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Biomedical subjects

H T Groeneveld

Publications and source records attributed to H T Groeneveld.

At least 55 records · Page 3Linked to original sources
PubMed1988

Evaluating obstetric risk scores by receiver operating characteristic curves.

The purpose of obstetric risk scoring systems is to identify pregnancies that will end in poor perinatal outcomes such as perinatal death. The proportion of such pregnancies identified by a risk scoring system can be increased by choosing a more lenient threshold criterion for the score beyond which the pregnancy is regarded as being at risk. This increase in sensitivity is gained at the expense of a decrease in specificity. Thresholds differ between published risk scoring systems, making it difficult to assess their relative merits using the measures of sensitivity and specificity. However, risk scores can be compared by constructing receiver operating characteristic curves, i.e., plotting the true positive rate against the false positive rate for multiple thresholds and calculating the area under the receiver operating characteristic curve (theta). In published systems used in this paper, values of theta, used to rank published obstetric risk scoring systems, ranged from 0.49-0.95. All scores used prepregnancy and early antenatal information. The risk scores with the highest predictive accuracy tended to include factors representing past reproductive experience and those from the late antenatal and intrapartum periods. Studies with statistical weighting of risk factors tended to use fewer late prenatal and intrapartum risk factors.

Female↗
PubMed1988

Fluctuating odontometric asymmetry in an urban South African black population.

The magnitude of fluctuating odontometric asymmetry is reported for a group of 106 urban South African Blacks by use of re-scaled asymmetry values and Euclidean map analyses. When these results were contrasted with those reported for South African Caucasoids and Paraguayan Lengua Indians, Blacks were found to be significantly more asymmetric. It is suggested that the disproportionately high levels of dental asymmetry may be ascribed to the high disease and malnutrition burden of South African Blacks and to decreased individual buffering ability. The present study failed to support Garn's model of x-chromosomal odontogenetic buffering in females, and also failed to confirm significant arcadal differences in the magnitude of fluctuating odontometric asymmetry.

Adolescent↗
PubMed1987

Static intraspecific maxillofacial allometry in the chacma baboon.

Adult static intraspecific allometry of jaw size and tooth area was evaluated in a sample of 104 Papio ursinus crania (52 male, 52 female). Tooth areas were calculated from mesiodistal and buccolingual measurements of all the teeth in both arcades and were scaled to four viscerocranial measurements: bimaxillary width, maxillo-alveolar length, mandibular length and bigonial width. Craniodental allometric analyses indicate that larger animals will tend to have proportionately shorter and narrower lower jaws. From the log-transformed interspecific analyses between P. ursinus and C. aethiops we conclude that males and females within each species share a common exponential value for jaw length. Hence increased sexual dimorphism for muzzle length in P. ursinus is attributable to increased divergence between the male and female slopes. Post-canine area was found to be significantly correlated to maxillary length and to canine size only in females, with exponential values similar to those reported for the same bivariate regressions in C. aethiops. A hypothesis of nutritional equivalence is advanced to account for these observations. Canine base area and the area of P3 were the only tooth areas that scaled in a positively allometric fashion to jaw size--but only in males. Hence the existence of a canine complex is confirmed in the male Chacma baboon, the size of which is related to jaw length.

Animals↗
PubMed1987

Some aspects of superovulation and fertilisation of Dorper sheep.

Response of Dorper sheep to treatment with FSH and PMSG and fertilisation after natural service, natural service following application of PGF2 alpha-containing gel on the posterior os cervix and surgical insemination with fresh semen were evaluated. FSH gave a significantly (P greater than 0.05) better response than PMSG. No significant differences between the different methods of fertilisation were observed.

Animals↗
PubMed1986

Fluctuating dental asymmetry as a measure of odontogenic canalization in man.

Fluctuating odontometric asymmetry was evaluated in 202 Lengua Indians and in 125 contemporary caucasoids using Euclidean map analyses, rescaled asymmetry values, and Naperian logarithmic transformations. Both populations showed bimodal distributions of canalizing ability, with significantly more Lengua Indians being less well canalized. Student t-tests indicated that significant interpopulation differences in rescaled asymmetry values centered around maxillary mesiodistal dimensions. Analyses of variance failed to show significant levels of sexual dimorphism in the magnitude of asymmetry for both populations. It is concluded that even in a relatively stress-free population, there exist some individuals who are less well canalized than others. When a population is subjected to elevated levels of parasitic and nutritional stress, the number of less-well-canalized individuals increases significantly.

Dental Pulp Cavity↗
PubMed1986

Cross-clamping of the thoracic aorta. Influence of aortic shunts, laminectomy, papaverine, calcium channel blocker, allopurinol, and superoxide dismutase on spinal cord blood flow and paraplegia in baboons.

