Assessment of Plasma Resistivity as a Surrogate for Extracellular Fluid Resistivity: Analytical Performance and Impact of Fluid Composition.

Bio-electrical impedance analysis (BIA) is frequently used to assess body composition in man. Its accuracy in patients is limited, possibly because the employed algorithms are based on the assumption that total body electrical resistance (TBER) is exclusively related to body water volume, and that variation in fluid composition and its effect on fluid resistivity can be ignored. This may introduce substantial calculation errors. The aim of this study was to develop an objective method to assess plasma resistivity (ρplasma) based on measurements by a conductivity probe, as a surrogate for extracellular fluid resistivity (ρe). Sample measurements were standardized at body temperature. Analytical variation was 0.6% within runs and 0.9% between runs. The critical difference, i.e. the smallest difference needed to consider changes within individuals significant, was 1.8% for measurements within runs and 4.3% for measurements between runs. The normal range was defined by a mean ± SD of 66.9 ± 1.8 Ω cm. Multiple regression demonstrated that ρplasma was inversely related to plasma sodium and chloride concentrations, and positively related to total protein (overall R2 = 0.92, p < 0.001). In conclusion, ρplasma measurements were sufficiently robust to be useful as a tool to examine and improve the validity of BIA in clinical settings.

Body hydration assessment using bioelectrical impedance vector analysis in neurologically impaired children.

Dehydration is common and frequently under-diagnosed in chronic malnourished children, leading to life-threatening conditions. In this pilot study we applied bioimpedance vector analysis (BIVA) to determine hydration status in 52 neurologically impaired (NI) paediatric patients (14.08 ± 5.32). Clinical and biochemical data were used to define malnutrition and dehydration. Body composition analysis and hydration were also assessed by BIVA and we considered 143 normal-weight healthy subjects (15.0 ± 1.7), as controls for hydration status assessment. BIVA revealed a pathological hydration status in NI children, showing higher resistance (p < 0.001) and reactance values (p = 0.001) compared to controls. No differences in reactance and resistance were detected between well-nourished and under-nourished subjects. Four patients out of 52 showed mild signs of dehydration; no severe dehydration was detected. Laboratory data, suggestive for dehydration, were similar in well-nourished and under-nourished NI subjects. In conclusion, in our sample of NI paediatrics, dehydration according to clinical signs and laboratory data was under-diagnosed. BIVA showed specific bioelectrical characteristics that could be compatible with impaired hydration status. Further studies are necessary to confirm that BIVA may an applicable tool for defining dehydration status and guiding rehydration in NI children.

Validating the use of bioimpedance spectroscopy for assessment of fluid status in children.

BACKGROUND: Bioimpedance spectroscopy (BIS) with a whole-body model to distinguish excess fluid from major body tissue hydration can provide objective assessment of fluid status. BIS is integrated into the Body Composition Monitor (BCM) and is validated in adults, but not children. This study aimed to (1) assess agreement between BCM-measured total body water (TBW) and a gold standard technique in healthy children, (2) compare TBW_BCM with TBW from Urea Kinetic Modelling (UKM) in haemodialysis children and (3) investigate systematic deviation from zero in measured excess fluid in healthy children across paediatric age range. METHODS: TBW_BCM and excess fluid was determined from standard wrist-to-ankle BCM measurement. TBW_D2O was determined from deuterium concentration decline in serial urine samples over 5 days in healthy children. UKM was used to measure body water in children receiving haemodialysis. Agreement between methods was analysed using paired t test and Bland-Altman method comparison. RESULTS: In 61 healthy children (6-14 years, 32 male), mean TBW_BCM and TBW_D2O were 21.1 ± 5.6 and 20.5 ± 5.8 L respectively. There was good agreement between TBW_BCM and TBW_D2O (R2 = 0.97). In six haemodialysis children (4-13 years, 4 male), 45 concomitant measurements over 8 months showed good TBW_BCM and TBW_UKM agreement (mean difference - 0.4 L, 2SD = ± 3.0 L). In 634 healthy children (2-17 years, 300 male), BCM-measured overhydration was - 0.1 ± 0.7 L (10-90th percentile - 0.8 to + 0.6 L). There was no correlation between age and OH (p = 0.28). CONCLUSIONS: These results suggest BCM can be used in children as young as 2 years to measure normally hydrated weight and assess fluid status.

The relationship of subepidermal moisture and early stage pressure injury by visual skin assessment.

