Can the response to dialysis treatment be predicted by using patient-specific modeling of fluid and solute exchanges? A multicentric evaluation

BACKGROUND

Parametric multipool kinetic models were used to describe the intradialytic trends of electrolytes, breakdown products, and body fluids volumes during hemodialysis. Therapy customization can be achieved by the identification of parameters, allowing patient-specific modulation of mass and fluid balance across dialyzer, capillary, and cell membranes. This study wants to evaluate the possibility to use this approach to predict the patient's intradialytic response.

METHODS

6 sessions of 68 patients (DialysIS© project) were considered. Data from the first three sessions were used to train the model, identifying the patient-specific parameters, that, together with the treatment settings and the patient's data at the session start, could be used for predicting the patient's specific time course of solutes and fluids along the sessions. Na+ , K+ , Cl- , Ca2+ , HCO3 - , and urea plasmatic concentrations and hematic volume deviations from clinical data were evaluated.

RESULTS

nRMSE predictive error is on average equal to 4.76% when describing the training sessions, and only increases by 0.97 percentage points on average in independent sessions of the same patient.

CONCLUSIONS

The proposed predictive approach represents a first step in the development of tools to support the clinician in tailoring the patient's prescription.

A comparative study of the definitions of intradialytic hypotension correlated with increased mortality to identify universal predictors

Intradialytic hypotension (IDH) is a common complication in patients undergoing hemodialysis therapy. No consensus on the definition of intradialytic hypotension has been established so far. As a result, coherent and consistent evaluation of its effects and causes is difficult. Some studies have highlighted existing correlations between certain definitions of IDH and the risk of mortality for the patients. This work is mainly focused on these definitions. Our aim is to understand if different IDH definitions, all correlated with increased mortality risk, catch the same onset mechanisms or dynamics. To check whether the dynamics captured by these definitions are similar, we performed analyses of the incidence, of the IDH event onset timing, and checked whether there were similarities between the definitions in those aspects. We evaluated how these definitions overlap with each other and we evaluated which common factors could allow identifying patients at risk of IDH at the beginning of a dialysis session. The definitions of IDH we analyzed through statistical and machine learning approaches, showed a variable incidence on the HD sessions and had different onset time. We found that the set of parameters relevant for the prediction of the IDH was not always the same for the definitions considered. However, it can be observed that some predictors, such as the presence of comorbidities such as diabetes or heart disease, and a low pre-dialysis diastolic blood pressure, have shown universal relevance in highlighting an increased risk of IDH during the treatment. Among those parameters, the one that showed a major importance is the diabetes status of the patients. Diabetes or heart disease presence are permanent risk factors pointing out an increased IDH risk during the treatments, while, pre-dialysis diastolic blood pressure is instead a parameter that can change at every session and should be used to evaluate the specific risk to develop IDH for each session. The identified parameters could be used in the future to train more complex prediction models.

Human umbilical cord blood cells suffer major modification by fixatives and anticoagulants

Introduction: Developing techniques for the tagless isolation of homogeneous cell populations in physiological-like conditions is of great interest in medical research. A particular case is Gravitational Field-Flow Fractionation (GrFFF), which can be run avoiding cell fixation, and that was already used to separate viable cells. Cell dimensions have a key role in this process. However, their dimensions under physiological-like conditions are not easily known since the most diffused measurement techniques are performed on fixed cells, and the fixation used to preserve tissues can alter the cell size. This work aims to obtain and compare cell size data under physiological-like conditions and in the presence of a fixative.

Methods: We developed a new protocol that allows the analysis of blood cells in different conditions. Then, we applied it to obtain a dataset of human cord blood cell dimensions from 32 subjects, comparing two tubes with anticoagulants (EDTA and Citrate) and two tubes with different preservatives (CellRescue and CellSave). We analyzed a total of 2071 cells by using confocal microscopy via bio-imaging to assess dimensions (cellular and nuclear) and morphology.

Results: Cell diameter measured does not differ when using the different anticoagulants, except for the increase reported for monocyte in the presence of citrate. Instead, cell dimensions differ when comparing anticoagulants and cell preservative tubes, with a few exceptions. Cells characterized by high cytoplasm content show a reduction in their size, while morphology appears always preserved. In a subgroup of cells, 3D reconstruction was performed. Cell and nucleus volumes were estimated using different methods (specific 3D tool or reconstruction from 2D projection).

Discussion: We found that some cell types benefit from a complete 3D analysis because they contain non-spherical structures (mainly for cells characterized by poly-lobated nucleus). Overall, we showed the effect of the preservatives mixture on cell dimensions. Such an effect must be considered when dealing with problems highly dependent on cell size, such as GrFFF. Additionally, such information is crucial in computational models increasingly being employed to simulate biological events.

