Comprehensive review of hepatocellular carcinoma with portal vein tumor thrombus:State of art and future perspectives

Background:Despite advances in the diagnosis of patients with hepatocellular carcinoma(HCC),70%-80%of patients are diagnosed with advanced stage disease.Portal vein tumor thrombus(PVTT)is among the most ominous signs of advanced stage disease and has been associated with poor survival if untreated.Data sources:A systematic search of MEDLINE(PubMed),Embase,Cochrane Library and Database for Systematic Reviews(CDSR),Google Scholar,and National Institute for Health and Clinical Excellence(NICE)databases until December 2022 was conducted using free text and MeSH terms:hepatocellular carcinoma,portal vein tumor thrombus,portal vein thrombosis,vascular invasion,liver and/or hepatic resection,liver transplantation,and systematic review.Results:Centers of surgical excellence have reported promising results related to the individualized surgical management of portal thrombus versus arterial chemoembolization or systemic chemotherapy.Critical elements to the individualized surgical management of HCC and portal thrombus include precise classification of the portal vein tumor thrombus,accurate identification of the subgroups of patients who may benefit from resection,as well as meticulous surgical technique.This review addressed five specific areas:(a)formation of PVTT;(b)classifications of PVTT;(c)controversies related to clinical guidelines;(d)surgical treatments versus non-surgical approaches;and(e)characterization of surgical techniques correlated with classifications of PVTT.Conclusions:Current evidence from Chinese and Japanese high-volume centers demonstrated that patients with HCC and associated PVTT can be managed with surgical resection with acceptable results.

Liver transplantation and resection in patients with hepatocellular cancer and portal vein tumor thrombosis: Feasible and effective?

Patients with locally advanced hepatocellular cancer(HCC)and portal vein tumor thrombosis(PVTT)have a dismal prognosis since limited treatment options are available for them.In recent years,effective systemic therapy,and advances in the understanding of technicalities and effectiveness of ablative therapies especially radiotherapy,have given some hope to prolong survival in them.This review summarized recent evidence in literature regarding the possible role of liver resection(LR)and liver transplantation(LT)in patients with locally advanced HCC and PVTT with no extrahepatic disease.Downstaging therapies have helped make curative resection or LT a reality in selected patients.This review emphasizes on the key points to focus on when considering surgery in these patients,who are usually relegated to palliative systemic therapy alone.Meticulous patient selection based on tumor biology,documented downstaging based on imaging and decrease in tumor marker levels,and an adequate waiting period to demonstrate stable disease,may help obtain satisfactory long-term outcomes post LR or LT in an intention to treat strategy in patients with HCC and PVTT.

Revascularization for Iliac-femoral Artery Pseudoaneurysm with Greater Saphenous Vein

Objective To investigate the role of revascularization procedures with autologous greater saphenous vein in surgical management of iliac-femoral artery pseudoaneurysm in parenteral drug abusers. Methods Twenty-one patients with iliac-femoral artery pseudoaneurysm caused by parenteral drug abuse from 2004 to 2007 were enrolled. Among them,15 patients were male and 6 were female; their average age was 31.3 years. The size of pseudoaneurysms ranged from 3.0 cm to 7.5 cm. Common femoral artery and distal external iliac artery were often involved. We performed arterial reconstruction on these patients with autologous greater saphenous vein as a graft after excising iliac-femoral artery pseudoaneurysm through a single curved inguinal incision. All patients were followed up,and the complications were recorded. Results The surgical procedures were finished without intraoperative mortality or perioperative complications. All patients were free of claudication symptoms after the surgery except one case with preoperative popliteal artery stenosis. One case of infection and wound tissue fistula was found later. One case had inguinal incisional hematoma and another complained of numbness in thigh skin. Conclusions The use of autologous greater saphenous venous grafts for arterial reconstruction after pseudoaneurysm excision in drug abusers is safe and effective. This technique offers more advantages than arterial ligation alone without revascularization. An optimal greater saphenous venous graft is a prerequisite for revascularization.

