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Biomedical subjects

H J Verhaar

Publications and source records attributed to H J Verhaar.

At least 19 recordsLinked to original sources
PubMed2003

[Percutaneous vertebroplasty in the treatment of osteoporotic vertebral compression fractures: review of the literature].

OBJECTIVE: To determine the effectiveness and safety of percutaneous vertebroplasty for the treatment of osteoporotic vertebral compression fractures as published in the scientific literature. DESIGN: Literature review. METHOD: Medline and the Cochrane library were searched with the terms 'percutaneous vertebroplasty', 'vertebral compression fractures', 'osteoporotic' and 'osteoporosis'. Criteria for inclusion were: (a) the studies had to have been published in the period January 1985-August 2002, (b) the study population had to include at least 10 patients, (c) the patients had to have been treated with percutaneous vertebroplasty, and (d) the diagnosis had to have been 'osteoporotic vertebral compression fracture'. RESULTS: Twelve studies met the inclusion criteria. Pain relief was seen in 60%-100% of the patients within the first 24 hours and this result improved to 78-100% in the long term (maximum 4 years). The complications immediately after the procedure were related to cement leakages and were mostly of no clinical consequence. Serious complications such as pulmonary embolism were rare. In the long term, percutaneous vertebroplasty was associated with an increased risk of fractures in the adjacent vertebrae. CONCLUSION: Percutaneous vertebroplasty seems to be effective and safe in the treatment of osteoporotic vertebral compression fractures. A prospective randomised intervention study has, however, not yet been performed. For the time being, percutaneous vertebroplasty should be reserved for carefully selected patients in whom conservative therapy has not produced results.

Adult↗
PubMed2001

Differences in gait parameters at a preferred walking speed in healthy subjects due to age, height and body weight.

The objective of our cross-sectional study was to investigate the changes associated with age and gender in walking speed, stride length and cadence of healthy women and men over the adult age range, and establish the effects of anthropometric indices such as height and body weight. We examined 118 women and 121 men (age range, 19-90 years). Subjects walked at their preferred speed over a 12-meter walkway crossing two Kistler force plates: cadence was calculated from heel strike times recorded from the Kistler force plates; walking speed was measured using an infrared reflecting system; and stride length was calculated from the walking speed and cadence. Older healthy subjects had lower values for walking speed and stride length than younger subjects. While there is little difference in the percentage reduction between women and men over the adult age range. the absolute values for walking speed are lower in women than men at all ages. In women, the percentage of explained variance for decline in walking speed was 30%, and for decline in stride length 400%. If body weight was also taken into account, the percentage of explained variance for walking speed was 37%, and for stride length 59%. A similar calculation for men yields 34% for decline in walking speed, and 42% for decline in stride length. Cadence was not associated with age, height and body weight. The standard errors for the estimates of walking speed in both women and men, respectively, are reduced by 8% and 3% using the multiple regression technique. The corresponding standard errors for stride length were reduced by, respectively, 19% and 13% if height in either sexes, or height and body weight in women, were taken into account. In conclusion, preferred walking speed and stride length decline with age in healthy people. Lower values found in old healthy subjects partly contributed to the difference in height and body weight between old and young subjects. Cadence was not correlated with age, height and body weight.

Adult↗
PubMed2001

The effect of tibolone on fat mass, fat-free mass, and total body water in postmenopausal women.

Changes in body composition occur around the menopausal transition. The major characteristics are a decline in fat-free mass and an increase in body fat as a percentage of body weight. These alterations might be affected by age only or by menopause-related changes in hormone concentration. In this study the effects of tibolone, a tissue-specific compound with favorable effects on bone, vagina, and climacteric symptoms, were determined on body composition using bioelectrical impedance analysis. The focus was especially on fat mass, fat-free mass, and total body water in a group of 85 healthy women (mean +/- SD age, 54.2 +/- 4.7 yr), between 1-15 yr postmenopausal. Participants were randomly assigned to either tibolone (2.5 mg; n = 42) or identically appearing placebo tablets (n = 43) daily for 12 months. All analyses were based on the intent to treat group and last visit. Compared with placebo, tibolone significantly increased fat-free mass by 0.85 kg (P = 0.003) and total body water by 0.78 liter (P = 0.001). No significant difference was observed on the fat mass parameter (P = 0.16). From these results it can be concluded that tibolone may counteract the postmenopausal changes in body composition.

