Quantifying changes in oxygen saturation of the internal jugular vein in vivo using deep neural networks and subject-specific three-dimensional Monte Carlo models.

Central venous oxygen saturation (ScvO2) is an important parameter for assessing global oxygen usage and guiding clinical interventions. However, measuring ScvO2 requires invasive catheterization. As an alternative, we aim to noninvasively and continuously measure changes in oxygen saturation of the internal jugular vein (SijvO2) by a multi-channel near-infrared spectroscopy system. The relation between the measured reflectance and changes in SijvO2 is modeled by Monte Carlo simulations and used to build a prediction model using deep neural networks (DNNs). The prediction model is tested with simulated data to show robustness to individual variations in tissue optical properties. The proposed technique is promising to provide a noninvasive tool for monitoring the stability of brain oxygenation in broad patient populations.

Jugular venous flow dynamics during acute weightlessness.

During spaceflight, fluids shift headward, causing internal jugular vein (IJV) distension and altered hemodynamics, including stasis and retrograde flow, that may increase the risk of thrombosis. This study's purpose was to determine the effects of acute exposure to weightlessness (0-G) on IJV dimensions and flow dynamics. We used two-dimensional (2-D) ultrasound to measure IJV cross-sectional area (CSA) and Doppler ultrasound to characterize venous blood flow patterns in the right and left IJV in 13 healthy participants (6 females) while 1) seated and supine on the ground, 2) supine during 0-G parabolic flight, and 3) supine during level flight (at 1-G). On Earth, in 1-G, moving from seated to supine posture increased CSA in both left (+62 [95% CI: +42 to 81] mm2, P < 0.0001) and right (+86 [95% CI: +58 to 113] mm2, P < 0.00012) IJV. Entry into 0-G further increased IJV CSA in both left (+27 [95% CI: +5 to 48] mm2, P = 0.02) and right (+30 [95% CI: +0.3 to 61] mm2, P = 0.02) relative to supine in 1-G. We observed stagnant flow in the left IJV of one participant during 0-G parabolic flight that remained during level flight but was not present during any imaging during preflight measures in the seated or supine postures; normal venous flow patterns were observed in the right IJV during all conditions in all participants. Alterations to cerebral outflow dynamics in the left IJV can occur during acute exposure to weightlessness and thus, may increase the risk of venous thrombosis during any duration of spaceflight.NEW & NOTEWORTHY The absence of hydrostatic pressure gradients in the vascular system and loss of tissue weight during weightlessness results in altered flow dynamics in the left internal jugular vein in some astronauts that may contribute to an increased risk of thromboembolism during spaceflight. Here, we report that the internal jugular veins distend bilaterally in healthy participants and that flow stasis can occur in the left internal jugular vein during acute weightlessness produced by parabolic flight.

Assessment of venous pressure by compression sonography of the internal jugular vein during 3 days of bed rest.

Compression sonography has been proposed as a method for non-invasive measurement of venous pressures during spaceflight, but initial reports of venous pressure measured by compression ultrasound conflict with prior reports of invasively measured central venous pressure (CVP). The aim of this study is to determine the agreement of compression sonography of the internal jugular vein (IJVP) with invasive measures of CVP over a range of pressures relevant to microgravity exposure. Ten healthy volunteers (18-55 years, five female) completed two 3-day sessions of supine bed rest to simulate microgravity. IJVP and CVP were measured in the seated position, and in the supine position throughout 3 days of bed rest. The range of CVP recorded was in line with previous reports of CVP during changes in posture on Earth and in microgravity. The correlation between IJVP and CVP was poor when measured during spontaneous breathing (r = 0.29; R2  = 0.09; P = 0.0002; standard error of the estimate (SEE) = 3.0 mmHg) or end-expiration CVP (CVPEE ; r = 0.19; R2  = 0.04; P = 0.121; SEE = 3.0 mmHg). There was a modest correlation between the change in CVP and the change in IJVP for both spontaneous ΔCVP (r = 0.49; R2  = 0.24; P < 0.0001) and ΔCVPEE (r = 0.58; R2  = 0.34; P < 0.0001). Bland-Altman analysis of IJVP revealed a large positive bias compared to spontaneous breathing CVP (3.6 mmHg; SD = 4.0; CV = 85%; P < 0.0001) and CVPEE (3.6 mmHg; SD = 4.2; CV = 84%; P < 0.0001). Assessment of absolute IJVP via compression sonography correlated poorly with direct measurements of CVP by invasive catheterization over a range of venous pressures that are physiologically relevant to spaceflight. However, compression sonography showed modest utility for tracking changes in venous pressure over time. NEW FINDINGS: What is the central question of this study? Compression sonography has been proposed as a novel method for non-invasive measurement of venous pressures during spaceflight. However, the accuracy has not yet been confirmed in the range of CVP experienced by astronauts during spaceflight. What is the main finding and its importance? Our data show that compression sonography of the internal jugular vein correlates poorly with direct measurement of central venous pressures in a range that is physiologically relevant to spaceflight. However, compression sonography showed modest utility for tracking changes in venous pressure over time.

