Biomedical subjects

A J Mogilner

Publications and source records attributed to A J Mogilner.

6 recordsLinked to original sources

PubMed2001

Accumulation of deficits as a proxy measure of aging.

This paper develops a method for appraising health status in elderly people. A frailty index was defined as the proportion of accumulated deficits (symptoms, signs, functional impairments, and laboratory abnormalities). It serves as an individual state variable, reflecting severity of illness and proximity to death. In a representative database of elderly Canadians we found that deficits accumulated at 3% per year, and show a gamma distribution, typical for systems with redundant components that can be used in case of failure of a given subsystem. Of note, the slope of the index is insensitive to the individual nature of the deficits, and serves as an important prognostic factor for life expectancy. The formula for estimating an individual's life span given the frailty index value is presented. For different patterns of cognitive impairments the average within-group index value increases with the severity of the cognitive impairment, and the relative variability of the index is significantly reduced. Finally, the statistical distribution of the frailty index sharply differs between well groups (gamma distribution) and morbid groups (normal distribution). This pattern reflects an increase in uncompensated deficits in impaired organisms, which would lead to illness of various etiologies, and ultimately to increased mortality. The accumulation of deficits is as an example of a macroscopic variable, i.e., one that reflects general properties of aging at the level of the whole organism rather than any given functional deficiency. In consequence, we propose that it may be used as a proxy measure of aging.

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PubMed1999

Dynamics of cognitive aging: distinguishing functional age and disease from chronologic age in a population.

This paper introduces a methodological approach to the dynamics of cognitively normal (i.e., successful) aging compared with aging accompanied by different types of cognitive impairment and dementia. Using secondary analysis of a national representative database (Canadian Study of Health and Aging, 1991-1992), the authors show that the occurrence of an adverse event (symptom, sign, or disease), or the accumulation of a number of events, may be modeled as a logistic function of chronologic age in a population. In the cognitively normal, a linear relation between the logarithm of the odds of events and chronologic age was present for the majority of symptoms and signs. This regression represents the accumulation of each sign in a cognitively successful, aging population. The authors then estimated which ages for this cognitively unimpaired group correspond to the odds of the occurrence of symptoms found for a cognitively impaired population at any given chronologic age. This may be regarded as functional age, based upon the accumulation of a particular functional deficit in the impaired population, analogous to the concept of frailty. The dynamics of aging are a complex process of accumulation of deficits (morbidity), whereby decline from some previously healthy level of synergistically associated symptoms and signs results in distinct patterns of disease and staging. The modeling of these dynamics takes us a step further toward the definition and refinement of disease and normal aging.

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PubMed1999

The rate of decline in function in Alzheimer's disease and other dementias.

BACKGROUND: Functional impairment over time is a necessary condition for the diagnosis of dementia. Increasingly, it is recognized that rates of decline may not follow a linear progression. This variability may indicate that dementia in Alzheimer's disease represents disease rather than inevitable aging. In order to investigate decline in function in dementia, we developed a model of the rate of decline in functions in Alzheimer's disease and in other dementias in comparison with normal aging. METHODS: Secondary analysis of a cross-sectional, representative sample of Canadians aged 65 and older (N = 2,914) was performed. We calculated a measure identified as an impairment index, defined as the probability of the occurrences of an impairment or disability in a structured clinical examination. RESULTS: The rate of functional decline varies for different diagnostic groups and increases with severity of the disease. The distribution for the rate of decline in dementia is distinct from that in aging without cognitive impairment. In those without cognitive impairment, the distribution is exponential. Elderly persons with dementia of any type showed a log-normal distribution. CONCLUSIONS: The difference in the distributions between aging with and without dementia likely reflects fundamental differences in the processes of decline in functions in the two groups. This suggests that the declines seen in persons with dementia are distinct from normal aging. It also has implications for the testing of antidementia medications, in that modeling treatment effects based on an assumption of linear decline is likely to be flawed.

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PubMed1997

Vector diagnostics in dementia derived from Bayes' theorem.

This paper introduces the concept of vector diagnostics. In contrast to the conventional approach where one diagnosis takes precedence, the authors propose an alternative strategy that addresses the clinical reality of comorbidity and multiple diagnoses for an individual. Based on a Bayesian approach, the probability distribution for the etiologically heterogeneous dementia diagnoses is estimated from the Canadian Study of Health and Aging database. These data were collected between February 1991 and May 1992. This method facilitates the establishment of a probability for more than one diagnosis within a given individual. By analyzing the correspondence between diagnostic groups, it is demonstrated that some clinical diagnoses are not reliably distinguished on the basis of the considered subset of symptoms and signs. As a consequence, the conventional diagnostic categories might require revision. The resulting probabilistic algorithm allows for the mining of existing epidemiologic databases for patterns of signs and symptoms that characterize emerging diagnostic categories which might better account for the heterogeneity of the dementia subtypes and individual variability.

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PubMedDate not supplied

An algorithmic approach to the differential diagnosis of dementia.

The careful definition of cases is fundamental to diagnosis and to any study of cognitive, behavioural and functional problems in dementia. This paper presents an algorithmic approach which mimics a crucial component of diagnostic decision-making; symptoms and signs do not occur independently, but are conditioned on each other. First, we examine whether the conditioned items can be assembled to yield a differential diagnosis of dementia which corresponds to clinical diagnoses, and second, we explore whether subjects whose algorithmic profiles do not fit the clinical diagnoses form new discernable patterns. Such a technique offers two advantages: it allows for the development of validation protocols which are crucial to epidemiological studies, and it allows for the analysis of new patterns of signs and symptoms for emerging criteria of dementia subtypes. This approach has the potential to refine and enhance criteria for the differential diagnosis of dementia and to have an impact on case identification and assessment, particularly in large epidemiologic studies.

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PubMedDate not supplied

Symptoms and signs in dementia: synergy and antagonism.

This paper addresses the synergy and antagonism between symptoms and signs among 2,914 elderly Canadians diagnosed in 15 categories, including no cognitive impairment, cognitive impairment but no dementia, mild, moderate and severe forms of Alzheimer's disease and vascular dementia, 4 subtypes of possible Alzheimer's disease, Parkinson's dementia, unspecified other dementias and unclassified dementias Attention is paid to the relationships between symptoms and signs rather than conventional analyses which assume independent signs. We demonstrate that dementia progression and specific aetiologies have characteristic patterns of decline and destruction from the strong synergy that exists between symptoms and signs among the population with no cognitive impairment. These findings have potential implications for the incorporation of new diagnostic criteria into existing databases.

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