Difference in acid-base state between venous and arterial blood during cardiopulmonary resuscitation

We investigated the acid-base condition of arterial and mixed venous blood during cardiopulmonary resuscitation in 16 critically ill patients who had arterial and pulmonary arterial catheters in place at the time of cardiac arrest. During cardiopulmonary resuscitation, the arterial blood pH averaged 7.41, whereas the average mixed venous blood pH was 7.15 (P less than 0.001). The mean arterial partial pressure of carbon dioxide (PCO2) was 32 mm Hg, whereas the mixed venous PCO2 was 74 mm Hg (P less than 0.001). In a subgroup of 13 patients in whom blood gases were measured before, as well as during, cardiac arrest, arterial pH, PCO2, and bicarbonate were not significantly changed during arrest. However, mixed venous blood demonstrated striking decreases in pH (P less than 0.001) and increases in PCO2 (P less than 0.004). We conclude that mixed venous blood most accurately reflects the acid-base state during cardiopulmonary resuscitation, especially the rapid increase in PCO2. Arterial blood does not reflect the marked reduction in mixed venous (and therefore tissue) pH, and thus arterial blood gases may fail as appropriate guides for acid-base management in this emergency.     

Hyperglycaemia alters the endothelium-dependent relaxation of canine coronary arteries

The aim of the present study was to investigate the effects of experimental diabetes and hyperglycaemia per se on the endothelium-dependent relaxation of isolated canine coronary arteries and to analyse the possible involvement of the cyclooxygenase pathway in the alterations induced by hyperglycaemia. Rings from the left anterior descending coronary arteries of 18 metabolically healthy, six alloxan-diabetic and six insulin-treated alloxan diabetic dogs were set up for isometric tension recording. Diabetic coronaries as well as healthy vessels subjected to in vitro hyperglycaemia (25.5 mmol L-1 glucose) showed impaired (P < 0.05) relaxation to acetylcholine (3 nmol L-1-10 micromol L-1) compared with normoglycaemic, i.e. metabolically healthy and insulin-treated diabetic controls, either before or after indomethacin (3 micromol L-1) administration. The maximal dilation elicited by acetylcholine was further decreased (P < 0.05) by the cyclooxygenase inhibitor in the diabetic coronaries only. Relaxation to sodium nitroprusside did not differ among groups. These results suggest that hyperglycaemia may result in impaired endothelium-dependent dilation of coronary arteries. Diminished relaxation of diabetic coronaries is worsened by the inhibition of the synthesis of vasodilator cyclooxygenase products.     

Hydrogel-electrospun mesh composites for coronary artery bypass grafts

The aim of the present study was to investigate the potential of hydrogel-electrospun mesh hybrid scaffolds as coronary artery bypass grafts. The circumferential mechanical properties of blood vessels modulate a broad range of phenomena, including vessel stress and mass transport, which, in turn, have a critical impact on cardiovascular function. Thus, coronary artery bypass grafts should mimic key features of the nonlinear stress-strain behavior characteristic of coronary arteries. In native arteries, this J-shaped circumferential stress-strain curve arises primarily from initial load transfer to low stiffness elastic fibers followed by progressive recruitment and tensing of higher stiffness arterial collagen fibers. This nonlinear mechanical response is difficult to achieve with a single-component scaffold while simultaneously meeting the suture retention strength and tensile strength requirements of an implantable graft. For instance, although electrospun scaffolds have a number of advantages for arterial tissue engineering, including relatively high tensile strengths, tubular mesh constructs formed by conventional electrospinning methods do not generally display biphasic stress-strain curves. In the present work, we demonstrate that a multicomponent scaffold comprised of polyurethane electrospun mesh layers (intended to mimic the role of arterial collagen fibers) bonded together by a fibrin hydrogel matrix (designed to mimic the role of arterial elastic fibers) results in a composite construct which retains the high tensile strength and suture retention strength of electrospun mesh but which displays a J-shaped mechanical response similar to that of native coronary artery. Moreover, we show that these hybrid constructs support cell infiltration and extracellular matrix accumulation following 12-day exposure to continuous cyclic distension.     

