Miguel Ángel Martínez Iradier
For a while it seemed that information and complexity theories, along with genetics, were going to give us a comprehensive description of life and its characteristic processes such as aging. Later we have learned that man has fewer genes than a banana or some fishes and monkeys, while definitions of entropy, another name for information, have proliferated almost as much as its applications, making the term increasingly fuzzy and less universal. Complexity sciences have grown under the impulse of the information explosion, but they have not brought much clarity, and they have certainly not made us any wiser. In this short article we do not intend to critically review such a vast field; instead, we would like to point out the real-life interest and relevance of using much more simpler, basic and physical categories.
Skepticism about the complexity theories has already begun to spread for some years, and after decades of speculative intoxication, the hangover was predictable even if the impetus of the computational paradigm does not subside. An astrophysicist like Eric Chaisson has shown that a measurement as elementally physical and simple as the energy flux density is far more reliable and expressive for the metric of complexity than any of the much more abstract definitions of entropy that proliferate. That already tells us something, even if that simpler measure could not take us too far.
Since so far so few lessons for life has been drawn using all the power of our arsenal of complexity theories, we believe it is appropriate to look in the opposite direction in search of simple and robust concepts that have not received enough attention —even at the risk, of course, of being over-simplistic. In any case, we believe that it is easier to see what is missing in something too simple, than what is in excess in something too complex.
After all, does modern medicine, with all its technological deployment, have even an acceptable definition of vitality or health? Not at all; at best, we will be told it is an optimal state of functioning of the body, which does not exclude certain subjective components —or something similar. Mere words and truisms that do not add even a hint of knowledge to what any of us knows without considering it for a moment.
Compare that to this early twentieth century definition due to the "vitalist" Ehret: vitality is power minus obstruction (V = P—O), actually the only mechanical and functional definition that has been given so far, and the more truthful and simple possible too. This is not the place to assess the dietary ideas of the German naturist or its viability in the modern world, but it is worth remembering that both those ideas, and their definition of vitality, are the same ones that a Taoist would have subscribed two thousand years ago.
What really interests us is that this definition, in addition to being full of meaning in the qualitative and subjective dominion, admits an immediate physical translation. And it is that, after physics and mechanics have served to model the rest of the experimental sciences, such as chemistry, anatomy and physiology, by the mere logic of specialization we have curiously come to assume that, at a basic level, they can not have anything else to say. And that depends on how we understand physics and mechanics.
Take for example something quite fundamental as Maxwell's electromagnetic theory. It is assumed that this has little to say about the human body and physiology, except, in a very mediated way, for the electrochemical potentials, which we consider to be part of biochemistry. But it turns out that Maxwell's original theory is a hybrid of mechanics and hydrodynamics indisputably based on ideas of flow and circulation. It is a mathematically written but totally phenomenological theory of closed currents and flux tubes, macroscopic, built from outside to inside, defined by integral equations and not by differential equations or vectors. That is, in its original form these equations, which are considered one of the deepest axes of theoretical physics —the main source of dualities-, although strictly mechanical and tautological, are more "holistic" than a number of medicine views that are taken as such.
Not only that, but, if we do the proper constitutive interpretation of those equations, we come, like Nicolae Mazilu, to the conclusion that the classical electric field is the form of the stresses that are not accompanied by strains, while the form of the deformations that are not accompanied by stresses is that which characterizes a classical magnetic field. And this definition is equally valid for materials, biomechanics, or even our self-perception, subjective as well as objective, in terms of tension, pressure and deformation.
That is to say, all this has global aspects that go far beyond our idea of electricity as a motion of charges. Maxwell's equations have a part defined by a metric associated with the electromagnetic force, and another part, much more universal, that can be applied to hydrodynamics, thermodynamics, seismology, and so on.
