Selective elevation in external carotid artery flow during acute gravitational transition to microgravity during parabolic flight.

This study sought to determine to what extent acute exposure to microgravity (0 G) and related increases in central blood volume (CBV) during parabolic flight influence the regional redistribution of intra and extra cranial cerebral blood flow (CBF). Eleven healthy participants performed during two parabolic flights campaigns aboard the Airbus A310-ZERO G aircraft. The response of select variables for each of the 15 parabolas involving exposure to both 0 G and hypergravity (1.8 G) were assessed in the seated position. Mean arterial blood pressure (MAP) and heart rate (HR) were continuously monitored and used to calculate stroke volume (SV), cardiac output ([Formula: see text]), and systemic vascular resistance (SVR). Changes in CBV were measured using an impedance monitor. Extracranial flow through the internal carotid, external carotid, and vertebral artery ([Formula: see text]ICA, [Formula: see text]ECA, and [Formula: see text]VA), and intracranial blood velocity was measured by duplex ultrasound. When compared with 1-G baseline condition, 0 G increased CBV (+375 ± 98 mL, P = 0.004) and [Formula: see text] (+16 ± 14%, P = 0.024) and decreased SVR (-7.3 ± 5 mmHg·min·L-1, P = 0.002) and MAP (-13 ± 4 mmHg, P = 0.001). [Formula: see text]ECA increased by 43 ± 46% in 0 G (P = 0.030), whereas no change was observed for CBF, [Formula: see text]ICA, or [Formula: see text]VA (P = 0.102, P = 0.637, and P = 0.095, respectively).NEW & NOTEWORTHY Our findings demonstrate that in microgravity there is a selective increase in external carotid artery blood flow whereas global and regional cerebral blood flow remained preserved. To what extent this reflects an adaptive, neuroprotective response to counter overperfusion remains to be established.

Effect of jump exercise training on long-term head-down bed rest-induced cerebral blood flow responses in arteries and veins.

NEW FINDINGS: What is the central question of this study? What is the effect of an exercise countermeasure on microgravity-induced change in cerebral blood flow? What is the main finding and its importance? Jump exercise training as a countermeasure did not modify the heterogeneous cerebral blood flow response to head-down bed rest, suggesting that this method is effective in preventing cardiovascular system deconditioning but is not good for cerebral haemodynamics. ABSTRACT: This study aimed to examine the effect of an exercise countermeasure on cerebral blood flow (CBF) response to long-term -6° head-down bed rest (HDBR) in all cerebral arteries and veins. Twenty male volunteers were exposed to HDBR for 60 days with (training group, n = 10) or without (control group, n = 10) jump exercise training as a countermeasure to spaceflight. The blood flow in the neck conduit arteries (internal carotid and vertebral artery; ICA and VA) and veins (internal jugular and vertebral veins; IJV and VV) was measured, using ultrasonography before (baseline) HDBR, on the 30th and 57th day of HDBR. Long-term HDBR causes a heterogeneous CBF response between the anterior and the posterior brain or between arteries and veins. Long-term HDBR decreased anterior cerebral arterial and venous blood flow, while posterior cerebral arterial and venous blood flows were well maintained. However, exercise jump training did not change each arterial and venous CBF responses to HDBR (control vs. training; ICA, P = 0.643; VA, P = 0.542; external carotid artery, P = 0.644; IJV, P = 0.980; VV, P = 0.999). These findings suggest that jump exercise training did not modify the heterogeneous CBF response to long-term HDBR.

Arterial and venous cerebral blood flow responses to long-term head-down bed rest in male volunteers.

NEW FINDINGS: What is the central question of this study? A heterogeneous cerebral blood flow (CBF) response in the cerebral arteries has been demonstrated in several physiological conditions, and it might be attributable to different physiological properties. However, the whole cerebral haemodynamic response to weightlessness remains unknown. What is the main finding and its importance? Long-term head-down bed rest caused a heterogeneous CBF response between the anterior and posterior cerebral arteries and between the cerebral arteries and veins. Especially, in contrast to the anterior cerebral circulation, the posterior arterial and venous CBFs were well maintained throughout weightlessness. ABSTRACT: In this study, we investigated the whole cerebral haemodynamic response to long-term head-down bed rest (HDBR). We hypothesized that long-term exposure to weightlessness influences cerebral blood flow (CBF) or CBF distribution among cerebral arteries and veins because of the different physiological roles of each cerebral vessel. To test this hypothesis, 10 male volunteers were exposed to -6 deg HDBR for 60 days. Blood flows in the internal carotid artery, external carotid artery and vertebral artery or internal jugular vein and vertebral vein were measured using ultrasonography before and on days 30 and 57 of the HDBR. The internal carotid artery blood flow was reduced on day 30 (P = 0.019) and had returned to the baseline level by day 57. In contrast, the vertebral artery blood flow remained unaltered throughout the HDBR (P = 0.626). The internal jugular vein blood flow was reduced on day 30 (P = 0.009), whereas the vertebral vein blood flow remained unaltered (P = 0.397). These findings suggest that long-term HDBR causes a heterogeneous CBF response between the anterior and posterior cerebral circulation in the both arteries and veins. The posterior arterial and venous CBFs were well maintained throughout HDBR, and these CBF responses to HDBR were different from the anterior cerebral circulation.