Effects of intubation technique on intracranial pressure: a cadaveric study.

Patients are at risk of increased intracranial pressure (ICP) during manipulation for endotracheal intubation. The aim of this cadaveric study was to quantify this relationship. Five fresh frozen adult cadaveric heads were used. The internal carotid artery (ICA) and internal jugular vein (IJV) were dissected bilaterally. All vessels were occluded on the right side. To mimic central venous pressures, the left IJV was cannulated and filled with water to maintain a pressure of approximately 7 cm H2O. The ICA cannula was attached to an oscillating water pump. Next, an ICP monitor was placed. Normophysiological volumes of water were infused to maintain normal ICP. Baseline ICP and IJV pressures were recorded. The heads were then placed in the sniffing position and in neutral position for nasal intubation, and finally an oral endotracheal tube was placed using standard head/neck maneuvers. The ICP was recorded. Mean baseline ICP was 13 mmHg (range 4-18 mmHg) and mean IJV pressure was 6 cm H2O. In the sniffing position, ICP increased in all specimens by a mean of 5 mmHg. In the neutral position, after intubation, the ICP increased in all specimens by a mean of 3 mmHg. Nasal intubation resulted in an increase in four of the five specimens. The mean increase in ICP with this maneuver was 2 mmHg. We present a cadaveric model of ICP measurement during neck manipulation using intracranial fluid dynamics. The ICP increased consistently. Following clinical studies, physicians involved in intubating patients with concern for raised ICP should change the technique to avoid complications.

Gravitational effects on carotid and jugular characteristics in graded head-up and head-down tilt.

Altered gravity affects hemodynamics and blood flow in the neck. At least one incidence of jugular venous thrombosis has been reported in an astronaut on the International Space Station. This investigation explores the impact of changes in the direction of the gravitational vector on the characteristics of the neck arteries and veins. Twelve subjects underwent graded tilt from 45° head-up to 45° head-down in 15° increments in both supine and prone positions. At each angle, the cross-sectional area of the left and right common carotid arteries (ACCA) and internal jugular veins (AIJV) were measured by ultrasound. Internal jugular venous pressure (IJVP) was also measured by compression sonography. Gravitational dose-response curves were generated from experimental data. ACCA did not show any gravitational dependence. Conversely, both AIJV and IJVP increased in a nonlinear fashion with head-down tilt. AIJV was significantly larger on the right side than the left side at all tilt angles. In addition, IJVP was significantly elevated in the prone position compared with the supine position, most likely because of raised intrathoracic pressure while prone. Dose-response curves were compared with existing experimental data from parabolic flight and spaceflight studies, showing good agreement on an acute timescale. The quantification of jugular hemodynamics as a function of changes in the gravitational vector presented here provides a terrestrial model to reference spaceflight-induced changes, contributes to the assessment of the pathogenesis of spaceflight venous thromboembolism events, and informs the development of countermeasures.NEW & NOTEWORTHY Flow stasis and thrombosis have been identified in the jugular vein during spaceflight. We measured the area and pressure of the internal jugular vein and the area of the common carotid artery in graded head-up and head-down tilt. Experimental data are used to generate gravitational dose-response curves for the measured variables, demonstrating that jugular vein area and pressure exhibit a nonlinear response to altered gravity. Gravitational dose-response curves show good agreement with spaceflight and parabolic flight studies.

