Individual reserve in aging and neurological disease

BACKGROUND AND OBJECTIVE

Cognitive and physical functions correlate and delineate aging and disease trajectories. Whereas cognitive reserve (CR) is well-established, physical reserve (PR) is poorly understood. We, therefore, developed and evaluated a novel and more comprehensive construct, individual reserve (IR), comprised of residual-derived CR and PR in older adults with and without multiple sclerosis (MS). We hypothesized that: (a) CR and PR would be positively correlated; (b) low CR, PR, and IR would be associated with worse study outcomes; (c) associations of brain atrophy with study outcomes would be stronger in lower compared to higher IR due to compensatory mechanisms conferred by the latter.

METHODS

Older adults with MS (n = 66, mean age = 64.48 ± 3.84 years) and controls (n = 66, mean age = 68.20 ± 6.09 years), underwent brain MRI, cognitive assessment, and motoric testing. We regressed the repeatable battery for the assessment of neuropsychological status and short physical performance battery on brain pathology and socio-demographic confounders to derive independent residual CR and PR measures, respectively. We combined CR and PR to define a 4-level IR variable. The oral symbol digit modalities test (SDMT) and timed-25-foot-walk-test (T25FW) served as outcome measures.

RESULTS

CR and PR were positively correlated. Low CR, PR and IR were associated with worse SDMT and T25FW performances. Reduced left thalamic volume, a marker of brain atrophy, was associated with poor SDMT and T25FW performances only in individuals with low IR. The presence of MS moderated associations between IR and T25FW performance.

CONCLUSION

IR is a novel construct comprised of cognitive and physical dimensions representing collective within-person reserve capacities.

Physical impairment and perceived general health preceding critical illness is predictive of survival

PURPOSE

We hypothesized that item response based assessment of physical reserve preceding ICU admission is a predictor of survival.

METHODS

We evaluated physical functioning using the Academic Medical Center Linear Disability Score (ALDS) and quality of life using the first question (SF-1) and the physical component score (PCS-12) from the Short-form 12 (SF-12) before admission by patients or by close proxies within 72 h after ICU admission during 1 year.

RESULTS

We developed four logistic regression models to predict 1 year mortality using the predictors age, gender, ALDS, SF-1, PCS-12. A total of 510 patients participated. Twelve months after ICU discharge, 110 patients (22%) had died. Pre-admission ALDS (p = .004), and SF-1 (p = .012) improved the prediction models with age and gender PCS-12 showed no association with mortality (p = .062). Adding the ALDS (p = .049) and the SF-1 (p = .048) to a model with age, gender and the APACHE II score (improved the model. Adding PCS-12 showed no association with mortality (p = .355).

CONCLUSIONS

Physical reserve as assessed by ALDS and perceived general health, preceding ICU admission is predictive of mortality. Obtaining patient's physical reserve or pre-existing perceived general health should be part of routine assessment whether a patient may benefit from ICU admission.