Modifications of lung microbiota structure in traumatic brain injury ventilated patients according to time and enteral feeding formulas: a prospective randomized study.

BACKGROUND: Specialized diets enriched with immune nutrients could be an important supplement in patients (pts) with acute traumatic brain injury (TBI). Omega-3 and arginine may interact with immune response and microbiota. No data are available about the role of the specialized diets in modulating the lung microbiota, and little is known about the influence of lung microbiota structure in development of ventilator-associated pneumonia (VAP) in TBI pts. The aims of this study are to evaluate the impact of specific nutrients on the lung microbiota and the variation of lung microbiota in TBI pts developing VAP. METHODS: A cohort of 31 TBI pts requiring mechanical ventilation in ICU was randomized for treatment with specialized (16pts) or standard nutrition (15pts). Alpha and beta diversity of lung microbiota were analyzed from bronco Alveolar Lavage (BAL) samples collected at admission and 7 days post-ICU admission in both groups. A further analysis was carried out on the same samples retrospectively grouped in VAP or no VAP pts. RESULTS: None developed VAP in the first week. Thereafter, ten out of thirty-one pts developed VAP. The BAL microbiota on VAP group showed significant differences in beta diversity and Staphylococcus and Acinetobacter Genera were high. The specialized nutrition had influence on beta diversity that reached statistical significance only in Bray-Curtis distance. CONCLUSION: Our data suggest that TBI patients who developed VAP during ICU stay have different structures of BAL microbiota either at admission and at 7 days post-ICU admission, while no correlation has been observed between different enteral formulas and microbiota composition in terms of richness and evenness. These findings suggest that targeting the lung microbiota may be a promising approach for preventing infections in critically ill patients.

Accountable care organization reform: past challenges and future opportunities for public health.

OBJECTIVES: This study aimed to analyze the regulatory landscape that governs accountable care organizations (ACOs) in the United States and the effects on organizational participation. STUDY DESIGN: This was a descriptive study of existing and prior regulations that govern ACOs in the United States. In addition, we analyze data on ACO participation over time. METHODS: We used content analysis methods to the regulatory framework governing ACOs. Authors read and analyzed all regulations since 2012. RESULTS: ACO participation has been undermined by a shifting regulatory landscape. Under the Trump administration, ACOs have had to take on additional risk earlier and that has contributed to the lowest number of participating organizations in the program's history. CONCLUSIONS: The Biden administration has the opportunity to remake regulations governing ACO development and support.

TICACOS international: A multi-center, randomized, prospective controlled study comparing tight calorie control versus Liberal calorie administration study.

Since the first TICACOS study, 3 additional studies have been published comparing a medical nutrition therapy guided by indirect calorimetry to a regimen prescribed on the basis of predictive equations. A recent guidelines document included a meta-analysis including these 4 papers and found a trend for improvement (OR 0.98-1.48) in favor of medical nutrition therapy guided by indirect calorimetry in terms of survival. The aim of our study was to perform a multicenter prospective, randomized, controlled non blinded study in critically patients to assess the added value for measuring daily resting energy expenditure as a guide for nutritional support. The primary objective was to decrease infectious rate of these critically ill patients. MATERIAL AND METHODS: This phase III, multi-center, randomized, controlled non blinded study was planned to include 580 newly-admitted, adult ventilated ICU patients that were planned to stay more than 48 h in the ICU departments. The nutritional support was aimed to meet 80-100% of energy requirement measured by indirect calorimetry. The calorie needs were determined by IC in the Study group and by an equation (20-25 kcal/kg ideal body weight/day) in the Control Group. The ICU staff was trained to strive to supply 80-100% of a patient's energy requirements through artificial nutrition, preferably enteral feeding. Primary endpoint was infection rate and secondary endpoints included other morbidities and mortality during ICU, at 90 and 180 days. Comparison between the study and the control group was performed using T test for equality of means (independent samples test). Correlations were performed using the Pearson correlation test. A p level of 0.05 or below was considered as significant. Cross tabs procedure used Chi-square test for testing differences in complication rates, length of stay and length of ventilation. Correlations between energy balances and complications was also be tested using one way analysis as well as ANOVA analysis between groups and within groups. Kaplan Meir curves assessed the proportion of surviving patients in the 2 groups. RESULTS: Seven centers with a calorimeter available participated to the study. Due to slow inclusion rate, the study was stopped after 6 years and after inclusion of 417 patients only. From the 417 intended to treat patients, 339 followed the protocol. There was no differences between control and study groups in terms of age, sex BMI, SOFA (7.1 ± 3.1 vs 7.4 ± 3.3) and APACHE II scores (22.4 ± 7.9 vs 22.2 ± 7.4). The rate of infection (40 vs 31), including pneumonia rate, need for surgery, dialysis requirement, length of ventilation, ICU length of stay, and hospital length of stay were not different between groups. Mortality (30 in the control vs 21 in the study group) was not significantly different between groups. The decreased mortality observed in the study group when added to previous studies may have a positive effect on the meta-analysis previously published. CONCLUSION: Tight Calorie Control guided by indirect calorimetry decreased the rate of infection and mortality but not significantly. This may be explained by the not relatively small sample size. There results together with the previous 4 prospective randomized studies, may improve the results of the meta-analysis exploring the effects of IC guided nutrition on mortality.

