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Biomedical subjects

M Kleiner

Publications and source records attributed to M Kleiner.

16 recordsLinked to original sources
PubMed2001

The value and limitations of the arm cephalic and basilic vein for arteriovenous access.

The National Kidney Foundation has identified the use arteriovenous grafts (AVG) and the interventions required to maintain their patency as two major causes of increased expenditure in the management of hemodialysis access in end-stage renal disease patients. They have issued an appeal for the increased use of native arteriovenous fistulae (AVF). Although the radialcephalic AVF is considered to be the procedure of choice for these patients, other veins should be sought after to maintain an all-autogenous AVF policy. We examined our experience of using arm veins that were transposed to the brachial artery. Over the last 2.5 years, 109 brachiocephalic AVF (BCAVF) and 63 brachiobasilic AVF (BBAVF) were placed in 163 patients with chronic renal failure. In each group, 40 and 25 patients were males, respectively. Ages ranged from 29 to 88 years (mean 67+/-1.4 years) and 37 to 84 years (mean 69+/-2.0 years) in each group. Diabetic patients comprised 56 and 65% of each group and hypertensive patients comprised 73 and 75% of each group. Data collection was via chart review, personal interviews, and review of the dialysis records. Patency was assessed by life-table analysis. The log-rank test was performed in conjunction with Kaplan-Meier survival analysis. Our results showed that the use of BCAVF and BBAVF appears to be a viable alternative to prosthetic arteriovenous grafts. On the basis of our experience, an algorithm for placement of AVF is suggested.

Adult↗
PubMed2001

The actor-observer effect in virtual reality presentations.

The use of virtual reality (VR) presentations are becoming a more and more frequent means of communicating information and displaying data to large groups of viewers. VR presentations put heavy demands on reproduction of visual, aural, and tactile information. A common situation in VR presentations is that one actor acts in the virtual environment (VE), while a group of people observes the actors actions in the VE, often from the perspective of the actor. The current paper aims to study actors' (participants actively interacting with the VE) and observers' (participants passively observing the actors' interaction with the VE) evaluations of the VR presentation. In an experiment, 16 actors and 16 observers either acted in or observed a VE and performed ratings of the quality of the presentation. The results showed that actors experienced higher presence and realism, and enjoyed the VR experience more than observers did. Observers, on the other hand, experienced that external events distracted their attention more than actors did. Finally, actors experienced more symptoms of simulation sickness. However, no differences between actors and observers were found for ratings of audio quality.

Adult↗
PubMed2001

Computation of edge diffraction for more accurate room acoustics auralization.

Inaccuracies in computation and auralization of room impulse responses are related in part to inadequate modeling of edge diffraction, i.e., the scattering from edges of finite surfaces. A validated time-domain model (based on analytical extensions to the Biot-Tolstoy-Medwin technique) is thus employed here to compute early room impulse responses with edge diffraction. Furthermore, the computations are extended to include combinations of specular and diffracted paths in the example problem of a stage-house. These combinations constitute a significant component of the total nonspecular scattering and also help to identify edge diffraction in measured impulse responses. The computed impulse responses are then convolved with anechoic signals with a variety of time-frequency characteristics. Initial listening tests with varying orders and combinations of diffraction suggest that (1) depending on the input signal, the diffraction contributions can be clearly audible even in nonshadow zones for this conservative open geometry and (2) second-order diffraction to nonshadowed receivers can often be neglected. Finally, a practical implementation for binaural simulation is proposed, based on the singular behavior of edge diffraction along the least-time path for a given source-edge-receiver orientation. This study thus provides a first major step toward computing edge diffraction for more accurate room acoustics auralization.

Journal Article↗
PubMed2001

Theory and experiments on the coupling of two Helmholtz resonators.

The acoustic coupling between closely located acoustic resonators can have a significant effect on the resonance properties. Examples of the influence of coupling include pipe musical instruments such as flue organs or flutes, where the coupling may affect the sound. Here, a physical model of a system of two coupled Helmholtz resonators is developed. The coupling is described by the mutual impedance between the neck openings, and an additive reflection impedance modification to the radiation impedance, which models the effect of reflections from the outer "shell" of the other resonator. The theoretical predictions show a good agreement with measurements also reported here. Finally, the effects of coupling on the present system are analyzed.

Journal Article↗
PubMed1999

Effect of hemodialysis on the signal-averaged electrocardiogram.

