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Biomedical subjects

C A Parvin

Publications and source records attributed to C A Parvin.

At least 37 records · Page 2Linked to original sources
PubMed1997

Dystrophic axonal swellings develop as a function of age and diabetes in human dorsal root ganglia.

Neuroaxonal dystrophy, characterized by swollen axon terminals and, to a lesser degree, enlarged initial segments of axons or perikaryal projections, develops in human dorsal root sensory ganglia as a function of aging and diabetes. Lesions are typically located within the satellite cell capsule and are intimately applied to sensory neuronal perikarya, which are compressed and distorted but are otherwise normal. Swollen axons contain large numbers of neurofilaments that are immunoreactive with antisera to highly phosphorylated neurofilament epitopes but fail to stain with antisera directed against hypophosphorylated neurofilament epitopes. Other dystrophic swellings contain collections of tubulovesicular profiles admixed with neurotransmitter granules. Neuroaxonal dystrophy involves subpopulations of intraganglionic axons and apparent terminals, notably those containing CGRP, while apparently sparing others, including noradrenergic sympathetic axons. Diabetic subjects develop lesions prematurely and in greater numbers than in aged subjects. Individual dystrophic axons in diabetics and aged human subjects are identical in their light microscopic, immunohistochemical and ultrastructural appearance, suggesting the possibility of shared pathogenetic mechanisms.

Adolescent↗
PubMed1997

Quality-control (QC) performance measures and the QC planning process.

Numerous outcome measures can be used to characterize and compare the performance of alternative quality-control (QC) strategies. The performance measure traditionally used in the QC planning process is the probability of rejecting an analytical run when a critical out-of-control error condition exists. Another performance measure that naturally fits within the total allowable error paradigm is the probability that a reported test result contains an analytical error that exceeds the total allowable error specification. In general, the out-of-control error conditions associated with the greatest chance of reporting an unacceptable test result are unrelated to the traditionally defined "critical" error conditions. If the probability of reporting an unacceptable test result is used as the primary performance measure, worst-case QC performance can be determined irrespective of the magnitude of any out-of-control error condition that may exist, thus eliminating the need for the concept of a "critical" out-of-control error.

Chemistry, Clinical↗
PubMed1997

Using Logical Observation Identifier Names and Codes (LOINC) to exchange laboratory data among three academic hospitals.

Using a standard set of names and codes to exchange electronic laboratory data would facilitate multiinstitutional research and data pooling. This need has led to the development of the Logical Observation Identifier Names and Codes (LOINC) database and its test naming convention. We conducted a study which required 3 academic hospitals (in 2 separate medical centers) to extract raw laboratory data from their local information system for a defined patient population, translate tests into LOINC, and provide aggregate data which could then be used to compare laboratory utilization. We found that the coding of local tests into LOINC can often be complex, especially the "Kind of Property" field, and apparently trivial differences in choices made by individual institutions can result in nonmatches in electronically pooled data. In our study, 72-86% of the failures of LOINC to match the same tests between different institutions were due to differences in local coding choices. LOINC has tremendous potential to eliminate the needing for detailed human inspection during the pooling of laboratory data from diverse sites, and perhaps even a built-in capability to adjust matching stringency by selecting subsets of LOINC fields required to match. However, a quality, standard coding procedure at all sites is critical.

Academic Medical Centers↗
PubMed1997

Effect of analytical run length on quality-control (QC) performance and the QC planning process.

The performance measure traditionally used in the quality-control (QC) planning process is the probability of rejecting an analytical run when an out-of-control error condition exists. A shortcoming of this performance measure is that it doesn't allow comparison of QC strategies that define analytical runs differently. Accommodating different analytical run definitions is straightforward if QC performance is measured in terms of the average number of patient samples to error detection, or the average number of patient samples containing an analytical error that exceeds total allowable error. By using these performance measures to investigate the impact of different analytical run definitions on QC performance demonstrates that during routine QC monitoring, the length of the interval between QC tests can have a major influence on the expected number of unacceptable results produced during the existence of an out-of-control error condition.

