Body Fluid Shifts Research Articles

A Randomized, Single-Blind, Crossover Study to Evaluate the Efficacy of a Novel Dietary Supplement Blend with L-Citrulline on Biomarkers of Hydration, Muscle Size, Affect, Inflammation, and Muscular Endurance

Introduction: Citrulline is a non-essential amino acid that has previously been shown to improve athletic performance, reduce fatigue, and increase blood flow. The purpose of this study was to examine the efficacy of a novel dietary supplement blend (3D PUMP BREAKTHROUGH®, 3DPump) vs. citrulline alone on changes in muscle volume, fluid shifts, markers of hydration, inflammation, recovery, affect, and muscular endurance. Methods: Twenty-eight recreationally active subjects (6 women, 22 men) participated in a randomized, positive-controlled, single-blind, crossover study which involved 4 testing visits (2 workout visits each with a 24-hr follow-up visit). Participants ingested 3DPump (containing 3g L-citrulline, 1.2g glycerol, 165mg Amla fruit extract) or 8g of L-citrulline alone 45min before an aerobic and resistance training workout. Assessments of body fluid shifts (via BIA), markers of hydration (urine and serum osmolality, USG, hemoglobin), and appendicular girth were taken before and after exercise while markers of damage and inflammation (neutrophils, CK, ESR, MCP-1, CRP) were taken before and 24 hours after exercise, muscular endurance (reps to failure) was assessed during resistance exercises, and subjective measures of affect and recovery were taken before, after and 24 hours after exercise. Mixed factorial ANOVAs with dependent t-tests were used to compare treatments. Results: A significant interaction occurred for right thigh circumference; however post hoc testing indicated both groups increased similarly in post workout girth (p<0.05). A significant interaction occurred for ECF/TBW indicating post workout was greater than pre workout in 3DPump only (p=0.002). An interaction trend (p≤0.010) occurred for SBP and DBP indicating that 3DPump was uniquely able to significantly lower blood pressure (SBP and DBP) post workout compared to baseline and 24 hours after exercise (p<0.001). Conclusions: 3DPump, which contains 3g L-citrulline was able to provide similar effects in muscular endurance, muscle pump and other subjective feelings of affect, hydration, damage and inflammation markers, and body fluid shifts as an 8g dose of L-citrulline alone. 3DPump may have unique benefits on improving post exercise vascular tone and ECF/TBW.

Thoracic, Peripheral, and Cerebral Volume, Circulatory and Pressure Responses To PEEP During Simulated Hemorrhage in a Pig Model: a Case Study.

Positive end-expiratory pressure (PEEP) is a respiratory/ventilation procedure that is used to maintain or improve breathing in clinical and experimental cases that exhibit impaired lung function. Body fluid shift movement is not monitored during PEEP application in intensive care units (ICU), which would be interesting specifically in hypotensive patients. Brain injured and hypotensive patients are known to have compromised cerebral blood flow (CBF) autoregulation (AR) but currently, there is no non-invasive way to assess the risk of implementing a hypotensive resuscitation strategy and PEEP use in these patients.The advantage of electrical bioimpedance measurement is that it is noninvasive, continuous, and convenient. Since it has good time resolution, it is ideal for monitoring in intensive care units (ICU). The basis of its future use is to establish physiological correlates. In this study, we demonstrate the use of electrical bioimpedance measurement during bleeding and the use of PEEP in pig measurement.In an anesthetized pig, we performed multimodal recording on the torso and head involving electrical bioimpedance spectroscopy (EIS), fixed frequency impedance plethysmography (IPG), and bipolar (rheoencephalography – REG) measurements and processed data offline. Challenges (n=16) were PEEP, bleeding, change of SAP, and CO2 inhalation. The total measurement time was 4.12 hours.Systemic circulatory results: Bleeding caused a continuous decrease of SAP, cardiac output (CO), and increase of heart rate, temperature, shock index (SI), vegetative - Kerdo index (KI). Pulse pressure (PP) decreased only after second bleeding which coincided with loss of CBF AR. Pulmonary arterial pressure (PAP) increased during PEEP challenges as a function of time and bleeding.EIS/IPG results: Body fluid shift change was characterized by EIS-related variables. Electrical Impedance Spectroscopy was used to quantify the intravascular, interstitial, and intracellular volume changes during the application of PEEP and simulated hemorrhage. The intravascular fluid compartment was the primary source of blood during hemorrhage. PEEP produced a large fluid shift out of the intravascular compartment during the first bleeding period and continued to lose more blood following the second and third bleeding. Fixed frequency IPG was used to quantify the circulatory responses of the calf during PEEP and simulated hemorrhage. PEEP reduced the arterial blood flow into the calf and venous outflow from the calf.Head results: CBF AR was evaluated as a function of SAP change. Before bleeding, and after moderate bleeding, intracranial pressure (ICP), REG, and carotid flow pulse amplitudes (CFa) increased. This change reflected vasodilatation and active CBF AR. After additional hemorrhaging during PEEP, SAP, ICP, REG, CFa signal amplitudes decreased, indicating passive CBF AR. 1) The indicators of active AR status by modalities was the following: REG (n=9, 56 %), CFa (n=7, 44 %), and ICP (n=6, 38 %); 2) CBF reactivity was better for REG than ICP; 3) REG and ICP correlation coefficient were high (R2 = 0.81) during CBF AR active status; 4) PRx and REGx reflected active CBF AR status. CBF AR monitoring with REG offers safety for patients by preventing decreased CBF and secondary brain injury.We used different types of bioimpedance instrumentation to identify physiologic responses in the different parts of the body (that have not been discussed before) and how the peripheral responses ultimately lead to decreased cardiac output and changes in the head. These bioimpedance methods can improve ICU monitoring, increase the adequacy of therapy, and decrease mortality and morbidity.

