Citizens consult their physicians when they feel that something is not in order, e.g. when they experience pain, fatigue or any other disorder. Physicians then examine them and specifically look for pathological changes. After investigation they make a provisional diagnosis and explore their patients further or treat them accordingly. This type of thinking goes back to the pathologist Rudolf Virchow, who in 1858 used 20 lectures to describe “cellular pathology”, a characterization of different diseases ¹ . Although the foundations of medicine have vastly changed since then, the general principles of medical practice have remained the same. Only over the past 20 years, complexity science has gradually entered into medicine ^{2, 3} . This has become particularly important for the interpretation of health and disease as different states of a complex adaptive system (CAS). The Meikirch model is a new definition of health that exhibits all the features of a CAS ⁴ . For such systems the concepts based on Virchow’s pathology are no longer appropriate. An understanding of health and disease now requires appreciation of complexity science. It introduces a new dimension for diagnosing and treating patients. It includes the potential to improve health in a way that hitherto was practiced only exceptionally. The purpose of this paper is to summarize the relevant features of the Meikirch model and to reveal in detail how the model and complexity science may be applied for a better understanding of a patient’s disease and for its treatment.

The Meikirch model is based on five components ( Box 1) and 10 complex interactions ( Figure 1). This framework allows to define health and disease as a complex adaptive system ( Box 2). Figure 1 depicts the five components from a to e. The interactions are exhibited as double-edged arrows from 1 – 10. A short explanation of the five components and their interactions is presented below. The complete description of the model with its scientific background is given in the original publications ^{4, 5} .

Box 1. a. 

Life's demands (LD)

Box 2. 1. 

Health is a dynamic state of wellbeing emergent from conducive interactions between an individual's potentials, life's demands, and social and environmental determinants.

Each human must fulfil his demands of life ⁶ . Physiological, psychosocial and environmental demands vary with time and circumstances. Physiological demands are related to the homeokinetic balance of nutrients, energy and water to maintain bodily functions including procreation; examples are work, pregnancy, childbirth and brain function. Psychosocial demands are the individual´s exposure and response to social conditions to succeed in social integration and mental, personal and spiritual development. Expectations and roles related to work, family and society as a whole combine with personal aspirations, values and lifestyle in changing settings and contexts. This includes also peace with the fact, that every human being must die. Environmental demands include availability and immediate or latent threats from living conditions (e.g. water, nutrients, climate, radioactivity, pollutants, carcinogens, workplace conditions).

The potential of an individual to meet his demands of life is partly biological e.g. a gift by nature - biologically given potential (BGP) - and partly acquired during life – personally acquired potential (PAP). At the time of birth the BGP is based on the genetic equipment, epigenetic regulation and quality of the pregnancy. The BGP diminishes throughout life and is zero at the time of death. During lifetime the BGP may be threatened or damaged by socioeconomic disadvantages, diseases, injuries and defects. The PAP results from the entirety of physiological, mental, spiritual and social resources acquired during lifetime. It may continue to grow when a person cares for it. Social and environmental conditions also influence the growth of the PAP by providing or withholding determinants of health.

Social determinants of health strongly interact with the demands of life and the potentials of the individual ⁴ . Equity and equality, social concerns, working conditions, autonomy and social participation affect health and longevity ^{7, 8} and are major determinants of health. Likewise, environmental determinants of health are factors in living and working conditions affecting each person. They may sometimes be of global significance like natural resources, population growth and climate change ^{9, 10} .

Based on these five components and their interactions with each other the Meikirch model represents a new definition of health and disease as shown in Box 2. Possible outcomes on individual and public health care as a result of a hypothetical implementation of the Meikirch model have been discussed elsewhere and suggestions for clinical and health systems research have been made ⁵ .

