Biomedical subjects

S E Vollset

Publications and source records attributed to S E Vollset.

At least 73 records · Page 4Linked to original sources

PubMed1995

Exact power computation for dose-response studies.

The toxicity of an agent or the therapeutic effect of a drug may be assessed by a dose-response study. We present a method for computing the exact power of exact and large sample statistical tests employed for binary response data from such a study. This method, based on recursive polynomial multiplications, enables fast computation of exact power for studies with up to a moderately large sample size. We demonstrate the efficiency of our method using three examples. The method is suitable for the design and power analysis of dose-response studies in which the usual asymptotic approximations are suspect.

Adenoma↗

PubMed1995

Do reproductive factors influence colorectal cancer survival?

During 29 years follow up of 63,090 Norwegian women, 1347 women had a diagnosed cancer of the colon or rectum. Seven hundred and fifty-five of these women (56%) subsequently died of colorectal cancer. We investigated possible relationships between reproductive history and cancer survival and found little evidence that reproductive history is of prognostic value for colorectal cancer survival.

Adult↗

PubMed1995

The effect of the type of cement on early revision of Charnley total hip prostheses. A review of eight thousand five hundred and seventy-nine primary arthroplasties from the Norwegian Arthroplasty Register.

We studied the survival of 8579 Charnley prostheses, in 7922 patients, according to the different types of cement that had been used. All of the patients had had a primary total hip replacement for primary coxarthrosis. The mean duration of follow-up was 3.2 years (range, zero to 6.4 years). The data were collected from the national Norwegian Arthroplasty Register. The duration of survival was defined as the time to revision due to aseptic loosening. The Kaplan-Meier estimate of survival at 5.5 years for the 1226 femoral components that had been implanted with low-viscosity cement was 94.1 per cent (95 per cent confidence interval, 92.1 to 96.2 per cent), compared with 98.1 per cent (95 per cent confidence interval, 97.5 to 98.6 per cent) for the 6589 components that had been implanted with high-viscosity cement (p < 0.0001). The remaining 764 femoral components had been implanted with Boneloc cement, which was classified as neither high nor low-viscosity, and these components were considered as a separate group in the analyses. The Boneloc cement had been used for only three years, and the two-year survival rate of these prostheses was 95.5 per cent (p < 0.0001). The cement contained an antibiotic in 2801 (42 per cent of the hips in which the femoral component had been implanted with high-viscosity cement, compared with only thirty (2 per cent) of those in which it had been implanted with low-viscosity cement.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗

PubMed1995

Early revision among 12,179 hip prostheses. A comparison of 10 different brands reported to the Norwegian Arthroplasty Register, 1987-1993.

On the basis of data from the Norwegian Arthroplasty Register during the period 1987-1993, we have compared times to revision for 10 different cemented total hip prostheses. A total of 11,169 patients, with 12,179 primary total hip replacements (THRs), performed with high viscosity cement for primary arthrosis and followed for a maximum of 6.4 years, were included in this study. The Kaplan-Meier estimate of the overall percentage revised after 5 years was 2.5 (95% Confidence Interval: 2.1-3.0). For the Charnley prosthesis (n 6,694), 2.9% were revised after 5 years (95% CI: 2.3-3.4). Using Cox regression to adjust for gender, age, type of cement and use of systemic antibiotic prophylaxis, the Charnley prosthesis was compared with the 9 other brands. The revision rate for the Spectron/ITH combination (Spectron acetabulum, ITH femur) (n 1,034) was only 0.35 (p 0.04) times that of the Charnley prostheses. The Elite/Charnley combination (Elite acetabulum, Charnley femur) (n 507) and the Müller Type prosthesis (n 116) showed poorer results with failure rates 2.3 (p 0.01) and 2.7 times (p 0.04) that of Charnley, respectively. Although the overall results for cemented THRs in general were good, clinically important differences in revision rates were demonstrated among the cemented prosthesis brands. Our findings underline the need for careful evaluation of different total hip replacements.

Hip Prosthesis↗

PubMed1995

Revision for aseptic loosening of uncemented cups in 4,352 primary total hip prostheses. A report from the Norwegian Arthroplasty Register.

From September 1987 until January 1994 the Norwegian Arthroplasty Register recorded 5,021 primary total hip replacements performed with uncemented acetabular components. We compared the survival until revision for aseptic loosening of the cup, in the 11 commonest types (n 4,352). The overall cumulative revision rate for the acetabular components was 3.2% after 5 years and 7.1% after 6 years, with large differences among the designs. With the hydroxyapatite (HA)-coated cups and the hemispheric porous-coated cups, the failure rate was less than 0.1%. Of the unthreaded hemispheric porous-coated cups, Harris-Galante and Gemini (n 626), none had been revised, and of the HA-coated cups, Atoll and Tropic (n 1,943), only 1 had been revised. For the threaded uncoated metal-backed cups, the results varied from no revisions of the PM cups (n 148) to a cumulative 6-year revision rate of 21% for the Ti-Fit (n 300). The all-polyethylene Endler cups (n 334) had a cumulative revision rate of 14%. Women and patients with inflammatory arthritis had poorer results. However, the type and the design of the cups were of far greater importance for the results than patient-related factors.

