Head-down tilt reduces the heart rate in postural tachycardia syndrome in acute setting: a pilot study.

BACKGROUND: Reduced preload and thoracic blood volume accompany postural tachycardia syndrome (POTS). Head-down tilt (HDT) increases both preload and intrathoracic blood volume. The objective of this study was to assess the safety and efficacy of HDT in POTS in acute settings. METHODS: This retrospective study evaluated POTS patients. Analyzed data included heart rate, blood pressure, cerebral blood flow velocity (CBFv) in the middle cerebral artery, and capnography. The baseline supine hemodynamic data were compared with the data obtained at the second minute of the -10° HDT. A linear mixed-effects model was used to assess the effect of HDT on hemodynamic variables. RESULTS: The HDT was explored in seven POTS patients and an additional seven POTS patients without HDT served as controls. In the HDT arm, four POTS patients had overlapping diagnoses of myalgic encephalopathy/chronic fatigue syndrome (ME/CFS) and one patient had comorbidity of post-acute sequelae of SARS-CoV-2 infection (PASC). HDT lowered heart rate by 10% and increased end-tidal CO2 by 8%. There was no change in other cardiovascular variables. CONCLUSIONS: In the acute setting, HDT is safe. HDT reduces the heart rate presumably by modulating baroreflex by enhancing preload and stroke volume, which in turn increases thoracic blood volume with a net effect of parasympathetic cardiovagal activation and/or sympathetic withdrawal. This pilot study provides a foundation to proceed with longitudinal studies exploring the long-term effect of repetitive HDT in conditions associated with preload failure such as POTS, ME/CSF, and PASC.

Head down tilt 15° to preserve salvageable brain tissue in acute ischemic stroke: A pre-clinical pooled analysis, with focus on cerebral hemodynamics.

Neurological outcome after ischemic stroke depends on residual salvageable brain tissue at the time of recanalization. Head down tilt 15° (HDT15) was proven effective in reducing infarct size and improving functional outcome in rats with transient middle cerebral artery occlusion (t-MCAO) by increasing cerebral perfusion within the ischemic penumbra. In this pooled analysis, individual animal-level data from three experimental series were combined in a study population of 104 t-MCAO rats (45 in HDT15 group and 59 in flat position group). Co-primary outcomes were infarct size and functional outcome at 24 h in both groups. The secondary outcome was hemodynamic change induced by HDT15 in ischemic and non-ischemic hemispheres in a subgroup of animals. Infarct size at 24 h was smaller in HDT15 group than in flat position group (absolute mean difference 31.69 mm3 , 95% CI 9.1-54.2, Cohen's d 0.56, p = 0.006). Functional outcome at 24 h was better in HDT15 group than in flat position group (median [IQR]: 13[10-16] vs. 11), with a shift in the distribution of the neurobehavioural scores in favour of HDT15. Mean cerebral perfusion in the ischemic hemisphere was higher during HDT15 than before its application (Perfusion Unit [P.U.], mean ± SD: 52.5 ± 19.52 P.U. vs. 41.25 ± 14.54 P.U., mean of differences 13.36, 95% CI 7.5-19.18, p = 0.0002). Mean cerebral perfusion in the non-ischemic hemisphere before and during HDT15 was unchanged (P.U., mean ± SD: 94.1 ± 33.8 P.U. vs. 100.25 ± 25.34 P.U., mean of differences 3.95, 95%, CI -1.9 to 9.6, p = 0.1576). This study confirmed that HDT15 improves the outcome in t-MCAO rats by promoting cerebral perfusion in the ischemic territory, without disrupting hemodynamics in non-ischemic areas.

The effect of head-down tilt in experimental acute ischemic stroke.

