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1 Vibrations in Physical Systems

1 2008

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Modal analysis of physiological model of avian embryos - identification experiment. Part I

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Iwaniec J. , Iwaniec M. , Pawlak K.

2008

tom Vol. 23

165--168

Avian embryos are commonly used as ethically acceptable physiological models for research into prenatal live. Although easily available, avian embryos are difficult objects for investigation. The main difficulties result from the presence of shell separating the embryo from environmental influences and, what is more important, from the presence and interference of many biomechanical, chemical, electrical and other phenomena. The tiny changes in the object parameters of different nature are hardly measurable by means of the indirect methods. Investigation into the embryo prenatal life requires application of the non-invasive methods, which complicates the measurements. Taking into account the fact that as early as in the second day of incubation the avian embryo hart begins to work being by itself at the beginning of mutual conversions, it is easy to become conscious of the scale of the measurements and resulting identification problems. In the process of forming and growth, the heart of avian embryo undergoes constant biomechanical modifications. This aspects of embryogenesis are correlated to electrical and hydro-dynamical activity. Only mechanical vibrations and acoustical effects can be analysed on the basis of the indirect non-invasive measurements. The research carried out by authors is presented in the series of two papers. The current paper (part I) concerns the innovative noninvasive method dedicated for measurements of low-amplitude vibrations induced by the work of cardiac muscles while in the second paper (part II) there is presented vibration analysis carried out by means of the classical LSCE modal analysis method. Although the biomechanical model of developing heart is characterized by significant nonlinearity of observed parameters resulting from rapid increase in the cardiac muscle mass, during a given measurement session the changes in the object parameters are negligible and the assumptions of modal analysis are valid. The changes in the proportions and organ masses as well as in time histories and values of forces generated by beating heart are the source of changes not only in the estimated modal model parameters but also in the model order. Some natural frequencies and corresponding mode shapes evolve and change their values, decay or appear. This variability can be observed in the longer time scale (e.g. days). In a single identification experiment lasting up to tens of minutes per day, after elimination of disturbances, the measured vibroacoustical signal can be treated as quasi stationary. Modal model parameters and the model order were determined for each separate measurement session lasting 10 to 40 minutes. Parameter values estimated for the consecutive measurement sessions made it possible to track the changes in modal model in the consecutive days of incubation.