Vena Cava Occlusion Research Articles

Nitric oxide in the kidney.

bastron and kaloyanides([2][1]) had already investigated the effects of sodium nitroprusside in the isolated kidney 8 years before the postulate of an endothelium-derived relaxing factor was made by Furchgott and Zawadzki ([14][2]). More recent studies aim at the importance of nitric oxide (NO) for

Cardiomyoplasty reduces myocardial oxygen consumption: implications for direct mechanical compression.

This study investigates the possibility of reducing myocardial oxygen consumption by dynamic cardiomyoplasty in chronic heart failure. The sheep model used is relevant for cardiac assist using direct mechanical cardiac compression. In 7 sheep, heart failure was induced by staged intracoronary microembolization followed by dynamic cardiomyoplasty. Six months later, the effect of latissimus dorsi muscle stimulation in the 2:1 mode (on, cardiomyoplasty; off, control) was studied. Left ventricular pressure-volume loops were obtained by conductance, micromanometer, and inferior vena cava occlusion catheter. Myocardial oxygen consumption was derived from left main coronary artery blood flow and oxygen content of arterial and coronary sinus blood. Cardiomyoplasty had no significant effect on left ventricular hemodynamic variables such as end-systolic pressure. However, cardiomyoplasty increased stroke volume and ejection fraction significantly by 11% +/- 12% and 11% +/- 10%, respectively. Although pressure-volume area and external work did not increase with cardiomyoplasty, myocardial oxygen consumption decreased by 21% +/- 11%. Therefore, cardiomyoplasty increased myocardial efficiency (external work/myocardial oxygen consumption) by 16% +/- 13%. Despite limited hemodynamic improvement from dynamic cardiac compression by cardiomyoplasty in sheep with chronic heart failure, myocardial oxygen consumption was significantly reduced. These findings provide a rationale for reverse remodeling of the failing heart using direct mechanical compression.

Nontraumatic vascular emergencies: imaging and intervention in acute venous occlusion.

Risk factors for acute venous occlusion range from prolonged immobilization to hypercoagulability syndromes, trauma, and malignancy. The aim of this review article is to illustrate the different imaging options for the diagnosis of acute venous occlusion and to assess the value of interventional strategies for venous thrombosis treatment in an emergency setting.First, diagnosis and treatment of the most common form of venous occlusion, at the level of the lower extremities, is presented, followed by pelvic vein and inferior vena cava occlusion, mesenteric venous thrombosis, upper extremity occlusion, acute cerebral vein thrombosis, and finally acute venous occlusion of hemodialysis access.In acute venous occlusion of the lower extremity phlebography is still the reference gold standard. Presently, duplex ultrasound with manual compression is the most sensitive and specific noninvasive test. Limitations of ultrasonography include isolated distal calf vein occlusion, obesity, and patients with lower extremity edema. If sonography is nondiagnostic, venography should be considered. Magnetic resonance venography can differentiate an acute occlusion from chronic thrombus, but because of its high cost and limited availability, it is not yet used for the routine diagnosis of lower extremity venous occlusion only. Regarding interventional treatment, catheter-directed thrombolysis can be applied to dissolve thrombus in charily selected patients with symptomatic occlusion and no contraindications to therapy. Acute occlusion of the pelvic veins and the inferior vena cava, often due to extension from the femoropopliteal system, represents a major risk for pulmonary embolism. Color flow Doppler imaging is often limited owing to obesity and bowel gas. Venography has long been considered the gold standard for identifying proximal venous occlusion. Both CT scanning and MR imaging, however, can even more accurately diagnose acute pelvis vein or inferior vena cava occlusion. MRI is preferred because it is noninvasive, does not require contrast agent, carries no exposure to ionizing radiation, and is highly accurate and reproducible. Apart from catheter-directed thrombolysis, mechanical thrombectomy has proven to be a quick and safe treatment modality by enabling the recanalization of thrombotic occlusions in conjunction with minimal invasiveness and a low bleeding risk. Mechanical thrombectomy devices should only be used in conjunction with a temporary cava filter.Contrast-enhanced CT is at present considered the examination of choice for acute mesenteric vein occlusion which has mortality rates as high as 80%. Patients with proven acute mesenteric venous occlusion and contraindications to surgical therapy and no identified bleeding disposition without looming bowel ischemia or infarction are possible contenders to the less invasive percutaneous approach either by (in)direct thrombolysis or mechanical means. Ultrasonography is the primary imaging modality for the diagnosis of upper extremity thrombosis. Computed tomography and MRI are in addition helpful in diagnosing central chest vein occlusions. The interventionalist is rarely involved in the treatment of this entity. Catheter-directed thrombolysis is known to improve lysis rates. Together with balloon angioplasty good results have been obtained. If stenosis or thrombus remains after thrombolysis and angioplasty, stent placement should follow. Within the first two weeks, thrombosed dural sinus and cerebral venous vessels are typically hyperdense on CT compared with brain parenchyma; after the course of 2 weeks, the thrombus will become isodense. In MRI an axial fluid-attenuated inversion recovery sequence, an axial diffusion-weighted MRI, coronal T1-weighted spin-echo and T2-weighted turbo-spin-echo sequences, a coronal gradient-echo and a 3D phase-contrast venous angiogram should be performed. Local thrombolysis is needed only when patients have an exacerbation of clinical symptoms or imaging signs of worsening disease despite sufficient anticoagulation therapy. Acute occlusions of dialysialysis grafts and fistulae are a frequently encountered complication. Among the various methods described for acute occlusion screening, ultrasonography and MRI have been proven to be accurate and noninvasive; however, if immediate treatment can be anticipated, imaging should be performed directly by digital subtraction angiography before the percutaneous intervention. Initial percutaneous thrombectomy is very effective with success rates and patency rates comparable to those of surgical thrombectomy. A short thrombosis can be treated with balloon angioplasty alone, whereas an extensive thrombosis requires a combination of mechanical devices and/or thrombolytic agents with adjunctive balloon angioplasty.