Fluid Shifts With Acute Exposure To Normobaric And Hypobaric Hypoxia

PURPOSE: To determine the body fluid shifts that occur with exposure to normobaric hypoxia (NH) and hypobaric hypoxia (HH) compared to normobaric normoxia (NN). METHODS: Eighteen males and females (male = 10, female = 8, age 35 ± 7 yrs) completed three trials on back to back days in a randomized order. NN was conducted at sea level, NH was conducted at sea level but breathing a gas mixture to simulate 4,617 m of elevation, and HH was conducted at 4,617 m of terrestrial elevation. The time and rate of hypoxia exposure was consistent between NN and HH (0 m to 4,617 m in 90 minutes). Finger-stick blood samples were taken after the 90 minute intervention and analyzed for hemoglobin and hematocrit to calculate plasma volume shifts and urine was collected to measure urine specific gravity. After 10 minutes of supine resting, body water was analyzed via BIA. RESULTS: Plasma volume change was not altered by NH relative to NN (-3.77 ± 8.36%, p = 0.073), but lower in HH relative to NN (-16.610 ± 7.84%, p < 0.001). Urine specific gravity was similar between all trials (p = 0.120, main effect). Total body water was not different between NN (43.8 ± 7.6 L) and NH (43.7 ± 7.7 L, p = 0.492), but was lower in HH (43.0 ± 7.6 L) than NN (p < 0.001) and NH (p < 0.001). Extracellular fluid was not different between NN (16.35 ± 2.85 L) and NH (16.32 ± 2.84 L, p = 0.696), but was lower in HH (16.08 ± 2.78 L) than NN (p < 0.001) and NH (p = 0.006). Intracellular Fluid was not different between NN (27.41 ± 4.81 L) and NH (27.33 ± 4.89 L, p = 0.420) but was lower in HH (26.97 ± 4.80 L) than NN (p < 0.001) and NH (p = 0.016). CONCLUSIONS: Body fluid shifts are stimulated by an alteration of barometric pressure and not by hypoxia. Caution should be made when applying data from studies conducted in NH to HH.

Fluid Shifts with Acute Exposure to Normobaric and Hypobaric Hypoxia

Purpose To determine the body fluid shifts that occur with exposure to normobaric hypoxia (NH) and hypobaric hypoxia (HH) compared to normobaric normoxia (NN). Methods Eighteen males and females (male=10, female=8, age 35±7 yrs) completed three trials on back to back days in a randomized order. NN was conducted at sea level, NH was conducted at sea level but breathing a gas mixture to simulate 4,617 m of elevation, and HH was conducted at 4,617 m of terrestrial elevation. The time and rate of hypoxia exposure was consistent between NN and HH (0 m to 4,617 m in 90 minutes). Finger-stick blood samples were taken after the 90 minute intervention and analyzed for hemoglobin and hematocrit to calculate plasma volume shifts and urine was collected to measure urine specific gravity. After 10 minutes of supine rest, body water was analyzed via BIA. Results Plasma volume change was not altered by NH relative to NN (-3.77±8.36%, p = 0.073), but lower in HH relative to NN (-16.610±7.84%, p<0.001). Urine specific gravity was similar between all trials (p=0.120, main effect). Total body water was not different between NN (43.8±7.6 L) and NH (43.7±7.7 L, p=0.492), but was lower in HH (43.0±7.6 L) than NN (p<0.001) and NH (p<0.001). Extracellular fluid was not different between NN (16.35±2.85 L) and NH (16.32±2.84 L, p=0.696), but was lower in HH (16.08±2.78 L) than NN (p<0.001) and NH (p=0.006). Intracellular Fluid was not different between NN (27.41±4.81 L) and NH (27.33±4.89 L, p=0.420) but was lower in HH (26.97±4.80 L) than NN (p<0.001) and NH (p=0.016). Conclusion Body fluid shifts are stimulated by an alteration of barometric pressure and not by hypoxia. Caution should be made when applying data from studies conducted in NH to HH.

