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Biomedical subjects

E F Vonesh

Publications and source records attributed to E F Vonesh.

At least 19 recordsLinked to original sources
PubMed1995

Peritonitis in an urban peritoneal dialysis program: an analysis of infecting pathogens.

We have previously found that race, level of education, and peritoneal dialysis system are factors that significantly and independently influence peritonitis rates in our patient population. We now extend these observations by assessing the pathogens responsible for peritonitis in these subgroups. Between January 1, 1981, and May 15, 1993, 248 peritoneal dialysis patients underwent dialysis at our facility. The rate of peritonitis by pathogen was determined in these patients using the fixed effects Poisson model. Total peritonitis rates in black patients (1.89 episodes/patient-year) were significantly greater compared with white patients (1.11 episodes/patient-year; P < 0.0001). Increased infection rates in black patients were significant for Staphylococcus epidermidis, Staphylococcus aureus, and gram-negative pathogens. The level of education had a negative correlation with peritonitis rates (< or = 8 years, 2.00 episodes/patient-year; 9 to 12 years, 1.64 episodes/patient-year; and > or = 13 years, 1.24 episodes/patient-year) with patients having > or = 13 years of education at the start of dialysis demonstrating a significantly lower total peritonitis rate compared with patients with 9 to 12 years (P = 0.001) or < or = 8 years (P < 0.001) of education. This was accounted for by a significant decrease in infection rates for S epidermidis, polymicrobial, and gram-negative organisms. Finally, patients on automated peritoneal dialysis had significantly lower total peritonitis rates (0.59 episodes/patient-year) compared with patients on either a connect (2.11 episodes/patient-year) or disconnect (1.46 episodes/patient-year) system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Blood pressures in hemodialysis and peritoneal dialysis using ambulatory blood pressure monitoring.

To define the influence that dialytic modality has on the blood pressure (BP) level and pattern, 33 hemodialysis (HD) and 27 peritoneal dialysis (PD) patients had their BP monitored hourly over an approximate 48-hour period using an ambulatory blood pressure monitoring (ABPM) device. A trigonometric cosine model was used to describe the diurnal BP pattern. Regression coefficients obtained from fitting this model to the observed hourly blood pressures were then compared between HD and PD patients to determine if the dialytic modality had any influence on BP level or pattern. The results indicate that HD and PD patients both exhibit similar diurnal patterns, but that HD patients have significantly higher average systolic BPs (142.1 +/- 16.3 v 130.4 +/- 17.1 mmHg, P < 0.01) and "systolic loads" (percent systolic values > 140 mmHg [54% +/- 29% v 30% +/- 31%, P < 0.01]) compared with PD patients. There were no significant differences in their diastolic BPs, diastolic loads, mean arterial pressures, or heart rates. No other factors (demographic or biochemical data, or medication usage) were found to significantly affect BP. In addition, a single BP reading for PD patients and predialysis and postdialysis BP readings for HD patients were measured by the dialysis nurse or technician on the day that the ABPM device was attached and removed, and were compared with the mean BP readings as determined by ABPM. These single values did not achieve good concordance with the 24-hour average BPs. ABPM and the cosine model have demonstrated that the diurnal pattern of BP is maintained in both PD and HD, and that HD is associated with higher systolic BPs and greater systolic loads than PD.

Adult↗
PubMed1994

Relationship between body size, fill volume, and mass transfer area coefficient in peritoneal dialysis.

A peritoneal dialysate fill volume of 2 L has become the standard of clinical practice, but the relationships between body size, fill volume, and mass transfer area coefficient (KoA) have not been well established. These relationships were studied in 10 stable peritoneal dialysis patients who underwent six peritoneal equilibration studies (2 h each) at fill volumes of 0.5, 1, 1.5, 2, 2.5, and 3 L. The concentration-time profiles for urea, creatinine, and glucose were measured at each fill volume, and residual volumes were calculated from the preceding dwell period. A modified Henderson equation was used to calculate the KoA for the three solutes as a function of fill volume. By normalizing the KoA for each solute to the value at 2 L, the data for all three solutes collapsed onto the same trend line when plotting the normalized KoA versus dialysate volume. Between 0.5- and 2-L fill volumes, the average normalized KoA increases in an almost linear fashion, its value almost doubling over this range. Between 2- and 3-L fill volumes, there is less than a 10% change in the normalized KoA. However, fill volumes for peak urea KoA were found to increase with increasing body surface area (R = 0.76), being around 2.5 L for an average-sized patient and increasing to between 3 and 3.5 L for body surface areas > 2 m2. To maximize solute transport, these relationships between body size, volume, and KoA should be considered when choosing fill volumes for continuous ambulatory peritoneal dialysis and automated peritoneal dialysis and when deciding reserve and tidal volumes for tidal peritoneal dialysis.

