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Biomedical subjects

William R Clark

Publications and source records attributed to William R Clark.

14 recordsLinked to original sources
PubMed2003

Kinetic comparison of different acute dialysis therapies.

Recent clinical data indicate both ultrafiltration rate (Qf) and timing of treatment initiation in continuous renal replacement therapy (CRRT) and therapy frequency in intermittent hemodialysis (HD) influence survival in critically ill patients with acute renal failure (ARF). In this study, kinetic modeling is used to compare effective dose delivery by three acute dialysis therapies: continuous venovenous hemofiltration (CVVH), daily HD, and sustained low-efficiency dialysis (SLED). A modified equivalent renal clearance (EKR) approach to account for the initial unsteady-state stage during dialysis is employed. Effective small solute clearance in CVVH is found to be 8% and 60% higher than in SLED and daily HD, respectively. Differences are more pronounced for middle and large solute categories, and EKR in CVVH is approximately 2-fold and 4-fold greater than the corresponding values in daily HD and SLED, respectively. The superior middle and large solute removal for CVVH is due to the powerful combination of convection and continuous operation. In CVVH, a decrease in the initial BUN from 150 to 50 mg/dL is predicted to decrease TAC and, therefore, increase EKR by approximately 35%. After clinical validation, the quantification method presented in this article could be a useful tool to assist in the dialytic management of critically ill ARF patients.

Acute Kidney Injury↗
PubMed2003

Dose determinants in continuous renal replacement therapy.

Increasing attention is being paid to quantifying the dose of dialysis prescribed and delivered to critically ill patients with acute renal failure (ARF). Recent trials in both the intermittent hemodialysis (IHD) and continuous renal replacement therapy (CRRT) realms have suggested that a direct relationship between dose and survival exists for both of these therapies. The purpose of this review, first, is to analyze critically the above-mentioned dose/outcome studies in acute dialysis. Subsequently, the factors influencing dose prescription and delivery are discussed, with the focus on continuous venovenous hemofiltration (CVVH). Specifically, differences between postdilution and predilution CVVH will be highlighted, and the importance of blood flow rate in dose delivery for these therapies will be discussed.

Acute Kidney Injury↗
PubMed2003

A numerical and experimental study of mass transfer in the artificial kidney.

To develop a more efficient and optimal artificial kidney, many experimental approaches have been used to study mass transfer inside, outside, and cross hollow fiber membranes with different kinds of membranes, solutes, and flow rates as parameters. However, these experimental approaches are expensive and time consuming. Numerical calculation and computer simulation is an effective way to study mass transfer in the artificial kidney, which can save substantial time and reduce experimental cost. This paper presents a new model to simulate mass transfer in artificial kidney by coupling together shell-side, lumen-side, and transmembrane flows. Darcy's equations were employed to simulate shell-side flow, Navier-Stokes equations were employed to simulate lumen-side flow, and Kedem-Katchalsky equations were used to compute transmembrane flow. Numerical results agreed well with experimental results within 10% error. Numerical results showed the nonuniform distribution of flow and solute concentration in shell-side flow due to the entry/exit effect and Darcy permeability. In the shell side, the axial velocity in the periphery is higher than that in the center. This numerical model presented a clear insight view of mass transfer in an artificial kidney and may be used to help design an optimal artificial kidney and its operation conditions to improve hemodialysis.

Biological Transport↗
PubMed2003

Effect of flow baffles on the dialysate flow distribution of hollow-fiber hemodialyzers: a nonintrusive experimental study using MRI.

We used an innovative, nonintrusive MRI technique called the two-dimensional (2D) Phase-Contrast (2DPC) velocity-imaging technique to investigate the effect of flow baffles on the dialysate-side flow distribution in two different hollow-fiber hemodialyzers (A and B); each with flow rates between 200 and 1000 mL/min (3.33 x 10(-6) and 1.67 x 10(-5) m3/s). Our experimental results show that (1) the dialysate-side flow distribution was nonuniform with channeling flow occurred at the peripheral cross section of these hollow-fiber hemodialyzers, and (2) the existing designs of flow baffles failed to promote uniform dialysate-side flow distribution for all flow rates studies.

Blood Flow Velocity↗
PubMed2002

The Acute Dialysis Quality Initiative--part IV: membranes for CRRT.

The extracorporeal membrane used in a continuous renal replacement therapy (CRRT) for the treatment of a critically ill patient with acute renal failure (ARF) is vitally important for several reasons, including its influence on biocompatibility and filter performance. The clinical relevance of membrane-related biocompatibility markers traditionally used in chronic hemodialysis remains unclear in CRRT. Numerous approaches may be used to assess membrane and filter performance in CRRT, but no specific methodology is accepted widely at present. Although a potential benefit of certain membranes used for CRRT is adsorptive removal of inflammatory mediators, this issue has not been assessed carefully in well-designed clinical trials. These and other issues should be the subject of future clinical research efforts.

