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Biomedical subjects

P Dijkstra

Publications and source records attributed to P Dijkstra.

12 recordsLinked to original sources
PubMed2003

Nitrogen stable isotope composition of leaves and roots of plants growing in a forest and a meadow.

In controlled N-nutrition experiments, differences in delta15N composition of leaves and roots are regularly found. In this paper we report results from a survey of nitrogen stable isotope signatures of leaves and roots of 16 plant species growing under natural conditions in a meadow and a forest understorey, which differed in nitrate and ammonium availability. Significant differences between leaf and root were observed. The range of delta15N [leaf-root] values was -0.97 to +0.86 per thousand, small compared to published values from controlled N-nutrition experiment, but almost as large as the range of leaf delta15N values (-1.04 to +1.08 per thousand). Forbs showed the largest differences between leaves and roots and showed a significant difference with respect to habitat. Grasses and legumes did not show significant differences in delta15N [leaf-root] between the two habitats. Care must be taken when using leaf delta15N values as representative for whole-plant 15N composition in these two habitats.

Ecosystem↗
PubMed2001

Rationalizations and defensive attributions for high-risk sex among heterosexuals.

A group of 39 respondents high at risk for HIV and a group of 39 respondents low at risk for HIV were selected from a larger sample to examine their rationalizations and attributions for having unprotected sex. Respondents high at risk for HIV used more often rationalizations and attributions to justify and excuse their risky behavior. At the same time, respondents high at risk were somewhat more fearful of contracting Acquired Immune Deficiency Syndrome (AIDS), and did not deny the riskiness of their behaviors compared with low-risk respondents. It is suggested that interventions should not focus on enhancing risk perceptions, but rather on challenging rationalizations and attributions that foster risky sexual behavior.

Attitude to Health↗
PubMed2000

Smallest detectable difference of maximal mouth opening in patients with painfully restricted temporomandibular joint function.

Changes in maximal mouth opening reflect the impact of temporomandibular disorders and the effect of a therapeutic intervention. No information about the amount of change in maximal mouth opening with regard to reasoned decision-making is available. The smallest detectable difference, as a measure of reliability assessment, provides this information and is expressed in the unit of the measurement instrument. Twenty-five consecutive patients (5 males, 20 females) with a painfully restricted temporomandibular joint participated in this study. Measurements of maximal mouth opening were performed by two well-trained observers on two separate measurement days, one week apart. The maximal mouth opening measurements were repeated three times. Inter-observer, intra-observer, and test-retest reliability varied between 0.90 and 0.96. Inconsistency in measurement results analyzed in terms of absolute error variance, i.e. the measurement facets plus all the interactions, represented 11% of total variance. The smallest detectable difference of maximal mouth opening varied from 9 to 6 mm. For being successful in painfully restricted temporomandibular joint patients, statistically as well as clinically, the clinician has to measure at least 9 mm of improvement in maximal mouth opening. To reduce the smallest detectable difference from 9 to 6 mm, repeated measurement is necessary.

Adult↗
PubMed1999

Decreased leaf-miner abundance in elevated CO2: reduced leaf quality and increased parasitoid attack.

Most studies on the effects of elevated CO2 have focused on the effects on plant growth and ecosystem processes. Fewer studies have examined the effects of elevated CO2 on herbivory, and of these, most have examined feeding rates in laboratory conditions. Our study takes advantage of an open-top CO2 fertilization study in a Florida scrub-oak community to examine the effects of elevated CO2 on herbivore densities, herbivore feeding rates, and levels of attack of herbivores by natural enemies. Higher atmospheric CO2 concentration reduced plant foliar nitrogen concentrations, decreased abundance of leaf-mining insect herbivores, increased per capita leaf consumption by leafminers, and increased leafminer mortality. As suggested by other authors, reduced foliar quality contributed to the increase in herbivore mortality, but only partly. The major factor increasing mortality was higher attack rate by parasitoids. Thus increasing CO2 concentrations may reduce the survivorship of insect herbivores directly, by reducing plant quality, but also indirectly, by changing herbivore feeding and eliciting greater top-down pressure from natural enemies.

Animals↗
PubMed1988

Persistent sternum synchondroses on bone scintigraphy.

This report describes the case history of two patients who showed a hyperactive midsternal area on bone scintigraphy due to a persistent sternal synchondrosis. Whereas this anatomical variant is diagnosed infrequently, midsternal hotspots can sometimes be related to arthrotic degeneration of these extra joint spaces. In the differential diagnosis of midsternal hotspots on bone scintigraphy, persistent sternum synchondroses should be considered.