Method of preload reduction during LVPVR analysis of systolic function: airway pressure elevation and vena cava occlusion.

A graded preload reduction during analysis of the left ventricular pressure-volume relationship (LVPVR) is required for derivation of end-systolic elastance (Ees) and preload recruitable stroke work (PRSW). The authors aimed to measure serial changes in these systolic function parameters before and during planned circulatory interventions using two different methods of preload alteration: a positive airway pressure plateau (APP) and inferior vena cava occlusion (IVCO). In eight animals, measurements were made at 38 degrees, 30 degrees, 32 degrees, 34 degrees, and posthypothermia 38 degrees C. In an additional eight animals, isoflurane, adrenaline, and aorta occlusion (balloon catheter occluder) were administered in series, each with a preintervention control measurement. Left ventricular volume was measured by conductance. Paired measurements of the systolic function parameters Ees and PRSW, each derived with two preload methods, were analyzed for bias. Circulatory alterations were achieved with the temperature, isoflurane, adrenaline, and aorta occlusion interventions. Measured changes in Ees and PRSW from control to intervention showed a strong correlation and no significant bias for APP in relation to IVCO. The APP-derived absolute values for Ees and PRSW demonstrated a consistent positive bias compared with IVCO. The APP method for preload reduction during LVPVR analysis detected changes in Ees and PRSW during the circulatory interventions in this model that were not different than those detected using another preload reduction method, IVCO. APP and IVCO are not interchangeable methods for preload reductions during LVPVR absolute quantitation of systolic function, and each needs to be used serially.

Preload-adjusted maximal power of right ventricle: contribution of end-systolic P-V relation intercept.

To assess whether preload-adjusted maximal power (PAMP), which is calculated as W(max)/V (where W(max) is maximal power and V(ed) is end-diastolic volume with beta = 2) is an index of right ventricular (RV) contractility, we measured RV pressure (P) and volume (V) and pulmonary artery pressure and flow in 10 dogs at baseline and after inotropic stimulation. PAMP was derived from steady-state data, whereas the slope (E(es)) and intercept (V(d)) of the end-systolic P-V relationship were derived from data obtained during vena caval occlusion. Inotropic stimulation increased E(es) (from 0.96 +/- 0.25 to 1.62 +/- 0.28 mmHg/ml; P < 0.001) and V(d) (from -3.0 +/- 17.2 to 12.4 +/- 10.8 ml; P < 0.05) but not PAMP (from 0.24 +/- 0.10 to 0.36 +/- 0.22 mW/ml(2); P = 0.09). We found a strong relationship between the optimal beta-factor for preload adjustment and V(d). A corrected PAMP, PAMP(c) = W(max)/(V(ed) - V(d))(2), which incorporated the V(d) dependency, was sensitive to the inotropic changes (from 0.23 +/- 0.12 to 0.54 +/- 0.17 mW/ml(2); P < 0.001) with a good correlation with E(es) (r = 0.88; P < 0.001).