BACKGROUND: Collateral therapeutics exert a promising protective effect on the outcome of acute ischemic stroke. Cerebral blood flow (CBF) may be modulated by different head positioning. The current study aimed to determine the effect of head-down tilt (HDT) on stroke in a rodent model. METHODS: The model of middle cerebral artery occlusion and reperfusion (MCAO/R) was used in this study. Neurological deficit scoring, 2,3,5-triphenyltetrazolium chloride staining, brain water content, perivascular aquaporin protein-4 (AQP4) localization, pericyte marker platelet-derived growth factor receptor ß (PDGFRß), and CBF velocity were evaluated at 24 h after MCAO/R and HDT treatment. RESULTS: In the rat model of MCAO/R, brain infarct volume and neurological deficit score were significantly alleviated in the -30° and -60° groups compared to those in the lying flat (0°) group. Compared with the 0° group, an increase in CBF velocity was detected in the -30° group through two-photon microscopy imaging at 24 h after MCAO/R. Compared with the SHAM group, a decrease in PDGFRß was observed in both the MCAO/R and HDT treatment (-30°) groups. The integrated optical density of PDGFRß was found to be higher in the HDT treatment (-30°) group than in the MCAO/R group. An impairment in perivascular AQP4 polarity and an increase in brain water content were observed after MCAO/R, which were not exacerbated by HDT treatment (-30°). CONCLUSIONS: Our findings suggest that HDT treatment at certain degrees may exert a neuroprotective effect after MCAO/R through improving CBF velocity and the protection of pericytes.

Effects of short-term -30° HDT on contrast sensitivity.

Potential cognitive and physiological alterations due to space environments have been investigated in long-term space flight and various microgravity-like conditions, for example, head-down tilt (HDT), confinement, isolation, and immobilization. However, little is known about the influence of simulated microgravity environments on visual function. Contrast sensitivity (CS), which indicates how much contrast a person requires to see a target, is a fundamental feature of human vision. Here, we investigated how the CS changed by 1-h -30° HDT and determined the corresponding mechanisms with a perceptual template model. A quick contrast sensitivity function procedure was used to assess the CS at ten spatial frequencies and three external noise levels. We found that (1) relative to the + 30° head-up tilt (HUT) position, 1-h -30° HDT significantly deteriorated the CS at intermediate frequencies when external noise was present; (2) CS loss was not detected in zero- or high-noise conditions; (3) HDT-induced CS loss was characterized by impaired perceptual template; and (4) self-reported questionnaires indicated that subjects felt less pleasure and more excitement, less comfort and more fatigued by screen light, less comfort in the area around the eye, and serious symptoms such as piercing pain, blur acid, strain, eye burning, and dizziness after HDT. These findings improve our understanding of the negative effects of simulated microgravity on visual function and elucidate the potential risks of astronauts during space flight.

Effects of head-down tilt on optic nerve sheath diameter in healthy subjects.

PURPOSE: Intracranial pressure increases in head-down tilt (HDT) body posture. This study evaluated the effect of HDT on the optic nerve sheath diameter (ONSD) in normal subjects. METHODS: Twenty six healthy adults (age 28 [4.7] years) participated in seated and 6° HDT visits. For each visit, subjects presented at 11:00 h for baseline seated scans and then maintained a seated or 6° HDT posture from 12:00 to 15:00 h. Three horizontal axial and three vertical axial scans were obtained at 11:00, 12:00 and 15:00 h with a 10 MHz ultrasonography probe on the same eye, randomly chosen per subject. At each time point, horizontal and vertical ONSD (mm) were quantified by averaging three measures taken 3 mm behind the globe. RESULTS: In the seated visit, ONSDs were similar across time (p > 0.05), with an overall mean (standard deviation) of 4.71 (0.48) horizontally and 5.08 (0.44) vertically. ONSD was larger vertically than horizontally at each time point (p < 0.001). In the HDT visit, ONSD was significantly enlarged from baseline at 12:00 and 15:00 h (p < 0.001 horizontal and p < 0.05 vertical). Mean (standard error) horizontal ONSD change from baseline was 0.37 (0.07) HDT versus 0.10 (0.05) seated at 12:00 h (p = 0.002) and 0.41 (0.09) HDT versus 0.12 (0.06) seated at 15:00 h (p = 0.002); mean vertical ONSD change was 0.14 (0.07) HDT versus -0.07 (0.04) seated at 12:00 h (p = 0.02) and 0.19 (0.06) HDT versus -0.03 (0.04) seated at 15:00 h (p = 0.01). ONSD change in HDT was similar between 12:00 and 15:00 h (p ≥ 0.30). Changes at 12:00 h correlated with those at 15:00 h for horizontal (r = 0.78, p < 0.001) and vertical ONSD (r = 0.73, p < 0.001). CONCLUSION: The ONSD increased when body posture transitioned from seated to HDT position without any further change at the end of the 3 h in HDT.

Segmental Tissue Resistance of Healthy Young Adults during Four Hours of 6-Degree Head-Down-Tilt Positioning.