Adipose Tissue↗
PubMed2000

Evaluation of the applicability of HRT as a preservative of muscle strength in women.

OBJECTIVES: To review the studies that have been undertaken on the effects of postmenopausal hormone replacement therapy (HRT); especially oestrogen (+progestin) regimens on the preservation of muscle strength. Current knowledge of the mechanisms and actions of steroid- and sex hormones on skeletal muscle tissue will be used in an attempt to clarify the mechanism of action of a possible effect. The objective is to arrive at an agreement on whether or not postmenopausal oestrogen administration has a positive influence on skeletal muscle tissue. METHODS: Peer-reviewed publications were assessed. RESULTS: An age-related decrement in muscle strength can be found in both men and women. However, in women, an extra decline can be observed around the time of menopause. A possible relationship between the additional diminution in muscle strength and altered hormone concentrations after the onset of menopause has been suggested. Since women nowadays spend one-third of their life postmenopausal, it is extremely important to keep the decline in muscle mass as small as possible. Besides the continuation of a physically active lifestyle, HRT was suggested to serve as a protective mechanism. Although, the usefulness of HRT as a preservative of muscle strength appeared controversial. CONCLUSIONS: Skeletal muscle strength is sensitive to training up to a high age, though continuation of physical activity does not appear to protect skeletal muscles completely from age-related decrements. Therefore, the development of another preventive method would be useful. Considering the present knowledge it has all the hallmarks that HRT can be a useful tool in the maintenance of muscle strength in postmenopausal women. None the less, further research is necessary to endorse this theory.

Aging↗
PubMed2000

Muscle strength, functional mobility and vitamin D in older women.

Vitamin D deficiency may lead to loss of type II muscle fibres, and thereby to atrophy of proximal muscles with an increased risk of falling and bone fractures. The aim of the study was to determine if six months of vitamin D treatment (0.5 microg alphacalcidol) could positively influence values for muscle strength and functional mobility in vitamin D-deficient older women. Twenty-seven women entered the study which took place at a teaching hospital outpatient department. Ten vitamin D-deficient (serum 25(OH)D3 <20 nmol/L) older (>70 years) women and 13 age-matched female subjects with normal vitamin D levels (serum 25(OH)D3 >30 nmol/L) completed the study. Preand post-treatment data were obtained for isometric knee extensor strength, handgrip strength and functional mobility (walking distance over 2 minutes and the timed i'Up & Go" test). Six months of treatment with alphacalcidol led to significant improvements (compared to the controls) in values of isometric knee extensor strength (left leg: 14.6% +/- 5.7%. p=0.03; right leg: 11.5% +/- 5.0%, p=0.02) (mean +/- SEM). The achievements in the timed "Up & Go" test and 2-minute walking test did not improve in the alphacalcidol group compared to the controls after 6 months. However, within the vitamin D-deficient group, 6 months of alphacalcidol treatment led to a significant increase in the walking distance over 2 minutes (increase from 137.6 +/- 12.6 to 151.3 +/- 11.2 meters, p=0.03). The controls, with normal vitamin D levels, did not exhibit improvements in performance of any of the tests over a period of 6 months. Summarized, alphacalcidol seems to improve muscle strength and walking distance over 2 minutes in vitamin D-deficient older women.

Aged↗
PubMed2000

Classifying environmental pollutants: Part 3. External validation of the classification system.