Aprotinin and Thromboembolism in Liver Transplantation: Is There Really a Causal Effect?

In Response: We would like to thank Drs. Molenaar and Porte for their response to our case report. They cite one case report (1) as suggesting aprotinin administration may be related to pulmonary thromboembolism. In fact, there are four case reports in which seven patients suffered pulmonary thromboemboli in the setting of aprotinin (1–4). They also state that many factors may predispose patients undergoing orthotopic liver transplant to pulmonary thromboemboli. We agree. A review of the prior case reports indicates that veno-venous bypass was used in five cases of thromboemboli (2–4) and not used in one (3), and the last case did not mention technique (1). Certainly venous stasis with infrahepatic inferior vena cava occlusion would seem to increase the risk of thrombus formation. In fact it may be that this subpopulation needs further study. Drs. Molenaar and Porte cite Garcia-Huete et al. (5) and Porte et al. (6) as studies that did not show any difference in thromboembolic complications between patients treated with and without aprotinin. They also cite a personal communication with Dr. Wolf indicating a 1%–1.5% incidence of thromboemboli in OLT. Garcia-Huete et al.’s (5) study group only had 40 patients; a larger population would be required to establish a true difference in the incidence of thromboemboli. Porte et al.’s (6) study did not control for surgical technique, which may be a significant factor. The treatment groups in this study were also too small to detect differences in the incidence of thromboemboli. Many differences exist between liver transplant surgery and cardiac surgery. Indeed, we believe that clinical outcome data generated during studies of cardiac surgery to which Drs. Molenaar and Porte refer may not apply to liver transplant recipients. Drs. Molenaar and Porte question the value of isolated case reports. A case report is by no means intended to provide definite evidence of a causal relationship between an intervention and an outcome. The goal of a case report is to provide communication between individual clinicians to raise awareness of phenomena that may require further formal study. Michael G. Fitzsimons, MD Robert A. Peterfreund, MD, PhD

Effects of moderate hypothermia on in situ cardiac sympathetic nerve endings

Although hypothermia is known to alter neuronal control of circulation, it has been uncertain whether clinically used hypothermia (moderate hypothermia) affects in situ cardiac sympathetic nerve endings. We examined the effects of moderate hypothermia on cardiac sympathetic nerve ending function in anesthetized cats. By use of a cardiac dialysis technique, we implanted dialysis probes in the midwall of the left ventricle and monitored dialysate norepinephrine (NE) levels as an index of NE output from cardiac sympathetic nerve endings. Hypothermia (27.0±0.5 °C) induced decreases in dialysate NE levels. Dialysate NE levels did not return to the control level at normothermia after rewarming. Dialysate NE response to inferior vena cava occlusion was attenuated at hypothermia but restored at normothermia after rewarming. Dialysate NE response to high K + (100 mM) was attenuated at hypothermia and was not restored at normothermia after rewarming. Hypothermia induced increases in dialysate dihydroxyphenylglycol (DHPG) levels. There were no differences in desipramine (neuronal NE uptake blocker, 10 μM) induced increment in dialysate NE level among control, hypothermia, and normothermia after rewarming. However, hypothermia induced an increase in DHPG/NE ratio. These data suggest that hypothermia impairs vesicle NE mobilization rather than membrane NE uptake. We conclude that moderate hypothermia suppresses exocytotic NE release via central mediated reflex and regional depolarization.

N-acetyl-L-cysteine improves renal medullary hypoperfusion in acute renal failure.