AIM: The purpose of this study was to examine the relationship of subepidermal moisture and early stage pressure injury by visual skin assessment in elderly Korean. METHODS: Twenty-nine elderly participated at a particular nursing home. Data were collected for 12 weeks by one wound care nurse. Visual skin assessment and subepidermal moisture value were measured at both buttocks, both ischia, both trochanters, sacrum, and coccyx of each subject once a week. RESULTS: Subepidermal moisture value of stage 1 pressure injury was significantly higher than that of no injury and blanching erythema. After adjustment with covariates, odds ratios of blanching erythema to normal skin and stage 1 pressure injury to blanching erythema/normal skin were statistically significant (p < 0.05). Odds ratio of blanching erythema to normal skin was 1.003 (p = .047) by 1-week prior subepidermal moisture value, and that of concurrent subepidermal moisture value was 1.004 (p = .011). Odds ratio of stage 1 pressure injury to normal skin/blanching erythema was 1.003 (p = .005) by 1-week prior subepidermal moisture value, and that for concurrent subepidermal moisture value was 1.007 (p = .030). Subepidermal moisture was associated with concurrent and future (1 week later) skin damage at both trochanters. CONCLUSION: Subepidermal moisture would be used to predict early skin damage in clinical nursing field for the effective pressure injury prevention.

Multiple-frequency bioimpedance devices for fluid management in people with chronic kidney disease receiving dialysis: a systematic review and economic evaluation.

BACKGROUND: Chronic kidney disease (CKD) is a long-term condition requiring treatment such as conservative management, kidney transplantation or dialysis. To optimise the volume of fluid removed during dialysis (to avoid underhydration or overhydration), people are assigned a 'target weight', which is commonly assessed using clinical methods, such as weight gain between dialysis sessions, pre- and post-dialysis blood pressure and patient-reported symptoms. However, these methods are not precise, and measurement devices based on bioimpedance technology are increasingly used in dialysis centres. Current evidence on the role of bioimpedance devices for fluid management in people with CKD receiving dialysis is limited. OBJECTIVES: To evaluate the clinical effectiveness and cost-effectiveness of multiple-frequency bioimpedance devices versus standard clinical assessment for fluid management in people with CKD receiving dialysis. DATA SOURCES: We searched major electronic databases [e.g. MEDLINE, MEDLINE In-Process & Other Non-Indexed Citations, EMBASE, Science Citation Index and Cochrane Central Register of Controlled Trials (CENTRAL)] conference abstracts and ongoing studies. There were no date restrictions. Searches were undertaken between June and October 2016. REVIEW METHODS: Evidence was considered from randomised controlled trials (RCTs) comparing fluid management by multiple-frequency bioimpedance devices and standard clinical assessment in people receiving dialysis, and non-randomised studies evaluating the use of the devices for fluid management in people receiving dialysis. One reviewer extracted data and assessed the risk of bias of included studies. A second reviewer cross-checked the extracted data. Standard meta-analyses techniques were used to combine results from included studies. A Markov model was developed to assess the cost-effectiveness of the interventions. RESULTS: Five RCTs (with 904 adult participants) and eight non-randomised studies (with 4915 adult participants) assessing the use of the Body Composition Monitor [(BCM) Fresenius Medical Care, Bad Homburg vor der Höhe, Germany] were included. Both absolute overhydration and relative overhydration were significantly lower in patients evaluated using BCM measurements than for those evaluated using standard clinical methods [weighted mean difference -0.44, 95% confidence interval (CI) -0.72 to -0.15, p = 0.003, I2 = 49%; and weighted mean difference -1.84, 95% CI -3.65 to -0.03; p = 0.05, I2 = 52%, respectively]. Pooled effects of bioimpedance monitoring on systolic blood pressure (SBP) (mean difference -2.46 mmHg, 95% CI -5.07 to 0.15 mmHg; p = 0.06, I2 = 0%), arterial stiffness (mean difference -1.18, 95% CI -3.14 to 0.78; p = 0.24, I2 = 92%) and mortality (hazard ratio = 0.689, 95% CI 0.23 to 2.08; p = 0.51) were not statistically significant. The economic evaluation showed that, when dialysis costs were included in the model, the probability of bioimpedance monitoring being cost-effective ranged from 13% to 26% at a willingness-to-pay threshold of £20,000 per quality-adjusted life-year gained. With dialysis costs excluded, the corresponding probabilities of cost-effectiveness ranged from 61% to 67%. LIMITATIONS: Lack of evidence on clinically relevant outcomes, children receiving dialysis, and any multifrequency bioimpedance devices, other than the BCM. CONCLUSIONS: BCM used in addition to clinical assessment may lower overhydration and potentially improve intermediate outcomes, such as SBP, but effects on mortality have not been demonstrated. If dialysis costs are not considered, the incremental cost-effectiveness ratio falls below £20,000, with modest effects on mortality and/or hospitalisation rates. The current findings are not generalisable to paediatric populations nor across other multifrequency bioimpedance devices. FUTURE WORK: Services that routinely use the BCM should report clinically relevant intermediate and long-term outcomes before and after introduction of the device to extend the current evidence base. STUDY REGISTRATION: This study is registered as PROSPERO CRD42016041785. FUNDING: The National Institute for Health Research Health Technology Assessment programme.