15 Use of Bioelectric Impedance Analysis in Burn Patients: A Pilot Study

Abstract Introduction Bioelectric Impedance Analysis (BIA) is a rapid, non-invasive, and inexpensive technology based on electrical conductivity. BIA assesses body composition, fluid shifts, and phase angle, an electrical force vector where smaller values suggest cellular injury. Our objective was to use BIA to longitudinally track the clinical status of burn patients. We hypothesized that BIA would detect progressive decreases in muscle mass throughout the patient’s hospital course and that low phase angle values would correlate with severity of injury. Methods A cohort study of 10 patients from January 1, 2020 to March 13, 2020 was performed at an ABA-verified burn center. Patient and burn characteristics and laboratory data were collected. BIA measurements were performed daily for the first 10 days of admission and then twice weekly until discharge. The primary outcome was to detect changes in body composition. The secondary objectives were to detect differences between low and high-risk patients in terms of water composition and phase angle. Patients with APACHE II &amp;gt; 15, measured at burn unit admission, were considered high risk for burn injury related morbidity and mortality. Results BIA detected a statistically significant negative correlation between time spent hospitalized and leg lean mass (LM) (r2=0.56, P&amp;lt; 0.0001), right arm LM (r2=0.52, P&amp;lt; 0.0001) and left leg LM (r2=0.57, P&amp;lt; 0.0001), and positive correlation between body fat mass (BFM) and time spent hospitalized (r2=0.50, P=0.0004). Water composition (volume of extracellular water (ECW) per total body water (TBW)) negatively correlated with low-risk patients: right arm (r2=0.51, P&amp;lt; 0.0001), left arm (0.71, P&amp;lt; 0.001), thorax (0.66, P&amp;lt; 0.0001), right leg (0.74, P&amp;lt; 0.0001), left leg (0.35, P=0.002). Full body phase angle increased with low-risk patients over their hospital course (r2=0.62, P&amp;lt; 0.0001), while phase angle decreased with high-risk patients (r2=0.71, P=0.0006). Full body phase angle differentiated high risk patients (P&amp;lt; 0.0001), and phase angle of thorax differentiated between patients with and without inhalation injury (P=0.002). Conclusions Our study demonstrates that BIA measures changes in body composition and fluid shifts, identifies inhalation injury, and correlates with severity of injury in hospitalized burn patients. This pilot study included a limited number of participants with varying anatomic injuries presenting unique measurement challenges. Regardless, our preliminary data justifies a larger prospective study to confirm these results and correlate them with clinical outcomes.

Non-Invasive Cardiac and Respiratory Activity Assessment From Various Human Body Locations Using Bioimpedance.

Objective: Bioimpedance sensing is a powerful technique that measures the tissue impedance and captures important physiological parameters including blood flow, lung movements, muscle contractions, body fluid shifts, and other cardiovascular parameters. This paper presents a comprehensive analysis of the modality at different arterial (ulnar, radial, tibial, and carotid arteries) and thoracic (side-rib cage and top thoracolumbar fascia) body regions and offers insights into the effectiveness of capturing various cardiac and respiratory activities. Methods: We assess the bioimpedance performance in estimating inter-beat (IBI) and inter -breath intervals (IBrI) on six-hours of data acquired in a pilot-study from five healthy participants at rest. Results: Overall, we achieve mean errors as low as 0.003 ± 0.002 and 0.67 ± 0.28 seconds for IBI and IBrI estimations, respectively. Conclusions: The results show that bioimpedance can be effectively used to monitor cardiac and respiratory activities both at limbs and upper body and demonstrate a strong potential to be adopted by wearables that aim to provide high-fidelity physiological sensing to address precision medicine needs.

Neural Working Memory Changes During a Spaceflight Analog With Elevated Carbon Dioxide: A Pilot Study.