Acetabulum↗

PubMed1995

Early aseptic loosening of uncemented femoral components in primary total hip replacement. A review based on the Norwegian Arthroplasty Register.

The Norwegian Arthroplasty Register recorded 24,408 primary total hip replacements from 1987 to 1993; 2907 of them (13%) were performed with uncemented femoral components. We have compared the results of eight different designs, each used in more than 100 patients. Survivorship of the components was estimated by the Kaplan-Meier method using revision for aseptic loosening of the femoral component as the end-point. At 4.5 years, the estimated probability of revision for aseptic loosening for all implants was 4.5%, for the Bio-Fit stem 18.6% (n = 210) and for the Femora stem 13.6% (n = 173). The PM-Prosthesis and the Harris/Galante stem prostheses needed revision in 5.6% and 3.6%, respectively. The clockwise threaded stem of the Femora implant needed revision in 20% of right hips, but in only 4% of left hips. The short-term results of the four best uncemented femoral components (Corail, LMT, Profile and Zweimüller) were similar to those for cemented stems, with revision for loosening in less than 1% at 4.5 years. The importance of the control of innovative designs and the registration of early results is discussed.

Adolescent↗

PubMed1994

Efficient power computation for exact and mid-P tests for the common odds ratio in several 2 x 2 tables.

When designing a study that may generate a set of sparse 2 x 2 tables, or when confronted with 'negative' results upon exact analysis of such tables, we need to compute the power of exact tests. In this paper we provide an efficient approach for computing exact unconditional power for four exact tests on the common odds ratio in a series of 2 x 2 tables. These tests are the traditional exact test; a test based on a probability ordering of the sample space; and two tests based on ordering the sample space according to distance from the mean, or median. For each test, we consider both a conservative version and a mid-P adjusted version. We explore three computational options for power determination: exact power computation, calculation of exact upper and lower bounds for power, and Monte Carlo confidence bounds for power. We present an interactive program implementing these options. For study design, the program may be run several times to arrive at a sample configuration with adequate power.

Case-Control Studies↗

PubMed1994

Cerebrospinal fluid protein concentrations related to clinical findings in patients with sciatica caused by disk herniation.

The protein concentration in the cerebrospinal fluid (CSF) is often increased in patients with sciatica, probably due to leaking of plasma proteins through the blood-nerve root barrier into CSF. Positive straight leg raising test, paresis, altered sensibility, reduced reflexes, and type of treatment were related to the CSF protein concentrations in 180 patients with sciatica caused by verified lumbar disk herniation. Significantly higher values of the CSF/serum albumin ratio and the CSF/serum immunoglobulin G ratio were found both in patients with positive straight leg raising test results and paresis compared with patients with no clinical findings. In the patients who had undergone emergency surgery, the same ratio parameters were significantly higher when compared with those who had undergone routine surgery and those had not undergone surgery. Elevated CSF proteins seem to be important indicators of the functional status of the nerve root and a measure of the degree of seriousness of sciatica. The interaction of smoking on CSF proteins was also studied.

Adult↗

PubMed1994

Infant survival in Norway and Sweden 1985-88.

In recent years, considerable attention has been attached to the disquieting fact that infant survival is much lower in Norway than in Sweden. In the present study, comprising all live single births in Norway and Sweden during 1985-88, the observed infant mortality was 1.5 times higher in Norway than in Sweden. The largest difference between Norway and Sweden was found in infants of young mothers with high birth order. Thus for the second births of mothers aged less than 20 years the observed mortality ratio of Norway to Sweden was 1.8. The infant mortality ratio decreased with increasing maternal age for all birth orders, and for the second births of mothers aged 35 years or more the mortality ratio was 1.0. The higher infant mortality in Norway was evident throughout the first year of life, with the highest mortality ratio observed at 6-8 months of life. Adjustment for maternal age, birth order and geographical region did not alter the observed infant mortality ratios. In both countries, the highest risk was found among infants of young mothers. this suggests a need for a more extensive preventive health care system directed at young mothers during their pregnancy and the infancy period.

Adolescent↗

PubMed1994

Prognostic factors and survival in amyotrophic lateral sclerosis.