This study evaluated the effects of N-acetyl-L-cysteine (NAC), a free radical scavenger, and N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthesis inhibitor, on the changes in renal function, intrarenal blood flow distribution (laser-Doppler flowmetry), and plasma peroxynitrite levels during the acute renal failure (ARF) produced by inferior vena cava occlusion (IVCO; 45 min) in anesthetized rats. Renal blood flow fell on reperfusion (whole kidney by -45.7%; cortex -58.7%, outer medulla -62.8%, and papilla -47.7%); glomerular filtration rate (GRF) also decreased (-68.6%), whereas fractional sodium excretion (FE(Na%)) and peroxynitrite and NO/NO plasma levels increased (189.5, 46.5, and 390%, respectively) after ischemia. Pretreatment with L-NAME (10 microg. kg(-1). min(-1)) aggravated the fall in renal blood flow seen during reperfusion (-60%). Pretreatment with NAC (150 mg/kg bolus + 715 microg. kg(-1). min(-1) iv) partially prevented those changes in renal function (GFR only fell by -29.2%, and FE(Na%) increased 119.4%) and laser-Doppler blood flow, especially in the outer medulla, where blood flow recovered to near control levels during reperfusion. These beneficial effects seen in rats given NAC seem to be dependent on the presence of NO, because they were abolished in rats pretreated with L-NAME. Also, the antioxidant effects of NAC prevented the increase in plasma peroxynitrite after ischemia. In conclusion, NAC ameliorates the renal failure and the outer medullary vasoconstriction induced by ICVO, effects that seem to be dependent on the presence of NO and the scavenging of peroxynitrite.

Retrograde cerebral perfusion provides negligible flow through brain capillaries in the pig

Objectives: Although retrograde cerebral perfusion is being used clinically during aortic arch surgery, whether retrograde flow perfuses the brain effectively is still uncertain. Methods: Fourteen pigs were cooled to 20°C with cardiopulmonary bypass and perfused retrogradely via the superior vena cava for 30 minutes: 7 underwent standard retrograde cerebral perfusion and 7 underwent retrograde perfusion with occlusion of the inferior vena cava. Antegrade and retrograde cerebral blood flow were calculated by quantitating fluorescent microspheres trapped in brain tissue after the animals were put to death; microspheres returning to the aortic arch, the inferior vena cava, and the descending aorta were also analyzed during retrograde cerebral perfusion. Results: Antegrade cerebral blood flow was 16 ± 7.7 mL · min–1 · 100 g–1 before retrograde cerebral perfusion and 22 ± 6.3 mL · min–1 · 100 g–1 before perfusion with caval occlusion (P =.14). During retrograde perfusion, calculations based on the number of microspheres trapped in the brain showed negligible flows (0.02 ± 0.02 mL · min–1 · 100 g–1 with retrograde cerebral perfusion and 0.04 ± 0.02 mL · min–1 · 100 g–1 with perfusion with caval occlusion; P =.09): only 0.01% and 0.02% of superior vena caval inflow, respectively. Less than 13% of retrograde superior vena caval inflow blood returned to the aortic arch with either technique. During retrograde cerebral perfusion, more than 90% of superior vena caval input was shunted to the inferior vena cava and was then recirculated, as indicated by rapid development of an equilibrium in microspheres between the superior and inferior venae cavae. With retrograde perfusion and inferior vena caval occlusion, less than 12% of inflow returned to the descending aorta and only 0.01% of microspheres. Conclusions: The paucity of microspheres trapped within the brain indicates that retrograde cerebral perfusion, either alone or combined with inferior vena caval occlusion, does not provide sufficient cerebral capillary perfusion to confer any metabolic benefit. The slightly improved outcome previously reported with retrograde cerebral perfusion during prolonged circulatory arrest in this model may be a consequence of enhanced cooling resulting from perfusion of nonbrain capillaries and from venoarterial and venovenous shunting.J Thorac Cardiovasc Surg 2001;122:331-8

Dynamic effects of positive-pressure ventilation on canine left ventricular pressure-volume relations.

Positive-pressure ventilation (PPV) may affect left ventricular (LV) performance by altering both LV diastolic compliance and pericardial pressure (Ppc). We measured the effect of PPV on LV intraluminal pressure, Ppc, LV volume, and LV cross-sectional area in 17 acute anesthetized dogs. To account for changes in lung volume independent of changes in Ppc and differences in contractility, measures were made during both open- and closed-chest conditions, during closed chest with and without chest wall binding, and after propranolol-induced acute ventricular failure (AVF). Apneic end-systolic pressure-volume relations (ESPVR) were generated by inferior vena caval occlusions. With the open chest, PPV had no effects. With the chest closed, PPV inspiration decreased LV end-diastolic volume (EDV) along its diastolic compliance curve and decreased end-systolic volume (ESV) such that the end-systolic pressure-volume domain was shifted to a point left of the LV ESPVR, even when referenced to Ppc. The decrease in EDV was greater in control than in AVF conditions, whereas the shift of the ESV to the left of the ESPVR was greater with AVF than in control conditions. We conclude that the hemodynamic effects of PPV inspiration are due primarily to changes in intrathoracic pressure and that the inspiration-induced decreases of LV EDV reflect direct effects of intrathoracic pressure on LV filling. The decreases in LV ESV exceed the amount explained solely by a reduction in LV ejection pressure.

