Biomedical subjects
Publications and source records attributed to A S Iberall.
This note attempts to focus a physical theory for the dynamics of mammalian thermoregulation, its relation to thermodynamic near-equilibrium, and its relation to a circadian component of that regulation. As such, it is an extension of the analysis and discussion carried on in earlier references. That earlier analysis is tested and extended by the use of two additional data sets not found in the earlier work.
The nominal uniformity of long-term mean pressure (approximately 100 mmHg at heart level) for all mammalian species belies the broad nature of its variance, which is found at many time scales. Such variations should be a useful index of physiologically normal and pathological processes. However, it is dubious whether a scientifically meaningful determination of central blood pressure at its many process scales can be achieved from a few isolated measurements: to cite a common and highly significant instance, measurement made by a physician on a patient during one or two office visits. The data presented here are far from exhaustive (a few reports in the literature and detailed longitudinal data on 1 subj), but they serve to illustrate a protocol and a sample of the physiological results that might be expected if data were gathered for larger populations. The basic scales of interest lie in the lower-frequency domain, involving periods of fluctuations longer than tens of minutes.
Human beings are confronted by how things, including themselves, work and how they ought to work. Human beings are also confronted, relatedly, by movement and language. The purpose of this note is to suggest an objective physical base within which these philosophic, psychological, and physiological properties of complex systems can be anchored.
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The current concepts for the functional unit of mammalian skeletal muscle are reviewed and shown to lack components that are required for determining the unit. To secure a definition for the functional unit, requisite criteria were selected, and the manner by which these criteria were used to define the functional unit are discussed. For deriving a definition of the unit the following values were obtained: the unit is associated with the total length of the muscle fiber, which may achieve a maximum length of 60 cm; it exhibits an average diameter of 40 micrometers/fiber; it is associated with a capillary net whose length (arteriole to venule) is about 750-1,000 micrometers max; the net exhibits a capillary-to-fiber ratio for long capillaries of approximately 1-1.5:1, with a transverse capillaries occurring approximately every 150 micrometers; and it has a fiber-to-motor end plate ratio of 1:1. The correlation between anatomic data and functional data indicate that a functional unit of muscle is delimited by about 1 mm2 of the cross-sectional area of a muscle bundle, since this is the maximum area under autonomic control of its particular arteriolar blood supply, the metabolic throttle that determines the power being expended by the muscle bundle.
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This paper continues the development begun in Part I (15), to show in what way it is meaningful to reduce biological phenomena to physical theory at any level of organization. The appropriate level-independent physics is comprised of thermostatics, thermodynamics of irreversible processes, statistical mechanics, and nonlinear mechanics. Generalized, these approaches lead to a spectroscopic description of the constellation of periodic processes that constitute the living states. The spectroscopic description is here applied also to the inputs received by living systems, from lethal, high-energy, nuclear particles and radiation to low-energy communicational signals that make up languages understandable at the various levels in an hierarchical system. The concept of language is then itself generalized, showing how the empirical relation discovered by Zipf can be derived from a thermodynamic basis. It is demonstrated that certain linguistic and statistical-mechanical distribution functions can be related. Applications of the field thermodynamic approach to two problems in transport phenomena are given in APPENDIX I; applications of field thermodynamics to language and communication are given in APPENDIX II.
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In this first of three articles on a physical basis for integrative physiology, statistical mechanical concepts are developed into a field thermodynamics. The development begins by comparing the different ways change is viewed in biology compared to physics. The Hamiltonian field concept unites the two. The requirements of a thermostatic description are introduced; then those of nonequilibrium thermodynamics are added. Conditions suitable for continuum, near-equilibrium analysis of systems are given; then the role of physical forces in organization is discussed. The development returns to statistical mechanics, and introduces conservation principles and equations of change for ensembles of interacting units. A general notion of systems and thermodynamic engines is discussed next, and a narrative account of the explanatory scope of field thermodynamics is given. Its applications to living systems are the subject of the subsequent two articles of this series.
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