a hospital diagnosis of atrial fibrillation and no prior diagnosis of stroke during 1980 to 1993. Data on other medical conditions were also available from 1977 to 1993, but medication data were not available. Patients were followed from the diagnosis of atrial fibrillation until the first diagnosis of stroke (nonfatal or fatal cerebral ischemic infarct and cerebral hemorrhage), death, or the end of 1993. The risk of stroke in these patients was compared with the risk in the Danish population using Poisson regression modeling to estimate relative risks (RR) and 95% confidence intervals (CI). RESULTS: For men with atrial fibrillation, the stroke rates increased by age, from 13 per 1,000 person-years in those ages 50 to 59 years, to 22 per 1,000 person-years in those ages 60 to 69 years, to 42 per 1,000 person-years in those ages 70 to 79 years, to 51 per 1,000 person-years in those ages 80 to 89 years. Age-specific stroke rates were similar in women with atrial fibrillation. Patients with a hospital diagnosis of atrial fibrillation had an increased risk of stroke (RR = 2.4; 95% CI, 2.3 to 2.5 in men and RR = 3.0; 95% CI, 2.9 to 3.2 in women) compared with the Danish population. Stroke risk was greatest during the first year after discharge and decreased thereafter. Hypertension, diabetes, and peripheral atherosclerosis were also associated with an increased risk of stroke among patients with atrial fibrillation. Ischemic heart disease and heart failure were risk factors in men only. There was no reduction in the risk of stroke from 1980 to 1993. CONCLUSIONS: Men and women with atrial fibrillation are at a substantially increased risk of stroke, particularly in the first year after the diagnosis.

Age Distribution↗
PubMed2000

Monitoring, modelling and environmental exposure assessment of industrial chemicals in the aquatic environment.

Monitoring and laboratory data play integral roles alongside fate and exposure models in comprehensive risk assessments. The principle in the European Union Technical Guidance Documents for risk assessment is that measured data may take precedence over model results but only after they are judged to be of adequate reliability and to be representative of the particular environmental compartments to which they are applied. In practice, laboratory and field data are used to provide parameters for the models, while monitoring data are used to validate the models' predictions. Thus, comprehensive risk assessments require the integration of laboratory and monitoring data with the model predictions. However, this interplay is often overlooked. Discrepancies between the results of models and monitoring should be investigated in terms of the representativeness of both. Certainly, in the context of the EU risk assessment of existing chemicals, the specific requirements for monitoring data have not been adequately addressed. The resources required for environmental monitoring, both in terms of manpower and equipment, can be very significant. The design of monitoring programmes to optimise the use of resources and the use of models as a cost-effective alternative are increasing in importance. Generic considerations and criteria for the design of new monitoring programmes to generate representative quality data for the aquatic compartment are outlined and the criteria for the use of existing data are discussed. In particular, there is a need to improve the accessibility to data sets, to standardise the data sets, to promote communication and harmonisation of programmes and to incorporate the flexibility to change monitoring protocols to amend the chemicals under investigation in line with changing needs and priorities.

Environmental Exposure↗
PubMed2000

The neurobiology of magnetoreception in vertebrate animals.

Diverse vertebrate animals can sense the earth's magnetic field, but little is known about the physiological mechanisms that underlie this sensory ability. Three major hypotheses of magnetic-field detection have been proposed. Electrosensitive marine fish might sense the geomagnetic field through electromagnetic induction, although definitive evidence that such fish actually do so has not yet been obtained. Studies with other vertebrates have provided evidence consistent with two different mechanisms: biogenic magnetite and chemical reactions that are modulated by magnetic fields. Despite recent progress, however, primary magnetoreceptors have not yet been identified unambiguously in any animal.

Animals↗
PubMed2000

A new model for evaluation of thrombosis and ischaemia/reperfusion injury.

BACKGROUND: The purpose of the present study was to describe infarct size and platelet accumulation when reperfusion injury was combined with a thrombogenic lesion in the coronary artery. The left anterior descending artery was damaged in 11 pigs and subsequently occluded proximal to the lesion for 50 min, followed by 4 h of reperfusion. RESULTS: The infarct size/area at risk was 40 (35 63)%. Infarct size correlated with troponin-T-3 h (p=0.85, p<0.002), but not with creatine kinase-3 h. Platelet aggregation decreased by 34% (p<0.01) at 15 min of reperfusion, but returned to baseline. Platelet accumulation in the left ventricle was significantly higher in the area at risk (194 (157-206)%) compared to the right ventricle (137 (120-142)%); p<0.05). CONCLUSION: A decreased platelet reactivity and increased accumulation of platelets in the area at risk indicates that activated platelets become entrapped in the myocardium. Troponin-T was a better marker of myocardial damage than creatine kinase in this in vivo model with pigs.

Animals↗
PubMed1999

16 degrees C rapid temperature variation in central greenland 70,000 years Ago

Variations in the (29)N(2)/(28)N(2) ratio of air bubbles trapped in polar ice cores and their relation to variations of the (18)O/(16)O of the ice allow past surface temperature variations and ice age-gas age differences to be determined. High-resolution measurements of (29)N(2)/(28)N(2) in Dansgaard-Oeschger event 19 (around 70,000 years before the present) in ice from Central Greenland show that at the beginning of the event, the ice age-gas age difference was 1090 +/- 100 years. With the use of a combined firn densification, temperature, and gas diffusion model, the delta(18)O(ice)-temperature coefficient alpha was determined to be 0. 42 +/- 0.05 per mil per kelvin. This coefficient implies a mean surface temperature change of 16.0 kelvin (between 14.3 and 18.1 kelvin), which differs substantially from values derived from borehole temperatures and modern spatial delta(18)O(ice)-surface temperature correlations.

