[Acute and chronic effects of standard hemodialysis and soft hemodiafiltration on interdialytic serum phosphate levels]. / Effetti acuti e cronici della emodialisi standard e dell'emodiafiltrazione-soft sui livelli interdialitici della fosforemia.

INTRODUCTION: The dialytic management of hyper-phosphoremia, which is inadequate because of insufficient intra-dialytic removal of phosphate (P), is further limited by PDR-P, i.e. the significant increase in serum P levels during the early postdialytic period. Patients and methods. To investigate the effects of enhanced P removal by haemodiafiltration on the inter-dialytic phosphoremia, we studied 12 uremic patients that were switched, with cross-over randomised modality, to a single session of standard hemodialysis (HD) and hemodiafiltration (HDF) (Acute Study). Blood samples were obtained before the treatment, at the end (T0), after 30, 60, 90 and 120 minutes, and at 24, 48 and 68 hours. During both dialytic treatments the whole effluent dialysate was collected to evaluate the intradialytic removal of P. Thereafter, patients were randomised to receive either HD or HDF for three months, in the presence of constantly similar Kt/V, food intake and dose of phosphate binder (Chronic Study). RESULTS: Acute Study. Compared to HD, P removal in HDF was about 44% greater in the presence of identical predialytic P levels (6.0+/-0.2 and 5.9+/-0.4 mg/dl) and Kt/V (1.35+/-0.06 and 1.34+/-0.05); however, the inter-dialytic decline of serum P levels did not differ (-50+/-3% versus -42+/-3%, p=0.098). In HDF, PDR-P was faster (30 min versus 90 min) and better (at T120: +69+/-6% versus +31+/-4%, p<0.001). The higher P levels were maintained throughout the inter-dialytic period whereas Ca x P changed in parallel. Chronic Study. During the three months, pre-dialytic serum P diminished in HDF (from 5.8+/-0.2 to 4.4+/-0.3 mg/dl, p<0.05), while it remained unchanged in HD. A similar pattern of changes was detected in Ca x P. CONCLUSIONS: Enhancement of P removal, acutely amplifies the extent of PDR-P, but allows better control of Ca-P homeostasis in the medium term. This effect is likely to be dependent on the enhanced mobilisation of phosphate from a deep compartment.

Modeling of ultrasonic wave propagation in teeth using PSpice: a comparison with finite element models.

Ultrasound is used extensively in the medical field for the detection and characterization of a variety of features in the human body. Finite element models used to understand ultrasonic wave propagation in teeth have been developed so that ultrasound techniques could be realized in dentistry. This paper presents a hypothesis that underlies one possible design of an ultrasonic tool that can be used in a clinical environment, as well as several models that describe acoustic field simulation, propagation, and interaction with the layers of several tooth structures. A complete PSpice model of a single-element transducer based on Redwood's version of Mason's equivalent circuit, a focusing lens, and a multi-layer tooth structure is used to illustrate the validity of this hypothesis. Transmission line theory is employed as a basis for the models of the piezoceramic, the lens, and the different tooth layers. Results clearly depict the transmission and reflection of the ultrasonic waves as they travel through the layers within the tooth structure and point out the noticeable similarity to longitudinal L-wave signatures produced by axisymmetric finite element models presented in earlier studies.

PSpice modelling of ultrasound transducers: comparison of software models to experiment.

This paper presents a complete PSpice model of an ultrasound single-element transducer, including electrical and mechanical matching as well as the focusing lens. By using this model, it is possible to obtain a relation between the electrical driving source and the acoustic velocity on the transducer surface. This boundary condition then allows the acoustic field to be calculated by numerical methods. Experimental data obtained with two different transducers are in good agreement with results predicted by the related models.