Tilt Position Research Articles

Analysis of external pressure on the left calf in the Lloyd-Davies position during colorectal surgery.

Well-leg compartment syndrome (WLCS) is a potentially life-threatening postoperative complication related to the Lloyd-Davies surgical position, which can place increased external pressure on the calf region. We conducted this study to analyze external pressure changes, by applying a leg holder system to the left calf region of patients placed in the Lloyd-Davies position during laparoscopic surgery. The study participants were 50 patients who underwent laparoscopic surgery for colorectal cancer in the Lloyd-Davies position. We assessed the maximum external pressure (MEP) on the left calf region using a pressure-distribution measurement system. Intraoperative measurements were taken continuously, and the MEP was evaluated with the patient horizontal and every 30min during surgery in the head and right-down tilt position. The intraoperative MEP increased gradually when the patient was in the head and right-down tilt position and decreased when the patient was returned to the horizontal position. The MEP was higher in patients aged < 60years, those who were obese, and those with a thick calf circumference. Both body mass index (BMI) and the maximum left calf circumference (MLCC) were found to correlate with the MEP. In addition to a high BMI, which is a well-known risk factor for WLCS, a high MLCC should be considered another risk factor, especially for patients under 60years.

Repositioning mattress: how a lateral tilt position reshapes the prevention of pressure ulcers in bedridden patients

Pressure ulcers have been part of tissue damage without effectiveness in medical, surgical, and intensive care units. This study aims to focus on developing lateral tilt positions for effective pressure ulcer relief for bedridden patients. A repositioning mattress was placed in the side-lying left lateral tilt position (15°, 30°, 45°), sheering (0.680, 1.323, 1.870), interface pressure (2.550, 2.290, 2.830), and placed at 1.5 m long piece of polyethylene rubber. The design strength was set at 6000 N and 2100 mm x 1105 mm ( = 42, = 34). The design shows the greatest supine position at 30°, 1.323, 2.290, pressure load ( = 1.125 (1820) 2050 psi, = 1.125 (620) 700 psi), tensile stress ( (MPa) = 42), compressive stress ( (MPa) = 34), and FOS ( = 42, = 34). The factor of safety illustrated that the 30° lateral tilt position is more consistent in repositioning for pressure ulcer prevention compared to the supine-to-tilt region. Further, an application of repositioning mattresses was developed to test in bedridden patients with tissue ulcers in nursing homes.

Gravitational Dose-Response Curves for Acute Cardiovascular Hemodynamics and Autonomic Responses in a Tilt Paradigm.

Background The cardiovascular system is strongly dependent on the gravitational environment. Gravitational changes cause mechanical fluid shifts and, in turn, autonomic effectors influence systemic circulation and cardiac control. We implemented a tilt paradigm to (1) investigate the acute hemodynamic response across a range of directions of the gravitational vector, and (2) to generate specific dose-response relationships of this gravitational dependency. Methods and Results Twelve male subjects were tilted from 45° head-up tilt to 45° head-down tilt in 15° increments, in both supine and prone postures. We measured the steady-state hemodynamic response in a range of variables including heart rate, stroke volume, cardiac output, oxygen consumption, total peripheral resistance, blood pressure, and autonomic indices derived from heart rate variability analysis. There is a strong gravitational dependence in almost all variables considered, with the exception of oxygen consumption, whereas systolic blood pressure remained controlled to within ≈3% across the tilt range. Hemodynamic responses are primarily driven by differential loading on the baroreflex receptors, combined with differences in venous return to the heart. Thorax compression in the prone position leads to reduced venous return and increased sympathetic nervous activity, raising heart rate, and systemic vascular resistance while lowering cardiac output and stroke volume. Conclusions Gravitational dose-response curves generated from these data provide a comprehensive baseline from which to assess the efficacy of potential spaceflight countermeasures. Results also assist clinical management of terrestrial surgery in prone posture or head-down tilt positions.

