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Biomedical subjects

Nathan W Levin

Publications and source records attributed to Nathan W Levin.

At least 73 records · Page 4Linked to original sources
PubMed2002

Relationships among inflammation nutrition and physiologic mechanisms establishing albumin levels in hemodialysis patients.

BACKGROUND: Serum albumin concentration is a balance among its synthesis rate, fractional catabolic rate (FCR), distribution, dilution in the plasma pool and external loss. The physiologic bases for establishing the level of serum albumin in hemodialysis patients have not been defined despite the association of hypoalbuminemia with excess mortality. Albumin concentration is associated with the levels of several acute phase proteins (APPs), C-reactive protein (CRP), alpha1 acid glycoprotein (alpha1 AG), or ceruloplasmin, and with nutritional markers, such as normalized protein catabolic rate (nPCR). METHODS: To establish the relationship among parameters that regulate albumin levels and markers of nutrition and inflammation, we injected [125I]-albumin, into 64 hemodialysis patients enrolled in the HEMO study to measure albumin distribution, synthesis and FCR. These variables were related to the levels of acute phase proteins (APPs), nPCR, body mass index (BMI), external albumin loss as well as demographic variables. Albumin distribution, synthesis and FCR were calculated from kinetic modeling, as was the initial plasma volume (PV). Serum albumin, transferrin, CRP, ceruloplasmin and alpha1 AG were measured weekly. Dialysate was collected during one dialysis each week to measure albumin loss. Results were analyzed by multiple linear regression. RESULTS: Albumin concentration correlated with its synthesis rate and FCR, but not with PV or its distribution between the vascular and extravascular pools. Albumin concentration also correlated with nPCR and alpha1 AG. However, albumin synthesis was directly related most strongly to PV and BMI (or nPCR), but not to levels of APPs. By contrast, albumin FCR correlated positively with both alpha1 AG and ceruloplasmin. CONCLUSION: Albumin concentration in dialysis patients changes with inflammation and nutritional status through their effects on albumin catabolism and synthesis, respectively. Within the range of albumin levels in these patients, nutritional variables primarily affected albumin synthesis while inflammation caused hypoalbuminemia by increasing albumin FCR. Albumin synthesis also increased in proportion to PV. The result of this is that PV expansion does not contribute to hypoalbuminemia.

Adult↗
PubMed2002

Relationship between volume status and blood pressure during chronic hemodialysis.

BACKGROUND: The relationship between volume status and blood pressure (BP) in chronic hemodialysis (HD) patients remains incompletely understood. Specifically, the effect of interdialytic fluid accumulation (or intradialytic fluid removal) on BP is controversial. METHODS: We determined the association of the intradialytic decrease in body weight (as an indicator of interdialytic fluid gain) and the intradialytic decrease in plasma volume (as an indicator of postdialysis volume status) with predialysis and postdialysis BP in a cross-sectional analysis of a subset of patients (N=468) from the Hemodialysis (HEMO) Study. Fifty-five percent of patients were female, 62% were black, 43% were diabetic and 72% were prescribed antihypertensive medications. Dry weight was defined as the postdialysis body weight below which the patient developed symptomatic hypotension or muscle cramps in the absence of edema. The intradialytic decrease in plasma volume was calculated from predialysis and postdialysis total plasma protein concentrations and was expressed as a percentage of the plasma volume at the beginning of HD. RESULTS: Predialysis systolic and diastolic BP values were 153.1 +/- 24.7 (mean +/- SD) and 81.7 +/- 14.8 mm Hg, respectively; postdialysis systolic and diastolic BP values were 136.6 +/- 22.7 and 73.9 +/- 13.6 mm Hg, respectively. As a result of HD, body weight was reduced by 3.1 +/- 1.3 kg and plasma volume was contracted by 10.1 +/- 9.5%. Multiple linear regression analyses showed that each kg reduction in body weight during HD was associated with a 2.95 mm Hg (P=0.004) and a 1.65 mm Hg (P=NS) higher predialysis and postdialysis systolic BP, respectively. In contrast, each 5% greater contraction of plasma volume during HD was associated with a 1.50 mm Hg (P=0.026) and a 2.56 mm Hg (P < 0.001) lower predialysis and postdialysis systolic BP, respectively. The effects of intradialytic decreases in body weight and plasma volume were greater on systolic BP than on diastolic BP. CONCLUSIONS: HD treatment generally reduces BP, and these reductions in BP are associated with intradialytic decreases in both body weight and plasma volume. The absolute predialysis and postdialysis BP levels are influenced differently by acute intradialytic decreases in body weight and acute intradialytic decreases in plasma volume; these parameters provide different information regarding volume status and may be dissociated from each other. Therefore, evaluation of volume status in chronic HD patients requires, at minimum, assessments of both interdialytic fluid accumulation (or the intradialytic decrease in body weight) and postdialysis volume overload.

