Reference values for multifrequency bioimpedance analysis in dialysis patients

BACKGROUND: The role of multifrequency bioimpedance(MF-BIA) in the assessment of fluid status in dialysis patients is still not fully elucidated. Especially, the predictive value of reference values for extracellular water (ECW) has not yet been addressed. Aim of the present study was to validate cut-off values for MF-BIA in the diagnosis of hypervolemia in dialysis patients, using strict clinical criteria and echocardiography as reference techniques. METHODS: 90 patients [42 on hemodialysis; 48 on peritoneal dialysis] were divided into the following groups: clinically normovolemic (mean 24- or 48-hour systolic blood pressure below 133 mm Hg without use of antihypertensive agents; n = 12), 'hypervolemic' (mean systolic blood pressure above 133 mm Hg with 2 or more antihypertensive agents; n = 34) or undetermined (n = 44). The 80th percentile for normalized ECW in the clinically normovolemic patients was used as reference value. 20 healthy age-matched controls were included for comparison. RESULTS: The 80th percentiles for ECW:body weight (BW) and ECW:height in 'normovolemic' subjects were, respectively, 0.245 liters/kg and 10.96 liters/m in males, and 0.232 liters/kg and 9.13 liters/m in females. ECW:BW and ECW:height were above these values in, respectively, 26 (sensitivity 76%) and 29 (sensitivity 86%) of the 34 'hypervolemic' patients. In the undetermined group, left ventricular end-diastolic diameter was significantly different between patients with normalized ECW below and above these cut-off values (49.0 +/- 5.1 vs. 52.4 +/- 5.7 mm; p < 0.05). Use of the ECW:TBW ratio resulted yielded low sensitivity (45%). ECW:height was lower in the 'normovolemic' dialysis patients compared to healthy controls (9.7 +/- 1.3 l/m versus 12.2 +/- 1.9 l/m). CONCLUSION: In our study population, ECW by MF-BIA, normalized for height was able to predict hypervolemia, based on strict clinical criteria, with a sensitivity of 86% and a specificity of 80%. The normalization procedure for ECW may influence the classification of hydration status. Strictly normotensive dialysis patients had lower normalized ECW than healthy control subjects.     

Effect of icodextrin on volume status,blood pressure and echocardiographic parameters: a randomized study

Overhydration is a risk factor for hypertension and left ventricular hypertrophy in peritoneal dialysis patients. Recently, a high prevalence of subclinical overhydration was observed in peritoneal dialysis patients. Aim of the present open-label randomized study was to assess the effect of a icodextrin 7.5% solution on fluid status [extracellular water (ECW) bromide dilution], blood pressure regulation (24-hour ambulatory measurements) and echocardiographic parameters during a study period of 4 months, and to relate the effect to peritoneal membrane characteristics (dialysate/plasma creatinine ratio). Forty peritoneal dialysis patients (22 treated with icodextrin, 18 controls) were randomized to either treatment with icodextrin during the long dwell or standard glucose solutions. Thirty-two patients (19 treated with icodextrin, 13 controls] completed the study. The use of icodextrin resulted in a significant increase in daily ultrafiltration volume (744 +/- 767 mL vs. 1670 +/- 1038 mL; P = 0.012) and a decrease in ECW (17.5 +/- 5.2 L vs. 15.8 +/- 3.8 L; P = 0.035). Also the change in ECW between controls and patients treated with icodextrin was significant (-1.7 +/- 3.3 L vs. +0.9 +/- 2.2 L; P = 0.013). The effect of icodextrin on ECW was not related to peritoneal membrane characteristics, but significantly related to the fluid state of the patients (ECW:height) (r = -0.72; P < 0.0001). Left ventricular mass (LVM) decreased significantly in the icodextrin-treated group (241 +/- 53 grams vs. 228 +/- 42 grams; P = 0.03), but not in the control group. In this randomized open-label study, the use of icodextrin resulted in a significant reduction in ECW and LVM. The effect of icodextrin on ECW was not related to peritoneal membrane characteristics, but was related to the initial fluid state of the patient.     