Progressive membrane-binding mechanism of SARS-CoV-2 variant spike proteins

SummaryMembrane recognition by viral spike proteins is critical for infection. Here we show the host cell membrane-binding surfaces of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike variants Alpha, Beta, Gamma, Delta, Epsilon, Kappa, and Omicron as well as SARS-CoV-1 and pangolin and bat relatives. They show increases in membrane binding propensities over time, with all spike head mutations in variants, and particularly BA.1, impacting the protein’s affinity to cell membranes. Comparison of hundreds of structures yields a progressive model of membrane docking in which spike protein trimers shift from initial perpendicular stances to increasingly tilted positions that draw viral particles alongside host cell membranes before optionally engaging angiotensin-converting enzyme 2 (ACE2) receptors. This culminates in the assembly of the symmetric fusion apparatus, with enhanced membrane interactions of variants explaining their unique cell fusion capacities and COVID-19 disease transmission rates.

Bone Metabolism During Strict Head-Down Tilt Bed Rest and CO2 Exposure

ObjectivesCarbon dioxide (CO2) levels on board the International Space Station reach 10× those of outdoor terrestrial levels. We report here studies assessing whether increased levels of ambient CO2 contribute to elevated bone resorption characteristically observed with bed rest as an analog for skeletal unloading during spaceflight.MethodsData are reported from two ground-based studies which included 12 male and 7 female subjects placed in a strict −6° head-down tilt (HDT) position for 30 days at 0.5% ambient CO2 or 60 days with nominal environment (0.04% CO2). Subjects were neither afforded a pillow nor allowed to use an elbow while eating to increase headward fluid pressure. Bone mineral density (BMD) and bone mineral content (BMC) were measured with dual-energy X-ray absorptiometry. Blood and urine were collected before and during HDT for analysis.ResultsThere was no change in BMD or BMC. Excretion of collagen crosslinks increased during HDT (p < 0.001) with no additive effect of CO2. Serum and urine mineral concentrations were not affected by CO2. Serum PTH and 1,25-deoxyhydroxyvitamin D were both reduced during bed rest (p < 0.0001), likely secondary to calcium efflux from bone, but with no additive effect of CO2 exposure. These changes reinforce the impact of decreased mechanical loading on bone and mineral homeostasis and the efficacy of the strict HDT model.ConclusionsExposure to 0.5% CO2 for 30 days did not exacerbate bone resorption during strict HDT bed rest. Future research on bone metabolism at varied CO2 levels is needed to clarify a risk ceiling for bone resorption, especially as missions progress beyond low-Earth orbit.Funding SourcesThe data reported here were from the NASA Human Research Program Standard Measures Cross-Cutting Project. Funding was provided by the NASA Human Research Program's Human Health Countermeasures Element. ERM was funded through a NASA Summer Science Institute Fellowship.

Effect of Different Positions During Surgical Preparation With Combined Spinal-Epidural Anesthesia for Elective Cesarean Delivery: A Randomized Controlled Trial

(Anesth Analg. 2021;133:1235–1243) A lateral tilt of the uterus is used to reduce pressure on the inferior vena cava in pregnant patients undergoing cesarean delivery. This may improve the fetal blood and oxygen supply. This position has been thought to improve the fetal acid-base status, though this has been recently called into question. This study aimed to evaluate whether moving the patient into a 30 degrees left lateral tilt position before elective cesarean delivery with combined spinal-epidural anesthesia could better improve the fetal acid-base status compared with a 15 degrees left lateral tilt or supine position.

Where should epistaxis education be focused? A comparative study between the public and healthcare workers on knowledge of first aid management methods of epistaxis.

