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Space agencies are looking for effective and efficient countermeasures for the degrading effects of weightlessness on the human body. The aim of this study was to assess the effects of a novel jump exercise countermeasure during bed rest on vitals, body mass, body composition, and jump performance. 23 male participants (29±6 years, 181±6 cm, 77±7 kg) were confined to a bed rest facility for 90 days: a 15-day ambulatory measurement phase, a 60-day six-degree head-down-tilt bed rest phase (HDT), and a 15-day ambulatory recovery phase. Participants were randomly allocated to the jump training group (JUMP, n = 12) or the control group (CTRL, n = 11). A typical training session consisted of 4x10 countermovement jumps and 2x10 hops in a sledge jump system. The training group had to complete 5-6 sessions per week. Peak force for the reactive hops (3.6±0.4 kN) as well as jump height (35±4 cm) and peak power (3.1±0.2 kW) for the countermovement jumps could be maintained over the 60 days of HDT. Lean body mass decreased in CTRL but not in JUMP (-1.6±1.9 kg and 0±1.0 kg, respectively, interaction effect p = 0.03). Resting heart rate during recovery was significantly increased for CTRL but not for JUMP (interaction effect p<0.001). Participants tolerated the near-daily high-intensity jump training and maintained high peak forces and high power output during 60 days of bed rest. The countermeasure was effective in preserving lean body mass and partly preventing cardiac deconditioning with only several minutes of training per day.

Prolonged exposure to microgravity, simulated via 6° head‐down tilt bed rest (HDT), induces musculoskeletal deconditioning and negatively impacts body composition. This study evaluated whether a combination of aerobic exercise with artificial gravity (AG) offers superior protection in comparison to exercise alone. Twenty‐four healthy male participants completed 60 days of HDT, randomized into control (C), exercise‐only (EX) and exercise with AG (EX‐AG) groups. Muscle volume, intramuscular fat, body composition and isokinetic strength were assessed via whole‐body MRI and isokinetic dynamometry. All groups experienced thigh fat‐free muscle volume loss: C (10.5% ± 2.6%), EX (6.9% ± 2.4%) and EX‐AG (4.3% ± 2.4%), with EX‐AG showing significantly less atrophy than C ( p  < 0.001). Compared with C, EX‐AG preserved more muscle in both anterior ( p   <  0.001) and posterior ( p  < 0.05) compartments, whilst EX preserved more muscle only anteriorly ( p  < 0.05). The fat ratio increased more in C (8.9% ± 6.0%) compared with EX‐AG (−0.8% ± 3.8%; p  < 0.05) but not EX (6.5% ± 9.8%). Muscle fat infiltration increased across all groups (C, 7.0% ± 3.7%; EX, 6.2% ± 4.3%; EX‐AG, 3.1% ± 4.7%) but was not different between groups ( p  > 0.05). Maximal isokinetic torque decreased in all groups over all measured angular velocities but was not different between groups ( p  > 0.05). This is the first study to investigate the combination of AG and exercise as a countermeasure to body composition changes induced by long‐term bed rest. We showed that EX‐AG provided partial protection against muscle atrophy and fat accumulation but did not outperform exercise alone in preserving muscle quality, strength or overall body composition. What is the central question of this study? Does a combination of aerobic exercise with artificial gravity provide superior protection against skeletal muscle atrophy and unfavourable body composition changes during prolonged bed rest, in comparison to exercise alone? What is the main finding and its importance? Our results demonstrate that the combination of aerobic exercise and artificial gravity offers partial protection against bed rest‐induced muscle atrophy and fat accumulation. However, it does not confer additional benefits over exercise alone in preserving muscle quality, strength or overall body composition. These findings inform the design of efficient countermeasures for musculoskeletal health in microgravity analogues.