Cannabis use and mood disorders: patterns of clinical presentations among adolescents in a developing country

Notwithstanding the increase use of cannabis among adolescents in both developing and developed countries, few studies have looked at cannabis use and mood disorders. In a series of case studies, this research project seeks to investigate patterns of clinical presentations seen among cannabis users in psychiatric outpatients in Trinidad. Five clinical patterns of presentations are identified among cannabis users and abusers based on variables of dosing, age of initial use, duration of use, tolerance and reverse tolerance and poly-drug abuse. All patients in these case studies were standardized for method of use and potency of cannabis used. Patients were screened by urine tests to determine co-morbid use of other substances. Other variables such as environmental factors and genetic vulnerability were reviewed as far as possible from historical accounts of family members. The five patterns described are low, controlled use with mild euphoria and heightened awareness, moderate use with mixed depressive symptoms and suicidal behaviour, heavy, short term use with manic symptoms, long term incremental use with psychotic symptoms due to the trumping of depressive symptoms and cannabis mixed with other substances resulting in florid psychosis. Mood disorders appear to be a common finding among adolescents using cannabis. Sensitization to symptomatic presentation and early detection of cannabis use in young adolescents are necessary. Further research is needed on the effect of cannabinoids on emotions, behaviour and thinking and its relationship to mental disorders. This study is useful as a guideline for the implementation of public health strategies and legislation concerning the use of cannabis in youths.     

Influence of adjacent low-dose fields on tolerance to high doses of protons in rat cervical spinal cord

PURPOSE: The dose-response relationship for a relatively short length (4 mm) of rat spinal cord has been shown to be significantly modified by adjacent low-dose fields. In an additional series of experiments, we have now established the dose-volume dependence of this effect. METHODS AND MATERIALS: Wistar rats were irradiated on the cervical spinal cord with single doses of unmodulated protons (150 MeV) to obtain sharp lateral penumbras, by use of the shoot-through technique, which employs the plateau of the depth-dose profile rather than the Bragg peak. Three types of inhomogeneous dose distributions were administered: Twenty millimeters of cervical spinal cord were irradiated with variable subthreshold (= bath) doses (4 and 18 Gy). At the center of the 20-mm segment, a short segment of 2 mm or 8 mm (= shower) was irradiated with variable single doses. These inhomogeneous dose distributions are referred to as symmetrical bath-and-shower experiments. An asymmetrical dose distribution was arranged by irradiation of 12 mm (= bath) of spinal cord with a dose of 4 Gy. The caudal 2 mm (= shower) of the 12-mm bath was additionally irradiated with variable single doses. This arrangement of inhomogeneous dose distribution is referred to as asymmetrical bath-and-shower experiment. The endpoint for estimation of the dose-response relationships was paralysis of the fore limbs or hind limbs and confirmation by histology. RESULTS: The 2-mm bath-and-shower experiments with a 4-Gy bath dose showed a large shift of the dose-response curves compared with the 2-mm single field, which give lower ED50 values of 61.2 Gy and 68.6 Gy for the symmetrical and asymmetrical arrangement, respectively, compared with an ED50 of 87.8 Gy after irradiation of a 2-mm field only. If the bath dose is increased to 18 Gy, the ED50 value is decreased further to 30.9 Gy. For an 8-mm field, addition of a 4-Gy bath dose did not modify the ED50 obtained for an 8-mm field only (23.2 and 23.1 Gy). CONCLUSIONS: The spinal cord tolerance of relatively small volumes (shower) is strongly affected by low-dose irradiation (= bath) of adjacent tissue. The results of all bath-and-shower experiments show the effect of a low bath dose to be highest for a field of 2 mm, less for 4 mm, and absent for 8 mm. Adding a 4-Gy bath to only 1 side of a 2-mm field still showed a large effect. Because glial progenitor cells are known to migrate over at least 2 to 3 mm, this observation indicates that interference with stem cell migration is not the most likely mechanism of a bath effect.     

Subcellular localization of 57Co-bleomycin in normal and tumor tissues.

57Co-bleomycin appears to be one of the best tumor detecting agents at the moment. The localization within the cells is not yet known. This preclinical investigation had the aim to study the subcellular distribution of 57Co-bleomycin in liver, spleen and tumors of rats and mice. Mice with transplanted lymphosarcoma and osteosarcoma were used and rats with transplanted rhabdomyosarcoma. The concentration of 57Co-bleomycin was 2 to 10 times higher in the tumors as compared to the (normal) liver. This accumulation property was not found with the control substance: 57CoCl2. The highest radioactivity of 57Co-bleomycin (cpm/mg protein) was observed in subcellular fractions containing mitocohndria and lysosomes. After treatment of these fractions with hypertonic solutions it could be shown that enzymes of the mitochondrial matrix remained inside the vesicles under conditions of almost complete release of 57Co-bleomycin. Half of the lysosomal enzyme acid phosphatase was released too. From these experiments it is concluded that 57Co-bleomycin is preferentially localized in heavy secondary lysomes which are more fragile than the lighter lysosomes in the cells.     