Epistaxis can be life-threatening. Simple first aid management can stem bleeding. This study compared knowledge of first aid management methods of epistaxis between the general public and healthcare workers. A cross-sectional study of 100 healthcare workers and 103 adult members of the public was conducted at a large London teaching hospital. Respondents completed a survey assessing knowledge on nasal pinching site, head tilt and appropriate adjunct treatment use for first aid management of epistaxis. Twenty-four per cent and 68 per cent of healthcare workers compared with 25.2 per cent and 37.9 per cent of the public answered correctly on nasal pinching position and head tilt position, respectively, with a statistical difference for head tilt position. Two per cent, 2 per cent and 24 per cent of healthcare workers mentioned ice use on the nose, ice use in the mouth or ice use but not site, respectively, compared with 0 per cent, 0 per cent and 4.9 per cent of the public, with a statistical difference for ice without site. Healthcare workers and the public lack knowledge on first aid management of epistaxis. Improved education on first aid management is required, targeting healthcare workers and the public.

Anatomical changes of the internal jugular vein with Trendelenburg position and head rotation. Evidence for a safer catheterization

IntroductionCentral venous catheterization (CVC) is procedure used in hospital settings for patient monitoring, diagnostic, and therapeutic means. The right internal jugular vein (RIJV) is the first choice recommended, with ultrasound (US)‐guided as the gold standard. This method is not always available, especially in rural settings or developing countries, and complications are still frequent even under expert hands.The head‐down tilt (Trendelenburg) position involves elevation of the lower limbs to favor venous return and increase neck veins regurgitation. Evidence is scarce and contradicting regarding the safety of degree of inclination and head rotation.The objective of this study was to determine the effects of different degrees of Trendelenburg and head rotation on the RIJV and right common carotid artery (RCCA).MethodsAn experimental, longitudinal, prospective, analytical study was performed. Healthy adults of both sexes were recruited to voluntarily participate.Inclusion criteria: adults between 18 and 29 years of age, with normal vital signs, and a BMI ≤24.9. Those with RIJV pathology, anatomical variations, neck surgeries, COVID, or metabolic diseases were excluded.Neck US‐imaging was performed, obtaining cross‐sectional area (CSA) measurements of RIJV and RCCA, and their relationship, at the inferior level of the thyroid cartilage. Randomization at Trendelenburg positions of 0°, 5°, 10° and 15° and left head‐rotation of 0°, 45° and 90° in each inclination were performed. Vital signs and oxygen saturation were monitored between each position, as well questioning for discomfort symptoms.ResultsMeasurement of the RIJV and RCCA area was performed in 54 healthy participants (30 men), age range 21‐32. RIJV basal CSA was 1.0±0.5mm2 in a supine position (0°) without head rotation (0°). Trendelenburg angle and head‐rotation increased the CSA of the RIJV in a statistically significant way, obtaining the greatest area in a 15° Trendelenburg position and maximum rotation (Table 1). This, in turn, had no statistically significant difference with 10° Trendelenburg and 45° rotation (Table 2).ConclusionsA 5º, 10º, or 15º Trendelenburg position and contralateral head rotation increase RIJV CSA. Head rotation also changes the location of the vein anterior to the RCCA at maximum rotation, but not significantly at 45º.Although the greatest area obtained is achieved at the 15º Trendelenburg position with 90º head rotation, this position is uncomfortable and does not have statistical difference with 10º Trendelenburg position with 45 to 90º head rotation, which represents an increase of the initial diameter of 60% of CSA, making it a feasible position.Although Ultrasound‐guided catheterization is the gold‐standard, Trendelenburg position and 45º head rotation help increase RIJV diameter, to create a safer procedure.Significance and implicationsThis study provides anatomical evidence of RIJV changes with Trendelenburg and head rotation. Most international guidelines focus on CVC approach, and fail to mention patient positioning. The publishing of this data will aid with future versions of CVC guidelines.

The Design of a Structural Hyper-Resisting Element for Life-Threatening Earthquake Risk (SHELTER) for Building Collapse Scenarios: The Safety Chairs

Project SHELTER, Structural Hyper-resisting Element for Life-Threatening Earthquake Risk, aims at developing a strong and stiff functional unit to protect its occupants in case of severe earthquakes that lead to structural collapse. In case of collapse, these units will suffer impacts, particularly if they are installed in upper floors. To avoid severe injuries or death of occupants caused by collapse, safety chairs were designed, provided with shock-absorber systems and auxiliary retaining devices, to keep the occupants properly seated and safe. Three downfall scenarios were evaluated, consisting of vertical and tilted positions. A comprehensive numerical model to represent the human body was developed, mainly focused on chest behaviour and considering the anatomic limits of the vertebral spine. The mechanical ability of the safety chair to ensure the occupants’ safety was evaluated under these harsh conditions. Experimental downfall-and-impact tests will later be performed on shelter units, with crash-test dummies seated on the safety chairs for final validation.