Spaceflight missions to the International Space Station (ISS) expose astronauts to microgravity, radiation, isolation, and elevated carbon dioxide (CO2), among other factors. Head down tilt bed rest (HDBR) is an Earth-based analog for spaceflight used to study body unloading, fluid shifts, and other factors unrelated to gravitational changes. While in space, astronauts need to use mental rotation strategies to facilitate their adaptation to the ISS environment. Therefore, spatial working memory is essential for crewmember performance. Although the effects of HDBR on spatial working memory have recently been studied, the results are still inconclusive. Here, we expand upon past work and examine the effects of HDBR with elevated CO2 (HDBR + CO2) on brain activation patterns during spatial working memory performance. In addition, we compare brain activation between 30 days of HDBR + CO2 and 70 days of HDBR to test the isolated effect of CO2. Eleven subjects (6 males, 5 females; mean age = 34 ± 8 years) underwent six functional magnetic resonance imaging (fMRI) sessions pre-, during, and post-HDBR + CO2. During the HDBR + CO2 intervention, we observed decreasing activation in the right middle frontal gyrus and left regions of the cerebellum, followed by post-intervention recovery. We detected several correlations between brain and behavioral slopes of change with the HDBR + CO2 intervention. For example, greater increases in activation in frontal, temporal and parietal regions were associated with larger spatial working memory improvements. Comparing the HDBR + CO2 group to data from our previous 70-day HDBR study, we found greater decreases in activation in the right hippocampus and left inferior temporal gyrus for the HDBR + CO2 group over the course of the intervention. Together, these findings increase our understanding of the neural mechanisms of HDBR, elevated levels of CO2 and spaceflight-related changes in spatial working memory performance.

Hypercapnia augments resistive exercise-induced elevations in intraocular pressure in older individuals.

What is the central question of this study? Astronauts on-board the International Space Station (ISS) perform daily exercises designed to prevent muscle atrophy and bone demineralization: what is the effect of resistive exercise performed by subjects while exposed to the same level of hypercapnia as on the ISS on intraocular pressure (IOP)? What is the main finding and its importance? The static exercise-induced elevation in IOP during 6° prone head-down tilt (simulating the headward shift of body fluids in microgravity) is augmented by hypercapnia and exceeds the ocular hypertension threshold. The present study assessed the effect of 6° head-down (establishing the cephalad fluid displacement noted in astronauts in microgravity) prone (simulating the effect on the eye) tilt during rest and exercise (simulating exercise performed by astronauts to mitigate the sarcopenia induced by unloading of weight-bearing limbs), in normocapnic and hypercapnic conditions (the latter simulating conditions on the International Space Station) on intraocular pressure (IOP). Volunteers (mean age=57.8±6 years, n=10) participated in two experimental sessions, each comprising: (i) 10min rest, (ii) 3min static handgrip exercise (30% max), and (iii) 2min recovery, inspiring either room air (NCAP) or a hypercapnic mixture (1% CO2 , HCAP). We measured IOP in the right eye, cardiac output (CO), stroke volume (SV), heart rate (HR) and mean arterial pressure (MAP) at regular intervals. Baseline IOP in the upright seated position while breathing room air was 14.1±2.9mmHg. Prone 6° head-down tilt significantly (P<0.01) elevated IOP in all three phases of the NCAP (rest: 27.0±3.7mmHg; exercise: 32.2±4.8mmHg; recovery: 27.4±4.0mmHg) and HCAP (rest: 27.3±4.3mmHg; exercise: 34.2±6.0mmHg; recovery: 29.1±5.8mmHg) trials, with hypercapnia augmenting the exercise-induced elevation in IOP (P<0.01). CO, SV, HR and MAP were significantly increased during handgrip dynamometry, but there was no effect of hypercapnia. The observed IOP measured during prone 6° HDT in all phases of the NCAP and HCAP trials exceeded the threshold pressure defining ocular hypertension. The exercise-induced increase in IOP is exacerbated by hypercapnia.

