Restitution Of Blood Flow Research Articles

Factors influencing recanalization of thrombotic venous occlusions.

The outcome of a thrombotic vessel occlusion is related to the resolution of thrombus and restitution of blood flow. Thrombus formation simultaneously activates an enzymatic process that mediates endogenous fibrinolysis to maintain vessel patency. The balance between coagulation and fibrinolysis determines the extent of thrombus formation, its resolution, and clinical outcome. Endogenic fibrinolysis is frequently unable to overcome coagulation and to resolve the thrombus. Therefore, for a complete resolution of thrombus in an acute phase, exogenic fibrinolytic agents are needed. Currently, tissue plasminogen activator (tPA) is most frequently used for therapeutic thrombolysis. Also, heparins, particularly low-molecular-weight heparins and direct oral anticoagulants which are known as anticoagulant drugs, have some pro-fibrinolytic properties. Besides the extent and age of a clot, different other factors influence the lysis of thrombus. Thrombus structure is one of the most important determinants of thrombus lysis. The concentration of thrombolytic agent (tPA) around and inside of thrombus importantly determines clot lysis velocity. Further, flow-induced mechanical forces which stimulate the transport of thrombolytic agent into the clot influence thrombolysis. Inflammation most probably represents a basic pathogenetic mechanism of activation of coagulation and influences the activity of the fibrinolytic system. Inflammation increases tissue factor release, platelet activity, fibrinogen concentration and inhibits fibrinolysis by increasing plasminogen activator inhibitor 1. Therefore, recanalization of a thrombotic vessel occlusion is inversely related to levels of some circulating inflammatory agents. Consequently, inhibition of inflammation with anti-inflammatory drugs may improve the efficacy of prevention of thromboembolic events and stimulate recanalization of thrombotic occlusions of veins.

Abstract 16907: A Light-powered Symbiosis With a Primordial Chloroplast Attenuates Myocardial Injury in the Absence of Blood Perfusion

Objective: The treatment for acute myocardial infarction (MI) is prompt revascularization. Our goal is to develop a novel therapy that mimics perfusion, but is not reliant on restitution of blood flow. We hypothesized that targeted delivery of a photosynthetic agent to the ischemic heart would restore myocardial energetics, attenuate damage, and improve long-term performance. Methods: Ten-week old male Wistar rats were used for the ischemia-reperfusion model. The left anterior descending artery (LAD) was temporarily ligated 2mm below the left atrial appendage via a left thoracotomy. Following ligation, animals were randomized to receive direct intramyocardial injection of 200μL PBS (n=7), 10x10 6 photosynthetic Synechecoccus elongatus (SE) of equivalent volume (n=10), or sham surgery (n=7). A light source illuminated the ischemic region for 1 hr after injection. The LAD tourniquet was subsequently removed and the heart reperfused. Ventricular function, geometry, and hemodynamics were assessed 4 weeks after surgery with MRI and LV catheterization. Results: Myocardial injury was attenuated by the photosynthetic agent: troponin-I concentration in peripheral blood was significantly lower in SE treated animals compared with controls 24 hrs post MI (6.5±4.8 vs. 16.5±10.5 ng/mL, P =0.05). Four weeks after MI, the mean LV ejection fraction was significantly greater in SE treated rats compared with controls (36.9±4.7 vs. 48.3±10.5%, P =0.02). Similarly, SE treated animals demonstrated a decreased end-systolic volume (327±133 vs. 487±140 μL, P =0.03) and a steeper slope of the end-systolic pressure-volume relationship (0.35±0.12 vs. 0.19±0.08, P =0.01). Histologic analyses revealed no evidence of intramyocardial abscess formation or persistent SE. Furthermore, the photosynthetic agent prevented upregulation of genes associated with hypoxia (downregulated Hsp-1b 11 fold). Conclusions: Delivery of a photosynthetic agent to ischemic myocardium creates a localized symbiotic relationship that safely attenuates myocardial injury and improves long-term ventricular function in a rat model of ischemia-reperfusion. Energizing myocardium with light in the absence of perfusion is a completely novel strategy for treating cardiac ischemia.

