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Biomedical subjects

R Svensson

Publications and source records attributed to R Svensson.

At least 37 records · Page 2Linked to original sources
PubMed1994

An analytical solution for the dynamic control of multileaf collimators.

All current optimization techniques in radiation therapy benefit from the use of strongly non-uniform radiation beams. The most flexible way of generating these fields under real time control is by elementary beam scanning and/or dynamic multileaf collimation. In this work general analytical expressions are derived for the required motion of the collimator leaves to achieve a desired energy fluence distribution or collimator opening density in the patient in the shortest possible time. By simplification of the general expressions the equations of motion have been derived for both the shrinking field and the curtain shutter techniques with the associated approximations clearly quantified. The mechanical limitations on leaf motion, caused by the finite velocity and acceleration, are taken into account. It is shown that almost any desired energy fluence distribution can be created even when the limitations on velocity and acceleration are considered. The basic rule with the curtain shutter technique is that when the energy fluence gradient along the direction of motion of the leaves is positive, the leading leaf should move at maximum speed and the lagging leaf should modulate the field. In regions where the gradient is negative the lagging leaf should instead move at full speed and the leading leaf should modulate the field. The overall treatment time is then proportional to the total increment in energy fluence or opening density between consecutive minima and maxima. For energy fluence profiles with numerous high peaks the treatment time may therefore increase considerably over that for conventional uniform dose delivery. However, in general the treatment time is prolonged by a factor of about two compared to a traditional uniform treatment. Obviously the method developed here for multileaf collimators is also suitable for simple block collimators since it can be used to deliver arbitrary regular or irregular 'dynamic wedge' profiles along the direction of motion of the collimator blocks.

Humans↗
PubMed1992

Efficacy and tolerance of roxithromycin in comparison with erythromycin stearate in patients with lower respiratory tract infections.

The efficacy and tolerance of roxithromycin 150 mg b.i.d. were compared with those of erythromycin stearate 500 mg b.i.d. in patients with lower respiratory tract infections. Out of 86 patients recruited for the study, 79 were evaluable for tolerance and 76 for efficacy. These patients were evenly distributed among the 3 investigational clinics, with 26, 25 and 28 patients, respectively. The diagnosis of lower respiratory tract infections was based on clinical, laboratory, radiological and/or physical findings and, when available, bacteriological and serological findings. The duration of treatment was 10 days, with follow-up at post-treatment visits directly after treatment and 6 weeks thereafter. The clinical outcome was satisfactory with no significant difference between the drugs. More patients reporting adverse events were on erythromycin than on roxithromycin (51.3% vs 17.5%; p = 0.003). The results suggest that roxithromycin is as effective as erythromycin stearate in the treatment of lower respiratory tract infections and causes fewer adverse effects.

Adult↗
PubMed1991

Computer-controlled mechanical testing machine for small samples of biological viscoelastic materials.

Time dependency in the mechanical properties of viscoelastic materials means that a variety of tests is often required to fully characterize their properties. Computer control is the best way of controlling loads and displacements and the rate at which they are applied, as well as recording and analysing the data produced. This paper describes apparatus for measuring the viscoelastic properties of articular cartilage in compression which is readily adaptable to any small sample in which accurate strain measurements require small, carefully controlled displacements. An IBM-type microcomputer is used to control a stepper motor driving a ball screw with a positional accuracy of about 1 micron.

Biomechanical Phenomena↗
PubMed1990

Assignment of an erbB-like DNA sequence to linkage group VI in fishes of the genus Xiphophorus (Poeciliidae).

The inheritance of 23 protein polymorphisms was compared with the inheritance of a DNA restriction fragment length polymorphism (RFLP) of a strongly cross-hybridizing erbB-related sequence, epidermal growth factor receptor-like-1 (EGFRL1), in Xiphophorus clemenciae X X. milleri-derived backcross hybrids. Two polymorphic bands were noted in this cross with a v-erbB probe after PstI digestion: a 10-kilobase (kb) band in X. clemenciae and a 9-kb band in X. milleri. Joint segregation analysis of the RFLPs and protein polymorphisms indicate that this erbB-related sequence can be assigned to Xiphophorus linkage group VI, which also comprises genes coding for glutamine synthetase (GLNS), nucleoside phosphorylase-2 (NP2), and transferin (TF). We have designated this RFLP as alleles at a locus called EGFRL1 because of very strong cross-hybridization with the v-erbB probe, known to be homologous to the mammalian EGFR gene. This mapping assignment is the first autosomal linkage of an oncogene sequence reported in fish, which provide a large number of genetically controlled experimental tumor models.

Animals↗
PubMed1989

Another Swedish family with complete properdin deficiency: association with fulminant meningococcal disease in one male family member.