Venous dynamics in anesthetized sheep govern postural-induced changes in cerebrospinal fluid pressure comparable to those in humans.

Sheep are popular large animals in which to model human disorders and to study physiological processes such as cerebrospinal fluid dynamics. However, little is known about vascular compensatory mechanisms affecting cerebrospinal fluid pressures during acute postural changes in sheep. Six female white Alpine sheep were anesthetized to investigate the interactions of the vascular and cerebrospinal fluid system by acquiring measurements of intracranial pressure and central and jugular venous pressure during passive postural changes induced by a tilt table. The cross-sectional area of the common jugular vein and venous blood flow velocity was recorded. Anesthetized sheep showed bi-phasic effects of postural changes on intracranial pressure during tilting. A marked collapse of the jugular vein was observed during head-over-body tilting; this is in accordance with findings in humans. Active regulatory effects of the arterial system on maintaining cerebral perfusion pressure were observed independent of tilting direction. Conclusion: Anesthetized sheep show venous dynamics in response to posture-induced changes in intracranial pressure that are comparable with those in humans.

The Physical Examination to Assess for Anemia and Hypovolemia.

Hypovolemia develops with the loss of extracellular fluid volume or blood. Rapidly identifying hypovolemia can be lifesaving. Indicators of hypovolemia on examination include supine or postural hypotension, increase in heart rate by 30 beats per minute or severe dizziness with standing, and a decrease in central venous pressure detected on visual inspection of the jugular venous pressure or ultrasound assessment of the inferior vena cava or internal jugular veins. Other findings with utility include a dry axilla and dry oral mucosa. With chronic anemia, hemodynamic changes detectable on examination may be minimal, as the body compensates by retaining extracellular volume.

Jugular Venous Pressure Response to Inspiration for Risk Assessment of Heart Failure.

Simplifying jugular venous pressure (JVP), visibility of the right internal jugular vein above the right clavicle in the sitting position, has been proposed in the management of heart failure (HF) because of its convenience. However, this method may be undervalued for the detection of mildly to moderately increased JVP. Increased JVP on inspiration, known as Kussmaul sign, may be a useful physical finding in this condition. This study consisted of 138 patients who were admitted for the management of HF. Using this simple method, JVP was assessed at rest in the sitting position before discharge; its response to inspiration was also examined if no high JVP was noted at rest. The primary outcome was a composite of cardiac death and hospitalization for worsening HF. Among all the patients, 16 patients (12%) had high JVP at rest and another 16 patients (12%) had high JVP not at rest but on inspiration. During a follow-up period of 249 ± 182 days, a primary outcome event occurred in 63 patients (46%). The incidence of adverse cardiac events was higher in patients with a high JVP at rest (69%; hazard ratio 3.31, 95% confidence interval 1.64 to 6.67, p = 0.0009) and in patients with a high JVP on inspiration (56%; hazard ratio 2.18, 95% confidence interval 1.02 to 4.63, p = 0.043) than in patients without a high JVP in both conditions (41%). In conclusion, a high JVP not only at rest but also on inspiration was associated with a poor prognosis. The response of JVP to inspiration using this simple technique of physical examination may be a new approach in the management of HF.

Cerebrovascular Effects of Lower Body Negative Pressure at 3T MRI: Implications for Long-Duration Space Travel.