Modified Acid Phosphatase Assay for Assessing the Extent of Heating of Canned Picnics and Hams: Interlaboratory Study

Determination of acid phosphatase (E.C. 3.1.3.2.) activity in meat and meat products Is based on spectrophotometric measurement of free phenol released from phenyl phosphate substrate during enzyme catalysis under prescribed conditions. Precision parameters of a new modified phosphatase assay, proposed for determination of extent of heating of canned picnics and hams, were evaluated in an interlaboratory study with 10 (1 German, 2 Italian, and 7 Hungarian) participating laboratories. The test materials were 5 lean meat batters subjected to different heat treatments (i.e., with different levels of phosphatase activity). The materials were presented to participants as 10 randomly coded samples (2 blind replicates of each material). The interlaboratory study was then repeated with 3 test materials and 2 blind replicates (3 × 2) prepared in the same way. The repeatability relative standard deviation (RSDr), outliers excluded, varied from 2.2 to 10.7%, and the reproducibility relative standard deviation (RSDR) varied from 12.6 to 25.3%. Results were compared with other data in the literature. The sensitivity of the new modified phosphatase assay was also compared with that of the original procedure described in USDA Chemistry Laboratory Guidebook. A higher sensitivity was observed for the method described in this paper. However, the method’s reproducibility was poorer than that of common analytical methods. Although high, the variability may still be acceptable for determining phosphatase activity to assess extent of heat treatment of canned picnics and hams.

A computational model for microcirculation including Fahraeus-Lindqvist effect, plasma skimming and fluid exchange with the tissue interstitium

We present a two-phase model for microcirculation that describes the interaction of plasma with red blood cells. The model takes into account of typical effects characterizing the microcirculation, such as the Fahraeus-Lindqvist effect and plasma skimming. Besides these features, the model describes the interaction of capillaries with the surrounding tissue. More precisely, the model accounts for the interaction of capillary transmural flow with the surrounding interstitial pressure. Furthermore, the capillaries are represented as one-dimensional channels with arbitrary, possibly curved configuration. The latter two features rely on the unique ability of the model to account for variations of flow rate and pressure along the axis of the capillary, according to a local differential formulation of mass and momentum conservation. Indeed, the model stands on a solid mathematical foundation, which is also addressed in this work. In particular, we present the model derivation, the variational formulation, and its approximation using the finite element method. Finally, we conclude the work with a comparative computational study of the importance of the Fahraeus-Lindqvist, plasma skimming, and capillary leakage effects on the distribution of flow in a microvascular network.

Numerical simulations of the microvascular fluid balance with a non-linear model of the lymphatic system

Fluid homeostasis is required for life. Processes involved in fluid balance are strongly related to exchanges at the microvascular level. Computational models have been presented in the literature to analyze the microvascular-interstitial interactions. As far as we know, none of those models consider a physiological description for the lymphatic drainage-interstitial pressure relation. We develop a computational model that consists of a network of straight cylindrical vessels and an isotropic porous media with a uniformly distributed sink term acting as the lymphatic system. In order to describe the lymphatic flow rate, a non-linear function of the interstitial pressure is defined, based on literature data on the lymphatic system. The proposed model of lymphatic drainage is compared to a linear one, as is typically used in computational models. To evaluate the response of the model, the two are compared with reference to both physiological and pathological conditions. Differences in the local fluid dynamic description have been observed using the non-linear model. In particular, the distribution of interstitial pressure is heterogeneous in all the cases analyzed. The resulting averaged values of the interstitial pressure are also different, and they agree with literature data when using the non-linear model. This work highlights the key role of lymphatic drainage and its modeling when studying the fluid balance in microcirculation for both to physiological and pathological conditions, e.g. uremia.

A Bayesian approach for the identification of patient-specific parameters in a dialysis kinetic model

Hemodialysis is the most common therapy to treat renal insufficiency. However, notwithstanding the recent improvements, hemodialysis is still associated with a non-negligible rate of comorbidities, which could be reduced by customizing the treatment. Many differential compartment models have been developed to describe the mass balance of blood electrolytes and catabolites during hemodialysis, with the goal of improving and controlling hemodialysis sessions. However, these models often refer to an average uremic patient, while on the contrary the clinical need for customization requires patient-specific models. In this work, we assume that the customization can be obtained by means of patient-specific model parameters. We propose and validate a Bayesian approach to estimate the patient-specific parameters of a multi-compartment model, and to predict the single patient's response to the treatment, in order to prevent intra-dialysis complications. The likelihood function is obtained by means of a discretized version of the multi-compartment model, where the discretization is in terms of a Runge-Kutta method to guarantee convergence, and the posterior densities of model parameters are obtained through Markov Chain Monte Carlo simulation. Results show fair estimations and the applicability in the clinical practice.