Journal Article↗
PubMed1999

The physical basis of transparency in biological tissue: ultrastructure and the minimization of light scattering

In the open ocean, many animals are highly transparent, some achieving near invisibility. However, little is known about how this transparency is attained. The effects of cellular ultrastructure on tissue transparency were mathematically modeled. Given a specific constant volume or surface area of a higher refractive index material (e.g. protein, lipid, etc.), within a lower refractive index cytoplasm or other matrix, the model calculates the total amount of light scattered as a function of how the volume or surface area is subdivided. Given a constant volume, the scattering peaks strongly when the volume is divided into spheres of critical radii. The critical radii depend upon the refractive index of the material relative to its surroundings. Similarly, given a constant surface area, the scattering increases rapidly with sphere size until critical radii (approximating the critical radii for constant volume) are reached, after which the scattering is relatively constant. Under both constraints, refractive index is critical when the particles are small, but becomes progressively less important as particle size increases. When only forward scattering is considered, the results are essentially similar to those found for total scattering. When scattering at only larger angles is considered, the critical radii are independent of refractive index, and the scattered radiance depends critically on refractive index at all particle sizes. The effects of particle shape on scattering depend on the geometric constraint and particle size. Under constant volume constraints, small particles of any shape scatter light equally, but large spheres scatter less light than other larger shapes. Under constant surface area constraints, small spheres scatter more light than any small shape, but large particles of any shape scatter equally. The effects of crowding and the refractive index of the surrounding medium on these predictions are discussed. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Intravenous magnesium reduces infarct size after ischemia/reperfusion injury combined with a thrombogenic lesion in the left anterior descending artery.

Experimental studies have demonstrated that intravenous magnesium (Mg) can protect the ischemic myocardium and has an antithrombotic effect. In patients with myocardial infarction, the reperfusion injury is complicated by the presence of a thrombogenic area in the affected coronary artery that may cause repetitive thrombus formation and embolization. We investigated the effect of Mg on infarct size in a randomized study in pigs. Myocardial infarction was induced by a 50-minute mechanical occlusion of the left anterior descending artery combined with an arterial injury, which stimulated a dynamic thrombus formation with emboli shedding on reperfusion. Magnesium sulfate (6 mmol/20 min plus 3 mmol/h) or saline was started at 30 minutes after coronary occlusion. Real-time ventricular pressure-volume loops were generated from the left ventricle by using a microtip pressure manometer and a conductance catheter. Platelet accumulation in the myocardium was evaluated by using 111In-labeled platelets. After 4 hours of reperfusion, the infarct size/area at risk ratio in the placebo group was 46+/-0.06% (n=8) compared with 22+/-0.07% (n=6) in the Mg-treated animals (P=0. 03). Ejection fraction decreased significantly in the control group but not in the Mg-treated animals (P=0.03). Platelet accumulation in the myocardium did not change significantly between the Mg- and placebo-treated animals (placebo group, 191+/-19%; Mg group, 177+/-29%; NS). The present study demonstrates that intravenous Mg infusion is able to reduce infarct size by >50% and preserve the ejection fraction in this model where ischemia/reperfusion injury was evaluated in the presence of a thrombogenic area in the nutrient artery.

Animals↗
PubMed1998

Penny ice cap cores, baffin island, canada, and the wisconsinan foxe dome connection: two states of hudson bay ice cover

Ice cores from Penny Ice Cap, Baffin Island, Canada, provide continuous Holocene records of oxygen isotopic composition (delta18O, proxy for temperature) and atmospheric impurities. A time scale was established with the use of altered seasonal variations, some volcanic horizons, and the age for the end of the Wisconsin ice age determined from the GRIP and GISP2 ice cores. There is pre-Holocene ice near the bed. The change in delta18O since the last glacial maximum (LGM) is at least 12.5 per mil, compared with an expected value of 7 per mil, suggesting that LGM ice originated at the much higher elevations of the then existing Foxe Dome and Foxe Ridge of the Laurentide Ice Sheet. The LGM delta18O values suggest thick ice frozen to the bed of Hudson Bay.

Journal Article↗
PubMed1997

Neutron sources in the Varian Clinac 2100C/2300C medical accelerator calculated by the EGS4 code.

The photoneutron yields produced in different components of the medical accelerator heads evaluated in these studies (24-MV Clinac 2500 and a Clinac 2100C/2300C running in the 10-MV, 15-MV, 18-MV and 20-MV modes) were calculated by the EGS4 Monte Carlo code using a modified version of the Combinatorial Geometry of MORSE-CG. Actual component dimensions and materials (i.e., targets, collimators, flattening filters, jaws and shielding for specific accelerator heads) were used in the geometric simulations. Calculated relative neutron yields in different components of a 24-MV Clinac 2500 were compared with the published measured data, and were found to agree to within +/-30%. Total neutron yields produced in the Clinac 2100/2300, as a function of primary electron energy and field size, are presented. A simplified Clinac 2100/2300C geometry is presented to calculate neutron yields, which were compared with those calculated by using the fully-described geometry.

Computer Simulation↗