Relative Blood Volume Research Articles

Merits and limitations of continuous blood volume monitoring during haemodialysis: Summary of the EDTNA|ERCA Journal Club discussion: winter 2005

The discussion explored and expanded on the issues raised by Dasselaar et al in their review of the measurement of relative blood volume (RBV) changes during dialysis (NDT 2005). Dialysis machines incorporating blood volume monitoring and control are widely available in Europe. The use of continuous blood volume monitoring (CBVM) to help establish dry weight; problems with CBVM due to connection and use of single needle dialysis; the physiological processes that cause RBV changes during eating, exercise and posture changes; and the application of blood volume based biofeedback control were discussed by participants from ten countries. The 'take-home' messages from the discussion were that CBVM can assist in setting target weight, but must be used together with traditional measures and experience. Biofeedback control may help to achieve symptom-free dialysis, but staff should be prepared to monitor patients systematically for several weeks to obtain individualised settings. Users of CBVM should be aware of factors that can alter the central haematocrit leading to apparent changes in RBV. Practical guidelines should be developed to help staff interpret CBVM data effectively.

Liver Tumor Model with Implanted Rhabdomyosarcoma in Rats: MR Imaging, Microangiography, and Histopathologic Analysis

In compliance with institutional regulations for care and use of laboratory animals, the aim of this study was to establish and characterize a rodent liver tumor model to provide a platform for preclinical assessment of new diagnostic and therapeutic strategies. A rhabdomyosarcoma tumor was implanted in the right and left liver lobes of 20 rats, for a total of 40 tumors. T1- and T2-weighted magnetic resonance (MR) images, diffusion-weighted images, and dynamic susceptibility contrast agent-enhanced perfusion-weighted images were obtained up to 16 days after tumor implantation and were compared with postmortem three-dimensional computed tomographic (CT) images, digital microangiograms, and histopathologic findings. Fifteen tumors were examined with proton ((1)H) MR spectroscopy. All tumors grew, with a mean volume doubling time of 2.2 days +/- 0.9 (standard deviation) and a final size of 591 mm(3)+/- 124. The rhabdomyosarcoma tumor showed hypervascularity at MR imaging, three-dimensional CT, microangiography, and histologic analysis. On dynamic susceptibility contrast-enhanced perfusion-weighted images, the maximum signal intensity decrease differed in time and extent between the tumor and the liver, with a significantly (P < .001) higher relative blood volume, relative blood flow, and permeability value in the tumor than in the liver. With (1)H MR spectroscopy, the rhabdomyosarcoma tumor and the liver featured significant (P < .001) choline and lipid peaks, respectively. Implantation of a rhabdomyosarcoma tumor in the livers of rats is feasible and reproducible, and this animal model seems promising for future testing of new diagnostic and therapeutic strategies.

Effect of High and Low Ultrafiltration Volume during Hemodialysis on Relative Blood Volume

Achieving an optimal post-hemodialysis hydration status may be difficult because objective criteria for dry weight are lacking. Both relative blood volume changes (DeltaRBV) at the end of hemodialysis and DeltaRBV normalized for ultrafiltration volume (DeltaRBV/UF ratio) have been reported to indicate post-hemodialysis volume status. A parameter for volume status should not be influenced by variations in ultrafiltration volume. However, if the volume that has to be ultrafiltrated to reach dry weight varies as a result of variations in pre-hemodialysis weight, either DeltaRBV or the DeltaRBV/UF ratio (or both) must change. To elucidate the relation between intradialytic ultrafiltration volume versus DeltaRBV and its derivative, the DeltaRBV/UF ratio, we studied the effect of a relatively high (mean+/- SD, 2.7+/- 0.5 l) and low (1.5+/- 0.3 l) intradialytic ultrafiltration volume on these parameters in eight patients. Post-hemodialysis weight was comparable in low and high ultrafiltration volume sessions. The average end-hemodialysis DeltaRBV did not differ between high (-6.7+/- 2.5%) and low ultrafiltration volume sessions (-7.3+/- 1.0%; NS), but the intraindividual variation was considerable. The DeltaRBV/UF ratio differed markedly (p<0.001) between high (-2.4+/- 0.8 %/l) and low (-4.9+/- 1.3 %/l) ultrafiltration volume sessions. In conclusion, the considerable random intraindividual variation of DeltaRBV and the systematic change of the DeltaRBV/UF ratio with variations in intradialytic ultrafiltration volume limit the use of these parameters as an aid to assess hydration status in hemodialysis patients.