Reducing the knowledge to action gap in hospital nutrition care - Developing and implementing nutritionDay 2.0.

BACKGROUND & AIMS: In hospital nutrition care the difficulty of translating knowledge to action often leads to inadequate management of patients with malnutrition. nutritionDay, an annual cross-sectional survey has been assessing nutrition care in healthcare institutions in 66 countries since 2006. While initial efforts led to increased awareness of malnutrition, specific local remedial actions rarely followed. Thus, reducing the Knowledge-to-action (KTA) gap in nutrition care requires more robust and focused strategies. This study describes the strategy, methods, instruments and experience of developing and implementing nutritionDay 2.0, an audit and feedback intervention that uses quality and economic indicators, feedback, benchmarking and self-defined action strategies to reduce the KTA gap in hospital nutrition care. METHODS: We used an evidence based multi-professional mixed-methods approach to develop and implement nutritionDay 2.0 This audit and feedback intervention is driven by a Knowledge-to-Action framework complemented with robust stakeholder analysis. Further evidence was synthesized from the literature, online surveys, a pilot study, World Cafés and individual expert feedback involving international health care professionals, nutrition care scientists and patients. RESULTS: The process of developing and implementing nutritionDay 2.0 over three years resulted in a new audit questionnaire based on 36 nutrition care quality and economic indicators at hospital, unit and patient levels, a new action-oriented feedback and benchmarking report and a unit-level personalizable action plan template. The evaluation of nutritionDay 2.0 is ongoing and will include satisfaction and utility of nutritionDay 2.0 tools and short-, mid- and long-term effects on the KTA gap. CONCLUSION: In clinical practice, nutritionDay 2.0 has the potential to promote behavioural and practice changes and improve hospital nutrition care outcomes. In research, the data generated advances knowledge about institutional malnutrition and quality of hospital nutrition care. The ongoing evaluation of the initiative will reveal how far the KTA gap in hospital nutrition care was addressed and facilitate the understanding of the mechanisms needed for successful audit and feedback. TRIAL REGISTRATION: Registration in clinicaltrials.gov: Identifier: NCT02820246.

GLIM criteria for the diagnosis of malnutrition - A consensus report from the global clinical nutrition community.

RATIONALE: This initiative is focused on building a global consensus around core diagnostic criteria for malnutrition in adults in clinical settings. METHODS: In January 2016, the Global Leadership Initiative on Malnutrition (GLIM) was convened by several of the major global clinical nutrition societies. GLIM appointed a core leadership committee and a supporting working group with representatives bringing additional global diversity and expertise. Empirical consensus was reached through a series of face-to-face meetings, telephone conferences, and e-mail communications. RESULTS: A two-step approach for the malnutrition diagnosis was selected, i.e., first screening to identify "at risk" status by the use of any validated screening tool, and second, assessment for diagnosis and grading the severity of malnutrition. The malnutrition criteria for consideration were retrieved from existing approaches for screening and assessment. Potential criteria were subjected to a ballot among the GLIM core and supporting working group members. The top five ranked criteria included three phenotypic criteria (weight loss, low body mass index, and reduced muscle mass) and two etiologic criteria (reduced food intake or assimilation, and inflammation or disease burden). To diagnose malnutrition at least one phenotypic criterion and one etiologic criterion should be present. Phenotypic metrics for grading severity as Stage 1 (moderate) and Stage 2 (severe) malnutrition are proposed. It is recommended that the etiologic criteria be used to guide intervention and anticipated outcomes. The recommended approach supports classification of malnutrition into four etiology-related diagnosis categories. CONCLUSION: A consensus scheme for diagnosing malnutrition in adults in clinical settings on a global scale is proposed. Next steps are to secure further collaboration and endorsements from leading nutrition professional societies, to identify overlaps with syndromes like cachexia and sarcopenia, and to promote dissemination, validation studies, and feedback. The diagnostic construct should be re-considered every 3-5 years.