Echocardiographic evidence of left ventricular untwisting-filling interplay.

BACKGROUND: Left ventricular untwisting generates an early diastolic intraventricular pressure gradient (DIVPG) than can be quantified by echocardiography. We sought to confirm the quantitative relationship between peak untwisting rate and peak DIVPG in a large adult population. METHODS: From our echocardiographic database, we retrieved all the echocardiograms with a normal left ventricular ejection fraction, for whom color Doppler M-Mode interrogation of mitral inflow was available, and left ventricular untwisting rate was measurable using speckle tracking. Standard indices of left ventricular early diastolic function were assessed by Doppler (peaks E, e' and Vp) and speckle tracking (peak strain rate Esr). Load dependency of DIVPG and untwisting rate was evaluated using a passive leg raising maneuver. RESULTS: We included 154 subjects, aged between 18 to 77 years old, 63% were male. Test-retest reliability for color Doppler-derived DIVPG measurements was good, the intraclass correlation coefficients were 0.97 [0.91-0.99] and 0.97 [0.67-0.99] for intra- and inter-observer reproducibility, respectively. Peak DIVPG was positively correlated with peak untwisting rate (r = 0.73, P <  0.001). On multivariate analysis, peak DIVPG was the only diastolic parameter that was independently associated with untwisting rate. Age and gender were the clinical predictive factors for peak untwisting rate, whereas only age was independently associated with peak DIVPG. Untwisting rate and DIVPG were both load-dependent, without affecting their relationship. CONCLUSIONS: Color Doppler-derived peak DIVPG was quantitatively and independently associated with peak untwisting rate. It thus provides a reliable flow-based index of early left ventricular diastolic function.

Internal carotid, external carotid and vertebral artery blood flow responses to 3 days of head-out dry immersion.

NEW FINDINGS: What is the central question of this study? The extent to which weightlessness associated with a fluid shift from the peripheral to the central circulation influences the blood flow in each cerebral artery remains unknown. The present study was designed to explore the effect of short-term weightlessness conditions on both anterior and posterior cerebral blood flow. What is the main finding and its importance? Short-term weightlessness affects both anterior and posterior cerebral vasculature. However, a heterogeneous cerebral blood flow response in each cerebral artery did not occur during 3 days of dry immersion. We have recently demonstrated that a heterogeneous cerebral blood flow (CBF) response in each cerebral artery might contribute to the maintenance of circulatory homeostasis in the brain. However, the extent to which weightlessness associated with a fluid shift from the peripheral to the central circulation influences the distribution of CBF in each cerebral artery remains unknown. We hypothesized that a dry immersion-induced fluid shift (weightlessness conditions) would cause a heterogeneous CBF response in each cerebral artery. During and after 3 days of dry immersion, the blood flows in the internal carotid (ICA), external carotid (ECA) and vertebral arteries (VA) were measured by Doppler ultrasonography using an 8 MHz linear transducer. Although the 3 days of dry immersion and the 2 days recovery period did not change the blood flow in each cerebral artery, the conductance in both ICA and VA decreased during dry immersion on days 2 and 3 (ICA, 2.95 and 3.23 ml min-1  mmHg-1 ; VA, 1.10 and 1.05 ml min-1  mmHg-1 , respectively) from the baseline (ICA, 3.47 ml min-1  mmHg-1 , P = 0.027; VA, 1.23 ml min-1  mmHg-1 , P = 0.004). In addition, Pearson correlation analysis demonstrated that the 3 days of dry immersion induced a decrease in cardiac output (P = 0.004) that was associated with changes in ICA (P = 0.046) and VA blood flow (P = 0.021), but not ECA blood flow (P = 0.466). These findings suggest that short exposures to weightlessness, acting via a cephalad redistribution of fluid volume and blood flow in the human body, influenced the cerebral vasculature in each cerebral artery but did not cause a heterogeneous CBF response in each cerebral artery.

Effect of an acute increase in central blood volume on cerebral hemodynamics.