Seeing beneath the surface:Harnessing point-of-care ultrasound for internal jugular vein evaluation

Point-of-care ultrasound(POCUS)of the internal jugular vein(IJV)offers a noninvasive means of estimating right atrial pressure(RAP),especially in cases where the inferior vena cava is inaccessible or unreliable due to conditions such as liver disease or abdominal surgery.While many clinicians are familiar with visually assessing jugular venous pressure through the internal jugular vein,this method lacks sensitivity.The utilization of POCUS significantly enhances the visualization of the vein,leading to a more accurate identification.It has been demonstrated that combining IJV POCUS with physical examination enhances the specificity of RAP estimation.This review aims to provide a comprehensive summary of the various sonographic techniques available for estimating RAP from the internal jugular vein,drawing upon existing data.

Conversion therapy of a giant hepatocellular carcinoma with portal vein thrombus and inferior vena cava thrombus:A case report and review of literature

BACKGROUND The prognosis of hepatocellular carcinoma(HCC)combined with portal and hepatic vein cancerous thrombosis is poor,for unresectable patients the combination of targeted therapy and immune therapy was the first-line recommended treatment for advanced HCC,with a median survival time of only about 2.7-6 months.In this case report,we present the case of a patient with portal and hepatic vein cancerous thrombosis who achieved pathologic complete response after conversion therapy.CASE SUMMARY In our center,a patient with giant HCC combined with portal vein tumor thrombus and hepatic vein tumor thrombus was treated with transcatheter arterial chemoembolization(TACE),radiotherapy,targeted therapy and immunotherapy,and was continuously given icaritin soft capsules for oral regulation.After 7 months of conversion therapy,the patient's tumor shrank and the tumor thrombus subsided significantly.The pathology of surgical resection was in complete remission,and there was no progression in the postoperative follow-up for 7 months,which provided a basis for the future strategy of combined conversion therapy.CONCLUSION In this case,atezolizumab,bevacizumab,icaritin soft capsules combined with radiotherapy and TACE had a good effect.For patients with hepatocellular carcinoma combined with hepatic vein/inferior vena cava tumor thrombus,adopting a high-intensity,multimodal proactive strategy under the guidance of multidisciplinary team(MDT)is an important attempt to break through the current treatment dilemma.

Intrahepatic portal venous systems in adult patients with cavernous transformation of portal vein: Imaging features and a new classification

Background: Cavernous transformation of the portal vein(CTPV) due to portal vein obstruction is a rare vascular anomaly defined as the formation of multiple collateral vessels in the hepatic hilum. This study aimed to investigate the imaging features of intrahepatic portal vein in adult patients with CTPV and establish the relationship between the manifestations of intrahepatic portal vein and the progression of CTPV. Methods: We retrospectively analyzed 14 CTPV patients in Beijing Tsinghua Changgung Hospital. All patients underwent both direct portal venography(DPV) and computed tomography angiography(CTA) to reveal the manifestations of the portal venous system. The vessels measured included the left portal vein(LPV), right portal vein(RPV), main portal vein(MPV) and the portal vein bifurcation(PVB). Results: Nine males and 5 females, with a median age of 40.5 years, were included in the study. No significant difference was found in the diameters of the LPV or RPV measured by DPV and CTA. The visualization in terms of LPV, RPV and PVB measured by DPV was higher than that by CTA. There was a significant association between LPV/RPV and PVB/MPV in term of visibility revealed with DPV( P = 0.01), while this association was not observed with CTA. According to the imaging features of the portal vein measured by DPV, CTPV was classified into three categories to facilitate the diagnosis and treatment. Conclusions: DPV was more accurate than CTA for revealing the course of the intrahepatic portal vein in patients with CTPV. The classification of CTPV, that originated from the imaging features of the portal vein revealed by DPV, may provide a new perspective for the diagnosis and treatment of CTPV.

Intelligent diagnosis of retinal vein occlusion based on color fundus photographs

AIM:To develop an artificial intelligence(AI)diagnosis model based on deep learning(DL)algorithm to diagnose different types of retinal vein occlusion(RVO)by recognizing color fundus photographs(CFPs).METHODS:Totally 914 CFPs of healthy people and patients with RVO were collected as experimental data sets,and used to train,verify and test the diagnostic model of RVO.All the images were divided into four categories[normal,central retinal vein occlusion(CRVO),branch retinal vein occlusion(BRVO),and macular retinal vein occlusion(MRVO)]by three fundus disease experts.Swin Transformer was used to build the RVO diagnosis model,and different types of RVO diagnosis experiments were conducted.The model’s performance was compared to that of the experts.RESULTS:The accuracy of the model in the diagnosis of normal,CRVO,BRVO,and MRVO reached 1.000,0.978,0.957,and 0.978;the specificity reached 1.000,0.986,0.982,and 0.976;the sensitivity reached 1.000,0.955,0.917,and 1.000;the F1-Sore reached 1.000,0.9550.943,and 0.887 respectively.In addition,the area under curve of normal,CRVO,BRVO,and MRVO diagnosed by the diagnostic model were 1.000,0.900,0.959 and 0.970,respectively.The diagnostic results were highly consistent with those of fundus disease experts,and the diagnostic performance was superior.CONCLUSION:The diagnostic model developed in this study can well diagnose different types of RVO,effectively relieve the work pressure of clinicians,and provide help for the follow-up clinical diagnosis and treatment of RVO patients.