Magnetic Resonance Imaging Workbench: Analysis and Visualization of Dynamic Contrast-enhanced MR Imaging Data

Magnetic Resonance Imaging Workbench (MRIW) allows analysis of T1- and T2*-weighted dynamic contrast-enhanced magnetic resonance imaging data sets to extract tissue permeability and perfusion characteristics by using standard pharmacokinetic models. Parametric maps are calculated from individual pixel enhancement curves in regions of interest (ROIs) and displayed as color overlays on the anatomic images. User-defined ROIs can be saved to ensure consistency of later reanalysis. Individual parametric maps are visualized together with user-selected parameter time-series plots. The following selections are available: overall ROI enhancement curve and fit, histogram, and individual pixel enhancement curve and fit. Summary data (transfer constant, leakage space, rate constant, integrated area under the gadolinium curve after 60 seconds, relative blood volume, relative blood flow, and mean transit time) may be exported to permanent storage along with per-pixel results for statistical analysis. Numerical values for parameters are displayed below the plot for easy reference. The dynamic range of plots and parametric map overlays is interactively adjustable. Viewing individual enhancement curves and parametric maps allows radiologists to investigate the heterogeneity of contrast agent kinetics for lesion characterization and to scrutinize serial changes in response to therapy. MRIW is written in IDL, enabling it to be used on a variety of computer systems.

Adenosine A1 receptor antagonist improves intradialytic hypotension

Intradialytic hypotension is a most frequent complication of hemodialysis and may contribute to cardiovascular events and high mortality. There is a hypothesis that an increase in adenosine generation during hemodialysis may cause vasodilation and a decrease in cardiac output, which results in systemic hypotension. We studied whether this can be blocked by an adenosine A1 receptor antagonist. We investigated the effects of an A1 antagonist, FK352, injection in 30 chronic hemodialysis patients with frequent intradialytic hypotension by a prospective, multicenter, double-blind placebo-controlled study for 4 weeks after 4 weeks of the observation period. Intradialytic hypotension was defined as systolic blood pressure (SBP) less than 110 mmHg, with SBP drop of more than 30 mmHg from the predialysis level. The efficacy of FK352 was primarily assessed by the reduction rate of dialysis hypotension between the FK352 and placebo groups. Incidence of emergency treatments caused by hypotension was evaluated. FK352 (50 mg, intravenous) or an equivalent placebo was injected into the dialysis circuit 1 h after starting dialysis. Blood pressure and heart rate were monitored every 30 min during dialysis. FK352 significantly improved intradialytic hypotension (P=0.046), in that the reduction rates of intradialytic hypotension in the FK352 and placebo groups were -12.8% (Q1 (first quantile), Q3 (third quantile): -27.5, -1.7), and +8.3% (Q1, Q3: -16.6, +16.7), respectively. The frequency of discontinuation of dialysis was significantly reduced by FK352. No apparent side effects were observed from treatment with FK352. In conclusion, the A1 antagonist FK352 may offer a novel therapeutic option for chronic dialysis patients associated with intradialytic hypotension.