Comparison of multiple fluid status assessment methods in patients on chronic hemodialysis.

PURPOSE: Control of hydration status is an important constituent of adequate and efficient hemodialysis (HD) treatment. Nevertheless, there are no precise clinical indices for early recognition of small changes in fluid status of patients undergoing chronic hemodialysis therapy. This study aimed to evaluate and compare the widely used and reliable method of indexed inferior vena cava diameter (IVCDi) with established and more recently available techniques (bioelectrical impedance analysis [BIA], continuous blood volume monitoring [Crit-line], and the B-line score [BLS] with lung ultrasonography) for estimating the hydration status of patients on HD. METHODS: Fifty-three patients undergoing chronic HD thrice weekly were included in the study. Evaluation of hydration status methods (IVCDi, BLS, BIA, and Crit-line) was performed thrice weekly before and after HD. Receiver operating characteristic curve analysis was performed to evaluate the discriminative power of (methods) the BLS, BIA, and Crit-line for predicting over- and underhydration of patients, as determined by the reference method, IVCDi. RESULTS: BLS showed the most promising results in predicting overhydration, as determined by IVCDi, compared with BIA and Crit-line and presented a sensitivity of 77% and specificity of 74%. The accuracy of the BLS was higher than that of BIA (0.81 vs. 0.71, p = 0.032) and Crit-line (0.61, p = 0.001). BLS also showed more promising results in predicting underhydration, as determined by IVCDi, than BIA and Crit-line and presented a sensitivity of 78% and a specificity of 73%. The accuracy of the BLS was higher than that of BIA (0.83 vs. 0.76, p = 0.035) and Crit-line (0.50, p < 0.001). CONCLUSIONS: The BLS is a useful and easily performed technique that has recently become available for accurate evaluation of dry weight and fluid status in patients with end-stage renal disease undergoing chronic HD. This method might help recognize asymptomatic lung congestion in these patients.

Urinary hydration biomarkers and dietary intake in children.

INTRODUCTION: The importance of hydration is undoubtable but reliable data on hydration status and its relation with diet is lacking. OBJECTIVES: We aimed to evaluate the hydration status and its relation to beverages and food intake in children. METHODS: A sample of 172 (50% male), 7-11 year-old children was included in this survey. Participants completed a 24 h urine collection; a 24 hours food recall corresponding to the day of urine collection was applied, weight and height were measured and parents/caregivers fi lled a lifestyle and socio-demographic questionnaire. The free water reserve was used to assess the hydration status. The intakes of food and beverages were compared according to hydration status using the t-test, Mann-Whitney test or unconditional regression models as appropriate. RESULTS: More than half of the participants were classifi ed as hypohydrated or at risk of hypohydration (57% in girls and 58% in boys). Compared to hypohydrated children, a signifi cant higher consumption of water (276.2 ± 208.4 vs 188.2 ± 187.4 g/day) and fruit juices (77.6 ± 139.4 vs 14.4 ± 57.2 g/day) was reported by euhydrated boys and girls, respectively. Lower consumers of water and fruit juices showed a higher risk of hypohydration (OR = 2.16, 95% CI: 1.02-4.58, p = 0.045), adjusting for confounders. CONCLUSIONS: Most of the children included in this analysis were classifi ed as at risk of hypohydration and those with higher water and fruit juices consumption showed a better hydration status.

Assessment of total vascular resistance and total body water in normotensive women during the first trimester of pregnancy. A key for the prevention of preeclampsia.

INTRODUCTION: Maternal cardiovascular system adapts to pregnancy, thanks to complex physiological mechanisms that involve cardiac output, total vascular resistance and water body distribution. Abnormalities of these adaptive mechanisms are connected with hypertensive disorders. OBJECTIVE: To identify patients at a high risk of developing hypertensive complications of pregnancy during the first trimester of pregnancy, through the use of non-invasive methods such as USCOM (Ultrasonic Cardiac Output Monitor) and Bioimpedance. MATERIALS AND METHODS: We enrolled 120 healthy normotensive women during the first trimester of pregnancy obtaining all measurements with the USCOM system and Bioimpedance. RESULTS: 20 patients were excluded for a bad USCOM signal. The remaining patients (n = 100) were retrospectively divided into two groups: Group A (n = 75) TVR<1200 dynes s cm(-5), Group B (n = 25) TVR>1200 dynes s cm(-5). No statistically significant difference was identified in terms of water distribution, Fat Free Mass, Systolic/Diastolic Blood Pressure, Heart Rate, Hematocrit, Flow Time Corrected and Water Balance Index between the two groups. In contrast, higher values of the Cardiac Output, Stroke Volume, Fat Mass and Inotropy Index have been highlighted in the Group A. Moreover, in the Group A we found a better maternal-neonatal outcome and a lower incidence of hypertensive complications. CONCLUSIONS: High TVR during the first weeks of gestation may be an early marker of cardiovascular maladaptation more than the evaluation of water distribution and, in particular, with respect to the single blood pressure assessment. Moreover lower values of Inotropy Index could be an indicative of the worst cardiac performance.