(1) Background: One effect of microgravity on the human body is fluid redistribution due to the removal of the hydrostatic gravitational gradient. These fluid shifts are expected to be the source of severe medical risks and it is critical to advance methods to monitor them in real-time. One technique to monitor fluid shifts captures the electrical impedance of segmental tissues, but limited research is available to evaluate if fluid shifts in response to microgravity are symmetrical due to the bilateral symmetry of the body. This study aims to evaluate this fluid shift symmetry. (2) Methods: Segmental tissue resistance at 10 kHz and 100 kHz was collected at 30 min intervals from the left/right arm, leg, and trunk of 12 healthy adults over 4 h of 6° head-down-tilt body positioning. (3) Results: Statistically significant increases were observed in the segmental leg resistances, first observed at 120 min and 90 min for 10 kHz and 100 kHz measurements, respectively. Median increases were approximately 11% to 12% for the 10 kHz resistance and 9% for the 100 kHz resistance. No statistically significant changes in the segmental arm or trunk resistance. Comparing the left and right segmental leg resistance, there were no statistically significant differences in the resistance changes based on the side of the body. (4) Conclusions: The fluid shifts induced by the 6° body position resulted in similar changes in both left and right body segments (that had statistically significant changes in this work). These findings support that future wearable systems to monitor microgravity-induced fluid shifts may only require monitoring of one side of body segments (reducing the hardware needed for the system).

Relationships between common carotid artery blood flow and anesthesia, pneumoperitoneum, and head-down tilt position: a linear mixed-effect analysis.

This study investigated the effects of pneumoperitoneum and the head-down tilt position on common carotid artery (CCA) blood flow in surgical patients. METHODS: This prospective observational study included 20 patients who underwent gynecological surgery. CCA blood flow was measured using Doppler ultrasound at four-time points: awake in the supine position [T1], 3 min after anesthesia induction in the supine position [T2], 3 min after pneumoperitoneum in the supine position [T3], and 3 min after pneumoperitoneum in the head-down tilt position [T4]. Hemodynamic and respiratory parameters were also recorded at each time point. Linear mixed-effect analyses were performed to compare CCA blood flow across the time points and assess its relationship with hemodynamic parameters. RESULTS: Compared with T1, CCA blood flow decreased significantly at T2 (345.4 [288.0-392.9] vs. 293.1 [253.0-342.6], P = 0.048). CCA blood flow were also significantly lower at T3 and T4 compared with T1 (345.4 [288.0-392.9] vs. 283.6 [258.8-307.6] and 287.1 [242.1-321.4], P = 0.005 and 0.016, respectively). CCA blood flow at T3 and T4 did not significantly differ from that at T2. Changes in CCA blood flow were significantly associated with changes in cardiac index and stroke volume index (P = 0.011 and 0.024, respectively). CONCLUSION: CCA blood flow was significantly decreased by anesthesia induction. Inducing pneumoperitoneum, with or without the head-down tilt position, did not further decrease CCA blood flow if the cardiac index remained unchanged. The cardiac index and stroke volume index were significantly associated with CCA blood flow. CLINICAL TRIAL REGISTRATION: Clinicaltrials.gov (NCT04233177, January 18, 2020).

Alteration in facial skin blood flow during acute exposure to -10 and -30° head-down tilt in young human volunteers.

NEW FINDINGS: What is the central question of this study? Facial skin blood flow (SBF) might increase during head-down tilt (HDT). However, the effect of HDT on facial SBF remains controversial. In addition, the changes in facial SBF in the cheek (cheek SBF) during a steeper angle of HDT (>-12° HDT) have not been investigated. What is the main finding and its importance? This study showed that cheek SBF decreased during -30° HDT, alongside increased vascular resistance. Furthermore, vascular impedance was suggested to be elevated, accompanied by an increased hydrostatic pressure gradient caused by HDT. Constriction of the facial skin vascular bed and congestion of venous return owing to the steep angle of HDT can decrease facial SBF. ABSTRACT: Head-down tilt (HDT) has been used to simulate microgravity in ground-based studies and clinical procedures including the Trendelenburg position or in certain surgical operations. Facial skin blood flow (SBF) might be altered by HDT, but the effect of a steeper angle of HDT (>-12° HDT) on facial SBF remains unclear. We examined alterations in facial SBF in the cheek (cheek SBF) using two different angles (-10 and -30°) of HDT and lying horizontal (0°) in a supine position for 10 min, to test the hypothesis that cheek SBF would increase with a steeper angle of HDT. Cheek SBF was measured continuously by laser Doppler flowmetry. Cheek skin vascular resistance and the pulsatility index of cheek SBF were calculated to assess the circulatory effects on the facial skin vascular bed in the cheek. Cheek SBF decreased significantly during -30° HDT. In addition, the resistance in cheek SBF increased significantly during -30° HDT. The pulsatility index of cheek SBF increased during both -10 and -30° HDT. Contrary to our hypothesis, cheek SBF decreased during -30° HDT along with increased skin vascular resistance. Vascular impedance, estimated by the pulsatility index in the cheek SBF, was elevated during both -10 and -30° HDT, and elevated vascular impedance would be related to increased hydrostatic pressure induced by HDT. Skin vascular constriction and venous return congestion would be induced by -30° HDT, leading to deceased cheek SBF. The present study suggested that facial SBF in the cheek decreased during acute exposure to a steep angle of HDT (∼-30° HDT).