A complex adaptive system is an entity with a more or less permeable boundary between it and its nearby environment ( Figure 2) ¹¹ . It can take up material and energy from the environment (input), release end products (output, e.g. entropy) and do work. Within the system there are many different parts called agents. In Figure 2 they are symbolized as circles. They continuously and autonomously interact with each other in a nonlinear manner, contributing to the product, the so called emergence of the CAS. The term emergence indicates a new and often unpredictable quality which is more than the sum of the functions of each part. A CAS always functions as a whole. Attractors are sites to which the energy flow of the system may be drawn. A CAS is equipped with a learning and bonus arrangement for the interactions among its agents. This gives it the possibility to adapt to changes in the environment, i.e. to learn. If for some reason this adaptation functions poorly, the CAS suffers. If it does not function at all the CAS becomes chaotic and goes into a crisis or vanishes. Repeated critical disturbances may lead to the so called butterfly effect ² . Examples of medical conditions are ventricular fibrillation, epileptic seizures, tantrum, or psychotic states. Every CAS has evolved from a prior condition and autonomously progresses toward an unforeseeable future state. A CAS may be part of a larger CAS or be composed of many CASs. Such structures are called nested CASs.

In the Meikirch model the five components (a–e) including their subcomponents are regarded as agents ( Figure 1). Interacting with each other they spontaneously arrange themselves in such a way that the evolving emergence, i.e. the state of health, is the result of the functioning of the system as a whole. In each case a specific working-arrangement is operational, but it is not necessarily the best solution for the system. Energy flow in humans has been called vitality, drive, or sense of purpose. This indicates that energy flow may also be regarded as immaterial, e.g. based on a desire to be loved, on pursuit of values, or on living for a spiritual purpose. Investigation of the material and immaterial double nature of human energy flow may help to better understand the health of a person.

The entire life is an evolutionary process. Biologically human life originates with the fertilization of an oocyte. This then passes through the stages of embryo and foetus to the maturity needed for birth. At some time during intrauterine life the personality of the individual is created. At the least, physicians and midwifes say that in the new-born it is clearly recognizable. From then on the complete Meikirch model is fully operational during all phases of the life course of each person. Thus evolution from birth to death demonstrates clearly how many adaptive processes occur as part of the different complex interactions described by the model. While the two potentials evolve, the demands of life, the social, and the environmental determinants also vary. Within these limiting and supporting contexts individuals follow an autonomously chosen life course. Under such conditions it is not surprizing that some adaptations may not be fully successful for some time or permanently. Challenging examples are malnutrition, infectious diseases, love deprivation, sexual maturation, pregnancy, genetic defects, professional stress, the raising of children, physical involution, aging, etc. Such changes may lead an individual as a system into a state of crisis. If it is minor, the two potentials still may manage the demands of life and the difficulties may resolve spontaneously after some time. Such situations are not considered to represent a disease. Yet, they may evolve into a chronic state that draws energy from the person and thereby may explain e.g. insomnia, chronic fatigue, or somatoform symptoms. If the defect gets more severe it may lead to a disease that requires more medical attention. In the Meikirch model the term disease implies that for any reason one or several adaptation processes are not successful enough to empower the two potentials to satisfy the demands of life.

Consequences of the Meikirch model and of the properties of CASs are explored with the purpose to better understand the state of health of patients, particularly in internal medicine and general practice. The individual as a patient, according to the Meikirch model, is considered to be a nested CAS, composed of grouped CASs and being embedded in higher CASs. For this purpose, the significance of each of the five components and of each interaction within the Meikirch model must be visualized. In addition, possibilities to support favourable evolutions of the respective CAS and its meaning for the whole person (nested CAS) were studied. In this process, the deduction and induction cycles were repeated until coherent results were received.

At the present time the Meikirch model is a hypothesis grounded on a theoretical framework. Yet, until now much of health care has not been concerned with an understanding of the nature of health; it used instead an intuitive notion of wellbeing which did not lead to new insights. In contrast, a rational understanding of health - as given by the Meikirch model - offers innovative opportunities. Today this model is better founded on scientific evidence than other definitions of health. Its ultimate validity, however, will be documented only by using it in practice. This must be done with due consideration to the special features of the model. Much further research is urgently needed.