Systemic blood distribution is an important factor involved in regulating cerebral blood flow (CBF). However, the effect of an acute change in central blood volume (CBV) on CBF regulation remains unclear. To address our question, we sought to examine the CBF and systemic hemodynamic responses to microgravity during parabolic flight. Twelve healthy subjects were seated upright and exposed to microgravity during parabolic flight. During the brief periods of microgravity, mean arterial pressure was decreased (-26 ± 1%, P < 0.001), despite an increase in cardiac output (+21 ± 6%, P < 0.001). During microgravity, central arterial pulse pressure and estimated carotid sinus pressure increased rapidly. In addition, this increase in central arterial pulse pressure was associated with an arterial baroreflex-mediated decrease in heart rate (r = -0.888, P < 0.0001) and an increase in total vascular conductance (r = 0.711, P < 0.001). The middle cerebral artery mean blood velocity (MCA Vmean) remained unchanged throughout parabolic flight (P = 0.30). During microgravity the contribution of cardiac output to MCA Vmean was gradually reduced (P < 0.05), and its contribution was negatively correlated with an increase in total vascular conductance (r = -0.683, P < 0.0001). These findings suggest that the acute loading of the arterial and cardiopulmonary baroreceptors by increases in CBV during microgravity results in acute and marked systemic vasodilation. Furthermore, we conclude that this marked systemic vasodilation decreases the contribution of cardiac output to CBF. These findings suggest that the arterial and cardiopulmonary baroreflex-mediated peripheral vasodilation along with dynamic cerebral autoregulation counteracts a cerebral overperfusion, which otherwise would occur during acute increases in CBV.

Noninvasive ventilation and breathing-swallowing interplay in chronic obstructive pulmonary disease*.

OBJECTIVES: To investigate breathing-swallowing interactions in patients with chronic obstructive pulmonary disease requiring noninvasive mechanical ventilation and, if needed, to develop a technical modification of the ventilator designed to eliminate ventilator insufflations during swallowing. DESIGN: We conducted a prospective, open-label, interventional study. PATIENTS: Fifteen consecutive chronic obstructive pulmonary disease patients with exacerbations requiring ICU admission and NIV. INTERVENTIONS: Swallowing performance and breathing-swallowing interactions were investigated noninvasively by chin electromyography, cervical piezoelectric sensor, and inductive respiratory plethysmography. Two water-bolus sizes (5 and 10 mL) were tested in random order. Swallowing was tested with and without noninvasive mechanical ventilation, in random order. First, a standard mechanical ventilator capable of delivering noninvasive mechanical ventilation was used. Second, a marketed device was equipped with an off-switch for use during swallowing. MEASUREMENTS AND MAIN RESULTS: Swallowing performance and breathing-swallowing interactions were investigated noninvasively by chin electromyography, cervical piezoelectric sensor, and inductive respiratory plethysmography. Two water bolus sizes (5 and 10 mL) were tested in random order. Swallowing was tested with and without noninvasive mechanical ventilation in random order. First, a standard mechanical ventilator capable of delivering noninvasive mechanical ventilation was used. Swallowing efficiency, breathing-swallowing synchronization, and Borg Scale dyspnea scores improved significantly with noninvasive mechanical ventilation. However, swallowing induced ventilator triggering followed by autotriggering. To improve patient-ventilator synchrony, a marketed device was equipped with an off-switch for use during swallowing. This device completely eliminated swallowing-induced ventilator triggering and postswallow autotriggering. CONCLUSION: Patients with chronic obstructive pulmonary disease admitted to the ICU for acute exacerbations had abnormal breathing-swallowing interactions and dyspnea, which improved with noninvasive mechanical ventilation. Furthermore, a ventilator device with a simple switch-off pushbutton to eliminate insufflations during swallows prevented swallowing-induced ventilator triggering and postswallow autotriggering.

Regional redistribution of blood flow in the external and internal carotid arteries during acute hypotension.

The present study examined to what extent an acute bout of hypotension influences blood flow in the external carotid artery (ECA) and the corresponding implications for blood flow regulation in the internal carotid artery (ICA). Nine healthy male participants were subjected to an abrupt decrease in arterial pressure via the thigh-cuff inflation-deflation technique. Duplex ultrasound was employed to measure beat-to-beat ECA and ICA blood flow. Compared with the baseline normotensive control, acute hypotension resulted in a heterogeneous blood flow response. ICA blood flow initially decreased following cuff release and then returned quickly to baseline levels. In contrast, the reduction in ECA blood flow persisted for 30 s following cuff release. Thus, the contribution of common carotid artery blood flow to the ECA circulation decreased during acute hypotension (-10 ± 4%, P < 0.001). This finding suggests that a preserved reduction in ECA blood flow, as well as dynamic cerebral autoregulation likely prevent a further decrease in intracranial blood flow during acute hypotension. The peripheral vasculature of the ECA may, thus, be considered an important vascular bed for intracranial cerebral blood flow regulation.

