Cerebral blood flow in the pig : a study of Xenon-133 clearance techniques

Cerebrovascular disease is an important cause of death. The number of cerebrovascular complaints is increasing, mainly as a consequence of increasing the mean lifetime. Functioning of the brain is dependent on blood supply. A temporary or prolonged reduction of total or regional cerebral blood flow (c.b.f.) may lead to irreversible damage of cerebral tissue and loss of neurological functions. Therefore the measurement of cerebral blood flow, preferably in different regions, is clinically important. Several methods of measuring c.b.f. have been developed. The applicability of a method in a clinical situation depends on its traumatic aspects. A brief survey of the methods of c.b.f. measurement is given at the end of this chapter. The clinical method used most frequently is the Xe-133 clearance technique. The Xe-133 is administered by three different routes, intra-arterial, intravenous or by inhalation. This thesis mainly deals with the intraarterial injection technique, evaluated on the pig as experimental animal

An analytical solution to solute transport in continuous arterio-venous hemodiafiltration (CAVHD)

In conventional intermittent hemodialysis, the overall mass transfer coefficient (Ko) of a dialyser is mostly calculated at zero ultrafiltration and at relatively high dialysate flow rates. In continuous arterio-venous hemodiafiltration (CAVHD), the dialysate flow rates are low as comparable to the rates of ultrafiltration flows, making the dialysis treatment as slow as possible. Therefore the overall mass transfer coefficient (Kd) of a CAVHD hemofilter has to be calculated in the presence of ultrafiltration. A mathematical model of CAVHD is presented in order to calculate the diffusive mass transfer coefficient (Kd) for a solute when blood, filtrate and dialysate flow rates and solute concentrations are known. The ultrafiltration volume flux (Jv) is assumed to vary linearly along the axial direction of the hemofilter. The calculated mass transfer coefficient Kd shows that at high values of dialysate flow and low values of ultrafiltration, the overall mass transfer coefficient (Kd) of a CAVHD hemofilter equals mass transfer coefficient (Ko) of a dialyser in conventional intermittent hemodialysis. Also, the calculated mass transfer coefficient Kd shows no significant differences when the ultrafiltration volume flux is assumed to be constant along the length of the hemofilter if no backfiltration occurs in the hemofilter

New concepts in relation to urge and detrusor activity

Investigations of micromotion characteristics of bladder wall strips and pressure wave phenomena in total bladders in vitro and in vivo indicate that micromotion phenomena occur in the bladder wall. Local contractions can occur without an increase in tension or pressure, because other parts are in antiphase. Local contractions stretch surrounding tissues, which can stimulate fast stretch receptors. Synchronisation of these micromotion phenomena appears to be possible. Hence, above threshold levels urge can theoretically occur, even in the absence of a pressure increase. This hypothesis could explain the weak relation between urge and pressure. The distinction between motor and sensory urge could be artifactual based on a misunderstanding of fundamental bladder wall processes

A mathematical model of continuous arterio-venous hemodiafiltration (CAVHD)

Abstract Continuous arterio-venous hemodiafiltration (CAVHD) differs from conventional hemofiltration and dialysis by the interaction of convection and diffusion, the use of very low dialysate flow rates and by the deterioration of membrane conditions during the treatment. In order to study the impact of these phenomena on diffusive transport, we developed a mathematical model of the kinetics of CAVHD solute transport from plasma water to dialysate. The model yields an expression of the diffusive mass transfer coefficient, Kd, as a function of blood, filtrate and dialysate flow rates and solute concentrations, which can be measured in the clinical setting. This paper gives a description of the model derivation. Kd is demonstrated to vary depending on dialysate flow and duration of treatment