Mannitol infusion immediately after reperfusion suppresses the development of focal cortical infarction after temporary cerebral ischemia in gerbils

Previously we found that, after temporary cerebral ischemia, microvasculogenic secondary focal cerebral cortical ischemia occurred, caused by microvascular obstruction due to compression by swollen astrocytic end-feet, resulting in focal infarction. Herein, we examined whether mannitol infusion immediately after restoration of blood flow could protect the cerebral cortex against the development of such an infarction. If so, the infusion of mannitol might improve the results of vascular reperfusion therapy. We selected stroke-positive animals during the first 10 min after left carotid occlusion performed twice with a 5-h interval, and allocated them into four groups: sham-operated control, no-treatment, mannitol-infusion, and saline-infusion groups. Light- and electron-microscopic studies were performed on cerebral cortices of coronal sections prepared at the chiasmatic level, where the focal infarction develops abruptly in the area where disseminated selective neuronal necrosis is maturing. Measurements were performed to determine the following: (A) infarct size in HE-stained specimens from all groups at 72 and 120 h after return of blood flow; (B) number of carbon-black-suspension-perfused microvessels in the control and at 0.5, 3, 5, 8, 12 and 24 h in the no-treatment and mannitol-infusion groups; (C) area of astrocytic end-feet; and (D) number of mitochondria in the astrocytic end-feet in electron microscopic pictures taken at 5 h. The average decimal fraction area ratio of infarct size in the mannitol group was significantly reduced at 72 and 120 h, associated with an increased decimal fraction number ratio of carbon-black-suspension-perfused microvessels at 3, 5 and 8 h, and a marked reduction in the size of the end-feet at 5 h. Mannitol infusion performed immediately after restitution of blood flow following temporary cerebral ischemia remarkably reduced the size of the cerebral cortical focal infarction by decreasing the swelling of the end-feet, thus preventing the microvascular compression and stasis and thereby microvasculogenic secondary focal cerebral ischemia.

Blood flow dynamics in reconstructed auricles

Ear reconstruction with autologous rib cartilage is performed in stages. Restitution of blood flow between the separate stages is crucial to obtain a good result. Laser Doppler perfusion imaging (LDPI) and local temperature were measured in reconstructed and normal ears in response to indirect heating. Ten persons who had had a unilateral ear reconstruction were included in the study. At a minimum, 157 days had passed since the last operation. LDPI showed no difference in blood flow between the reconstructed ear and the normal ear, neither before nor after indirect heating. The upper part of the normal ear was slightly cooler than the corresponding part in the reconstructed ear. Indirect heating caused an increase of LDPI-values and temperatures in the upper, middle, and lower part of the ear both in the reconstructed ear and the normal one. Skin blood flow recovers after 3-stage ear reconstruction and shows normal dynamic response upon indirect heating.

High-Density Lipoproteins and Their Constituent, Sphingosine-1-Phosphate, Directly Protect the Heart Against Ischemia/Reperfusion Injury In Vivo via the S1P 3 Lysophospholipid Receptor

All treatments of acute myocardial infarction are aimed at rapid revascularization of the occluded vessel; however, no clinical strategies are currently available to protect the heart from ischemia/reperfusion injury after restitution of blood flow. We hypothesized that some of the cholesterol transport-independent biological properties of high-density lipoprotein (HDL) implied in atheroprotection may also be beneficial in settings of acute myocardial reperfusion injury. In an in vivo mouse model of myocardial ischemia/reperfusion, we observed that HDL and its sphingolipid component, sphingosine-1-phosphate (S1P), dramatically attenuated infarction size by approximately 20% and 40%, respectively. The underlying mechanism was an inhibition of inflammatory neutrophil recruitment and cardiomyocyte apoptosis in the infarcted area. In vitro, HDL and S1P potently suppressed leukocyte adhesion to activated endothelium under flow and protected rat neonatal cardiomyocytes against apoptosis. In vivo, HDL- and S1P-mediated cardioprotection was dependent on nitric oxide (NO) and the S1P3 lysophospholipid receptor, because it was abolished by pharmacological NO synthase inhibition and was completely absent in S1P3-deficient mice. Our data demonstrate that HDL and its constituent, S1P, acutely protect the heart against ischemia/reperfusion injury in vivo via an S1P3-mediated and NO-dependent pathway. A rapid therapeutic elevation of S1P-containing HDL plasma levels may be beneficial in patients at high risk of acute myocardial ischemia.

The effect of inducible nitric oxide synthase inhibitor on microvascular permeability after cerebral ischemia/reperfusion

Our objective was to study the effect of inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine (AG) on microvascular permeability after cerebral ischemia/reperfusion (I/R) injury. Cerebral I/R injury was produced by occlusion of both the carotid arteries for 60 min with restitution of blood flow for 60 min. AG (200 mg/kg) was intraperitoneally administrated 5 min before the onset of ischemia and again 5 min before reperfusion. Microvascular permeability was evaluated by 0.75% sodium fluorescein (FINa) extravasation during early 300 s. Cerebral I/R injury increased the permeability of microvessel to fluorescein and the concentration of fluorescein outside of microvessels was significantly higher than that in microvessels after 110 s. However, after AG administration, FINa extravasation appears much faster. From 80 s on, the fluorescence intensity outside is higher. I/R increased microvascular permeability. Nitric oxide derived from iNOS may maintain microvascular permeability at the early stage after I/R.