A comparison between left ventricular ejection time measurement methods during physiological changes induced by simulated microgravity.

NEW FINDINGS: What is the central question of this study? First, we validated easy-to-use oscillometric left ventricular ejection time (LVET) against echocardiographic LVET. Second, we investigated progression of left ventricular ejection time index (LVETI), pre-ejection period index (PEPI), total electromechanical systole index (QS2I) and PEP/LVET ratio during 60 days of head-down tilt (HDT). What is the main finding and its importance? The LVETosci and LVETecho showed good agreement in effect direction. Hence, LVETosci might be useful to evaluate cardiovascular responses during space flight. Moreover, the approach might be useful for individual follow-up of patients with altered ejection times. Furthermore, significant effects of 60 days of HDT were captured by measurements of LVETI, PEPI, QS2I and PEP/LVET ratio. ABSTRACT: Systolic time intervals that are easy to detect might be used as parameters reflecting cardiovascular deconditioning. We compared left ventricular ejection time (LVET) measured via ultrasound Doppler on the left ventricular outflow tract with oscillometrically measured LVET, measured at the brachialis. Furthermore, we assessed the progression of the left ventricular ejection time index (LVETI), the pre-ejection period index (PEPI), the Weissler index (PEP/LVET) and the total electromechanical systole index (QS2I) during prolonged strict head-down tilt (HDT) bed rest, including 16 male and eight female subjects. Simultaneous oscillometric and echocardiographic LVET measurements showed significant correlation (r = 0.53 with P = 0.0084 before bed rest and r = 0.73 with P < 0.05 on the last day of bed rest). The shortening of LVET during HDT bed rest measured with both approaches was highly concordant in their effect direction, with a concordance rate of 0.96. Our results also demonstrated a significant decrease of LVETI (P < 0.0001) and QS2I (P = 0.0992) and a prolongation of PEPI (P = 0.0049) and PEP/LVET (P = 0.0003) during HDT bed rest over 60 days. Four days after bed rest, LVETI recovered completely to its baseline value. Owing to the relationship between shortening of LVETI and heart failure progression, the easy-to-use oscillometric method might not only be a useful way to evaluate the cardiovascular system during space flights, but could also be of high value in a clinical setting.

Trendelenburg (Head-Down tilt) and head rotation: Ultrasonographic effects on the internal jugular vein for catheterization safety.

Most guidelines fail to specify patient positioning during central venous catheterization. The objective was to determine the effects of head-down tilt (Trendelenburg position) and head rotation on the internal jugular vein (IJV). A prospective, observational, longitudinal, and descriptive study using healthy adult volunteers, of both sexes, was performed. The change in position and cross-sectional areas (CSA) of the right IJV and common carotid artery (CA) were measured by ultrasonography during Trendelenburg position (TP) (0°, 5°, 10°, and 15°) and contralateral head-rotation (HR) (0°, 45°, and 90°) for a total of 12 positions. The neutral supine position was first, randomizing the other 11 positions, with 5-min rest intervals in between. Vital signs and symptoms were recorded. A total of 54 volunteers were recruited between the ages of 21 and 32, of which 30 were men. Any degree of TP or HR significantly increased the CSA. The largest area obtained was 1.78 cm2 with a TP15HR90 which did not have a statistical difference with TP10HR45 1.59 cm2 . A HR90 tended to displace the IJV medially, overlaying the CA. Any degree of TP or HR will significantly increase CSA or the right IJV. A 5° to 10° TP is recommended when the patient's condition allows it, with a 45° HR, without significantly displacing the IJV anterior to the CCA.

