On The Continued Need For A New (Bio)Medical Model

Abstract

In 1977, George Engel suggested that there was a need for a new medical model. He complained that the dominant model took an inappropriately reductionist stance. There was little or no scope for any consideration of the psychological, social or behavioural aspects of being unwell. To facilitate a move away from this situation and inspired by the work of Ludwig von Bertalanffy and his General Systems Theory, Engel proposed what he called the Biopsychosocial model (BPS). This attempted to represent a hierarchy of interacting levels comprising and relating to the well-being of the individual.

Contemporaneous with the genesis of the BPS was the emergence of the debate about the definitions of disease and health – a debate which is still on-going. Although the work of Christopher Boorse has sought to distil a definition of disease from the way in which the word is used – and might, therefore, be said to be a depiction of the mental framework or model within which this usage occurs – the debate cannot be said to have drawn extensively on the BPS or any other such model. It may be that part of the reason the debate has not reached a conclusion or a greater level of agreement is due to the very absence of such models. Thus, the debate may well be assisted by the development of a viable model which can accommodate the diverse aspects of individual suffering.

This paper will present the outline of such a model with the intention that it may prove useful in the aforementioned debate. This model also takes a lead from systems thinking but does so founded on the tenets of evolutionary biology. However, instead of emphasising gene or population level phenomena or, indeed, reproductive success – as is commonly the case in modern biology – it is the survival and quality of life of the individual which is emphasised. Instead of using a single linear hierarchy to represent the individual, different orthogonal axes are used to represent concurrent aspects of the state of the individual and that individual's ability to interact with the world. A basic two-dimensional version of the model uses axes to represent an individual's level of physical disorder and experiential disturbance while a three-dimensional version adds an axis which represents the level of behavioural constraint experienced by the individual. Features represented by each axis have a direct bearing on the survival chances of the individual and it is within this framework that the concepts of disease and health may be further explored. The model does not use axes representing what might be considered 'typical' biological or medical parameters nor are the axes used as might be expected. Nevertheless, those aspects of the individual which Engel considered important are included, albeit in a different (non-hierarchical) way and using different terminology.

Introduction

In 1977, in an article entitled 'The need for a new medical model: a challenge for biomedicine', the American psychiatrist George Engel (1913-1999) suggested that the prevailing medical model was inadequate for both clinical and research purposes. In what follows, I would like to propose that this remains the case. Not only that but I wish also to propose that this continued need has a bearing upon the on-going debate about the definitions of disease and health. I wish, therefore, to raise some issues and questions relevant to that debate. To that end, I shall also offer a brief description of a model – or 'thinking tool' – that I believe can aid our understanding of the individual from both a biological and medical perspective as well as contribute something to the aforementioned debate. Hence, in my title, I have written '(Bio)Medical' in this somewhat unconventional way.

The approach clinicians take to their patients and the problems they present is very much influenced by the conceptual models around which their knowledge is organised. Engel complained that the dominant medical model took an inappropriately somatic and reductionist stance. In effect, the medical model could be described as 'Newtonian'. It typically seeks causal explanations and mechanical fixes for medical problems often focussing on smaller and smaller physical levels. Engel also complained that within this approach there was little or no scope allowed for a complete consideration of the psychological, social and behavioural aspects contributing to a patient being unwell.

To facilitate a move away from this situation and inspired by the work of Ludwig von Bertalanffy (1901-1972) and his General Systems Theory (GST) – or General Systems Thinking as it was originally christened – Engel proposed what he called the Biopsychosocial model (BPS). GST was itself proposed to counter the tendency towards reductionism and to accommodate the problems of explaining complexity and order. To that end, the BPS attempted to represent a hierarchy of interacting levels – which Engel represented in different ways – relating to the well-being of the individual. In so-doing, the BPS was an attempt at understanding how these multiple levels of organisation were affected by and could contribute to the condition of the patient as a whole.

Engel, in common with many current textbooks of anatomy and physiology, used a ladder of levels or layers representing an organisational hierarchy. This idea of organisational levels was not in itself new – although exactly where it originated, I have not been able to determine for sure. However, it certainly pre-dated Engel's use of the idea. Significantly, this ladder of levels forms the basis for the way in which the human body continues to be depicted in current textbooks of anatomy and physiology. These models generally stop at the level of the organism, whereas Engel added levels above this so as to provide entry for the psychological and social aspects of well-being he saw as missing.