Adult↗
PubMed1986

Hypertelorism in neurofibromatosis.

In eight out of thirty-four patients with neurofibromatosis hypertelorism was seen. This hypertelorism was diagnosed by measuring the intercanthal distance and calculating the interpupillary distance from it. The high incidence of hypertelorism in our group of patients (24%) makes its direct association with neurofibromatosis feasible. Moreover, hypertelorism was found exclusively in neurofibromatosis patients with brain involvement (8 out 11) and therefore seems to herald a severe expression of Morbus Recklinghausen. The bones of the face and the base of the skull are mesenchymal structures of neural crest origin and skull dysplasias - e.g. hypertelorism - fit well into the neurocristopathy concept of neurofibromatosis. Its ease of clinical recognition and its presence at birth makes the hypertelorism an early diagnostic criterium.

Adolescent↗
PubMed1984

Physical impairment, stress, and cardiovascular disorders.

Physical impairments bring about social and psychological consequences leading to stress. Here Dutch epidemiological data were used to test whether the physically disabled have an increased risk of CD. Results indicated this was partly so. Possible confounding variables, however, severely limit a firm statement concerning the relationship between disabling impairments and cardiovascular disorders.

Adolescent↗
PubMed1984

Neurofibromatosis and hypertelorism.

Hypertelorism was observed in eight of 34 patients with neurofibromatosis. This diagnosis was made by measuring the intercanthal distance and calculating the interpupillary distance from it. The bones of the base of the skull and of the face are mesenchymal structures of neural crest origin. Skull dysplasias, in which hypertelorism can be included, fit well into the neurocristopathy concept of neurofibromatosis. Hypertelorism seems to herald a severe expression of neurofibromatosis, eg, with brain involvement, and would therefore be an indication for doing a computed tomographic scan. The high prevalence of hypertelorism in our group of patients (24%) makes its direct association with neurofibromatosis highly feasible. Its ease of clinical recognition and its presence at birth would make it a valuable early diagnostic criterion.

Adolescent↗
PubMed1980

[Life styles of myocardial infarct patients and of control groups: various similarities and differences].

In a population sample of 'healthy' males (N = 136; age 39-41) the classifications on the Jenkins Activity Survey (JAS) for assessing the Type A/B coronary-prone behavior pattern, and on the Maastricht Questionnaire (MQ), measuring emotional drain and subsequent depression, were investigated in relation to retrospective reporting of life changes on a newly developed Middle Adulthood Life Changes Questionnaire (MALC). In ANOVA, Type A subjects (N = 70) did report significantly more life changes in their work environment and family situation over the last two years than their Type B counterparts (N = 66). For subjects reporting clearcut manifestations of vital exhaustion and depression (N = 32) the same statistical associations do hold. Also, these latter subjects did evaluate their life changes as significantly 'more distressing' or as 'requiring more adjustment'. A group of male myocardial infarction (MI) patients (N = 35; average age 52) was compared with this control group on the MQ and the MALC. The MI-group showed a significantly lower average MQ-score than the section of the control group with clearcut manifestations of emotional drain and depression. Mean 'adjustment' scores, however, were significantly higher in the MI-group. In the discussion, the requirements for a dynamic life-span developmental model for explaining the assumedly different life-courses of MI-cases and controls are enunciated.

Adult↗
PubMedDate not supplied

Effects of elevated carbon dioxide on soils in a Florida scrub oak ecosystem.

The results of a 3-yr study on the effects of elevated CO2 on soil N and P, soil pCO2, and calculated CO2 efflux in a fire-regenerated Florida scrub oak ecosystem are summarized. We hypothesized that elevated CO2 would cause (i) increases in soil pCO2 and soil respiration and (ii) reduced levels of soil-available N and P. The effects of elevated CO2 on soil N availability differed according to the method used. Results of resin lysimeter collections and anion exchange membrane tests in the field showed reduced NO3- in soils in Years 1 and 3. On the other hand, re-analysis of homogenized, buried soil bags after 1 yr suggested a relative increase in N availability (lower C to N ratio) under elevated CO2. In the case of P, the buried bags and membranes suggested a negative effect of CO2 on P during the first year; this faded over time, however, as P availability declined overall, probably in response to P uptake. Elevated CO2 had no effect on soil pCO2 or calculated soil respiration at any time, further suggesting that plant rather than microbial uptake was the primary factor responsible for the observed changes in N and P availability with elevated CO2.

Biological Availability↗