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Biomedical subjects

K Ritchie

Publications and source records attributed to K Ritchie.

At least 73 records · Page 4Linked to original sources
PubMed1997

Establishing the limits and characteristics of normal age-related cognitive decline.

BACKGROUND: Research into ageing-related pathology relies not only on exploration of disease aetiology, but also a clear understanding of the normal ageing process. The present study aims to examine the characteristics of elderly subjects who lie on the borderline between normal and pathological ageing. METHOD: Cognitive functioning is examined using computerized neuropsychometric assessment in a population of 833 normal elderly from which a cohort of 397 subjects with sub-clinical cognitive impairment are followed over three years. Subjects receive a standardized neurological examination and ApoE genotypes are established. RESULTS: Analysis of covariance revealed no cross-sectional age differences for syntax comprehension (p = 0.19), articulation (p = 0.46), semantic matching (p = 0.12), reading (p = 0.79), and implicit memory (p = 0.21) while explicit memory, language skills and visuospatial skills were found to deteriorate both in the cross-sectional age comparisons and across time. An overall intellectual ability factor, derived from Principal Components Analysis, was found by regression to decline principally in persons with low education, and a high initial IQ level was observed to provide a protective effect over age 75. Persons with higher levels of education show relative stability over time on language and secondary memory tasks but deteriorate as rapidly as persons with low education on visuospatial tasks. Five separate patterns of sub-clinical cognitive deficit were isolated by cluster analysis. Two groups, with differing clinical profiles (of which only one manifested the ApoE4 allele), were found to have an increased risk of developing senile dementia (OR = 4.4 and 3.9). A third group had a high prevalence of depressive illness, and the remaining two showed very little change. CONCLUSION: Ageing does not affect all cognitive functions uniformly: a high initial education level slowing rate of decline for certain tasks. Separate patterns of cognitive change are observed in early senile dementia, benign change and changes related to depressive illness. Results suggest the need for more stringent selection of normal control groups.

Age Factors↗
PubMed1996

Does education level determine the course of cognitive decline?

Many studies have implicated low education as a risk factor for cognitive impairment in elderly people. Findings are, however, inconsistent and the mechanism by which education level may intervene in senescent cognitive change is uncertain. The present study examines cognitive change over a 1-year period in 283 elderly persons manifesting recent subclinical deterioration in at least one area of cognitive functioning. The results suggest that the impact of both education level and young adult IQ on the degree of cognitive change over the year is greater in the older age groups. Secondary memory and language functions were found to be more resistant to decline in the high-education group, while attention, implicit memory and visuospatial skills are found to decline irrespective of education level.

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PubMed1996

A typology of sub-clinical senescent cognitive disorder.

BACKGROUND: Cognitive impairment without dementia is commonly observed in ageing populations. The present study aims to describe types of impairment and evolution over a one-year period. METHOD: Three hundred and ninety-seven normal French elderly persons demonstrating recent, observable change in cognitive performance were examined annually using a computerised cognitive examination. RESULTS: Five subtypes were differentiated by cluster analysis. Two of the groups were predicted by logistic regression to be at high risk of senile dementia. Of 16 incident cases of senile dementia diagnosed in the following year, 13 were found to have derived from these two groups. The typology was also found to be useful in the description of age-associated memory impairment. CONCLUSIONS: Subclinical cognitive impairment was found to not constitute a unitary phenomenon and heterogeneous subgroups could be differentiated. The concept of 'normality' in elderly cohorts is reconsidered in the light of these findings.

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PubMed1996

Mass transfer in the biological fast lane: high CO2 and a shallow root zone.

Elevated atmospheric CO2, which is common in regenerative systems, increases photosynthesis, plant growth, and root respiration, which increases the O2 demand in the root zone. Closed systems must make efficient use of volume and thus have shallow root zones. The root density and O2 demand in these artificial systems is 10 to 100 times higher than in field environments. Rapid hydroponic flow rates supply O2 to the root zone, but anaerobic microsites occur because of nonuniform flow rates. Our measurements suggest that, probably because of low O2 in such microsites, up to 30% of the nitrogen can volatilize from denitrification. We improved nitrogen recovery to about 85% by increasing the solution flow rate and reducing the nitrate concentration in solution to 100 micromoles.