The effect of respiration and body position on terminal thoracic duct diameter and the lymphovenous junction: An exploratory ultrasound study.

The thoracic duct (TD) drains most of the body's lymph back to the venous system via its lymphovenous junction (LVJ), playing a pivotal role in fluid homeostasis, fat absorption and the systemic immune response. The respiratory cycle is thought to assist with lymph flow, but the precise mechanism underpinning terminal TD lymph flow into the central veins is not well understood. The aim of this study was to use ultrasonography (US) to explore the relationship between terminal TD lymph flow, the respiratory cycle, and gravity. The left supraclavicular fossa was scanned in healthy non-fasted volunteers using high-resolution (13-5 MHz) US to identify the terminal TD and the presence of a lymphovenous valve (LVV). The TD's internal diameter was measured in relation to respiration (inspiration vs. expiration) and body positioning (supine vs. Trendelenburg). The terminal TD was visualized in 20/33 (61%) healthy volunteers. An LVV was visualized in only 4/20 (20%) cases. The mean terminal TD diameter in the supine position was 1.7 mm (range 0.8-3.1 mm); this increased in full inspiration (mean 1.8 mm, range 0.9-3.2 mm, p < 0.05), and in the Trendelenburg position (mean 1.8 mm, range 1.2-3.1 mm, p < 0.05). The smallest mean terminal TD diameter occurred in full expiration (1.6 mm, range 0.7-3.1 mm, p < 0.05). Respiration and gravity impact the terminal TD diameter. Due to the challenges of visualizing the TD and LVJ, other techniques such as dynamic magnetic resonance imaging will be required to fully understand the factors governing TD lymph flow.

The effects of a spaceflight analog with elevated CO2 on sensorimotor adaptation.

Aboard the International Space Station (ISS), astronauts must adapt to altered vestibular and somatosensory inputs due to microgravity. Sensorimotor adaptation on Earth is often studied with a task that introduces visuomotor conflict. Retention of the adaptation process, known as savings, can be measured when subjects are exposed to the same adaptive task multiple times. It is unclear how adaptation demands found on the ISS might interfere with the ability to adapt to other sensory conflict at the same time. In the present study, we investigated the impact of 30 days' head-down tilt bed rest combined with elevated carbon dioxide (HDBR + CO2) as a spaceflight analog on sensorimotor adaptation. Eleven subjects used a joystick to move a cursor to targets presented on a computer screen under veridical cursor feedback and 45° rotated feedback. During this NASA campaign, five individuals presented with optic disk edema, a sign of spaceflight-associated neuro-ocular syndrome (SANS). Thus, we also performed post hoc exploratory analyses between subgroups who did and did not show signs of SANS. HDBR + CO2 had some impact on sensorimotor adaptation, with a lack of savings across the whole group. SANS individuals showed larger, more persistent after-effects, suggesting a shift from relying on cognitive to more implicit processing of adaptive behaviors. Overall, these findings suggest that HDBR + CO2 alters the way in which individuals engage in sensorimotor processing. These findings have important implications for missions and mission training, which require individuals to adapt to altered sensory inputs over long periods in space.NEW & NOTEWORTHY This is the first bed rest campaign examining sensorimotor adaptation and savings in response to the combined effect of HDBR + CO2 and to observe signs of spaceflight-associated neuro-ocular syndrome (SANS) in HDBR participants. Our findings suggest that HDBR + CO2 alters the way that individuals engage in sensorimotor processing. Individuals who developed signs of SANS seem to rely more on implicit rather than cognitive processing of adaptive behaviors than subjects who did not present signs of SANS.

Altered cerebral perfusion in response to chronic mild hypercapnia and head-down tilt Bed rest as an analog for Spaceflight.