There is a high incidence of paraplegia associated with thoracic aortic cross-clamping, even when cardiopulmonary bypass or shunts are used. In 56 adult baboons, spinal cord blood flow (SCBF), vascular anatomy, and paraplegia rates were evaluated. Tissue blood flow was measured by radioactive microspheres. Various procedures were used to increase SCBF and to prevent ischemia-reperfusion injury. It was found that the rate of paraplegia was inversely correlated with neural tissue ischemia (SCBF) and directly correlated with reperfusion hyperemia. Two methods completely prevented paraplegia. These two methods were a thoracic shunt with occlusion of the infrarenal aorta or cerebrospinal fluid drainage plus intrathecal papaverine injection, both of which were associated with an increased SCBF. Furthermore, papaverine dilated the anterior spinal artery (ASA) (p = 0.007) and increased the blood flow through the lower ASA. Whereas procedures utilizing a calcium channel blocker (flunarizine), allopurinol, superoxide dismutase (SOD), laminectomy alone, and a thoracoabdominal shunt not perfusing the arteria radicularis magna (ARM) all failed to prevent paraplegia, allopurinol (p = 0.026) and SOD (p = 0.004) did prevent gastric stress lesions, indicating that their failure to prevent paraplegia was not due to a lack of activity. Of great clinical interest is that, if a shunt is used and the ARM is perfused, infrarenal aortic cross-clamping increases SCBF, thus preventing paraplegia. Intrathecal application of papaverine proved to be even more effective in increasing SCBF and also completely prevented paraplegia. As this is a safer procedure than the insertion of shunts, this is the method of choice for the prevention of paraplegia associated with thoracic aortic cross-clamping. The preliminary trial using intrathecal papaverine in human beings has thus far shown no adverse side effects from the drug, and no paraplegia has occurred.

Allopurinol↗
PubMed1986

On the non-existence of compensatory tooth size interaction in a contemporary human population.

Compensatory tooth size interactions between early and later developing teeth within the same tooth class were empirically evaluated in a sample of 125 study casts of Caucasoid children. Mean buccolingual and mesiodistal diameters for first and second molars, pre-molars, and incisors were calculated, and those first developing teeth that were either larger of smaller than the mean were identified. Pearsonian correlation coefficients and chi-square tests revealed highly significant positive correlations between smaller of larger early developing teeth and their later developing neighbors. This total lack of compensatory tooth size interaction was also confirmed when outsized teeth (larger of smaller than one standard deviation from the mean) were used. Similar results were obtained when tooth size was corrected for arcade length, hence allowing for the rejection of Sofaer's model of compensatory tooth size interaction.

Bicuspid↗
PubMed1986

The assessment of fluctuating odontometric asymmetry from incomplete hominid fossil data.

Problems of small sample size and incompleteness of fossil data in the evaluation of metric asymmetry may be overcome by the application of cluster sampling techniques together with factorial analyses of variance. Degrees of fluctuating odontometric asymmetry are reported in Australopithecus, Homo erectus and Homo neanderthalensis. In all three populations mesiodistal dimensions were shown to be more asymmetric than buccolingual dimensions, with maxillary teeth exhibiting significantly greater degrees of asymmetry than mandibular teeth. Neanderthal teeth were significantly more metrically asymmetric than those of either Australopithecus or H. erectus, with population differences in asymmetry centered in the maxillary teeth.

Animals↗
PubMed1985

Patterns of dental wear in the Lengua Indians of Paraguay.

Wear patterns were examined on dental casts of 202 living Lengua Indians from the Chaco area of Paraguay. Consideration was given to the development of the molar helicoidal plane, age-related changes in occlusal attrition, coalescence of dentine exposures, interproximal attrition, and erupted crown height. This study lends support to Osborn's theory of the helicoidal plane development by showing that attrition enhances rather than modifies posteruption molar occlusal planes. The rate of interproximal attrition was found to slow down with the eruption and functional initiation of the third molars. Sinuous and cavo-convex interproximal contact areas that are generated with age, however, appeared to be less abrasion resistant than straight surfaces, hence leading to an increase in interproximal attrition rates with advanced age. Maximum crown height reduction occurred between the ages of 20 and 40 years in central incisors, canines, and first molars. Kruskal-Wallis tests and log linera models failed to demonstrate significant sexually dimorphic or antimeric differences in wear patterns of Lengua teeth.

Adult↗
PubMed1985

Relative observer accuracy for dichotomized variables.

We suggest that the relative accuracy of several observers of a disease manifestation can be assessed by comparing the strength of association between their observations and a known cause of that disease. In principle, the observer whose findings are most strongly associated with the causal variable has the least error. In practice many observations appear binary ("normal" or "abnormal") when the underlying distribution of the variable they measure is continuous. For this case of a dichotomized variable, several observers may find different prevalences of abnormality in the same sample either because their accuracy differs or because they use different thresholds above which they regard abnormality as present. A comparison of how strongly their observations are associated with a causal variable using statistical methods for binary observations may lead to incorrect conclusions about the relative accuracy of the observers. We suggest and evaluate a method, based on the biserial correlation coefficient, for comparing the relative accuracy of several observers who may differ in the thresholds they use.

Asbestosis↗
PubMed1985

A threshold model for punctuated gradualism.

A model for continuous and discontinuous evolutionary change is proposed that accommodates both punctuated equilibrium and phyletic gradualism. Natural selection operating on a gaussian distribution of phenotypes subjected to severe stress will result in a skewing of the normal distribution in the direction of the favoured phenotype. If a reproductive isolation threshold is imposed upon this model, rapid crossing of the threshold by large numbers of individuals within the skewed distribution will result in the sudden achievement of a critical descendant population mass. Mild directional selection however, will result in gentle shifts of the gaussian mean thus leading us to suggest that stasis and incipient speciatior are extremes of the same spectrum, defined by the rates of mean-shift in response to varying severities of selection pressure. Both punctuated and gradualistic evolution as accommodated in our model may further be described within Thom's cusp catastrophe theory.

Biological Evolution↗