Ammonia↗
PubMed1995

Is senile dementia "age-related" or "ageing-related"?--evidence from meta-analysis of dementia prevalence in the oldest old.

The observation of an exponential increase in senile dementia prevalence with age has led to the conclusion that this disease may be inevitable in those who live long enough. The alternative view is that at very high ages the prevalence rate levels off. Studies conducted to date have not included sufficient numbers of very old people to resolve this difference of opinion. The question is important both to our understanding of the biological mechanisms involved and for public health planning. We have carried out a meta-analysis of nine epidemiological studies of senile dementia that used DSM III diagnostic criteria and that included samples of elderly people over age 80. The resulting curve was best described as a flattened S curve that fitted a modified logistic function rather than an exponential pattern. The rate of increase in senile dementia prevalence was found to fall in the age range 80-84, and at around the age of 95 prevalence was seen to level off to about 40%. It seems that senile dementia is better conceptualised as an "age-related" (ie, occurring within a specific age range) rather than as an "ageing-related" disorder (that is, caused by the ageing process itself). Very elderly survivors may be at diminishing risk of dementia and this has implications for public health policy.

Age Factors↗
PubMed1995

Sensitive force technique to probe molecular adhesion and structural linkages at biological interfaces.

Adhesion and cytoskeletal structure are intimately related in biological cell function. Even with the vast amount of biological and biochemical data that exist, little is known at the molecular level about physical mechanisms involved in attachments between cells or about consequences of adhesion on the material structure. To expose physical actions at soft biological interfaces, we have combined an ultrasensitive transducer and reflection interference microscopy to image submicroscopic displacements of probe contact with a test surface under minuscule forces. The transducer is a cell-size membrane capsule pressurized by micropipette suction where displacement normal to the membrane under tension is proportional to the applied force. Pressure control of the tension tunes the sensitivity in operation over four orders of magnitude through a range of force from 0.01 pN up to the strength of covalent bonds (approximately 1000 pN)! As the surface probe, a microscopic bead is biochemically glued to the transducer with a densely-bound ligand that is indifferent to the test surface. Movements of the probe under applied force are resolved down to an accuracy of approximately 5 nm from the interference fringe pattern created by light reflected from the bead. With this arrangement, we show that local mechanical compliance of a cell surface can be measured at a displacement resolution set by structural fluctuations. When desired, a second ligand is bound sparsely to the probe for focal adhesion to specific receptors in the test surface. We demonstrate that monitoring fluctuations in probe position at low transducer stiffness enhances detection of molecular adhesion and activation of cytoskeletal structure. Subsequent loading of an attachment tests mechanical response of the receptor-substrate linkage throughout the force-driven process of detachment.

Animals↗
PubMed1995

The application of disability data from epidemiological surveys to the development of indicators of service needs for dependent elderly people.

Increases in the prevalence of disability due to the ageing of the population have given rise to the need for simple indicators which may be used to estimate service needs and to assess whether resources have been fairly distributed. The present study involved the validation of an indicator based on confinement level by reference to epidemiological studies of disability, social support, and living conditions in three regions of France. Using factorial correspondence analysis and regression methods it was found that such an indicator could adequately summarize more complex empirical observations and thus provide a means of classifying elderly populations into four dependency groups. While comparisons of the percentage of persons classified at each level with national data suggest that the observations from the three studies may be reasonably representative of France as a whole, the application of this indicator to other European countries should be preceded by a preliminary validation involving regional or national health survey data for each country. The use of this indicator should also be complemented by individual need assessment procedures.

Activities of Daily Living↗
PubMed1995

Mental status examination of an exceptional case of longevity J. C. aged 118 years.

BACKGROUND: The mental status examination of an extreme case of longevity, J. C., aged 118 years and 9 months, is documented in order to further knowledge regarding profiles of morbidity in the extremely elderly. J. C. is presently considered to have the longest authenticated life-span in the history of the human species. METHOD: Neuropsychological tests were improvised taking into account the subject's severe perceptual deficits. The examination was carried out over a six-month period. A CT scan was also conducted. RESULTS: The subject's performance on tests of verbal memory and language fluency is comparable to that of persons with the same level of education in their eighties and nineties. Frontal lobe functions are relatively spared and there is no evidence of depressive symptomatology or other functional illness. Cognitive functioning was found to slightly improve over a six-month period. CONCLUSIONS: The subject shows no evidence of progressive neurological disease. A high initial level of intellectual ability may have constituted a protective factor.

