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Biomedical subjects

Jonas Björk

Publications and source records attributed to Jonas Björk.

At least 19 recordsLinked to original sources
PubMed2006

Comparison between neural networks and multiple logistic regression to predict acute coronary syndrome in the emergency room.

OBJECTIVE: Patients with suspicion of acute coronary syndrome (ACS) are difficult to diagnose and they represent a very heterogeneous group. Some require immediate treatment while others, with only minor disorders, may be sent home. Detecting ACS patients using a machine learning approach would be advantageous in many situations. METHODS AND MATERIALS: Artificial neural network (ANN) ensembles and logistic regression models were trained on data from 634 patients presenting an emergency department with chest pain. Only data immediately available at patient presentation were used, including electrocardiogram (ECG) data. The models were analyzed using receiver operating characteristics (ROC) curve analysis, calibration assessments, inter- and intra-method variations. Effective odds ratios for the ANN ensembles were compared with the odds ratios obtained from the logistic model. RESULTS: The ANN ensemble approach together with ECG data preprocessed using principal component analysis resulted in an area under the ROC curve of 80%. At the sensitivity of 95% the specificity was 41%, corresponding to a negative predictive value of 97%, given the ACS prevalence of 21%. Adding clinical data available at presentation did not improve the ANN ensemble performance. Using the area under the ROC curve and model calibration as measures of performance we found an advantage using the ANN ensemble models compared to the logistic regression models. CONCLUSION: Clinically, a prediction model of the present type, combined with the judgment of trained emergency department personnel, could be useful for the early discharge of chest pain patients in populations with a low prevalence of ACS.

Acute Disease↗
PubMed2006

Gadolinium contrast media are more nephrotoxic than iodine media. The importance of osmolality in direct renal artery injections.

A study was undertaken of the role of osmotoxicity in gadolinium (Gd) and iodine contrast media (CM) nephrotoxicity in ischemic porcine kidneys. Test solutions: mannitol iso-osmotic to 0.5 M: gadopentetate (1.96 Osm/kg H2O), 0.5 M: gadodiamide (0.78 Osm/kg H2O) and 0.5 M: iohexol (190 mg I/ml, 0.42 Osm/kg H2O). Each solution was injected [3 ml/kg body weight (BW)] into the balloon-occluded (10 min) renal artery of eight left-sided nephrectomized pigs. The plasma half-life of a glomerular filtration rate (GFR) marker was used to compare their effects on GFR 1-3 h post-injection. The median half-lives of the GFR marker after injection of gadopentetate (1,730 min) and mannitol 1.96 Osm/kg H2O (2,782 min) did not differ statistically (P = 0.28), but were significantly longer than after all other solutions (P < 0.001). There was no significant difference (P = 0.06) between gadodiamide (218 min) and mannitol 0.82 Osm/kg H2O (169 min), while there was (P = 0.03) between iohexol (181 min) and mannitol 0.43 Osm/kg H2O (148 min). The difference between gadodiamide and iohexol was significant (P = 0.01). Reduction in GFR, as a marker of nephrotoxicity, induced by gadopentetate correlated with its high osmolality, while the effect of gadodiamide and iohexol may include chemotoxicity. Iohexol molecules were less nephrotoxic than the Gd-CM molecules and contain three-times the number of attenuating atoms per molecule.

Animals↗
PubMed2006

A simple statistical model for prediction of acute coronary syndrome in chest pain patients in the emergency department.

BACKGROUND: Several models for prediction of acute coronary syndrome (ACS) among chest pain patients in the emergency department (ED) have been presented, but many models predict only the likelihood of acute myocardial infarction, or include a large number of variables, which make them less than optimal for implementation at a busy ED. We report here a simple statistical model for ACS prediction that could be used in routine care at a busy ED. METHODS: Multivariable analysis and logistic regression were used on data from 634 ED visits for chest pain. Only data immediately available at patient presentation were used. To make ACS prediction stable and the model useful for personnel inexperienced in electrocardiogram (ECG) reading, simple ECG data suitable for computerized reading were included. RESULTS: Besides ECG, eight variables were found to be important for ACS prediction, and included in the model: age, chest discomfort at presentation, symptom duration and previous hypertension, angina pectoris, AMI, congestive heart failure or PCI/CABG. At an ACS prevalence of 21% and a set sensitivity of 95%, the negative predictive value of the model was 96%. CONCLUSION: The present prediction model, combined with the clinical judgment of ED personnel, could be useful for the early discharge of chest pain patients in populations with a low prevalence of ACS.