Quantification of chromatographic effects of vitamin B supplementation in urine and implications for hydration assessment.

Changes in body water elicit reflex adjustments at the kidney, thus maintaining fluid volume homeostasis. These renal adjustments change the concentration and color of urine, variables that can, in turn, be used as biomarkers of hydration status. It has been suggested that vitamin supplementation alters urine color; it is unclear whether any such alteration would confound hydration assessment via colorimetric evaluation. We tested the hypothesis that overnight vitamin B2 and/or B12 supplementation alters urine color as a marker of hydration status. Thirty healthy volunteers were monitored during a 3-day euhydrated baseline, confirmed via first morning nude body mass, urine specific gravity, and urine osmolality. Volunteers then randomly received B2 (n = 10), B12 (n = 10), or B2 + B12 (n = 10) at ∼200 × recommended dietary allowance. Euhydration was verified on trial days (two of the following: body mass ± 1.0% of the mean of visits 1-3, urine specific gravity < 1.02, urine osmolality < 700 mmol/kg). Vitamin purity and urinary B2 concentration ([B2]) and [B12] were quantified via ultraperformance liquid chromatography. Two independent observers assessed urine color using an eight-point standardized color chart. Following supplementation, urinary [B2] was elevated; however, urine color was not different between nonsupplemented and supplemented trials. For example, in the B2 trial, urinary [B2] increased from 8.6 × 10(4) ± 7.7 × 10(4) to 5.7 × 10(6) ± 5.3 × 10(6) nmol/l (P < 0.05), and urine color went from 4 ± 1 to 5 ± 1 (P > 0.05). Both conditions met the euhydrated color classification. We conclude that a large overnight dose of vitamins B2 and B12 does not confound assessment of euhydrated status via urine color.

Assessment of beverage intake and hydration status.

UNLABELLED: Water is the main constituent of the human body. It is involved in practically all its functions. It is particularly important for thermoregulation and in the physical and cognitive performance. Water balance reflects water intake and loss. Intake of water is done mainly through consumption of drinking water and beverages (70 to 80%) plus water containing foods (20 to 30%). Water loss is mainly due to excretion of water in urine, faeces and sweat. The interest in the type and quantity of beverage consumption is not new, and numerous approaches have been used to assess beverage intake, but the validity of these approaches has not been well established. There is no standardized questionnaire developed as a research tool for the evaluation of water intake in the general population. Sometimes, the information comes from different sources or from different methodological characteristics which raises problems of the comparability. In the European Union, current epidemiological studies that focus exclusively on beverage intake are scarce. Biomarkers of intake are able to objectively assess dietary intake/status without the bias of self-reported dietary intake errors and also overcome the problem of intra-individual diet variability. Furthermore, some methods of measuring dietary intake used biomarkers to validate the data it collects. Biological markers may offer advantages and be able to improve the estimates of dietary intake assessment, which impact into the statistical power of the study. There is a surprising paucity of studies that systematically examine the correlation of beverages intake and hydration biomarker in different populations. A pilot investigation was developed to evaluate the comparative validity and reliability of newly developed interactive multimedia (IMM) versions compared to validated paper-administered (PP) versions of the Hedrick et al. beverage questionnaire. The study showed that the IMM appears to be a valid and reliable measure to assess habitual beverage intake. Similar study was developed in China, but in this case, the use of Smartphone technology was employed for beverage assessment. CONCLUSION: The methodology for measuring beverage intake in population studies remains controversial. There are few validated and reproducible studies, so there is still lacking an ideal method (ie, short, easy to administer, inexpensive and accurate) in this regard. Clearly, this is an area of scientific interest that is still in development and seems to be very promising for improving health research.

