Ultrasound assessments of organs and blood vessels before and after 40 days isolation in a cavern (deep time experiment 2021).

Introduction: Spaceflight simulation studies like confinement in small volume habitat with limited physical activity have reported even after 60 days an abnormal arterial wall adaptation with increase thickness or stiffness. The purpose of the current study was to determine the effects on blood vessel and organ structure of 40 days of isolation in a huge habitat with intensive physical activity. Method: Data were collected from 14 individuals (7 male) who isolated in a cavern for 40-days while performing normal daily activities without time references. Ultrasound assessments were performed pre- and post-isolation using a teleoperated system with eight different acoustic windows to obtain 19 measurements on 12 different organ/vascular structures which included the common carotid artery, femoral artery, tibial artery, jugular vein, portal vein, bile duct, kidney, pancreas, abdominal aorta, cervical and lumbar vertebral distance, and Achilles tendon. Results: Common carotid artery measures, including the intima media thickness, stiffness index, and the index of reflectivity measured from the radiofrequency signal, were not changed with isolation. Similarly, no differences were found for femoral artery measurements or measurements of any of the other organs/vessels assessed. There were no sex differences for any of the assessments. Discussion: Results from this study indicate a lack of physiological effects of 40-days of isolation in a cavern, contrary to what observed in previous 60 days confinement. This suggests a potential protective effect of sustained physical activity, or reduced environmental stress inside the huge volume of the confined facility.

Continuous forearm cooling attenuates gastrointestinal temperature increase during cycling.

Hot environmental conditions can challenge thermoregulation resulting in exacerbated heat strain. This study evaluated the influence of continuous inner forearm cooling on gastrointestinal temperature (TGI) and physiological responses to exercise in hot (30°C) and humid (relative humidity: 70%) conditions. Eleven trained cyclists (seven male age: 37±12 years; four female age: 41±15 years; mean±standard deviation) performed two experimental trials, cycling at 66% of their self-reported functional threshold power (average work rate over an hour of maximum effort cycling; 175±34W) for 45 minutes in an environmental chamber. One trial employed continuous inner forearm cooling (COOL) with 5°C water passing through aluminum heat exchangers, while the other had no cooling (CONTROL). Heat was removed from the body at an average rate of 30.3±6.6W during the COOL trial resulting in an attenuation of TGI rise (CONTROL: 2.46±0.70, COOL: 2.03±0.63°C·h-1; p=0.002). The change in heart rate from the 10th minute to the end of exercise, as an indicator of cardiovascular drift, was reduced (CONTROL: 20±7, COOL: 17±6beats·min-1; p=0.050) and end-exercise thermal comfort was improved in the COOL trial with a trend for reduced rating of perceived exertion (p=0.055). Findings suggest that continuous cooling of the inner forearms can attenuate the rise of TGI and help mitigate the risk of heat injury during exercise in hot and humid conditions.

DI-5-Cuffs: Lumbar Intervertebral Disc Proteoglycan and Water Content Changes in Humans after Five Days of Dry Immersion to Simulate Microgravity.

Most astronauts experience back pain after spaceflight, primarily located in the lumbar region. Intervertebral disc herniations have been observed after real and simulated microgravity. Spinal deconditioning after exposure to microgravity has been described, but the underlying mechanisms are not well understood. The dry immersion (DI) model of microgravity was used with eighteen male volunteers. Half of the participants wore thigh cuffs as a potential countermeasure. The spinal changes and intervertebral disc (IVD) content changes were investigated using magnetic resonance imaging (MRI) analyses with T1-T2 mapping sequences. IVD water content was estimated by the apparent diffusion coefficient (ADC), with proteoglycan content measured using MRI T1-mapping sequences centered in the nucleus pulposus. The use of thigh cuffs had no effect on any of the spinal variables measured. There was significant spinal lengthening for all of the subjects. The ADC and IVD proteoglycan content both increased significantly with DI (7.34 ± 2.23% and 10.09 ± 1.39%, respectively; mean ± standard deviation), p < 0.05). The ADC changes suggest dynamic and rapid water diffusion inside IVDs, linked to gravitational unloading. Further investigation is needed to determine whether similar changes occur in the cervical IVDs. A better understanding of the mechanisms involved in spinal deconditioning with spaceflight would assist in the development of alternative countermeasures to prevent IVD herniation.