Acute Disease↗
PubMed2006

Road traffic noise in southern Sweden and its relation to annoyance, disturbance of daily activities and health.

OBJECTIVES: This study investigated residential noise from road traffic and its relation to annoyance, disturbance of daily activities, and general health. METHODS: A large public health survey in southern Sweden in 1999-2000 supplied data (N=13 557; 54% participation rate) on the demography, annoyance, and disturbance of daily activities, and on general health problems regarding concentration, sleep, stress, and treatment for hypertension. Residential road noise exposure was assessed with a geographic information system. Associations with 24-hour equivalent (average) and maximum road noise level were investigated for all participants and for selected subgroups using the Cochran-Armitage trend test and Cox regression analysis. RESULTS: Annoyance from road traffic noise and the disturbance of daily activities increased markedly with road noise exposure. More than 25% reported at least occasional disturbance from traffic noise during relaxation and sleep in the highest exposure category for each noise measure. No overall pattern between road noise exposure and general health problems emerged. Among the participants that reported annoyance from road traffic noise (N=623), the average road noise level was associated with concentration problems (P for trend = 0.03) and with treatment for hypertension (P for trend = 0.02). Positive associations between average road noise exposure and health problems were found among females (hypertension), persons born outside Sweden (sleep), the unemployed (stress), and participants that reported financial problems (concentration problems). CONCLUSIONS: Exposure to road traffic noise at high levels was common and produced frequent disturbances of daily activities. Negative health effects from road traffic noise were observed in important subgroups. The findings are of concern for southern Sweden, as well as for other regions with similar or higher traffic intensity.

Activities of Daily Living↗
PubMed2005

The utility of the growth hormone (GH) releasing hormone-arginine test for diagnosing GH deficiency in adults with childhood acute lymphoblastic leukemia treated with cranial irradiation.

CONTEXT: The insulin tolerance test (ITT) is the current standard diagnostic test for the diagnosis of adult GH deficiency (GHD), but alternative tests, such as the GHRH-arginine test, have been proposed. OBJECTIVE: We investigated the sensitivity and specificity of the GHRH-arginine test using ITT as the gold standard in diagnosing GHD in a group of young adults treated with cranial irradiation (CRT) for childhood acute lymphoblastic leukemia (ALL). We estimated the positive and negative predictive values of the GHRH-arginine test among patients as well as a number of individual characteristics and therapy-related factors during both the GHRH-arginine test and ITT. DESIGN: Forty-three young adults, treated for childhood ALL with 18-30 Gy CRT and chemotherapy, were studied, and comparison was made with matched controls. RESULTS AND CONCLUSIONS: We evaluated four different cutoff levels for GHD in the GHRH-arginine test: 5, 7.5, 9, and 16.5 microg/liter. Using 7.5 microg/liter as the cutoff yielded high specificity (94%), but at the same time the sensitivity was only 66%, which leads to a low negative predictive value (27%). In contrast, a failed GH response to the GHRH-arginine test accurately reflects the presence of radiation-induced GHD, illustrated by a high positive predictive value (95% at 7.5 microg/liter). Only age at CRT and body mass index remained significant predictors of the peak GH during the GHRH-arginine test. Because a high proportion of GHD patients show a normal response to the GHRH-arginine test, it cannot be used reliably to exclude GHD in these patients. Complementary ITT is also warranted to confirm GHD in obese patients.

Adult↗
PubMed2005

Simple cystatin C-based prediction equations for glomerular filtration rate compared with the modification of diet in renal disease prediction equation for adults and the Schwartz and the Counahan-Barratt prediction equations for children.