Prognostic value of energy expenditure and respiratory quotient measuring in patients with liver cirrhosis.

BACKGROUND & AIMS: Resting energy expenditure (REE) and respiratory quotient (RQ) as measured by indirect calorimetry (IC) may correlate with muscle mass and represent prognostic indicators in treating patients with liver cirrhosis. We aimed to assess the correlation of IC-measured REE and RQ with skeletal muscle mass (SM), mortality, and REE values as estimated by Harris-Benedict, European guidelines (EG), and Brazilian guidelines-DITEN (BG) equations in patients with liver cirrhosis. METHODS: In this prospectively designed study, REE was measured in 126 male patients with liver cirrhosis by IC and predicted by Harris-Benedict, EG (35 kcal/kg current weight), and BG (30 kcal/kg current weight) guidelines. Measurements were obtained at the time of admission to the study. Body composition was determined by whole-body dual-energy X-ray absorptiometry. The association between REE and 3-year survival was investigated. RESULTS: Cirrhosis etiology was classified as alcohol related (59.0%), viral (20.1%), cryptogenic (11.8%), or other (9.0%). Mean Child-Pugh and MELD indexes were 8.30 ± 2.0 and 14.38 ± 6.12, respectively. RQ showed a moderate correlation with SM (r = 0.64), while IC-measured REE was inversely associated with mortality (multivariate Cox Regression, HR = 0.88, 95% CI: 0.78; 1, p = 0.04). Among the predictive equations for REE, only Harris-Benedict yielded values close to the IC, with a positive Pearson correlation (r = 0.77), excellent accuracy (Cb = 0.98), and positive Lin's concordance correlation (CCC = 0.75). However, a large standard deviation was observed; HB-measured REE did not correlate with mortality. CONCLUSIONS: RQ and REE, as measured by IC, may be valuable tools for evaluating the severity of cirrhosis, by reflecting SM and predicting mortality, respectively. The predictive equations for REE included in this study cannot replace IC for this purpose. REGISTERED AT: www.clinicalTrials.gov (NCT02421848).

GLIM criteria for the diagnosis of malnutrition - A consensus report from the global clinical nutrition community.

RATIONALE: This initiative is focused on building a global consensus around core diagnostic criteria for malnutrition in adults in clinical settings. METHODS: In January 2016, the Global Leadership Initiative on Malnutrition (GLIM) was convened by several of the major global clinical nutrition societies. GLIM appointed a core leadership committee and a supporting working group with representatives bringing additional global diversity and expertise. Empirical consensus was reached through a series of face-to-face meetings, telephone conferences, and e-mail communications. RESULTS: A two-step approach for the malnutrition diagnosis was selected, i.e., first screening to identify "at risk" status by the use of any validated screening tool, and second, assessment for diagnosis and grading the severity of malnutrition. The malnutrition criteria for consideration were retrieved from existing approaches for screening and assessment. Potential criteria were subjected to a ballot among the GLIM core and supporting working group members. The top five ranked criteria included three phenotypic criteria (non-volitional weight loss, low body mass index, and reduced muscle mass) and two etiologic criteria (reduced food intake or assimilation, and inflammation or disease burden). To diagnose malnutrition at least one phenotypic criterion and one etiologic criterion should be present. Phenotypic metrics for grading severity as Stage 1 (moderate) and Stage 2 (severe) malnutrition are proposed. It is recommended that the etiologic criteria be used to guide intervention and anticipated outcomes. The recommended approach supports classification of malnutrition into four etiology-related diagnosis categories. CONCLUSION: A consensus scheme for diagnosing malnutrition in adults in clinical settings on a global scale is proposed. Next steps are to secure further collaboration and endorsements from leading nutrition professional societies, to identify overlaps with syndromes like cachexia and sarcopenia, and to promote dissemination, validation studies, and feedback. The diagnostic construct should be re-considered every 3-5 years.