Norepinephrine-induced vasoconstriction results in decreased blood volume in dialysis patients

Hypotension during haemodialysis results from an inadequate cardiovascular response to ultrafiltration-induced hypovolaemia. It has been suggested that plasma volume could be increased as a result of systemic vasoconstriction. We studied the effect of a norepinephrine (NOR) infusion (30 min), compared with no infusion, on relative blood volume (RBV) in six haemodialysis patients. During infusion we measured RBV, systolic blood pressure (SAP), heart rate (HR), stroke volume index (SI), total peripheral resistance (TPRI), ejection fraction (EF), inferior vena cava diameter (VCD) and core temperature. At the end of the NOR infusion, we observed a significant increase in TPRI (47+/-47% vs 4+/-17%; P<0.01) and SAP (27+/-12% vs 0+/-8%; P<0.01). Norepinephrine-induced vasoconstriction resulted in a significant decrease in RBV (-9+/-3% vs 0+/-1%; P<0.01). No significant changes were seen in SI (-4+/-21% vs 0+/-8%), HR (-5+/-19% vs -4+/-5%), EF (7+/-14% vs -2+/-10%), VCD or temperature. We conclude that norepinephrine-induced vasoconstriction results in a decrease in RBV. This indicates that improved haemodynamic stability during haemodialysis through vasoconstriction can be accompanied by a decrease in RBV and that part of the variability in blood volume may be due to changes in arterial tone. Such changes must be taken into account if RBV measurements are used to improve the haemodynamic tolerance of dialysis.

Validierung von Modellannahmen einer MR-Sauerstoffextraktionsbildgebung mittels einer Phantomstudie

Oxygen supply is an important parameter for the evaluation of tissue viability and therefore of high interest in cancer diagnosis and therapy. One promising approach to extract relevant information from imaging data is the determination of oxygen saturation by means of the BOLD-effect. Using a simple model of tissue structure allows to evaluate the susceptibility difference between tissue and venous blood, from which the blood oxygen extraction fraction can be derived indirectly.The present study tested the validity of two model assumptions needed for exact quantification: the independence of the results of both capillary diameter d and the relative blood volume λ. For this purpose a phantom was built, which allows the evaluation of susceptibility differences depending on d (27 m–238 m) and λ (3%–12%). In agreement with model assumptions, Δχ(λ) was widely constant and independent of λ. In contradiction to the model, Δχ(d) showed a positive slope (Δχ range: 0.35–0.57 ppm). The present study suggests that the simple model investigated here has shortcomings in the quantification of oxygen extraction due to insufficient model assumptions.

Altered regional blood volume in chronic cannabis smokers.

The quantitative measurement of cerebral perfusion is crucial for the study of both normal and impaired human brain function. Although cannabis is the most commonly abused illicit substance in the United States, its effects on cerebral blood volume (CBV) have not been fully examined. The objective of the present study was to examine differences in relative regional blood volume in focal regions of interest--including the frontal lobe, the temporal lobe, and the cerebellum--during a period of supervised abstinence from cannabis. Dynamic susceptibility contrast MRI data were collected on 12 current, long-term daily cannabis users between 6 and 36 hr after the subjects' last reported cannabis use. Resting-state CBV images were also acquired in 17 healthy comparison subjects. Data were acquired in the axial plane with a 1.5-Tesla GE Signa scanner following a bolus of gadolinium contrast agent. Cannabis users demonstrated significantly increased blood volumes in the right frontal area (p < .05), in the left temporal area (p < .005), and in the cerebellum (p < .005) relative to comparison subjects. Among the cannabis users, there were no significant correlations between regional blood volumes and either total lifetime episodes of smoking or urinary tetrahydrocannabinol concentrations. These findings have important implications for understanding the effects of chronic heavy cannabis use on brain function. It would be of interest to extend the investigation beyond 6-36 hr of abstinence from cannabis to determine whether increased CBV values persist for several weeks or eventually normalize.