Long-term outcomes of percutaneous coronary interventions within coronary artery bypass grafts

IntroductionThe long-term outcomes of percutaneous coronary interventions (PCIs) within coronary artery bypasses are still poor as compared to those within native coronary arteries. Thus, we aimed to assess predictors of long-term clinical outcomes after PCIs of coronary bypasses.Material and methodsWe enrolled 194 patients after PCIs of coronary artery bypasses at the mean age of 69.5 ±8.3 years (73.2% male). The primary study endpoint was a combination of target-vessel revascularization (TVR), target-lesion revascularization (TLR), myocardial infarction (MI), stroke, coronary artery bypass grafting (CABG) and death. The mean follow-up was 964 ±799.1 days and was completed among 156 patients. Multivariate analysis was used to assess determinants of study endpoints during follow-up. Moreover, we compared survival curves according to the type of PCI and presence of anti-embolic protection.ResultsThe primary endpoint of the study occurred in 59.7% of patients after the mean time of 669.6 ±598.7 days. The TVR occurred in 37.9% of individuals, TLR in 24.2%, MI in 26.3%, stroke in 4.2%, CABG in 2.1% and death in 30.5% of patients. In Cox multivariate analysis, PCI of two or more bypasses (p < 0.01), post-dilatation (p < 0.05) and no-reflow (p < 0.05) were the independent determinants of the primary study endpoint. No significant impact of anti-embolic protection devices on long-term outcomes was observed.ConclusionsPercutaneous coronary interventions of two or more bypasses, post-dilatation and no-reflow are predictors of worse outcome in patients undergoing PCI within coronary artery bypass grafts.     

Mesh-constricted varicose and dilated veins used as arterial bypass grafts.

To avoid non-autogenous vascular prostheses in coronary and peripheral vascular procedures, otherwise unusable dilated, varicose or thin-walled veins can be implanted as naturally endothelialized grafts after being calibrated by insertion into mesh tubes. In six sheep the 14 mm diameter jugular vein was inserted into a 12 cm long, 6 mm diameter Dacron mesh tube and implanted as a femoropopliteal graft. On the contralateral side the femoral vein with a maximal diameter of 7 to 8 mm was implanted. At control angiography after two months all grafts were patent, none of the wrapped grafts showed wrinkles or signs of anastomotic hyperplasia. Segments of wrapped veins were casted in paraffin under physiological pressure and cut transversely. In all cases the vein wall was pressed against the mesh tubes without forming folds. Mesh-wrapped varicose veins were used for three femorocrural and seven femoropopliteal reconstructions. All grafts showed a smooth flow surface at control angiography. Indentations occurred only at sites where thick-walled side branches had been ligated rather than oversewn. One popliteo-pedal reconstruction occluded after two months and one patient with a crural reconstruction died two months after surgery with a patent graft. The remaining grafts were patent after 11 (2-32) months. Oversized veins can be considerably constricted by tubes without forming wrinkles. By this technique varicose veins can be used as bypass grafts and in general vein grafts can be matched in size to the recipient vessel.     

Theoretical model for assessing haemodynamics in arterial networks which include bypass grafts

The paper presents a theoretical model which can be used to simulate a vascular network which includes loops and bypass grafts, a feature not possible with previous models. Using the linearised Navier-Stokes equations, the linearised equation of a uniform thick-walled viscoelastic tube, and the equation of continuity, the model is applied to a vascular network which includes a bypass graft. This method represents each segment of an artery or graft by a four-terminal-network whose A, B, C, D parameters are functions of the frequency and physical characteristics of the segment. The model predicts the flow and pressure waveforms at any point in the human arterial network very accurately when compared with data obtained from normal patients, patients with arterial stenoses and for hypertensive patients. The model also gives results which are in close agreement with hydraulic experimental data for the input impedance of systems with bypass loops.     

Intimal hyperplasia and hemodynamic factors in arterial bypass and arteriovenous grafts: a review

Stenosis at the graft–vein junction caused by intimal hyperplasia (IH) is the major cause of failure of vascular access grafts used for hemodialysis. There is a strong relationship between hemodynamic factors and formation of IH. The hemodynamic pattern and the location of IH are different in arterial bypass grafts (ABGs) compared with arteriovenous grafts (AVGs). In an ABG, end-to-side anastomosis of the expanded polytetrafluoroethylene graft and artery produces hemodynamic changes around the junction. IH develops at the arterial floor and the toe and heel of the distal anastomosis. Low shear stress and oscillating shear forces at the arterial floor and the heel plus a high wall sheer stress (WSS) gradient at the toe probably promote IH development. Compliance mismatch between the graft and artery causes turbulence that may contribute to IH formation. The blood flow rate in AVGs is 5–10 times greater than that in ABGs. High flow causes turbulence that injures endothelial cells and eventually results in IH. The peak WSS in AVGs is about 6N/m², much higher than that in ABGs. Excessively high WSS may effect IH formation in AVGs. Several venous cuff or patch anastomotic designs have been used in attempts to regulate hemodynamic factors in grafts. In ABGs, these designs appear to help decrease IH formation. In AVGs, however, they generally have not improved patency rates. In a high-flow system such as an AVG, more drastic changes in anastomotic design may be required.     

