Estimation of pulmonary vascular resistance for Glenn physiology.

Children with single ventricle heart disease typically require a series of three operations, (1) Norwood, (2) Glenn, and (3) Fontan, which ultimately results in complete separation of the pulmonary and systemic circuits to improve pulmonary/systemic circulation. In the last stage, the Fontan operation, the inferior vena cava (IVC) is connected to the pulmonary arteries (PAs), allowing the remainder of deoxygenated blood to passively flow to the pulmonary circuit. It is hypothesized that optimizing the Fontan anatomy would lead to decreased power loss and more balanced hepatic flow distribution. One approach to optimizing the geometry is to create a patient-specific digital twin to simulate various configurations of the Fontan conduit, which requires a computational model of the proximal PA anatomy and resistance, as well as the distal Pulmonary Vascular Resistance (PVR), at the Glenn stage. To that end, an optimization pipeline was developed using 3D computational fluid dynamics (CFD) and 0D lumped parameter (LP) simulations to iteratively refine the PVR of each lung by minimizing the simulated flow and pressure error relative to patients' cardiac magnetic resonance (CMR) and catheterization (CATH) data. While the PVR can also be estimated directly by computing the ratio of pressure gradients and flow from CATH and CMR data, the computational approach can separately identify the different components of PVR along the Glenn pathway, allowing for a more detailed depiction of the Glenn vasculature. Results indicate good correlation between the optimized PVR of the CFD and LP models (n = 16), with an intraclass correlation coefficient (ICC) of 0.998 (p = 0.976) and 0.991 (p = 0.943) for the left and right lung, respectively. Furthermore, compared to CMR flow and CATH pressure data, the optimized PVR estimates result in mean outlet flow and pressure errors of less than 5%. The optimized PVR estimates also agree well with the computed PVR estimates from CATH pressure and CMR flow for both lungs, yielding a mean difference of less than 4%.

Quantifying Inferior Vena Cava Compliance and Distensibility in an In Vivo Ovine Model Using 3D Angiography.

Synthetic vascular grafts overcome some challenges of allografts, autografts, and xenografts but are often more rigid and less compliant than the native vessel into which they are implanted. Compliance matching with the native vessel is emerging as a key property for graft success. The current gold standard for assessing vessel compliance involves the vessel's excision and ex vivo biaxial mechanical testing. We developed an in vivo method to assess venous compliance and distensibility that better reflects natural physiology and takes into consideration the impact of a pressure change caused by flowing blood and by any morphologic changes present. This method is designed as a survival procedure, facilitating longitudinal studies while potentially reducing the need for animal use. Our method involves injecting a 20 mL/kg saline bolus into the venous vasculature, followed by the acquisition of pre and post bolus 3D angiograms to observe alterations induced by the bolus, concurrently with intravascular pressure measurements in target regions. We are then able to measure the circumference and the cross-sectional area of the vessel pre and post bolus. With these data and the intravascular pressure, we are able to calculate the compliance and distensibility with specific equations. This method was used to compare the inferior vena cava's compliance and distensibility in native unoperated sheep to the conduit of sheep implanted with a long-term expanded polytetrafluorethylene (PTFE) graft. The native vessel was found to be more compliant and distensible than the PTFE graft at all measured locations. We conclude that this method safely provides in vivo measurements of vein compliance and distensibility.

What every intensivist should know about the IVC.

Assessment of the IVC by point-of-care ultrasound in the context of resuscitation has been a controversial topic in the last decades. Most of the focus had been on its use as a surrogate marker for fluid responsiveness, with results being equivocal. We review its important anatomical aspects as well as the physiological rationale behind ultrasound assessment and propose a new way to do so, as well as explain its central role in the concept of fluid tolerance.

Is caval index a sufficient parameter for determining and monitoring dehydration in intoxication patients?