The role of body fluid shifts on hindlimb bone loss in tail suspended rats using a novel body fluid alteration device

In space, the mechanical loading of the weight-bearing bone decreases and the body fluid shifts cephalad. However, the correlative researches are rarely reported on how the body fluid shift affects the bone, especially how it affects the weight-bearing bone in space or in bed rest on the ground. In our study, a novel model was designed to investigate the effect of body fluid shifts on the bone loss of the hindlimbs in the tail-suspended rats. The model can keep the rat hindlimb unloaded, and change the distribution of the body fluid by altering rats’ body position. The study was conducted for 21 days. Thirty-six female Sprague-Dawley rats were randomly divided into four groups (n = 9, each): control group (CON), head-down tail-suspension group (HDT), head-horizontal tail-suspension group (HHT), head-up tail-suspension group (HUT). The results indicated that body fluid shifting towards the tail end may inhibit the bone loss of the rat hindlimbs, that means the absence of cephalad body fluid shifting resulted in the positive effect on the bone microstructure parameters and the mechanical properties. The results suggested that the backflow of the body fluid in rat hindlimbs was able to alleviate the disuse osteoporosis in a certain extent.

Exercise effects on bed rest-induced brain changes.

PurposeSpaceflight negatively affects sensorimotor behavior; exercise mitigates some of these effects. Head down tilt bed rest (HDBR) induces body unloading and fluid shifts, and is often used to investigate spaceflight effects. Here, we examined whether exercise mitigates effects of 70 days HDBR on the brain and if fitness and brain changes with HDBR are related.MethodsHDBR subjects were randomized to no-exercise (n = 5) or traditional aerobic and resistance exercise (n = 5). Additionally, a flywheel exercise group was included (n = 8). Exercise protocols for exercise groups were similar in intensity, therefore these groups were pooled in statistical analyses. Pre and post-HDBR MRI (structure and structural/functional connectivity) and physical fitness measures (lower body strength, muscle cross sectional area, VO2 max, body composition) were collected. Voxel-wise permutation analyses were used to test group differences in brain changes, and their associations with fitness changes.ResultsComparisons of exercisers to controls revealed that exercise led to smaller fitness deterioration with HDBR but did not affect brain volume or connectivity. Group comparisons showed that exercise modulated post-HDBR recovery of brain connectivity in somatosensory regions. Posthoc analysis showed that this was related to functional connectivity decrease with HDBR in non-exercisers but not in exercisers. Correlational analyses between fitness and brain changes showed that fitness decreases were associated with functional connectivity and volumetric increases (all r >.74), potentially reflecting compensation. Modest brain changes or even decreases in connectivity and volume were observed in subjects who maintained or showed small fitness gains. These results did not survive Bonferroni correction, but can be considered meaningful because of the large effect sizes.ConclusionExercise performed during HDBR mitigates declines in fitness and strength. Associations between fitness and brain connectivity and volume changes, although unadjusted for multiple comparisons in this small sample, suggest that supine exercise reduces compensatory HDBR-induced brain changes.

Vestibular brain changes within 70 days of head down bed rest.

Head-down-tilt bed rest (HDBR) is frequently utilized as a spaceflight analog research environment to study the effects of axial body unloading and fluid shifts that are associated with spaceflight in the absence of gravitational modifications. HDBR has been shown to result in balance changes, presumably due to sensory reweighting and adaptation processes. Here, we examined whether HDBR results in changes in the neural correlates of vestibular processing. Thirteen men participated in a 70-day HDBR intervention; we measured balance, functional mobility, and functional brain activity in response to vestibular stimulation at 7 time points before, during, and after HDBR. Vestibular stimulation was administered by means of skull taps, resulting in activation of the vestibular cortex and deactivation of the cerebellar, motor, and somatosensory cortices. Activation in the bilateral insular cortex, part of the vestibular network, gradually increased across the course of HDBR, suggesting an upregulation of vestibular inputs in response to the reduced somatosensory inputs experienced during bed rest. Furthermore, greater increase of activation in multiple frontal, parietal, and occipital regions in response to vestibular stimulation during HDBR was associated with greater decrements in balance and mobility from before to after HDBR, suggesting reduced neural efficiency. These findings shed light on neuroplastic changes occurring with conditions of altered sensory inputs, and reveal the potential for central vestibular-somatosensory convergence and reweighting with bed rest.

Wearable Multi-Frequency and Multi-Segment Bioelectrical Impedance Spectroscopy for Unobtrusively Tracking Body Fluid Shifts during Physical Activity in Real-Field Applications: A Preliminary Study.