Haemodynamic and cerebrovascular effects of intermittent lower-leg compression as countermeasure to orthostatic stress.

NEW FINDINGS: What is the central question of this study? Does smartly timed intermittent compression of the lower legs alter cerebral blood velocity and oxygenation during acute orthostatic challenges? What is the main finding and its importance? Intermittent compression timed to the local diastolic phase increased the blood flux through the legs and heart after two different orthostatic stress tests. Cerebral blood velocity improved during the first minute of recovery, and indices of cerebral tissue oxygenation remained elevated for 2 min. These results provide promise for the use of lower-leg active compression as a therapeutic tool for individuals vulnerable to initial orthostatic hypotension and orthostatic stress. ABSTRACT: Intermittent compression of the lower legs provides the possibility of improving orthostatic tolerance by actively promoting venous return and improving central haemodynamics. We tested the hypothesis that intermittent compression of 65 mmHg timed to occur only within the local diastolic phase of each cardiac cycle would attenuate the decrease in blood pressure and improve cerebral haemodynamics during the first minute of recovery from two different orthostatic stress tests. Fourteen subjects (seven female) performed four squat-to-stand transitions and four repeats of standing bilateral thigh-cuff occlusion and release (TCR), with intermittent compression of the lower legs applied in half of the trials. Blood flow in the superficial femoral artery, mean arterial pressure, Doppler ultrasound cardiac output, total peripheral resistance, middle cerebral artery blood velocity (MCAv) and cerebral tissue saturation index (TSI%) were monitored. With both orthostatic stress tests, there was a significant compression × time interaction for superficial femoral artery flow (P < 0.001). The hypotensive state was attenuated with intermittent compression despite decreased total peripheral resistance (squat-to-stand, compression × time interaction, P < 0.001; TCR, compression × time interaction, P = 0.002) as a consequence of elevated cardiac output in both tests (P < 0.001). Intermittent compression also increased MCAv (P = 0.001) and TSI% (P < 0.001) during the squat-to-stand transition and during TCR (MCAv and TSI%, compression × time interaction, P < 0.001). Intermittent compression of the lower legs during quiet standing after an active orthostatic challenge augmented local, central and cerebral haemodynamics, providing potential as a therapeutic tool for individuals vulnerable to orthostatic stress.

Superficial femoral artery blood flow with intermittent pneumatic compression of the lower leg applied during walking exercise and recovery.

The purpose of this study was to determine if muscle blood flow during walking exercise and postexercise recovery can be augmented through the application of intermittent compression of the lower legs applied during the diastolic phase of the cardiac cycle. Results from four conditions were assessed: no compression (NoComp), compression during walking (ExComp), compression during postexercise recovery (RecComp), and compression applied throughout (AllComp). Superficial femoral artery (SFA) blood flow was measured (Doppler ultrasound) during rest and postexercise recovery. Mean arterial blood pressure (MAP, finger photoplethysmography) was used to calculate vascular conductance as VC = SFA flow/MAP. Near infrared spectroscopy measured changes in oxygenated (O2Hb) and deoxygenated hemoglobin concentration throughout the test. Compression during exercise increased SFA blood flow measured over the first 15 s of postexercise recovery (AllComp: 532.2 ± 123.1 mL/min; ExComp: 529.8 ± 99.2 mL/min) compared with NoComp (462.3 ± 87.3 mL/min P < 0.05) and corresponded to increased VC (NoComp: 4.7 ± 0.9 mL·min-1·mmHg-1 versus ExComp: 5.5 ± 1.0 mL·min-1·mmHg-1, P < 0.05). Similarly, compression throughout postexercise recovery also resulted in increased SFA flow (AllComp: 190.5 ± 57.1 mL/min; RecComp: 158.7 ± 49.1 mL/min versus NoComp: 108.8 ± 28.5 mL/min, P < 0.05) and vascular conductance. Muscle contractions during exercise reduced total hemoglobin with O2Hb comprising ~57% of the observed reduction. Compression during exercise augmented this reduction (P < 0.05) with O2HB again comprising ~55% of the reduction. Total hemoglobin was reduced with compression during postexercise recovery (P < 0.05) with O2Hb accounting for ~40% of this reduction. Results from this study indicate that intermittent compression applied during walking and during postexercise recovery enhanced vascular conductance during exercise and elevated postexercise SFA blood flow and tissue oxygenation during recovery.NEW & NOTEWORTHY Intermittent compression mimics the mechanical actions of voluntary muscle contraction on venous volume. This study demonstrates that compression applied during the diastolic phase of the cardiac cycle while walking accentuates the actions of the muscle pump resulting in increased immediate postexercise muscle blood flow and vascular conductance. Similarly, compression applied during the recovery period independently increased arterial flow and tissue oxygenation, potentially providing conditions conducive to faster recovery.