BACKGROUND: Cases of intoxication are increasing day by day and these patients are presenting to emergency departments. These patients are usually individuals with poor self-care, inadequate oral intake, and unable to meet their own needs, and may have significant dehydration due to the agents they have taken. The caval index (CI) is a recently used index to determine fluid requirement and response. AIMS: We aimed to evaluate the success of CI in determining and monitoring dehydration in intoxication patients. METHODS: Our study was conducted prospectively in the emergency department of a single tertiary care center. A total of ninety patients were included in the study. Caval index was calculated by measuring inspiratory and expiratory inferior vena cava diameters. Caval index measurements were repeated after 2 and 4 h. RESULTS: Patients who were hospitalized, took multiple drugs, or needed inotropic agents had significantly higher caval index levels. A further increase in caval index levels was observed on second and third caval index evaluations in patients who received inotropic agents along with fluid resuscitation. Levels of systolic blood pressure recorded at admission (0. hour) showed a significant correlation with caval index and shock index. Caval index and the shock index were highly sensitive and specific at predicting mortality. CONCLUSION: In our study, we found that CI can be used as an index to assist emergency clinicians in determining and monitoring fluid requirement in cases of intoxication presenting to the emergency department.

Use of POCUS for the assessment of dehydration in pediatric patients-a narrative review.

In pediatric practice, POCUS (point-of-care ultrasound) has been mostly implemented to recognize lung conditions and pleural and pericardial effusions, but less to evaluate fluid depletion. The main aim of this review is to analyze the current literature on the assessment of dehydration in pediatric patients by using POCUS. The size of the inferior vena cava (IVC) and its change in diameter in response to respiration have been investigated as a tool to screen for hypovolemia. A dilated IVC with decreased collapsibility (< 50%) is a sign of increased right atrial pressure. On the contrary, a collapsed IVC may be indicative of hypovolemia. The IVC collapsibility index (cIVC) reflects the decrease in the diameter upon inspiration. Altogether the IVC diameter and collapsibility index can be easily determined, but their role in children has not been fully demonstrated, and an estimation of volume status solely by assessing the IVC should thus be interpreted with caution. The inferior vena cava/abdominal aorta (IVC/AO) ratio may be a suitable parameter to assess the volume status in pediatric patients even though there is a need to define age-based thresholds. A combination of vascular, lung, and cardiac POCUS could be a valuable supplementary tool in the assessment of dehydration in several clinical scenarios, enabling rapid identification of life-threatening primary etiologies and helping physicians avoid inappropriate therapeutic interventions.   Conclusion: POCUS can provide important information in the assessment of intravascular fluid status in emergency scenarios, but measurements may be confounded by a number of other clinical variables. The inclusion of lung and cardiac views may assist in better understanding the patient's physiology and etiology regarding volume status. What is Known: • In pediatric practice, POCUS (point-of-care ultrasound) has been mostly implemented to recognize lung conditions (like pneumonia and bronchiolitis) and pleural and pericardial effusions, but less to evaluate fluid depletion. • The size of the IVC (inferior vena cava) and its change in diameter in response to respiration have been studied as a possible screening tool to assess the volume status, predict fluid responsiveness, and assess potential intolerance to fluid loading. What is New: • The IVC diameter and collapsibility index can be easily assessed, but their role in predicting dehydration in pediatric age has not been fully demonstrated, and an estimation of volume status only by assessing the IVC should be interpreted carefully. • The IVC /AO(inferior vena cava/abdominal aorta) ratio may be a suitable parameter to assess the volume status in pediatric patients even though there is a need to define age-based thresholds. A combination of vascular, lung, and cardiac POCUS can be a valuable supplementary tool in the assessment of intravascular volume in several clinical scenarios.

Establishment of Reference Intervals for Caudal Vena Cava-to-Aorta Ratio Measured Ultrasonographically in Healthy Nonsedated Dogs.

The ultrasonographic assessment of the caudal vena cava-to-aorta ratio (CVC:Ao) appears to be a promising method for early recognition of alterations of intravascular volume status in veterinary medicine. The primary objective of this study was to establish the reference intervals of the CVC:Ao ratio with ultrasound in nonsedated healthy dogs. Secondary objectives were to determine the influence of the respiratory cycle and to evaluate correlations between ultrasonographic measurements, signalment and physical exam findings. Ultrasonographic measurements of Ao and CVC diameters were successfully obtained for all sixty dogs included. No evidence of a difference was observed between the measurements of Ao and CVC diameters, and CVC:Ao ratio between inspiration and expiration (P = .373, P = .318, and P = .537, respectively). The reference interval for CVC:Ao ratio (95% CI), generated from US measurements performed at any moment of the respiratory cycle was defined as 0.93 (0.91-0.95) -1.32 (1.30-1.34). The CVC:Ao ratio was significantly negatively correlated with age (r = -0.341, P = .008) and positively correlated with respiratory rate (r = 0.423, P < .001), but not with heart rate (P = .573) or arterial systolic blood pressure (P = .166). A low inter- and intraoperator variability in repeated measurements was observed for each operator and between operators. The ultrasonographic measurement of the CVC:Ao ratio appears as a simple method with low inter- and intraoperator variability using the ultrasonographic protocol described in the current study. With the reference interval established in the present study in healthy nonsedated dogs, further studies should evaluate the utility of this simple method in assessing and monitoring volume status in hypo- and hypervolemic dogs.