For the past 150 years medicine has been working with methods derived from Newtonian natural science and obviously has achieved major advances. They are based, however, predominantly on materialism and neglect the social and spiritual features of the human nature. In addition, until recently medicine has not considered systems theory. It appears that these two aspects offer new opportunities for health care to become even more effective. Systems thinking implies that science based on Newton must be complemented by complexity science. Particularly for the purpose of health care a phenomenological, narrative, evolutionary holism must be added to analytical reductionism ¹¹ . Poorly functioning parts are not simply corrected by appropriate drugs or surgical operations. Instead considerations of the evolution of the patient’s health to the present state, earlier successes in self-management and failures in the handling of his present crises can be evaluated. Antonovsky’s sense of coherence and meaningfulness also may be very helpful ¹² . Necessary changes a patient has to realize must not come top-down from the physician, but rather bottom-up, originating in the patient himself, e.g. by new insights. For this purpose mutually trusting patient-physician interactions are critical for a successful future: the physician must believe in the patient’s abilities to evolve to a new state and must accompany and support him with loving wisdom in this endeavour.

When speaking with older and experienced general practitioners, and when reading about how they managed their difficult patients, it becomes evident, that they knew their patients from the past quite well. In many difficult situations they often had to accompany rather than to treat them. Such patients remained very loyal because they understood what their doctor had contributed to their health. At the same time physicians realized that they had nothing more to offer than their personal support as a professional human being. The Meikirch model offers now a rational approach to such difficult cases and it is hoped that it will give new opportunities for patients to move toward better health. At the first glance the described system’s approach to patient care is similar to what Michael Balint intended with his groups ¹³ . He was psychiatrist and pursued the purpose to train general practitioners in psychotherapy. In contrast, the systems theory focusses on a new look at a patient’s possible unresolved evolutionary steps, analyses the biological given and personally acquired potentials and offers him an opportunity to progress further in his personal biography. More research is needed to validate the promises and limitations of this approach.

The Meikirch model distinguishes two types of very different potentials with which the demands of life must be met, the biologically given potential (BGP) and the personally acquired potential (PAP). The latter is the resource that continuously pilots the adjustment to new life situations. It is the locus of executive functions ¹⁴ . For this purpose it interacts with all components of the system. The PAP is the seat of memory, visions, fantasy, reasoning, attentional control and inhibitory control, and problem solving. Its sustained evolution toward more and more wisdom is critical for the maintenance of health. The PAP can learn to compensate in part for losses of the BGP. This leads to an interesting aspect of the relationship between the two potentials. It may be compared to rider and horse. If the rider wants that his horse serves him well he has to take good care of his horse. It appears that the neglect of the PAP in modern medicine is well perceived by patients. Therefore they turn to complementary or alternative medicine. In fact, much of the success of homeopathy and other methods might be explained by the physician patient interaction with its effects on the complex adaptive system that expresses the patient’s health. This mechanism may be relevant also for much of the success of other complementary or alternative treatments. It is our opinion, however, that it will be better to work with the CAS in a planned and scientifically justifiable manner based on the Meikirch model than to apply unproven methods. The model would also serve as an excellent framework for a proper practice of evidence based medicine as defined by David L. Sackett: “Evidence-based medicine (EBM) requires the integration of the best research evidence with our clinical expertise and our patient’s unique values and circumstances ¹⁵ .” This applies also to the newly evolving holistic clinical approach “Integrative Medicine and Health” that “reaffirms the importance of the relationship between practitioner and patient, focuses on the whole person, is informed by evidence, and makes use of all appropriate therapeutic and lifestyle approaches, healthcare professionals and disciplines to achieve optimal health” ¹⁶ .

When looking at health as a lifelong and complex evolutionary process, it is not surprising that crises do occur frequently. Throughout human life there are several major and many minor evolutionary steps to be taken. End of breastfeeding, beginning of school, puberty, professional formation and advancement, partnership, family, menopause, and involution of old age are some of the more demanding processes. Today they must be overcome in a society that offers insufficient respect for the personality of each individual. Lack of a motivating purpose in life and insufficient social support have become almost normal. Economic exploitation, power plays, isolation, social neglect and even wars weigh heavy on the demands of life. A culture that is really concerned with the health and wellbeing of its individuals needs to strongly support lifelong human development by investing in life-affirming compassion and truth ⁵ . The Meikirch model gives a framework for how this could be achieved.