Use of thigh pressure cuffs to modulate simulated microgravity-induced changes in the skin measured with high-resolution B-scan ultrasound

Mechanical countermeasures to headward fluid shifts

Head-to-foot gravitationally induced hydrostatic pressure gradients in the upright posture on Earth are absent in weightlessness. This results in a relative headward fluid shift in the vascular and cerebrospinal fluid compartments and may underlie multiple physiological consequences of spaceflight, including the spaceflight-associated neuro-ocular syndrome. Here, we tested three mechanical countermeasures [lower body negative pressure (LBNP), venoconstrictive thigh cuffs (VTC), and impedance threshold device (ITD) resistive inspiratory breathing] individually and in combination to reduce a posture-induced headward fluid shift as a ground-based spaceflight analog. Ten healthy subjects (5 male) underwent baseline measures (seated and supine postures) followed by countermeasure exposure in the supine posture. Noninvasive measurements included ultrasound [internal jugular veins (IJV) cross-sectional area, cardiac stroke volume, optic nerve sheath diameter, noninvasive IJV pressure], transient evoked otoacoustic emissions (OAE; intracranial pressure index), intraocular pressure, choroidal thickness from optical coherence tomography imaging, and brachial blood pressure. Compared with the supine posture, IJV area decreased 48% with application of LBNP [mean ratio: 0.52, 95% confidence interval (CI): 0.44-0.60, P < 0.001], 31% with VTC (mean ratio: 0.69, 95% CI: 0.55-0.87, P < 0.001), and 56% with ITD (mean ratio: 0.44, 95% CI: 0.12-1.70, P = 0.46), measured at end-inspiration. LBNP was the only individual countermeasure to decrease the OAE phase angle (Δ -12.9 degrees, 95% CI: -25 to -0.9, P = 0.027), and use of combined countermeasures did not result in greater effects. Thus, LBNP, and to a lesser extent VTC and ITD, represents promising headward fluid shift countermeasures but will require future testing in analog and spaceflight environments.NEW & NOTEWORTHY As a weightlessness-induced headward fluid shift is hypothesized to be a primary factor underlying several physiological consequences of spaceflight, countermeasures aimed at reversing the fluid shift will likely be crucial during exploration-class spaceflight missions. Here, we tested three mechanical countermeasures individually and in various combinations to reduce a posture-induced headward fluid shift as a ground-based spaceflight analog.

Reducing intracranial pressure by reducing central venous pressure: assessment of potential countermeasures to spaceflight-associated neuro-ocular syndrome

Spaceflight-associated neuro-ocular syndrome (SANS) involves unilateral or bilateral optic disc edema, widening of the optic nerve sheath, and posterior globe flattening. Owing to posterior globe flattening, it is hypothesized that microgravity causes a disproportionate change in intracranial pressure (ICP) relative to intraocular pressure. Countermeasures capable of reducing ICP include thigh cuffs and breathing against inspiratory resistance. Owing to the coupling of central venous pressure (CVP) and intracranial pressure, we hypothesized that both ICP and CVP will be reduced during both countermeasures. In four male participants (32 ± 13 yr) who were previously implanted with Ommaya reservoirs for treatment of unrelated clinical conditions, ICP was measured invasively through these ports. Subjects were healthy at the time of testing. CVP was measured invasively by a peripherally inserted central catheter. Participants breathed through an impedance threshold device (ITD, -7 cmH₂O) to generate negative intrathoracic pressure for 5 min, and subsequently, wore bilateral thigh cuffs inflated to 30 mmHg for 2 min. Breathing through an ITD reduced both CVP (6 ± 2 vs. 3 ± 1 mmHg; P = 0.02) and ICP (16 ± 3 vs. 12 ± 1 mmHg; P = 0.04) compared to baseline, a result that was not observed during the free breathing condition (CVP, 6 ± 2 vs. 6 ± 2 mmHg, P = 0.87; ICP, 15 ± 3 vs. 15 ± 4 mmHg, P = 0.68). Inflation of the thigh cuffs to 30 mmHg caused no meaningful reduction in CVP in all four individuals (5 ± 4 vs. 5 ± 4 mmHg; P = 0.1), coincident with minimal reduction in ICP (15 ± 3 vs. 14 ± 4 mmHg; P = 0.13). The application of inspiratory resistance breathing resulted in reductions in both ICP and CVP, likely due to intrathoracic unloading.NEW & NOTEWORTHY Spaceflight causes pathological changes in the eye that may be due to the absence of gravitational unloading of intracranial pressure (ICP) under microgravity conditions commonly referred to as spaceflight-associated neuro-ocular syndrome (SANS), whereby countermeasures aimed at lowering ICP are necessary. These data show that impedance threshold breathing acutely reduces ICP via a reduction in central venous pressure (CVP). Whereas, acute thigh cuff inflation, a popular known spaceflight-associated countermeasure, had little effect on ICP and CVP.