Inferior vena cava occlusion catheter for pediatric patients with heart disease: For more detailed cardiovascular assessments

Traditional evaluation of cardiac function is too often limited by reliance on measurements with complex interdependence between cardiac properties and loading factors. Analysis by ventricular pressure-volume (P-V), -area (P-A), or -dimension (P-D) relations during inferior vena caval (IVC) occlusion independently quantifies ventricular properties and loading conditions, providing detailed information about cardiovascular dynamics. However, there has been no appropriate size of balloon catheter that can effectively occlude IVC of pediatric patients, hindering the application of P-V (P-A, or P-D) analysis to children with heart disease despite its potential benefit. To address this problem, we have developed a new balloon catheter for IVC occlusion in children. The catheter effectively occluded IVC in 92 pediatric patients with varying forms of heart disease who underwent cardiac catheterization, yielding end-systolic pressure-area relations. Thus a newly developed balloon catheter would contribute to establishing more accurate and detailed cardiovascular assessments in children with heart disease. Cathet Cardiovasc Intervent 2001;53:392-396.

Update 2001: Right latissimus dorsi cardiomyoplasty augments left ventricular systolic performance

As Originally Published in 1993:Right Latissimus Dorsi Cardiomyoplasty Augments Left Ventricular Systolic Performance by Stephen E. Park, MD, Brian L. Cmolik, MD, Robert R. Lazzara, MD, Dennis R. Trumble, MS, and James A. Magovern, MD. Department of Surgery, Allegheny General Hospital, Surgical Research, Allegheny-Singer Research Institute, and Allegheny Campus, The Medical College of Pennsylvania, Pittsburgh, Pennsylvania, USAWe hypothesized that the right latissimus dorsi cardiomyoplasty augments left ventricular performance. Five dogs underwent staged right latissimus dorsi cardiomyoplasty. Ventricular function was studied 1 to 3 weeks later. Left ventricular pressure was measured with a micromanometer and left ventricular dimensions with piezoelectric crystals. Inferior vena caval occlusion was used to vary preload. Pressure-volume data were collected with the muscle unstimulated and stimulated at 1:2 and 1:1 muscle/heart ratios. The end-systolic pressure-volume relation (mm Hg/mL), stroke work, preload recruitable stroke work, left ventricular end-diastolic volume, and the diastolic relaxation constant were calculated and expressed as mean ± standard deviation. Stimulated beats at a 1:2 ratio showed an increase in stroke work of 42.1% (978 ± 381 to 1,390 ± 449 g · cm; p < 0.01) and preload recruitable stroke work of 28.8% (59.4 ± 20.7 to 76.6 ± 11.0 g · cm/cm3; p = 0.05) compared with the unstimulated beats. With the stimulator on at 1:1, smaller changes occurred: stroke work increased 9% (1,167 ± 390 to 1,273 ± 363 g · cm; not significant) and preload recruitable stroke work increased 27% (63.9 ± 22.7 to 80.9 ± 23.1 g · cm/cm3; p = 0.05). There were no significant changes in the end-systolic pressure-volume relation. The diastolic relaxation constant did not change at 1:1 (36 ± 9.7 to 37 ± 6.4 ms; not significant) or 1:2 (36 ± 9.3 to 39 ± 8.2 ms; not significant). Left ventricular end-diastolic volume was unchanged at 1:1 (34 ± 10.7 to 32 ± 10.3 mL) and at 1:2 (31 ± 9.0 to 32 ± 8.7 mL). Right unconditioned latissimus dorsi cardiomyoplasty in anesthetized dogs with normal hearts resulted in enhanced systolic work and contractility with no change in diastolic relaxation at stimulation rates of 1:2 and 1:1.

Nitric oxide donor FK409 and 8-bromoguanosine-cyclic monophosphate attenuate cardiac contractility assessed by Emax.