Comparison of pulse contour, aortic Doppler ultrasound and bioelectrical impedance estimates of stroke volume during rapid changes in blood pressure.

NEW FINDINGS: What is the central question of this study? Pulse contour analysis of the finger arterial pressure by Windkessel modelling is commonly used to estimate stroke volume continuously. But is it valid during dynamic changes in blood pressure? What is the main finding and its importance? Second-by-second analysis revealed that pulse contour analysis underestimated stroke volume by up to 25% after standing from a squat, and 16% after standing thigh-cuff release, when compared with aortic Doppler ultrasound estimates. These results reveal that pulse contour analysis of stroke volume should be interpreted with caution during rapid changes in physiological state. ABSTRACT: Dynamic measurements of stroke volume (SV) and cardiac output provide an index of central haemodynamics during transitional states, such as postural changes and onset of exercise. The most widely used method to assess dynamic fluctuations in SV is the Modelflow method, which uses the arterial blood pressure waveform along with age- and sex-specific aortic properties to compute beat-to-beat estimates of aortic flow. Modelflow has been validated against more direct methods in steady-state conditions, but not during dynamic changes in physiological state, such as active orthostatic stress testing. In the present study, we compared the dynamic SV responses from Modelflow (SVMF ), aortic Doppler ultrasound (SVU/S ) and bioelectrical impedance analysis (SVBIA ) during two different orthostatic stress tests, a squat-to-stand (S-S) transition and a standing bilateral thigh-cuff release (TCR), in 15 adults (six females). Second-by-second analysis revealed that when compared with estimates of SV by aortic Doppler ultrasound, Modelflow underestimated SV by up to 25% from 3 to 11 s after standing from the squat position and by up to 16% from 3 to 7 s after TCR (P < 0.05). The SVMF and SVBIA were similar during the first minute of the S-S transition, but were different 3 s after TCR and at intermittent time points between 34 and 44 s (P < 0.05). These findings indicate that the physiological conditions elicited by orthostatic stress testing violate some of the inherent assumptions of Modelflow and challenge models used to interpret bioelectrical impedance responses, resulting in an underestimation in SV during rapid changes in physiological state.

Remote Echography between a Ground Control Center and the International Space Station Using a Tele-operated Echograph with Motorized Probe.

Echography is the most appropriate imaging modality for investigating astronauts. Unfortunately, it requires a great deal of training to perform ultrasound examinations, which can be difficult and time consuming, especially if the astronaut does not have a medical background. We designed a new echography system with motorized probes that allows for the majority of exam functions to be controlled by a ground-based sonographer. Using tele-operation, the sonographer controls the orientation of the transducer (tilt, rotation) and echograph settings (gain, depth, freeze) and triggers ultrasound functions (pulsed wave color Doppler, 3-D capture, radiofrequency data collection, elastography). With this system, astronauts are required to hold the motorized probe only at the locations indicated, with the remainder of the exam being conducted by the ground-based sonographer. During spaceflight, ultrasound imaging of the carotid artery, jugular vein, thyroid, liver, gallbladder, biliary tract and portal vein (2-D, 3-D, color, pulsed wave, radiofrequency) were successfully performed.