Histopathological Studies on Some Vital Organs of Mice Exposed To Extremely Low Frequency Magnetic Field

Twenty five male Swiss albino mice were used in this study to detect the effect of extremely low frequency magnetic field (ELFMF) 2 milli Tesla-50 Hertz (2 mT,50 Hz) 8 hours/day at different time intervals. Mice were divided into five groups, control group and 4 treated groups, two groups represented the direct effect of (ELFMF) and the other two represented the late effect. The direct effect groups were sacrificed direcly after the end of exposure to (ELFMF), while the late effect groups were sacrificed after certain duration period of the exposure away from (ELFMF). In the present work, histopathological studies revealed severe degeneration changes in kidney, spleen and testes of all groups of mice direct and late effect groups and no sign of complete recovery could be detected in the late effect groups. Glomerular volume, number of glomeruli, relative glomerular blood volume (RGBV) of the kidney; and the mean number cells of spermatogenesis cells of the testes were calculated in control and treated groups. The histopathological changes observed in the kidney, spleen and testes of treated mice were less in direct effect groups than that observed in late effect groups.

Analysis of near-infrared spectroscopy and indocyanine green dye dilution with Monte Carlo simulation of light propagation in the adult brain

Near-infrared spectroscopy (NIRS) combined with indocyanine green (ICG) dilution is applied externally on the head to determine the cerebral hemodynamics of neurointensive care patients. We applied Monte Carlo simulation for the analysis of a number of problems associated with this method. First, the contamination of the optical density (OD) signal due to the extracerebral tissue was assessed. Second, the measured OD signal depends essentially on the relative blood content (with respect to its absorption) in the various transilluminated tissues. To take this into account, we weighted the calculated densities of the photon distribution under baseline conditions within the different tissues with the changes and aberration of the relative blood volumes that are typically observed under healthy and pathologic conditions. Third, in case of NIRS ICG dye dilution, an ICG bolus replaces part of the blood such that a transient change of absorption in the brain tissues occurs that can be recorded in the OD signal. Our results indicate that for an exchange fraction of Delta=30% of the relative blood volume within the intracerebral tissue, the OD signal is determined from 64 to 74% by the gray matter and between 8 to 16% by the white matter maximally for a distance of d=4.5 cm.

Automatic feedback control of relative blood volume changes during hemodialysis improves blood pressure stability during and after dialysis

Automatic feedback systems have been designed to control relative blood volume changes during hemodialysis (HD) as hypovolemia plays a major role in the development of dialysis hypotension. Of these systems, one is based on the concept of blood volume tracking (BVT). BVT has been shown to improve intra-HD hemodynamic stability. We first questioned whether BVT also improves post-HD blood pressure stability in hypotension-prone patients and second, whether BVT is effective in reducing the post-HD weight as many hypotension-prone patients are overhydrated because of an inability to reach dry weight. After a 3-week period on standard HD, 12 hypotension-prone patients were treated with two consecutive BVT treatment protocols. During the first BVT period of 3 weeks, the post-HD target weight was kept identical compared with the standard HD period (BVT-constant weight; BVT-cw). During the second BVT period of 6 weeks, we gradually tried to lower the post-HD target weight (BVT-reduced weight; BVT-rw). In the last week of each period, we studied intra-HD and 24 hr post-HD blood pressure behavior by ambulatory blood pressure measurement (ABPM). Pre- and post-HD weight did not differ between standard HD and either BVT-cw or BVT-rw. Heart size on a standing pre-dialysis chest X-ray did not change significantly throughout the study. There were less episodes of dialysis hypotension during BVT compared with standard HD (both BVT periods: p<0.01). ABPM data were complete in 10 patients. During the first 16 hr post-HD, systolic blood pressure was significantly higher with BVT in comparison with standard HD (both BVT periods: p<0.05). The use of BVT in hypotension-prone patients is associated with higher systolic blood pressures for as long as 16 hr post-HD. BVT was not effective in reducing the post-HD target weight in this patient group.