BACKGROUND: Serum creatinine is the most commonly used marker for estimation of glomerular filtration rate (GFR). To compensate for its drawbacks as a GFR marker, several prediction equations including several parameters are being used, with the Modification of Diet in Renal Disease (MDRD), Schwartz, and Counahan-Barratt equations being the ones most widely accepted for estimation of relative GFR in mL x min(-1) x (1.73 m(2))(-1). The present study analyzes whether these GFR prediction equations for adults and children might be replaced by simple prediction equations based on plasma concentrations of cystatin C. METHODS: Data from 536 patients (0.3-93 years), consecutively referred for determination of GFR by an invasive gold standard procedure, were used for the analysis. Calculations of bias (median percentage of error), correlation (adjusted R(2)), and percentage of estimates within 30% and 50% of measured GFR were used in the comparisons. RESULTS: A cystatin C-based prediction equation using only concentration in mg/L and a prepubertal factor: GFR [mL x min(-1) x (1.73 m(2))(-1)] = 84.69 x cystatin C (mg/L)(-1.680) x 1.384 (if a child <14 years) assessed GFR equally well or better than the simplified MDRD, the Schwartz, and the Counahan-Barratt prediction equations for the adult (> or =18 years) and juvenile groups of the investigated cohort. Age did not influence the cystatin C-based prediction equation for adults, whereas gender did, but with a factor close to unity (0.948 for females). CONCLUSION: A GFR prediction equation based solely on cystatin C (in mg/L) and a prepubertal factor might replace the simplified MDRD prediction equation for adults and the Schwartz and Counahan-Barratt prediction equations for children.

Adolescent↗
PubMed2005

Constitutional short telomeres are strong genetic susceptibility markers for bladder cancer.

Lack of functional telomeres can cause chromosomal aberrations. This type of genetic instability may promote tumorigenesis. We have investigated the association between mean telomere length in buccal cells (assessed with quantitative real-time PCR) and bladder cancer risk in a case-control study. Patients with bladder cancer displayed significantly shorter telomeres than control subjects (P = 0.001). Median telomere length ratio was 0.95 (range 0.53-3.2) for cases and 1.1 (0.51-2.4) for controls. Moreover, the adjusted odds ratio (OR) for bladder cancer was significantly increased in the quartile with the shortest telomere length OR = 4.5 [95% confidence interval (CI) 1.7-12]. It is known that oxidative stress, alkylation or UV radiation increases shortening of telomeres. Therefore, we also analyzed whether environmental and genetic factors associated with DNA damage, i.e. smoking and polymorphisms in the genes involved in the metabolism of genotoxic carcinogens (EPHX1, GSTA1, GSTM1, GSTP1, GSTT1, NAT1, NAT2 and NQO1) or DNA repair (APE1, NBS1, XPC, XPD, XRCC1, XRCC3 and XRCC4), could modify the association between telomere length and cancer risk. A clear effect of smoking and telomere length could be observed. Current smokers with short telomeres had more than six times as higher risk as non-smokers/former smokers with long telomeres (OR = 6.3, 95% CI 1.7-23). Lack of the biotransformation gene GSTM1 and short telomeres were associated with OR = 6.5 (95% CI 2.4-18), whereas homozygous carriers of 312Asn in the DNA repair gene XPD, with short telomeres, displayed an OR of 17 (95% CI 1.9-150). However, no significant interaction for cancer risk could be proven for telomere length, smoking and susceptibility genotypes of metabolizing and DNA-repairing genes.

Adult↗
PubMed2005

Model specification and unmeasured confounders in partially ecologic analyses based on group proportions of exposed.

OBJECTIVES: The aim of this study was to quantify bias from a partially ecologic analysis due to (i) model misspecification and (ii) an unmeasured confounder, considering various scenarios that may occur in occupational and environmental epidemiology. A study with an aggregate exposure variable, PE, but with outcome, group membership, and covariates assessed individually is partially ecologic. In this paper, PE is the proportion exposed; PE can vary across geographic areas or occupational groups. METHODS: Several hypothetical scenarios were considered, varying the baseline risk, the exposure effect, the exposure distribution across groups, the impact of the (unmeasured) confounder, and the confounder distribution across groups. First, confounding within groups was introduced. Thereafter, confounding between groups was introduced by co-varying PE and the confounder prevalence across the groups. The expected odds ratio (exposed versus unexposed) was calculated in two alternative models, the logistic regression and linear odds models, both with PE as the independent variable. Moreover, empirical data on noise exposure and sleeping disturbances were analyzed. RESULTS: Compared with the logistic regression model, the linear odds model yielded a markedly less biased odds ratio (OR) when the outcome was rare (< or = 5% baseline risk). Confounding within groups resulted in marginal bias, whereas confounding between groups resulted in more pronounced bias. CONCLUSIONS: A logistic regression analysis, with PE as an independent variable, can yield substantial model misspecification bias. By contrast, the linear odds model is valid when the outcome is rare. Confounding between groups should be of more concern than confounding within groups in partially ecologic analyses.