A Quantitative Method to Measure Skin Thickness in Leg Edema in Pregnant Women Using B-Scan Portable Ultrasonography: A Comparison Between Obese and Non-Obese Women

BACKGROUND This study aimed to use a portable ultrasound method to quantitatively measure skin thickness and to compare leg edema in obese and non-obese pregnant women. MATERIAL AND METHODS Thirty-six pregnant women (17 primiparas and 19 multiparas) at 27/28 and 37/38 weeks of pregnancy, with and without leg edema, had their lower leg skin thickness measured using a B-scan portable ultrasonography device (72 legs and maximum of 98 measurements). Measurements were compared between women who were obese prior to pregnancy, with a body mass index (BMI) ≥25 kg/m² and non-obese with a BMI <25 kg/m². RESULTS Skin thickness of the legs in pregnant women with edema was significantly increased compared with that in pregnant women without edema (6.4±0.3 mm vs. 4.6±0.4 mm) (p=0.0001). There was a significant correlation between the degree of pitting edema and skin thickness in all edematous legs (r=0.56; n=98; p<0.0001). The cutoff level of edema measured by portable ultrasound in non-obese pregnant women was 4.7 mm (sensitivity 83.9%, specificity 66.7%) and was 7.5 mm in obese pregnant women. Obese pregnant women with edema had a significantly increased leg skin thickness compared with non-obese pregnant women with edema (11.3±1.3 mm vs. 5.7±0.2 mm) (p<0.0001). CONCLUSIONS Portable ultrasonography is a reliable method of quantitatively measuring skin thickness of the lower leg in edema associated with pregnancy. The thickness of the skin in obese pregnant women with edema can be expected to be significantly increased compared with non-obese pregnant women with edema.

Evaluation of a mobile NMR sensor for determining skin layers and locally estimating the T(2eff) relaxation time in the lower arm

OBJECT

The nuclear magnetic resonance (NMR) mobile-universal-surface-explorer (MOUSE) was evaluated in a pilot study to determine its ability to detect physiological changes in human skin caused by physical or pharmacological interventions.

MATERIALS AND METHODS

The left lower arm skin thicknesses of ten male subjects were measured five times using a Profile NMR-MOUSE(®) ((1)H, 19 MHz) before and after a venous occlusion manoeuvre. In five of the subjects, the T(2eff) relaxation times were derived from a bi-exponential fitting and were determined in the dermis and subcutis before and after applying a salve containing capsaicin.

RESULTS

The dermis (including the epidermis) showed rather homogeneous signal amplitudes. The subcutis was characterised by higher and more variable amplitudes. The full-skin thickness values were affirmed by ultrasound imaging. The NMR profiles did not show significant skin swelling due to venous occlusion. In the dermis, capsaicin caused significant (p < 0.05) decreases in both components of T(2eff) (100 ± 19 ms-19 ± 10 ms; 9.5 ± 0.5 ms-7.2 ± 1.6 ms). In the subcutis, the T(2eff) was not affected.

CONCLUSION

In principle, NMR-MOUSE profiles are capable of detecting skin structure. However, precise measurements are jeopardised by poor reproducibility, long acquisition times, and incompatibility between the geometries of the sensitive area of the instrument and the non-planar structure of the skin. In the dermis, T(2eff) contrast could be used to detect the changes in tissue composition caused by inflammatory reactions.