Adult↗
PubMed2002

Cost-quality trade-offs in dialysis care: a national survey of dialysis facility administrators.

Dialysis facilities face important trade-offs between cost and quality under constrained capitated reimbursement. How management at dialysis facilities makes decisions affecting cost and quality of care and views opportunities and threats is unknown. We conducted a national survey of dialysis facility administrators. We asked administrators what changes they would make in response to increases or decreases in reimbursement, their views on linking dialysis care payment to quality-of-care measures, and their views on providing patients with treatment options and outcomes information. One hundred fifty-seven of 280 dialysis facility administrators (56%) responded. If dialysis reimbursement were to increase by 20%, the five most common responses were to: improve patient education programs (62% of respondents), improve facility amenities (42%), purchase new equipment (30%), provide more money for staff salaries (28%), and increase number of nursing staff (21%). Conversely, if dialysis reimbursement were to decrease by 20%, the most common responses were to: limit staff salary (45% of respondents), decrease nursing staff (41%), not replace dialysis equipment (43%), increase dialyzer reuse (37%), and return less to investors (36%). Differences in rank order of responses were observed according to professional training of the administrator and profit status of the facility. Administrators uniformly believe that it is very acceptable to provide facility-specific outcomes data to the public, as well as information on modalities of treatment provided by facilities. However, administrators varied in their views regarding whether reimbursement should be based on quality by using a process-of-care measure, such as the average dose of dialysis, or an outcome-of-care measure, such as case-mix-adjusted mortality rates. We conclude that increases in facility reimbursement generally would be used by dialysis facility administrators for the benefit of patients, whereas decreases (or inflation erosion) in payment rates might compromise staffing. US dialysis administrators support sharing treatment options and outcomes information with patients, but appear to be ambivalent with regard to linking reimbursement to adequacy of dialysis or patient outcomes. These results have important implications regarding proposed changes in the US capitated dialysis payment rate and current efforts to empower consumers of dialysis care.

Adult↗
PubMed2002

Heat accumulation with relative blood volume decrease.

BACKGROUND: Both hypovolemia and heat accumulation act as powerful perturbations of blood pressure control. In hemodialysis, hypovolemia and heat accumulation often develop simultaneously, and the question arises of whether and to what extent these perturbations are linked. METHODS: Heat accumulation was measured by the amount of thermal energy (E) removed from a patient during prescribed ultrafiltration under isothermic hemodialysis conditions, ie, constant patient temperature. Measurement and control of temperatures and thermal energies were performed using the blood temperature monitor. Relative blood volume (RBV) was measured using the blood volume monitor. RESULTS: Thirty-eight treatments were analyzed in 12 patients (3 women). During treatments lasting 189 +/- 28 minutes, 5.1% +/- 1.3% of postdialysis body weight were removed from patients by ultrafiltration at a mean rate of 1.1 +/- 0.3 L/h. Blood volumes decreased to 85% +/- 7% of initial values, and 229 +/- 106 kJ of E were removed from patients at a cooling rate (J) of 20 +/- 8 W, corresponding to 28% +/- 11% of estimated energy expenditure (H%). E, J, and H% significantly increased as RBV decreased (P < 0.05). Linear regression analysis between J and RBV showed that approximately 1 W had to be removed from the patient for each percentage of change in blood volume (J = -102.38 + 0.97* RBV; r2 = 0.63). CONCLUSION: Results show that the probability for the effect of heat stress during hemodialysis increases with ultrafiltration-induced blood volume changes. Temperature control is an important aspect of hemodialysis treatment.

Adaptation, Physiological↗
PubMed2002

Serum markers of periodontal disease status and inflammation in hemodialysis patients.