Relationship between hypoxemia and fibrillation potential firing rate in denervated muscle

The effects of hypoxia and ischemia on the firing rate of fibrillation potentials in denervated rat muscle were examined. We recorded electromyograms from the denervated left extensor digitorum longus muscle. Hypoxia was induced by low-oxygen ventilation. Ischemia was established by ligating the abdominal aorta and inferior vena cava, with or without extracorporeal hindlimb perfusion. The fibrillation potential firing rate correlated with the PaO2 (P < 0.0001) and temperature (P = 0.0001). Fibrillation potentials disappeared after the initiation of ischemia and reappeared after restitution of blood flow; they disappeared during ischemia with extracorporeal perfusion. The attenuation curves for the firing rate of fibrillation potentials during ischemia were well-described by exponential curves, but there was no significant difference in the attenuation constants for circulatory arrest and perfusion with a physiologic salt solution. We conclude that the fibrillation potential firing rate is proportional to oxygen supply, presumably because of the rate of aerobic metabolism. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 933–936, 1999

Extracellular glucose concentration in mammalian brain: continuous monitoring of changes during increased neuronal activity and upon limitation in oxygen supply in normo-, hypo-, and hyperglycemic animals

The concentration of extracellular glucose in anesthetized rat brain was measured continuously with two types of substrate-specific microelectrodes in a number of physiological and pathological conditions. Extracellular glucose level increased in hyperglycemia and decreased in hypoglycemia, paralleling the changes in blood sugar. Increased neuronal activity and in particular spreading depression, evoked triphasic alterations in extracellular glucose concentration: an initial rapid fall was followed by an equally swift overshoot above the baseline and a subsequent return to it. Limitation in O2 supply led to a decline in extracellular content of glucose: respiration with 5% O2 reduced the level by 7-20% and that with 3% O2 by 75-85%. Decreases to undetectable concentrations were seen in ischemia despite the use of an oxygen-insensitive microglucose sensor. Restoration of oxygen supply to the brain was accompanied by increases in extracellular glucose content above the original normoxic level, which returned to baseline values after 10-15 min. In hyperglycemic animals ischemia-induced leakage of K+ was delayed while the rate of recovery to control levels after restitution of blood flow was enhanced. It is concluded that continuous monitoring of glucose with glucose-specific microelectrodes provides a new and important insight into brain energy metabolism.

Magnetic resonance imaging of thrombosed dural sinuses.

Magnetic resonance imaging should have the potential to replace angiography in the diagnosis of dural sinus thrombosis. Concerning time-dependent signal changes of the thrombus, we intended to develop a standardized examination protocol for routine use in suspected dural sinus thrombosis. The time-dependent signal changes of thrombosed dural sinuses were studied in 23 consecutive patients by multiplanar spin-echo and flow-sensitive sequences. Signal intensities and thrombus homogeneity were graded and related to the time after clinical onset and the results of the magnetic resonance angiography. Four stages of the thrombus evolution could be observed. The acute thrombosis (days 1 to 5) appeared strongly hypointense in T2-weighted images and isointense in spin density- and T1-weighted images. In the subacute stage (up to day 15) the thrombus signal was strongly hyperintense in T1- and T2-weighted images. The third stage began in the third week after clinical onset. The thrombus signal was decreased in all sequences and showed an increasing inhomogeneity. The fourth (late) stage was characterized by either the restitution of blood flow or the persistence of a residual thrombus. Each stage requires a different diagnostic approach. With the combined use of spin-echo and gradient-echo sequences, it is possible to make the diagnosis of acute thrombosis; in the second stage, multiplanar spin-echo sequences are sufficient. Diagnosis of dural sinus thrombosis can be established accurately with magnetic resonance imaging in the first two stages. However, the diagnosis of the later stages is difficult because of inhomogeneous signs of recanalization and flow phenomena. Therefore, a suspected older dural sinus thrombus still requires intra-arterial angiography as the primary diagnostic tool.

Relationship between ions and energy metabolism: cerebral calcium movements during ischaemia and subsequent recovery.