BACKGROUND: Optic disc edema develops in most astronauts during long-duration spaceflight. It is hypothesized to result from weightlessness-induced venous congestion of the head and neck and is an unresolved health risk of space travel. PURPOSE: Determine if short-term application of lower body negative pressure (LBNP) could reduce internal jugular vein (IJV) expansion associated with the supine posture without negatively impacting cerebral perfusion or causing IJV flow stasis. STUDY TYPE: Prospective. SUBJECTS: Nine healthy volunteers (six women). FIELD STRENGTH/SEQUENCE: 3T/cine two-dimensional phase-contrast gradient echo; pseudo-continuous arterial spin labeling single-shot gradient echo echo-planar. ASSESSMENT: The study was performed with two sequential conditions in randomized order: supine posture and supine posture with 25 mmHg LBNP (LBNP25 ). LBNP was achieved by enclosing the lower extremities in a semi-airtight acrylic chamber connected to a vacuum. Heart rate, bulk cerebrovasculature flow, IJV cross-sectional area, fractional IJV outflow relative to arterial inflow, and cerebral perfusion were assessed in each condition. STATISTICAL TESTS: Paired t-tests were used to compare measurement means across conditions. Significance was defined as P < 0.05. RESULTS: LBNP25 significantly increased heart rate from 64 ± 9 to 71 ± 8 beats per minute and significantly decreased IJV cross-sectional area, IJV outflow fraction, cerebral arterial flow rate, and cerebral arterial stroke volume from 1.28 ± 0.64 to 0.56 ± 0.31 cm2 , 0.75 ± 0.20 to 0.66 ± 0.28, 780 ± 154 to 708 ± 137 mL/min and 12.2 ± 2.8 to 9.7 ± 1.7 mL/cycle, respectively. During LBNP25 , there was no significant change in gray or white matter cerebral perfusion (P = 0.26 and P = 0.24 respectively) and IJV absolute mean peak flow velocity remained ≥4 cm/sec in all subjects. DATA CONCLUSION: Short-term application of LBNP25 reduced IJV expansion without decreasing cerebral perfusion or inducing IJV flow stasis. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 1.

Sex-dependent jugular vein optical attenuation and distension during head-down tilt and lower body negative pressure.

Non-contact coded hemodynamic imaging (CHI) is a novel wide-field near-infrared spectroscopy system which monitors blood volume by quantifying attenuation of light passing through the underlying vessels. This study tested the hypothesis that CHI-based jugular venous attenuation (JVA) would be larger in men, and change in JVA would be greater in men compared to women during two fluid shift challenges. The association of JVA with ultrasound-based cross-sectional area (CSA) was also tested. Ten men and 10 women completed three levels of head-down tilt (HDT) and four levels of lower body negative pressure (LBNP). Both JVA and CSA were increased by HDT and reduced by LBNP (all p < 0.001). Main effects of sex indicated that JVA was higher in men than women during both HDT (p = 0.003) and LBNP (p = 0.011). Interaction effects of sex and condition were observed for JVA during HDT (p = 0.005) and LBNP (p < 0.001). We observed moderate repeated-measures correlations (rrm ) between JVA and CSA in women during HDT (rrm  = 0.57, p = 0.011) and in both men (rrm  = 0.74, p < 0.001) and women (rrm  = 0.66, p < 0.001) during LBNP. While median within-person correlation coefficients indicated an even stronger association between JVA and CSA, this association became unreliable for small changes in CSA. As hypothesized, JVA was greater and changed more in men compared to women during both HDT and LBNP. CHI provides a non-contact method of tracking large changes in internal jugular vein blood volume that occur with acute fluid shifts, but data should be interpreted in a sex-dependent manner.

Effect of a neck collar on brain turgor: a potential role in preventing concussions?

BACKGROUND: Mild internal jugular vein (IJV) compression, aimed at increasing intracranial fluid volume to prevent motion of the brain relative to the skull, has reduced brain injury markers in athletes suffering repeated traumatic brain injuries. However, an increase in intracranial volume with IJV compression has not been well demonstrated. This study used transorbital ultrasound to identify changes in optic nerve sheath diameter (ONSD) as a direct marker of accompanying changes in intracranial volume. METHODS: Nineteen young, healthy adult volunteers (13 males and 6 females) underwent IJV compression of 20 cm H2O low in the neck, while in upright posture. IJV cross-sectional area at the level of the cricoid cartilage, and the change in right ONSD 3 mm behind the papillary segment of the optic nerve, were measured by ultrasound. Statistical analysis was performed using a paired t-test with Bonferroni correction. RESULTS: Mean (SD) cross-sectional area for the right IJV before and after IJV compression was 0.10 (0.05) cm2 and 0.57 (0.37) cm2, respectively (p=0.001). ONSD before and after IJV compression was 4.6 (0.5) mm and 4.9 (0.5) mm, respectively (p=0.001). CONCLUSIONS: These data verify increased cerebral volume following IJV compression, supporting the potential for reduced brain 'slosh' as a mechanism connecting IJV compression to possibly reducing traumatic brain injury following head trauma.