Impact of head-up tilt on expiratory negative airway pressure ventilation-induced cardiovascular hemodynamics in the halothane-anesthetized intact microminipigs.

Elevation of the head and expiratory negative airway pressure (ENAP) ventilation can both significantly alter cardiovascular hemodynamics. The impact of head-up tilt (HUT) position on mechanically regulated ENAP ventilation-induced hemodynamics was assessed in microminipigs under halothane anesthesia (n = 4) in the absence and presence of adrenergic blockade. Supine ENAP ventilation increased cardiac output, but decreased mean right atrial, systolic pulmonary arterial, and mean left atrial pressures without significantly altering heart rate or aortic pressure. With HUT, the magnitude of ENAP ventilation-induced reduction in right and left atrial pressures was attenuated. HUT minimally altered ENAP ventilation-induced increase in cardiac output and reduction in pulmonary arterial systolic pressure. In addition, with up to 10cm of HUT there was a significant increase in mean right atrial pressure with and without the ENAP ventilation, whereas HUT did not alter the other hemodynamic variables irrespective of ENAP ventilation. These observations suggest that head elevation augments venous return from the brain irrespective of the ENAP ventilation. Additional studies with pharmacological adrenergic blockade revealed that ENAP ventilation-induced increases in cardiac output and decreases in pulmonary systolic pressure were minimally altered by sympathetic nerve activity, irrespective of the head position. However, the observed ENAP ventilation-induced decreases in right and left atrial pressures were largely dependent upon adrenergic activity. These experimental findings may provide insight into future clinical application of HUT and ENAP for patients with head injury and hypotension.

Incidence of Spinal Anesthesia Induced Severe Hypotension among the Pregnant Women Undergoing Cesarean Section at Muhima Hospital

BackgroundThe spinal induced severe hypotension is frequently reported during cesarean section; the literature counts 70% of severe hypotension following spinal anesthesia for cesarean section. This complication is thought to be serious and even fatal, when not well managed; however, in Rwanda, we have a limited data about that spinal induced life-threatening complication. ObjectivesTo determine the incidence and factors associated with spinal anesthesia induced severe hypotension during caesarian section at Muhima hospital.MethodologyThe study was cross-sectional, descriptive and analytical in design. The study population was the pregnant women scheduled for cesarean section, and a sample size of 108 was used. A self-developed questionnaire was used as data collection tool. ResultsForty percent of participants’ experienced spinal anesthesia induced severe hypotension; while preloading, left tilt position and infusion of ephedrine, were associated with lower incidence of severe hypotension.ConclusionThe incidence of spinal induced severe hypotension is high, however, preloading; left lateral position and co-infusion of ephedrine were found to protect the participants from spinal induced severe hypotension. Therefore, these techniques should be promoted.&#x0D; Rwanda J Med Health Sci 2022;5(1):62-70

Analysis of process efficiency: Role of flow and thermal characteristics on entropy production and heat transfer rates for thermal convection in porous beds confined within triangular configurations with hot slanted walls

Flow and heating characteristics associated with heat transfer rates vis-a-vis entropy generation based on flow and thermal irreversibilities are numerically studied for thermal convection in the porous bed confined within various configurations of triangular enclosures. The triangular configurations involve various vertex angles ( and ) with three tilt positions (configurations 1–3) subjected to a linear heating pattern of the slanted walls. Numerical studies are carried out for various dimensionless parameters (Prm and Dam ) at fixed Ram . Simulation results infer that the triangular configuration 3 [configuration 3: triangle is tilted perpendicularly from horizontal position (configuration 1 or 2)] involving is the optimal configuration based on the larger rate of heat transfer and moderate entropy production at larger porosities () for buoyancy dominant scenarios () irrespective of Prm .