El agua es el principal constituyente del cuerpo humano. Está implicado en prácticamente la totalidad de sus funciones. Es especialmente importante en la termorregulación y en el rendimiento físico y cognitivo. El balance de agua refleja la ingesta y la pérdida de agua. La ingesta se realiza principalmente a través del consumo de agua potable y de bebidas (70 a 80%) más el agua que contienen los alimentos (20 a 30%). La pérdida de agua se realiza gracias a su excreción a través de la orina, las heces y el sudor. El interés por el tipo y la cantidad de bebidas consumidas no es nuevo, y numerosos enfoques se han utilizado para evaluarla, pero la validez de estos enfoques no se han establecido correctamente. Aún no existe, en población general, un cuestionario estandarizado desarrollado como herramienta de investigación para la evaluación de la ingesta de agua. El uso de información de diferentes fuentes y diferentes características metodológicas plantea problemas de comparabilidad entre estudios. En Europa los estudios epidemiológicos actuales que se centran exclusivamente en el consumo de bebidas son escasos. Los biomarcadores de ingesta permiten evaluar objetivamente la ingesta dietética sin el sesgo producido por los errores del auto-reporte. Además permiten superar el problema de la variabilidad intra-individual. Algunos métodos para medir ingesta alimentaria utilizan biomarcadores para validar los datos que recoge. Los marcadores biológicos ofrecen ventajas y son capaces de mejorar las estimaciones de la evaluación de ingesta dietética. Sin embargo, existen muy pocos estudios que examinen sistemáticamente la correlación entre la ingesta de bebidas y los biomarcadores de hidratación en diferentes poblaciones. Utilizando el cuestionario de bebidas de Hedrick y col. se realizó un estudio piloto para evaluar la validez y fiabilidad de un modelo multimedia interactivo (IMM) y para compararlo con una versión en papel-auto administrado (PP). El estudio mostró que el IMM parece ser un modelo válido y fiable para evaluar la ingesta de bebidas habitual. Un estudio similar se realizó en China, pero en este caso, se empleó para evaluar ingesta de bebidas la tecnología Smartphone. Conclusión: La metodología para valorar el consumo de bebidas en estudios poblacionales sigue siendo un tema controvertido. Existen pocos estudios validados y reproducibles, por lo que todavía no se dispone de un método ideal (corto, fácil de administrar, económico y preciso). Esta es un área de interés científico que aún está en desarrollo y que parece ser muy prometedora para mejorar las investigaciones en el área de la salud.

Marcadores de estrés oxidativo y su relación con el estado nutricional en adultos, Ecuador / Relationships between biomarkers of oxidative stress and nutritional status in adults, Ecuador

Se evaluó la relación entre biomarcadores de estrés oxidativo (ácido úrico, bilirrubina y proteína C-reactiva) con el estado nutricional en 321 adultos de Ecuador, pertenecientes al personal administrativo de la Universidad Técnica del Norte, con edades de 43 ± 10 años, (46,30% femenino y 53,61% masculino). Se obtuvo información sociodemográfica, de estilo de vida y epidemiológica; se calculó el índice de Masa Corporal (IMC), porcentaje de grasa y agua corporal, se midió la circunferencia de la cintura (CC) y la presión arterial y se determinó las concentraciones de ácido úrico, bilirrubina y Proteína C reactiva (PCR). Se encontró que 17,9% de la población presentó obesidad y 51,72% sobrepeso. Los valores más elevados de ácido úrico se encontraron en obesos, hipertensos y en quienes realizan actividad física. La bilirrubina total, directa e indirecta se encontró en límites superiores en los grupos con obesidad abdominal, y con actividad física. Las variables % de grasa y de agua influyen en la PCR en el grupo con baja grasa corporal y en las mujeres. En hombres, la PCR se asocia con IMC y CC. En los grupos sobrepeso, alta grasa corporal y PHT, el ácido úrico mostró relación con el % de grasa y la CC En los obesos con el % de agua e IMC y en los grupos obesidad abdominal e HT se asoció con % de agua y CC Se concluye que el porcentaje de agua corporal es un importante indicador nutricional para el desarrollo de estrés oxidativo en esta población.

In this work it was evaluated the relationship between oxidative stress biomarkers (uric acid, bilirubin and C-reactive protein) with nutritional status in 321 adults of Ecuador, belonging to administrative staff of of the Universidad Tècnica del Norte , aged 43 ± 10 years old (46 30% female and 53.61% male). Socio demographic and epidemiological information and lifestyle were obtained through a survey; The Body Mass Index (BMI) and body fat and body water percentages were calculated; waist circumference (WC) and blood pressure was measured. Determinations of uric acid, bilirubin, and serum C-reactive protein (PCR) were performed. 17.9% of the populations were obese and 51.72% overweight. The highest values of uric acid were found in obese, hypertensive and physical activity groups. The total direct and indirect bilirubin were found in upper limits in abdominal obesity and physical activity groups. The CRP level was influenced by % fat and % water in the low body fat group and in females. In male, BMI and WC were associated with CRP. Uric acid showed relationship with % fat and WC in overweight, high body fat and PHT groups, uric acid was associated with the % water and BMI in obese. Finally, uric acid was associated with % water and the WC in the abdominal obesity, and HT groups’ .The body water percentage is an important indicator to development of oxidative stress in this population.

