Even flocks of starlings can teach us about frailty and resilience

04 October 2018

Dr Shibley Rahman is an academic physician interested mainly in dementia and frailty. He tweets at @dr_shibley

Existing frailty models have revealed, perhaps, an over-simplistic approach to frailty so far.

Until recently, frailty has been almost entirely seen through the prism of 'deficits', but there has been growing attention to protective factors, or ‘assets’, and the importance of 'resilience'.

This, I feel, is a good thing.

Arguably, global shocks such as the 2014-2016 Ebola outbreak have also catalysed an increasing attention to the concept of resilience. The challenge now is to look at systems, consisting of a person and his/her environment, as a whole, and rarely is this approach more important than in examining frailty. The recognition of this new approach has profound consequences for how we conceptualise 'interventions' in frailty.

To quote a formulation from a seminal paper by Andy Clegg and colleagues in the Lancet, frailty can be defined as a state of increased vulnerability to poor resolution of homeostasis following a stress. This increases the risk of adverse outcomes, with consequent erosion of homeostatic reserve and vulnerability to disproportionate changes in health status following relatively minor stressor events.

For England, it has been recently reported that, whilst language over time has shifted from “health promotion” to “illness prevention”, the whole approach for frailty services has been rather more stick than carrot.

A "reductionist" perspective says that a human being is too complex to be studied whole and must be separated into smaller and smaller parts for examination.  Indeed, the "electronic frailty index" has been calculated as the presence or absence of individual deficits as a proportion of the total possible, consistent with a cumulative decline in multiple physiological systems that characterises frailty.

But frailty is probably an emergent property of a complex adaptive system ("CAS") requiring a "holistic" approach, where the information from study of the parts becomes even more valuable when the parts are viewed in context – in their relationships with other parts and with the wider environment.

Conversely, resilience reflects an ability to continue to perform functions in the face of significant challenges, and can indeed be considered as another emergent property of complex adaptive systems; and there are a number of possible reasons for this. For example, "collateral pathways enhance resilience by providing for alternative courses of action; when a system experiences disruption or challenges on one pathway, an alternative pathway is utilized to achieve the same goal."

The real beauty is that complex adaptive systems can now be elegantly modelled.

"Flocking" in birds flying on a sunset is a typical example of emergent collective behaviour, where interactions between individuals produce collective patterns on the large scale. Mathematical modelling exists of 'flocks' of starlings flying, and the effect of "stressors" on the swarm dynamics can be investigated systematically. Less resilient flocks are easily put off by a bit of noise in the mathematical model.

Interestingly, Arnold Mitnitski and colleagues have already produced a brilliant (different) model of a complex network model for frailty consisting of many interactive nodes.  Their model convincingly explains how age-dependent acceleration of the frailty index and of mortality emerges.

But they mention (p.436):

"To be clear, not all nodes are or need be deficits— deficits arise when nodes are in a damaged state.”

So, if the nodes aren’t all deficits, what are they?

Assets, of course.

It may be necessary for us to change tack from looking at 'interventions', albeit at a multicomponent level, but consider how interactions between different protective factors can build up resilience in adults, perhaps before  deficits come to dominate the network.

Furthermore, one concedes that, whilst there are lots of internal physiological threats, such as immunosenescence causing a reduced ability to adapt to exposure to external agents such as treatment side effects or polypharmacy, assets also exist in the internal (e.g. nutrition) and external environment (e.g. unpaid family carers). These assets can be mobilised over time.

Interestingly, current models of the complexity of frailty have downplayed the importance of assets and resilience, and perhaps more attention could be given in future to these, in pursuit of an explanation for healthy ageing. Whilst endless new models of frailty are not to be encouraged, if the models have improved benefit for patients, this can only be a good thing.

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