Background The aim of our study is to compare the effect of the 30° reverse Trendelenburg position combined with the beach chair position on respiratory parameters in laparoscopic sleeve gastrectomy (LSG) with the 30° reverse Trendelenburg position alone. Material and method Fifty patients with body mass index > 30 were included in the study. The patients were divided into two groups; in the control group, the standard 30° reverse Trendelenburg. In the beach chair group, the feet were positioned at 30° flexion from the hips after a 30° RTP. For both positions, blood pressures, pulses, saturations, EtCO2, respiratory rate, inspiratory pressure (Pins), positive end-expiratory pressure (PEEP), minute volume, tidal volume, peak airway pressure (Ppeak), and dynamic compliance were recorded. In addition, the general surgeon was asked about his satisfaction with the intra-abdominal operation site view and whether he was uncomfortable with the position. Results Regardless of the group, the average age of the cases was 36.7 ± 12.1 years. There was no difference between the groups in terms of age, gender, BMI, operation time, blood pressures, heart rates, EtCO2, respiratory rate, PEEP, minute volume, tidal volume, and postoperative oxygen saturation ( p  > 0.05). Inspiratory and peak pressure were lower and dynamic compliance was higher in the beach chair position ( p  < 0.05). It was observed that the beach chair position decreased inspiratory and peak pressures and increased dynamic compliances in patients with a BMI between 35.1 and 40 ( p  < 0.05). Surgical satisfaction was high for both positions and there was no discomfort with the position. Conclusion It was determined that the beach chair position in LSGs reduced inspiratory and peak pressures and increased dynamic compliance. These parameters were related to BMI, and the beach chair position was more positive in terms of intraoperative lung pressures and dynamic compliance, especially in patients with a BMI between 35.1 and 40. ClinicalTrials.gov ID: NCT06402474 .

Dry immersion, which is a ground-based model of prolonged conditions of microgravity, is widely used in Russia but is less well known elsewhere. Dry immersion involves immersing the subject in thermoneutral water covered with an elastic waterproof fabric. As a result, the immersed subject, who is freely suspended in the water mass, remains dry. For a relatively short duration, the model can faithfully reproduce most physiological effects of actual microgravity, including centralization of body fluids, support unloading, and hypokinesia. Unlike bed rest, dry immersion provides a unique opportunity to study the physiological effects of the lack of a supporting structure for the body (a phenomenon we call ‘supportlessness’). In this review, we attempt to provide a detailed description of dry immersion. The main sections of the paper discuss the changes induced by long-term dry immersion in the neuromuscular and sensorimotor systems, fluid–electrolyte regulation, the cardiovascular system, metabolism, blood and immunity, respiration, and thermoregulation. The long-term effects of dry immersion are compared with those of bed rest and actual space flight. The actual and potential uses of dry immersion are discussed in the context of fundamental studies and applications for medical support during space flight and terrestrial health care.

ObjectiveTo evaluate functional myocardial contractility after 21 days of head-down bed rest (HDBR) in sedentary control (CON) or with a resistive vibration exercise (RVE) countermeasure (CM) applied, by using 4D echocardiographic (4D echo) imaging and speckle tracking strain quantification.MethodsTwelve volunteers were enrolled in a crossover HDBR design, and 4D echo was performed in supine position (REST) at BDC-2 and at R + 2, and in − 6° HDT at day 18, and during the first and the last minute of the 80° head-up step of tilt test performed at both BDC-2 and R + 2. Radial (Rad-Str), longitudinal (Lg-Str) and twist (Tw-Str) strains were measured by 4D speckle tracking, as well as left ventricle diastolic volume (LVDV) and mass (LVmass).ResultsOn HDT 18: in the CON group, LVDV and LVmass were reduced (p < 0.05), the Rad-Str decreased (p < 0.05) and Tw-Str showed a tendency to increase (p < 0.11), with no changes in Lg-Str. In RVE group, LVDV and LV mass, as well as all the strain parameters remained unchanged. On R + 2: in the CON group, LVDV and LVmass were not recovered in all subjects compared to pre-HDBR (p < 0.08) and Rad-Str was still decreased (p < 0.05), while Tw-Str tended to increase (p < 0.09). These parameters remained unchanged in the RVE group. Tilt 80°: Rad-Str and Lg-Str values at 80° tilt were similar post-HDT in both groups.ConclusionThe 4D echo and speckle tracking analysis showed that in the CON group, Rad-Str decreased concomitant with LVmass and LVDV with HDBR, but this observation did not allow concluding if HDBR induced a real remodeling or a muscle atrophy. RVE was able to preserve LVmass, LVDV and contractility during HDBR, thus proving its effectiveness to this aim. Nevertheless, the significant HDBR-induced changes observed in the CON group had only a limited effect on the cardiac contractile response as observed during post-HDBR tilt test. The level of contractility at 80° Tilt position was not affected either by HDBR or by RVE CM.