FK409 decomposes and releases nitric oxide (NO) spontaneously when it is dissolved in phosphate buffer solution at 37 degrees C. With the use of this NO donor, the effect of exogenous NO on cardiac contractility was examined by assessing Emax. alpha-chloralose-anaesthetized dogs were instrumented for measurements of left ventricular (LV) pressure and volume and coronary blood flow (CBF) in the left anterior descending artery (LAD). FK409, 8-bromoguanosine-cyclic-monophosphate (8-Br-cGMP) and papaverine were infused into the LAD, and Emax was determined by transient inferior vena cava occlusion when CBF was increased and reached its peak. Neither drug affected heart rate nor LV pressure just before the measurement of Emax. FK409 increased CBF and decreased Emax in a dose-dependent manner. 8-Br-cGMP also increased CBF and decreased Emax in a dose-dependent manner. Pretreating with propranolol did not affect the effects of FK4098-Br-cGMP on CBF and Emax. Papaverine increased mean CBF but did not affect Emax. In conclusion NO attenuates cardiac contractility in vivo, while increasing CBF. This effect seems to be mediated by cyclic-guanosine monophosphate, a second messenger of NO.

Recurrent thromboembolism in patients with vena cava filters

Background: Patients with venous thromboembolic disease are treated with anticoagulation or vena cava filter placement to prevent pulmonary embolism. A recent report suggested that filter placement may increase the risk of recurrent deep venous thrombosis (DVT) and prompted a review of our experience. Methods: Prospectively collected data on 2109 consecutive patients receiving filters were evaluated for recurrent thromboembolism, vena cava occlusion, or venous stasis ulceration. Outcomes were stratified and analyzed according to the use of anticoagulants at the time of insertion and at follow-up. Incidence rates were also compared with reports in the literature. Results: Of 1191 patients with DVT at filter placement, complete follow-up data at a mean of 9 years were available for 465. Recurrent DVT was found in 12% of the 241 patients who were given anticoagulants and 15% of the 224 who were not (P >.05). We also failed to find a significant association between the use of anticoagulation and the incidence of pulmonary embolism (2%), stasis ulceration (2%), and vena cava occlusion (0.0). Conclusions: Recurrent DVT in patients with existing thromboembolic disease is not an unexpected event, which, in our experience, is not associated with anticoagulant or filter use. Anticoagulation should be used when possible to treat existing DVT to reduce thrombus progression and potentially to reduce subsequent complications but does not seem to reduce the rate of recurrent DVT. Rates of recurrent thromboembolism were consistently less than the 20% to 50% reported in the literature. (J Vasc Surg 2001;33:510-4.)

LEFT VENTRICULAR END-DIASTOLIC VOLUME FROM EJECTION FRACTION AND STROKE VOLUME IN PIGS DURING INFERIOR VENA CAVAL OCCLUSION

Purpose: Measurement of left ventricular (LV) end-diastolic volume (EDV) is essential for assessment of intraoperative systolic and diastolic LV function. In a study submitted for review, our laboratory demonstrated the validity of stroke volume divided by ejection fraction (SV/EFa) for calculation of LV EDV in the steady-state, but the utility of this measurement, EDVsv, during dynamic changes in preload has not been examined. This study was undertaken to validate EDVsv during preload reduction. The utility of compliance data based on EDVsv was also examined. Methods: Five anesthetized pigs (40–45kg) underwent median sternotomy and pericardiotomy. An ultrasound transit-time flow probe was placed on the ascending aorta to provide cardiac output (CO). A micromonameter provided LV EDP. LV short-axis cross sections (SACS) and ECGs were also obtained. These data were obtained during the steady-state and during inferior vena caval (IVC) occlusion. End-diastolic and end-systolic areas (EDA and ESA) were measured to obtain EFa. EDVsv was determined from CO, heart rate, and EFa during IVC occlusion. EDV in the steady-state (EDVe) was also determined using a three-plane echocardiography model. EDVe was compared to the corresponding EDA and that relation was used to derive EDVeda from EDAs measured during IVC occlusion. The pressure-EDVsv relation during the IVC occlusion was then compared to the pressure-EDVeda relation. Results: Correlation coefficients for linear and pressure-volume relation analysis generally ranged from 0.70 to 0.99. The two methods (EDVsv and EDAeda) for measuring LV EDV generated compliance curves with comparable α and β-values (p>0.05). The EDVsv method may facilitate real-time determination of LV mechanics. Accuracy and utility of EDVsv in these preliminary studies are acceptable and merit further investigation.