Evaluation of Biointegration and Inflammatory Response to Blood Vessels Produced by Tissue Engineering-Experimental Model in Rabbits.

Peripheral arterial disease (PAD) is the main cause of mortality in the western population and requires surgical intervention with the use of vascular substitutes, such as autologous veins or Dacron or PTFE prostheses. When this is not possible, it progresses to limb amputation. For cases where there is no autologous vascular substitute, tissue engineering with the production of neovessels may be a promising option. Previous experimental studies have shown in vitro that rabbit vena cava can be decellularized and serve as a scaffold for receiving mesenchymal stem cells (MSC), with subsequent differentiation into endothelial cells. The current study aimed to evaluate the behavior of a 3D product structure based on decellularized rabbit inferior vena cava (IVC) scaffolds seeded with adipose-tissue-derived stem cells (ASCs) and implanted in rabbits dorsally subcutaneously. We evaluated the induction of the inflammatory response in the animal. We found that stem cells were positive in reducing the inflammatory response induced by the decellularized scaffolds.

Design and Haemodynamic Analysis of a Novel Anchoring System for Central Venous Pressure Measurement.

BACKGROUND/OBJECTIVE: In recent years, treatment of heart failure patients has proved to benefit from implantation of pressure sensors in the pulmonary artery (PA). While longitudinal measurement of PA pressure profoundly improves a clinician's ability to manage HF, the full potential of central venous pressure as a clinical tool has yet to be unlocked. Central venous pressure serves as a surrogate for the right atrial pressure, and thus could potentially predict a wider range of heart failure conditions. However, it is unclear if current sensor anchoring methods, designed for the PA, are suitable to hold pressure sensors safely in the inferior vena cava. The purpose of this study was to design an anchoring system for accurate apposition in inferior vena cava and evaluate whether it is a potential site for central venous pressure measurement. MATERIALS AND METHODS: A location inferior to the renal veins was selected as an optimal site based on a CT scan analysis. Three anchor designs, a 10-strut anchor, and 5-struts with and without loops, were tested on a custom-made silicone bench model of Vena Cava targeting the infra-renal vena cava. The model was connected to a pulsatile pump system and a heated water bath that constituted an in-vitro simulation unit. Delivery of the inferior vena cava implant was accomplished using a preloaded introducer and a dilator as a push rod to deploy the device at the target area. The anchors were subjected to manual compression tests to evaluate their stability against dislodgement. Computational Fluid Dynamics (CFD) analysis was completed to characterize blood flow in the anchor's environment using pressure-based transient solver. Any potential recirculation zones or disturbances in the blood flow caused by the struts were identified. RESULTS: We demonstrated successful anchorage and deployment of the 10-strut anchor in the Vena Cava bench model. The 10-strut anchor remained stable during several compression attempts as compared with the other two 5-strut anchor designs. The 10-strut design provided the maximum number of contact points with the vessel in a circular layout and was less susceptible to movement or dislodgement during compression tests. Furthermore, the CFD simulation provided haemodynamic analysis of the optimum 10-strut anchor design. CONCLUSIONS: This study successfully demonstrated the design and deployment of an inferior vena cava anchoring system in a bench test model. The 10-strut anchor is an optimal design as compared with the two other 5-strut designs; however, substantial in-vivo experiments are required to validate the safety and accuracy of such implants. The CFD simulation enabled better understanding of the haemodynamic parameters and any disturbances in the blood flow due to the presence of the anchor. The ability to place a sensor technology in the vena cava could provide a simple and minimally invasive approach for heart failure patients.

First-in-human experience of preload regulation with percutaneous transluminal caval flow regulation in heart failure with reduced ejection fraction patients.