Validation of carbon dioxide production (VCO2) as a tool to calculate resting energy expenditure (REE) in mechanically ventilated critically ill patients: a retrospective observational study.

BACKGROUND: Indirect calorimetry (IC) measurement is considered the gold standard for the assessment of resting energy expenditure (REE). It is based on the measurement of oxygen and carbon dioxide consumption (VO2 and VCO2, respectively). However, its use is limited by cost and technical issues. It has been proposed that, in critically ill patients, the analysis of VCO2 obtained from the ventilator alone may be used as an accurate method to assess REE in ventilated patients. This retrospective study aimed to assess the accuracy of VCO2 measurement alone in the determination of REE. METHODS: This was a retrospective study conducted at the general intensive care unit of a single university-affiliated tertiary medical center. Patients included were invasively ventilated and their REE was measured by using IC. The respiratory quotients (RQs) were set at 0.8, 0.85, and 0.89. Data were collected from computerized patient files. REE obtained from the ventilator by using VCO2 (REE-VCO2) alone was compared with REE obtained from IC (REE-IC). RESULTS: Measurements were obtained for 80 patients, and 497 REE-IC measurements were compared with REE-VCO2 obtained at the same time. The mean REE-IC was 2059.5 ± 491.7 kcal/d. The mean REE-RQs corresponding to RQs of 0.80, 0.85, and 0.89 were 1936.8 ± 680.0, 2017.8 ± 708.8, and 2122.1 ± 745.4 kcal/d, respectively. REE-VCO2 derived from an RQ of 0.85 had the lowest mean difference from REE-IC. Whereas accuracy was higher using an RQ of 0.85, agreement (between 85% and 115%) was highest using an RQ of 0.89. CONCLUSIONS: The level of agreement of REE obtained from VCO2 readings with REE obtained from IC was generally low. IC continues to be the recommended method for REE assessment.

Randomised clinical trial: 2% taurolidine versus 0.9% saline locking in patients on home parenteral nutrition.

BACKGROUND: The catheter lock solutions 2% taurolidine and 0.9% saline are both used to prevent catheter-related bloodstream infections (CRBSIs) in home parenteral nutrition patients. AIMS: To compare the effectiveness and safety of taurolidine and saline. METHODS: This multicentre double-blinded trial randomly assigned home parenteral nutrition patients to use either 2% taurolidine or 0.9% saline for 1 year. Patients were stratified in a new catheter group and a pre-existing catheter group. Primary outcome was the rate of CRBSIs/1000 catheter days in the new catheter group and pre-existing catheter group, separately. RESULTS: We randomised 105 patients, of which 102 were analysed as modified intention-to-treat population. In the new catheter group, rates of CRBSIs/1000 catheter days were 0.29 and 1.49 in the taurolidine and saline arm respectively (relative risk, 0.20; 95% CI, 0.04-0.71; P = 0.009). In the pre-existing catheter group, rates of CRBSIs/1000 catheter days were 0.39 and 1.32 in the taurolidine and saline arm respectively (relative risk, 0.30; 95% CI, 0.03-1.82; P = 0.25). Excluding one outlier patient in the taurolidine arm, mean costs per patient were $1865 for taurolidine and $4454 for saline (P = 0.03). Drug-related adverse events were rare and generally mild. CONCLUSIONS: In the new catheter group, taurolidine showed a clear decrease in CRBSI rate. In the pre-existing catheter group, no superiority of taurolidine could be demonstrated, most likely due to underpowering. Overall, taurolidine reduced the risk for CRBSIs by more than four times. Given its favourable safety and cost profile, taurolidine locking should be considered as an additional strategy to prevent CRBSIs. TRIAL REGISTRATION: Clinicaltrials.gov, identifier: NCT01826526.

NMR spin-rotation relaxation and diffusion of methane.