Sub-millimeter imaging of brain-free water for rapid volume assessment in atrophic brains.

INTRODUCTION: Cerebral atrophy occurs in healthy aging, and in disease processes such as multiple sclerosis (MS), it correlates with disability accumulation. Imaging measurements of brain atrophy are commonly based on tissue segmentation, which is susceptible to classification errors and inconsistencies. High-resolution imaging techniques with strong contrast between brain parenchyma and cerebrospinal fluid (CSF) might allow fully automated, rapid, threshold-based determination of the free water in the brain. We hypothesized that total brain-free-water (BFW) volume and BFW volume expressed as a normalized fraction of the intracranial volume ("BFW fraction"), determined from heavily T2-weighted images, would be useful surrogates for cerebral atrophy and therefore would correlate with clinical measures of disability in MS. METHODS: Whole brains of 83 MS cases and 7 healthy volunteers were imaged with a 4.7-min, heavily T2-weighted sequence on a 3T MRI scanner, acquiring 650-µm isotropic voxels. MS cases were clinically assessed on the Expanded Disability Status Scale (EDSS), Scripps Neurological Rating Scale (SNRS), Paced Auditory Serial Addition Test (PASAT), 9-Hole Peg Test (9HPT), Symbol Digit Modalities Test (SDMT), and 25-Foot Timed Walk. Twelve of the MS cases were rescanned within an average of 1.8 months to assess reproducibility. Automated calculations of BFW volume and BFW fraction were correlated with clinical measures of disability upon adjusting for age and sex. Results were compared to data from T1-based approaches (SIENAX and Lesion-TOADS). RESULTS AND DISCUSSION: BFW volume was automatically derived from heavily T2-weighted images with no need for separate skull stripping. BFW volume and fraction had mean scan-rescan coefficients of variation of 1.5% and 1.9%, respectively, similar to the T1-based approaches tested here. BFW fraction more strongly correlated with clinical measures than T1-derived results. Among those clinical measures, modality-specific disability scores, such as SDMT and 9HPT, were more strongly associated with BFW fraction than composite measures, such as EDSS and SNRS. CONCLUSION: The BFW method robustly estimates cerebral atrophy in an automated, fast, and reliable manner, and as such may prove a useful addition to imaging protocols for clinical practice and trials.

Novel hydration assessment techniques employing thirst and a water intake challenge in healthy men.

Exploring novel hydration indices is important because no human biomarker has been shown to be incontrovertibly valid in all life situations. The present investigation was designed to identify inexpensive, nontechnical methods to use when self-assessing hydration status. This investigation evaluated the validity and efficacy of 2 novel techniques (i.e., thirst sensation and urine volume) to assess hydration state of 29 active men (mean ± SD; age, 23 ± 4 years; body mass, 76.02 ± 11.94 kg) at rest. Eight combinations of 4 water challenges (4.8, 9.3, 11.0, or 14 mL·kg(-1)) and 2 hydration states (mildly hypohydrated (HY), -2.0%; euhydrated (EU), -0.2% body mass) were employed. First, thirst was linearly related to body water loss, and ratings of thirst distinguished HY from EU (p < 0.001) subsequent to 19 h of controlled food and fluid intake. Second, measurements of urine volume 60 min after consuming a water bolus (11.0 or 14 mL·kg(-1)) were strongly and inversely correlated with entering hydration state, assessed by urine specific gravity (r(2) = 0.76, p < 0.0001) and urine osmolality (r(2) = 0.77, p < 0.0001). We concluded that healthy men can employ simple measurements of morning thirst sensation and urine volume to identify the presence of mild hypohydration and to guide fluid replacement. These 2 techniques are relevant because HY (-2% body mass) is the approximate threshold for the onset of thirst, reduced endurance exercise performance, and decrements of working memory and mood.

[Relationships between biomarkers of oxidative stress and nutritional status in adults, Ecuador]. / Marcadores de estrés oxidativo y su relación con el estado nutricional en adultos, Ecuador.