Transcatheter arterial chemoembolization combined with PD-1 inhibitors and Lenvatinib for hepatocellular carcinoma with portal vein tumor thrombus

BACKGROUND Hepatocellular carcinoma(HCC)patients complicated with portal vein tumor thrombus(PVTT)exhibit poor prognoses and treatment responses.AIM To investigate efficacies and safety of the combination of PD-1 inhibitor,transcatheter arterial chemoembolization(TACE)and Lenvatinib in HCC subjects comorbid with PVTT.METHODS From January 2019 to December 2020,HCC patients with PVTT types Ⅰ-Ⅳ were retrospectively enrolled at Beijing Ditan Hospital.They were distributed to either the PTL or TACE/Lenvatinib(TL)group.The median progression-free survival(mPFS)was set as the primary endpoint,while parameters like median overall survival,objective response rate,disease control rate(DCR),and toxicity level served as secondary endpoints.RESULTS Forty-one eligible patients were finally recruited for this study and divided into the PTL(n=18)and TL(n=23)groups.For a median follow-up of 21.8 months,the DCRs were 88.9%and 60.9%in the PTL and TL groups(P=0.046),res-pectively.Moreover,mPFS indicated significant improvement(HR=0.25;P<0.001)in PTL-treated patients(5.4 months)compared to TL-treated(2.7 months)patients.There were no treatment-related deaths or differences in adverse events in either group.CONCLUSION A triplet regimen of PTL was safe and well-tolerated as well as exhibited favorable efficacy over the TL regimen for advanced-stage HCC patients with PVTT types Ⅰ-Ⅳ.

Simultaneous portal vein thrombosis and splenic vein thrombosis in a COVID-19 patient:A case report and review of literature

BACKGROUND It is well-described that the coronavirus disease 2019(COVID-19)infection is associated with an increased risk of thrombotic complications.While there have been many cases of pulmonary emboli and deep vein thrombosis in these patients,reports of COVID-19 associated portal vein thrombosis(PVT)have been uncommon.We present a unique case of concomitant PVT and splenic artery thrombosis in a COVID-19 patient.CASE SUMMARY A 77-year-old-male with no history of liver disease presented with three days of left-sided abdominal pain.One week earlier,the patient was diagnosed with mildly symptomatic COVID-19 and was treated with nirmatrelvir/ritonavir.Physical exam revealed mild right and left lower quadrant tenderness,but was otherwise unremarkable.Significant laboratory findings included white blood cell count 12.5 K/μL,total bilirubin 1.6 mg/dL,aminoaspartate transferase 40 U/L,and alanine aminotransferase 61 U/L.Computed tomography of the abdomen and pelvis revealed acute PVT with thrombus extending from the distal portion of the main portal vein into the right and left branches.Also noted was a thrombus within the distal portion of the splenic artery with resulting splenic infarct.Hypercoagulable workup including prothrombin gene analysis,factor V Leiden,cardiolipin antibody,and JAK2 mutation were all negative.Anticoagulation with enoxaparin was initiated,and the patient’s pain improved.He was discharged on apixaban.CONCLUSION It is quite uncommon for PVT to present simultaneously with an arterial thrombotic occlusion,as in the case of our patient.Unusual thrombotic manifestations are classically linked to hypercoagulable states including malignancy and hereditary and autoimmune disorders.Viral infections such as Epstein-Barr virus,cytomegalovirus,viral hepatitis,and COVID-19 have all been found to increase the risk of splanchnic venous occlusions,including PVT.In our patient,prompt abdominal imaging led to early detection of thrombus,early treatment,and an excellent outcome.This case is unique in that it is the second known case within the literature of simultaneous PVT and splenic artery thrombosis in a COVID-19 patient.