Surgical reconstruction of iliofemoral veins and the inferior vena cava for nonmalignant occlusive disease

Purpose: Venous reconstructions are rarely performed, and factors affecting long-term results of bypass grafts implanted in the venous system are not well defined. In this report we updated our experience. Methods: The clinical data of all patients who underwent venous reconstruction for iliofemoral or inferior vena caval (IVC) occlusion due to nonmalignant disease between January 1985 and June 1999 were retrospectively reviewed. Patients were classified, and outcomes were compared according to the guidelines of the Joint Vascular Societies. Results: Forty-two patients, 23 males and 19 females (mean age, 40 years; range, 16-81), underwent 44 venous reconstructions. Thirty-six patients had limb swelling or venous claudication, 38 had pain, and 14 had healed or active ulcers. The cause of obstruction was congenital in two and acquired in 40 (deep vein thrombosis, 25; trauma, 5; retroperitoneal fibrosis, 4; IVC occlusion devices, 4; others, 2). Eighteen patients underwent saphenous vein crossover grafts (Palma procedure), 17 had expanded polytetrafluoroethylene (ePTFE) grafts implanted (femorocaval, 8; iliocaval, 5; crossfemoral, 3; cavoatrial, 1), 6 patients had spiral vein grafts (5 iliac/femoral and 1 cavoatrial), and 1 underwent femoral vein patch angioplasty. Clinical follow-up averaged 3.5 years (median, 2.5), and graft follow-up with imaging studies averaged 2.6 years (median, 1.6). Seven patients were lost to follow-up. The secondary 3-year patency rate for all reconstructions was 62%. Palma procedures had a 4-year patency rate of 83%. The secondary patency rate of iliocaval and femorocaval ePTFE bypass grafts at 2 years was 54%. The secondary patency was lower in patients with an arteriovenous fistula (P =.023). All ePTFE grafts had a 45% patency rate at 2 years, not significantly different from saphenous vein grafts (83%, P =.16). Clinical scores improved with graft patency (median, 0.0 vs 1.5; P =.044). Conclusions: Venous reconstructions for iliofemoral or IVC obstruction offer 3-year patency rates of 62%. The Palma procedure with autologous saphenous vein had the best long-term patency, whereas long-term success with ePTFE was moderate. The use of an arteriovenous fistula to improve graft patency remains controversial. (J Vasc Surg 2001;33:320-8.)

Effect of acutely increased left ventricular afterload on work output from the right ventricle in conscious dogs

Objective: To determine the effect of acute increments in left ventricular afterload on the stroke work output of the right ventricle in vivo. Methods: After pharmacologic attenuation of autonomic reflexes, left and right ventricular pressure-volume data were obtained in 9 conscious dogs during vena caval occlusions performed before and during aortic constriction. Results: The relationship between right ventricular stroke work and end-diastolic volume during vena caval occlusion was highly linear (r = 0.97 ± 0.02), but the slope decreased by 20% ± 13% during aortic constriction sufficient to increase left ventricular mean ejection pressure by 25% ± 14% (P < .05). The volume-axis intercept remained constant. Similarly, the slope of the linear relationship between right ventricular free wall regional segment work and end-diastolic segment length declined by 22% ± 10% during aortic constriction (P < .05), without significant change in the length-axis intercept. The reduction in both global and regional right ventricular stroke work at any given preload with increased left ventricular afterload was due entirely to decreased right ventricular stroke volume and free wall shortening, because right ventricular mean ejection pressure was unchanged. Additional experiments were performed in 5 open-chest dogs to produce a greater reduction in left ventricular free wall shortening than observed with aortic constriction by transient constriction of the left circumflex coronary artery. However, this intervention had no effect on right ventricular free wall segment work output. Conclusion: Increased left ventricular afterload decreases global and regional right ventricular stroke work at any given preload, a direct, negative systolic ventricular interaction. (J Thorac Cardiovasc Surg 2001;121:116-24)

Influence of cyclic variation of right ventricular volume on left ventricular mechanical parameters measured with conductance catheter.