PURPOSE: Following prolonged stays on the International Space Station (ISS), some astronauts exhibit visual acuity changes, ophthalmological findings, and mildly elevated intracranial pressures as part of a novel process called spaceflight-associated neuro-ocular syndrome (SANS). To determine the pathophysiology of SANS, NASA conducted a multi-investigator study in which 11 healthy participants underwent head-down tilt bed rest, mimicking microgravity-induced cephalad fluid shifts, combined with elevated ambient CO2 levels similar to those on the ISS (HDT+CO2). As part of that study, we examined the effects of HDT+CO2 on cerebral perfusion. METHODS: Using arterial spin labeling, we compared cerebral perfusion before, during, and after HDT+CO2 in participants who developed SANS (n = 5) with those who did not (n = 6). RESULTS: All participants demonstrated a decrease in perfusion during HDT+CO2 (mean decrease of 25.1% at HDT7 and 16.2% at HDT29); however, the timing and degree of change varied between the groups. At day 7 of HDT+CO2, the SANS group experienced a greater reduction in perfusion than the non-SANS group (p =.05, 95% CI:-0.19 to 16.11, d=.94, large effect). Conversely, by day 29 of HDT+CO2, the SANS group had significantly higher perfusion (approaching their baseline) than the non-SANS group (p = .04, 95% CI:0.33 to 13.07, d=1.01, large effect). CONCLUSION: Compared with baseline and recovery, HDT+CO2 resulted in reduced cerebral perfusion which varied based on SANS status. Further studies are needed to unravel the relative role of HDT vs hypercapnia, to determine if these perfusion changes are clinically relevant, and whether perfusion changes contribute to the development of SANS during spaceflight.

Effects of acquisition device, sampling rate, and record length on kinocardiography during position-induced haemodynamic changes.

BACKGROUND: Kinocardiography (KCG) is a promising new technique used to monitor cardiac mechanical function remotely. KCG is based on ballistocardiography (BCG) and seismocardiography (SCG), and measures 12 degrees-of-freedom (DOF) of body motion produced by myocardial contraction and blood flow through the cardiac chambers and major vessels. RESULTS: The integral of kinetic energy ([Formula: see text]) obtained from the linear and rotational SCG/BCG signals was computed over each dimension over the cardiac cycle, and used as a marker of cardiac mechanical function. We tested the hypotheses that KCG metrics can be acquired using different sensors, and at 50 Hz. We also tested the effect of record length on the ensemble average on which the metrics were computed. Twelve healthy males were tested in the supine, head-down tilt, and head-up tilt positions to expand the haemodynamic states on which the validation was performed. CONCLUSIONS: KCG metrics computed on 50 Hz and 1 kHz SCG/BCG signals were very similar. Most of the metrics were highly similar when computed on different sensors, and with less than 5% of error when computed on record length longer than 60 s. These results suggest that KCG may be a robust and non-invasive method to monitor cardiac inotropic activity. Trial registration Clinicaltrials.gov, NCT03107351. Registered 11 April 2017, https://clinicaltrials.gov/ct2/show/NCT03107351?term=NCT03107351&draw=2&rank=1 .

Comparing the effect of positioning on cerebral autoregulation during radical prostatectomy: a prospective observational study.

PURPOSE: Surgery in the prolonged extreme Trendelenburg position may lead to elevated intracranial pressure and compromise cerebral hemodynamic regulation. We hypothesized that robot-assisted radical prostatectomy with head-down tilt causes impairment of cerebral autoregulation compared with open retropubic radical prostatectomy in the supine position. METHODS: Patients scheduled for elective radical prostatectomy were included at a tertiary care prostate cancer clinic. Continuous monitoring of the cerebral autoregulation was performed using the correlation method. Based on measurements of cerebral oxygenation with near-infrared spectroscopy and invasive mean arterial blood pressure (MAP), a moving correlation coefficient was calculated to obtain the cerebral oxygenation index as an indicator of cerebral autoregulation. Cerebral autoregulation was measured continuously from induction until recovery from anesthesia. RESULTS: There was no significant difference in cerebral autoregulation between robot-assisted and open retropubic radical prostatectomy during induction (p = 0.089), intraoperatively (p = 0.162), and during recovery from anesthesia (p = 0.620). Age (B = 0.311 [95% CI 0.039; 0.583], p = 0.025) and a higher difference between baseline MAP and intraoperative MAP (B = 0.200 [95% CI 0.073; 0.327], p = 0.002) were associated with impaired cerebral autoregulation, whereas surgical technique was not (B = 3.339 [95% CI 1.275; 7.952], p = 0.155). CONCLUSION: Compared with open radical prostatectomy in the supine position, robot-assisted surgery in the extreme Trendelenburg position with capnoperitoneum did not lead to an impairment of cerebral autoregulation during the perioperative period in our study population. TRIAL REGISTRATION NUMBER: DRKS00010014, date of registration: 21.03.2016, retrospectively registered.

Cerebral oxygenation in 45-degree trendelenburg position for robot-assisted radical prostatectomy: a single-center, open, controlled pilot study.