Although the work of Christopher Boorse has sought to distil a definition of disease from the way in which the word has been used – and might, therefore, be said to be a depiction of the mental framework or model within which this usage occurs – the debate about the definitions of disease and health cannot be said to have drawn overtly or substantively on the medical model, the BPS or any other such model. No model has been called upon in order to help the debate significantly. However, it is perhaps possible – if not probable – that there has been tacit adherence to the medical model. If so, this may have hindered the debate since, if the medical model is flawed, as Engel and others suggest, then what follows from it – tacitly or otherwise – may equally be flawed. It may even be that part of the reason that the debate has not reached a conclusion or a greater level of agreement is due to the absence of a viable model of the individual – which, after all, is what the words 'disease' and 'health' seek to describe.

At least, that is one of the questions I would like to pose. Rather than answer that question as such – which would require a careful analysis of the debate as an object of enquiry in and of itself (which is not my intention today) – I would like to consider the question of modelling the human organism as I believe this to be particularly important.

On Models

So far, in the debate about the definitions of disease and health, there has been an emphasis on producing adequate verbal definitions of these concepts. What we have not been trying to do is find pictures or some form of mental image of these concepts. Thus, another question I would like to raise is whether we have been following the best course of action.

Medicine is frequently described as an 'art'. However, it is an art with a distinct scientific basis. When we look at the sciences upon which medicine is based, we notice that they are full of models and metaphors. Pictures – mental and otherwise – play a significant role in how things are understood and described. For example, at the lower reaches of the BPS are the atom and sub-atomic particles. One of the most famous models in science is the Bohr model of the atom proposed by Niels Bohr (1885-1962) in 1913. Historically, this was but one of a series of atomic models proposed in the first couple of decades of the twentieth century and was itself an extension of the model proposed by Ernest Rutherford (1871-1937) a couple of years earlier. Around this time, the following models were mooted:

· Cubic model (Gilbert N. Lewis - 1902)

- Extended by Irving Langmuir in 1919 as the cubical octet atom model

· Plum-pudding model (J. J. Thompson - 1900)

· Saturnian model (Hanataro Nagaoka - 1904)

· Rutherford (or Planetary) model (Ernest Rutherford - 1911)

- of which the Bohr model (1913) was an extension

Interestingly, today, when we see a representation of an atom, it is really Rutherford's model that is usually depicted.

This, in turn, bears only passing resemblance to more recent models where the complexities of electron orbits (if that is really the right word) are depicted. More to the point, this raises the issue of a distinction that can be made between 'models of' and 'models for'.

'Models of' are attempts at depicting something akin to reality, whereas 'models for' seek primarily to serve a specific purpose. As such, the Rutherford model is not an accurate 'model of' the atom but it serves as a useful 'model for' teaching elementary physics and chemistry. Indeed, it is this model which is used in those textbooks of anatomy and physiology to which I referred earlier; textbooks from which much of the mental imagery fundamental to medical science is derived.

The first science upon which medicine is based is not physics or chemistry but biology. (If one were to take a reductionist approach, one might say that physics should perhaps be considered to be the 'last' such science.) However, medicine tends to use biological techniques and ways of producing proximate explanations more than it uses fundamental biological theory or thinking.

As Theodosius Dobzhansky (1900-1975) famously opined, 'Nothing in biology makes sense except in the light of evolution' (Dobzhansky, 1973). In response, Nesse and Williams proposed that 'Nothing in medicine makes sense except in the light of evolution' (Williams and Nesse, 1995). However, it is not enough to simply overlay medicine with a veneer drawn from prevailing evolutionary thought. There is, importantly, something missing from evolutionary biology and that is a theory of the organism as an individual entity. The 'evolution' that Dobzhansky, Nesse and Williams emphasize is a modern extension of neo-Darwinism, a form of evolutionary theory largely understood in terms of gene frequencies, population level phenomena and reproductive success. Individuals tend to be overlooked; they are the products of an evolving germ line; they are not evolving entities in themselves. They are but points along a species' lineage. The place of the individual in evolution has been somewhat overlooked. Yet, it is the individual and their needs which lies at the heart of medicine. So, if evolution – or more accurately evolutionary theory – is to help make sense of medicine, it must first have a better understanding of the individual.

On The Place of the Individual in Evolution

The frontispiece of the book that launched modern evolutionary biology per se gives us a clue as to what we should be focussing upon when it comes to a theory of the individual organism. In the subtitle, Darwin refers to '… the Struggle for Life.' That is, individual survival. This is indeed something that Herbert Spencer (1820-1903) recognised when he coined the phrase 'survival of the fittest'.

That survival entails a struggle is something that is easily overlooked by those of us living comfortably in the developed Western world. Life, especially in its natural state, is a daily struggle in a wide variety of ways.

