Weighing the impact of microgravity on vestibular and visual functions

Numerous technological challenges have been overcome to realize human space exploration. As mission durations gradually lengthen, the next obstacle is a set of physical limitations. Extended exposure to microgravity poses multiple threats to various bodily systems. Two of these systems are of particular concern for the success of future space missions. The vestibular system includes the otolith organs, which are stimulated in gravity but unloaded in microgravity. This impairs perception, posture, and coordination, all of which are relevant to mission success. Similarly, vision is impaired in many space travelers due to possible intracranial pressure changes or fluid shifts in the brain. As humankind prepares for extended missions to Mars and beyond, it is imperative to compensate for these perils in prolonged weightlessness. Possible countermeasures are considered such as exercise regimens, improved nutrition, and artificial gravity achieved with a centrifuge or spacecraft rotation.

Feasibility study using longitudinal bioelectrical impedance analysis to evaluate body water status during fluid resuscitation in a swine sepsis model

Fluid resuscitation is crucial in the initial management of sepsis; however, little is known about the serial changes and overall distribution of fluids administered into the body. To identify the feasibility of longitudinal bioelectrical impedance analysis during fluid treatment, a preclinical porcine model of Escherichia coli-induced sepsis was used. After sepsis induction, pigs were treated with fluid and vasopressors and monitored for up to 12 h after bacterial infusion or until death. Bipolar electrodes for bioelectrical impedance analysis were attached to the left extremities and measurements were performed every 10 min. Among the 12 subjects, 7 pigs expired during the experiment, and the median survival was 9.5 h. As sepsis progressed with an increase in cumulative fluid balance, R₀ [∝ 1/extracellular water (ECW)] decreased, while R_i [∝ 1/intracellular water (ICW)] and ratio of extracellular water to total body water (ECW/TBW) increased. The phase angle constantly decreased throughout the monitoring period, and all non-survivors died when the phase angle decreased by more than 10%. Among the variables, ΔR₀ and Δphase angle showed moderate negative correlations, and ΔECW/TBW showed a moderate positive correlation with the hourly fluid balance. Compared to survivors, a greater increase in ΔECW/TBW and a decrease in phase angle were observed in non-survivors over time, with an increase in cumulative fluid balance. Differences in ΔECW/TBW and phase angle emerged at 240 min when the difference in cumulative fluid balance between the two groups (survivors vs non-survivors) exceeded 1000 mL. In conclusion, continuous measurements of bioelectrical impedance analysis in a porcine sepsis model are feasible and may reflect changes in the body water profile during fluid resuscitation.

[Fluid management in shock patients : New targets in the initial phase of shock]

BACKGROUND

Early i.v. fluid administration is a cornerstone in modern therapy of shock, especially in septic shock. However, there is much uncertainty concerning the amount and rate of fluid and which goals and measures could guide fluid management. Administering the optimal fluid volume is important because fluid overload can lead to severe negative consequences like organ failure and worsening of patient's outcome.

AIM

This review aims to describe the importance of fluid therapy and discuss possible strategies in fluid management as well as possible measurements and goals to guide such therapy.

RECENT FINDINGS

There is no single measurement to guide fluid management alone. It is important to assess fluid responsiveness, which together with multiple other parameters can be used to repeatedly assess optimal fluid management. However, it has also not been shown that assessing fluid responsiveness can improve outcome.

CONCLUSIONS

After the initial resuscitation, further fluid administration should be determined by individual patient factors and measures of fluid responsiveness. A more restrictive fluid management with early vasopressor administration seems to be increasingly used in modern fluid management. However many questions regarding optimal fluid management remain to be solved.

Weight gain in the first week of life and its association with morbidity and mortality in extremely low birthweight (ELBW) infants

BACKGROUND

Weight gain in the first week of life is indicative of fluid excess in preterm neonates.

AIMS

To determine if morbidity and/or mortality of extremely low birthweight (ELBW) infants was lower in those who did not have excess weight gain in the first week of life, compared with those who did.

STUDY DESIGN

Retrospective cohort study.

SUBJECTS

ELBW infants born from 1st May 2014 - 31st May 2019.

EXCLUSIONS

major congenital abnormalities (including hydrops), died within the first 7 days, no recorded weight on day 6, 7 or 8.

OUTCOME MEASURES

We compared infants whose weight was greater than birthweight by day 7 and infants whose weight remained at, or below, birthweight by day 7.

RESULTS

There were 312 ELBW infants in the study population: 15 (5%) died before discharge from hospital. Holding birthweight and gestational age (GA) constant, the odds of death in neonates with day 7 weight >birthweight was about 3 times the odds of death in neonates with day 7 weight ≤birthweight (adjusted odds ratio 3.18, 95% confidence interval 0.66-15.26, p = 0.15). Neonates with day 7 weight >birthweight were more likely to have had a PDA that required treatment than those with day 7 weight ≤birthweight (65% versus 43% respectively; p <0.001).