AIMS: This study aims to investigate the acute haemodynamic effects of percutaneous transluminal flow regulation (PTCR®) with an inferior vena cava regulator balloon in heart failure patients. Preload reduction in heart failure has been achieved with high potency diuretics. However, no study has been conducted in humans to assess the effect of inferior vena cava intermittent occlusion for preload reduction. METHODS AND RESULTS: Six patients were included in the study: four men (55 ± 6 years old) and two women (63 ± 4 years old). Baseline evaluations included Doppler echocardiogram, coronary angiogram, and right heart catheterization. Caval balloon was kept inflated for 30 min, and right catheterization and control echocardiogram were performed while the balloon was still inflated. The balloon was then deflated and removed. Right haemodynamic variables were evaluated before balloon insertion and with the inflated balloon. The mean right atrial pressure decreased by 42.59% (P = 0.005); systolic right ventricular pressure decreased by 30.19% (P < 0.003); mean pulmonary arterial pressure decreased by 25.33% (P < 0.043); mean pulmonary capillary wedge pressure decreased by 31.37% (P > 0.016); and cardiac output increased by 9.92% (P < 0.175). CONCLUSIONS: The haemodynamic and echocardiographic changes obtained in our study using PTCR® suggest that this innovative approach can play a beneficial role in the heart failure treatment.

Effect of breathing on venous return during delayed cord clamping: an observational study.

OBJECTIVE: To investigate the effect of spontaneous breathing on venous return in term infants during delayed cord clamping at birth. METHODS: Echocardiographic ultrasound recordings were obtained directly after birth in healthy term-born infants. A subcostal view was used to obtain an optimal view of the inferior vena cava (IVC) entering the right atrium, including both the ductus venosus (DV) and the hepatic vein (HV). Colour Doppler was used to assess flow direction and flow velocity. Recordings continued until the umbilical cord was clamped and were stored in digital format for offline analyses. RESULTS: Ultrasound recordings were obtained in 15 infants, with a median (IQR) gestational age of 39.6 (39.0-40.9) weeks and a birth weight of 3560 (3195-4205) g. Flow was observed to be antegrade in the DV and HV in 98% and 82% of inspirations, respectively, with flow velocity increasing in 74% of inspirations. Retrograde flow in the DV was observed sporadically and only occurred during expiration. Collapse of the IVC occurred during 58% of inspirations and all occurred caudal to the DV inlet (100%). CONCLUSION: Spontaneous breathing was associated with collapse of the IVC and increased antegrade DV and HV flow velocity during inspiration. Therefore, inspiration appears to preferentially direct blood flow from the DV into the right atrium. This indicates that inspiration could be a factor driving placental transfusion in infants.

Effects of reverse deployment of cone-shaped vena cava filter on improvements in hemodynamic performance in vena cava.

BACKGROUND: Cone-shaped vena cava filters (VCFs) are widely used to treat venous thromboembolism. However, in the long term, the problem of occlusion persists even after the filter is deployed. A previous study hypothesized that the reverse deployment of a cone-shaped VCFs may prevent filter blockage. METHODS: To explore this hypothesis, a comparative study of the traditional and reverse deployments of VCFs was conducted using a computational fluid dynamics approach. The distribution of wall shear stress (WSS) and shear stress-related parameters were calculated to evaluate the differences in hemodynamic effects between both conditions. In the animal experiment, we reversely deployed a filter in the vena cava of a goat and analyzed the blood clot distribution in the filter. RESULTS: The numerical simulation showed that the reverse deployment of a VCF resulted in a slightly higher shear rate on the thrombus, and no reductions in the oscillating shear index (OSI) and relative residence time (RRT) on the vessel wall. Comparing the traditional method with the reversely deployed cases, the shear rate values is 16.49 and 16.48 1/s, respectively; the minimal OSI values are 0.01 and 0.04, respectively; in the vicinity of the VCF, the RRT values are both approximately 5 1/Pa; and the WSS is approximately 0.3 Pa for both cases. Therefore, the reverse deployment of cone-shaped filters is not advantageous when compared with the traditional method in terms of local hemodynamics. However, it is effective in capturing thrombi in the short term, as demonstrated via animal experiments. The reversely deployed cone-shaped filter captured the thrombi at its center in the experiments. CONCLUSIONS: Thus, the reverse deployment of cone-shaped filters is not advantageous when compared with the traditional method in terms of local hemodynamics. Therefore, we would not suggest the reverse deployment of the cone-shaped filter in the vena cava to prevent a potentially fatal pulmonary embolism.

