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Biomedical subjects

M Y Jaffrin

Publications and source records attributed to M Y Jaffrin.

At least 55 records · Page 3Linked to original sources
PubMed1982

Aortic input impedance in normal man and arterial hypertension: its modification during changes in aortic pressure.

The purpose of this work was to study the factors determining aortic input impedance in hypertensive patients. Aortic input impedance (simultaneous measurements of aortic pressure and blood flow), mean (Wm) and pulsatile (Wp) powers and the Wp/Wm ratio were compared in normal subjects (n = 13) and hypertensive patients (n = 12) under basal conditions and during blood pressure manipulation--angiotensin infusion in five normal patients and nitroprusside infusion in six hypertensive patients. Pulse wave velocity (Möens-Korteweg equation; simultaneous measurement of aortic pressure and radius) was determined under basal conditions in normal subjects and in 11 hypertensive patients. The results show that: 1) the changes in impedance curves in hypertensive patients are related to increased peripheral resistance, pulse wave velocity, wave reflection and aortic radius; 2) in most hypertensive patients impedance curves are normalised when blood pressure is reduced, whereas the Wp/Wm ratio remains higher. This latter result demonstrates that pulsatile energy losses are greater in hypertensive patients and suggests either that the aortic wall remains stiffer, despite the reduction in aortic pressure, or that the flow wave becomes more pulsatile since impedance curves of hypertensive patients seen after lowering blood pressure are similar to those of normal subjects.

Adult↗
PubMed1982

A three-layer semi-empirical model for flow of blood and other particulate suspensions through narrow tubes.

A three-layer mathematical model has been developed and tested for calculating the velocity profile and wall layer thickness for the flow of blood and other particulate suspensions in narrow tubes, from measurements of apparent viscosity and mean concentration in tube. The model consists of a thin cell-free layer, accounting for wall exclusion effect, a cell-depleted one due to radial cell migration and a central core with uniform cell concentration. It is shown that this model contains several previously published models as particular cases and that it gives more realistic predictions of velocity profiles from the same data than less refined models. With proper adjustment of its parameters it is applicable satisfactorily to a wide variety of suspensions. The model results confirm the importance of cell deformability on blood rheological properties in capillaries less than 100 mu.

Blood Circulation↗
PubMed1982

Flows of red blood cell suspensions through narrow two-dimensional channels.

Apparent viscosity and mean channel hematocrits have been measured at various shear rates and feed hematocrits for red blood cell (RBC) suspensions flowing in two-dimensional channels. Three types of RBC were used in the suspensions : normal, partially hardened by heating at 50 degrees C and completely hardened by glutaraldehyde fixation. Channel height was varied from 20 to 200 mu and feed hematocrit from 5 to 55%. Measurements show that RBC deformability plays a dominant role in narrow channels and viscosity increases rapidly with decreasing cell deformability. Like in narrow tubes the apparent viscosity as well as the mean channel hematocrits decrease as the channel height is reduced. However the apparent viscosity in a channel remains slightly higher than the viscosity in a tube of diameter equal to the channel height. These results are consistent with the existence of a cell-depleted layer near the channel walls.

Blood Viscosity↗
PubMed1981

A one-dimensional model of simultaneous hemodialysis and ultrafiltration with highly permeable membranes.

A one-dimensional model of combined convective and diffusive mass transfer in a hemodialyser is presented. Solutions and results are given for two regimes of ultrafiltration (UF): at low transmembrane pressures when UF flow is proportional to transmembrane pressure and in the limit of large transmembrane pressures when UF is limited by protein concentration polarization. It is found that the overall clearance is always less than the sum of dialytic and UF clearances due to interaction between convective and diffusive transfers. For a given UF flow the clearance is not sensitive to UF flux distribution along the membrane. Model predictions of urea clearance are in good agreement with measurements obtained in vitro with saline on hemodialysers equipped with a polyacrylonitrile membrane.

Blood↗
PubMed1980

[Aortic pressure and velocity signals processing: application to human aorta characterization (author's transl)].

The input to and characteristic impedances of the ascending aorta and the mean, pulsatile and maximum hydraulic powers generated by the left ventricle have been determined in 16 patients by simultaneous measurements of aortic pressure (by miniature transducer), velocity (by electromagnetic probe) and diameter (by cineangiography). Eight patients had normal blood pressure and eight were hypertensive. Harmonics of pressure and flow were calculated by processing the signals for 40 cycles, taking into account the frequency response of the velocity probe (Figs. 1 and 2). 1. The invariance of input impedance with heart frequency confirms the linearity of the arterial system under resting conditions (Fig. 3). 2. The characteristic impedances calculated by averaging the input impedance modulus above 2 Hz (Fig. 5) and from cineangiography are in good agreement for normotensive patients but discrepancies arise for hypertensive patients (Fig. 4). 3. Comparison of input impedance spectra (Fig. 6) reveals that in hypertensive patients the point of minimum modulus and zero phase is shifted towards higher frequencies while the characteristic impedance is higher. 4. The hydraulic power generated by the left ventricle is higher for hypertensive patients (Table I) and the increase in pulsatile power is almost entirely due to the increase in pressure harmonics (Figs. 7 and 8). These results suggest that the aorta plays an important role in left ventricular performance and that it may be characterized by its input impedance spectrum.