Bias↗
PubMed2004

Incorporating group-level exposure information in case-control studies with missing data on dichotomous exposures.

In case-control studies with exposure data obtained from interviews, participation is an issue of concern. Use of external group-level exposure information, available for all cases and controls (including nonparticipants), can reduce participation bias and improve precision of effect estimates. Our methodologic investigation was motivated by a population-based case-control study on occupational exposures and leukemia. We assessed exposure using dichotomous data collected in interviews, and also using census data on past and current occupational groups for all subjects. Based on information from a job-exposure database, a group-level probability of exposure was assigned to each subject. We studied the performance of the iterative expectation-maximization method for estimating the odds ratio (OR) by using the individual-level exposure data on the interviewed participants together with the assigned group-level exposure probabilities for the nonparticipants. In each iteration, the expected numbers of exposed and unexposed among the nonparticipating cases and controls were calculated from their assigned exposure probabilities and, for the cases only, from the current OR estimate. We then estimated the OR based on the total (observed plus expected) numbers and repeated the procedure until convergence. The expectation-maximization method eliminated participation bias and improved precision for scenarios with error-free group-level exposures and individual-level exposure data missing at random conditional on disease status and group affiliation. We specifically addressed consequences of assigning erroneous exposure probabilities to the nonparticipating subjects. In such situations, the expectation-maximization method can produce biased estimates if the participation rates among the cases and controls differ substantially.

Bias↗
PubMed2004

Growth hormone deficiency predicts cardiovascular risk in young adults treated for acute lymphoblastic leukemia in childhood.

Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy, and until recently prophylactic cranial radiotherapy (CRT) was important for achieving long-term survival. Hypothalamic-pituitary hormone insufficiency is a well-recognized consequence of CRT for childhood cancer. Another problem is increased cardiovascular risk, which has been shown in long-term survivors of other childhood cancers. In the only previously reported study on cardiovascular risk after childhood ALL, obesity and dyslipidemia were recorded in a small subgroup treated with CRT, compared with patients treated with chemotherapy. The mechanisms behind the increase in cardiovascular risk in survivors of childhood cancer are not clarified. The aim of the present study was to elucidate mechanisms of increased cardiovascular risk in former childhood ALL patients. A group of 44 ALL survivors (23 males, median age 25 yr, range 19-32 yr at the time of study) treated with CRT (median 24 Gy, 18-30 Gy) at a median age of 5 yr (1-18 yr) and chemotherapy were investigated for prevalence of GH deficiency and cardiovascular risk factors. Comparison was made with controls randomly selected from the general population and individually matched for sex, age, smoking habits, and residence. All patients and controls underwent a GHRH-arginine test, and patients with a peak GH 3.9 microg/liter or greater were further investigated with an additional insulin tolerance test. Significantly higher plasma levels of insulin (P = 0.002), blood glucose (P = 0.01), and serum levels of low-density lipoprotein cholesterol, apolipoprotein (Apo) B, triglycerides, fibrinogen, and leptin (all P <or= 0.05) were recorded among the ALL patients, compared with controls. Furthermore, the serum levels of high-density lipoprotein cholesterol (P = 0.03) and Apo A1 (P = 0.005) were significantly lower among the patients. Compared with controls, the patients had higher body mass index and waist to hip ratio, and body composition measured with dual-energy x-ray absorptiometry showed significantly higher fat mass and lower lean mass (P < 0.001). Forty of 44 ALL patients (91%) were considered GH deficient according to the insulin tolerance test and/or the GHRH-arginine test, and the rest were considered GH insufficient. In patients, peak GH during GHRH-arginine was significantly negatively correlated to total body fat mass measured with dual-energy x-ray absorptiometry (r = -0.48, P = 0.001), waist to hip ratio (r = -0.32, P = 0.03), plasma insulin (r = -0.49, P = 0.001), and leptin (r = -0.46, P = 0.002). Moreover, a significantly positive correlation was recorded with high-density lipoprotein cholesterol (r = 0.38, P = 0.012). Using Doppler echocardiography, a marked reduction in cardiac dimensions and performance (ejection fraction P < 0.001 and fractional shortening P = 0.01), compared with controls, was recorded. In conclusion, at a median 17 yr after treatment with CRT and chemotherapy in former childhood ALL patients, a significant increase in cardiovascular risk factors was recorded. We suggest that GH deficiency, induced by CRT, is a primary cause for this because strong correlations between the stimulated GH peak and several of the cardiovascular risk factors were observed.