Influence of panoramic cues during prolonged roll-tilt adaptation on the percept of vertical.

The percept of vertical, which mainly relies on vestibular and visual cues, is known to be affected after sustained whole-body roll tilt, mostly at roll positions adjacent to the position of adaptation. Here we ask whether the viewing of panoramic visual cues during the adaptation further influences the percept of the visual vertical. Participants were rotated in the frontal plane to a 90° clockwise tilt position, which was maintained for 4-minutes. During this period, the subject was either kept in darkness, or viewed panoramic pictures that were either veridical (aligned with gravity) or oriented along the body longitudinal axis. Errors of the subsequent subjective visual vertical (SVV), measured at various tilt angles, showed that the adaptation effect of panoramic cues is local, i.e. for a narrow range of tilts in the direction of the adaptation angle. This distortion was found irrespective of the orientation of the panoramic cues. We conclude that sustained exposure to panoramic and vestibular cues does not adapt the subsequent percept of vertical to the direction of the panoramic cue. Rather, our results suggest that sustained panoramic cues affect the SVV by an indirect effect on head orientation, with a 90° periodicity, that interacts with a vestibular cue to determine the percept of vertical.

The impact examination of the head tilt size on the subjective visual vertical (SVV) among the normal individuals with ages ranged from 18 to 35 years

Objective: The subjective visual vertical (SVV) is commonly considered as an indicator of the sense of orientation. The present study aims to assess the impact of head tilt size (by 0°, 15°, 30° and 45° to the left or to the right) on SVV among the normal individuals with ages ranged from 18 to 35 years. Methods: Four healthy participants (30 males and 17 females; mean ± SD age: 22.14 ± 3.463) were included in current study. SVV was measured using a forced-choice paradigm and was applied (in different head tilt positions) for every individual twice the time. In addition, difference in averages of SVV in zero and non-zero positions was compared. A p-value of .05 or below was considered to be statistically significant. Results: There is statistically significant different between head tilt size by 15° and without head tilt for averages of SVV responses (p ˂ .001). Averages of SVV responses were not different between the head tilt size by 30° and 45° and without head tilt (p > .05). In addition, there is statistically significant different between head tilt size by 15° to the left and to the right (p ˂ .001). This rate was not statistically significant between 30° to the left and to the right and 40° to the left and to the right (p > .05). Conclusion: Our results showed that head tilt size by 15° have an impact on the evaluation of the SVV. These findings must be taken into account in the growing body of research that uses the SVV paradigm in disease settings.

Visuospatial orientation: Differential effects of head and body positions

To orientate in space, the brain must integrate sensory information that encodes the position of the body with the visual cues from the surrounding environment. In this process, the extent of reliance on visual information is known as the visual dependence. Here, we asked whether the relative positions of the head and body can modulate such visual dependence (VD). We used the effect of optokinetic stimulation (30°/s) on subjective visual vertical (SVV) to quantify VD as the average optokinetic-induced SVV bias in clockwise and counter-clockwise directions. The VD bias was measured in eight subjects with a head-on-body tilt (HBT) where only the head was tilted on the body, and also with a whole-body tilt (WBT) where the head and body were tilted together. The VD bias with HBT of 20° was in the same direction of the head tilt position (left tilt VD −1.35 ± 0.1.2°; right VD 1.60 ± 0.9°), whereas the VD bias with WBT of 20° was in a direction away from the body tilt position (left tilt VD 2.5 ± 1.1°; right tilt VD −2.1 ± 0.9°). These findings show differential effects of relative head and body positions on visual cue integration, a process which could facilitate optimal interaction with the surrounding environment for spatial orientation.