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PubMed1995

On the use of antibiotics to reduce rhizoplane microbial populations in root physiology and ecology investigations.

No straightforward method exists for separating the proportion of ion exchange and respiration due to rhizoplane microbial organisms from that of root ion exchange and respiration. We examined several antibiotics that might be used for the temporary elimination of rhizoplane bacteria from hydroponically grown wheat roots (Triticum aestivum cv. Veery 10). Each antibiotic was tested for herbicidal activity and plate counts were used to enumerate bacteria and evaluate antibiotic kinetics. Only lactam antibiotics (penicillins and cephalosporins) did not reduce wheat growth rates. Aminoglycosides, the pyrimidine trimethoprim, colistin and rifampicin reduced growth rates substantially. Antibiotics acted slowly, with maximum reductions in rhizoplane bacteria occurring after more than 48 h of exposure. Combinations of nonphytotoxic antibiotics reduced platable rhizoplane bacteria by as much as 98%; however, this was generally a reduction from about 10(9) to 10(6) colony forming units per gram of dry root mass, so that many viable bacteria remained on root surfaces. We present evidence which suggests that insufficient bacterial biomass exists on root surfaces of nonstressed plants grown under well-aerated conditions to quantitatively interfere with root nitrogen absorption measurements.

Aminoglycosides↗
PubMed1994

Dementia-free life expectancy in Australia.

Dementia-free life expectancy is a synthetic indicator of an important aspect of mental health which may have considerable use in public health decision making. Dementia expectancies were derived from senile dementia prevalence rates in Australia in 1991-1992 in conjunction with national life tables using Sullivan's method. Dementia-free life expectancy for Australian women aged 70 years was found to be 14 years within a total life expectancy of 15 years, and 11 years for men within a total life expectancy of 12 years. Between 70 and 85 years there is a constant average expectation of about one year of life expectancy with dementia. The age at which the largest number of persons with dementia is found is 82 years. Australians appear to have very similar dementia-free life expectancies to those reported in the European studies, with small differences probably due to sampling variation or to differences in case-finding methods.

Age Factors↗
PubMed1994

Dementia-free life expectancy in France.

OBJECTIVES: Increasing concern with the quality of gains in life years has led to the development of a new synthetic indicator of population health:health expectancy. Until now, calculations have been made for physical disabilities only. A first estimate of mental health expectancy is presented: dementia-free life expectancy. METHODS: Sullivan's method was used to calculate dementia-free life expectancy for a random representative sample of 4134 persons over 65 years of age in the Bordeaux region of France. The diagnosis of senile dementia was made in two stages, based on Diagnostic and Statistical Manual of Mental Disorders (DSM-III-R) criteria. RESULTS: At 65 years of age, a person's dementia-free life expectancy is 16.9 years within a total life-expectancy of 17.7 years; it decreases with age in parallel with the decrease in total life expectancy so that life expectancy with dementia stays constant at 0.8 years. Although dementia prevalence increases with age, if the prevalence is adjusted for mortality, the largest number of persons with dementia are in their early eighties. At each age women have a higher dementia-free life expectancy. CONCLUSIONS: Trends in dementia-free life expectancy are similar to those found in disability-free life expectancy. Because the dementia prevalence rates used in this estimate resemble a general model derived from meta-analysis, it can be assumed that similar results will be found in other Western countries with similar mortality rates.

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PubMed1992

A comparative study of the performance of screening tests for senile dementia using receiver operating characteristics analysis.

The discriminability of three types of test for the detection of senile dementia was assessed within a French sample of 155 normal elderly and 120 persons with mild or moderate senile dementia using Receiver Operating Characteristics (ROC) analysis. Results suggest that despite differences in the content of the three instruments, they are equally discriminant. Methods involving direct cognitive examination were found to lose discriminability in relation to milder forms of dementia, whereas an informant questionnaire was found to perform equally as well on cases of mild and moderate dementia. The informant questionnaire was also found to produce lower refusal rates and to be less influenced by the place of residence of the elderly person. The problem of selecting cut-off points according to the range of predicted prevalence rates of dementia for the general population is also discussed.

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