The translational diffusion-coefficient and the spin-rotation contribution to the 1H NMR relaxation rate for methane (CH4) are investigated using MD (molecular dynamics) simulations, over a wide range of densities and temperatures, spanning the liquid, supercritical, and gas phases. The simulated diffusion-coefficients agree well with measurements, without any adjustable parameters in the interpretation of the simulations. A minimization technique is developed to compute the angular velocity for non-rigid spherical molecules, which is used to simulate the autocorrelation function for spin-rotation interactions. With increasing diffusivity, the autocorrelation function shows increasing deviations from the single-exponential decay predicted by the Langevin theory for rigid spheres, and the deviations are quantified using inverse Laplace transforms. The 1H spin-rotation relaxation rate derived from the autocorrelation function using the "kinetic model" agrees well with measurements in the supercritical/gas phase, while the relaxation rate derived using the "diffusion model" agrees well with measurements in the liquid phase. 1H spin-rotation relaxation is shown to dominate over the MD-simulated 1H-1H dipole-dipole relaxation at high diffusivity, while the opposite is found at low diffusivity. At high diffusivity, the simulated spin-rotation correlation time agrees with the kinetic collision time for gases, which is used to derive a new expression for 1H spin-rotation relaxation, without any adjustable parameters.

Role of internal motions and molecular geometry on the NMR relaxation of hydrocarbons.

The role of internal motions and molecular geometry on 1H NMR relaxation rates in liquid-state hydrocarbons is investigated using MD (molecular dynamics) simulations of the autocorrelation functions for intramolecular and intermolecular 1H-1H dipole-dipole interactions. The effects of molecular geometry and internal motions on the functional form of the autocorrelation functions are studied by comparing symmetric molecules such as neopentane and benzene to corresponding straight-chain alkanes n-pentane and n-hexane, respectively. Comparison of rigid versus flexible molecules shows that internal motions cause the intramolecular and intermolecular correlation-times to get significantly shorter, and the corresponding relaxation rates to get significantly smaller, especially for longer-chain n-alkanes. Site-by-site simulations of 1H's across the chains indicate significant variations in correlation times and relaxation rates across the molecule, and comparison with measurements reveals insights into cross-relaxation effects. Furthermore, the simulations reveal new insights into the relative strength of intramolecular versus intermolecular relaxation as a function of internal motions, as a function of molecular geometry, and on a site-by-site basis across the chain.

Emergency electroencephalogram: Usefulness in the diagnosis of nonconvulsive status epilepticus by the on-call neurologist. / Uso de la electroencefalografía urgente por el neurólogo de guardia: utilidad en el diagnóstico del estatus epiléptico no convulsivo.

INTRODUCTION: We aim to describe the use of emergency electroencephalogram (EmEEG) by the on-call neurologist when nonconvulsive status epilepticus (NCSE) is suspected, and in other indications, in a tertiary hospital. SUBJECTS AND METHODS: Observational retrospective cohort study of emergency EEG (EmEEG) recordings with 8-channel systems performed and analysed by the on-call neurologist in the emergency department and in-hospital wards between July 2013 and May 2015. Variables recorded were sex, age, symptoms, first diagnosis, previous seizure and cause, previous stroke, cancer, brain computed tomography, diagnosis after EEG, treatment, patient progress, routine control EEG (rEEG), and final diagnosis. We analysed frequency data, sensitivity, and specificity in the diagnosis of NCSE. RESULTS: The study included 135 EEG recordings performed in 129 patients; 51.4% were men and their median age was 69 years. In 112 cases (83%), doctors ruled out suspected NCSE because of altered level of consciousness in 42 (37.5%), behavioural abnormalities in 38 (33.9%), and aphasia in 32 (28.5%). The EmEEG diagnosis was NCSE in 37 patients (33%), and this was confirmed in 35 (94.6%) as the final diagnosis. In 3 other cases, NCSE was the diagnosis on discharge as confirmed by rEEG although the EmEEG missed this condition at first. EmEEG performed to rule out NCSE showed 92.1% sensitivity, 97.2% specificity, a positive predictive value of 94.6%, and a negative predictive value of 96%. CONCLUSIONS: Our experience finds that, in an appropriate clinical context, EmEEG performed by the on-call neurologist is a sensitive and specific tool for diagnosing NCSE.

ESPEN guidelines on definitions and terminology of clinical nutrition.