Improvement in Microvascular Reflow and Reduction of Infarct Size With Adenosine in Patients Undergoing Primary Coronary Stenting

The aim of this study was to use myocardial contrast echocardiography to evaluate the effect of intravenous adenosine on microvascular reflow in patients with acute myocardial infarction who underwent primary coronary stenting (PCS). Thirty patients who underwent primary PCS for acute myocardial infarction were randomized to intravenous adenosine (50 to 70 mug/kg/min) or vehicle for 3 hours. Myocardial contrast echocardiography was performed before and sequentially after PCS to determine the risk area during coronary occlusion and infarct size. The risk area was similar in the adenosine- and placebo-treated patients. The infarct size as a ratio to the risk area was smaller in patients treated with adenosine when measured at 3 to 5 days (0.37 +/- 0.29 vs 0.68 +/- 0.25, p <0.01) and at 4 weeks (0.34 +/- 0.26 vs 0.60 +/- 0.21, p <0.01) after PCS. This effect was greatest when patency was achieved <4 hours after symptom onset (0.18 +/- 0.18 vs 0.74 +/- 0.31, p <0.05), with little effect after 4 hours. The relative microvascular blood volume in the risk area at 4 weeks was higher in patients receiving adenosine than in those receiving placebo (0.73 +/- 0.22 vs 0.57 +/- 0.20, p <0.01), and was highest when patency was achieved in <4 hours. In conclusion, the adjunctive use of intravenous adenosine after PCS reduces the infarct size relative to the risk area. This beneficial effect occurs primarily in those undergoing early intervention.

The Hemodynamic Effect of Calcium Ion Concentration in the Infusate During Predilution Hemofiltration in Chronic Renal Failure

It is the prevailing view that convective dialysis techniques stabilize blood pressure. Calcium concentration in the substitution fluid may be important in this respect. The aim of this study is to investigate the influence of calcium ion concentration in the substitution fluid on hemodynamic stability during predilution hemofiltration (HF). We conducted a randomized, crossover, blinded, controlled trial with 12 stable long-term hemodialysis patients without diabetes. Each patient was randomly assigned to substitution fluid with a calcium ion (iCa) concentration of 2.5 mEq/L (1.25 mmol/L; low-calcium session [L-HF]) or 3.5 mEq/L (1.75 mmol/L; high-calcium session [H-HF]) during 4.5 hours of predilution HF with a volume of 1.24 +/- 0.09 L/kg dry body weight and a temperature of 37 degrees C. Ultrafiltration was kept constant in each patient. Blood pressure (mean, systolic [SBP], and diastolic blood pressure [DBP]), pulse rate, arterial and venous temperature, energy transfer, and relative blood volume were measured at 15-minute intervals. Cardiac output, total peripheral resistance, stroke volume, and iCa were measured hourly. The 2 treatments were matched with the exception of iCa concentration. A significant intratreatment reduction in cardiac output and stroke volume was shown to the same extent for both groups. Intertreatment comparisons showed a significantly lower mean arterial pressure, SBP, DBP, and total peripheral resistance in the L-HF compared with the H-HF group. iCa concentration of 3.5 versus 2.5. mEq/L (1.75 versus 1.25 mmol/L) in the infusate during predilution HF stabilized blood pressure, possibly because of greater peripheral resistance rather than through changes in cardiac performance.

Imaging of VEGF Receptor Kinase Inhibitor-Induced Antiangiogenic Effects in Drug-Resistant Human Adenocarcinoma Model