Postural fluid shifts may directly affect respiratory control via a complex interaction of baro‐ and chemo‐reflexes, and cerebral blood flow. Few data exist concerning the steady state ventilatory responses during head‐down tilt. We examined the cardiorespiratory responses during acute 50° head‐down tilt (HDT) in 18 healthy subjects (mean [SD] age 27 [10] years). Protocol 1 (n = 8, two female) was 50° HDT from 60° head‐up posture sustained for 10 min, while exposed to normoxia, normoxic hypercapnia (5% CO2), hypoxia (12% inspired O2) or hyperoxic hypercapnia (95% O2, 5% CO2). Protocol 2 (n = 10, four female) was 50° HDT from supine, sustained for 10 min, while breathing either medical air or normoxic hypercapnic (5% CO2) gas. Ventilation (V̇E ${{\\dot{V}}_E}$ , pneumotachograph), end‐tidal O2 and CO2 concentration and blood pressure (Finapres) were measured continuously throughout each protocol. Middle cerebral artery blood flow velocity (MCAv; transcranial Doppler) was also measured during protocol 2. Ventilation increased significantly (P < 0.05) compared to baseline during HDT in both hyperoxic hypercapnia (protocol 1 by mean [SD] 139 [26]%) and normoxic hypercapnia (protocol 1 by mean [SD] 131 [21]% and protocol 2 by 129 [23]%), despite no change in PETCO2 ${{P}_{{\\mathrm{ETC}}{{{\\mathrm{O}}}_2}}}$or PETO2 ${{P}_{{\\mathrm{ET}}{{{\\mathrm{O}}}_2}}}$from baseline. No change in V̇E ${{\\dot{V}}_E}$was observed during HDT with medical air or hypoxia, and there was no significant change in MCAv during HDT compared to baseline. The absence of change in cerebral blood flow leads us to postulate that the augmented ventilatory response during steep HDT may involve mechanisms related to cerebral venous pressure and venous outflow. What is the central question of this study? Postural fluid shifts affect respiratory control via complex interactions between baroreceptor and chemoreceptor reflexes, and cerebral blood flow. Few data exist concerning steady state ventilatory responses during head down tilt. What is the main finding and its importance? Acute 50° head‐down tilt augments the ventilatory response to steady state normoxic and hyperoxic hypercapnia possibly via mechanisms involving cerebral blood flow. These findings are relevant clinically during procedures performed in a steep head‐down position and microgravity environments where individuals are exposed to fluid shifts and elevated atmospheric CO2.

Purpose The lateral Trendelenburg position (LTP) may hinder the primary pathophysiologic mechanism of ventilator-associated pneumonia (VAP). We investigated whether placing patients in the LTP would reduce the incidence of VAP in comparison with the semirecumbent position (SRP). Methods This was a randomized, multicenter, controlled study in invasively ventilated critically ill patients. Two preplanned interim analyses were performed. Patients were randomized to be placed in the LTP or the SRP. The primary outcome, assessed by intention-to-treat analysis, was incidence of microbiologically confirmed VAP. Major secondary outcomes included mortality, duration of mechanical ventilation, and intensive care unit length of stay. Results At the second interim analysis, the trial was stopped because of low incidence of VAP, lack of benefit in secondary outcomes, and occurrence of adverse events. A total of 194 patients in the LTP group and 201 in the SRP group were included in the final intention-to-treat analysis. The incidence of microbiologically confirmed VAP was 0.5% (1/194) and 4.0% (8/201) in LTP and SRP patients, respectively (relative risk 0.13, 95% CI 0.02–1.03, p  = 0.04). The 28-day mortality was 30.9% (60/194) and 26.4% (53/201) in LTP and SRP patients, respectively (relative risk 1.17, 95% CI 0.86–1.60, p  = 0.32). Likewise, no differences were found in other secondary outcomes. Six serious adverse events were described in LTP patients ( p  = 0.01 vs. SRP). Conclusions The LTP slightly decreased the incidence of microbiologically confirmed VAP. Nevertheless, given the early termination of the trial, the low incidence of VAP, and the adverse events associated with the LTP, the study failed to prove any significant benefit. Further clinical investigation is strongly warranted; however, at this time, the LTP cannot be recommended as a VAP preventive measure. ClinicalTrials.gov identifier NCT01138540.

The effects of a recruitment manoeuvre (RM) with positive end-expiratory pressure (PEEP) on lung compliance (CLUNG) are not well characterised in robot-assisted laparoscopic radical prostatectomy (RARP). Patients were allocated to group R (n = 10; with an RM) or C (n = 9; without an RM). An RM involved sustained inflation of 30 cmH2O for 30 s. The lungs were ventilated with volume-controlled ventilation with tidal volume of 7 mL kg−1 of predicted body weight and fraction of inspired oxygen of 0.5. End-tidal carbon dioxide pressure was maintained at normocapnia. Patients were in the horizontal lithotomy position (pre-op). After pneumoperitoneum, patients underwent RARP in a steep Trendelenburg lithotomy position at a PEEP level of 0 cmH2O (RARP0). An RM was used in the R group but not in the C group. Patients were then ventilated with 5 cmH2O PEEP for 1 h after RARP0 (RARP5.1) and 2 h after RARP0 (RARP5.2). Oesophageal pressure and airway pressure were measured for calculating CLUNG and chest wall compliance. CLUNG significantly decreased from pre-op to RARP0 and did not significantly increase from RARP0 to RARP5.1 and RARP5.2 in either group. CLUNG differed significantly between groups at RARP5.1 and RARP5.2 (103 ± 30 vs. 68 ± 11 mL cm−1 H2O and 106 ± 35 vs. 72 ± 9 mL cm−1 H2O; P < 0.05). In patients undergoing RARP, with the addition of RM, the CLUNG was effectively increased from the horizontal lithotomy position to the steep Trendelenburg lithotomy position under pneumoperitoneum.