Inter-season training effects on cardiovascular health in American-style football players.

BACKGROUND: Recent studies on American-style football (ASF) athletes raised questions about the impact of training on the cardiovascular phenotype, particularly among linemen players who engage mostly in static exercise during competition and who exhibit concentric cardiac remodeling, often considered maladaptive. We aimed to examine the cardiovascular adaptation to the inter-season mixed-team training program among ASF players. METHODS: A prospective, longitudinal, cohort study was conducted among competitive male ASF players from the University of Montreal before and after an inter-season training, which lasted 7 months. This program includes, for all players, combined dynamic and static exercises. Clinical and echocardiographic examinations were performed at both steps. Left atrial (LA) and ventricular (LV) morphological and functional changes were assessed using a multiparametric echocardiographic approach (2D and 3D-echo, Doppler, and speckle tracking). Two-way ANOVA was performed to analyze the impacts of time and field position (linemen versus non-linemen). RESULTS: Fifty-nine players (20 linemen and 39 non-linemen) were included. At baseline, linemen had higher blood pressure (65% were prehypertensive and 10% were hypertensive), thicker LV walls, lower LV systolic and diastolic functions, lower LA-reservoir and conduit functions than non-linemen. After training, linemen significantly reduced weight (Δ-3.4%, P < 0.001) and systolic blood pressure (Δ-4.5%, P < 0.001), whereas non-linemen maintained their weight and significantly increased their systolic (Δ+4.2%, P = 0.037) and diastolic (Δ+16%, P < 0.001) blood pressure ). Mixed training was associated with significant increases in 2D-LA volume (P < 0.001), 3D-LV end-diastolic volume (P < 0.001), 3D-LV mass (P < 0.001), and an improvement in LV systolic function, independently of the field position. Non-linemen remodeled their LV in a more concentric fashion and showed reductions in LV diastolic and LA reservoir functions. CONCLUSIONS: Our study underscored the influence of field position on cardiovascular adaptation among university-level ASF players, and emphasized the potential of inter-season training to modulate cardiovascular risk factors, particularly among linemen.

Effects of a 20-Week High-Intensity Strength Training Program on Muscle Strength Gain and Cardiac Adaptation in Untrained Men: Preliminary Results of a Prospective Longitudinal Study.

BACKGROUND: As strength sports gain popularity, there is a growing need to explore the impact of sustained strength training on cardiac biventricular structure and function, an area that has received less attention compared to the well-established physiological cardiac adaptation to endurance training. OBJECTIVE: This study aims to implement a 20-week high-intensity strength training program to enhance maximal muscle strength and evaluate its impact on cardiac biventricular adaptation in healthy, untrained men. METHODS: A total of 27 healthy and untrained young men (mean age 22.8, SD 3.2 years) participated in a strength training program designed to increase muscle strength. The training program involved concentric, eccentric, and isometric exercise phases, conducted over a consecutive 20-week time frame with a frequency of 3 weekly training sessions. Participants were evaluated before and after 12 and 20 weeks of training through body composition analysis (bioelectrical impedance), a 12-lead resting electrocardiogram, 3D transthoracic echocardiography, cardiopulmonary exercise testing, and muscle isokinetic dynamometry. The progression of strength training loads was guided by 1-repetition maximum (RM) testing during the training program. RESULTS: Of the initial cohort, 22 participants completed the study protocol. No injuries were reported. The BMI (mean 69.8, SD 10.8 kg/m² vs mean 72, SD 11 kg/m²; P=.72) and the fat mass (mean 15.3%, SD 7.5% vs mean 16.5%, SD 7%; P=.87) remained unchanged after training. The strength training program led to significant gains in 1-RM exercise testing as early as 4 weeks into training for leg extension (mean 69.6, SD 17.7 kg vs mean 96.5, SD 31 kg; P<.001), leg curl (mean 43.2, SD 9.7 kg vs mean 52.8, SD 13.4 kg; P<.001), inclined press (mean 174.1, SD 41.1 kg vs mean 229.2, SD 50.4 kg; P<.001), butterfly (mean 26.3, SD 6.2 kg vs mean 32.5, SD 6.6 kg; P<.001), and curl biceps on desk (mean 22.9, SD 5.2 kg vs mean 29.6, SD 5.2 kg; P<.001). After 20 weeks, the 1-RM leg curl, bench press, pullover, butterfly, leg extension, curl biceps on desk, and inclined press showed significant mean percentage gains of +40%, +41.1%, +50.3%, +63.5%, +80.1%, +105%, and +106%, respectively (P<.001). Additionally, the isokinetic evaluation confirmed increases in maximal strength for the biceps (+9.2 Nm), triceps (+11.6 Nm), quadriceps (+46.8 Nm), and hamstrings (+25.3 Nm). In this paper, only the training and muscular aspects are presented; the cardiac analysis will be addressed separately. CONCLUSIONS: This study demonstrated that a short-term high-intensity strength training program was successful in achieving significant gains in muscle strength among previously untrained young men. We intend to use this protocol to gain a better understanding of the impact of high-intensity strength training on cardiac physiological remodeling, thereby providing new insights into the cardiac global response in strength athletes. TRIAL REGISTRATION: ClinicalTrials.gov NCT04187170; https://clinicaltrials.gov/study/NCT04187170.

