Some mathematical models of frailty and their clinical implications

Abstract

Frailty is a term that is used often, but commonly not defined precisely. As reviewed elsewhere most definitions share several features. Typically, older adults who are frail have a greater rate of dependence on others, so-called ‘loss of physiological reserve’ and multiple diseases. A dynamic component is often included (e.g. ‘loss of reserve’ and such synonyms as ‘unstable disability’ and ‘impaired homeostenosis’) and is manifest when, over time, patients respond less well to stress, or when those with given levels of frailty have higher rates of adverse outcomes. Still, the imprecision of the term frailty has led some to question its merit, and either to develop alternative means of classification or to stay with the concept of function and disability. Alternative methods of classification are either broadly or narrowly focussed.

A global clinical measure of fitness and frailty in elderly people

“…The index approach might better serve where such access is unavailable. The index approach also appears to have some important mathematical advantages in its scaling that might lead to novel insights, 2,38,39 especially into matters such as physiologic reserve, which is often invoked in relation to frailty but little measured. Given the increasingly elderly population, and the particular challenge posed by elderly people who are frail, the important questions for researchers now are how to measure frailty more precisely and how to better translate frailty measurement into clinically sensible tools and practices.…”

“…All significance tests were 2-sided; differences were assessed for significance (p ≤ 0.05) with the log-rank test. In the multivariable analyses, having first checked for proportionality, we used Cox regression analyses to estimate hazard ratios and construct 95% confidence intervals (CIs) independently for the 3MS score 22 and outcomes of the CSHA Clinical Frailty Scale, and the Cumulative Illness Rating Scale, 23 as well as the CSHA's Function Scale, rules-based frailty definition 12,16 and Frailty Index, 2 adjusting each for age, sex and years of education. Receiver operating characteristic (ROC) curves 27 were calculated to estimate the areas under the curves for relevant predictor variables in relation to death and entrance into an institutional facility.…”

“…It appears to be a valid construct, but how exactly to define it remains unclear. [1][2][3][4][5][6][7][8] There are many operational definitions, 1,5,[9][10][11][12][13] which typically are rules-based; for example, a person may be defined as frail if 3 or more symptoms (of unintentional weight loss, feeling exhausted, weak grip strength, slow walking speed and low physical activity) are present. 5 Rules-based definitions often are derived from multiple regression analyses and can be speciously precise, for example in requiring combinations of factors that might not apply to an individual case.…”

“…2 Despite its strong predictive validity, 2,14,15 this approach is time-consuming and not widely used clinically. A third class of operational classifications, which in this report we attempt to extend, relies on clinical judgment to interpret the results of history-taking and clinical examination.…”

One Operational Definition by Population: The Need for Local Evaluations of Frailty

“…The most used phenotype of frailty is that developed by Fried et al (2001), which operationalizes frailty using the following criteria: shrinking (unintentional weight loss in the last 12 months), weakness (grip strength), poor endurance and energy (self-reported exhaustion), slowness (gait speed), and low physical activity level (self-reported); individuals who meet Ն3 of these criteria are considered "frail," those who meet 1 or 2 criteria are considered "pre-frail," and persons who do not meet any of these five criteria are considered "robust." The mathematical approach describes biological aging by building a frailty index through the addition of age-related deficits (Rockwood et al, 2002). This approach assumes that the more deficits people accumulate, the more likely they are to be frail.…”