The effect of maternal position on venous return for pregnant women during MRI.

Magnetic resonance imaging (MRI) in pregnancy is commonly undertaken in the left lateral tilt (LLT) position to prevent inferior vena cava (IVC) compression and supine hypotensive events, although this may be suboptimal for image quality. The supine position may also have an adverse effect on fetal well-being. The spinal venous plexus may provide an alternative pathway for venous return in the presence of IVC compression. This study assesses morphology and blood flow of the IVC and spinal venous plexus for pregnant women in LLT and supine positions to ascertain the effect of maternal position on venous return during MRI. Eighty-two pregnant women underwent phase contrast MRI (PC-MRI) of the IVC and spinal venous plexus in the supine position; 25 were also imaged in the LLT position. Differences in life monitoring, IVC, spinal venous plexus and total venous return between the two positions were assessed. A linear regression assessed the relationship between flow in the IVC and the spinal venous plexus in the supine position. Increasing gestational age and the right-sided position of the uterus on IVC and spinal venous plexus venous return were also evaluated. Hypotension symptoms were similar in supine (10%) and LLT (8%) positioning. Supine positioning decreased IVC height (p < 0.004) and flow (p = 0.045) but flow in the spinal venous plexus increased (p < 0.001) compared with the LLT position. Total venous return showed no difference (p = 0.989) between the two positions. Additional measurements of flow in the aorta also showed no significant difference between the two groups (p = 0.866). Reduced IVC flow in the supine position was associated with increasing gestational age (p = 0.004) and degree of right-sided uterine position (p = 0.004). Women in the left lateral decubitus position who then rotated supine had greater flow in the IVC (p = 0.008) and spinal venous plexus (p = 0.029) than those who started supine. For the majority of women, the spinal venous plexus acts as a complementary venous return system for pregnant women in the supine position, maintaining vascular homeostasis. Further study is needed to assess the effects on the health of the fetus.

[Evaluation of infrahepatic inferior vena cava clamping in robot-assisted laparoscopic liver resection].

Objective: To evalutate the safety and efficacy of infrahepatic inferior vena cava clamping robot-assisted laparoscopic liver resection. Methods: All data about 24 patients with robotic liver resection at Hepatic Surgery Center,Tongji Hospital,Tongji Medical College,Huazhong University of Science and Technology between February 2015 and December 2017 were collected and analyzed. These patients were divided into two groups based on different methods to decrease central venous pressure. Eight patients(6 males and 2 females,aged 49 years(range:50 to 56 years)) were applied with infrahepatic inferior vena cava clamping,and the other 16 matched cases (15 males and 1 female,aged 53 years(range:38 to 69 years)) were categorized into lowering central venous pressure group. Intraoperative blood loss,blood transfusion,intraoperative hemodynamic parameters,postoperative complications,and renal function were compared by t-test,non-parametric test,χ2 test,or Fisher exact test. Results: There was significantly difference in the intraoperative blood loss between the infrahepatic vena cava clamping group and the lowering central venous group(200(220) ml (range:100 to 400 ml) vs. 750(800) ml (range:100 to 2 000 ml),Z=‒2.169,P=0.030). The clamping time of portal triad and infrahepatic inferior vena cava were 24 (18) minutes and 29 (20) minutes in the infrahepatic inferior vena cava clamping group, and portal triad clamping time was 23 (23) minutes in the low central venous group. There was no significant difference between the two groups (Z=‒0.323, P=0.747). There was no intraoperative blood transfusion in the infrahepatic inferior vena cava clamping group, and 5 cases in the low central venous group, with a transfusion volume of 1.5(1.5)U. The difference between the two groups was statistically significant (Z=‒3.353, P=0.001). However, the mean arterial pressure in the infrahepatic vena cava clamping group decreased from (88.6±4.9) mmHg to (67.4±3.8) mmHg(1 mmHg=0.133 kPa), which was lower than that of lowering central venous group (72.4±3.3) mmHg (t=2.315,P=0.003). And there were no significant differences related to postoperative complications rate or hepatic and renal function in both groups. Conclusion: The infrahepatic inferior vena cava technology is safe and feasible to decrease central venous pressure during robotic liver resections,which will not affect the recovery of hepatic and renal functions.