Comprehensive assessment of physiological responses in women during the ESA dry immersion VIVALDI microgravity simulation.

Astronauts in microgravity experience multi-system deconditioning, impacting their inflight efficiency and inducing dysfunctions upon return to Earth gravity. To fill the sex gap of knowledge in the health impact of spaceflights, we simulate microgravity with a 5-day dry immersion in 18 healthy women (ClinicalTrials.gov Identifier: NCT05043974). Here we show that dry immersion rapidly induces a sedentarily-like metabolism shift mimicking the beginning of a metabolic syndrome with a drop in glucose tolerance, an increase in the atherogenic index of plasma, and an impaired lipid profile. Bone remodeling markers suggest a decreased bone formation coupled with an increased bone resorption. Fluid shifts and muscular unloading participate to a marked cardiovascular and sensorimotor deconditioning with decreased orthostatic tolerance, aerobic capacity, and postural balance. Collected datasets provide a comprehensive multi-systemic assessment of dry immersion effects in women and pave the way for future sex-based evaluations of countermeasures.

Age impacts left atrial functional remodeling in athletes.

AIM: Age-associated changes in cardiac filling and function are well known in the general population. Yet, the effect of aging on left atrial (LA) function, and its interaction with left ventricular (LV) adaptation, remain less described when combined with high-intensity chronic training. We aimed to analyze the effects of aging on LA and LV functions in trained athletes. METHODS AND RESULTS: Ninety-five healthy highly-trained athletes referred for resting echocardiography were included. Two groups of athletes were retrospectively defined based on age: young athletes aged <35 years (n = 54), and master athletes aged ≥35 years (n = 41). All subjects were questioned about their sports practice. Echocardiographic analysis of LV systolic and diastolic functions (2D-echo, 3D-echo, and Doppler), as well as LA 2D dimensions and phasic deformations assessed by speckle tracking, were analyzed. Master athletes (mean age = 46.3 ± 8.3 years, mean duration of sustained training = 13.7 ± 8.9 years) exhibited significantly stiffer LV and LA with reduced LV early diastolic functional parameters (ratio E/A, peak e', and ratio e'/a'), LA reservoir and conduit strain, whereas LA volume, LA contractile strain and LV peak a' were higher, compared to young athletes. Multivariate regression analysis confirmed that age was predictive of peak e', LA reservoir strain and LA conduit strain, independently of training variables. LA phasic strains were strongly associated with LV diastolic function. CONCLUSIONS: Regardless of chronic sports practice, master athletes exhibited age-related changes in LA function closely coupled to LV diastolic properties, which led to LV filling shifts to late diastole.

Mouth and nasal inspiratory pressure: learning effect and reproducibility in healthy adults.

BACKGROUND: Inspiratory muscle strength measurements have become a cornerstone in monitoring neuromuscular disorders. Usually, sniff nasal inspiratory pressure (SNIP) and maximal inspiratory pressure (MIP) are performed. To our knowledge the session-to-session learning effect has rarely been evaluated for MIP performance and has never been done for SNIP performance. OBJECTIVES: We hypothesized that the sniff manoeuvre was natural and did not need to be learned, whereas the Muller manoeuvre, used for MIP measurement, was an isometric contraction which needed to be learned because it is rarely performed in real life conditions. This hypothesis suggests that from the first session and continuing through a subsequent one, the maximal SNIP value and the number of sniff trials necessary to attain it are more reproducible than the maximal MIP value and the number of Muller manoeuvre trials necessary to attain it. METHODS: Seventy-one healthy subjects were included. SNIP and MIP manoeuvres were repeated 12 and 6 times, respectively, per week during 2 sessions a week apart. RESULTS: We observed a session effect on MIP but not on SNIP. Maximal value for MIP was higher during the second session, whereas SNIP maximal value did not increase during the second session. The number of trials needed to obtain the maximal value for MIP was lower during the second session whereas it was not different for SNIP. CONCLUSIONS: SNIP is less sensitive to a learning effect than is MIP. It requires only a routine warm-up. We suggest that SNIP is preferable to MIP for repeated measurement of inspiratory muscle performance.