This study of clinical outcome in amyotrophic lateral sclerosis (ALS) evaluated 148 patients (93 men and 55 women) diagnosed in Hordaland county, Norway, during the period 1970 to 1990. In addition to evaluation of clinical data, data were available on sex, age at diagnosis, time from appearance of symptoms to diagnosis, family history, EMG and spinal fluid. Sixty-nine cases were bulbar ALS and 79 were spinal ALS. Median survival from diagnosis was 16.5 months, 26.0 months in the spinal and 12.1 months in the bulbar form. The survival time decreased with increasing age at the start of disease. A brief interval from start of symptoms to diagnosis was also a poor prognostic factor. Cases with mainly spastic clinical appearance had longer survival than those with marked atrophy. Sex, appearance of familial cases, increased protein level in the spinal fluid, or disease confirmed or not by EMG had no influence on the prognosis. The importance of the prognostic variables was assessed simultaneously using a proportional hazards model. To test the validity of the prognostic factors, a binary survival outcome was established and a predictive rule determined by logistic regression. The data were applied on 11 ALS cases collected outside Hordaland county. Only 1 out of 7 patients with a predicted probability of living more than 1 year actually died within this time period. Two out of 4 patients in the poor prognostic group were dead within a year from the time of diagnosis.

Adult↗

PubMed1994

Methylmalonic acid and homocysteine in plasma as indicators of functional cobalamin deficiency in infants on macrobiotic diets.

Methylmalonic acid and total homocysteine in plasma and serum have previously been used as indicators of intracellular cobalamin function in adults. To assess the usefulness of quantitation of these metabolites in the diagnosis of dietary cobalamin deficiency in infants, they were determined in plasma from 41 infants (aged 10-20 mo) on a macrobiotic diet and in 50 healthy group-matched omnivorous controls. In the macrobiotic infants, both methylmalonic acid and total homocysteine were markedly increased compared with controls (8-fold and 2-fold, respectively). Both metabolites showed an inverse relation to the plasma cobalamin level. The very low cobalamin content of the macrobiotic diet and low plasma cobalamin in macrobiotic infants makes an impaired cobalamin function likely in these infants. We therefore used dietary group as an independent indicator of cobalamin status. Different test parameters for cobalamin status were evaluated by comparing their ability to discriminate between the two dietary groups. Logistic regression analysis showed that methylmalonic acid followed by total homocysteine and cobalamin, in that order, were the strongest predictors of dietary group. Mean corpuscular volume and Hb had low discriminative power. We conclude that the determination of methylmalonic acid and total homocysteine represents a sensitive and specific test for the diagnosis and follow-up of nutritional cobalamin deficiency in infants. Furthermore, the finding of high methylmalonic acid and total homocysteine in plasma of most macrobiotic infants demonstrates a functional cobalamin deficiency in these subjects.

Diet, Macrobiotic↗

PubMed1994

Early failures among 14,009 cemented and 1,326 uncemented prostheses for primary coxarthrosis. The Norwegian Arthroplasty Register, 1987-1992.

In the Norwegian Arthroplasty Register, 15,335 primary total hip replacements (THR) in patients with primary arthrosis were followed for 0-5.4 years. The Kaplan-Meier estimate of cumulative failure (revision) after 4.5 years was 2.7 percent for cemented THR, compared to 6.5 percent for uncemented. In patients under 65 years the cumulative revisions for cemented and uncemented THR were 3.3 and 7.9 percent. For the acetabular components, the cumulative failures were 0.6 percent for cemented and 1.7 percent for uncemented, and for femoral components 1.7 and 3.9 percent after 4.5 years. Adjusting for age and sex using a Cox regression model, 2 times higher rates of failure were found comparing uncemented to cemented THR. The results for uncemented prostheses were more unfavorable in young patients. In men and women under 60, the revision rates were increased 6 and 3 times, respectively, for patients with uncemented THR compared to those with cemented THR. Restriction of the end-point to revision for aseptic loosening gave results similar to the over-all results. No difference between cemented and uncemented THR was seen for revisions due to infection, whereas the most unfavorable results for uncemented THR were seen when revisions due to causes other than infection and aseptic loosening were considered.

Adult↗

PubMed1993

Reproductive factors and survival from ovarian cancer.

During a 29-year screening follow-up of 63,090 Norwegian women, 644 women were found to have an ovarian cancer with known metastatic status as their first malignancy. Of these women, 419 subsequently died of ovarian cancer. As reproductive factors, particularly parity, are risk factors for ovarian cancer, we investigated possible relationships between reproductive history and survival from ovarian cancer. Except for an improved survival in women with more than one abortion, no significant relationships were found.

Abortion, Spontaneous↗

PubMed1993

Confidence intervals for a binomial proportion.