Bioelectrical Impedance Spectroscopy (BIS) allows assessing the composition of body districts noninvasively and quickly, potentially providing important physiological/clinical information. However, neither portable commercial instruments nor more advanced wearable prototypes simultaneously satisfy the demanding needs of unobtrusively tracking body fluid shifts in different segments simultaneously, over a broad frequency range, for long periods and with high measurements rate. These needs are often required to evaluate exercise tests in sports or rehabilitation medicine, or to assess gravitational stresses in aerospace medicine. Therefore, the aim of this work is to present a new wearable prototype for monitoring multi-segment and multi-frequency BIS unobtrusively over long periods. Our prototype guarantees low weight, small size and low power consumption. An analog board with current-injecting and voltage-sensing electrodes across three body segments interfaces a digital board that generates square-wave current stimuli and computes impedance at 10 frequencies from 1 to 796 kHz. To evaluate the information derivable from our device, we monitored the BIS of three body segments in a volunteer before, during and after physical exercise and postural shift. We show that it can describe the dynamics of exercise-induced changes and the effect of a sit-to-stand maneuver in active and inactive muscular districts separately and simultaneously.

Spaceflight-Induced Intracranial Hypertension.

Although once a widely speculated about and largely theoretical topic, spaceflight-induced intracranial hypertension has gained acceptance as a distinct clinical phenomenon, yet the underlying physiological mechanisms are still poorly understood. In the past, many terms were used to describe the symptoms of malaise, nausea, vomiting, and vertigo, though longer duration spaceflights have increased the prevalence of overlapping symptoms of headache and visual disturbance. Spaceflight-induced visual pathology is thought to be a manifestation of increased intracranial pressure (ICP) because of its similar presentation to cases of known intracranial hypertension on Earth as well as the documentation of increased ICP by lumbar puncture in symptomatic astronauts upon return to gravity. The most likely mechanisms of spaceflight-induced increased ICP include a cephalad shift of body fluids, venous outflow obstruction, blood-brain barrier breakdown, and disruption to CSF flow. The relative contribution of increased ICP to the symptoms experienced during spaceflight is currently unknown, though other factors recently posited to contribute include local effects on ocular structures, individual differences in metabolism, and the vasodilator effects of carbon dioxide. This review article attempts to consolidate the literature regarding spaceflight-induced intracranial hypertension and distinguish it from other pathologies with similar symptomatology. It discusses the proposed physiological causes and the pathological manifestations of increased ICP in the spaceflight environment and provides considerations for future long-term space travel. In the future, it will be critical to develop countermeasures so that astronauts can participate at their peak potential and return safely to Earth.

Obstructive Sleep Apnea Severity and Overnight Body Fluid Shift before and after Hemodialysis.

Obstructive sleep apnea is associated with significantly increased cardiovascular morbidity and mortality. Fluid overload may promote obstructive sleep apnea in patients with ESRD through an overnight fluid shift from the legs to the neck soft tissues. Body fluid shift and severity of obstructive sleep apnea before and after hemodialysis were compared in patients with ESRD. Seventeen patients with hemodialysis and moderate to severe obstructive sleep apnea were included. Polysomnographies were performed the night before and after hemodialysis to assess obstructive sleep apnea, and bioimpedance was used to measure fluid overload and leg fluid volume. The mean overnight rostral fluid shift was 1.27±0.41 L prehemodialysis; it correlated positively with fluid overload volume (r=0.39; P=0.02) and was significantly lower posthemodialysis (0.78±0.38 L; P<0.001). There was no significant difference in the mean obstructive apnea-hypopnea index before and after hemodialysis (46.8±22.0 versus 42.1±18.6 per hour; P=0.21), but obstructive apnea-hypopnea index was significantly lower posthemodialysis (-10.1±10.8 per hour) in the group of 12 patients, with a concomitant reduction of fluid overload compared with participants without change in fluid overload (obstructive apnea-hypopnea index +8.2±16.1 per hour; P<0.01). A lower fluid overload after hemodialysis was significantly correlated (r=0.49; P=0.04) with a lower obstructive apnea-hypopnea index. Fluid overload-assessed by bioimpedance-was the best predictor of the change in obstructive apnea-hypopnea index observed after hemodialysis (standardized r=-0.68; P=0.01) in multivariate regression analysis. Fluid overload influences overnight rostral fluid shift and obstructive sleep apnea severity in patients with ESRD undergoing intermittent hemodialysis. Although no benefit of hemodialysis on obstructive sleep apnea severity was observed in the whole group, the change in obstructive apnea-hypopnea index was significantly correlated with the change in fluid overload after hemodialysis. Moreover, the subgroup with lower fluid overload posthemodialysis showed a significantly lower obstructive sleep apnea severity, which provides a strong incentive to further study whether optimizing fluid status in patients with obstructive sleep apnea and ESRD will improve the obstructive apnea-hypopnea index.

Influence of posture and frequency modes in total body water estimation using bioelectrical impedance spectroscopy in boys and adult males.

