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H Groeneveld

Publications and source records attributed to H Groeneveld.

13 recordsLinked to original sources
PubMed1997

A clinical evaluation of a novel toothbrush design.

A new toothbrush design, the Snakebrush, was clinically evaluated along with the Flexible and Precision brushes. In this parallel, random-allocation investigation, the plaque removing qualities of the 3 brushes were evaluated over a period of 30 days. 60 patients of good dental health between the ages of 20 and 30 years formed the basis of the clinical trial. Mean plaque area scores were evaluated and recorded after a 1-min brush at baseline, day 15 and day 30. Gingivitis indices and bleeding on probing indices were also recorded at the same time intervals. Both uni- and multivariate analyses of our data suggested that the Snakebrush removed significantly more plaque than the 2 controls. For both lingual and buccal surfaces, subjects who had used the Snakebrush showed a significant decline in bleeding on probing and qinqivitis indices.

Adult↗
PubMed1996

RNA phage KU1 has an insertion of 18 nucleotides in the start codon of its lysis gene.

We have determined the nucleotide sequence of group II RNA phage KU1. The most conspicuous difference in the comparison with other group II members such as GA and JP34 is the presence of an insertion in the start codon of the lysis gene. In GA and JP34, the coat and lysis genes overlap by one nucleotide in the configuration UAAUG. The 18-nt insertion in KU1 is positioned between the A and the U of the start codon. It does not affect the coat reading frame, but it destroys the AUG start codon and separates the previously overlapping genes by 17 nts. The insert creates a UUG codon at its 3' border which serves as the start site for lysis protein synthesis in KU1. We also show that analogous to the group I phages, such as MS2 and fr, expression of the lysis gene in KU1 and JP34 is coupled to termination of translation at the coat gene. RNA secondary structure models for the central parts of KU1 and JP34 are suggested which can account for the insertion as a separate stem-loop structure.

Base Sequence↗
PubMed1995

Translational control of maturation-protein synthesis in phage MS2: a role for the kinetics of RNA folding?

The gene for the maturation (A) protein of the single-stranded RNA coliphage MS2 is preceded by an untranslated leader of 130 nt. Secondary structure of the leader was deduced by phylogenetic comparison and by probing with enzymes and chemicals. The RNA folds into a cloverleaf, i.e., three stem-loop structures enclosed by a long-distance interaction (LDI). This LDI is essential for translational control. Its 3'moiety contains the Shine-Dalgarno region of the A-protein gene, whereas its complement is located 80 nt upstream, i.e., about 30 nt from the 5'-terminus of the RNA chain. Mutational analysis shows that this base pairing represses expression of the A-protein gene. We present a model in which translational starts can only take place on nonequilibrated RNA, in which base pairing between the complementary regions has not yet taken place. We suggest that this pairing is kinetically delayed by the intervening sequence, which contains the three hairpins of the cloverleaf. The model is mainly based on the observation that reducing the length of the intervening sequence reduces expression, whereas increasing the length has the opposite effect. In addition, further stabilization of the LDI by a stronger base pair does not lead to a decrease in A-protein synthesis. Such a decrease is predicted to occur if translation would be controlled by the equilibrium structure of the leader RNA. These and other observations fit a kinetic model of translational control by RNA folding.

Base Sequence↗
PubMed1992

A stochastic model for medium-term estimation of the prevalence of HIV infection in a South African heterosexual population.

This paper describes the development of a micro-simulation model to estimate the extent of HIV infection among black heterosexual South Africans and attempts to predict the number of newly acquired cases of HIV infection for the period 1985-2000. Owing to the lack of key data inputs, many assumptions are made. The inputs used are estimated demographic transition, HIV-positive immigrants, probability of being HIV-positive, probability of acquisition of infection upon at-risk contact by gender, time to AIDS distribution, average number of new sexual partners over time by age and gender, average number of sexual contacts per partner by gender and age group, and probability of sexual contact by age group between genders. Paediatric, homosexual and intravenous HIV cases are excluded from the model. The results indicate a fairly rapid increase in HIV infection from 1988 until the year 2000, when 5,664,487 adults, i.e. approximately 27% of the total adult (15-60 years) black population, could have become HIV-positive. This first phase of the model does not include the effect of a change in behaviour or the possible effect of effective drugs or vaccines and is therefore a worst-case scenario, maximum-potential estimate. The results are very similar to previously published South African actuarial and macro-simulation models.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Multivariate models for compliance with phase 3 cardiac rehabilitation services in Johannesburg.

The efficacy of an exercise cardiac rehabilitation programme depends on an adequate compliance of its participants. A 50% dropout rate after 12 months has been reported by most rehabilitation programmes. Compliance with attendance and the exercise prescription are monitored daily at the Johannesburg Cardiac Rehabilitation Centre. This study evaluated the attendance of 711 patients admitted to the programme between June 1986 and March 1990 and looked at possible differences in attendance and intensity rates of compliers and dropouts prior to dropout. Multiple regression analyses were performed on all patients using different measures of exercise compliance as dependent variables and patient characteristics on admission as explanatory variables in order to establish possible associations which could identify potential dropouts at an early stage. We found that 36% of patients dropped out by 12 months and that 50% managed to complete our 18 month programme. Dropouts complied less than compliers in terms of attendance and intensity before dropping out. Significant associations were found between the measures of compliance and patient characteristics. Age, smoking, peak oxygen uptake and a measure of hostility were identified as predictive factors. With the exception of the energy expended per session the variation in the other measures of compliance was poorly explained by the explanatory variables suggesting that other factors could be related to compliance at the Johannesburg Cardiac Rehabilitation Centre and need to be further evaluated.

