Search PubMed⌕ Search

Biomedical subjects

J Juchmes

Publications and source records attributed to J Juchmes.

72 records · Page 4Linked to original sources
PubMedDate not supplied

Identification of three-element windkessel model: comparison of time and frequency domain techniques.

The problem of the parameter identification of the three-element windkessel model is studied. Minimization by least-square technique--LSQ--in time domain and frequential techniques--FFT--are compared. Continuous pressure and flow curves were recorded in the proximal aorta of an open chest dog. Comparison shows very high correlations between the parameter estimations obtained by LSQ and FFT methods. However, systematic differences appear between the calculated values, but do not seem to endanger physiological interpretation of the results.

Animals↗
PubMedDate not supplied

Modelling the arterial wall by finite elements.

The mechanical behaviour of the arterial wall was determined theoretically utilizing some parameters of blood flow measured in vivo. Continuous experimental measurements of pressure and diameter were recorded in anesthetized dogs on the thoracic ascending and midabdominal aorta. The pressure was measured by using a catheter, and the diameter firstly, at the same site, by a plethysmograph with mercury gauge and secondly, by a sonomicrometer with ferroelectric ceramic transducers. The unstressed radius and thickness were measured at the end of each experiment in situ. Considering that the viscous component is not important relatively to the nonlinear component of the elasticity and utilizing several equations for Young modulus calculation (thick and thin wall circular cylindrical tube formulas and Bergel's equation) the following values were obtained for this parameter: 0.6 MPa-2 MPa in midabdominal aorta and 2 MPa-6.5 MPa in thoracic ascending aorta. The behaviour of the aorta wall was modelled considering an elastic law and using the finite element program "Lagamine" working in large deformations. The discretized equilibrium equations are non-linear and a unique axi-symmetric, iso-parametric element of 1 cm in length with 8 knots was used for this bi-dimensional problem. The theoretical estimation of radius vessel, utilizing a constant 5 MPa Young modulus and also a variable one, are in good agreement with the experimental results, showing that this finite element model can be applied to study mechanical properties of the arteries in physiological and pathological conditions.

Animals↗
PubMedDate not supplied

[Psychopharmacology and neurohumoral transmission].

The authors remind neurobiologists that, if it is necessary to analyze the mechanisms of neurotransmission, it is altogether necessary to integrate them in a circuit. If there is e.g. a noradrenergic transmission, there is neither a noradrenergic function nor a noradrenergic system. Moreover, the same neurone may release different transmittors; the response of the effector depends on its level of excitability; the identification of a mediator--especially in the urine--does not tell how its activity is modulated etc. A few examples are given.

Animals↗