Carotid and Femoral Arterial Wall Distensibility During Long-Duration Spaceflight.

INTRODUCTION: This study aimed to assess changes in common carotid (CA) and superficial femoral (FA) arterial stiffness during long-duration spaceflight. METHODS: Ultrasound imaging was used to investigate the CA and FA of 10 astronauts preflight (PRE), on flight day 15 (FD15), after 4-5 mo (FD4-5m), and 4 d after return to Earth (R+4). Arterial wall properties were assessed through the calculation of strain, stiffness (ß), pressure-strain elastic modulus (Ep), and distensibility (DI). Stiffness indices were assessed for potential correlations to measurements of intima-media thickness (IMT). RESULTS: Significant effects of spaceflight were found for all CA stiffness indices, indicating an increase in arterial stiffness. CA strain was reduced by 34 ± 31% on FD15 and 50 ± 16% on FD4-5m and remained reduced by 42 ± 14% on R+4 with respect to PRE values. On FD4-5m, with respect to PRE values, DI was reduced by 46 ± 25% and ß and Ep were increased by 124 ± 95% and 118 ± 92%, respectively. FA arterial stiffness indices appeared to show similar changes; however, a main effect of spaceflight was only found for strain. Correlation analysis showed weak but significant relationships between measurements of CA IMT and arterial stiffness indices, but no relationships were found for FA measurements. DISCUSSION: The observed change in CA and FA stiffness indices suggest that spaceflight results in an increase in arterial stiffness. That these changes were not strongly related to measurements of IMT suggests the possibility of different mechanisms contributing to the observed results.Arbeille P, Provost R, Zuj K. Carotid and femoral arterial wall distensibility during long-duration spaceflight. Aerosp Med Hum Perform. 2017; 88(10):924-930.

Altered Venous Function during Long-Duration Spaceflights.

Aims: Venous adaptation to microgravity, associated with cardiovascular deconditioning, may contribute to orthostatic intolerance following spaceflight. The aim of this study was to analyze the main parameters of venous hemodynamics with long-duration spaceflight. Methods: Venous plethysmography was performed on 24 cosmonauts before, during, and after spaceflights aboard the International Space Station. Venous plethysmography assessed venous filling and emptying functions as well as microvascular filtration, in response to different levels of venous occlusion pressure. Calf volume was assessed using calf circumference measurements. Results: Calf volume decreased during spaceflight from 2.3 ± 0.3 to 1.7 ± 0.2 L (p < 0.001), and recovered after it (2.3 ± 0.3 L). Venous compliance, determined as the relationship between occlusion pressure and the change in venous volume, increased during spaceflight from 0.090 ± 0.005 to 0.120 ± 0.007 (p < 0.01) and recovered 8 days after landing (0.071 ± 0.005, arbitrary units). The index of venous emptying rate decreased during spaceflight from -0.004 ± 0.022 to -0.212 ± 0.033 (p < 0.001, arbitrary units). The index of vascular microfiltration increased during spaceflight from 6.1 ± 1.8 to 10.6 ± 7.9 (p < 0.05, arbitrary units). Conclusion: This study demonstrated that overall venous function is changed during spaceflight. In future, venous function should be considered when developing countermeasures to prevent cardiovascular deconditioning and orthostatic intolerance with long-duration spaceflight.

Jugular and Portal Vein Volume, Middle Cerebral Vein Velocity, and Intracranial Pressure in Dry Immersion.