Difference in effect of inhibitors of energy metabolism on endothelium-dependent relaxation of rat pulmonary artery and aorta

Previous studies have suggested that systemic artery endothelial cell production of the nitrovasodilator endothelium-derived relaxing factor (EDRF) is dependent upon oxidative energy production. This study was undertaken to test if pulmonary artery (PA) EDRF has a similar requirement for oxidative phosphorylation. The effects of inhibitors of oxidative phosphorylation and glycolysis on endothelium-dependent relaxation were studied in rat aortic and PA rings. In aortic rings, 0.1 microM rotenone and 0.1 microM antimycin A, and, to a lesser extent, 50 mM 2-deoxyglucose, inhibited endothelium-dependent relaxation to acetylcholine and adenosine diphosphate. Relaxation to the receptor-independent calcium ionophore A23187 was less severely affected, and relaxation to the direct smooth muscle dilator sodium nitroprusside was unaffected. The inhibitors had much less effect on PA relaxation, decreasing the potency but not the efficacy of the endothelium-dependent dilators. These results suggest that the dependence on oxidative energy production for endothelium-dependent relaxation may differ between the systemic and pulmonary vascular beds, and that in pulmonary arterial endothelium, oxidative energy production may not be required for receptor-mediated production and/or release of EDRF. The resistance of PA endothelium to decreases in oxidative energy production may contribute to the normally low tone maintained in this circuit in vivo.     

beta-Adrenergic relaxation and cAMP kinase activation in coronary arterial smooth muscle

If beta-adrenergic relaxation of smooth muscle is partly mediated by the adenosine 3',5'-cyclic monophosphate (cAMP) system, then beta-stimulation should be correlated to activation of cAMP-dependent protein kinase (cPK). Studies were performed with bovine coronary arterial strips to identify isozymic forms of cPK and to determine if beta-relaxation is correlated to activation of cPK (reflected by elevated ratios of cPK activity without cAMP to cPK activity with cAMP). Both ion exchange chromatography and a new electrophoretic technique revealed two cPK isozymes (types I and II). No change in cPK activity occurred in strips contracted with 30 mM KCl. In contrast, dose- and time-dependent relaxation during beta-stimulation with isoproterenol was highly correlated to parallel increases in cPK activity. Increased cPK activity was inhibited in assays performed with a specific inhibitor of cPK. Both relaxation and activation of cPK were abolished during beta-adrenergic blockade with propranolol. Relaxation by KCl removal or the ionophore R02-2985, unlike beta-mediated relaxation, did not increase cPK activity. These findings show that beta-mediated relaxation of isolated coronary arterial strips specifically activates cPK, and they support the hypothesis that beta-induced relaxation of vascular smooth muscle involves the cAMP system.     

Constrictive calcific pericarditis following coronary arterial bypass surgery

A case of postsurgical constrictive calcific pericarditis is reported. The unusual features of this case are the short interval (two months) from surgery to the development of pericarditis and the involvement of the coronary arterial grafts, resulting in tearing of the vessels and the death of the patient during decortication.     

In vivo validation of numerical prediction of blood flow in arterial bypass grafts

In planning operations for patients with cardiovascular disease, vascular surgeons rely on their training, past experiences with patients with similar conditions, and diagnostic imaging data. However, variability in patient anatomy and physiology makes it difficult to quantitatively predict the surgical outcome for a specific patient a priori. We have developed a simulation-based medical planning system that utilizes three-dimensional finite-element analysis methods and patient-specific anatomic and physiologic information to predict changes in blood flow resulting from surgical bypass procedures. In order to apply these computational methods, they must be validated against direct experimental measurements. In this study, we compared in vivo flow measurements obtained using magnetic resonance imaging techniques to calculated flow values predicted using our analysis methods in thoraco–thoraco aortic bypass procedures in eight pigs. Predicted average flow rates and flow rate waveforms were compared for two locations. The predicted and measured waveforms had similar shapes and amplitudes, while flow distribution predictions were within 10.6% of the experimental data. The average absolute difference in the bypass-to-inlet blood flow ratio was 5.4±2.8%. For the aorta-to-inlet blood flow ratio, the average absolute difference was 6.0±3.3%. © 2002 Biomedical Engineering Society. PAC2002: 8761Lh, 8719Uv     

The relative anatomy of the coronary arterial and venous systems

An anatomical understanding of human coronary arterial and venous systems is necessary for device development and therapy applications that utilize these vessels. We investigated the unique use of contrast‐CT scans from perfusion‐fixed human hearts for three‐dimensional visualization and analysis of anatomical features of the coronary systems. The coronary arterial and venous systems of eleven perfusion‐fixed human hearts were modeled using contrast‐CT and Mimics software. The coronary arteries that coursed near the major coronary veins, how close coronary arteries were to coronary veins, and the size of adjacent coronary arteries were recorded and analyzed. The majority of coronary veins were within 5 mm of a coronary artery somewhere along its length. Interventricular veins elicited the largest occurrence of overlaps. There was significant variability in the percentage of each vein that coursed within 0.5, 1, 2, and 5 mm of a nearby artery. The left marginal veins and anterior interventricular vein had the largest portion of the vein that coursed near a coronary artery. The right coronary artery most often coursed near the middle cardiac vein. The inferior veins of the left ventricle elicited the most variation in adjacent arteries. The left circumflex artery and/or branches of the circumflex artery coursed near the left marginal vein in all cases where there was an artery near the marginal vein. The wide variation of measurements reinforces the importance of a precise understanding of individualized cardiac anatomy in order to provide the highest quality care to cardiac patients. Clin. Anat. 27:1023–1029, 2014. © 2014 Wiley Periodicals, Inc.     