Cardiac Care Facilities↗
PubMed1989

Construction and properties of an Epstein-Barr-virus-derived cDNA expression vector for human cells.

A cDNA expression vector containing the element oriP and the sequence encoding the Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) as well as the hygromycin B-resistance dominant marker gene has been constructed. Its characteristics have been compared to a similar vector lacking the EBV sequences. (a) The EBV+ vector is maintained as an episome with a copy number of approx. 50 per cell, whereas the number of the integrated EBV- copies is in general smaller than 10, when simian virus 40-transformed xeroderma pigmentosum fibroblasts (XP20S-SV) constitute the recipient cell line. (b) The presence of the EBV sequences in the vector resulted in a five- to ten-fold higher transfection efficiency with the Ca.phosphate precipitation technique. (c) cDNA inserts in the EBV+ vector are shown to be efficiently and properly expressed in the recipient cell. (d) If transfection is performed with a mixture of EBV+ vectors with different inserts, transfectants are shown to harbour different plasmids within one cell. (e) The ratio between these plasmids in one cell can be shifted in favour of a vector with a particular insert, when selection for this insert is performed. (f) Reconstruction experiments indicated that isolation of a low-abundance sequence from a mixture of vectors is at least 100-fold more efficient with the EBV+ system, than with the EBV- system. (g) Rescue of the episomal vector from transfected cells can be readily achieved.

Antigens, Viral↗
PubMed1988

Relationship of lung function loss to level of initial function: correcting for measurement error using the reliability coefficient.

The regression of lung function change on the initial lung function level is biased when the initial level is measured with random error. Several methods have been proposed to obtain unbiased estimates of regression coefficients in such circumstances. We apply these methods to examine the relationship between lung function loss over 11 years and its initial level in 433 men aged about 20 when first seen. On theoretical and practical grounds the best method is the correction of the regression coefficient using the reliability coefficient. This is defined as the ratio of the error free variance to the variance of the variable measured with error, and is easily estimated as the correlation between repeat measurements of the underlying level. In young men the loss of some lung functions (forced vital capacity [FVC], forced expiratory volume in one second [FEV1], forced expiratory flow in the middle half of expiration, and the ratio FEV1/FVC) do not appear to be related to initial level.

Adult↗
PubMed1984

Tuberculosis management in Soweto.

Despite the availability of highly effective therapy, tuberculosis (TB) remains a major problem in South Africa, even in urban centres such as Soweto which is relatively well provided with health services. We therefore assessed two aspects of TB management in Soweto: (i) the proportion of known tuberculous patients adequately treated; (ii) whether case finding through investigation of home contacts of notified patients was effective. In 1978 patients with TB were required to take chemotherapy for at least a year. Only 28% of newly notified patients attended the clinics frequently enough and/or were hospitalized long enough to obtain 80% or more of the treatment they required during that first year. A major part of this problem of non-compliance was infrequent attendance; these patients received therapy of an adequate duration, but at an inadequate dosage. At least 17% of patients over 10 years of age had tubercle bacilli in their sputa on microscopy more than 4 months after therapy was started. About two-thirds of known home contacts were investigated by the health services in accordance with their stated policy, and 5% of contacts were subsequently notified. Home-contact tracing therefore seems worthwhile.

Adolescent↗
PubMedDate not supplied

Predictors of exercise capacity and adaptability to training in patients with coronary artery disease.

PURPOSE: Systolic left ventricular dysfunction is a weak predictor of exercise tolerance in patients with chronic congestive heart failure. This study aimed to determine physiologic and other predictors of effort tolerance and adaptability to training in a wide variety of patients with coronary artery disease. METHODS: One hundred seventy-one patients (group 0) with documented coronary artery disease and various degrees of left ventricular dysfunction were enrolled into a medically supervised exercise training program for 6 months. One hundred six patients had an ejection fraction greater than 50% (group 1), 38 patients between 35% and 50% (group 2), and 27 patients less than 35% (group 3). RESULTS: Resting parameters of systolic and diastolic left ventricular function did not predict the effort tolerance of patients with coronary artery disease at any level of left ventricular impairment. Noncardiac factors including age, gender, Broca index, and forced vital capacity explained 50% of the variation in peak oxygen uptake in group 0. Peak oxygen uptake, ventilatory threshold, and treadmill time to exhaustion increased significantly after training in all groups. The magnitude of the improvement in these variables was the same for all groups. CONCLUSIONS: Noncardiac factors were better predictors of the effort tolerance of patients with coronary artery disease than parameters of left ventricular function at entry to an exercise program or after 6 months of training. A similar degree of adaptation to training was seen in all patients regardless of their degree of left ventricular systolic or diastolic dysfunction.

Adaptation, Physiological↗