Body Surface Area↗
PubMed1993

A retrospective assessment of risk factors for peritonitis among an urban CAPD population.

Peritonitis is a major reason why patients transfer from peritoneal dialysis (PD) to hemodialysis. We evaluated the peritonitis infection rates in 146 peritoneal dialysis patients who underwent dialysis at our facility between 1 January 1981 and 31 December 1989. Peritonitis was the primary cause for changing treatment, with 24 (16.4%) of the patients transferring because of this complication. This represented 54.5% of all patients discontinuing CAPD due to method failure. A gamma-Poisson regression analysis was performed in an attempt to identify potential risk factors associated with an increased incidence of peritonitis. The results indicated that race, education level, and PD system used were significantly associated with the rate at which peritonitis occurred in our patient population. There was an almost twofold increase in the rate of peritonitis among blacks as compared to whites (2.2 vs 1.2 episodes/patient year). The level of education completed at the start of dialysis had a negative correlation with peritonitis rates. Patients with < or = 8, 9-12, and > or = 13 years of education had peritonitis rates of 2.4, 1.8, and 1.2 episodes/patient year, respectively. Finally, the system used had a significant effect with our patients on CCPD having lower peritonitis rates as compared to patients on either a connect or disconnect system (0.6 vs 2.5 vs 1.8 episodes/patient year, respectively). Recognizing potential risk factors for peritonitis will help us better understand and address this significant problem in our PD programs. Reducing peritonitis rates should facilitate a decrease in patient transfer due to method failure.

Adolescent↗
PubMed1992

A random coefficient growth curve analysis of mental development in low-birth-weight infants.

In many medical studies, longitudinal data are collected on each of a sample of patients. The objectives of such studies often are: to estimate and test bivariate or multivariate relationships within each of several groups of patients from these repeated measures data; to compare these relationships among groups; and to test for the effects of baseline covariates on the relationships. This paper illustrates the use of statistical methods for growth curve analysis recently proposed by Vonesh and Carter for achieving these goals by relating a measure of preschool cognitive development to age in four race by sex groups of low-birth-weight infants. Significant declines in Bayley's Mental Development Index (MDI) with increasing age were found in all groups. Birth-weight did not significantly influence the rate of decline but did influence the overall level of performance. Even so, in the group most comparable to Bayley's normative population, predicted MDI was near the norm even for extremely low-birth-weight infants (that is, 1000 grams). Although there is some risk of mental deficit associated with prematurity, eventual developmental delays in low-birth-weight infants frequently are acquired with age. The rate of decline in MDI was significantly associated with race and mother's education. Assumptions required for the valid application of these methods are discussed and tested in the setting of this applied problem. The assumptions appeared valid in this application. We conclude with a brief discussion of available alternatives when the assumptions are violated and point to areas for future research.

Age Factors↗
PubMed1992

Net fluid absorption under membrane transport models of peritoneal dialysis.

The effect of oncotic pressure and lymphatic flow on intraperitoneal dialysate volumes in peritoneal dialysis is investigated under each of two membrane transport models: one assuming a homogeneous single-pore membrane and the other a heteroporous three-pore membrane. In both cases, solute and fluid removal are assumed to occur via a mass transport model in which the peritoneum acts like a synthetic membrane separating two well-mixed compartments (body and dialysate). The homoporous mass transport model of Pyle and Popovich and the three-pore model of Rippe et al., although conceptually different, are shown to be equivalent mathematically. This feature allows one to apply the analytical solutions of Vonesh et al. to either model. It also enables one to apply parameter estimates from one model to another; for example, one can apply the lumped sum reflection coefficients of the three-pore model to a homoporous membrane model. A comparison is made between the use of empirically estimated rejection coefficients computed under the homoporous membrane model of Pyle and Popovich versus lumped-sum reflection coefficients calculated in accordance with the three-pore model of Rippe et al. The two models predict similar drain volumes provided the exchange is conducted using glucose as the osmotic agent. However, one does see a significantly different contribution of protein oncotic pressure and lymphatic drainage to fluid absorption under the two sets of osmotic reflection coefficients. Moreover, for a simulated exchange employing an osmotic agent with a molecular weight of 20,000 daltons, the use of reflection coefficients calculated under the three-pore model yields net ultrafiltration values which are more consistent and physiological than results obtained using the empirically estimated rejection coefficients. Since estimates of 'lymphatic flow' will vary according to the quantity and quality of input parameter values (i.e., hydrostatic pressure, protein concentrations, osmotic reflection coefficients), it would be better to label these estimates as the sum of lymphatic and unmodeled net fluid absorption.