In order to validate a classification system for the prediction of the toxic effect concentrations of organic environmental pollutants to fish, all available fish acute toxicity data were retrieved from the ECETOC database, a database of quality-evaluated aquatic toxicity measurements created and maintained by the European Centre for the Ecotoxicology and Toxicology of Chemicals. The individual chemicals for which these data were available were classified according to the rulebase under consideration and predictions of effect concentrations or ranges of possible effect concentrations were generated. These predictions were compared to the actual toxicity data retrieved from the database. The results of this comparison show that generally, the classification system provides adequate predictions of either the aquatic toxicity (class 1) or the possible range of toxicity (other classes) of organic compounds. A slight underestimation of effect concentrations occurs for some highly water soluble, reactive chemicals with low log K(ow) values. On the other end of the scale, some compounds that are classified as belonging to a relatively toxic class appear to belong to the so-called baseline toxicity compounds. For some of these, additional classification rules are proposed. Furthermore, some groups of compounds cannot be classified, although they should be amenable to predictions. For these compounds additional research as to class membership and associated prediction rules is proposed.

Animals↗
PubMed2000

Relationships between physical performance measures, age, height and body weight in healthy adults.

OBJECTIVE: we measured muscle strength and functional mobility in healthy men and women over the adult age range to investigate the changes with age and sex, and to establish the effects of the anthropometric indices height and weight. DESIGN: cross-sectional study. SUBJECTS AND METHODS: we recruited 74 healthy women (mean age 49.0, range 20-90) and 81 healthy men (mean age 51.6, range 20-90). We measured maximum isometric knee extension strength, handgrip strength and explosive leg extensor power. We assessed functional mobility quantitatively with the timed 'get up and go' test and the modified Cooper test. RESULTS: older subjects had lower values for muscle strength and muscle power than young subjects. Times for the timed 'get up and go' test were longer and distances in the modified Cooper test shorter. At about the age of 55, women showed an acceleration in the decline of isometric knee extension strength and handgrip strength (between 20 and 55 years, knee strength decreased by 10.3% and handgrip strength decreased by 8.2%, between 55 and 80 years the decreases were 40.2% and 28% respectively). Men showed a more gradual declines over the adult age range, with decreases in knee and handgrip strength of 24% and 19.6% between 20 and 55 years, and 23% and 17.4% between 55 and 80 years. The age-related decline is partly associated with differences in height and body weight. Women had higher correlations between muscle strength and functional mobility tests than men. CONCLUSIONS: muscle strength and functional mobility decline with age in healthy people; in women we observed an accelerated decrement in muscle strength above the age of 55. Lower values in healthy old subjects are partly associated with differences in height and body weight.

Adult↗
PubMed2000

Age-sensitive cognitive function, growth hormone and insulin-like growth factor 1 plasma levels in healthy older men.

Circulating levels of growth hormone (GH) change during the process of aging. Decline of cognitive functioning with aging is also well established. In this study, we investigated whether insulin-like growth factor 1 (IGF-1) and the GH response to a challenge of GH-releasing hormone and GH-releasing peptide 6 were associated with age-sensitive cognitive functions, but not with functions that do not decline with aging, in 17 healthy male subjects aged between 66 and 76 years. In addition, relations with anthropometric measures were examined. Neuropsychological performance was scored on tests of variables not sensitive to aging (general knowledge, vocabulary, basic visual perception and reading ability), and of variables sensitive to aging (visuoconstructive ability, perceptual motor and mental processing speed, and verbal long-term memory). After correcting for education, the serum GH response was significantly associated with two age-sensitive cognitive tests (measures of mental processing speed), but with none of the tests not sensitive to aging. However, the direction of the association was opposite to the relation between IGF-1 and these cognitive tests: higher levels of GH response were associated with poorer cognitive performance, whereas higher levels of IGF-1 were associated with better performance. GH response, but not IGF-1, was inversely correlated with body mass index. The results are in accordance with previous research suggesting a disruption of the relation between IGF-1 and GH secretion in older age.

Aged↗
PubMed1999

Insulin-like growth factor-I and cognitive function in healthy older men.