In this work it was evaluated the relationship between oxidative stress biomarkers (uric acid, bilirubin and C-reactive protein) with nutritional status in 321 adults of Ecuador, belonging to administrative staff of of the Universidad Tècnica del Norte, aged 43 ± 10 years old (46 30% female and 53.61% male). Socio demographic and epidemiological information and lifestyle were obtained through a survey; The Body Mass Index (BMI) and body fat and body water percentages were calculated; waist circumference (WC) and blood pressure was measured. Determinations of uric acid, bilirubin, and serum C-reactive protein (PCR) were performed. 17.9% of the populations were obese and 51.72% overweight. The highest values of uric acid were found in obese, hypertensive and physical activity groups. The total direct and indirect bilirubin were found in upper limits in abdominal obesity and physical activity groups. The CRP level was influenced by % fat and % water in the low body fat group and in females. In male, BMI and WC were associated with CRP. Uric acid showed relationship with % fat and WC in overweight, high body fat and PHT groups, uric acid was associated with the % water and BMI in obese. Finally, uric acid was associated with % water and the WC in the abdominal obesity, and HT groups'. The body water percentage is an important indicator to development of oxidative stress in this population.

Assessment of hydration biomarkers including salivary osmolality during passive and active dehydration.

BACKGROUND/OBJECTIVES: Hydration state can be assessed via body mass change (BMΔ), serum and urine osmolality (Sosm, Uosm), urine-specific gravity (Usg) and urine volume (Uvol). As no hydration index has been shown to be valid in all circumstances, value exists in exploring novel biomarkers such as salivary osmolality (Vosm). Utilizing acute BMΔ as the reference standard, this research examined the efficacy of Sosm, Vosm, Uosm, Uvol and Usg, during passive (PAS) and active (ACT) heat exposure. SUBJECTS/METHODS: Twenty-three healthy men (age, 22±3 years; mass, 77.3±12.8 kg; height, 179.9±8.8cm; body fat, 10.6±4.5%) completed two randomized 5-h dehydration trials (36±1 °C). During PAS, subjects sat quietly, and during ACT, participants cycled at 68±6% maximal heart rate. Investigators measured all biomarkers at each 1% BMΔ. RESULTS: Average mass loss during PAS was 1.4±0.3%, and 4.1±0.7% during ACT. Significant between-treatment differences at -1% BMΔ were observed for Sosm (PAS, 296±4; ACT, 301±4 mOsm/kg) and Uosm (PAS, 895±207; ACT, 661±192 mOsm/kg). During PAS, only Uosm, Uvol and Usg increased significantly (-1 and -2% BMΔ versus baseline). During ACT, Vosm most effectively diagnosed dehydration 2% (sensitivity=86%; specificity=91%), followed by Sosm (sensitivity=83%; specificity=83%). Reference change values were validated for Sosm, Usg and BMΔ. CONCLUSIONS: The efficacy of indices to detect dehydration 2% differed across treatments. At rest (PAS), only urinary indices increased in concert with body water loss. During exercise (ACT), Sosm and Vosm exhibited the highest sensitivity and specificity. Sosm, Usg and BMΔ exhibited validity in serial measurements. These findings indicate hydration biomarkers should be selected by considering daily activities.

Physiologic basis for understanding quantitative dehydration assessment.

Dehydration (body water deficit) is a physiologic state that can have profound implications for human health and performance. Unfortunately, dehydration can be difficult to assess, and there is no single, universal gold standard for decision making. In this article, we review the physiologic basis for understanding quantitative dehydration assessment. We highlight how phenomenologic interpretations of dehydration depend critically on the type (dehydration compared with volume depletion) and magnitude (moderate compared with severe) of dehydration, which in turn influence the osmotic (plasma osmolality) and blood volume-dependent compensatory thresholds for antidiuretic and thirst responses. In particular, we review new findings regarding the biological variation in osmotic responses to dehydration and discuss how this variation can help provide a quantitative and clinically relevant link between the physiology and phenomenology of dehydration. Practical measures with empirical thresholds are provided as a starting point for improving the practice of dehydration assessment.

Probing tissue microstructure with restriction spectrum imaging: Histological and theoretical validation.

Water diffusion magnetic resonance imaging (dMRI) is a powerful tool for studying biological tissue microarchitectures in vivo. Recently, there has been increased effort to develop quantitative dMRI methods to probe both length scale and orientation information in diffusion media. Diffusion spectrum imaging (DSI) is one such approach that aims to resolve such information based on the three-dimensional diffusion propagator at each voxel. However, in practice, only the orientation component of the propagator function is preserved when deriving the orientation distribution function. Here, we demonstrate how a straightforward extension of the linear spherical deconvolution (SD) model can be used to probe tissue orientation structures over a range (or "spectrum") of length scales with minimal assumptions on the underlying microarchitecture. Using high b-value Cartesian q-space data on a rat brain tissue sample, we demonstrate how this "restriction spectrum imaging" (RSI) model allows for separating the volume fraction and orientation distribution of hindered and restricted diffusion, which we argue stems primarily from diffusion in the extraneurite and intraneurite water compartment, respectively. Moreover, we demonstrate how empirical RSI estimates of the neurite orientation distribution and volume fraction capture important additional structure not afforded by traditional DSI or fixed-scale SD-like reconstructions, particularly in gray matter. We conclude that incorporating length scale information in geometric models of diffusion offers promise for advancing state-of-the-art dMRI methods beyond white matter into gray matter structures while allowing more detailed quantitative characterization of water compartmentalization and histoarchitecture of healthy and diseased tissue.