Ascitic Fluid↗
PubMed1992

Mixed-effects nonlinear regression for unbalanced repeated measures.

Repeated measures data, such as clinical pharmacokinetic data, growth data, and dose-response data, are often inherently nonlinear with respect to a given response function and are frequently incomplete and/or unbalanced. Nonlinear random-effects models together with a variety of estimation procedures have been proposed for the analysis of such data. This paper is concerned with a straightforward procedure for estimating and comparing the parameters of a generalized mixed-effects nonlinear regression model. The asymptotic properties of the proposed estimators are given and large-sample tests of hypothesis provided. The results are applied to in vitro data on the water transport kinetics of hemodialyzers used in the treatment of patients with chronic renal failure.

Biological Transport, Active↗
PubMed1991

Patient and technique survival among an urban population of peritoneal dialysis patients: an 8-year experience.

Estimates of patient and technique survival are given for 146 peritoneal dialysis (PD) patients who underwent dialysis between January 1, 1981 through December 31, 1989. In all, 33 patients died and 44 patients changed treatment. Patient survival was 92% at 1 year, 80% at 2 years, and 55% at 4 years, while technique survival was 85% at 1 year, 74% at 2 years, and 47% at 4 years. Cox's proportional hazards regression model was used to assess the effects of sex, age, diabetes, cardiovascular disease (CVD), education, and training time on both patient and technique survival. Both patient age (P = 0.001) and CVD (P = 0.03) had a significant impact on patient survival. On the average, for every 10 years' increase in age, the risk of death increased by a factor of 1.71. Patients with CVD had a risk of death 2.57 times higher than the risk of death among patients without CVD. With respect to technique or method survival, black patients had a risk of changing treatment 2.24 times higher than that for white patients. Our patient and technique survivals are similar to that reported in the national CAPD registry over a comparable period (1981 to 1988).

Adolescent↗
PubMed1991

Nutritional assessment of continuous ambulatory peritoneal dialysis patients: an international study.

We examined the nutritional status of 224 patients from six centers in Europe and North America to assess the incidence of protein-energy malnutrition. A "subjective nutritional assessment" was made, using 21 variables derived from history and clinical examination, or anthropometry and biochemistry. Eighteen patients (8%) were severely malnourished, 73 (32.6%) were mildly to moderately malnourished, and 133 (59.4%) did not show evidence for malnutrition. There was a higher incidence of mild to moderate malnutrition in diabetics than in nondiabetics. A statistical analysis identified 12 variables, seven objective and five subjective, that correlated with subjective nutritional assessment. Actual intercenter differences for the incidence of malnutrition were related to patient age, nutritional status at the commencement of continuous ambulatory peritoneal dialysis (CAPD), the length of time on CAPD, and residual renal function. Variables that were most frequently correlated with subjective nutritional assessment and with one another included plasma albumin, mid-arm muscle circumference (MAMC), weight loss, and the clinical judgement of muscle wasting and loss of subcutaneous fat. Loss of residual renal function correlated with muscle wasting and months on CAPD. Our data identified differences between the two sexes. In women there was a trend for more anorexia, greater weight loss from muscle wasting, and a larger decrease in albumin, whereas in men there was a more gradual decrease in nutritional status. Loss of residual renal function contributed to anorexia and symptoms of severe malnutrition.

Adolescent↗
PubMed1991

The effect of hematocrit on peritoneal transport.

Eight stable patients, from our institution, on continuous ambulatory peritoneal dialysis (CAPD) were entered into a multicenter, randomized, double-blind, placebo-controlled study with erythropoietin (EP]. To assess the effect of hematocrit on peritoneal solute transport, we performed peritoneal equilibration tests (PET) on each patient on a quarterly basis throughout the study. Patients on EPO had a significant increase in hematocrit at 3 (32% +/- 5%), 6 (32% +/- 2%), and 9 (38% +/- 3%) months compared with baseline (22% +/- 4%). The D/P creatinine (Cr) at 4 hours was also significantly reduced in the patients on EPO at 3 (.70 +/- .1), 6 (.66 +/- .12) months when compared with baseline (.76 +/- .11). No significant change in D/Do glucose at 4 hours or in the 4-hour ultrafiltrate (except at 9 months) was found. Based on mixed-effects regression analysis, the 4-hour D/P Cr, peritoneal Cr clearance, and Cr mass transfer area coefficient significantly decreased as hematocrit levels increased. The 4-hour D/Do glucose and the 4-hour ultrafiltrate both demonstrated a positive correlation with increasing hematocrit levels, but this did not reach statistical significance. Although larger studies are needed, it appears that increasing hematocrit levels may negatively affect peritoneal solute transport in CAPD patients as determined by PET.