Chemistry, Clinical↗
PubMed1996

Evaluating the appropriateness of red blood cell transfusions: the limitations of retrospective medical record reviews.

OBJECTIVE: Several studies have looked at the appropriateness of red blood cell transfusions, using retrospective chart reviews to assess compliance with guidelines. The goal of this study was to determine the quality of medical chart documentation, and assess the validity and the feasibility of using retrospective chart review data as part of a quality improvement (QI) program, to evaluate the appropriateness of peri-operative transfusions. DESIGN: The charts of 188 patients admitted for elective orthopedic surgery were reviewed. Both intra-operative and post-operative transfusion events (n = 353) were analyzed. RESULTS: Only 68% of post-operative transfusion events on the day of surgery and 35% of transfusion events on days after surgery were accompanied by documentation of blood loss and/or change in vital signs. Symptoms were recorded in only 10% of post-operative transfusion events. The rationale for transfusion was recorded in only 16% of post-operative transfusion events on the day of surgery, in 27% on post-operative days and in 95% of intra-operative transfusions. The documentation of rationale was not different for transfusion events involving autologous blood (31%) or allogeneic blood (32%). This study provided information on transfusion practices. Single unit transfusions occurred in only 47 and 34% of patients receiving autologous and allogeneic blood, respectively. Only 19% of patients transfused with more than one allogeneic blood units, were clinically reassessed between blood units, compared to 34% of patients receiving more than one autologous blood unit. We conclude that retrospective chart reviews are limited by inadequate documentation and may not be the optimal source of information to determine the appropriateness of a transfusion. Improved methods (e.g. prospective reviews, or other system-level data collection methods) are needed for QI programs to influence practice. Despite its limitations, the information obtained suggests that current practice could be improved.

Adult↗
PubMed1996

Impact of point-of-care testing on patients' length of stay in a large emergency department.

We prospectively investigated whether routine use of a point-of-care testing (POCT) device by nonlaboratory operators in the emergency department (ED) for all patients requiring the available tests could shorten patient length of stay (LOS) in the ED. ED patient LOS, defined as the length of time between triage (initial patient interview) and discharge (released to home or admitted to hospital), was examined during a 5-week experimental period in which ED personnel used a hand-held POCT device to perform Na, K, Cl, glucose (Gluc), and blood urea nitrogen (BUN) testing. Preliminary data demonstrated acceptable accuracy of the hand-held device. Patient LOS distribution during the experimental period was compared with the LOS distribution during a 5-week control period before institution of the POCT device and with a 3-week control period after its use. Among nearly 15 000 ED patient visits during the study period, 4985 patients (2067 during the experimental period and 2918 during the two control periods) had at least one Na, K, Cl, BUN, or Gluc test ordered from the ED. However, no decrease in ED LOS was observed in the tested patients during the experimental period. Median LOS during the experimental period was 209 min vs 201 min for the combined control periods. Stratifying patients by presenting condition (chest pain, trauma, etc.), discharge/admit status, or presence/absence of other central laboratory tests did not reveal a decrease in patient LOS for any patient subgroup during the experimental period. From these observations, we consider it unlikely that routine use of a hand-held POCT device in a large ED such as ours is sufficient by itself to impact ED patient LOS.

Blood Chemical Analysis↗
PubMed1996

Comparative sensitivity of cardiac troponin I and lactate dehydrogenase isoenzymes for diagnosing acute myocardial infarction.