Adolescent↗
PubMed2004

Prevalence of current and chronic pain and their influences upon work and healthcare-seeking: a population study.

OBJECTIVE: To investigate the prevalence of current and chronic pain and their relationship to pain intensity, sex, age, income, employment status, citizenship, marital status, urban residence, occupational activity, and healthcare-seeking based on a representative sample from a Swedish county. METHODS: A cross-sectional survey using a postal questionnaire was sent to a representative sample (n = 9952) of the target population (284,073 people, age 18-74 yrs) in a county (Ostergötland) in southern Sweden. A questionnaire was mailed and followed by 2 postal reminders if necessary. RESULTS: The participation rate was 76.7% (n = 7637); nonparticipants were on average younger, male, and earned less money. The overall point prevalence of pain was 48.9%. The corresponding one-month period prevalence was 63.0%, and pain on several occasions during the previous 3 months was reported by 61.3% of participants. The prevalence of chronic pain (pain > 3 months) was 53.7%. Female sex, age, and sick leave/early retirement were generally of significant importance in the regressions of pain. No sex factor was found in the regressions of pain frequency and pain intensity. Chronic pain especially frequent and intensive pain showed clear associations with healthcare-seeking and occupational activity. CONCLUSION: High prevalence of current pain (48.9%) and chronic pain (53.7%) were found in this community-based study. Being female, older, and on sick leave or early retirement were generally of significant importance in the regressions of pain. Chronic pain showed clear associations with healthcare-seeking and occupational activity, indicating considerable socioeconomic costs.

Acute Disease↗
PubMed2003

Cytogenetic and morphologic subgroups of myelodysplastic syndromes in relation to occupational and hobby exposures.

OBJECTIVES: This study investigated the association between occupational and hobby exposure and the risk of myelodysplastic syndromes (MDS) while focusing on differential patterns of clonal chromosome aberrations and morphologic subgroups. METHODS: A case-referent study was conducted with 330 MDS patients investigated cytogenetically in 1976-1993 (cases) and matched referents. Telephone interviews with either the person or a next-of-kin were used. The participation rate of the cases and referents was 85% and 60%, respectively. Information was obtained from the next-of-kin more often for the cases (88%) than for the referents (26%). Occupational hygienists assessed the exposure using interview data on worktasks and hobbies. Associations with disease risk were evaluated for 10 exposures with a logistic regression analysis. RESULTS: The investigated exposures were generally not associated with cytogenetically abnormal MDS. Effect estimates for specific cytogenetic or morphologic subgroups were generally imprecise. Occupational exposure to extremely low-frequency magnetic fields (EMF) was associated with MDS with a normal karyotype [odds ratio (OR) 2.0, 95% confidence interval (95% CI) 1.0-4.0]. The exposure-response association was consistent for intensity but inconclusive for duration. A decreased risk was observed for MDS, irrespective of karyotypic pattern, among farmers and farmhands (OR 0.53, 95% CI 0.35-0.81). CONCLUSIONS: Cytogenetically abnormal MDS was generally not associated with occupational or hobby exposure to known or suspected genotoxic agents. However, exposure prevalences and intensities were low for several agents. An association was suggested between occupational exposure to EMF and MDS with a normal karyotype. Biases due to differential information quality and selective participation cannot be ruled out.

Case-Control Studies↗
PubMed2002

Myosin heavy chain isoforms influence surface EMG parameters: a study of the trapezius muscle in cleaners with and without myalgia and in healthy teachers.