The presence of late potentials (LPs) on signal-averaged electrocardiography (SAECG) is predictive of ventricular tachycardia. The effect of hemodialysis (HD) on SAECG has not been well studied. SAECG was evaluated in 28 patients with chronic renal failure immediately before and after HD. In each SAECG, QRS duration, low-amplitude signal duration (LASd), and root-mean-square voltage of the terminal 40 milliseconds of the QRS (RMS40) were measured. To evaluate the effect of fluid removal on SAECG, the last 12 patients were studied during two different HD sessions, one with and one without fluid removal. Two-dimensional echocardiography was performed before and after HD on these 12 patients. At baseline, four patients met the criteria for LPs on SAECG. Only one patient met the criteria for LPs on SAECG after HD. After HD, the mean LASd decreased (28.3 +/- 12.9 to 24.9 +/- 10.1 milliseconds; P = 0.041) and RMS40 increased (63.0 +/- 56.9 to 79.0 +/- 59.2 microV; P = 0. 006). Among the 12 patients who underwent HD with and without fluid removal, left ventricular end-diastolic dimension decreased with (5. 4 +/- 0.6 to 5.1 +/- 0.6 cm; P = 0.024) but not without fluid removal (5.2 +/- 0.3 to 5.1 +/- 0.4 cm; P = not significant [NS]). RMS40 improved with (43.8 +/- 23.1 to 53.2 +/- 22.6 microV; P = 0. 03) but not without fluid removal (51.0 +/- 26.5 to 51.5 +/- 24.2 microV; P = NS). A significant negative correlation was found between change in body weight and change in RMS40 parameter (r = 0. 456; P = 0.0381). SAECG parameters are abnormal in a significant proportion of patients with chronic renal failure and improve with HD despite electrolyte and other proarrhythmic changes. Decreased left ventricular dimension because of fluid removal during HD is one possible explanation for this improvement.

Electrocardiography↗
PubMed1999

Near infra-red interactance for nutritional assessment of dialysis patients.

BACKGROUND: Malnutrition is a common problem in dialysis patients and may affect up to one-third of patients. Near-infrared interactance (NIR) is a novel approach to estimate body composition and per cent total body fat. METHODS: We used near-infrared interactance (Futrex 5000) to estimate the body composition including body fat percentage, as well as subjective global assessment (SGA), anthropometric measurements including mid-arm circumference (MAC), triceps and biceps skinfold thickness, calculated mid-arm muscle circumference (MAMC), body mass index (BMI), and laboratory values. NIR score, SGA assessment and anthropometric parameters were measured shortly after the end of a dialysis session. NIR measurement was made by placing a Futrex sensor on the nonaccess upper arm for several seconds. Serum albumin, transferrin (reflected by total iron binding capacity), and total cholesterol concentrations were performed as well. RESULTS: Thirty-four patients (20 men and 14 women) were selected from a pool of 120 haemodialysis patients. Their ages ranged from 26 to 86 years (58+/-14 years). Time on dialysis ranged from 8 months to 19 years (4.5+/-4.6 years). NIR scores were significantly different in three SGA groups: (A) well-nourished, 32.5+/-6.9%; (B) mildly to moderately malnourished, 29.2+/-5.3%; and (C) severely malnourished, 23.2+/-10.2% (P<0.001). Pearson correlation coefficients (r) between the NIR score and nutritionally relevant parameters were significant (P<0.001) for body mass index (r=+0.81), mid-arm circumference (r=+0.74), triceps skin fold (r=+0.54), biceps skin fold (r=+0.55), and mid-arm muscle circumference (r=+0.54). An inverse correlation was also found between NIR and years dialysed (r=-0.49, P=0.004), denoting a lesser body fat percentage according to NIR for patients dialysed longer. NIR was correlated with serum transferrin (r=+0.41, P=0.016) and cholesterol (r=+0.39, P=0.022) and marginally with serum albumin (r=+0.29, P=0.097). CONCLUSIONS: We conclude that NIR, which can be performed within seconds, may serve as an objective indicator of nutritional status in haemodialysis patients. More comparative and longitudinal studies are needed to confirm the validity of NIR measurements in nutritional evaluation of dialysis patients.

Adipose Tissue↗
PubMed1999

A modified quantitative subjective global assessment of nutrition for dialysis patients.