BACKGROUND: Hemodialysis (HD) patients face a 25% annual mortality rate, with 50% of reported deaths attributed to cardiovascular disease. All-cause and cardiovascular mortality correlate with such acute-phase proteins as C-reactive protein (CRP). Hepatic CRP synthesis is upregulated by inflammation; however, elevated CRP values frequently are found in the absence of apparent infection or inflammation. Because destructive periodontal diseases have been associated with elevated CRP levels, we questioned whether destructive periodontal diseases could contribute to elevated CRP values in HD populations. METHODS: Sera from 86 consecutive dentate HD patients were assayed for levels of immunoglobulin G (IgG) antibody to six periodontal species by means of an enzyme-linked immunosorbent assay. RESULTS: CRP values for the subject population ranged from less than 6.9 to 159 mg/L (median, 8.2 mg/L). Univariate comparisons between subjects with or without elevated CRP levels (>10 mg/L) showed that CRP level elevation was associated significantly (P < 0.05) with greater doses of human recombinant erythropoietin and lower levels of hemoglobin, serum iron, transferrin saturation (TSat), albumin averaged over the 3 preceding months, total cholesterol, and triglycerides. Log serum IgG antibody levels to Porphyromonas gingivalis also were significantly greater in the group with elevated CRP levels (P = 0.013). Subsequent multivariate logistic regression showed that log serum antibody levels to P gingivalis remained significant (P = 0.02) after controlling for nonperiodontal sources of elevated CRP, hemoglobin, TSat, and triglyceride values. CONCLUSION: These results suggest that elevated levels of IgG antibody to bacterial species associated with destructive periodontal diseases are associated with elevated CRP values in HD populations.

Actinobacillus Infections↗
PubMed2002

Online monitoring of cerebral hemodynamics during hemodialysis.

BACKGROUND: Several factors, including anemia, diabetes, and hypertension, potentially could disturb the cerebral autoregulation mechanism in hemodialysis (HD) patients. This study examined the effect of hemodynamic and rheological changes on mean cerebral blood flow (CBF) velocity (MV) during HD. METHODS: Continuous online monitoring of MV and pulsatility index in the middle cerebral artery were performed in 18 HD patients by transcranial Doppler ultrasound during the entire HD period (range, 3 to 4 hours). In addition, blood pressure, hematocrit (Hct), and relative decrease in blood volume were continuously monitored. Blood samples were obtained at the beginning and end of HD to measure hemorheological variables. RESULTS: After HD, Hct increased significantly from 33.6% +/- 5.9% to 41.4% +/- 5.7% (P < 0.001). Blood and plasma viscosity increased significantly from 3.33 +/- 0.77 to 4.36 +/- 1.3 mPa.s (P < 0.001) and from 1.35 +/- 0.29 to 1.54 +/- 0.38 mPa.s (P < 0.001), respectively. The change in MV (DeltaMV) was not significantly different from zero and correlated significantly with change in Hct. During HD, mean arterial pressure (MAP) in 15 patients changed within the normal range (group I), whereas 3 patients developed hypotension (group II) and their MAP decreased from 99 +/- 5 to 60 +/- 8 mm Hg (P < 0.05). In both groups, DeltaMV were not significant. CONCLUSION: Results of this study suggest that CBF does not appear to be diminished significantly during HD.

Aged↗
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

Seasonal variations in clinical and laboratory variables among chronic hemodialysis patients.

Seasonal variations in BP among chronic hemodialysis patients have been reported. It was hypothesized that other characteristics of these patients might also vary with the seasons. Twenty-one clinical and laboratory variables were examined for seasonal variations among 1445 patients enrolled in the Hemodialysis Study, sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases. Mixed-effects models were applied to longitudinal changes (up to 45 mo) for individual patients for 19 of the 21 variables, which were measured at least twice each year, to determine the seasonal component of each variable. Seasonal variations in the other two variables, i.e., protein and energy intakes determined from annual dietary records, were assessed in cross-sectional comparisons of intakes of patients entering the study at different time points. Thirteen of the 21 variables examined demonstrated statistically significant (P < 0.01) seasonal components in their longitudinal variations. Predialysis blood urea nitrogen concentrations peaked in March, which coincided approximately with the peak protein catabolic rates, as well as protein and energy intakes (determined by dietary recall). Predialysis systolic and diastolic BP values were highest in winter and lowest in summer, corroborating previous reports. In addition, the lower predialysis BP values in summer were associated with higher outdoor temperatures and less interdialytic fluid gain. The mean predialysis hematocrit values were highest in July, which could not be attributed solely to the estimated changes in plasma volume. Seasonal variations in clinical and laboratory variables occur commonly among chronic hemodialysis patients. The reasons for most of these variations are not apparent and require further investigation. Nonetheless, failure to consider these variations might lead to biases in the interpretation of clinical studies. In addition, awareness of these variations might facilitate the interpretation of laboratory results and the clinical treatment of these patients.

Adult↗
PubMed2002

Catheter design for continuous flow peritoneal dialysis.