Evaluation of gravity effect on inferior vena cava and abdominal aortic flow using multi-posture MRI.

BACKGROUND: Inferior vena cava flow (IVCF) and abdominal aortic flow (AAF) are essential components of the systemic circulation. Although postural changes might alter IVCF and AAF by the gravity effect, the exact details are unknown. PURPOSE: To evaluate the effect of gravity on IVCF and AAF using a novel magnetic resonance imaging (MRI) system that can image in any position. MATERIAL AND METHODS: Caval velocity-mapped images were obtained using the cine phase-contrast technique in the upright and supine positions with multi-posture MRI (n = 12). The mean IVCF/AAF velocity, maximum IVCF/AAF velocity, cross-sectional area of IVC/AA, mean IVCF/AAF, maximum IVCF/AAF, and heart rate in the two positions were assessed. RESULTS: The mean IVCF velocity, maximum IVCF velocity, cross-sectional area of IVC, mean IVCF, maximum IVCF, mean AAF velocity, maximum AAF velocity, mean AAF, and maximum AAF were significantly lower in the upright position compared with the supine position (P < 0.05 for all), with differences of 52% ± 33%, 36% ± 19%, 56% ± 18%, 26% ± 18%, 19% ± 11%, 33% ± 13%, 33% ± 22%, 42% ± 21%, and 37% ± 28%, respectively. Heart rate was significantly higher in the upright position compared with the supine position (116% ± 9.2%; P = 0.003). There were no differences in cross-sectional area of AA between the two positions (108% ± 22%; P = 0.583). CONCLUSION: The effect of gravity decreases IVCF and AAF. Clarifying the effect of gravity on IVCF and AAF during a postural change may help to improve the management of patients with circulatory disease.

Fetal cardiovascular hemodynamics in type 1 diabetic pregnancies at near-term gestation.

INTRODUCTION: Poor glycemic control in maternal type 1 diabetes mellitus during pregnancy can affect fetal cardiac and placental function. However, studies concerning fetal central hemodynamics have revealed conflicting results. We hypothesized that in pregnancies complicated by maternal type 1 diabetes, fetal cardiovascular and placental hemodynamics are comparable to the control fetuses at near-term gestation. In addition, we investigated the relation between newborn serum biomarkers of cardiac function and fetal cardiovascular and placental hemodynamics. Furthermore, we studied whether maternal diabetes is associated with placental inflammation. MATERIAL AND METHODS: In this prospective case-control study, fetal central and peripheral hemodynamics were assessed by ultrasonography in 33 women with type 1 diabetes and in 67 controls with singleton pregnancies between 34+2 and 40+2 gestational weeks. Newborn umbilical cord serum was collected to analyze cardiac natriuretic peptides (atrial and B-type natriuretic peptides) and troponin T concentrations. Placental tissue samples were obtained for cytokine analyses. RESULTS: Fetal ventricular wall thicknesses were greater and weight-adjusted stroke volumes and cardiac outputs were lower in the type 1 diabetes group than in the control group. Pulsatility in the aortic isthmus and inferior vena cava blood flow velocity waveforms was greater in the type 1 diabetes group fetuses than in the controls. A positive correlation was found between branch pulmonary artery and aortic isthmus pulsatility index values. Umbilical artery pulsatility indices were comparable between the groups. Umbilical cord serum natriuretic peptide and troponin T concentrations were elevated in the type 1 diabetes fetuses. These cardiac biomarkers correlated significantly with cardiovascular hemodynamics. Placental cytokine levels were not different between the groups. CONCLUSIONS: In maternal type 1 diabetes pregnancies, fetal cardiovascular hemodynamics is impaired. Maternal type 1 diabetes does not seem to alter placental vascular impedance or induce placental inflammation.

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.

Multi-directional Assessment of Respiratory and Cardiac Pulsatility of the Inferior Vena Cava From Ultrasound Imaging in Short Axis.