Immunocytochemical features of obstructed saphenous vein coronary artery bypass grafts.

The peroxidase-immunoperoxidase immunocytochemical method was used on 27 saphenous vein coronary artery bypass grafts, which had been resected because of recurrent angina, to identify in situ cellular and humoral elements possibly associated with graft occlusion. Immunostaining was performed on paraffin wax embedded control saphenous vein and graft sections incubated directly with primary antibodies against von Willebrand antigen (vWFAg), fibronectin, fibrinogen, leucocyte common antigen (LCA), lysozyme, vimentin, desmin, platelet factor 4, and thrombospondin. Antigens were visualised by a chromogen providing an orange-red immunoprecipitate at the site of epitope localisation. The intraluminal, amorphous exudate present in most grafts was not composed simply of fibrin or fibrinogen, as previously thought, but was a multiprotein complex including wWFAg, fibronectin, thrombospondin and platelet factor 4. Along with macrophages, these components probably enter the graft after haemodynamic, physical, and chemical injury to, and disruption of, the endothelial cell. Progressive myointimal proliferation and fibrosis of these grafts may be local repetitive responses to macrophages and platelets, cells previously known to participate in vascular disease.     

高血糖症对大鼠血管内皮舒张功能的影响

目的：复制高血糖症动物模型，研究高糖对大鼠血管内皮舒张功能的影响及其机制。方法：采用血管功能检测、组织培养及放射免疫分析方法。结果：①高血糖组血管乙酰胆硷依赖性血管舒张反应明显降低（Ｐ＜００１）；②高血糖组血浆ＮＯ－２含量、主动脉一氧化氮合成酶（ＮＯＳ）活性及环磷酸鸟苷（ｃＧＭＰ）含量明显低于对照组（Ｐ＜００５，Ｐ＜００１）。结论：长期高血糖症可引起血管内皮源性血管舒张因子／一氧化氮（ＥＤＲＦ／ＮＯ）系统出现严重障碍，从而降低了血管舒张功能     

Abnormal endothelium-dependent vascular relaxation in patients with essential hypertension

BACKGROUND. Endothelium regulates vascular tone by influencing the contractile activity of vascular smooth muscle. This regulatory effect of the endothelium on blood vessels has been shown to be impaired in atherosclerotic arteries in humans and animals and in animal models of hypertension. METHODS. To determine whether patients with essential hypertension have an endothelium-dependent abnormality in vascular relaxation, we studied the response of the forearm vasculature to acetylcholine (an endothelium-dependent vasodilator) and sodium nitroprusside (a direct dilator of smooth muscle) in 18 hypertensive patients (mean age [+/- SD], 50.7 +/- 10 years; 10 men and 8 women) two weeks after the withdrawal of antihypertensive medications and in 18 normal controls (mean age, 49.9 +/- 9; 9 men and 9 women). The drugs were infused at increasing concentrations into the brachial artery, and the response in forearm blood flow was measured by strain-gauge plethysmography. RESULTS. The basal forearm blood flow was similar in the patients and controls (mean +/- SD, 3.4 +/- 1.3 and 3.7 +/- 0.8 ml per minute per 100 ml of forearm tissue, respectively; P not significant). The responses of blood flow and vascular resistance to acetylcholine were significantly reduced in the hypertensive patients (P less than 0.0001); maximal forearm flow was 9.1 +/- 5 ml per minute per 100 ml in the patients and 20.0 +/- 8 ml per minute per 100 ml in the controls (P less than 0.0002). However, there were no significant differences between groups in the responses of blood flow and vascular resistance to sodium nitroprusside. Because the vasodilator effect of acetylcholine might also be due to presynaptic inhibition of the release of norepinephrine by adrenergic nerve terminals, the effect of acetylcholine was assessed during phentolamine-induced alpha-adrenergic blockade. Under these conditions, it was also evident that the responses to acetylcholine were significantly blunted in the hypertensive patients (P less than 0.03). CONCLUSIONS. Endothelium-mediated vasodilation is impaired in patients with essential hypertension. This defect may play an important part in the functional abnormalities of resistance vessels that are observed in hypertensive patients.