Effect of maternal positioning during cardiopulmonary resuscitation: a systematic review and meta-analyses

BackgroundAlthough rare, cardiac arrest during pregnancy is the leading cause of maternal death. Recently, its incidence has been increasing worldwide because more pregnant women have risk factors. The provision of early, high-quality cardiopulmonary resuscitation (CPR) plays a major role in the increased likelihood of survival; therefore, it is important for clinicians to know how to manage it. Due to the aortocaval compression caused by the gravid uterus, clinical guidelines often emphasise the importance of maternal positioning during CPR, but there has been little evidence regarding which position is most effective.MethodsWe searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, and OpenGrey (updated on April 3, 2021). We included clinical trials and observational studies with reported outcomes related to successful resuscitations.ResultsWe included eight studies from the 1,490 screened. The eight studies were simulation-based, crossover trials that examine the quality of chest compressions. No data were available about the survival rates of mothers or foetuses/neonates. The meta-analyses showed that resuscitation of pregnant women in the 27°–30° left-lateral tilt position resulted in lower quality chest compressions. The difference is an 19% and 9% reduction in correct compression depth rate and correct hand position rate, respectively, compared with resuscitations in the supine position. Inexperienced clinicians find it difficult to perform chest compressions in the left-lateral tilt position.ConclusionsGiven that manual left uterine displacement allows the patient to remain supine, the resuscitation of women in the supine position using manual left uterine displacement should continue to be supported. Further research is needed to fill knowledge gaps regarding the effects of maternal positioning on clinical outcomes, such as survival rates following maternal cardiac arrest.

Optimizing the Working Space for Single-Port Laparoscopic Totally Extraperitoneal Closure of Inguinal Hernia with TPV Protocol in Infants and Young Children.

Purpose: To evaluate the outcomes of single-port laparoscopic internal ring closure of inguinal hernia, optimized according to TPV (tilt, pad, and void) protocol, in infants and young children. Methods: From August 2018 to March 2021, a prospective cohort study was conducted including 400 patients younger than 3 years with either left- or right-side inguinal hernia treated with single-port laparoscopic totally extraperitoneal (TEP) closure of the internal ring using a two-hooked core needle apparatus. Patients whose hospitalization ID ended with an odd number were included in group A (n = 200). They were surgically treated with single-port laparoscopy optimized according to TPV protocol, in which the operating table was placed at a 30° head-down tilt position (tilt), the hip was padded by 4-5 cm (pad), and the bladder was voided (void). The remaining patients in group B (n = 200) were conventionally treated with single-port laparoscopic TEP closure of the internal ring. Success rate of surgery, surgery duration, and postoperative complications of two groups were compared. Results: A significantly higher success rate of surgery was detected in group A than in group B (198/200 versus 182/200, P < .05). Regardless of unilateral or bilateral inguinal hernia, surgery duration was significantly shorter in group A than in group B (unilateral inguinal hernia, 14.38 ± 2.85 minutes versus 21.17 ± 4.47 minutes; bilateral inguinal hernia, 20.73 ± 4.58 minutes versus 28.99 ± 4.12 minutes, both P < .05). In addition, the incidence of postoperative complications was significantly lower in group A (1/200 versus 8/200). Conclusions: TPV protocol to optimize working space for single-port laparoscopic TEP closure of inguinal hernia can increase the success rate, shorten surgery duration, and decrease the incidence of postoperative complications.

Pelvic tilt and functional acetabular position after total hip arthroplasty: an EOS 2D/3D radiographic study.