Acute Kidney Injury↗
PubMed2002

Determinants of uraemic toxin removal.

The inability to excrete a wide spectrum of toxins is one of the hallmarks of uraemia and is responsible for many of the signs and symptoms of this syndrome. Therefore, an understanding of the factors influencing uraemic toxin removal, during both the pre-dialysis and dialytic phases, is critically important. This review addresses many of these factors, which include the importance of preserved residual renal function and the effect of therapy frequency. In addition, specifically with respect to larger uraemic toxins, the importance of convection and treatment duration is discussed. All of these issues will be major considerations as new dialytic therapies for end-stage renal disease patients are developed and implemented.

Humans↗
PubMed2002

Low-molecular weight proteins in end-stage renal disease: potential toxicity and dialytic removal mechanisms.

Low-molecular-weight proteins (LMWP) are now recognized as a distinct class of uremic toxins, and numerous compounds in this category have been identified. Dr. Henderson has spent much of his career investigating ways to enhance the removal of intermediate- and large-sized uremic retention molecules. As LMWP clearly fall under this category, it is fitting to provide a review of several aspects of this molecular class. Normal renal metabolism of LMWP is discussed along with the changes that occur during chronic renal insufficiency. The effect of end-stage renal disease on plasma LMWP concentrations is assessed. As examples of the potential uremic toxicity of this molecular class, leptin, adrenomedullin, and the compounds associated with increased susceptibility to infection are highlighted. Finally, an overview of LMWP removal mechanisms for both hemodialysis and the convective therapies is provided.

Hemodiafiltration↗
PubMedDate not supplied

Properties of membranes used for hemodialysis therapy.

Recent trends show a progressive increase in the use of modified cellulosic and synthetic dialyzers and a corresponding decrease in the utilization rate of unmodified cellulosic dialyzers. The purpose of this article is to describe current membrane and dialyzer technology, with the focus almost entirely on modified cellulosic and synthetic membranes. A general overview of membrane-related determinants of dialyzer performance is first presented, followed by a discussion of specific characteristics of some of the more commonly used membranes and dialyzers.

Cellulose↗
PubMedDate not supplied

Laryngeal and phonatory status after burn/inhalation injury: a long term follow-up study.

Although persistent hoarseness has been recognized in patients who have sustained burn and/or smoke inhalation injuries, there is little documentation to support this observation. Furthermore, there is no quantification of either the pervasiveness of the problem or the severity of the dysphonia resulting. It was the intent of this study to examine the laryngeal condition and voice production of a group of patients who were long-term survivors of burns and inhalation injuries. Only 10 patients (8 male and 2 female) of a larger cohort were willing to return for this examination. They were ambulatory and did not require respiratory assistance, and it had been 16 to 25 years since their initial traumas. Videostrobolaryngoscopic examinations were performed and analyzed, measures of various acoustic and aerodynamic parameters were made, and severity of dysphonia was judged. Seven of the 10 subjects were rated by experienced listeners as having some degree of dysphonia. All subjects had some abnormality of the laryngeal mucosa. Stroboscopic examination was found to be helpful in identifying laryngeal abnormalities in at least half of the subjects. Early attention to these problems, many of which are treatable surgically or behaviorally or both could lead to an improved voice for the patient and for this reason an improved quality of life.

Acoustics↗
PubMedDate not supplied

Effect of spacer yarns on the dialysate flow distribution of hemodialyzers: a magnetic resonance imaging study.

Blood side and dialysate side flow distributions play an important role in determining the optimal use of dialysis membrane in hemodialyzers for the removal of uremic solutes. In this article, we used two nonintrusive magnetic resonance imaging (MRI) techniques called the two-dimensional phase contrast (2DPC) and two-dimensional Fourier transform (2DFT) velocity imaging techniques to (1) study the effect of space yarns on the dialysate side flow distribution, (2) investigate the effect of flow baffle on the dialysate side flow distribution, and (3) characterize the blood side and dialysate side flow profiles of hemodialyzers with flow rates ranging from 200 to 1000 ml/min. We investigated two types of hollow fiber hemodialyzers: hemodialyzers A (with spacer yarns) and B (without spacer yarns). We used a 3 mmol cupric sulfate solution as the compartmental fluid and imaged five transverse cross sections of these hemodialyzers. The hemodialyzer with spacer yarns had a more uniform dialysate side spatial flow distribution than that without spacer yarns. In addition, the design of flow baffle in these hemodialyzers can be further improved to promote uniform dialysate side flow distribution, and the blood side flow had a fully developed laminar flow profile. Our experimental results showed that these velocity imaging techniques provide an innovative, nonintrusive tool for characterizing flow distribution in hemodialyzers.

Blood Flow Velocity↗