BACKGROUND: Within the last decade, robotically-assisted laparoscopic prostatectomy (RALP) has become the standard for treating localized prostate cancer, causing a revival of the 45° Trendelenburg position. In this pilot study we investigated effects of Trendelenburg position on hemodynamics and cerebral oxygenation in patients undergoing RALP. METHODS: We enrolled 58 patients undergoing RALP and 22 patients undergoing robot-assisted partial nephrectomy (RAPN) (control group) in our study. Demographic patient data and intraoperative parameters including cerebral oxygenation and cerebral hemodynamics were recorded for all patients. Cerebral function was also assessed pre- and postoperatively via the Mini Mental Status (MMS) exam. Changes in parameters during surgery were modelled by a mixed effects model; changes in the MMS result were evaluated using the Wilcoxon signed rank test. RESULTS: Preoperative assessment of patient characteristics, standard blood values and vital parameters revealed no difference between the two groups. CONCLUSIONS: Applying a 45° Trendelenburg position causes no difference in postoperative brain function, and does not alter cerebral oxygenation during a surgical procedure lasting up to 5 h. Further studies in larger patient cohorts will have to confirm these findings. TRIAL REGISTRATION: German Clinical Trial Registry; DRKS00005094; Registered 12th December 2013-Retrospectively registered; https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00005094 .

Intraoperative changes in whole-blood viscosity in patients undergoing robot-assisted laparoscopic prostatectomy in the steep Trendelenburg position with pneumoperitoneum: a prospective nonrandomized observational cohort study.

BACKGROUND: The aim of this study was to investigate the effect of the steep Trendelenburg position (STP) with pneumoperitoneum on whole-blood viscosity (WBV) in patients undergoing robot-assisted laparoscopic prostatectomy (RALP). The study also analyzed the associations of clinical patient-specific and time-dependent variables with WBV and recorded postoperative outcomes. METHODS: Fifty-eight adult male patients (ASA physical status of I or II) undergoing elective RALP were prospectively analyzed in this study. WBV was intraoperatively measured three times: at the beginning of surgery in the supine position without pneumoperitoneum; after 30 min in the STP with pneumoperitoneum; and at the end of surgery in the supine position without pneumoperitoneum. The WBV at a high shear rate (300 s- 1) was recorded as systolic blood viscosity (SBV) and that at a low shear rate (5 s- 1) was recorded as diastolic blood viscosity (DBV). Systolic blood hyperviscosity was defined as > 13.0 cP at 300 s- 1 and diastolic blood hyperviscosity was defined as > 4.1 cP at 5 s- 1. RESULTS: The WBV and incidences of systolic and diastolic blood hyperviscosity significantly increased from the supine position without pneumoperitoneum to the STP with pneumoperitoneum. When RALP was performed in the STP with pneumoperitoneum, 12 patients (27.3%) who had normal SBV at the beginning of surgery and 11 patients (26.8%) who had normal DBV at the beginning of surgery developed new systolic and diastolic blood hyperviscosity, respectively. The degree of increase in WBV after positioning with the STP and pneumoperitoneum was higher in the patients with hyperviscosity than in those without hyperviscosity at the beginning of surgery. Higher preoperative body mass index (BMI) and hematocrit level were associated with the development of both systolic and diastolic blood hyperviscosity in the STP with pneumoperitoneum. All patients were postoperatively discharged without fatal complications. CONCLUSIONS: Changes in surgical position may influence WBV, and higher preoperative BMI and hematocrit level are independent factors associated with the risk of hyperviscosity during RALP in the STP with pneumoperitoneum. TRIAL REGISTRATION: Clinical Research Information Service, Republic of Korea, approval number: KCT0003295 on October 25, 2018.

Autonomic cardiovascular adaptations to acute head-out water immersion, head-down tilt and supine position.