Criteria for the retrospective diagnosis of acute myocardial infarction rely heavily on increases in lactate dehydrogenase (LD) isoenzymes. However, increases of LD isoenzyme activities are not specific for myocardial injury. Recently, increased concentrations of cardiac troponin I (cTnI) have been shown to be highly specific for myocardial damage and to have sensitivity comparable with that of creatine kinase MB isoenzyme for detecting cardiac injury. Furthermore, increases of cTnI persist in plasma for at least several days. The present study was designed to determine the relative sensitivities of cTnI and LD isoenzymes over time for the diagnosis of infarction. The results indicate that cTnI values are at least as sensitive as LD isoenzymes: 90% of patients with myocardial infarction had above-normal concentrations of cTnI on the 4th day after admission to the coronary care unit. Criteria based on cTnI should improve the accuracy of retrospective diagnoses of acute myocardial infarction.

Animals↗
PubMed1995

The endogenous erythropoietin response and the erythropoietic response to blood loss anemia: the effects of age and gender.

The endogenous erythropoietin (EPO) response and the erythropoietic response to anemia in the elderly, as compared with that in younger subjects, is controversial. We therefore studied autologous blood donors undergoing aggressive phlebotomy to determine the effect of age and gender on the EPO response to blood loss anemia, along with the erythropoietic response to endogenous EPO and to exogenous recombinant human EPO therapy. Seventy-one patients underwent phlebotomy, up to 6 units over 3 weeks, and received either placebo (n = 18), EPO 150 U/kg (n = 16), EPO 300 U/kg (n = 18), or EPO 600 U/kg (n = 19) at each of the six visits. Linear regression analysis of the hemoglobin/log EPO relationship for 18 placebo patients revealed no differences in the endogenous EPO response to phlebotomy, as determined by the slopes and intercepts, for males versus females or as a function of age. We found no differences in endogenous EPO-stimulated red blood cell (RBC) volume expansion for males and females (7.06 +/- 2.4 and 7.22 +/- 2.2 ml/kg, respectively, p = 0.88) or as a function of age (estimated rate of change = -0.58 +/- 0.33 ml/kg for every 10 years of life, p = 0.10). Similarly, we found no differences in RBC response to EPO for males versus females (1.4 +/- 0.3 ml/kg vs 1.5 +/- 0.3 ml/kg per 1000 U/kg EPO, respectively, p = 0.80) or as a function of age (estimated rate of change = 0.051 +/- 0.15 ml/kg per 1000 U/kg EPO for every 10 years of life, p = 0.74).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Erythropoietin response to anaemia is not altered by surgery or recombinant human erythropoietin therapy.

Recombinant human erythropoietin (EPO) therapy has been shown to increase red blood cell (RBC) production and facilitate autologous blood donation before elective surgery. However, recent reports have suggested that surgery and/or EPO therapy may suppress endogenous erythropoietin secretion in response to anaemia. We therefore analysed the haemoglobin/erythropoietin relationship preoperatively and postoperatively in 71 autologous blood donors subjected to aggressive phlebotomy and six treatments with either EPO (150 U/kg, n = 16, 300 U/kg, n = 18, or 600 U/kg, n = 19) or placebo (n = 18). Using data from the three preoperative study visits, the linear relationship between log erythropoietin and haemoglobin was determined for each of the 18 placebo patients. We found no significant differences in the slopes of the relationships in this group during aggressive phlebotomy. Furthermore, there was no evidence of a significant difference in the erythropoietin level recorded postoperatively for each patient to that predicted from the patient's postoperative haemoglobin level, based on the haemoglobin/log erythropoietin relationship preoperatively. Similarly, for each of the EPO-treated groups, there was no evidence of a significant difference when comparing the recorded erythropoietin level to that predicted from each patient's postoperative haemoglobin level, based on the haemoglobin/log erythropoietin relationship preoperatively. We conclude that preoperative recombinant human erythropoietin therapy and/or surgery do not adversely affect the postoperative erythropoietin response to anaemia.

Adult↗
PubMed1993

Effect of diabetes and aging on human sympathetic autonomic ganglia.