Usability of the Level of the S100B Protein, the Gosling Pulsatility Index, and the Jugular Venous Oxygen Saturation for the Prediction of Mortality and Morbidity in Patients with Severe Traumatic Brain Injury.

The high frequency of traumatic brain injury imposes severe economic stress on health and insurance services. The objective of this study was to analyze the association between the serum S100B protein, the Gosling pulsatility index (PI), and the level of oxygen saturation at the tip of the internal jugular vein (SjVO2%) in patients diagnosed with severe TBI. The severity of TBI was assessed by a GCS score ≤ 8 stratified by Glasgow outcome scale (GOS) measured on the day of discharge from the hospital. Two groups were included: GOS < 4 (unfavorable group (UG)) and GOS ≥ 4 (favorable group (UG)). S100B levels were higher in the UG than in the FG. PI levels in the UG were also substantially higher than in the FG. There were similar levels of SjVO2 in the two groups. This study confirmed that serum S100B levels were higher in patients with unfavorable outcomes than in those with favorable outcomes. Moreover, a clear demarcation in PI between unfavorable and FGs was observed. This report shows that mortality and morbidity rates in patients with traumatic brain injury can be assessed within the first 4 days of hospitalization using the S100B protein, PI values, and SjVO2.

Internal Jugular Vein Velocity and Spontaneous Echo Contrast Correlate with Alzheimer's Disease and Cognitive Function.

BACKGROUND: Many issues persist in the today's Alzheimer's disease (AD) screening and the breakthrough method is desired. OBJECTIVE: We aim to validate the association between venous reflux and AD, and to develop a new method for AD screening. METHODS: We examined spontaneous echo contrast, area, diameter, retrograde velocity, and anterograde velocity of the bilateral cervical internal jugular vein (IJV) using carotid ultrasonography. RESULTS: A total of 112 patients participated in this study, with 26 diagnosed as AD. The proportion of both or either IJV spontaneous echo contrast (+) occupied 25 of total 26 AD patients, which showed 96.2%of sensitivity and 98.5%negative predictive value. The IJV velocities also showed significant correlation with AD diagnosis, although the IJV area or diameter did not. CONCLUSION: Our results indicate that the validation of the spontaneous echo contrast or velocities of the IJV are convenient AD diagnosis screening methods and that the venous reflux disturbance correlates with AD development.

Proposed mechanism for reduced jugular vein flow in microgravity.

Internal jugular flow is reduced in space compared with supine values, which can be associated with internal jugular vein (IJV) thrombosis. The mechanism is unknown but important to understand to prevent potentially serious vein thromboses on long duration flights. We used a novel, microgravity-focused numerical model of the cranial vascular circulation to develop hypotheses for the reduced flow. This model includes the effects of removing hydrostatic gradients and tissue compressive forces - unique effects of weightlessness. The IJV in the model incorporates sensitivity to transmural pressure across the vein, which can dramatically affect resistance and flow in the vein. The model predicts reduced IJV flow in space. Although tissue weight in the neck is reduced in weightlessness, increasing transmural pressure, this is more than offset by the reduction in venous pressure produced by the loss of hydrostatic gradients and tissue pressures throughout the body. This results in a negative transmural pressure and increased IJV resistance. Unlike the IJV, the walls of the vertebral plexus are rigid; transmural pressure does not affect its resistance and so its flow increases in microgravity. This overall result is supported by spaceflight measurements, showing reduced IJV area inflight compared with supine values preflight. Significantly, this hypothesis suggests that interventions that further decrease internal IJV pressure (such as lower body negative pressure), which are not assisted by other drainage mechanisms (e.g. gravity), might lead to stagnant flow or IJV collapse with reduced flow, which could increase rather than decrease the risk of venous thrombosis.