A new catheter for continuous flow peritoneal dialysis is presented. One of the main issues in this field is the safety and good clinical tolerance of the catheter. In this case, the size and diameter of the cannula has not been increased in comparison to previous PD catheters. Furthermore, the materials utilized are designed for maximum comfort of the patient and minimal traumatisation of the peritoneal membrane. Nevertheless, the two compartments of the catheter allow for high dialysate flows without creating high resistance and the rate of recirculation is minimal in conditions of simulated continuous flow PD. Furthermore, the characteristic of the new catheter is the presence in the inflow branch of a special diffuser designed like a shower cap that is intended to improve the dialysate inflow distribution in the peritoneal cavity and to increase the contact of the peritoneal membrane with the solution. At the same time, the diffuser prevents a traumatic effect of the inflow dialysate due to high speed infusion or jet flow conditions.

Biocompatible Materials↗
PubMed2002

Intravenous catheter for intracorporeal plasma filtration.

Future advances in dialysis of end-stage renal disease patients may include improvements in therapeutic continuity and patient mobility. Continuous renal replacement therapies could lead to self-contained, mobile and potentially wearable dialysis units. We investigated an experimental, intravenous slow-continuous plasma separation system (IPSS) as a precursor to direct intravenous hemofiltration. An intracorporeal catheter employs asymmetric hollow fibers to separate blood cells from plasma in vivo. The fibers possess a sieving coefficient of 0.7 microm and remove 99.99% of all platelets. In vivo, catheters sustain an average plasma separation flow rate of 3 ml/min over 22 h, sufficient to remove 2 net liters of water from pigs through an extracorporeal hemofilter. Used catheter fibers are relatively free of protein deposition or clots in situ. In vitro studies suggest that human catheters may perform at 3-4 times the rate of porcine catheters. IPSS is proposed for acute fluid removal in CHF patients refractory to diuretics.

Animals↗
PubMed2002

The next step from high-flux dialysis: application of sorbent technology.

The current foci of renal replacement therapy with dialysis are middle molecular weight toxins, consisting of small proteins, polypeptides and products of glycosylation and lipoxygenation. Conventional high-flux dialysis is not efficient at removing these molecules, explaining the increased interest in using sorbents to supplement dialysis techniques. Prototype biocompatible sorbents have been developed and investigated for middle molecule removal; these have been shown, in man, to remove beta(2)-microglobulin, angiogenin, leptin, cytokines and other molecules, without reducing platelets and leukocytes. Extensive clinical studies are underway to demonstrate the clinical utility and safety of adding routinely a sorbent hemoperfusion device to hemodialysis.

Adsorption↗
PubMed2002

Impact of the new K/DOQI guidelines.

During the course of developing clinical practice guidelines to improve outcomes of dialysis patients, it became evident that there existed an even greater opportunity to improve outcomes for all individuals with kidney disease, from the earliest stage of kidney injury through the entire spectrum of its progression to kidney failure, when replacement therapy becomes necessary. The development and adoption of a public health approach to the progressive course of chronic kidney disease could allow for the application of interventional strategies to prevent the loss of kidney function in some cases, to slow the progression of kidney disease in many others, and to ameliorate the complication or comorbidities in those with progressive kidney disease. In order to respond to this need, a new initiative, termed the Kidney Disease Outcomes Quality Initiative (K/DOQI), was launched in January of 2000. This article summarizes the recommendations of the first three set of clinical practice guidelines being developed under this new initiative: Chronic Kidney Disease: Evaluation, Classification and Stratification; Bone Metabolism and Disease in Chronic Kidney Disease, and Dyslipidemias in Kidney Failure.

Bone Diseases, Metabolic↗
PubMed2002

Importance of periodontal disease in the kidney patient.

End-stage renal disease (ESRD) patients on hemodialysis experience a greatly increased rate of atherosclerotic complications. In both hemodialysis and general populations, it has become evident that inflammation plays a central role in the pathogenesis of atherosclerotic complications. C-reactive protein (CRP), the major acute phase protein in man, has been found to predict all-cause and cardiovascular mortality in ESRD patients on hemodialysis maintenance therapy. Hepatic CRP synthesis is upregulated by proinflammatory cytokines released locally at sites of infection or inflammation, although many patients experience elevated CRP values in the absence of overt infection or inflammation. Destructive periodontal diseases in the general population have been associated with both an increased prevalence of atherosclerotic complications and an elevation in serum CRP values. In view of the prevalence of destructive periodontal diseases in the general population, and since periodontal evaluations are normally not performed as part of a medical assessment, destructive periodontal diseases may be an over looked source of inflammation in ESRD patients on hemodialysis therapy. The intent of this report is to review the possible role destructive periodontal diseases and associated periodontal infections may play in the management of the ESRD patient on hemodialysis maintenance therapy.

Acute-Phase Reaction↗