Anemia↗
PubMed1991

Kinetic modeling as a prescription aid in peritoneal dialysis.

Methods for calculating fluid and mass removal in peritoneal dialysis are presented in order to aid clinicians in their care and management of patients and to assist them in their understanding of the physiological mechanisms which govern peritoneal transport. These methods are based on the Pyle-Popovich peritoneal mass transport model which encompasses both diffuse and convective transport as well as lymphatic flow and residual renal function. Algebraic solutions to the mass balance equations governing solute transport are provided. Since these solutions are expressed explicitly as functions of time, they are easily programmed for use on a personal computer or calculator. This offers considerable advantage over the more computer-intensive numerical solutions which had been previously required since one can now calculate both mass removal and changes in blood concentration at the end of an exchange without requiring any intermediate calculations. This computational advantage and the ability to model changes in blood concentration are shown to be of particular importance when modeling more dynamic therapies such as CCPD or Tidal peritoneal dialysis. Finally, the model and solutions, when assessed clinically among 5 patients on two separate occasions, resulted in predicted fluid and mass removals which were in high concordance with measured fluid and mass removals (concordance correlation coefficients in excess of 0.97). Our findings suggest that kinetic modeling can provide the kind of analytical tools necessary to guide clinicians in their care and management of peritoneal dialysis patients.

Algorithms↗
PubMed1991

A multicenter, selection-adjusted comparison of patient and technique survivals on CAPD and hemodialysis.

Four hundred and eighty CAPD and 373 HD patients started regular dialysis treatment between 1981 and 1987 in 6 dialysis centers. The CAPD patients were 6 years older, on average, than the HD patients and had more complicating conditions (43.3% with 3 or more coexisting risk factors versus 28.9% with coexisting complications). The 7-year patient survival rate was not significantly different. Cox's proportional hazards regression showed that age, cardiovascular disease, cerebrovascular disease, peripheral vascular disease, diabetes, malignancy and multisystem disease had significant adverse effects on patient survival. After correcting for the influence of these factors, no significant differences in patient survival were seen. However, after 53.5 years of age, the increase in the risk of death was significantly higher in HD than in CAPD patients. Technique survival was significantly different in the 6 centers and was better for HD than for CAPD. There was no statistically significant difference between CAPD and HD technique survival when peritonitis was eliminated as a cause of failure. Based on this 7 year analysis, CAPD would appear to be an excellent alternative to HD.

Female↗
PubMed1990

Modelling peritonitis rates and associated risk factors for individuals on continuous ambulatory peritoneal dialysis.

A mixed effects Poisson regression model is proposed for analysing potential risk factors associated with peritonitis, a bacterial infection of the peritoneum which is common among individuals on continuous ambulatory peritoneal dialysis (CAPD). The model incorporates a set of fixed effects corresponding to concomitant information collected across individuals as well as a random effect due to individuals. The method of maximum likelihood is used to estimate the unknown parameters. When applied to clinical data obtained on 81 CAPD patients from four centres, the mixed effects model demonstrated a much better fit than the corresponding fixed effects Poisson regression model.

Adult↗
PubMed1990

Plasma and dialysate immunoglobulin G in continuous ambulatory peritoneal dialysis patients: a multicenter study.

Peritoneal dialysate immunoglobulin (Ig)G concentrations were measured in 120 continuous ambulatory peritoneal dialysis (CAPD) patients evaluated at four dialysis centers in different countries to assess the normal range for dialysate IgG and to investigate the relationships of this protein levels with peritoneal episodes, For 65 of these patients, plasma IgG levels were determined, and IgG clearances were calculated. The mean dialysate concentration of IgG was 6.9 +/- 4.2 mg/dl, and there was no difference between men and women or between patients who had or had not previously undergone hemodialysis. Dialysate IgG concentrations were significantly related to residual renal creatinine clearance and negatively correlated with dialysate volume, plasma albumin and total protein. There were no significant correlations between IgG levels in the dialysate and age, protein losses in the dialysate, time on CAPD or time from the last peritonitis episode. Plasma and dialysate IgG were unrelated to the incidence of peritonitis, statistical analysis being performed with different methods. These results suggest that IgG levels in the dialysate or plasma are not a major factor in the prevention of CAPD peritonitis.

Ascitic Fluid↗