The GH/insulin-like growth factor-I (GH/IGF-I) axis is known to be involved in aging of physiological functions. Recent studies indicate that the GH/IGF-I axis may be associated with cognitive functioning. The aim of the present study was to determine whether the age-related decline in circulating levels of IGF-I, as an index of anabolic status, is associated with cognitive functions that are known to decline with aging, but not with cognitive functions not sensitive to aging. Twenty five healthy older men with well-preserved functional ability participated in the study. We also administered neuropsychological tests of general knowledge, vocabulary, basic visual perception, reading ability, visuoconstructive ability, perceptual-motor speed, mental tracking, and verbal long-term memory. Performance on the last four tests decline with aging, whereas the first four of these tests have been shown not to be sensitive to cognitive aging. Mean age of the subjects was 69.1 +/- 3.4 (SD) yr (range 65-76 yr), their mean body mass index was 27.0 +/- 2.4 kg/m2, and their mean IGF-I level was 122 ng/mL (range: 50-220). We found IGF-I levels to be significantly associated with the performances (controlled for education) on the Digit Symbol Substitution test (r = 0.52, P = 0.009) and the Concept Shifting Task (r = -0.55, P = 0.005), which measure perceptual-motor and mental processing speed. Subjects with higher IGF-I levels performed better on these tests, performance on which is known to decline with aging. In conclusion, the results of this study support the hypothesis that circulating IGF-I may play a role in the age-related reduction of certain cognitive functions, specifically speed of information processing.

Aged↗
PubMed1998

Role of kinetics in acute lethality of nonreactive volatile organic compounds (VOCs).

The role of kinetics in the acute inhalation toxicity of nonreactive, volatile organic compounds (VOCs), including lipophilic and hydrophilic compounds, was analyzed with a physiologically based pharmacokinetic (PB-PK) model for the rat. For 15 VOCs, a total of 23 LC50 values were retrieved from the literature. It was observed that the external exposure parameter (LC50.exposure length; in ppm.h), varied approximately 60-fold. Concentrations of compounds in the lipoid brain fraction were simulated using a kinetic model. This lead to a more than 10-fold reduction in the toxic range of the 15 VOCs. The average value for this simulated dose surrogate was 70 +/- 31 mM for all VOCs. These observations support the presumption that nonspecific, acute narcotic lethality is directly related to the extent of VOC distribution into lipoid brain constituents. The present results can be used for estimation of the acute lethality of nonreactive VOCs on the basis of kinetic simulations. In addition, the presently calculated dose surrogate for VOC lethality in rats is found to be very similar to the reported internal lethal concentrations of so-called "baseline toxicity compounds" in fish. This indicates a common mechanism of acute VOC toxicity among mammalian and aquatic species.

Alkanes↗
PubMed1998

Are arm span measurements useful in the prediction of osteoporosis in postmenopausal women?

A consensus report on osteoporosis in The Netherlands recommends general practitioners to use an arm span-height difference of at least 3 cm as one of the criteria for suspecting osteoporosis. In this study it was investigated how well this criterion discriminates between patients with established osteoporosis and controls in a group of postmenopausal women. When the Dutch general practitioners criterion of arm span-height difference exceeding 3 cm was applied in a logistic regression analysis to predict the probability of having osteoporosis, a resultant sensitivity of 58% and a specificity of 56% were found. In order to improve the predicted probability of osteoporosis, two more predictors in addition to the arm span-height difference were introduced in the logistic regression model. The first additional predictor related to information whether subject's age was below or above 70 years, and the second whether the arm span was below or above 160 cm. All three predictors appeared to be highly significant. It was shown that the predicted probability of osteoporosis by this model could be considerably improved when the age category and the arm span category were also taken into account, leading to a sensitivity of 81% while the specificity amounts to 64%. This seems quite satisfactory for such a simple method and clearly improves on the original single criterion of arm span-height difference.

Age Factors↗
PubMed1998

Understanding and estimating membrane/water partition coefficients: approaches to derive quantitative structure property relationships.

In the current study we describe three approaches to derive quantitative structure property relationships (QSPRs) that give insight in the interactions that are important in membrane/water partitioning. In the first model only semiempirically (AM1) calculated descriptors are used to model membrane/water partition coefficients. Additionally, differences between the n-octanol/water and membrane/water partition coefficients are explored using a small selection of calculated descriptors. The results from both these models show that besides the partitioning between an organic phase and water, additional hydrogen-bonding parameters (epsilonLUMO, Q-, and Q+) should be taken into account. Finally, using structural fragment values, a QSPR was derived to correct the n-octanol/water partition coefficient to obtain membrane/water partition coefficients, in case that obtaining AM1 descriptors is not feasible. The QSPRs that are presented here include only alcohols, benzenes, anilines, phenols, nitrobenzenes, quinoline, esters, and amines. Due to the data limitation, the models should be regarded preliminary for other structures, and caution is necessary when modeling charged species.