BACKGROUND: A lack of agreement on definitions and terminology used for nutrition-related concepts and procedures limits the development of clinical nutrition practice and research. OBJECTIVE: This initiative aimed to reach a consensus for terminology for core nutritional concepts and procedures. METHODS: The European Society of Clinical Nutrition and Metabolism (ESPEN) appointed a consensus group of clinical scientists to perform a modified Delphi process that encompassed e-mail communication, face-to-face meetings, in-group ballots and an electronic ESPEN membership Delphi round. RESULTS: Five key areas related to clinical nutrition were identified: concepts; procedures; organisation; delivery; and products. One core concept of clinical nutrition is malnutrition/undernutrition, which includes disease-related malnutrition (DRM) with (eq. cachexia) and without inflammation, and malnutrition/undernutrition without disease, e.g. hunger-related malnutrition. Over-nutrition (overweight and obesity) is another core concept. Sarcopenia and frailty were agreed to be separate conditions often associated with malnutrition. Examples of nutritional procedures identified include screening for subjects at nutritional risk followed by a complete nutritional assessment. Hospital and care facility catering are the basic organizational forms for providing nutrition. Oral nutritional supplementation is the preferred way of nutrition therapy but if inadequate then other forms of medical nutrition therapy, i.e. enteral tube feeding and parenteral (intravenous) nutrition, becomes the major way of nutrient delivery. CONCLUSION: An agreement of basic nutritional terminology to be used in clinical practice, research, and the ESPEN guideline developments has been established. This terminology consensus may help to support future global consensus efforts and updates of classification systems such as the International Classification of Disease (ICD). The continuous growth of knowledge in all areas addressed in this statement will provide the foundation for future revisions.

Carbohydrates and insulin resistance in clinical nutrition: Recommendations from the ESPEN expert group.

Growing evidence underscores the important role of glycemic control in health and recovery from illness. Carbohydrate ingestion in the diet or administration in nutritional support is mandatory, but carbohydrate intake can adversely affect major body organs and tissues if resulting plasma glucose becomes too high, too low, or highly variable. Plasma glucose control is especially important for patients with conditions such as diabetes or metabolic stress resulting from critical illness or surgery. These patients are particularly in need of glycemic management to help lessen glycemic variability and its negative health consequences when nutritional support is administered. Here we report on recent findings and emerging trends in the field based on an ESPEN workshop held in Venice, Italy, 8-9 November 2015. Evidence was discussed on pathophysiology, clinical impact, and nutritional recommendations for carbohydrate utilization and management in nutritional support. The main conclusions were: a) excess glucose and fructose availability may exacerbate metabolic complications in skeletal muscle, adipose tissue, and liver and can result in negative clinical impact; b) low-glycemic index and high-fiber diets, including specialty products for nutritional support, may provide metabolic and clinical benefits in individuals with obesity, insulin resistance, and diabetes; c) in acute conditions such as surgery and critical illness, insulin resistance and elevated circulating glucose levels have a negative impact on patient outcomes and should be prevented through nutritional and/or pharmacological intervention. In such acute settings, efforts should be implemented towards defining optimal plasma glucose targets, avoiding excessive plasma glucose variability, and optimizing glucose control relative to nutritional support.

Characterizing dispersivity and stagnation in porous media using NMR flow propagators.

Low-field nuclear magnetic resonance (NMR) displacement probability distributions (flow propagators) are presented for water flowing through heterogeneous porous materials. Four sedimentary rocks have been chosen as example systems: Dolostone, Bentheimer sandstone, Berea sandstone, and Indiana limestone (in order of decreasing permeability). The fluid displacement is characterized by pre-asymptotic Stokes' flow and so the probability distributions are bimodal, with peaks corresponding to stagnant fluid in dead-end pores and flowing fluid in the connected porosity. Cut-off Gaussian functions are used to fit the flowing and stagnant peaks independently. An effective dispersivity length scale Lv (also known as the mixing length scale) is estimated by fitting the portion of the probability distribution corresponding to the flowing fluid. For the relatively homogeneous Bentheimer sandstone, the ratio of effective dispersivity length scale to effective transport diameter dt is Lv/dt≈16, which is an order of magnitude larger than for randomly packed glass beads where Lv/dt≈1.8. We compare these dispersivity parameters to similar values extracted from a cumulant analysis of the entire propagator. Fitting a cut-off Gaussian avoids the usual complications of analyzing dispersion in the presence of the ubiquitous stagnant fluid, and results in a clear demonstration of the influence of long-range heterogeneities on the dispersivity for flow in real sedimentary rocks.