Lower extremity peripherally inserted central catheter placement ectopic to the ascending lumbar vein:A case report

BACKGROUND Peripherally inserted central catheters(PICCs)are an essential infusion route for oncology patients receiving intravenous treatments,but lower extremity veni-puncture is the preferred technique for patients with superior vena cava syndrome(SVCS).We report the case of a patient with a lower extremity PICC ectopic to the ascending lumbar vein,to indicate and verify PICC catheterisation in the lower extremity is safe and feasible.And hope to provide different per-spectives for clinical PICC venipuncture to get the attention of peers.CASE SUMMARY On 24 August 2022,a 58-year-old male was admitted to our department due to an intermittent cough persisting for over a month,which worsened 10 d prior.Imaging and laboratory investigations suggested the patient with pulmonary malignancy and SVCS.Chemotherapy was not an absolute contraindication in this patient.Lower extremity venipuncture is the preferred technique because administering upper extremity venous transfusion to patients with SVCS can exacerbate oedema in the head,neck,and upper extremities.The patient and his family were informed about the procedure,and informed consent was obtained.After successful puncture and prompt treatment,the patient was discharged,experiencing some relief from symptoms.CONCLUSION Inferior vena cava catheterisation is rare and important for cancer patients with SVCS,particularly in complex situations involving ectopic placement.

Current concepts in the management of non-cirrhotic non-malignant portal vein thrombosis

Non-cirrhotic non-malignant portal vein thrombosis(NCPVT)is an uncommon condition characterised by thrombosis of the portal vein,with or without extension into other mesenteric veins,in the absence of cirrhosis or intra-abdominal malignancy.Complications can include intestinal infarction,variceal bleeding and portal biliopathy.In this article,we address current concepts in the management of NCPVT including identification of risk factors,classification and treatment,and review the latest evidence on medical and interventional management options.

Percutaneous transhepatic stenting for acute superior mesenteric vein stenosis after pancreaticoduodenectomy with portal vein reconstruction:A case report

BACKGROUND Percutaneous transhepatic stent placement has become a common strategy for the postoperative treatment of portal vein(PV)/superior mesenteric veins(SMV)stenosis/occlusion.It has been widely used after liver transplantation surgery;however,reports on stent placement for acute PV/SMV stenosis after pancreatic surgery within postoperative 3 d are rare.CASE SUMMARY Herein,we reported a case of intestinal edema and SMV stenosis 2 d after pancreatic surgery.The patient was successfully treated using stent grafts.Although the stenosis resolved after stent placement,complications,including bleeding,pancreatic fistula,bile leakage,and infection,made the treatment highly challenging.The use of anticoagulants was adjusted multiple times to prevent venous thromboembolism and the risk of bleeding.After careful treatment,the patient stabilized,and stent placement effectively managed postoperative PV/SMV stenosis.CONCLUSION Stent placement is effective and feasible for treating acute PV/SMV stenosis after pancreatic surgery even within postoperative 3 d.

Geology and Geochemistry of K-feldspar Veins in Lamprophyre at the Zhenyuan Gold Deposit,Yunnan,Southwest China:Implications for Gold Mineralization

Lamprophyres typically appear in hydrothermal gold deposits.The relationship between lamprophyres and gold deposits is investigated widely.Some researchers suggest that the emplacement of lamprophyres triggers gold mineralization,whereas others hypothesize that the formation of lamprophyres increases the fertility of mantle sources and ore-forming fluids.K-feldspar veins,with ages between those of lamprophyres and gold deposits,appear in lamprophyres in Zhenyuan.Therefore,K-feldspar veins are ideal for investigating the relationship between lamprophyres and gold deposits.Phlogopite in K-feldspar veins has lower Mg#,Ni,and Cr contents and higher TiO2,Li,Ba,Sr,Sc,Zr,Nb,and Cs contents than phlogopite in lamprophyres.The in-situ Sr isotopic values of apatites(0.7063–0.7066)in K-feldspar veins are within the range for apatites(0.7064–0.7078)from lamprophyres.High large-ion lithophile element concentrations and low Nb and Ta concentrations in phlogopite from lamprophyres,in addition to high(87Sr/86Sr)i values of apatite(0.7064–0.7078),indicate that the magma parental to these phlogopite and apatite crystals is derived from an enriched mantle.Kfeldspar veins are genetically correlated with lamprophyres,whereas sulfide mineral assemblage and trace element compositions of pyrite in K-feldspar veins suggest that K-feldspar veins in lamprophyres are not directly related to gold mineralization of the Zhenyuan deposit.