Amines↗
PubMed1998

Spatial-temporal analysis of mobility over the adult age range using the Postural-Locomotor-Manual Test.

BACKGROUND: Mobility measurements were performed on healthy adult subjects to investigate changes over the adult age range and to obtain reference values. METHODS: Ninety-five males (19-90 years, mean 58.2) and 122 females (19-90 years, mean 51.8) were measured using the commercially available Postural-Locomotor-Manual Test (PLM-test). Subjects are required to perform a standard maneuver that is recorded using an optoelectronic technique. RESULTS: Older subjects carried out all phases of the maneuver more slowly than younger subjects. At about the age of 50 years, females showed a more rapid slowing down. Males showed a more gradual decrease over the adult age range. CONCLUSION: The PLM-test provides a fairly simple noninvasive method of assessing motor performance. However, it is important to separate male and female data in the determination of reference values.

Adult↗
PubMed1998

Approaches to developing alternative and predictive toxicology based on PBPK/PD and QSAR modeling.

Systematic toxicity testing, using conventional toxicology methodologies, of single chemicals and chemical mixtures is highly impractical because of the immense numbers of chemicals and chemical mixtures involved and the limited scientific resources. Therefore, the development of unconventional, efficient, and predictive toxicology methods is imperative. Using carcinogenicity as an end point, we present approaches for developing predictive tools for toxicologic evaluation of chemicals and chemical mixtures relevant to environmental contamination. Central to the approaches presented is the integration of physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) and quantitative structure--activity relationship (QSAR) modeling with focused mechanistically based experimental toxicology. In this development, molecular and cellular biomarkers critical to the carcinogenesis process are evaluated quantitatively between different chemicals and/or chemical mixtures. Examples presented include the integration of PBPK/PD and QSAR modeling with a time-course medium-term liver foci assay, molecular biology and cell proliferation studies. Fourier transform infrared spectroscopic analyses of DNA changes, and cancer modeling to assess and attempt to predict the carcinogenicity of the series of 12 chlorobenzene isomers. Also presented is an ongoing effort to develop and apply a similar approach to chemical mixtures using in vitro cell culture (Syrian hamster embryo cell transformation assay and human keratinocytes) methodologies and in vivo studies. The promise and pitfalls of these developments are elaborated. When successfully applied, these approaches may greatly reduce animal usage, personnel, resources, and time required to evaluate the carcinogenicity of chemicals and chemical mixtures.

Algorithms↗
PubMed1997

A quantitative property-property relationship (QPPR) approach to estimate in vitro tissue-blood partition coefficients of organic chemicals in rats and humans.

The present study describes quantitative property-property relationships (QPPRs) for the partitioning of organic chemicals between blood and tissue homogenates from both rats and humans. The n-octanol/water partition coefficient (K[ow]) is used as a non-biological descriptor. QPPRs for human tissue-blood partition coefficients (PCs) were derived from a dataset of 24 volatile organic compounds in blood, liver, muscle, fat, kidney and brain tissue homogenates. QPPRs were also derived for the PCs of rat tissues, using a dataset of 42 volatile organic compounds in blood, liver, muscle and fat tissue homogenates. These QPPRs were evaluated using a test set of 10 compounds for human tissues and a test set of 14 compounds for rat tissues. For both human and rat test sets, it was generally observed that most estimated PCs were within a range of 50-200% of their experimental values. The present approach is concluded to offer a rapid means for the estimation of tissue-blood PCs of compounds on the basis of K(ow) values. In addition, indications for a possible role of tissue components other than lipid and water in the tissue-blood partitioning process of compounds were observed from the calibration results of the model.

1-Octanol↗