The present study had two aims: (1) to investigate potential differences in proportion of myosin heavy chain isoforms in the trapezius muscle between female cleaners with and without trapezius myalgia and healthy teachers, and (2) to elucidate if myosin heavy chain composition and surface electromyogram (EMG) during an isokinetic endurance test of shoulder flexors are significantly related. The subjects were divided into three groups: (1) 25 female cleaners with diagnosed work-related trapezius myalgia; (2) 25 female cleaners without work-related trapezius myalgia; (3) a control group of 21 healthy female teachers who were not exposed to repetitive or static muscle work. All subjects performed a test involving150 forward flexions using an isokinetic dynamometer. During the test surface EMG was recorded from the trapezius muscle. Muscle samples were obtained from the descending part of the trapezius muscle. The fibre type area percentage based on ATPase staining and the proportions of different MHC isoforms as determined by gel electrophoresis. The trapezius was dominated by MHC I (71%), followed by MHC IIA (22-24%), and MHC IIX (5-7%); no significant differences between the three groups of subjects were found. The proportion of MHC I correlated negatively with MHC IIA ( r=-0.78; P<0.001) and MHC IIX ( r=-0.53; P<0.001). Significant correlations existed between the proportion of the MHC isoforms and the corresponding proportion of the fibre type area; 27-45% of the variance was explained. The multivariate analysis of the three groups of subjects revealed that MHC variables showed intercorrelations with EMG (both amplitude and frequency variables). However, the directions of the relationships differed among the three groups; the cleaners with myalgia and the teachers showed the greatest similarities in patterns. Intrinsic muscle properties appear to influence the frequency content of the EMG, which is in contrast to some of the theoretical models of the EMG. Our data could suggest that monotonous work such as professional cleaning can change the relationships between muscle structure and the frequency content of the EMG.

Electromyography↗
PubMed2002

Effects of systematic exposure assessment errors in partially ecologic case-control studies.

BACKGROUND: In ecologic studies, group-level rather than individual-level exposure data are used. When using group-level exposure data, established by sufficiently large samples of individual exposure assessments, the bias of the effect estimate due to sampling errors or random assessment errors at the individual-level is generally negligible. In contrast, systematic assessment errors may produce more pronounced errors in the group-level exposure measures, leading to bias in ecologic analyses. METHODS: We focus on effects of systematic exposure assessment errors in partially ecologic case-control studies. Individual-level information on disease status, group membership, and covariates is obtained from registries, whereas the exposure is a group-level measure obtained from an established exposure database. Effects on bias and coverage of 95% CI in various error situations are investigated under the linear risk model, using both simulated and empirical ecologic data on exposures that are binary at the individual level. RESULTS: Our simulations suggest that the bias produced by systematic exposure assessment errors under the linear risk model is generally approximately equal to the ratio of the slope bias and the intercept bias in ordinary linear regression with measurement errors in the independent variable. Consequently, bias in either direction can occur. Exposure assessment errors that systematically distort the group-level exposure measures have more pronounced effects on bias and coverage than errors producing random fluctuations of the group-level measures, which imply bias towards the null. CONCLUSIONS: The results indicate the need for careful consideration of potential effects of systematic distortions of the group-level exposure measures when constructing and applying group-level exposure databases, such as probabilistic job exposure matrices.

Bias↗
PubMed2002

Estimating attributable fraction in partially ecologic case-control studies.

Partially ecologic case-control studies combine group-level exposure data with individual-level data on disease status, group membership, and covariates. If the exposure measure is the exposure prevalence of various groups, the attributable fraction (AF; the estimated proportion of cases that are attributable to exposure) can be estimated by classifying all subjects in groups with exposure prevalence above zero as exposed. Such a threshold AF estimator ([AF]T) is unbiased in confounding-free situations if the threshold is 100% sensitive, but it might be imprecise. We propose an alternative AF estimator, [AF]L, for partially ecologic case-control studies under a linear model for the association between the exposure prevalence and the odds ratio. The proposed estimator can also be applied to situations in which covariate adjustment is necessary. [AF]T and [AF]L are compared with respect to precision and bias. [AF]L is also unbiased when the exposure prevalence is zero in the group(s) assessed as unexposed. Using [AF]L will consistently result in improved precision compared with [AF]T, although the results may not differ substantially. The 95% confidence intervals for both AF estimators show satisfactory coverage in bias-free exposure scenarios. Pronounced negative bias and decreased coverage result for both AF estimators even when small fractions (3-9%) of exposed subjects are included in the group assessed as unexposed.

Bias↗