Clues for diagnosing misplaced central venous catheter in the right ascending lumbar vein during right femoral venous access

The right ascending lumbar vein is difficult to detect on anteroposterior abdominalradiographs because it overlaps with the inferior vena cava on anteroposteriorradiographs.Intensive observation by medical providers may be a cue fordiagnosis.However,knowledge of catheter misplacement of the right ascendinglumbar vein is also necessary,because misplacement cannot be suspected withoutthat awareness.

Vein visualization enhancement by dual-wavelength phase-locked denoising technology

Visual near-infrared imaging equipment has broad applications in various fields such as venipuncture,facial injections,and safety verification due to its noncontact,compact,and portable design.Currently,most studies utilize near-infrared single-wavelength for image acquisition of veins.However,many substances in the skin,including water,protein,and melanin can create significant background noise,which hinders accurate detection.In this paper,we developed a dual-wavelength imaging system with phase-locked denoising technology to acquire vein image.The signals in the effective region are compared by using the absorption valley and peak of hemoglobin at 700nm and 940nm,respectively.The phase-locked denoising algorithm is applied to decrease the noise and interference of complex surroundings from the images.The imaging results of the vein are successfully extracted in complex noise environment.It is demonstrated that the denoising effect on hand veins imaging can be improved with 57.3%by using our dual-wavelength phase-locked denoising technology.Consequently,this work proposes a novel approach for venous imaging with dual-wavelengths and phase-locked denoising algorithm to extract venous imaging results in complex noisy environment better.

Effect of an Airbag-selective Portal Vein Blood Arrester on the Liver after Hepatectomy:A New Technique for Selective Clamping of the Portal Vein

Objective:A novel technique was explored using an airbag-selective portal vein blood arrester that circumvents the need for an intraoperative assessment of anatomical variations in patients with complex intrahepatic space-occupying lesions.Methods:Rabbits undergoing hepatectomy were randomly assigned to 4 groups:intermittent portal triad clamping(PTC),intermittent portal vein clamping(PVC),intermittent portal vein blocker with an airbag-selective portal vein blood arrester(APC),and without portal blood occlusion(control).Hepatic ischemia and reperfusion injury were assessed by measuring the 7-day survival rate,blood loss,liver function,hepatic pathology,hepatic inflammatory cytokine infiltration,hepatic malondialdehyde levels,and proliferating cell nuclear antigen levels.Results:Liver damage was substantially reduced in the APC and PVC groups.The APC animals exhibited transaminase levels similar to or less oxidative stress damage and inflammatory hepatocellular injury compared to those exhibited by the PVC animals.Bleeding was significantly higher in the control group than in the other groups.The APC group had less bleeding than the PVC group because of the avoidance of portal vein skeletonization during hepatectomy.Thus,more operative time was saved in the APC group than in the PVC group.Moreover,the total 7-day survival rate in the APC group was higher than that in the PTC group.Conclusion:Airbag-selective portal vein blood arresters may help protect against hepatic ischemia and reperfusion injury in rabbits undergoing partial hepatectomy.This technique may also help prevent liver damage in patients requiring hepatectomy.

Extraction of intersecting palm-vein and palmprint features for cancellable identity verification

A novel method based on the cross-modality intersecting features of the palm-vein and the palmprint is proposed for identity verification.Capitalising on the unique geometrical relationship between the two biometric modalities,the cross-modality intersecting points provides a stable set of features for identity verification.To facilitate flexibility in template changes,a template transformation is proposed.While maintaining non-invertibility,the template transformation allows transformation sizes beyond that offered by the con-ventional means.Extensive experiments using three public palm databases are conducted to verify the effectiveness the proposed system for identity recognition.