Small molecule vascular endothelial growth factor (VEGF) receptor tyrosinase kinase inhibitors (VEGFRTKIs) show great promise in inducing antiangiogenic responses in tumors. We investigated whether antiangiogenic tumor responses induced by an experimental VEGFR-TKI (AG013925; Pfizer Global Research, Development) could be reported by magnetic resonance imaging (MRI) during the initial phase of treatment. We used MRI, superparamagnetic nanoparticles for measuring relative vascular volume fraction (rVVF) in a drug-resistant colon carcinoma model. Athymic mice harboring MV522 xenografts were treated with VEGFR-TKI (25 mg/kg, p.o., with a 12-hour interval in between treatments), were imaged after three consecutive treatments. Relative tumor blood volume fractions were calculated using ΔR2* maps that were scaled by the known VVF value of an in-plane skeletal muscle (1.9%). There was a pronounced, statistically significant (P < .001) decrease of tumor rVVF in treated animals (0.95 ± 0.24%; mean ± SEM, n= 66 slices, eight mice) compared to mice that received a placebo (2.91 ± 0.24%; mean SEM, n = 66 slices, nine mice). Tumor histology confirmed a three-fold decrease of vascular density, a concomitant increase of apoptotic cell index. Hence, we demonstrated that: 1) the VEGFR-TKI resulted in antiangiogenic effects that were manifested by a decrease or rVVF;, 2) iron oxide nanoparticles, steadystate MRI enable an early detection of tumor response to antiangiogenic therapies.

Measurement of relative blood volume changes during haemodialysis: merits and limitations

Dialysis hypotension is estimated to occur in 20% ofhaemodialysis (HD) sessions [1] and can lead to seriousvascular complications such as cerebral infarctionand cardiac and mesenteric ischaemia [2,3]. It maycontribute to chronic overhydration due to an inabilityto reach dry weight and may lead to under-dialysis[1,2,4]. Prevention of dialysis hypotension, therefore,is an important challenge to the dialysis staff. Theinitiating factor in the pathogenesis of dialysis hypo-tension is a decrease in blood volume which resultsfrom the imbalance between the ultrafiltration rate andthe plasma refilling rate [5]. Devices that continuouslyand non-invasively monitor relative blood volume(RBV) changes during HD are being advocated as atool to maintain an adequate volume of the intravas-cular compartment in order to avoid dialysis hypo-tension [6–8]. Nowadays, most manufacturers haveincorporated an RBV monitor in their dialysis appa-ratus, but evidence-based knowledge on how to use theRBV data in order to optimize the dialysis prescriptionof the individual patient is lacking. Moreover, there areconflicting data in the literature on the predictive valueof RBV changes for the occurrence of dialysis hypoten-sion. In this review, we will outline the pathophysio-logical response to ultrafiltration-induced reductionsinbloodvolume,evaluatetheRBVmeasuringmethods,discuss the relationship between RBV changes andbloodpressureanddiscussseveralfactorsthatinfluencethe validity of RBV measurements.

PTK787/ZK222584, a tyrosine kinase inhibitor of vascular endothelial growth factor receptor, reduces uptake of the contrast agent GdDOTA by murine orthotopic B16/BL6 melanoma tumours and inhibits their growth in vivo

Assessment of tumour vascularity may characterize malignancy as well as predict responsiveness to anti-angiogenic therapy. Non-invasive measurement of tumour perfusion and blood vessel permeability assessed as the transfer constant, K(trans), can be provided by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Using the orthotopic murine tumour model B16/BL6 melanoma, the small contrast agent GdDOTA (DOTAREM(R); Guerbet, Paris) was applied to assess the vascular transfer constant, K(trans), and interstitial leakage space, whereas intravascular iron oxide nanoparticles (Endorem(R); Guerbet, Paris) were used to detect relative tumour blood volume (rTBV), and in one experiment blood flow index (BFI). No correlations were observed between these four parameters (r(2) always <0.05). The B16/BL6 primary tumour and lymph-node cervical (neck) metastases produced high levels of the permeability/growth factor, VEGF. To probe the model, the novel VEGF receptor (VEGF-R) tyrosine kinase inhibitor, PTK787/ZK222584 (PTK/ZK) was tested for anti-tumour efficacy and its effects on DCE-MRI measured parameters of tumour vascularity. Data from the non-invasive measure of tumour vascularity were compared with a histological measurement of vasculature using the DNA-staining dye H33342. PTK/ZK inhibited growth of the primary and, particularly, cervical tumour metastases following chronic treatment for 2 weeks (50 or 100 mg/kg daily) of 1-week-old tumours, or with 1 week of treatment against more established (2-week-old) tumours. After chronic treatment with PTK/ZK, DCE-MRI detected significant decreases in K(trans) and interstitial leakage space, but not rTBV of both primary tumours and cervical metastases. Histological data at this time-point showed a significant decrease in blood vessel density of the cervical metastases but not the primary tumours. However, in the cervical metastases, the mean blood vessel width was increased by 38%, suggesting overall no marked change in blood volume. After acute (2-4 day) treatment, DCE-MRI of the cervical metastases demonstrated a significant decrease in K(trans) and interstitial leakage space and also in the initial area under the enhancement curve for GdDOTA (IAUC), but no change in the rTBV or BFI. Thus, significant changes could be detected in the DCE-MRI measurement of tumour uptake of a small contrast agent prior to changes in tumour size, which suggests that DCE-MRI could be applied in the clinic as a rapid and sensitive biomarker for the effects of VEGF-R inhibition on tumour blood vessel permeability and thus may provide an early marker for eventual tumour response.