A New Method to Evaluate Patient Characteristic Response to Ultrafiltration during Hemodialysis

Background.

Several factors are involved in the pathogenesis of dialysis discomfort interfering with optimal fluid removal and reducing the efficacy of the treatment; the most important one is a decrease in blood volume caused by an imbalance between ultrafiltration (UF) and plasma refilling (PR) rates.

Objectives.

This study is aimed at devising a method to tailor the dialysis therapy to each individual patient, by analyzing the relationship between PR and UF during the sessions in stable patients and widening the knowledge of fluid exchanges during the treatment.

Methods.

Thirty stable patients undergoing maintenance hemodialysis were enrolled. Three dialysis sessions were monitored for each patient; systemic pressure, blood composition, blood volume % variation, weight loss and conductivity were recorded repeatedly. A Plasma Refilling Index (PRI), defined and calculated by means of parameters measured throughout the dialysis, was introduced as a novel instrument to study plasma refilling phenomena.

Results.

The PRI provides understanding of patient response (in terms of plasma refilling) to the set UF. In the monitored sessions, the PRI trend is found to be characteristic of each patient; a PRI course that is at variance with the characteristic trend is a signal of inadequate or unusual dialysis scheduling. Moreover, statistical analysis highlights two different PRI trends during the first hour and during the rest of the treatment, suggesting the presence of different treatment phases.

Conclusion.

The main advantage of the PRI index is that it is non-invasive peculiar to each patient and easy to compute in a dialysis routine based on online data recorded by the monitor. A deviation from the characteristic trend may be a warning for the clinician. The analysis of the PRI trend also suggests how to modulate UF as a function of interstitial to intravascular fluid removal balance during dialysis.

Assessment of intradialysis calcium mass balance by a single pool variable-volume calcium kinetic model

INTRODUCTION

A reliable method of intradialysis calcium mass balance quantification is far from been established. We herein investigated the use of a single-pool variable-volume Calcium kinetic model to assess calcium mass balance in chronic and stable dialysis patients.

METHODS

Thirty-four patients on thrice-weekly HD were studied during 240 dialysis sessions. All patients were dialyzed with a nominal total calcium concentration of 1.50 mmol/L. The main assumption of the model is that the calcium distribution volume is equal to the extracellular volume during dialysis. This hypothesis is assumed valid if measured and predicted end dialysis plasma water ionized calcium concentrations are equal. A difference between predicted and measured end-dialysis ionized plasma water calcium concentration is a deviation on our main hypothesis, meaning that a substantial amount of calcium is exchanged between the extracellular volume and a nonmodeled compartment.

FINDINGS

The difference between predicted and measured values was 0.02 mmol/L (range -0.08:0.16 mmol/L). With a mean ionized dialysate calcium concentration of 1.25 mmol/L, calcium mass balance was on average negative (mean ± SD -0.84 ± 1.33 mmol, range -5.42:2.75). Predialysis ionized plasma water concentration and total ultrafiltrate were the most important predictors of calcium mass balance. A significant mobilization of calcium from the extracellular pool to a nonmodeled pool was calculated in a group of patients.

DISCUSSION

The proposed single pool variable-volume Calcium kinetic model is adequate for prediction and quantification of intradialysis calcium mass balance, it can evaluate the eventual calcium transfer outside the extracellular pool in clinical practice.

How to extract clinically useful information from large amount of dialysis related stored data

The basic storage infrastructure used to gather data from the technological evolution also in the healthcare field was leading to the storing into public or private repository of even higher quantities of data related to patients and their pathological evolution. Big data techniques are spreading also in medical research. By these techniques is possible extract information from complex heterogeneous sources, realizing longitudinal studies focused to correlate the patient status with biometric parameters. In our work we develop a common data infrastructure involving 4 clinical dialysis centers between Lombardy and Switzerland. The common platform has been build to store large amount of clinical data related to 716 dialysis session of 70 patient. The platform is made up by a combination of a MySQL(®) database (Dialysis Database) and a MATLAB-based mining library (Dialysis MATlib). A statistical analysis of these data has been performed on the data gathered. These analyses led to the development of two clinical indexes, representing an example of transformation of big data into clinical information.