Further study on the genesis of lamellar calcite veins in lacustrine black shale--A case study of Paleogene in Dongying Depression, China

Lamellar calcite veins are prevalent in carbonate-rich,lacustrine dark shale.The formation mechanisms of these veins have been extensively debated,focusing on factors such as timing,depth,material source,and driving forces.This paper examines dark lacustrine shale lamellar calcite veins in the Paleogene strata of Dongying Depression,using various analytical techniques:petrography,isotope geochemistry,cathodoluminescence,inclusion thermometry,and electron probe micro-analysis.Two distinct types of calcite veins have been identified:granular calcite veins and sparry calcite veins.These two types differ significantly in color,grain structure,morphology,and inclusions.Through further investigation,it was observed that vein generation occurred from the shallow burial period to the maturation of organic matter,with a transition from granular calcite veins to sparry calcite veins.The granular calcite veins exhibit characteristics associated with the shallow burial period,including plastically deformed laminae and veins,the development of strawberry pyrite,the absence of oil and gas,weak fractionation in oxygen isotopes,and their contact relationship with sparry calcite veins.These granular calcite veins were likely influenced by the reduction of sulfate bacteria.On the other hand,sparry calcite veins with fibrous grains are antitaxial and closely linked to the evolution and maturation of organic matter.They contain oil and gas inclusions and show a distribution range of homogenization temperature between 90℃ and 120℃ and strong fractionation in oxygen isotopes,indicating formation during the hydrocarbon expulsion period.The carbon isotope analysis of the surrounding rocks and veins suggests that the material for vein formation originates from the shale itself,specifically authigenic micritic calcite modified by the action of methanogens.The opening of horizontal fractures and vein formation is likely driven by fluid overpressure resulting from undercompaction and hydrocarbon expulsion.Veins may form rapidly or through multi-stage composite processes.Early veins are predominantly formed in situ,while late veins are a result of continuous fluid migration and convergence.Furthermore,the veins continue to undergo modification even after formation.This study emphasizes that the formation of lamellar calcite veins in shale is a complex diagenetic process influenced by multiple factors:biology,organic matter,and inorganic processes,all operating at various stages throughout the shale's diagenetic history.

Inhibiting MMP13 Attenuates Deep Vein Thrombosis in a Mouse Model by Reducing the Expression of Pdpn

Objective:Matrix metalloproteinase 13(MMP13)is an extracellular matrix protease that affects the progression of atherosclerotic plaques and arterial thrombi by degrading collagens,modifying protein structures and regulating inflammatory responses,but its role in deep vein thrombosis(DVT)has not been determined.The purpose of this study was to investigate the potential effects of MMP13 and MMP13-related genes on the formation of DVT.Methods:We altered the expression level of MMP13 in vivo and conducted a transcriptome study to examine the expression and relationship between MMP13 and MMP13-related genes in a mouse model of DVT.After screening genes possibly related to MMP13 in DVT mice,the expression levels of candidate genes in human umbilical vein endothelial cells(HUVECs)and the venous wall were evaluated.The effect of MMP13 on platelet aggregation in HUVECs was investigated in vitro.Results:Among the differentially expressed genes,interleukin 1 beta,podoplanin(Pdpn),and factor VIII von Willebrand factor(F8VWF)were selected for analysis in mice.When MMP13 was inhibited,the expression level of PDPN decreased significantly in vitro.In HUVECs,overexpression of MMP13 led to an increase in the expression level of PDPN and induced platelet aggregation,while transfection of PDPN-siRNA weakened the ability of MMP13 to increase platelet aggregation.Conclusions:Inhibiting the expression of MMP13 could reduce the burden of DVT in mice.The mechanism involves downregulating the expression of Pdpn through MMP13,which could provide a novel gene target for DVT diagnosis and treatment.

Modeling Blood Flow in Veins of Uniform Properties (Giraffe Jugular Vein)

This paper models the giraffe’s jugular veins as a uniform collapsible tube from a rigid skull. The equations governing one-dimensional steady flow through such a tube for various conditions have been developed. The effects of inertial and inclination angles that have not been discussed previously have been included. It has been shown that different flows for a uniform tube (vein) are possible. However, this flow matches that of a jugular vein which is supercritical, and the steady solution has been given by the balance between the driving forces of gravity and the viscous resistance to the flow at the right atrium of the heart must be sub-critical for a fixed right-atrium pressure which means that an elastic jump is required to return the flow to sub-critical from the supercritical flow upstream this type of relationship gives rise to flow limitation at the same time given any right atrium fixed pressure there exists a maximum flow rate which when exceeded the boundary conditions of the flow do not hold boundary conditions at the right atrium are not satisfied hence making the steady flow impossible this mechanism of flow limitation is slightly different from the other one in that causes airways through forced expiration from the observation made it is clearly shown that there is an intravascular pressure difference with a change in height.