Assessment of concordance between diffusion of carbon monoxide through the lung using the 10 s breath-hold method, and the simultaneous NO/CO technique, in healthy participants.

INTRODUCTION: There is limited, large sample size, healthy control data comparing measurement of diffusing capacity of the lungs for carbon monoxide (DLCO) via the 10 s single-breath carbon monoxide uptake method (DLCO10) and using a DLCO-DLNO double diffusion test performed with a 5 s time of apnoea (DLCO5). OBJECTIVES: The primary objective was to compare DLCO5 and DLCO10 in healthy participants. The secondary objective was to evaluate the reproducibility of DLCO5. MATERIAL AND METHODS: We included medical students at Caen University Hospital, from 2008 to 2011. We performed a standard single-breath carbon monoxide uptake and combined DLCO and DLNO measurement for each participant. The combined test was repeated one week later. RESULTS: Among the 153 study participants, there was no statistically significant difference between the mean values of DLCO10 (10.2 ±â€¯2.2 mmol.min-1 kPa-1) and DLCO5 (10.3 ±â€¯2.2 mmol.min-1 kPa-1; paired t-test p = 0.19). Corrected for the same FiO2, DLCO5 was calculated at 10.5 ±â€¯2.3 mmol.min-1 kPa-1 and was significantly different from DLCO10 (paired t-test p < 0.001). DLCO5 deviates from 1,6 mmol.min-1 kPa-1 (4,6 mL.min-1. mmHg-1) or 15 % of DLCO10 (17 % above and 13% below, for 95 % of the subjects). Forty-seven participants were included in the DLCO5 reproducibility test. The 2 test sessions were carried out at 6 ±â€¯2 day intervals. Reproducibilities for DLCO, DLNO, DmCO and Vc was respectively 1.2 (11 %), 6.8 (13%), 16.5 (32 %), 12.5 (17 %) mmol.min-1 kPa-1. CONCLUSION: In healthy participants, discrepancies between DLCO measured during the double diffusion and DLCO measured on an apnoea of 10 s are quite large. It may be an indication that the Roughton and Forster interpretation to describe this type of measurements is inadequate.

Analysis of inter-system variability of systolic and diastolic intraventricular pressure gradients derived from color Doppler M-mode echocardiography.

Assessment of intraventricular pressure gradients (IVPG) using color Doppler M-mode echocardiography has gained increasing interest in the evaluation of cardiac function. However, standardized analysis tools for IVPG quantification are missing. We aimed to evaluate the feasibility, the test-retest observer reproducibility, and the inter-system variability of a semi-automated IVPG quantification algorithm. The study included forty healthy volunteers (50% were men). All volunteers were examined using two ultrasound systems, the Philips Epiq 7 and the General Electric Vivid 6. Left ventricular diastolic (DIVPG) and systolic (SIVPG) intraventricular pressure gradients were measured from the spatiotemporal distribution of intraventricular propagation flow velocities using color Doppler M-mode in standard apical views. There was good feasibility for both systolic and diastolic IVPG measurements (82.5% and 85%, respectively). Intra and inter-observer test-retest variability measured with the intraclass correlation coefficient were 0.98 and 0.93 for DIVPG respectively, and 0.95 and 0.89 for SIVPG respectively. The inter-system concordance was weak to moderate with Lin's concordance correlation coefficient of 0.59 for DIVPG and 0.25 for SIVPG. In conclusion, it is feasible and reproducible to assess systolic and diastolic IVPG using color Doppler M-mode in healthy volunteers. However, the inter-system variability in IVPG analysis needs to be taken into account, especially when using displayed data.

Gravitational Transitions Increase Posterior Cerebral Perfusion and Systemic Oxidative-nitrosative Stress: Implications for Neurovascular Unit Integrity.