The conductance catheter is widely used for the continuous measurement of the left ventricular (LV) pressure-volume loops. Cyclical change of the right ventricular (RV) volume may alter the parallel conductance volume, thereby affecting the LV mechanical parameters. Using 8 open-chest adult mongrel dogs, multiple LV pressure-volume loops were obtained by 2 methods: first with a vena cava occlusion (VCO) method, which involved RV volume alteration, and second with a right-heart-bypass (RHB) preparation, which decompressed the right ventricle completely. The slope of the end-systolic pressure-volume relation (Ees), the end-systolic volume associated with the end-systolic pressure of 100 mmHg (V100,es), stiffness constant (beta), and the end-diastolic volume associated with the end-diastolic pressure of 9 mmHg (V9,ed) were calculated from each loop. There was minimal influence from RV volume alteration on systolic-phase indices [Ees (VCO method, 6.37 +/- 1.91 mmHg/ml; RHB preparation, 6.60 +/- 1.66mmHg/ml; p=0.356), and V100,es (VCO method, 18.4 +/- 9.3ml; RHB preparation, 17.8 +/- 9.0 ml; p=0.681)], but there was a significant influence on diastolic-phase indices [beta (VCO method, 0.0599 +/- 0.0152; RHB preparation, 0.0839 +/- 0.0150; p=0.007), and V9,ed (VCO method, 35.6 +/- 11.3 ml; RHB preparation, 31.9 +/- 12.3 ml; p=0.001)]. The increase in the RV volume in the diastolic phase increased the parallel conductance volume, causing overestimation of the LV diastolic volume measured by the conductance catheter.

Predicting systolic and diastolic aortic blood pressure and stroke volume in the intact sheep

We developed a mathematical model describing the interaction between the heart and the arterial system. The model was constructed and tested on basis of invasive hemodynamic data in six sheep. Data from a first group of three animals (49 cardiac cycles) were used to assess a template time-varying elastance curve for the left ventricle, while the baseline steady-state data of a second group of three animals were used to assess reference cardiac and arterial parameters in sheep. The model is fully characterized by nine parameters, which were converted into 6 dimensionless numbers using the Buckingham Π theorem. The model was then used to generate LV pressure and volume and aortic pressure and flow for 86 conditions obtained by varying parameters 50 to 200% of their reference value. Systolic (SBP) and diastolic (DBP) blood pressure and stroke volume (SV) were determined from these model-generated curves and multiple linear regression analysis yielded the following expressions: SBP= P isovolumic[0.638−0.0773 E max C+0.0507 RC/ T] ( r 2=0.89); DBP= P isovolumic [0.438–0.0712 E max C+0.0655 RC/ T] ( r 2=0.88) and SV=LVEDV [1.265–1.040 LVEDV/(LVEDV− V d)+0.125 E max C–0.0777 RC/ T] ( r 2=0.93) with P isovolumic= E max(LVEDV− V d), E max and V d being the slope and intercept of the end-systolic pressure–volume relation, R and C the total peripheral resistance and compliance, LVEDV the left ventricular end-diastolic volume, and T the cardiac cycle length. These expressions were validated using data from the second group of three animals obtained during vena cava occlusion at baseline and during administration of dobutamine (61 cycles). The correlation between measured and predicted values was 0.98, 0.97 and 0.92 for SBP, DBP and SV, respectively. Compared to the measured values, SBP and DBP were, on average, underestimated by 5 and 6 mmHg, respectively, and SV overestimated by 1.4 ml. We conclude that the derived expressions for blood pressure and stroke volume remain valid in the intact sheep for various hemodynamic conditions, and, taking into account their dimensionless form, may hold in other species and in humans.

Limitations of unidimensional indexes of right ventricular contractile function in conscious dogs

Objective: Our goal was to examine the validity of unidimensional indexes of right ventricular contractile performance in vivo. Methods: Unidimensional indexes and global measurements of right ventricular volume and contractile performance were compared in 6 conscious dogs. Vena caval occlusions were performed before (control) and during pulmonary arterial or aortic constriction. Results: Moderately strong relationships were demonstrated between right ventricular septal–free wall indexes and global measurements of right ventricular end-diastolic and end-systolic volumes, stroke volume, stroke work, and the slope of the preload recruitable stroke work relationship, respectively, under control conditions (mean r2 range 0.69-0.94). These relationships were shifted significantly, however, by increased right ventricular afterload. Increased left ventricular afterload significantly shifted the relationships between right ventricular septal–free wall dimensions and end-diastolic and end-systolic volumes. Relationships between the corresponding regional right ventricular free wall segmental indexes and global measurements under control conditions were weaker (mean r2 range 0.12-0.65) and were significantly more sensitive to distortion by both increased right and left ventricular afterload, the effects of which were generally in opposite directions. These observations are consistent with significant ventricular interactive effects on the relationship between single right ventricular dimensions and right ventricular volume. Conclusion: Unidimensional right ventricular measurements are not reliable surrogates for right ventricular volume when assessing right ventricular contractile performance in the intact heart. (J Thorac Cardiovasc Surg 2000;120:302-12)