Inherited deficiency of the complement component properdin is described in a Swedish family without any previous history of meningococcal infections. The properdin-deficient index patient died from a fulminant infection caused by Neisseria meningitidis serogroup Y. Family investigation revealed properdin deficiency in the patient's half-brother and in the maternal grandfather. The half-brother had a history of pneumococcal pneumonia and meningitis probably caused by Borrelia burgdorferi. Opsonic and bactericidal functions of serum were examined in the half-brother after immunization with tetravalent meningococcal vaccine. Vaccination promoted opsonization of N. meningitidis serogroups C and Y but not of serogroups A and W-135. The serum bactericidal activity increased against serogroup C and to some extent against serogroup W-135. This report emphasizes the importance of investigating the complement system even in families with single cases of fulminant meningococcal disease. Individuals with properdin deficiency might be protected from infection by immunization.

Adolescent↗
PubMed1986

The role of psychiatric factors in symptoms of hiatus hernia or gastric reflux.

The study comprised 26 patients with somatic symptoms indicating a hernia-reflux syndrome referred to a university hospital ear, nose and throat department. The aim was to throw light on the hypothesis that this syndrome is largely a psychosomatic problem. The patients were divided into two groups: subjects with and without laboratory findings of physical pathology of hernia and/or reflux. Intergroup comparisons were made of symptoms, a psychological test and psychiatric ratings. Those who had no laboratory findings of physical pathology often reported "phobia" and "feeling of lump in the throat", which were interpreted as signs of hysterical or somatizing mechanisms. Most of these patients showed a high level of anxiety in the psychological test. "Agitation", "depression" and "frustration" were characteristics of patients with laboratory findings of reflux. "Depression" was interpreted as a reaction to the somatic illness. The group with reflux contained more old male patients and that without more younger female patients.

Adult↗
PubMed1983

Influence of exteroceptive contextual conditions upon internal drug stimulus control.

Rats were trained in a spatial T-maze discrimination either in a drugged (D = pentobarbital, 17.5 mg/kg) or in a non-drugged (N = saline) state (drug discrimination learning). Either of two external discriminative stimulus sets (light vs complete darkness) was consistently associated with the D or N state. When tested in the presence of the external stimulus previously associated with training in the D state, the animals made more drug-appropriate choices when tested with low pentobarbital doses as compared to testing in the external stimulus condition previously associated with the N state. This was reflected both in the ED50 values and the slopes of the dose-generalization gradients. The gradients of the controls were intermediate to those of the experimental rats. The present data suggest a new approach for studying interactions between controlling features in environmental events and the internal state.

Animals↗
PubMed1983

Ceftazidime in clinical practice.

In an open trial, the efficacy of intravenously administered ceftazidime was evaluated in 106 adult patients with urinary or respiratory tract infections, soft tissue infections, osteitis and septicaemia. The most commonly isolated pathogens were Escherichia coli, Pseudomonas spp. and Staphylococcus aureus. Of 85 organisms isolated before treatment, 79% were cleared and 15% were cleared but later relapsed often because of the underlying conditions. Clinical cure was achieved in 70%, improvement occurred in 25% of the patients and 6% failed to respond. Marked increases in serum creatinine occurred in three patients with pre-existing renal impairment treated with ceftazidime in unmodified dosage. Exanthema, diarrhoea or local thrombophlebitis was noted in 13 patients.

Adult↗
PubMed1982

Low dose trimethoprim prophylaxis in long term control of chronic recurrent urinary tract infection.

26 patients with chronic urinary tract infections (UTI) were treated with 1 tablet of 100 mg trimethoprim (TMP) once daily for up to 6 months as long term prophylaxis. The recurrence rate before prophylaxis was 26/100 months, compared to a significantly lower frequency (3.3 recurrences/100 months, p less than 0.001) during prophylaxis. The post-prophylactic rate returned to the pre-prophylaxis rate: 23 recurrences/100 months. All Escherichia coli strains causing post-prophylactic UTI were TMP sensitive. The number of rectal enterobacteria were markedly reduced during prophylaxis (p less than 0.05). A 10% recovery of TMP resistant enterobacteria from rectal swabs was noted early (less than or equal to 1 month) during prophylaxis, but no significant further accumulation occurred.

Adolescent↗
PubMed1977

Listeric meningitis in the non-compromised host.

A small epidemic of listeric infection among non-compromised adults recently occurred in the western part of Sweden. All ten patients survived and the prognosis of listeric meningitis in non-compromised patients would seem to be considerably better than in the compromised host. A rapid initiation of ampicillin treatment (10-20 mg/kg of body weight daily) within 48 hours after onset of symptoms may be contributed to the excellent outcome in the present series besides a well-functioning intracellular killing mechanism which seems to be of the greatest importance in listeric infeciton.

Adult↗