Thirteen methods for computing binomial confidence intervals are compared based on their coverage properties, widths and errors relative to exact limits. The use of the standard textbook method, x/n +/- 1.96 square root of [(x/n)(1-x/n)/n], or its continuity corrected version, is strongly discouraged. A commonly cited rule of thumb stating that alternatives to exact methods may be used when the estimated proportion p is such that np and n(1(-)p) both exceed 5 does not ensure adequate accuracy. Score limits are easily calculated from closed form solutions to quadratic equations and can be used at all times. Based on coverage functions, the continuity corrected score method is recommended over exact methods. Its conservative nature should be kept in mind, as should the wider fluctuation of actual coverage that accompanies omission of the continuity correction.

Binomial Distribution↗

PubMed1993

Association of hepatitis B and human immunodeficiency virus infections in Tanzanian population groups.

A study was performed to determine whether there is a correlation between hepatitis B virus (HBV) and human immunodeficiency virus (HIV) infection in population groups in the Dar es Salaam area in Tanzania where HBV infection is endemic. A panel of 460 sera from army recruits, health personnel and pregnant women was tested. In the whole group seromarkers of HBV infection were found in 61.9% of 134 HIV positive subjects versus 51.5% of 326 seronegative subjects, a difference which was not statistically significant (p > 0.05). In the group of pregnant women, however, 66.7% of 120 HIV positive subjects had markers of HBV infection versus 49.0% of the 157 HIV seronegative subjects (p < 0.01). This shows that a considerable proportion of young females are also exposed to HBV at the time they acquire HIV infection.

Female↗

PubMed1993

Reduction of exercise-induced ventricular arrhythmias in mild symptomatic heart failure by benazepril.

We studied 14 patients who had exercise-induced ventricular arrhythmias after a previous Q-wave myocardial infarction. All had symptomatic mild heart failure in New York Heart Association class II and a maximal oxygen consumption between 16 and 20 ml/kg/min. They were treated with the angiotensin converting enzyme inhibitor benazepril (20 mg) and hydrochlorothiazide (50 mg) for 3 months in a double-blind randomized cross-over study. Benazepril improved the maximal oxygen uptake by 15% and exercise time by 18%. Hydrochlorothiazide slightly increased exercise time (5%) and the respiratory exchange ratio but not oxygen consumption. The arrhythmias were nonsustained and reproducible in two baseline recordings. Compared with baseline, benazepril reduced the mean number (3.5 +/- 2.5) (+/- SD) of episodes of ventricular tachycardia by 66%, and total (47.4 +/- 40.9) and paired (5.2 +/- 4.5) premature ventricular contractions by 61% and 62%, respectively. Hydrochlorothiazide did not reduce the number of arrhythmias. Thus an improved cardiac function induced by benazepril is associated with a reduction in exercise-induced ventricular arrhythmias in patients with symptomatic mild heart failure after infarction.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1993

Risk factors for bacteriuria and clinical urinary tract infection in patients treated with clean intermittent catheterization.

To study factors that may predict the occurrence of bacteriuria and clinical urinary tract infection, a total of 302 patients using clean intermittent catheterization was followed. Bacteriuria was found equally in men and women, while clinical urinary tract infection was significantly higher among women. Predictive factors of clinical urinary tract infection were low age and high mean catheterization volume in women. In men low age, neurogenic bladder dysfunction and nonself-catheterization were predictors in addition to urine leakage in patients with neurogenic dysfunction. Bacteriuria was a risk factor of future clinical infection and bacteriuria. No other risk factor of bacteriuria could be identified in the female population, while low frequency of catheterization, high age and nonself-catheterization were predictive in men. Patients using anti-infective agents had fewer episodes of bacteriuria but significantly more clinical urinary tract infections compared to nonusers.

Adolescent↗

PubMed1993

Cerebrospinal fluid proteins as indicators of nerve root compression in patients with sciatica caused by disc herniation.

Patients with sciatica caused by lumbar disc herniation were studied to identify biochemical changes in the cerebrospinal fluid related to myelographic findings and clinical observations. One hundred forty-three patients were evaluated by myelography with regard to involvement of the dural sac and the nerve root. A medial group (20 patients) with evidence of dural sac impingement was compared to a lateral group (63 patients) and an extreme lateral group (9 patients) whose condition primarily affected the nerve root. The remaining 51 patients comprised a mixed group with involvement of both the dural sac and the nerve root. The mean cerebrospinal fluid/serum albumin ratio, cerebrospinal fluid/serum immunoglobulin G ratio, and cerebrospinal fluid total proteins showed a significantly increasing trend from the medial through the lateral to the extreme lateral groups. Patients with lateral lumbar disc herniations more often showed neurologic deficits. These results indicate that the elevated cerebrospinal fluid total protein found in the patients with sciatica is due to leaking of plasma proteins primarily from the nerve root into the cerebrospinal fluid. The cerebrospinal fluid proteins may be used as diagnostic parameters of nerve root compression, especially when surgery is a consideration or in patients in whom sciatica is unlikely.

Adolescent↗