In Ehret's formula, power is synonymous with pressure. Solids and liquids behave in a similar way under pressure; it is said that under tangential stress "the solid deforms, and the liquid flows". This already gives us the general idea of how to shift from stresses to currents; and thus, through hydrodynamics, we find another completely natural way of bringing together the fundamental structure of electromagnetism as a theory of continuum mechanics to biology.
It is well known that one of the most tracked vital signs in modern medicine is blood pressure, that we use to call hypertension when it's too high; actually the pressure is exerted by the blood, the tension or stress affects the surface of the vessel. In truth, with the increase of the flow velocity in a vessel, the pressure on its walls decreases, and in general terms it is the stagnation of the blood which increases the pressure and the tension to which the vessels are subjected.
It is clear that if we only want to know about the stress indices, we don't need more than Bernoulli's general principle of hydrodynamics or the Laplace equation which connect the former with the potencial theory. The Bernoulli principle can be derived directly from the Second Law and tells us that the sum of the kinetic, potential and internal (pressure) energy remain constant; the Laplace equation gives us a distribution of lines of flow in a current and leads us to the Poisson equation and Maxwell's second equation.
The very hemodynamics of the cardiovascular system finds a good approximation, often used by scholars, in Ohm's law (pressure is equal to the product of flow and resistance, or also, in terms of electrodynamics, the potential difference is equal to the product of intensity and resistance); this electric law naturally corresponds to the Poiseuille equation of laminar flow usually applied to the case. Although Ohm's law is considered empirical, it has been verified with precision up to the vicinity of the atomic level.
The Poiseuille equation gives the pressure drop of the laminar flow in the cross section of the vessel; this in turn originates a Bessel function of the first order, the vibration modes of the cross section. Old pulsology manuals tried to draw this feature of the pulse shape, so different from the time profile of the wave.
The presence of these well-contrasted equations strongly suggests that in the mere pulse signal there is much more useful information than what currently we are able to interpret —information with a direct and clear physical meaning. Until recently it has not been possible to faithfully track the pulse signal without the use of catheters, but now the applanation tonometry makes this possible non-invasively and easily.
Measurements apart, if what defines our idea of health is the flow and circulation, the structural element that define them is the tube, exactly as in Faraday and Maxwell approach; and the external differential forms developed by Cartan are the most natural, elegant and compact way to consider their contours and global, geometric and topological changes.
Cylinders or tubes of flow occur in the body at a much wider range of levels than the cell, currently considered the fundamental biological unit. We have tubes and channels at the level of macromolecules, at the intracellular level, at the multicellular level in ducts and blood vessels, in the organs, and finally, in the most elementary topology of the human body as a digestive tube that external matter passes through. Above or below, tubes or channels are a much more general structure for life than cells. To say that life is functionally a matter of tubular flow is pertinent and adjusted to reality, although it has not yet been considered with a keen integral strategy.
As for the molecular level, which until recently was considered the ground level of univocal information —remember the so-called "central dogma of molecular biology"- we now know that genes have multiple expressions and that enzymes are capable of perform very diverse functions depending on the environment. What ever happened to reductionism? And yet we see that physics, supposedly the most reductionist of sciences, naturally allows a more global vision. Moreover, the classical, macroscopic version of electromagnetism already contains a rich statistical structure, with conservative and dissipative aspects.
The current clinical knowledge about hypertension, mainly based on biochemistry, ignores such basic mechanical things as the role of respiration, and breathing is already a first-order circulatory function, even if we only consider the gaseous exchange that generates. Now that there is so much talk of evolutionary medicine, we can ask which organ would take Nature for something as critical as circulation as a first choice, if one with a given volume, or another with four times its volume and therefore much greater adaptation capacity. And we don't mean only of the lungs and the thoracic pump, also of the diaphragm and the so-called abdominal pump.