Impact of body reserves on energy expenditure, water flux, and mating success in breeding male northern elephant seals.

In capital breeders, individual differences in body size and condition can impact mating effort and success. In addition to the collateral advantages of large body size in competition, large nutrient reserves may offer advantages in endurance rivalry and enable the high rates of energy expenditure associated with mating success. We examined the impacts of body reserves and dominance rank on energy expenditure, water flux, mating success, and breeding tenure in the adult male northern elephant seal, a polygynous, capital breeder. Adult males expended energy at a rate of 159 ± 49 MJ d (-1), which is equivalent to 3.1 times the standard metabolic rate predicted by Kleiber's equation. Despite high rates of energy expenditure and a long fasting duration, males spared lean tissue effectively, deriving a mean of 7% of their metabolism from protein catabolism. Body composition had a strong impact on the ability to spare lean tissue during breeding. When controlling for body size, energy expenditure, depletion of blubber reserves, and water efflux were significantly greater in alpha males than in subordinate males. Large body size was associated with increased reproductive effort, tenure on shore, dominance rank, and reproductive success. Terrestrial locomotion and topography appeared to strongly influence energy expenditure. Comparisons with conspecific females suggest greater total seasonal reproductive effort in male northern elephant seals when controlling for the effects of body mass. In polygynous capital breeding systems, male effort may be strongly influenced by physiological state and exceed that of females.

Maximal sustained levels of energy expenditure in humans during exercise.

UNLABELLED: Migrating birds have been able to sustain an energy expenditure (EE) that is five times their basal metabolic rate. Although humans can readily reach these levels, it is not yet clear what levels can be sustained for several days. PURPOSE: The study's purposes were 1) to determine the upper limits of human EE and whether or not those levels can be sustained without inducing catabolism of body tissues and 2) to determine whether initial body weight is related to the levels that can be sustained. METHODS: We compiled data on documented EE as measured by doubly labeled water during high levels of physical activity (minimum of five consecutive days). We calculated the physical activity level (PAL) of each individual studied (PAL = total EE / basal metabolic rate) from the published data. Correlations were run to examine the relationship between initial body weight and body weight lost with both total EE and PAL. RESULTS: The uppermost limit of EE was a peak PAL of 6.94 that was sustained for 10 consecutive days of a 95-d race. Only two studies reported PALs above 5.0; however, significant decreases in body mass were found in each study (0.45-1.39 kg·wk(-1) of weight loss). To test whether initial weight affects the ability to sustain high PALs, we found a significant positive correlation between TEE and initial body weight (r = 0.46, P < 0.05) but no correlation between PAL and body weight (r = 0.27, not statistically significant). CONCLUSIONS: Some elite humans are able to sustain PALs above 5.0 for a minimum of 10 d. Although significant decreases in body weight occur at this level, catabolism of body tissue may be preventable in situations with proper energy intake. Further, initial body weight does not seem to affect the sustainability of PALs.

Parallel assessment of nutrition and activity in athletes: validation against doubly labelled water, 24-h urea excretion, and indirect calorimetry.

The assessment of nutrition and activity in athletes requires accurate and precise methods. The aim of this study was to validate a protocol for parallel assessment of diet and exercise against doubly labelled water, 24-h urea excretion, and respiratory gas exchange. The participants were 14 male triathletes under normal training conditions. Energy intake and doubly labelled water were weakly associated with each other (r = 0.69, standard error of estimate [SEE] = 304 kcal x day(-1)). Protein intake was strongly correlated with 24-h urea (r = 0.89) but showed considerable individual variation (SEE = 0.34 g kg(-1) x day(-1)). Total energy expenditure based on recorded activities was highly correlated with doubly labelled water (r = 0.95, SEE = 195 kcal x day(-1)) but was proportionally biased. During running and cycling, estimated exercise energy expenditure was highly correlated with gas exchange (running: r = 0.89, SEE = 1.6 kcal x min(-1); cycling: r = 0.95, SEE = 1.4 kcal x min(-1)). High exercise energy expenditure was slightly underestimated during running. For nutrition data, variations appear too large for precise measurements in individual athletes, which is a common problem of dietary assessment methods. Despite the high correlations of total energy expenditure and exercise energy expenditure with reference methods, a correction for systematic errors is necessary for the valid estimation of energetic requirements in individual athletes.