Online measurement of haemoglobin concentration

Regular monitoring of haemoglobin in chronic haemodialysis patients is essential to ensure that targets for anaemia management are consistently achieved. Repeated blood sampling can be time consuming, invasive and, for pragmatic reasons, only infrequently performed, often delaying therapeutic change. On-line optical continuous monitoring of the haemoglobin concentration would allow non-invasive assessment of haemoglobin, and immediate therapeutic changes could be implemented, thereby improving the efficiency of anaemia management. This study aimed to evaluate the use of on-line haemoglobin concentration measurement. Eleven dialysis monitors (Integra Hospal) were calibrated using at least five haemoglobin samples spread over at least 4 g/dl. Optical measurement of haemoglobin concentration is already incorporated into the dialysis monitor to allow the study of relative blood volume. Fifteen patients were studied with paired haemoglobin measurements (i.e. dialysis monitor value and conventional laboratory assessment) taken at intervals over 7 months (mean 11.0+/-0.28 g/dl, range 7.5-14.8). Haemoglobin measured by Hemoscan correlated well with the laboratory measurements (r2 = 0.83, P<0.0001), indicating that the machine values are broadly comparable with laboratory figures. There was a mean underestimate of haemoglobin by Hemoscan of 0.34%. There was no significant deterioration in the quality of this correlation over the study period (r2>0.8). The ability of the dialysis monitor to measure the optical concentration of haemoglobin compared with conventional laboratory assessment is both precise and accurate. Regular on-line assessment of haemoglobin may allow more proactive micromanagement of renal anaemia, with a reduction in the time taken to achieve clinically important targets and give early warning of suboptimal response to treatment.

Hypotension during hemodialysis results from an impairment of arteriolar tone and left ventricular function

Hypotensive episodes are a major complication of hemodialysis. Hypotension during dialysis could be directly related to a reduction in blood volume or to a decrease in cardiovascular activation as a response to decreased cardiac filling. A decreased cardiovascular activation could be due to patient-related or to dialysis-related factors. In order to study the isolated effect of a reduction in filling pressure, lower body negative pressure (LBNP) causes activation of the cardiovascular reactivity with a decrease in cardiac filling, but without the influence of the dialysis procedure that could affect cardiovascular reactivity. We studied the relationship between relative blood volume (RBV), central venous pressure (CVP), systolic arterial pressure, heart rate, stroke volume index (SI), and total peripheral resistance index (TPRI) during a combined dialysis/ultrafiltration and during LBNP to -40 mmHg in 21 hemodialysis patients with a high incidence of hypotension. Systolic arterial pressure, heart rate, SI and TPRI were measured by Finapres. CVP was measured after cannulation of the jugular vein. During dialysis RBV was measured by a blood volume monitor (BVM). In order to study the conditions in which hypotension occurred after dialysis, we divided the patients into 2 groups: hypotensive (H) and non-hypotensive (NH) during dialysis. Baseline levels did not show any significant differences. During dialysis systolic arterial pressure declined gradually in the H group from 30 minutes before the onset of hypotension. There was a similar decrease of RBV and increase of heart rate in both groups with a large interindividual variation. At hypotension, H patients showed a significantly smaller increase in TPRI as compared to NH patients. The reduction in SI tended to be greater at hypotension, while CVP decreased to a similar extent in both groups. Moreover, during LBNP, a similar reduction in CVP resulted in a much smaller decrease in SI. Systolic arterial pressure was only slightly lowered due to a much greater increase in TPRI. We conclude that dialysis-related hypotension in our patient group did not result from an inability to maintain blood volume or from decreased cardiac filling. Hypotension appeared to result from the inability to adequately increase arteriolar tone and a reduction in left ventricular function. Both vascular tone and left ventricular function appeared to be impaired by the dialysis procedure.