BACKGROUND: Malnutrition, a predictor of increased mortality in dialysis patients, can be estimated using the subjective global assessment (SGA), a semiquantitative scale with three severity levels. This semiquantitative feature restricts the SGA's reliability and precision. METHODS: Using the components of the conventional SGA, we developed a fully quantitative scoring system (the dialysis malnutrition score) consisting of seven variables: weight change, dietary intake, gastrointestinal symptoms, functional capacity, comorbidity, subcutaneous fat and signs of muscle wasting. Each component was assigned a score from 1 (normal) to 5 (very severe). The sum of all seven components in this malnutrition score lies between 7 (normal) and 35 (severely malnourished). To evaluate nutritional status in chronic dialysis patients, anthropometric measurements including mid-arm circumference (MAC), triceps skin-fold thickness, calculated mid-arm muscle circumference (MAMC), body mass index (BMI, ratio of weight to square of height) and laboratory parameters were used. Forty-one patients (20 men and 21 women) were randomly selected from a pool of 120 haemodialysis patients. Patients were aged between 26 and 81 years (mean SD, 57 +/- 12 years) and had undergone haemodialysis for between 7 months and 12 years (mean +/- SD, 3.0 +/- 2.1 years). RESULTS: The malnutrition score of each patient was assessed by a dietitian within 5-20 min (12.0 +/- 3.5 min) with no knowledge of anthropometric findings. Pearson correlation coefficients between the malnutrition score and biceps skin-fold (r= -0.32) MAC (r= -0.55), MAMC (r= -0.66), BMI (r= -0.35), total iron-binding capacity (TIBC, r= -0.77), the serum albumin concentration (r= -0.36) and total protein (r= -0.33) were all significant, whereas the conventional SGA had significant correlation only with TIBC (r= -0.35) and MAMC (r= -0.37). Malnutrition score showed a significant correlation with age (r= +0.34) and years dialysed (r= +0.28). Multiple regression analysis showed a significant correlation between the malnutrition score and the combination of the MAMC, BMI, serum albumin concentration and TIBC (r= 0.81, P<0.001). There was no correlation between the malnutrition score and sex, urea reduction ratio, protein catabolic rate, and the absolute lymphocyte count. CONCLUSIONS: We conclude that our invented malnutrition score, which can be performed in minutes, reliably assesses the nutritional status of haemodialysis patients. We suggest that our malnutrition score may be superior to the SGA. More comparative and longitudinal studies are needed to confirm the validity of this scoring system in nutritional evaluation of dialysis patients.

Adult↗
PubMed1998

Total iron-binding capacity-estimated transferrin correlates with the nutritional subjective global assessment in hemodialysis patients.

We examined the value of transferrin concentrations in estimating nutritional status as determined by the subjective global assessment (SGA) score. Fifty-nine hemodialysis patients (37 men and 22 women, aged 59+/-16 years, dialyzed for 3.6+/-3.9 years) were selected by predetermined criteria. All received erythropoietin (EPO) and oral iron therapy. SGA evaluation was conducted twice by both a dietitian and a physician. Serum iron, total iron-binding capacity (TIBC; which is linearly correlated with transferrin), transferrin saturation ratio, ferritin, albumin, total protein, and cholesterol were measured. Twenty-seven (46%) patients were well nourished (group A), 20 (34%) were moderately nourished (group B), and 12 (20%) were poorly nourished (group C) according to the SGA. TIBC values were 276+/-47 mg/dL, 217+/-54 mg/dL, and 176+/-41 mg/dL, respectively (P < 0.00001), and thus directly correlated with the state of nutrition. The relationship between TIBC and nutritional status was independent of age and number of years on hemodialysis. Serum ferritin values were 104+/-93 ng/mL, 161+/-154 ng/mL, and 363+/-305 ng/mL, respectively (P < 0.0003), and thus inversely correlated with the state of nutrition. Transferrin saturation ratios were slightly higher in the severely malnourished patients. The number of years on dialysis were a determinant of nutritional status. These values were 2.4+/-2.4 years for group A, 3.9+/-4.0 years for group B, and 5.7+/-3.9 years for group C (P < 0.05). The average age of the poorly nourished patients was 10 years older than the well-nourished patients. Serum iron values were lower but transferrin saturation ratios were higher in the severely malnourished patients. The required EPO doses were higher in the poorly nourished patients. We suggest that transferrin values are superior to other laboratory tests in assessing nutrition and will supplement SGA criteria. Serum ferritin may be useful as a predictor of illness. Older patients who have been on dialysis longer warrant special concern. Malnutrition may be an indicator of EPO resistance in dialysis patients. Finally, since a decreased TIBC level in poorly nourished patients may erroneously increase the transferrin saturation ratio, our findings may have implications in making the diagnosis and treatment of anemia and iron deficiency in malnourished dialysis patients.