Development of an MR-safe tracking catheter with a laser-driven tip coil

We developed a magnetic resonance (MR)-safe tracking catheter using an optical fiber with a light-diffusing tip segment to transport laser energy through the catheter. This energy is converted to a DC current running through a small coil at the catheter tip. Our method is inherently MR-safe since the use of long conducting wires is avoided. The intravoxel dephasing induced by the tip coil was clearly visible for laser powers between 250 mW and 750 mW for all angular positions of the catheter. J. Magn. Reson. Imaging 2001;13:131-135.     

Thermal effects and blood pressure response during postdilution hemodiafiltration and hemodialysis: the effect of amount of replacement fluid and dialysate temperature

It has been suggested that the incidence of hypotensive episodes is less with hemodiafiltration (HDF) than with hemodialysis (HD). The aim of the present study was to assess the BP response during HD and postdilution HDF in relation to the thermal effects of these different treatment modalities by manipulating the dialysate temperature (Td) during HD and the amount of replacement fluid during HDF. In 12 patients, energy transfer rate (in watts) and maximal decline in mean arterial pressure during HD at Td 37.5 degrees C, HD at Td 35.5 degrees C, and postdilution HDF with amounts of replacement fluids infused at room temperature of 1 L/h and 2.5 L/h, respectively, were assessed. All measurements were done twice in each patient. Energy transfer rate was comparable between HD 35.5 degrees C (-26.61 +/- 5.33) and HDF 2.5 L/h (-25.25 +/- 7.91) and was significantly more negative compared with HD 37.5 degrees C (-3.53 +/- 6.44) and HDF 1 L/h (-15.88 +/- 6.94). The maximum decline in mean arterial pressure was significantly higher during HD 37.5 degrees C (-25.6 +/- 13.5) than during HD 35.5 degrees C (-15.1 +/- 13.8) and HDF 2.5 L/h (-19.2 +/- 17.7), whereas there was no significant difference with HDF 1 L/h (-23.0 +/- 14.0). In conclusion, thermal effects during postdilution HDF are dependent on the amount of replacement fluid. Also during HDF, the BP response is strongly related to thermal effects. The use of postdilution HDF with low or intermediate amounts of replacement fluids infused at room temperature seems to have no advantage in preventing hemodynamic instability, compared with HD 35.5 degrees C.     

Techniques for precision irradiation of the lateral half of the rat cervical spinal cord using 150 MeV protons [corrected].

Techniques for high precision irradiation experiments with protons, to investigate the volume dependence of the tolerance dose of the rat cervical spinal cord are described. In the present study, 50% of the lateral cross section of the spinal cord was irradiated. The diameter of the cross section of this part of the rat spinal cord is at maximum 3.5 mm. Therefore, a dedicated procedure was developed to comply with the needs for a very high positioning accuracy and high spatial resolution dosimetry. By using 150 MeV protons a steep dose gradient (20-80% = 1 mm) in the centre of the spinal cord was achieved. This yields a good dose contrast between the left and right halves of the cord. A home-made digital x-ray imager with a pixel resolution of 0.18 mm/pixel was used for position verification of the spinal cord. A positioning accuracy of 0.09 mm was obtained by using information of multiple pixels. The average position stability during the irradiation was found to be 0.08 mm (1 SD) without significant systematic deviations. Profiles of the dose distribution were measured with a 2D dosimetry system consisting of a scintillating screen and a CCD camera. Dose volume histograms of the whole spinal cord as well as separately of the white and grey matters were calculated using MRI imaging of the cross section of the rat cervical spinal cord. From the irradiation of 20 animals a dose-response curve has been established. MRI showed radiation-induced damage at the high dose side of the spinal cord. Analysis of the preliminary dose-response data shows a significant dose-volume effect. With the described procedure and equipment it is possible to perform high precision irradiations on selected parts of the spinal cord.