Predilution hemodiafiltration displays no hemodynamic advantage over low-flux hemodialysis under matched conditions

It is the prevailing view that convective dialysis techniques stabilize blood pressure. The aim of this study was to compare the intrasession hemodynamics during high-dose predilution hemodiafiltration (HDF) and low-flux hemodialsis, under strict controlled conditions. Twelve stable hemodialysis patients were investigated in a randomized crossover blinded controlled trial. The patients were allocated to one session of predilution HDF (substitution fluid 1.20 +/- 0.10 L/kg body weight) and one session of hemodialysis at 4(1/2) hours. To eliminate confounding factors, dialysis dose, ultrafiltration volume and arterial temperature were matched. At the start of the dialysis the patients' core temperature was "locked" by an automatic feedback system regulating the dialysate temperature; thereby, patients' temperature was kept stable throughout the whole treatment. The calcium-ion concentration in the substitution/dialysis fluid was 1.25 mmol/L. Cardiac output was measured hourly by the ultrasound velocity dilution method. Mean blood pressure, cardiac output, stroke volume, cardiac work, and relative blood volume was significantly reduced in both treatments. Total peripheral resistance increased significantly in both groups. Ultrafiltration volume, cardiopulmonary recirculation, Kt/V, and total energy transfer were similar for hemodialysis and HDF. The pulse rate showed no significant change throughout both sessions. No significant differences were revealed between hemodialysis and HDF. The hemodynamics of predilution HDF and low-flux hemodialysis displayed a similar profile during matched conditions. An acute circulatory benefit of convective solute removal over diffusive could not be demonstrated.

The Effect of Age on Optic Nerve Head Blood Flow

To examine whether optic nerve head blood flow changes with aging. One randomly chosen eye of each of 103 healthy subjects (age range, 22-76 years) was examined by laser Doppler flowmetry. Relative capillary blood flow, velocity, and volume of the moving red blood cells were measured at the temporal and nasal neuroretinal rim of the optic nerve head. For statistical analysis, linear regression analysis and partial correlations were calculated. Velocity increased with age. The Pearson correlation coefficient (R) between age and velocity was 0.49 temporally and 0.56 nasally. The correlation was significantly different from 0 (both P < 0.0005). Volume decreased with increasing age. The Pearson correlation coefficient between age and volume was -0.47 temporally and -0.40 nasally. The correlation was significantly different from 0 (both P < 0.0005). Flow decreased with increasing age. The Pearson correlation coefficient between age and flow was -0.27 temporally and -0.31 nasally. The correlations were significantly different from 0 (P = 0.006 and P = 0.002, respectively). Partial correlation coefficients between the perfusion parameters and age, after correcting for systolic and diastolic blood pressure, heart rate, gender, and IOP, were similar compared to the Pearson correlation coefficients and remained statistically significant. The perfusion of the optic nerve head is altered with increasing age. The results suggest that the blood supply is reduced in elderly subjects.