Jugular vagal ganglia neurons and airway nociception: A target for treating chronic cough.

The airways receive a dense supply of sensory nerve fibers that are responsive to damaging or potentially injurious stimuli. These airway nociceptors are mainly derived from the jugular and nodose vagal ganglia, and when activated they induce a range of reflexes and sensations that play an essential role in airway protection. Jugular nociceptors differ from nodose nociceptors in their embryonic origins, molecular profile and termination patterns in the airways and the brain, and recent discoveries suggest that excessive activity in jugular nociceptors may be central to the development of chronic cough. For these reasons, targeting jugular airway nociceptor signaling processes at different levels of the neuraxis may be a promising target for therapeutic development. In this focused review, we present the current understanding of jugular ganglia nociceptors, how they may contribute to chronic cough and mechanisms that could be targeted to bring about cough suppression.

The effect of microgravity on the human venous system and blood coagulation: a systematic review.

NEW FINDINGS: What is the central question of this study? Recently, an internal jugular venous thrombus was identified during spaceflight: does microgravity induce venous and/or coagulation pathophysiology, and thus an increased risk of venous thromboembolism (VTE)? What is the main finding and its importance? Whilst data are limited, this systematic review suggests that microgravity and its analogues may induce an enhanced coagulation state due to venous changes most prominent in the cephalad venous system, as a consequence of changes in venous flow, distension, pressures, endothelial damage and possibly hypercoagulability in microgravity and its analogues. However, whether such changes precipitate an increased VTE risk in spaceflight remains to be determined. ABSTRACT: Recently, an internal jugular venous thrombus was identified during spaceflight, but whether microgravity induces venous and/or coagulation pathophysiology, and thus, an increased risk of venous thromboembolism (VTE) is unclear. Therefore, a systematic (Cochrane compliant) review was performed of venous system or coagulation parameters in actual spaceflight (microgravity) or ground-based analogues in PubMed, MEDLINE, Ovid EMBASE, Cochrane Library, European Space Agency, National Aeronautics and Space Administration, and Deutsches Zentrum für Luft-und Raumfahrt databases. Seven-hundred and eight articles were retrieved, of which 26 were included for evaluation with 21 evaluating venous, and five coagulation parameters. Nine articles contained spaceflight data, whereas the rest reported ground-based analogue data. There is substantial variability in study design, objectives and outcomes. Yet, data suggested cephalad venous system dilatation, increased venous pressures and decreased/reversed flow in microgravity. Increased fibrinogen levels, presence of thrombin generation markers and endothelial damage were also reported. Limited human venous and coagulation system data exist in spaceflight, or its analogues. Nevertheless, data suggest spaceflight may induce an enhanced coagulation state in the cephalad venous system, as a consequence of changes in venous flow, distension, pressures, endothelial damage and possibly hypercoagulability. Whether such changes precipitate an increased VTE risk in spaceflight remains to be determined.

Reverse blood flow in cervicofacial veins after venous ligations: Potential implications in microsurgery.

INTRODUCTION: The consequences on the cervicofacial venous circulation of major cervicofacial vein ligations are poorly known. We aimed to highlight by using Doppler Ultrasound flow differences in the cervicofacial venous network in the case of unilateral or bilateral ligation of main venous collector trunks (external jugular vein [EJV] and internal jugular vein [IJV]) METHODS: A Doppler ultrasound was performed on 10 healthy volunteers, 8 patients with previous bilateral ligation of the EJV, 8 with a unilateral ligation of the EJV, and 8 with a unilateral ligation of the EJV and IJV, after modified radical neck dissection. The diameter, the flow direction and the peak systolic velocity (PSV) of the superficial temporal vein, the facial vein (FV) and the IJV were measured. RESULTS: Healthy patients had a similar right and left PSV for all the veins studied, with always antegrade flows. Patients with previous ligations had some significant right/left differences and retrograde flows. CONCLUSION: A redistribution of venous blood flow on the contralateral side of the face and neck seems to take place in the case of unilateral ligation of the EJV and/or IJV. Retrograde flows are sometimes observed in the case of previous ligation of the EJV and/or IJV and might compromise the success of venous microanastomoses.