Adult↗
PubMedDate not supplied

Kinetic modelling as a tool for the design of a vascular bioartificial pancreas: feedback between modelling and experimental validation.

A bioartificial pancreas is a system which contains isolated islets of Langerhans protected against immune rejection by an artificial membrane, permeable to glucose and insulin, but not to lymphocytes and immunoglobulins. However, it is necessary to design a device which performs as a closed-loop insulin delivery system, more specifically which rapidly responds to a change in the recipient's blood glucose concentration by an appropriate change in insulin release. We have designed a system intended to be connected as an arteriovenous shunt of the recipient; islets are placed between two flat ultrafiltration membranes, and blood circulates successively above the upper, and below the lower, membrane, in reverse direction. A complete kinetic model of glucose transfer from blood to the islet compartment, of insulin generation by the islets displaying a biphasic insulin pattern, and of insulin transfer into the bloodstream was described, and parameters were calculated on the basis of experimental data obtained when islets of Langerhans were perfused in vitro with a synthetic buffer. The resulting calculations indicated that both diffusional and convective transfers were involved in glucose and insulin mass transfer across the membrane, the contribution of diffusion being the most important. The geometry of the system was therefore modified in order to decrease the resistance to flow inside the blood channel. This should increase, at a given hydrostatic pressure, the blood flow rate, and thereby improve the diffusional transfer of insulin. This should also decrease the thrombogenicity of the device.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Extracellular and intracellular fluid volume monitoring during dialysis by multifrequency impedancemetry.

Impedance techniques can, in principle, permit non-invasive monitoring of extracellular (Ve) and intracellular (Vi) fluid volumes during dialysis. The authors present a method that determines the resistances Re and Ri of extracellular and intracellular compartments, respectively, by extrapolating impedance measurement toward zero, as well as infinite frequencies, according to the Cole-Cole model of biologic issues. These measurements were made using a XITRON 4000 B impedance meter (Xitron Technologies Inc., San Diego, CA) at frequencies ranging from 5 kHz to 1 MHz. The fact that the body is not a cylindric, homogeneous conductor is taken into account by introducing shape factors ke and ki and different resistivities pe and pi for the extracellular and intracellular fluid compartments. Assuming that these four unknown parameters can be regarded as constant during dialysis, the authors obtain: [formula: see text] where subscript o denotes initial values at start of dialysis. Impedances were measured at 30 min intervals on 11 pediatric patients and two adults, whereas total body water volume was determined by measuring urea in collected dialysate. Without ultrafiltration, Ve and Vi do not change significantly in percentage whereas, in the presence of ultrafiltration, Ve decreased by 15% to 25%. In cases when Vi does not change, it is possible to determine Ve and its variation during dialysis.

Adolescent↗
PubMedDate not supplied

Time and pressure dependence of sieving coefficients during membrane plasma fractionation.

The apparent sieving coefficient (S') of a membrane, defined as the ratio of permeate to feed concentration, is not an intrinsic property of the membrane, but depends upon operating conditions. The variation of albumin, IgG, and IgM sieving coefficients with time during dead-end filtration was investigated using human pooled plasma and two types of hollow fiber filters (cellulose acetate PF 100 and ethylene vinyl alcohol Eval 2A). For the same filtrate flux (3.6 10(-3) cm/min) the transmembrane pressure (TMP) rises faster with time for the Eval filter because of its smaller hydraulic permeability (0.26 10(-4) cm/min mmHg vs. 7.3 10(-4). The albumin S' of the PF 100 reaches 0.95 after 20 min of filtration but drops to 0.4 after 50 min, whereas the S' of the Eval filter, which never exceeds 0.6, remains at this level for at least 50 min. By varying the inlet flow rate the authors show that for a given membrane, the critical parameter that governs the S' is the TMP. These data suggest that it is essential to specify the TMP when quoting a value of S', and the most permeable membrane, with the highest maximum S', is not necessarily the one that maximizes the overall recovery over a long period.

Cell Membrane Permeability↗
PubMedDate not supplied

Rationale of filtration enhancement in membrane plasmapheresis by pulsatile blood flow.

It has been demonstrated in our laboratory that blood flow pulsations enhance plasma filtration rate by 30-60 per cent. The increase in plasmafiltration over the steady flow value is found to be a function of the parameter F. delta V'/QB where F denotes the pulsation frequency, delta V' the volume amplitude of pulsed blood in the filter and QB is the time mean blood flow. The increment in plasma filtration may be related to the increase in time-mean absolute value of shear rate.

Animals↗