Although autonomic dysfunction frequently complicates the clinical course of patients with diabetes, relatively little is known of its underlying neuropathology. Using experimental animal models as a guide, the prevertebral superior mesenteric (SMG) and paravertebral superior cervical (SCG) sympathetic ganglia have been examined in a series of adult autopsied diabetic and non-diabetic patients of various ages using histochemical, ultrastructural, morphometric, and immunohistochemical methods. Quantitative studies demonstrated that markedly swollen argyrophilic terminal axons (neuroaxonal dystrophy) containing large numbers of disorganized neurofilaments developed in the SMG but not SCG as a function of diabetes, increasing age, and gender (males were more severely affected than females). As in experimental animals, diabetic (types I and II) patients developed histologically identical lesions prematurely and in greater numbers than age-matched nondiabetic patients. Morphometric studies showed a small but statistically significant decrease in neuronal density in the SMG but not SCG of diabetic patients. The dimensions of individual sympathetic neurons were not significantly different in aging or diabetes. The pathological lesions identified in the SMG may contribute to the autonomic dysfunction so commonly observed in diabetic patients.

Adolescent↗
PubMed1993

New insight into the comparative power of quality-control rules that use control observations within a single analytical run.

The error detection characteristics of quality-control (QC) rules that use control observations within a single analytical run are investigated. Unlike the evaluation of QC rules that span multiple analytical runs, most of the fundamental results regarding the performance of QC rules applied within a single analytical run can be obtained from statistical theory, without the need for simulation studies. The case of two control observations per run is investigated for ease of graphical display, but the conclusions can be extended to more than two control observations per run. Results are summarized in a graphical format that offers many interesting insights into the relations among the various QC rules. The graphs provide heuristic support to the theoretical conclusions that no QC rule is best under all error conditions, but the multirule that combines the mean rule and a within-run standard deviation rule offers an attractive compromise.

Chemistry, Clinical↗
PubMed1992

Comparing the power of quality-control rules to detect persistent systematic error.

A simulation approach that allows direct estimation of the power of a quality-control rule to detect error that persists until detection is used to compare and evaluate the error detection capabilities of a group of quality-control rules. Two persistent error situations are considered: a constant shift and a linear trend in the quality-control mean. A recently proposed "moving slope" quality-control test for the detection of linear trends is shown to have poor error detection characteristics. A multimean quality-control rule is introduced to illustrate the strategy underlying multirule procedures, which is to increase power without sacrificing response rate. This strategy is shown to provide superior error detection capability when compared with other rules evaluated under both error situations.

Chemistry, Clinical↗
PubMed1992

Comparing the power of quality-control rules to detect persistent increases in random error.

This paper continues an investigation into the merits of an alternative approach to the statistical evaluation of quality-control rules. In this report, computer simulation is used to evaluate and compare quality-control rules designed to detect increases in within-run or between-run imprecision. When out-of-control conditions are evaluated in terms of their impact on total analytical imprecision, the error detection ability of a rule depends on the relative magnitudes of the between-run and within-run error components under stable operating conditions. A recently proposed rule based on the F-test, designed to detect increases in between-run imprecision, is shown to have relatively poor performance characteristics. Additionally, several issues are examined that have been difficult to address with the traditional evaluation approach.

Chemistry, Clinical↗
PubMed1991

Germinal center T cells are distinct helper-inducer T cells.