If we look at individual organisms – with ourselves very much in mind – there are three concurrent features essential for individual survival. Firstly, organisms must have an orderly physical form – that is, an orderly anatomical organisation. It is this to which the ladder of levels model alludes. However, adopting this model can be misleading. We perhaps tend to think of organisms as physical objects, albeit of a special kind. We should instead think of them as systems consisting of physiological processes which give rise to orderly physical forms – not as physical forms within which there happen to be physiological processes occurring.

To be a living organism, anatomical organisation is not enough. Numerous interlinked, internal physiological processes must be maintained. This requires a form of self-referential communication or internal information flow to occur. In this way, the integrity of the whole organism is maintained. We usually think of this in merely mechanical terms as feedback mechanisms and other biochemical and physiological pathways. However in sentient beings, such as ourselves, some of this information flow reaches the level of consciousness; there is a degree of conscious self-awareness which is used to survival effect. For example, we have feelings of hunger, thirst, of being too hot or too cold, of pain and of being what we call 'unwell' or ill. These are, in effect, important forms of information about our physical state requiring different responses in order to ensure continued survival.

Furthermore, the organism is not a closed system; matter and energy flow through it. Things like food and drink are essential for survival and must be obtained externally. Thus, an organism must be able to interact with its surroundings in order to ensure that its needs are obtained.

These three features – which may be characterised as 'physical', 'experiential' (or 'informational') and 'behavioural' (or 'interactional') – operate concurrently. They constitute what might be described as a 'Survival Triad'. Each can be represented graphically with its own axis.

By notionally plotting a measure of the physical, experiential and behavioural state of an individual, some idea of the overall state of that individual can be depicted.

Importantly here, each axis is used to represent a notional measure of the individual's level of physical disorder, experiential disturbance and behavioural constraint, respectively. The further one moves along each axis (in the direction of the arrows), the greater the risk to individual survival.

The organism is, in effect, a self-organising material system maintaining itself in the face of its inevitable entropic demise by interacting with its environment. This graphical representation can be used to depict an individual's survival chances – extraneous factors notwithstanding. The closer one is to the origin, the better. This is where states most conducive to survival are represented.

Significantly for this discussion, these three aspects of survival have direct clinical relevance.

Clinical Relevance

It is not unreasonable to suggest that medicine can be seen as being concerned with the struggle for life – or at least certain important aspects of it – and with the quality of that life. That being the case, a biological model based upon individual survivability in qualitative terms should prove relevant to medicine.

Using this model, the physical, experiential and behavioural states of individuals can be represented by a position on each axis. As a result, one can envisage the overall state of an individual as a single point within a phase space formed by these three axes where each axis represents an area of particular health care concern.

The horizontal axis is the axis relevant to physical or somatic medicine; it is the axis representing the level of disorder in the body as a physical system. The vertical axis is the axis relevant to how one feels – for example, what symptoms one might report to one's doctor. However, this axis may also be relevant to psychological and psychiatric medicine. The third (z-axis) is the axis relevant to physical ability/disability; how well or otherwise one is able to interact with the world and go about the tasks essential for survival.

Presented graphically, this is a 'model of' qualities key to the survival of the organism. It is not a model of the organism simply as a physical object but of different qualities demonstrated by that object as a living system. As such, it can also serve as a 'model for' envisaging the overall state of an individual patient in health care terms.

Conclusion

The three axes are not strictly synonymous with the 'bio', 'psycho' and 'social' aspects of a patient's life as portrayed by Engel. However, as a thinking tool, it could help clinicians to envisage the patient as a whole more readily, which was, in part, Engel's intention. Instead of using a ladder of levels or concentric layers, this model draws attention to those concurrently operating aspects of a patient's life in terms of their physical state, how they feel and their ability to go about daily life.

As a thinking tool for philosophers of medicine, this model may also be potentially helpful in the debate about the definitions of disease and health. Instead of a patho-physiological focus and instead of a humanistic (or participatory) approach, a broader biological perspective emphasising the fundamental need for survival is offered. In so doing, this model may allow one to see the individual in a different light. The overall state of an individual is represented here by a point somewhere within a phase space. It is to states such as these – that is, different points within that phase space – that the terms disease, health, illness etc. are applied. So, when it comes to defining these words, it may be informative to refer to imagery such as this, which has been largely absent from the debate so far, in order to see what it may be able to offer.

References

Dobzhansky, T. (1973). Nothing in Biology Makes Sense Except in the Light of Evolution. The American Biology Teacher 35:125-129.

Engel, G. (1977). The Need for a New Medical Model: a Challenge for Biomedicine. Science, 196: 129-136.

Nesse, R.M. & Williams, G.C. (1995). Why We Get Sick: The New Science of Darwinian Medicine. New York, Times Books, 1995.

(Published in the UK as 'Evolution and Healing: The new science of Darwinian medicine)