Cardiac and vascular responses to thigh cuffs and respiratory maneuvers on crewmembers of the International Space Station

Background: the transition to microgravity eliminates the hydrostatic gradients in the vascular system. The resulting fluid redistribution commonly manifests as facial edema, engorgement of the external neck veins, nasal congestion, and headache. This experiment examined the responses to modified Valsalva and Mueller maneuvers measured by cardiac and vascular ultrasound (ECHO) in a baseline steady state and under the influence of thigh occlusion cuffs available as a countermeasure device (Braslet cuffs). Methods: nine International Space Station crewmember subjects (expeditions 16–20) were examined in 15 experiment sessions 101 ± 46 days after launch (mean ± SD; 33–185). Twenty-seven cardiac and vascular parameters were obtained with/without respiratory maneuvers before and after tightening of the Braslet cuffs (162 parameter states/session). Quality of cardiac and vascular ultrasound examinations was assured through remote monitoring and guidance by investigators from the NASA Telescience Center in Houston, TX, and the Mission Control Center in Korolyov, Moscow region, Russia. Results: 14 of 81 conditions (27 parameters measured at baseline, Valsalva, and Mueller maneuver) were significantly different when the Braslet was applied. Seven of 27 parameters were found to respond differently to respiratory maneuvers depending on the presence or absence of thigh compression. Conclusions: acute application of Braslet occlusion cuffs causes lower extremity fluid sequestration and exerts commensurate measurable effects on cardiac performance in microgravity. Ultrasound techniques to measure the hemodynamic effects of thigh cuffs in combination with respiratory maneuvers may serve as an effective tool in determining the volume status of a cardiac or hemodynamically compromised patient at the “microgravity bedside.”

Effect of thigh cuffs on haemodynamic changes of the middle cerebral artery and on orthostatic intolerance induced by 10 days head-down bed rest

Thigh cuffs are used by cosmonauts to limit fluid shift during space flight, but the appropriate level of cuff pressure and the duration of application to optimize their beneficial effects require further detailed investigations. In the present study, 10 days head-down tilt (HDT) bed rest was performed to assess the effects of thigh cuffs (40 mmHg, 10 h/day) on haemodynamic changes of the middle cerebral artery (MCA) and on orthostatic tolerance in six healthy male volunteers. Another six healthy male volunteers without thigh cuffs served as the control group. Haemodynamic parameters of the MCA were measured using transcranial Doppler. Orthostatic tolerance was assessed before and after HDT. After HDT, the mean upright time in the control and thigh cuff groups was 14.0 +/- 4.1 and 19.2 +/- 0.7 min, respectively. Compared with values before HDT, the percentage increase in heart rate from baseline in the upright position after HDT was significantly higher in the control group and the percentage change from baseline of mean diastolic arterial blood decreased more after HDT in this group. In the control group, systolic blood velocity (Vs) and mean blood velocity (Vm) of the right MCA decreased significantly during HDT. In the thigh cuffs group, the Vs of the right MCA decreased significantly on Days 3 and 7 of HDT and the Vm of the right MCA decreased significantly on Day 7 of HDT. The results indicate that daily use of thigh cuffs during 10 days of HDT does not completely prevent the decrease in haemodynamics of the right MCA, but is effective in preventing orthostatic intolerance.

WISE-2005: tibial and gastrocnemius vein and calf tissue response to LBNP after a 60-day bed rest with and without countermeasures

The objective of this study was to quantify by echography the changes in the intramuscular [gastrocnemius (Gast)] and nonintramuscular [posterior tibial (Tib)] calf veins cross-sectional area (CSA) and the superficial tissue thickness (STth) in response to lower body negative pressure (LBNP) after 60-day head-down bed rest (HDBR). Twenty-four healthy women (25–40 yr) were divided into three groups: control (Con), treadmill-LBNP and flywheel (Ex-Lb), nutrition (Nut; protein supplement). All underwent a LBNP (0 and −45 mmHg) before and on day 55 of HDBR. Subjects were identified as finisher (F) or nonfinisher (NF) of a 10-min tilt test after 60 days of HDBR. There were no differences in resting CSA of the Tib and Gast veins on HDBR day 55 compared with pre-HDBR for the Ex-Lb, Con and Nut, or the F groups; however, for NF both the Tib and Gast vein CSA at rest were significantly smaller after HDBR. At −45 mmHg LBNP, Tib and Gast CSAs were not significantly different from before HDBR in all groups (Ex-Lb, Con, Nut, F, NF). However, percent change in CSA of both veins from rest to −45 mmHg LBNP was significantly greater in the Con and Nut groups compared with Ex-Lb, and also NF compared with F. Similarly, the percent increase in STth on going from rest to −45 mmHg was higher after HDBR in the Con and Nut groups compared with Ex-Lb, as well as NF compared with F. These results showed that the Ex-Lb countermeasure minimized the bed rest effect on leg vein capacitance (CSA percent change) and STth increase during LBNP, whereas Nut had no effect and that higher leg vein and superficial tissue capacitance were associated with reduced orthostatic tolerance.