The aim of the study was to examine differences in total body water (TBW) measured using single-frequency (SF) and multi-frequency (MF) modes of bioelectrical impedance spectroscopy (BIS) in children and adults measured in different postures using the deuterium (2H) dilution technique as the reference. Twenty-three boys and 26 adult males underwent assessment of TBW using the dilution technique and BIS measured in supine and standing positions using two frequencies of the SF mode (50 kHz and 100 kHz) and the MF mode. While TBW estimated from the MF mode was comparable, extra-cellular fluid (ECF) and intra-cellular fluid (ICF) values differed significantly (p < 0.01) between the different postures in both groups. In addition, while estimated TBW in adult males using the MF mode was significantly (p < 0.01) greater than the result from the dilution technique, TBW estimated using the SF mode and prediction equation was significantly (p < 0.01) lower in boys. Measurement posture may not affect estimation of TBW in boys and adult males, however, body fluid shifts may still occur. In addition, technical factors, including selection of prediction equation, may be important when TBW is estimated from measured impedance.

Lower body negative pressure counters headward fluid shifts in the brain and eye (1103.3)

Recent ophthalmic evaluations of 7 astronauts after 6‐month missions to International Space Station show unexpected vision impairment. In addition, lumbar punctures in 4 astronauts with optic disc edema showed moderate elevations of cerebral spinal fluid pressure after returning to Earth. This Visual Impairment Intracranial Pressure (VIIP) syndrome is likely due to a head‐ward body fluid shift that elevates intracranial pressure (ICP). We hypothesized that a moderate level of lower body negative pressure (LBNP) would counteract headdown, body‐tilt, induced elevations in intraocular pressure (IOP) and ICP. Seven healthy non‐smoking volunteers participated in this study (mean age: 36 years). Right and left IOP, ICP (ultrasound pulse phase lock loop), arm blood pressure, and heart rate were measured during the last minute of each testing condition. Subjects were positioned supine (5 mins), sitting (5 mins), 15‐degrees head‐down tilt (HDT) (5 mins) and ten minutes of HDT with LBNP (25 mmHg). The order of HDT and HDT+LBNP tests were balanced. The right and left IOP values were averaged and used for statistical analysis (p&lt;0.05). Data are presented as mean ± standard deviation. The change from supine was calculated for IOP values. IOP significantly decreased from supine to sitting posture by 2.4 ± 0.7 mmHg, and increased by 1.3 ± 2.4 mmHg from supine to the HDT position. LBNP during head‐down‐tilt significantly lowered IOP to supine levels (difference from supine, 0.1 ± 0.8 mmHg). In addition, added LBNP during HDT significantly decreased ICP pulse amplitudes by 2.8±4.3 microns. Mean blood pressure and heart rate did not change significantly across all conditions. These data demonstrate that short duration exposures to HDT increase IOP and ICP significantly and further, that LBNP counteracts these elevations of IOP and ICP. Therefore, LBNP may help counteract vision impairments in space. Supported by NSBRI postdoctoral fellowship (BRM), la Caixa fellowship (NNG), and NASA grant NNX13AJ12G (ARH).

Is intensified diuretic therapy an effective new treatment strategy in obstructive sleep apnoea patients with uncontrolled hypertension?

There is evidence of an important mutual interaction between sleep disorders and cardiovascular problems. Patients with cardiovascular diseases often complain of several sleep disturbances such as sleep fragmentation, insomnia and breathing disorders during sleep. On the contrary, patients with sleep disorders are more frequently affected by cardiovascular problems. Such a reciprocal interaction makes it often difficult to determine which is the cause and which is the effect between these conditions. Sleep-related breathing disorders, particularly obstructive sleep apnoea syndrome (OSAS), formerly named Pickwickian syndrome, are highly prevalent in the general population, OSAS affecting at least 4% of middle-aged men and 2% of middle-aged women in the developed world, with its prevalence increasing in parallel with the growing prevalence of obesity. Individuals with OSAS are also characterized by a worsened quality of life and by excessive daytime somnolence, and are at an increased risk of road traffic and workplace accidents when compared with nonapnoeic individuals [1–3]. From a public health viewpoint, also the reported increased risk of cardiovascular morbidity and mortality associated with a diagnosis of obstructive sleep apnoea (OSA) is of particular importance [4,5]. OSA is associated with a higher prevalence of hypertension, in particular resistant hypertension, myocardial infarction, cardiac arrhythmias, congestive heart failure and stroke. Indeed, untreated severe OSA confers a three-fold increased risk of death from cardiovascular causes [1,2,6]. Prevalence of hypertension in OSA patients ranges from 35 to 80% and appears to be influenced by OSA severity. In fact, more than 60% of individuals with respiratory disturbance index greater than 30 were found to be hypertensive. Conversely, approximately 40% of hypertensive patients are diagnosed with OSA. Finally, when focussing on patients with resistant hypertension, OSA prevalence is significantly higher, reaching 83% [7]. Given this background, and the relevant interaction between OSA and cardiovascular disorders, it is evident that strategies for OSA treatment also play a key role in cardiovascular diseases prevention.