BACKGROUND: The objective was to determine if short term exposure to dry immersion (DI) results in a cephalic fluid shift similar to what has been observed with spaceflight. METHODS: Data were collected from 10 individuals at rest and during the first 2 h of dry immersion. Jugular vein (JV), portal vein (PV), and thyroid volume were measured using 3D echography. Middle cerebral vein velocity (MCVv) was determined using transcranial Doppler ultrasound. The cochlear response to audio stimulation was used to derive an estimate of intracranial pressure (dICP). RESULTS: After 2 h of DI, there was a significant increase (mean ± SD) in JV (2.21 ± 1.10 mL), PV (1.05 ± 0.48 mL), and thyroid (0.428 ± 0.313 mL) volume. MCVv was also significantly increased with DI (3.90 ± 5.03 cm · s-1). There was no change in dICP with DI in part due to large individual variability. The range of dICP changes appeared to be related to MCVv, with participants with the largest increase in MCVv also showing increased dICP. DISCUSSION: The results suggest that DI induces a significant cephalic fluid shift similar to what is observed with spaceflight. The increased thyroid volume suggests that cerebral tissue may also be subjected to similar fluid filtration, with implications for changes in intracranial pressure. However, despite all participants having an increase in JV and thyroid volume, only half showed an increase in dICP, suggesting that increased venous pooling alone is not sufficient to cause increased intracranial pressure.Arbeille P, Avan P, Treffel L, Zuj K, Normand H, Denise P. Jugular and portal vein volume, middle cerebral vein velocity, and intracranial pressure in dry immersion. Aerosp Med Hum Perform. 2017; 88(5):457-462.

Tele-Operated Echography and Remote Guidance for Performing Tele-Echography on Geographically Isolated Patients.

OBJECTIVE: To evaluate the performance of three tele-echography systems for routine use in isolated medical centers. METHODS: Three systems were used for deep (abdomen, pelvis, fetal) and superficial (muscle, thyroid, carotid artery) examinations: (a) a robotic arm (RA) holding an echographic probe; (b) an echograph with a motorized probe (MP); and (c) remote guidance (RG) where the patient site operator performed the examination assisted by an expert via videoconference. All systems were tested in the same medical center located 60 km away from the university hospital. RESULTS: A total of 340 remote echography examinations were performed (41% RA and MP, 59% RG). MP and RA allowed full control of the probe orientation by the expert, and provided diagnoses in 97% of cases. The use of RG was sufficient for superficial vessel examinations and provided diagnoses in 98% of cases but was not suited for deep or superficial organs. Assessment of superficial organs was best accomplished using the MP. DISCUSSION: Both teleoperated systems provided control of the probe orientation by the expert necessary for obtaining appropriate views of deep organs but the MP was much more ergonomic and easier to use than the RA. RG was appropriate for superficial vessels while the MP was better for superficial volumic organs.

Carotid and Femoral Artery Intima-Media Thickness During 6 Months of Spaceflight.

INTRODUCTION: The objective was to determine the effects of 6 mo of microgravity exposure on conduit artery diameter and wall thickness. METHODS: Diagnostic images of the common carotid artery (CC) and superficial femoral artery (FA) were obtained using echography which astronauts performed on themselves after receiving minimal training in the use of ultrasound imaging. Echographic video was recorded using a volume capture method directed by a trained sonographer on the ground through videoconferencing. Vessel properties were later assessed by processing the downlinked video. Data were collected from 10 astronauts who performed the echographic video capture at the beginning of the spaceflight (day 15) and near the end of the spaceflight (day 115 to 165). In-flight and postflight measurements were compared to preflight assessments. RESULTS: No significant changes with spaceflight were found for CC and FA diameter. Intima-media thickness (IMT) of the CC was found to be significantly increased (12% ± 4) in all astronauts during the spaceflight (early and late flight) and remained elevated 4 d after returning to Earth. Similarly, FA IMT was increased during the flight but returned to preflight levels 4 d postflight. CONCLUSION: The experiment demonstrated that, using the volume capture method of echography, untrained astronauts were able to capture enough echographic data to display vessel images of good quality for analysis. The increase in both CC and FA IMT during the flight suggest an adaptation to microgravity and to the confined environment of spaceflight which deserves further investigation.

Teleoperated Echograph and Probe Transducer for Remote Ultrasound Investigation on Isolated Patients (Study of 100 Cases).