The pulsatility of the inferior vena cava (IVC) reflects the volume status of patients. It can be investigated by ultrasounds (US), offering an important non-invasive tool supporting fluid management. However, the method has limitations attributable to many confounding factors, e.g., related to IVC movements and non-regular shapes. Short- or long-axis views have been used, both having advantages and limitations in counteracting such confounding factors, depending on the specific condition. The aim of this study is to investigate IVC pulsatility in the different directions on the transverse plane and to assess its variability. Moreover, different components of this pulsatility (induced by either respiratory or cardiac activity) are investigated. The method is tested on 10 healthy patients, with large variations across them of IVC section (mean diameters in the range 1 cm to 3 cm), shape and pulsatility (average caval index [CI] ranging from approximately 20% to 70%). The average coefficient of variation of the CI estimated on 10 different directions was 13% (21% and 20% for the respiratory and cardiac components, respectively), with a range that was approximately 50% of the mean CI across different directions (approximately the same for the 2 different components). The minimum and maximum CI were found close to the directions of maximum and minimum IVC diameter, respectively. The investigation of IVC dynamics in the entire cross-section is crucial to obtain a more repeatable and reliable characterization of IVC pulsatility. The calculation of a CI based on the "equivalent" diameter (proportional to the square root of the IVC cross-sectional area) is encouraged.

The effect of positioning on maternal anatomy and hemodynamics during late pregnancy.

INTRODUCTION: Supine positioning during late pregnancy causes dramatic compression of maternal abdominal vasculature and is a risk factor for stillbirth. The azygos vein has been shown to provide collateral circulation in this scenario. There are many well-known anatomical differences in abdominal vasculature between the left and right sides of the body. However, the effect of left and right positioning in pregnancy has not been well studied. MATERIALS AND METHODS: After obtaining ethics approval, 10 women with uncomplicated pregnancies between 34 and 38 weeks gestation underwent magnetic resonance imaging in the left and right lateral positions. Phase contrast images were evaluated to measure blood flow through the abdominal aorta, inferior vena cava, and azygos vein. RESULTS: No significant differences between left and right lateral positions were found in blood flow through the IVC at its formation (mean difference -0.15 L/min [CI -0.47, 0.18], p = .34) or through the azygos vein (mean difference 0.02 L/min [CI -0.22, 0.26], p = .87). Blood flow through the IVC just above the level of the renal veins was found to be reduced by 35% in the right lateral position when compared to the left (mean difference 1.01 L/min [CI 0.25, 1.43], p = .03). There were no significant differences in cardiac output or blood flow through the abdominal aorta. CONCLUSIONS: While it was noted that blood flow through the IVC immediately above the level of the renal veins was reduced in the right lateral position, this did not appear to impact significantly on maternal cardiac output or blood flow through the azygos vein.

The renal transport of hippurate and protein-bound solutes.

Measurement of the concentration of hippurate in the inferior vena cava and renal blood samples performed in 13 subjects with normal or near-normal serum creatinine concentrations confirmed the prediction that endogenous hippurate was cleared on a single pass through the kidney with the same avidity as that reported for infused para-amino hippurate. This suggests that a timed urine collection without infusion would provide a measure of effective renal plasma flow. Comparison of the arteriovenous concentration differences for a panel of protein-bound solutes identified solutes that were secreted by the renal tubule and solutes that were subjected to tubular reabsorption.

Venous Mechanical Properties After Arteriovenous Fistulae in Mice.

BACKGROUND: An arteriovenous fistula (AVF) exposes the outflow vein to arterial magnitudes and frequencies of blood pressure and flow, triggering molecular pathways that result in venous remodeling and AVF maturation. It is unknown, however, how venous remodeling, that is lumen dilation and wall thickening, affects venous mechanical properties. We hypothesized that a fistula is more compliant compared with a vein because of altered contributions of collagen and elastin to the mechanical properties. METHODS: Ephb4+/- and littermate wild-type (WT) male mice were treated with sham surgery or needle puncture to create an abdominal aortocaval fistulae. The thoracic inferior vena cava was harvested 3 wk postoperatively for mechanical testing and histological analyses of collagen and elastin. RESULTS: Mechanical testing of the thoracic inferior vena cava from Ephb4+/- and WT mice showed increased distensibility and increased compliance of downstream veins after AVF compared with sham. Although Ephb4+/- veins were thicker than WT veins at the baseline, after AVF, both Ephb4+/- and WT veins showed similar wall thickness as well as similar collagen and elastin area fractions, but increased collagen undulation compared with sham. CONCLUSIONS: Fistula-induced remodeling of the outflow vein results in circumferentially increased distensibility and compliance, likely due to post-translational modifications to collagen.