Structural recirculation and refractory hypoxemia under femoro-jugular veno-venous extracorporeal membrane oxygenation.

The performance of each veno-venous extracorporeal membrane oxygenation (vv-ECMO) configuration is determined by the anatomic context and cannula position. A mathematical model was built considering bicaval specificities to simulate femoro-jugular configuration. The main parameters to define were cardiac output (QC ), blood flow in the superior vena cava (QSVC ), extracorporeal pump flow (QEC ), and pulmonary shunt (kS-PULM ). The obtained variables were extracorporeal flow ratio in the superior vena cava (EFRSVC  = QEC /[QEC  + QSVC ]), recirculation coefficient (R), effective extracorporeal pump flow (Qeff-EC  = [1 - R] × QEC ), Qeff-EC /QC ratio, and arterial blood oxygen saturation (SaO2 ). EFRSVC increased logarithmically when QEC increased. High QC or high QSVC /QC decreased EFRSVC (range, 68%-85% for QEC of 5 L/min). R also increased following a logarithmic shape when QEC increased. The R rise was earlier and higher for low QC and high QSVC /QC (range, 12%-49% for QEC of 5 L/min). The Qeff-EC /QC ratio (between 0 and 1) was equal to EFRSVC for moderate and high QEC . The Qeff-EC /QC ratio presented the same logarithmic profile when QEC increased, reaching a plateau (range, 0.67-0.91 for QEC /QC  = 1; range, 0.75-0.94 for QEC /QC  = 1.5). The Qeff-EC /QC ratio was linearly associated with SaO2 for a given pulmonary shunt. SaO2  < 90% was observed when the pulmonary shunt was high (Qeff-EC /QC  ≤ 0.7 with kS-PULM  = 0.7 or Qeff-EC /QC  ≤ 0.8 with kS-PULM  = 0.8). Femoro-jugular vv-ECMO generates a systematic structural recirculation that gradually increases with QEC . EFRSVC determines the Qeff-EC /QC ratio, and thereby oxygen delivery and the superior cava shunt. EFRSVC cannot exceed a limit value, explaining refractory hypoxemia in extreme situations.

An alternative explanation for the phasic variations in venous flow.

BACKGROUND: Phasic venous flow variation with respiration is surrounded by controversy and not well understood. The current concept assigns a major role to the "abdominal pump." According to this model, inspiratory increases in abdominal pressure compress the vena cava, increasing its internal venous pressure and propelling blood upstream. Some have assigned a secondary role to the "thoracic pump," with the negative intrapleural pressure aiding blood flow toward the heart. The aim of the present study was to examine the phasic changes in flow, pressure, and volume in the central veins and named tributaries. METHODS: Caliber area changes were measured using intravascular ultrasonography in 37 patients undergoing iliac vein stenting. The pressure was measured in 48 patients using transducer tip catheters with electronic zero calibration. Duplex ultrasound flow in the head and neck and truncal and limb veins during inspiration and expiration was measured in 15 normal volunteers. RESULTS: The caliber of the abdominal inferior vena cava had increased by 32% and its lateral pressure had decreased significantly during inspiration. Intravenous pressure in the central veins of the chest and right atrium was positive at 6 to 14 mm Hg. Negative pressures were rarely seen and then only transiently. The internal jugular vein displayed little phasic variation. The upper limb veins displayed weak inspiratory phasicity. Phase polarity was reversed in the lower limbs, with near flow stoppage during inspiration. CONCLUSIONS: These observations conflict with the current notions of venous flow phasicity, which are based on push-pull pressure changes in the abdominal and thoracic veins. The paradoxical inspiratory inferior vena cava caliber increase probably explains the concurrent pressure decrease. Sustained negative pressures in the thoracic central veins and right atrium did not occur. We have proposed an alternate hypothesis for venous flow phasicity based on alternate stretching and relaxation of the mobile section of the great veins with respiratory movement.