PURPOSE: Thermoneutral head-out water immersion (WI) and 6° head-down tilt (HDT) have been considered as suitable models to increase central blood volume and simulate autonomic cardiovascular adaptations to microgravity, swimming or scuba diving. However, any differences in autonomic cardiovascular adaptations are still unclear. In this study, we hypothesized that WI induces a higher activation of arterial baroreceptors and the parasympathetic system. METHODS: Ten healthy men underwent 30 min of WI, HDT, and a supine position (SP). RR intervals (RRI) and blood pressure (BP) were continuously monitored. High frequency power (HF), low frequency power (LF) and LF/HF ratio were calculated to study sympathetic and parasympathetic activities, and a spontaneous baroreflex method was used to study arterial baroreflex sensitivity (aBRS). Lung transfer of nitric oxide and carbon monoxide (TLNO/TLCO), vital capacity and alveolar volume (Vc/VA) were measured to study central blood redistribution. RESULTS: We observed (1) a similar increase in RRI and decrease in BP; (2) a similar increase in HF power during all experimental conditions, whereas LF increased after; (3) a similar rise in aBRS; (4) a similar increase in Vc/VA and decrease in TLNO/TLCO in all experimental conditions. CONCLUSIONS: These results showed a cardiac parasympathetic dominance to the same extent, underpinned by a similar arterial baroreflex activation during WI and HDT as well as control SP. Future studies may address their association with cold or hyperoxia to assess their ability to replicate autonomic cardiovascular adaptations to microgravity, swimming or scuba diving.

[Effects of different intraoperative lithotomy positions on the absorption of irrigation fluid during bipolar plasmakinetic resection of the prostate].

OBJECTIVE: To investigate the effect of intraoperative lithotomy position (LP) with a head-down tilt (HDT) on the absorption of intraoperative irrigation fluid in patients undergoing bipolar plasmakinetic resection of the prostate (PKRP). METHODS: Eighty BPH patients underwent PKRP, 40 in a conventional 0-degree position (0° LP) and the other 40 in a －10-degree HDT position (－10° LP), with 0.9% saline containing 1% ethanol as intraoperative irrigation fluid. We determined the alcohol concentration in the exhaled breath of the patients with a digital alcohol detector at the start of the operation and every 10 minutes afterwards. Meanwhile we recorded the operation time, the volume of intraoperative intravenous crystalloid infusion and the weight of the resected prostatic tissue, monitored the mean arterial pressure (MAP) and heart rate (HR) at 5 minutes before surgery, 30 minutes after the start of surgery and the end of surgery, and measured the concentrations of Na+, K+, Cl－ and Ca2+ with an arterial blood gas analyzer at 5 minutes before surgery and 1 hour after the start of surgery. RESULTS: There were no statistically significant differences in age, height, body weight and prostate volume, or in intraoperative MAP and HR between the 0° LP and －10° LP groups. Compared with the baseline, at 1 hour after the start of PKRP, the patients in the 0° LP group showed significantly decreased concentrations of K+ (ï¼»3.64 ± 0.29ï¼½ vs ï¼»3.49 ± 0.22ï¼½ mmol/L, P = 0.002) and Ca2+ (ï¼»1.16 ± 0.03ï¼½ vs ï¼»1.13 ± 0.04ï¼½ mmol/L, P = 0.001), increased concentration of Cl－ (ï¼»106.9 ± 2.2ï¼½ vs ï¼»108.7 ± 2.3ï¼½ mmol/L, P = 0.006), but no significant difference in the concentration of Na+ (ï¼»139.7 ± 1.5ï¼½ vs ï¼»139.4 ± 1.6ï¼½ mmol/L, P = 0.231), while those in the －10° LP group exhibited remarkably decreased concentration of Ca2+ (ï¼»1.14 ± 0.04ï¼½ vs ï¼»1.13 ± 0.04ï¼½ mmol/L, P = 0.016) but no statistically significant differences in the concentrations of Na+ (ï¼»140.3 ± 1.8ï¼½ vs ï¼»140.0 ± 2.0ï¼½ mmol/L, P = 0.156), K+ (ï¼»3.49 ± 0.36ï¼½ vs ï¼»3.47 ± 0.34ï¼½ mmol/L, P = 0.506) and Cl－ (ï¼»108.2 ± 2.6ï¼½ vs ï¼»109.1 ± 2.5ï¼½ mmol/L, P = 0.071). Over 1 500 ml of intraoperative irrigation fluid absorption was observed in 6 cases (15%) in the 0° LP group as compared with 4 cases (10%) in the －10°LP group, with no significant difference between the two groups. CONCLUSIONS: Lithotomy position with a 10-degree head-down tilt can reduce PKRP-induced decrease in the concentration of K+ and increase in that of Cl－ without affecting the levels of the other electrolytes.

Effects of exercise countermeasure on myocardial contractility measured by 4D speckle tracking during a 21-day head-down bed rest.

OBJECTIVE: To 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. METHODS: Twelve 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). RESULTS: On 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. CONCLUSION: The 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.