In total hip arthroplasty (THA), the functional anatomy of the spinopelvic unit should be taken into account to provide the correct functional positioning of the implant. The relationship between the spine and the pelvis in the sagittal plane is represented by pelvic tilt (PT). The sacral slope (SS) has been proposed as a more reliable parameter than the anterior pelvic plane (APP) to express the PT. This study investigated the relationship between the APP and the SS; and the relationship between the APP and the SS, respectively, with the postoperative acetabular orientation. 45 patients undergoing primary THA were prospectively enrolled. The EOS 2D/3D system was used to perform the radiographic evaluation before and 3 months after surgery. The following parameters were measured in both standing and sitting position: SS, APP, acetabular anteversion (AA) and inclination (AI). The SS values did not show any correlation with the values of the APP angle. The changes of the SS in the transition from the standing to the sitting position significantly correlated with the changes of the AA (r = -0.61; p < 0.0001). A weak correlation was found between the APP angle and the AA in standing position (r = -0.35; p = 0.02). The SS accurately expresses the functional orientation of the pelvis in the sagittal plane, and the functional orientation of the cup after hip replacement. Therefore, SS could be taken into account by navigation systems in order to achieve a patient-specific functional position of the acetabular cup.

Development of an apparatus and procedure for evaluating the efficiency of nasal irrigation.

Although different methods of nasal irrigation have been utilized, irrigation efficiency in nasal cavities has not been well assessed. The objective of this study was to develop an apparatus and procedure for evaluating the irrigation efficiency and to explore the optimal head position during irrigation. Casts of the left sinonasal cavity from a healthy volunteer were made from high-resolution-computed tomography data using 3D printing with composite materials. An adjustable apparatus that allowed cast fixation at the different head positions was built. The yogurt was used to simulate mucus. The cast with 5ml yogurt filled around the superior, middle, and inferior turbinate was fixed in six head positions including head tilt 10°, 45°, and 60° forward with or without leaning 30° to the right. The cast was irrigated with 120ml, 175ml, and 240ml dyed water and was video recorded. The irrigation efficiency was calculated based on the weight difference of the cast before and after the irrigation. Most residual yogurt was located around the superior meatus after the irrigation under different volumes and head positions. The irrigation efficiency of the rinse bottle or the pulsatile device was volume dependent, with the highest irrigation efficiency under 240ml water. When the left sinonasal cavity was irrigated, the head position of tilt 45° forward with leaning 30° to the right was the optimal head position for these two devices when compared to other positions. The pulsatile device with 240ml water performed better than the rinse bottle with 240ml water regarding the irrigation efficiency under the optimal head position (0.8700 ± 0.0138 vs 0.7536 ± 0.0099, p = 0.003). The developed apparatus provided a potential method for evaluating the irrigation efficiency. The head position of tilt 45° forward with leaning 30° was suitable for patients to perform the nasal irrigation.

Acute Gravitational Stress Selectively Impairs Dynamic Cerebrovascular Reactivity in the Anterior Circulation Independent of Changes to the Central Respiratory Chemoreflex.

Cerebrovascular reactivity (CVR) to changes in the partial pressure of arterial carbon dioxide (PaCO2) is an important mechanism that maintains CO2 or pH homeostasis in the brain. To what extent this is influenced by gravitational stress and corresponding implications for the regulation of cerebral blood flow (CBF) remain unclear. The present study examined the onset responses of pulmonary ventilation (V̇E) and anterior middle (MCA) and posterior (PCA) cerebral artery mean blood velocity (Vmean) responses to acute hypercapnia (5% CO2) to infer dynamic changes in the central respiratory chemoreflex and cerebrovascular reactivity (CVR), in supine and 50° head-up tilt (HUT) positions. Each onset response was evaluated using a single-exponential regression model consisting of the response time latency [CO2-response delay (t0)] and time constant (τ). Onset response of V̇E and PCA Vmean to changes in CO2 was unchanged during 50° HUT compared with supine (τ: V̇E, p = 0.707; PCA Vmean, p = 0.071 vs. supine) but the MCA Vmean onset response was faster during supine than during 50° HUT (τ: p = 0.003 vs. supine). These data indicate that gravitational stress selectively impaired dynamic CVR in the anterior cerebral circulation, whereas the posterior circulation was preserved, independent of any changes to the central respiratory chemoreflex. Collectively, our findings highlight the regional heterogeneity underlying CBF regulation that may have translational implications for the microgravity (and hypercapnia) associated with deep-space flight notwithstanding terrestrial orthostatic diseases that have been linked to accelerated cognitive decline and neurodegeneration.