CONCLUSIONS

ELBW infants who gain weight in the first week of postnatal life, have a greater risk of PDA requiring treatment and may have a higher risk of mortality than infants who lose weight in the first week of life.

A computer simulation of short-term adaptations of cardiovascular hemodynamics in microgravity

Astronauts in the microgravity environment experience significant changes in their cardiovascular hemodynamics. In this study, a system-level numerical model has been utilized to simulate the short-term adaptations of hemodynamic parameters due to the gravitational removal in space. The effect of lower body negative pressure (LBNP) as a countermeasure has also been simulated. The numerical model was built upon a lumped-parameter Windkessel model by incorporating gravity-induced hydrostatic pressure and transcapillary fluid exchange modules. The short-term (in the time scale of seconds and minutes) adaptations of the cardiac functions, blood pressure, and fluid volumes have been analyzed and compared with physiological data. The simulation results suggest microgravity induces a decrease in aortic pressure, heart rate, lower body capillary pressure and volume, and an increase in stroke volume, upper body capillary pressure and volume. The activation of LBNP causes an immediate increase in lower body blood volume and a gradual decrease in upper body blood volume. As a result, the fluid shift due to microgravity could be reversed by the LBNP application. LBNP also counters the impacts of microgravity on the cardiac functions, including heart rate and stroke volume. The simulation results have been validated using available physiological data obtained from spaceflight and parabolic flight experiments.

Does insulin impact cold-induced fluid- and protein-extravasation?

BACKGROUND

Insulin has been shown to stabilize the endothelial barrier via inactivation of the endothelial contractile machinery and enhancement of cell-cell adhesions. Here we explored if insulin by its endothelial-stabilizing and anti-inflammatory properties could influence the increase of fluid- and protein-extravasation during hypothermia.

METHODS

Two groups of animals (n=10, each) were cooled to 28°C, with insulin-infusion (I-group) or without (C-group), in a randomly controlled study. Fluid balance, hemodynamics, plasma volume (PV), colloid osmotic pressures in plasma (COPp) and interstitial fluid (COPi), hematocrit (Hct), cytokine profiles, serum-albumin- and protein-concentrations were measured and fluid extravasation rate (FER) and albumin-and protein-masses calculated.

RESULTS

During 240 min of hypothermia the albumin- and protein-masses together with COPp decreased significantly in both groups. COPi remained essentially unchanged. Plasma volume decreased significantly in the C-group, whereas only a decreasing trend was present in the I-group. Hemoconcentration was significant in both study groups reflected by the Hct-values. A slight increasing trend of FER was seen in both groups from 0.10 (0.04) ml/kg/min and 0.09 (0.05) mg/kg/min, C-group and I-group, respectively, to 0.14 (0.05) mg/kg/min and 0.12 (0.03) mg/kg/min, during the hypothermic period. Between-group differences were absent for all listed parameters including FER.

CONCLUSION

Insulin administration does not impact fluid and protein extravasation significantly in animals undergoing cooling and prolonged hypothermia.

Effect of below-the-knee compression stockings on severity of obstructive sleep apnea

BACKGROUND

Overnight fluid shift from the legs to the neck may narrow the upper airway and contribute to obstructive sleep apnea (OSA) pathogenesis. We hypothesized that below-the-knee compression stockings will decrease OSA severity in a general OSA population by decreasing daytime leg fluid accumulation and overnight fluid shift and increasing upper-airway size.

METHODS

Patients with OSA (apnea-hypopnea index ≥ 10) were randomized to wear compression stockings during the daytime or to a control group for 2 weeks. Overnight polysomnography with measurement of leg and neck fluid volumes and upper-airway cross-sectional area before and after sleep was performed at baseline and follow-up. The primary outcome was change in the apnea-hypopnea index.

RESULTS

Twenty-two patients randomized to compression stockings and 23 to control completed the study. The apnea-hypopnea index decreased significantly more in the compression stockings than in the control group (from 32.4 ± 20.0 to 23.8 ± 15.5 vs. from 31.2 ± 25.0 to 30.3 ± 23.8, p = 0.042), in association with a significantly greater reduction in the overnight decrease in leg fluid volume (p = 0.028), and a significantly greater increase in morning upper-airway cross-sectional area (p = 0.006). Overnight change in neck fluid volume was unchanged.

CONCLUSION

These observations suggest that in, a general OSA population, below-the-knee compression stockings decrease OSA severity modestly via attenuation of overnight fluid shift and consequent upper-airway dilatation.