From a global point of view the heart is more a control valve than a pump driving the blood; We should have drop this idea for what it is ... another primitive representation. And the mere fact that the diaphragm requires more blood than the heart would have to tell us something. The first and most important measure to reduce hypertension should be to use about half the capacity of our diaphragm, instead of the usual quarter or fifth. The hypertension is due to the stagnation of the venous blood that fails to be evacuated, and that saturates the capillary circulation; when it is full it has to overflow raising the blood pressure. This piece of logic can not be more mechanical nor the empirical evidence more overwhelming, and yet, in 2018, both continue to be systematically ignored.
In the formula (V = P—O) P represents energy and O represents matter. Conservative systems are governed by minimal energy variations; dissipative and far from equilibrium systems, and biological systems with their own internal homeostasis, try to minimize the use of matter for reasons of obvious scarcity. More energy usually leads to more incorporation and more elimination of matter; if the first predominates, one tends to the plethora, if the second, to the consumption. The first also tends to a uniform fullness, but also to gradual obstruction; the second tends to contraction, differentiation and wrinkling, also to increasing fragility. Both are forms of increasing restriction, though. They are very generic patterns of temporal evolution that we all can observe in our fellowmen and in ourselves, and, as simple as they are, they contain important indications.
Naturally, the interplay of energy and matter flows is called metabolism —the balance of catabolic and anabolic reactions releasing energy and forming matter.
It would seem that anabolic reactions seek to get the maximum of matter with the least amount of energy possible, and catabolic reactions, to get maximum energy with whatever matter content; in this sense, both sides mix conservative and dissipative aspects. In other words, they are not only antagonistic, they also contradict themselves to some extent though. Circulation and alternation takes place when two states can not be satisfied simultaneously.
It is well known that bistability is a fundamental attribute of cell function at many levels, and its impairment affects the loss of cellular homeostasis associated with degenerative processes and cancer; it is also known that it depends on complex feedback circuits with ultrasensitive regulatory barriers.
A prototypical macroscopic bistable system whose importance is still unknown, is the nasal cycle, which alternates between the two nostrils with an average duration of about two hours and a half or three hours. Thus far, there are indications that this alternation and its flow rate could have considerable influence on the metabolic activity and the afferent and efferent functions of the nervous system and the brain, but we are still lacking a global understanding of the phenomenon. Why is there alternation here, why circulation? In this case, as in any other, we must ask ourselves which two conditions can not be satisfied simultaneously and demand such a period.
It seems that the periodicity of this nasal cycle has been studied more than its flow rate, which both quantitatively and qualitatively should be relevant. It is very doubtful that this respiratory bistability is a mere cumulative effect of the sum of local cellular cycles, since in fact it is very easy to modify it intentionally or switching sides when lying down. Even ignoring the depth of its regulatory effect, its global nature is quite evident.
It is a priority then to proceed from the global to the local, not the other way around; in the same way, as a matter of fact, than in the original view of electromagnetism. Two complementary approaches come to mind. The first is biofeedback, since, being a function that can be modified at will, it allows us to follow its more immediate incidence in other physiological, cellular and biochemical functions. Biofeedback allows to set experimental situations that are usually out of control, and it is relatively easy to reach equilibrium situations in which the respiratory function does not fall in any of the two valleys and remains with a relative stability in the middle of the potential barrier.
The second approach is the construction of bistable electromagnetic systems with a significant dissipative component, for example, with metamaterials. Here, the point is to search, by reverse engineering, for systems that generate an analogous, as close response as possible. This is not absurd at all if we start from the idea that the (generalized) "electromagnetic" component, in the most universal sense already mentioned, of living systems is constitutive and not accidental; and on the other hand, and complemented by the previous approach, this allows a certain constructive or bottom-up approach, since metamaterials are in phase aggregates of unit cells such as split ring resonators —and not only unit cells, we could speak of "unit tubes" too.
The phase modulation allows here to alter macroscopic properties of the equations such as permittivity and permeability, thus obtaining negative indexes that seem to violate elementary laws and make possible exotic properties such as optical cloaking, etc.