Body cell mass evaluation in critically ill patients: killing two birds with one stone.

Body cell mass (BCM) is the metabolically active cell mass involved in O2 consumption, CO2 production and energy expenditure. BCM measurement has been suggested as a tool for the evaluation of nutritional status. Since BCM is closely related to energy expenditure, it could also represent a good reference value for the calculation of nutrient needs. In a recent issue of Critical Care, Ismael and colleagues used bioelectrical impedance analysis parameters and anthropometric variables to evaluate BCM in patients with acute kidney injury, before and after a hemodialysis session. The results of this study suggest that BCM is relatively insensitive to major body fluid shifts, a well known factor interfering with nutritional evaluation/monitoring and energy need calculations in the ICU. Thus, BCM seems to be a more 'stable' nutritional variable, as it is apparently less influenced by non-nutritional factors. The results of this paper emphasize the need to identify biologically sound parameters for nutritional status evaluation and energy need calculation in critically ill patients; in this regard, BCM could fulfill these expectations.

Diurnal Pattern of Intraocular Pressure is Affected by Microgravity When Measured in Space With the Pressure Phosphene Tonometer (PPT)

This study was designed to evaluate the effect of microgravity on the diurnal variation of intraocular pressure (IOP). IOPs were measured with the pressure phosphene tonometer in 1 subject (the first Korean astronaut) during spaceflight. IOPs were measured every 3 hours during day time (6 times per day) at 2 separate days in space with 3 repeated measurements at each time on both eyes. A total of 72 measurements were obtained during spaceflight. To obtain control IOP data, IOP was measured using the same protocol on ground before spaceflight. Mean IOP increased by 26.3% during spaceflight compared with that on ground [16.47 ± 0.60 (SD) mm Hg vs. 13.04 ± 0.74 mm Hg, P<0.001). The IOP elevation was maintained until Launch+8 days. There was no significant difference in IOP increase between right and left eyes (16.4 2 ± 0.65 mm Hg right eye vs. 16.53 ± 0.56 mm Hg left eye). There was a different pattern of diurnal variation of IOP during spaceflight compared with that on ground. The IOP at 7 AM was the lowest under microgravity, whereas it was the highest on ground. The slope of the best fit line for diurnal IOP measures was 0.0349 mm Hg/h (95% confidence interval: 0.0082-0.0616) under microgravity and -0.0294 mm Hg/h (95% confidence interval: -0.0063-0.0041) on ground. The study showed a different diurnal pattern of IOP under microgravity compared with that on ground. This result suggests that gravity and subsequent body fluid shift is one of the determining factors of IOP diurnal variation.

The Flame Photometer as Engine of Nephrology: A Biography

In the 1940s, the flame photometer made possible for the first time relatively simple and quick measurements of sodium and potassium in serum and urine. During World War II, it unexpectedly fell into the hands of John P. Peters of Yale University, who sought to understand water and electrolyte physiology and apply such knowledge to patient problems. Pupils and young associates of Peters would seed the early nephrology divisions and training programs in the United States; the flame photometer was essential to their work and that of their trainees, both Americans and international visitors. Hyponatremia and the syndrome of inappropriate antidiuretic hormone secretion became the "attribute" disorders of nephrologists. Invention of a microflame photometer fostered the revival of micropuncture and transport studies. In the 1960s, the flame photometer was linked to Leonard Skeggs' sequential automated analysis system, leading to enormous numbers of routine measurements of electrolytes. The growing number of nephrologists, then based mostly at teaching hospitals, thus found plentiful instances of sodium and potassium abnormalities to address. The autoanalyzer also catalyzed use of the anion gap, another emblem of nephrology in its early decades. Not only ideas and theories, but also the usually invisible machinery, enable the growth of a knowledge base and formation of a scientific discipline or medical specialty. Of course, the flame photometer did not itself shape the agenda of nephrology, but it allowed the most influential group of progenitors and their progeny to explore normal function and bring a strongly physiologic imperative to their daily work with patients.