Integrated model of endothelial NO regulation and systemic circulation for the comparison between pulsatile and continuous perfusion

Many experimental studies concerning nitric oxide (NO) release from endothelium and its vasodilative action are available in the literature, but no analytical description or modeling of these phenomena can be found. On the contrary, a large modeling literature is available concerning the other cardiovascular control mechanisms, such as the myogenic and metabolic control. In order to analytically describe these phenomena, a model of the endothelial control (defined in the Laplace domain and based on experimental data) was implemented and integrated with a lumped-parameter model of the systemic circulation, consisting of large artery segments and peripheral networks. The endothelial regulation model was based on the hypothesis proposed by Kuchan and Frangos, considering that NO release from the endothelium is generated by two parallel paths. The whole model was then applied to study the different vascular constriction or dilation under continuous or pulsatile perfusion, in order to better understand the clinical evidences of a poor organ perfusion in the presence of continuous with respect to pulsatile cardiopulmonary bypass. According to the experimental evidences, the main results obtained from the model revealed a widespread vascular constriction under continuous perfusion with respect to pulsatile. This result remains constant in the presence of different conditions of blood parameters and flow waveform.

The morphotype in a group of peri-pubertal soccer players

Few morphological data are available for adolescent soccer players (SP), a lack that could affect young-age talent selection. In order to collect lacking data for SP, 50 performers aged 13.1 +/- 0.5 years old were checked in one of the main "vivariums" of talented "A League" SP. All subjects were measured according to the Heath/Carter anthropometric somatotype method and subsequently, the results were compared with those found in relevant literature for adolescents. To gain further insight, the sample was subdivided into two classes, according to their performance level: beginners (B, n = 26) and those experienced (E, n = 24). Between B and E subjects significant differences were found for: weight, abdominal skinfold, calf circumference, body density (0.05 < p < 0.01); height, tricipital skinfold, humerus biepicondylar width, ponderal index, LBW, endo and ectomorph components (p < 0.01). B somatotype resulted to be: 1.6-4.3-3.5; while E: 2.2-4.5-2.9. Both in E and B sub-groups the distribution of somatotypes according to their component dominance revealed to be rather similar, indicating a substantial homogeneity inside the subgroups. When compared with adult SP, the whole sample shows a morphotype that is already adapted for soccer. Observing this, it is possible to infer that our adolescent group contains the morphotype needed to perform well (and probably to excel), in the considered sporting activity.

Somatotype of Italian rugby players

Our aim was to collect lacking first-hand data on Italian rugby players. The Heath/Carter anthropometric somatotype method was applied to 28 "A" League performers (RP) aged 25 +/- 3.9 years of age. Their somatotypes and dimensions were compared with those found in previous studies on athletes involved in the same sporting activity, with data collected on 25 "sedentary" young Italians, and with Bailey et al.'s study on Canadians (1982). On average, the RP group resulted as being endomorphic mesomorphs (3.1 +/- 1.1 - 5.6 +/- 1.3 - 1.4 +/- 1.1), a result that is congruent with international data. They differed significantly from the balanced mesomorph CG (2.3 +/- 1.0 - 4.5 +/- 1.2 - 2.5 +/- 1.4) for all the measurements taken, apart from bi-epycondylar width. The peculiar somatotype scores found are congruent with the needs of rugby, an aerobic-anaerobic discipline which requires performers with great muscular power associated with a capacity to furnish energy, mainly through the anaerobic metabolism.

[Evaluation of the compliance to the proposal of anti-rubella vaccination]

The incidence of acquired rubella in the females who have been interested by the proposal of vaccination, according to the selective strategy adopted in Italy, allows to appraise the national adhesion to this proposal lower than 50%. The values registered in Venetia suggest an adhesion rate near 80%, which is confirmed by datas about the regional use of vaccine. The punctual verify of vaccinal covering rate in a little Sanitary District in the Province of Treviso points out values higher than 90%.

Alcohol-induced bone marrow damage: status before and after a 4-week period of abstinence from alcohol with or without disulfiram. A randomized bone marrow study in alcohol-dependent individuals

The investigation described in this paper has confirmed the existence of alcohol-induced bone marrow damage as a nosological entity in alcohol-dependent individuals. In our patients total abstinence from alcohol without disulfiram or similar drugs led to reversal of the pathological findings in peripheral blood and in bone marrow. In patients undergoing detoxification while taking disulfiram, on the other hand, the pathological bone marrow findings, especially erythropoiesis associated with impaired iron utilization, persisted. The metabolic pathway of disulfiram is discussed. It is probably justifiable to assume that the toxin responsible for alcohol-induced bone marrow damage is the ethanol metabolite acetaldehyde. The persistence of erythropoiesis with impaired iron utilization during abstinence from alcohol and treatment with disulfiram is also of importance in differential diagnosis from the myelodysplastic syndrome (MDS), and especially from refractory anaemia with ring sideroblasts (RARS). For this reason, where the situation is unclear, it is essential that a diagnosis of MDS be supported by specific investigations such as cell cultures, cytogenetic analyses, etc. It is the first time that the toxic, alcohol-like-effect of disulfiram on haematopoiesis is discussed.