Adult↗
PubMed1998

Severe hyponatremia, neuroleptic malignant syndrome, rhabdomyolysis and acute renal failure: a case report.

Acute renal failure secondary to myoglobinuria is a rare yet possible complication of malignant neuroleptic syndrome associated with the use of dopamine antagonists. We describe the case of a 42-year-old schizophrenic man who presented with severe hyponatremia, and proceeded to acute malignant neuroleptic syndrome, rhabdomyolysis, and acute renal failure. We contend that the acute hyponatremia may have served as a precipitating factor.

Acute Kidney Injury↗
PubMed1996

Case report: severe hyperkalemia in a geriatric patient receiving standard doses of trimethoprim-sulfamethoxazole.

A case is reported of a 96-year-old woman with congestive heart failure, hypertension, and chronic obstructive pulmonary disease who presented with altered mental status and severe hyperkalemia, a serum potassium 9.3 meq/L, and electrocardiograph changes. The patient was discharged 1 week prior, with a normal serum potassium, receiving trimethoprim-sulfamethoxazole for urinary tract infection and pneumonia. Serum potassium measurements returned to normal after discontinuation of the drug. Other causes of hyperkalemia were ruled out. Mild hyperkalemia due to trimethoprim-sulfamethoxazole was first reported in 1983 in a 69-year-old woman in whom leukemia with leukopenia developed. In literature to date, mild hyperkalemia in younger geriatric patients has been described. Trimethoprim is thought to act by inhibiting amiloride sensitive sodium channels in the distal nephron and impairing renal potassium secretion in a dose dependent manner. The authors report the case, review the literature, and discuss age-related reduction in renal function as a possible etiology.

Aged↗
PubMed1995

Diagnosis of iron deficiency anemia in renal failure patients during the post-erythropoietin era.

The purpose of this study was to evaluate the sensitivity and specificity of laboratory methods in the diagnosis of posterythropoietin-era, iron-deficient, chronic renal failure patients. The patient population comprised 25 anemic (hemoglobin < 11 g/dL) patients with creatinine greater than 3 mg/dL; 20 were dialysis patients, two were transplant patients, and three patients had renal failure from other causes. Criteria for study inclusion were as follows: bone marrow iron was the reference standard and was graded 0 to +4, ranging from absent to diffuse homogeneous iron staining; serum ferritin concentration and serum transferrin saturation were tested in terms of sensitivity and specificity. The reference standard indicated that iron deficiency existed in 40% of patients. Neither serum ferritin nor transferrin saturation were completely adequate diagnostic tools. Serum ferritin levels less than 200 ng/dL were 100% specific for the diagnosis but only 41% sensitive. Transferrin saturation of less than 20% was 88% sensitive, but only 63% specific. By excluding patients with hypoproteinemia (transferrin values of < 150 mg/dL), the sensitivity of the test increased to 100% and the specificity to 80%. We conclude that transferrin saturation is an adequate screening tool in anemic chronic renal failure patients, provided that hypoproteinemia is not present. By determining both the serum ferritin concentration and the transferrin saturation, a high sensitivity and specificity can be achieved, even in patients with hypoproteinemia. Furthermore, we believe that on this basis, iron therapy in patients with renal insufficiency can be improved.

Adult↗
PubMed1978

A multidisciplinary approach to the expression of pain in psychic depression.

The expression of cold pressor pain was measured by recording simultaneously verbal magnitude estimates, heart rates, and facial displays of 16 recently hospitalized depressed patients, and 16 nondepressed adults. Independence of the two groups for the depression factor was verified using the Hamilton Scale for Depression and the 100-mm line self-rating scale. Verbal responses and amount of time the ice bath was tolerated, as well as heart-rate measures, indicated that depressed individuals were significantly more sensitive to the pain stimulus. However, this elevated intolerance to pain was not reflected by marked changes of facial display. Reasons for this discrepancy are discussed. Nondepressed subjects, although clearly able to verbalize intensity of pain, were much less reactive to the pain along all dimensions.

Adult↗