PURPOSE: The objective of this study was to design and validate a "Tele-Operated UltRasound System" ("TOURS") to perform ultrasound examinations on patients located in isolated areas. MATERIALS AND METHODS: A commercially available portable echograph was modified to allow functions (Doppler, two-dimensional, three-dimensional, elastography, etc.) and settings (gain, depth, freeze, record, etc.) to be teleoperated through an Internet connection. Specialized probes were developed that contained motorized transducers that could be teleoperated to change the transducer orientation. The system was installed and tested in four medical centers 50 km, 60 km, 1,800 km, and 7,000 km away from the university hospital. RESULTS: Using the teleoperated system, 100 examinations were performed on the abdomen and pelvis (36%), vascular structures (42%), and small parts (thyroid and muscle, 22%), and 15 were performed on fetuses. During these examinations the expert sonographer was able to teleoperate the echograph and motorized probe to obtain images of sufficient quality for diagnoses in 97% of the cases. The average time for one examination was 17 ± 4 min. This new system (dimensions of 400 cm(3) and weighing 430 g) was found to be more ergonomic that a robotic arm previously developed by us for tele-echography (dimensions of 35 × 40 × 40 cm(3) and weighing 3-4 kg). In addition, the teleoperation of the echograph settings and functions allowed for greater ease in acquiring images, resulting in faster examinations with improved quality images. CONCLUSIONS: The results of this study demonstrate that the teleoperated echograph and probe system developed by our research group can be successfully used for ultrasound examinations in areas isolated from trained sonographers.

5-Day Bed Rest: Portal and Lower Limb Veins With and Without Artificial Gravity Countermeasures.

PURPOSE: The objective of the study was to evaluate the effect of short-term, head-down bed rest (HDBR), with and without artificial gravity countermeasures, on splanchnic and lower limb vein properties. METHODS: Data were collected from 12 men before and after 5 d of continuous -6° HDBR without countermeasures (CON) and with two artificial gravity countermeasure protocols: 30-min continuous centrifugation (AG1), and 30-min intermittent centrifugation (AG2). Portal (PV), tibial (TibV), and gastrocnemius (GastV) veins were investigated by echography supine and after 30 min of head-up tilt. RESULTS: After HDBR, there was no change in PV, TibV, or GastV cross-sectional area at rest in any of the three conditions. In response to tilt, GastV and TibV area increased (168±141% and 192±124%, respectively) with no change in this response post-HDBR in any of the experimental conditions (P>0.05). PV area decreased with tilt (-33±13%) and was not different pre- to post-HDBR in the CON or AG1 conditions. However, there was a greater reduction in PV area in the AG2 group post-HDBR (-32±10% pre, -49±9% post-HDBR, P=0.003). CONCLUSIONS: Calf veins were not significantly affected by 5 d of HDBR and did not appear to be negatively impacted by the artificial gravity countermeasures over this time period. In addition, the intermittent protocol resulted in better splanchnic vasoconstriction in response to head-up tilt, which may have contributed to a better maintenance of orthostatic tolerance post-HDBR.

Teles-operated echocardiography using a robotic arm and an internet connection.

The objective was to design and validate a method of tele-operated echocardiography. The method was tested in a hospital facility with an expert sonographer located in a room 10 m away from the patient. An ultrasound probe, fixed to a motorized probe holder, was located on the patient by a non-sonographer and was remotely controlled by the expert sonographer via an Internet connection. Scans were performed on 41 cardiac patients. The quality of the cardiac views obtained using tele-echocardiography was lower than that of reference echocardiography, but generated similar measurements in 93%-100% of the cases. Bland-Altman plots and statistical comparison of tele- and reference echocardiography measures revealed no differences (p > 0.05). Of the 71 valve leaks or aortic stenoses present, 61 (86%) were detected using tele-echocardiography. These results indicate that tele-echocardiography provided reliable diagnoses and acceptable measurements in 86% and 93% of cases, respectively, with no false-positive diagnoses being reported.

Cerebrovascular autoregulation: lessons learned from spaceflight research.