Germinal centers (GCs) contain a significant number of CD4+ T cells, but what role these T cells may play in the development of GC B cells has not been determined. To gain insight into their role, we studied the phenotype of GC T cells and the lymphokines secreted by GC T cells isolated from human tonsils obtained after tonsillectomies. In addition to confirming that a large fraction of GC T cells are Leu-7(CD57)+ and Leu-8-, we found that they have no binding sites for peanut agglutinin. Furthermore, we found that they are CD45RA- and CD45R0+, the phenotype of helper-inducer T cells. We also found that Leu-7(CD57)+ cells display CD69, a phenotypic marker of very early cell activation, but do not display three other markers of cell activation: CD25 [interleukin-2 (IL-2) receptor], CD71 (transferrin receptor), and DR. When isolated, Leu-7(CD57)+ cells were stimulated in vitro with a mitogen that can induce peripheral blood T cells with the helper-inducer phenotype to produce various cytokines, Leu-7(CD57)+ cells did not produce IL-2, interleukin-4 (IL-4), interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha) in significant amounts. Taken together, GC T cells from a distinct subpopulation of T cells with helper-inducer phenotype by their histologic location, by their surface phenotype, and by their ability to produce lymphokines. This finding is consistent with the possibility that GC T cells have been selectively recruited to actively help B cells develop in GCs.

Antigens, CD↗
PubMed1991

Insulin and glucagon in prevention of hypoglycemia during exercise in humans.

To assess the roles of decrements in insulin and increments in glucagon in the prevention of hypoglycemia during moderate exercise (approximately 60% peak O2 consumption for 60 min), normal young men were studied during somatostatin infusions with insulin and glucagon infused to 1) hold insulin and glucagon levels constant, 2) decrease insulin, 3) increase glucagon, and 4) decrease insulin and increase glucagon during exercise. In contrast to a comparison study (saline infusion), when insulin and glucagon were held constant, glucose production did not increase and plasma glucose decreased from 5.5 +/- 0.2 to 3.4 +/- 0.2 mmol/l (P less than 0.001) initially during exercise. Notably, plasma glucose then plateaued and was 3.3 +/- 0.2 mmol/l at the end of exercise. This decrease was at most only delayed when either insulin was decreased or glucagon was increased independently. However, when insulin was decreased and glucagon was increased simultaneously, there was an initial increase in glucose production, and the glucose level was 4.5 +/- 0.2 mmol/l at 60 min, a value not different from that in the comparison study. Thus we conclude that both decrements in insulin and increments in glucagon play important roles in the prevention of hypoglycemia during exercise and do so by signaling increments in glucose production. However, since hypoglycemia did not develop during exercise when changes in insulin and glucagon were prevented, an additional counterregulatory factor, such as epinephrine, must be involved in the prevention of hypoglycemia during exercise, at least when the primary factors, insulin and glucagon, are inoperative.

3-Hydroxybutyric Acid↗
PubMed1991

Catecholamines in prevention of hypoglycemia during exercise in humans.

To assess the role of catecholamines in the prevention of hypoglycemia during moderate exercise (approximately 60% peak O2 consumption for 60 min), normal humans were studied with combined alpha- and beta-adrenergic blockade and with adrenergic blockade while changes in insulin and glucagon were prevented with the islet clamp technique (somatostatin infusion with insulin and glucagon infused at fixed rates). The results were compared with those from an islet clamp alone study. In contrast to a comparison study (saline infusion), adrenergic blockade resulted in a small initial decrease in plasma glucose during exercise, from 5.0 +/- 0.2 to 4.4 +/- 0.2 mmol/l (P less than 0.01), but the level then plateaued. There was a substantial exercise-associated decrement in plasma glucose when insulin and glucagon were held constant, i.e., from 5.5 +/- 0.2 to 3.4 +/- 0.2 mmol/l (P less than 0.0001), but the level again plateaued. However, when insulin and glucagon were held constant and catecholamine actions were blocked simultaneously, progressive hypoglycemia, to 2.6 +/- 0.6 mmol/l (P less than 0.001), developed during exercise. Hypoglycemia was the result of an absent increase in glucose production and an exaggerated initial increase in glucose utilization. Thus we conclude that sympathochromaffin activation plays a minor role when insulin and glucagon are operative, but a catecholamine, probably epinephrine, becomes critical to the prevention of hypoglycemia during exercise when changes in insulin and glucagon do not occur.

3-Hydroxybutyric Acid↗