Both approaches are highly complementary, proceeding top-down and bottom-up, and the thinning of the potential barrier by self-feedback allowing also to enter the domain of phase modulation and attainment of negative indices. We must not forget the overdetermined Maxwell equations emerge from an indeterminate background.
In the same way a metastable or bistable system is a small island of stability in a sea of matter and energy that always remains undetermined but that is actualized by the interactions: the same matter and energy that make it possible define its limits. An obvious statement that has many non-trivial aspects.
The potential barrier of a bistable system should faithfully reflect its metabolic limitations in the use of matter and energy —and what of its restrictions are reversible or irreversible. This would give us the still missing global idea of the aging process.
Aging as an increasing restriction
In this article we assume that aging is a global and macroscopic rather than a microscopic process, and that the microscopic aspects are always hostages of an internal environment and local context, which in normal conditions obeys the global balance more than the other way around. In any case, we already have chemical markers by myriads, but not a general vision that delves deeper into what we already see.
We are used to see the increase in complexity of systems as an opening to endless possibilities, but this increase in complexity inexorably leads to a tighter restriction and closing operation. It's clear that old age is complex, not in the sense of greater possibilities, but rather on the contrary: it is increasingly complicated, more difficult, also more characteristic. What were once dispositions have now become structures that increasingly limit the free flow of energy. As pure differentiation, it is a highly personal, individual process —there is not, there can not be anything more individualized than this.
Simplifying it to the maximum, physical aging is an increasing lack of elimination of the obstructions, which accumulates in the form of more or less characteristic material structures. Put another way, it is the cumulative growth of the obstruction. Although, needless to say, an organism can eliminate too much without eliminating all the obstructions. Nature in fullness knows very well what to eliminate and how; it is the impeded nature that must be helped, by means that may be lesser, or greater in cases such as surgery.
This is what really matters, the rest are corollaries. Obstruction is superfluous by definition, then it can not be characteristic but in the most external or limiting sense. It is the least individual if we understand the individual as an infinite singularity, and it is the most individual that if we understand the individual as a mere material limitation, as limitation par excellence.
Matter and energy are the two faces of metabolism; to this it could be added that matter can support information, but it can not transmit it, while energy can transmit information, but it can not support and retain it. The self-organization that we attribute to living organisms is their capacity to shape themselves, to produce or alter their structure from the information obtained from their very dissipated energy (Margalef, Barragán).
Thus we return to the trinomial matter-energy-form of the founder of biology, none other than Aristotle; only that the form, as information, has now become a quantitative category of a statistical nature.
The microscopic description of metabolism, its biochemistry and the reactions and cycles it draws at the cellular level, is a science that although always incomplete is extraordinarily developed and does not have great problems to define its method. But all those pieces of the puzzle are still missing the model to assemble, the macroscopic perspective, without which all that information and statistics will never reach the directly appreciable and higher rank of the Form in capitals.
Since the metabolic rates can be followed in ascending order from the reduction-oxidation reactions and cellular respiration rates to the overall profile of the respiratory system as a bistable system by the nasal potential barrier, this is the form and axis of symmetry needed. It is even something else: it is the space and the metric that defines in each moment the relative value of the parameters of the system. Our appeal to electromagnetism in its most universal aspect was not vain, neither our appeal to reverse engineering with metamaterial structures.
In fact, from the constitutive view of the continuum that finds its limit in the field, and in which there is no space without matter or matter without space, just as there is no rigidity without matter, neither exists deformation -changes of form- without energy.
Then we can consider what we call "form" at a constitutive level, as a balance between rigidity and elasticity. This applies even to molecular mechanics, and it's already known that the elasticity of a rigid molecule depends on the energy while that of a flexible molecule depends on the entropy of its configuration (on the other hand, the inelastic forces produce heat and the elastic ones mechanically recoverable tension). This constitutive form is the limiting form, the most external aspect of the individual profile.