To analyze the effects of pressure-controlled ventilation-volume guaranteed (PCV-VG) and volume controlled ventilation (VCV) on airway pressures and respiratory and circulatory indicators during laparoscopic surgery in Trendelenburg position. Prospective randomized comparative clinical study. Tertiary hospital. Forty ASA physical status 1 and 2 patients who underwent elective laparoscopic surgery in Trendelenburg position. Patients were randomly allocated to either VCV group (n=20) or the PCV-VG group (n=20). After induction of anesthesia, for both modes of ventilation, the target tidal volume (VT) was 8mL/kg and the respiratory rate was adjusted to avoid hypercarbia. The peak and mean inspiratory pressures, dynamic compliance, exhaled VT, oxygenation index and physiological dead space were calculated and recorded at T1, 5minutes after induction of anesthesia in supine position, T2, 5minutes after stabilization of pneumoperitoneum, T3 and T4, 15 and 60minutes after 30° Trendelenburg position with pneumoperitoneum respectively. PCV-VG group had significantly lower peak inspiratory pressure and greater dynamic compliance than VCV group (P<.001). In patients who underwent laparoscopic surgery in Trendelenburg position, PCV-VG was superior to VCV in its ability to provide ventilation with lower peak inspiratory pressure and greater dynamic compliance. •We compared PCV-VG and VCV on respiratory mechanics during laparoscopic surgery.•PCV-VG had significantly lower PIP and greater dynamic compliance than VCV group.•PCV-VG has the advantage to lower incidence of barotrauma.

Many astronauts experience ocular structural and functional changes during long‐duration spaceflight, including choroidal folds, optic disc edema, globe flattening, optic nerve sheath diameter (ONSD) distension, retinal nerve fiber layer thickening, and decreased visual acuity. The leading hypothesis suggests that weightlessness‐induced cephalad fluid shifts increase intracranial pressure (ICP), which contributes to the ocular structural changes, but elevated ambient CO2 levels on the International Space Station may also be a factor. We used the spaceflight analog of 6° head‐down tilt (HDT) to investigate possible mechanisms for ocular changes in eight male subjects during three 1‐h conditions: Seated, HDT, and HDT with 1% inspired CO2 (HDT + CO2). Noninvasive ICP, intraocular pressure (IOP), translaminar pressure difference (TLPD = IOP‐ICP), cerebral and ocular ultrasound, and optical coherence tomography (OCT) scans of the macula and the optic disc were obtained. Analysis of one‐carbon pathway genetics previously associated with spaceflight‐induced ocular changes was conducted. Relative to Seated, IOP and ICP increased and TLPD decreased during HDT. During HDT + CO2 IOP increased relative to HDT, but there was no significant difference in TLPD between the HDT conditions. ONSD and subfoveal choroidal thickness increased during HDT relative to Seated, but there was no difference between HDT and HDT + CO2. Visual acuity and ocular structures assessed with OCT imaging did not change across conditions. Genetic polymorphisms were associated with differences in IOP, ICP, and end‐tidal PCO2. In conclusion, acute exposure to mild hypercapnia during HDT did not augment cardiovascular outcomes, ICP, or TLPD relative to the HDT condition. Many astronauts experience ocular structural and functional changes during long‐duration spaceflight, including choroidal folds, optic disc edema, globe flattening, optic nerve sheath diameter distension, retinal nerve fiber layer thickening, and decreased visual acuity. This study investigated whether acute exposure to mild hypercapnia combined with a cephalad fluid shift induced by head‐down tilt (HDT) would increase cerebral or ocular blood flow, result in an increase in intracranial pressure, a reduction in translaminar pressure difference, and a mild accumulation of fluid at the optic nerve. Breathing 1% CO2 for 60 min did not change our cardiovascular, ocular, or intracranial pressure measures, but genetic polymorphisms within the one‐carbon pathway may lead to differential responses between subjects.