The present study examined if repeated bouts of micro- and hypergravity during parabolic flight (PF) alter structural integrity of the neurovascular unit (NVU) subsequent to free radical-mediated changes in regional cerebral perfusion. Six participants (5♂, 1♀) aged 29 ±â€¯11 years were examined before, during and after a 3 h PF and compared to six sex and age-matched (27 ±â€¯6 years) normogravity controls. Blood flow was measured in the anterior (middle cerebral artery, MCA; internal carotid artery, ICA) and posterior (vertebral artery, VA) circulation (duplex ultrasound) in-flight over the course of 15 parabolas. Venous blood was assayed for free radicals (electron paramagnetic resonance spectroscopy), nitric oxide (NO, ozone-based chemiluminescence) and NVU integrity (chemiluminescence/ELISA) in normogravity before and after exposure to 31 parabolas. While MCA velocity did not change (P > 0.05), a selective increase in VA flow was observed during the most marked gravitational transition from micro- to hypergravity (P < 0.05). Increased oxidative-nitrosative stress defined by a free radical-mediated reduction in NO and elevations in glio-vascular GFAP and S100ß were observed after PF (P < 0.05), the latter proportional to the increase in VA flow (r = 0.908, P < 0.05). In contrast, biomarkers of neuronal-axonal damage (neuron-specific enolase, neurofilament light-chain, ubiquitin carboxy-terminal hydrolase L1 and tau) did not change (P > 0.05). Collectively, these findings suggest that the cumulative effects of repeated gravitational transitions may promote minor blood-brain barrier disruption, potentially related to the combined effects of haemodynamic (posterior cerebral hyperperfusion) and molecular (systemic oxidative-nitrosative) stress.

Noninvasive in-ear monitoring of intracranial pressure during microgravity in parabolic flights.

Among possible causes of visual impairment or headache experienced by astronauts in microgravity or postflight and that hamper their performance, elevated intracranial pressure (ICP) has been invoked but never measured for lack of noninvasive methods. The goal of this work was to test two noninvasive methods of ICP monitoring using in-ear detectors of ICP-dependent auditory responses, acoustic and electric, in acute microgravity afforded by parabolic flights. The devices detecting these responses were handheld tablets routinely used in otolaryngology for hearing diagnosis, which were customized for ICP extraction and serviceable by unskilled operators. These methods had been previously validated against invasive ICP measurements in neurosurgery patients. The two methods concurred in their estimation of ICP changes with microgravity, i.e., 11.0 ± 7.7 mmHg for the acoustic method ( n = 7 subjects with valid results out of 30, auditory responses being masked by excessive in-flight noise in 23 subjects) and 11.3 ± 10.6 mmHg for the electric method ( n = 10 subjects with valid results out of 10 tested despite the in-flight noise). These results agree with recent publications using invasive access to cerebrospinal fluid in parabolic flights and suggest that acute microgravity has a moderate average effect on ICP, similar to body tilt from upright to supine, yet with some subjects undergoing large effects whereas others seem immune. The electric in-ear method would be suitable for ICP monitoring in circumstances and with subjects such that invasive measurements are excluded. NEW & NOTEWORTHY In-ear detectors of intracranial pressure-dependent auditory responses allow intracranial pressure to be monitored noninvasively during acute microgravity. The average pressure increase during 20-s long sessions in microgravity is 11 mmHg, comparable with an effect of body tilt. However, intersubject variability is large, with subjects who repeatedly experience from nothing to twice the average effect. A systematic in-flight use would allow the relationship between space adaptation syndrome and ICP to be established or dismissed.

Interaction between graviception and carotid baroreflex function in humans during parabolic flight-induced microgravity.

The aim of the present study was to assess carotid baroreflex (CBR) function during acute changes in otolithic activity in humans. To address this question, we designed a set of experiments to identify the modulatory effects of microgravity on CBR function at a tilt angle of -2°, which was identified to minimize changes in central blood volume during parabolic flight. During parabolic flight at 0 and 1 g, CBR function curves were modeled from the heart rate (HR) and mean arterial pressure (MAP) responses to rapid pulse trains of neck pressure and neck suction ranging from +40 to -80 Torr; CBR control of HR (carotid-HR) and MAP (carotid-MAP) function curves, respectively. The maximal gain of both carotid-HR and carotid-MAP baroreflex function curves were augmented during microgravity compared with 1 g (carotid-HR, -0.53 to -0.80 beats·min-1·mmHg-1, P < 0.05; carotid-MAP, -0.24 to -0.30 mmHg/mmHg, P < 0.05). These findings suggest that parabolic flight-induced acute change of otolithic activity may modify CBR function and identifies that the vestibular system contributes to blood pressure regulation under fluctuations in gravitational forces. NEW & NOTEWORTHY The effect of acute changes in vestibular activity on arterial baroreflex function remains unclear. In the present study, we assessed carotid baroreflex function without changes in central blood volume during parabolic flight, which causes acute changes in otolithic activity. The sensitivity of both carotid heart rate and carotid mean arterial pressure baroreflex function was augmented in microgravity compared with 1 g, suggesting that the vestibular system contributes to blood pressure regulation in humans on Earth.