This review summarizes our current understanding of cerebral blood flow regulation with exposure to microgravity, outlines potential mechanisms associated with post-flight orthostatic intolerance, and proposes future directions for research and linkages with cerebrovascular disorders found in the general population. It encompasses research from cellular mechanisms (e.g. hind limb suspension: tissue, animal studies) to whole body analysis with respect to understanding human responses using space analogue studies (bed rest, parabolic flight) as well as data collected before, during, and after spaceflight. Recent evidence indicates that cerebrovascular autoregulation may be impaired in some astronauts leading to increased susceptibility to syncope upon return to a gravitational environment. The proposed review not only provides insights into the mechanisms of post-flight orthostatic intolerance, but also increases our understanding of the mechanisms associated with pathophysiological conditions (e.g. unexplained syncope) with clinical applications in relation to postural hypotension or intradialytic hypotension.

Temporal artery Doppler spectrum morphology responses to tilt and LBNP as an early indicator of syncope.

OBJECTIVE: In a study to identify an early hemodynamic predictor of syncope, 12 men (25-40 yr) underwent 30 min of 80 degrees head-up tilt, followed by progressive lower body negative pressure (LBNP) until presyncope. METHODS: Temporal (supplying extracranial tissues: TEMP), middle cerebral (MCA), and superficial femoral (FEM) arterial flow velocity (V) and vascular resistance indices (VR) were evaluated continuously using Doppler ultrasound. Ratios of the Doppler V(MEAN) (V(MCA)/V(FEM) or V(MCA)/ V(TEMP)) were used to assess flow redistribution between these areas. RESULTS: The progression of the testing protocol showed increases in vascular resistance in all territories. At presyncope, both MCA(VR) and FEM(VR) were reduced while there was a large increase in TEMP(VR). Vasoconstriction of the vascular bed supplied by the temporal artery occurred early during central hypovolemia resulting in the appearance of negative velocity deflections, which could be used for the early detection of impending syncope. Analysis of the velocity ratios showed little change until the onset of presyncope where there was an increase in V(MCA)/V(TEMP) which confirmed that vasoconstriction of the vascular bed supplied by the TEMP artery contributed to cardiac output redistribution in favor of the brain, and a reduction in V(MCA)/V(FEM) suggesting a redistribution of cardiac output toward the legs. DISCUSSION: In 67% of the tests, the appearance of the negative component of V(TEMP) was an early sign of increasing TEMP(VR) that occurred before visually detectable changes in VE(FEM) or V(MCA) and within 5 min before presyncope. Such easily identifiable in real time Doppler signs allowed experimenters to anticipate test termination.

WISE-2005: prolongation of left ventricular pre-ejection period with 56 days head-down bed rest in women.

This study tested the hypothesis that prolonged physical deconditioning affects the coupling of left ventricular depolarization to its ejection (the pre-ejection period, PEPi) and that this effect is minimized by exercise countermeasures. Following assignment to non-exercise (Control) and exercise groups (Exercise), 14 females performed 56 days of continuous head-down tilt bed rest. Measurements of the electrocardiogram (ECG) and stroke volume (Doppler ultrasound) during supine rest were obtained at baseline prior to (Pre) and after (Post) the head-down tilt bed rest (HDBR) period. Compared with Pre, the PEPi was increased following head-down tilt bed rest (main effect, P < 0.005). This effect was most dominant in the Control group [Pre = 0.038 ± 0.06 s (s.d.) versus Post = 0.054 ± 0.011 s; P < 0.001]. In the Exercise group, PEPi was 0.032 ± 0.005 s Pre and 0.038 ± 0.018 s Post; P= 0.08. Neither the QRS interval nor cardiac afterload was modified by head-down tilt bed rest in Control or Exercise groups. Low-dose isoprenaline infusion reversed the head-down tilt bed rest-induced delay in the PEPi. These results suggest that head-down tilt bed rest leads to a delayed onset of systolic ejection following left ventricular depolarization in a manner that is affected little by the exercise countermeasure but is related to ß-adrenergic pathways. The delayed onset of systole following head-down tilt bed rest appears to be related to mechanism(s) affecting contraction of the left ventricle rather than its depolarization.