Then there would be the innermost and less limited "form" of individuality, which, in reality, lacking limits in a tangible sense, can not be form in the sensory sense. It is, more properly speaking, the space that defines them.
Thus, we could speak of a more external form governed by the balance of matter and energy, tension and deformation; another more internal form, which is the "metric" arising from its interpenetration and which is not properly a metric but rather a fluctuating plateau; and finally an intimate form, which is beyond the distinction between the external and the internal ones. This latter is the most universal aspect, but, seen from the outside, it has to be the utterly undifferentiated.
With some ambition we could figure out the singular function that drives life in each individual —the most comprehensive and constituve individual context for the vital signs of an organism. This one would encompass all the specific details as a by-product.
A framework like this has allowed us to indicate a lot with very few words. While it's not my intention to consider any biochemical detail here, maybe we should mention that the prevalent theory of cellular metabolism and respiration typically ignores the important role that radiation and the corresponding photochemical agents can play with respect to chemical energy, and the extremely variable margin that this aspects may imply.
Temporal evolution of complex systems
Aging as an increasing restriction presents us with a face of temporal evolution that, despite being the most evident of all, continues to be the least attended in our modern culture. This is coincidental, as neither theoretical nor technical means are missing. On the other hand, we constantly talk about the increase in complexity as an increase in possibilities, and, of course, evolution as natural selection, competition and competitive advantage —words that serve for everything and can't explain anything.
I don't think this has to do with science but with discourses in the line of least resistance to the powers that be; It is a horizontal narrative that is considered appropriate for the "atomic levels" of the social body, read individuals. The vertical logic, much more concretely structured, thinks nevertheless in the more "ecological" marketing terms —in the exploitation of niches and ecosystems. Thus, there is an intensely publicized narrative for the many while there is a vertical logic implacably managed by the least.
Whether power is interested or not, we live in increasingly aging societies and this increase in age is far from being only a matter of population average. In the era of diminishing returns, this general circumstance invites to apply even more exhaustively the vertical logic of exploitation. Just as in mechanics and engineering, there is a method of flexibility and a method of rigidity, but to the extent that structures are ossified, rigidity is wining the game as it approaches the breaking point.
Undoubtedly a good part of what applies for a biological organism like the human being would have to apply also, to the extent that it does not depend on particular elements, for the social organization. Here there is also an opposition between free circulation and obstruction, but the arbitrary element, imposed from above, can have more scope and depth. It is the component of self-organization by feedback, and puts us at the heart of control and stability theory, which in its day was called cybernetics.
There is no doubt that biology can be affected by monitoring its output rates —as in the case of breathing and its inconspicuous bistability; but of course there are always limits for intervention, which depend, of course, on the very profile of stability of the system, which in turn can have a margin of evolution over time, to the extent that the organism evolves. Thus, the interest of the more general bistable profile is self-evident and does not need further justification. The lower levels are already the basis of stability with which the higher level is confronted.
The potential barrier that separates the valleys is not internal or external, it belongs to both perspectives and, in a certain sense, it is apart from them. It is Form in a higher sense than that of visible forms, it is Matter in a lower and more generic sense than that of matter that we can see and touch. We can understand it in the terms of the continuum only.
The main question is quite specific: what is reversible and what irreversible in an evolution that tends to an increasing restriction and to an abrupt outcome long before the total uniformity of thermal death. All this is approachable in an experimental and non-speculative fashion, and has a deep theoretical and practical interest.
References
Ramón Margalef, La ecología: entre la vida real y la física teórica
Eric Chaisson, Energy rate density as a Complexity Metric and Evolutionary Driver
Jorge Barragán, Sobre la termodinámica de los sistemas físicos biológicos
Nicolae Mazilu, Mechanical problem of Ether
Elliott, S, The Valsava wave. The changing landscape of Heart Rate Variability Biofeedback
M. A. M. Iradier, Between stress and pressure
M. A. M. Iradier, Beyond control - Feedback and potential