Long-duration bed rest modifies sympathetic neural recruitment strategies in male and female participants.

To understand the impact of physical deconditioning with head-down tilt bed rest (HDBR) on the malleability of sympathetic discharge patterns, we studied 1) baseline integrated muscle sympathetic nerve activity (MSNA; microneurography) from 13 female participants in the WISE-2005 60-day HDBR study (retrospective analysis), 2) integrated MSNA and multiunit action potential (AP) analysis in 13 male participants performed on data collected at baseline and during physiological stress imposed by end-inspiratory apnea in a new 60-day HDBR study, and 3) a repeatability study (control; n = 6, retrospective analysis, 4 wk between tests). Neither baseline integrated burst frequency nor incidence were altered with HDBR (both P > 0.35). However, baseline integrated burst latency increased in both HDBR studies (male: 1.35 ± 0.02 to 1.39 ± 0.02 s, P < 0.01; female: 1.23 ± 0.02 to 1.29 ± 0.02 s, P < 0.01), whereas controls exhibited no change across two visits (1.25 ± 0.02 to 1.25 ± 0.02 s, group-by-time interaction, P = 0.02). With the exception of increased AP latency ( P = 0.03), male baseline AP data did not change with HDBR (all P > 0.19). The change in AP frequency on going from baseline to apnea (∆94 ± 25 to ∆317 ± 55 AP/min, P < 0.01) and the number of active sympathetic clusters per burst (∆0 ± 0.2 to ∆1 ± 0.2 clusters/burst, P = 0.02) were greater post- compared with pre-HDBR. The change in total clusters with apnea was ∆0 ± 0.5 clusters pre- and ∆2 ± 0.7 clusters post-HDBR ( P = 0.07). These data indicate that 60-day HDBR modified discharge characteristics in baseline burst latency and sympathetic neural recruitment during apneic stress. NEW & NOTEWORTHY Long-duration bed rest did not modify baseline sympathetic burst frequency in male and female participants, but examination of additional features of the multiunit signal provided novel evidence to suggest augmented synaptic delays or processing times at baseline for all sympathetic action potentials. Furthermore, long-duration bed rest increased reflex-sympathetic arousal to apneic stress in male participants primarily by mechanisms involving an augmented firing rate of action potential clusters active at baseline.

Physiological predictors of respiratory and cough assistance needs after extubation.

BACKGROUND: Identifying patients at high risk of post-extubation acute respiratory failure requiring respiratory or mechanical cough assistance remains challenging. Here, our primary aim was to evaluate the accuracy of easily collected parameters obtained before or just after extubation in predicting the risk of post-extubation acute respiratory failure requiring, at best, noninvasive mechanical ventilation (NIV) and/or mechanical cough assistance and, at worst, reintubation after extubation. METHODS: We conducted a multicenter prospective, open-label, observational study from April 2012 through April 2015. Patients who passed a weaning test after at least 72 h of endotracheal mechanical ventilation (MV) were included. Just before extubation, spirometry and maximal pressures were measured by a technician. The results were not disclosed to the bedside physicians. Patients were followed until discharge or death. RESULTS: Among 3458 patients admitted to the ICU, 730 received endotracheal MV for longer than 72 h and were then extubated; among these, 130 were included. At inclusion, the 130 patients had mean ICU stay and endotracheal MV durations both equal to 11 ± 4.2 days. After extubation, 36 patients required curative NIV, 7 both curative NIV and mechanical cough assistance, and 8 only mechanical cough assistance; 6 patients, all of whom first received NIV, required reintubation within 48 h. The group that required NIV after extubation had a significantly higher proportion of patients with chronic respiratory disease (P = 0.015), longer endotracheal MV duration at inclusion, and lower Medical Research Council (MRC) score (P = 0.02, P = 0.01, and P = 0.004, respectively). By multivariate analysis, forced vital capacity (FVC) and peak cough expiratory flow (PCEF) were independently associated with (NIV) and/or mechanical cough assistance and/or reintubation after extubation. Areas under the ROC curves for pre-extubation PCEF and FVC were 0.71 and 0.76, respectively. CONCLUSION: In conclusion, FVC measured before extubation correlates closely with FVC after extubation and may serve as an objective predictor of post-extubation respiratory failure requiring NIV and/or mechanical cough assistance and/or reintubation in heterogeneous populations of medical ICU patients. ClinicalTrials.gov as #NCT01564745.