Intra- and extra-cellular concentrations of calcium were measured in hippocampal neurons of areas CA1 and CA3 during 8 min ischaemia and short-term (up to 60 min) recovery. During an ischaemic insult, [Ca2+]i increased progressively and [Ca2+]e decreased. There were large interneuronal differences, although, in general, rises in [Ca2+]i were much larger in area CA1 than in CA3. Restitution of blood flow was followed by movements of calcium in the directions opposite to those seen during ischaemia: [Ca2+] in the extracellular space gradually rose whereas that inside neurones fell. Within 30-60 min, calcium balance was restored to the original pre-ischaemic level. It is postulated that (i) large increases in [Ca2+]i in cerebral neurones during ischaemia are related to the high density of pathways on neurones that allow calcium entry; (ii) differences in the amount of calcium accumulated during periods of oxygen deprivation between neurones of the Ca1 and CA3 regions are linked to the level of glutamatergic input (and hence excitatory synapses) that the two areas receive; (iii) restitution of blood flow and consequent rapid restoration of ATP synthesis permit reactivation of calcium-eliminating mechanisms. These latter involve especially sequestration by the mitochondria and extrusion by the plasma membrane Ca pump, which restore the low cytoplasmic [Ca2+].

Surgical treatment versus thrombolysis in acute arterial occlusion: A randomised controlled study

Thrombolytic treatment has been tried in various forms for acute limb ischaemia with varying degrees of success but is also often accompanied by bleeding problems. The present investigation compares the effect of surgical thrombectomy (TE) and thrombolysis (TL) using recombinant tissue plasminogen activator (rt-PA). Twenty patients with a need for intervention owing to ischaemia lasting more than 24 h but less than 14 days were included. Patients randomised to TE were operated under epidural anaesthesia and patients in the TL group received 30 mg rt-PA during a 3 h period through a catheter placed into the thrombus and advanced as lysis was achieved. Thrombectomy resulted in an immediate restitution of blood flow in six out of nine cases, in three cases a bypass procedure was performed, and one of these failed with a resultant amputation. Thrombolysis gave a good primary result in six cases which lasted in four of them. Three had a subsequent percutaneous transluminal angioplasty. Partial lysis was seen in two cases and a further two failed. Five went to surgery with three bypass and two fogarty procedures being necessary. There was no hospital mortality and there were no bleeding complications due to the rt-PA treatment in this series. In 19 out of 20 patients the circulation was re-established. Appropriate handling of acute ischaemic conditions implies the use of both thrombolysis and appropriate surgical procedures, including distal bypass grafts.

Susceptibility of feline spinal cord energy metabolism to severe incomplete ischemia.

Feline spinal cords were subjected to 10 to 30 minutes of severe incomplete ischemia (average reduction in blood flow of 92%) with and without 90 minutes of recirculation, and the L-2 segment was analyzed for high-energy phosphates and certain glycolytic metabolites. Spinal cord tissue lactic acid levels were stepwise elevated, and adenosine triphosphate (ATP), phosphocreatine (P-creatine), and glucose were progressively consumed by increasing durations of ischemia. However, upon restoration of blood flow, there was extensive recovery of energy metabolites and normalized lactic acid, demonstrating resumption of mitochondrial oxidative metabolism. These data indicate that the spinal cord can tolerate at least 30 minutes of severely reduced blood flow before recovery of energy metabolism is significantly impaired upon restitution of blood flow.

Metabolic Changes in Blood and Skeletal Muscle in Reconstructive Aortic Surgery

The declamping shock has been attributed to reactive hyperemia with pooling of blood in the legs, metabolic acidosis following lactate accumulation in the ischemic leg muscles and hyperkalemia. We have studied eight patients undergoing arterial reconstruction with temporary aortic occlusion, in six cases because of obstructive arteriosclerotic disease and in two cases for aortic aneurysm. Muscle biopsies from the lateral vastus muscle as well as blood samples from the iliac vein, the superior caval vein and the radial artery were taken before clamping of the aorta, just before declamping, and 20 minutes after restitution of leg blood flow. ATP, ADP, AMP, phosphocreatine (PCr), creatine (Cr), glycogen, glucose, lactate, pyruvate and NH4+ from the immediately frozen muscle biopsies as well as lactate and pyruvate in the iliac vein and central venous blood were determined with an enzymatic, fluorometric technique. Only one patient reacted with a temporary hypotension at declamping. Arterial pH was unaffected during the operation, and no hyperkalemia was noted. During clamping of the aorta an increased lactate/pyruvate ratio in muscle indicated tissue hypoxia. Energy charge (EC) was, however, unchanged and the adenylate pool was maintained possibly due to a decrease in PCr. In spite of the restitution of blood flow after declamping of the aorta, no normalization of the metabolic state was seen, not even 20 minutes after the release of the clamp. EC was still unchanged but a significant decrease of both the adenylate and creatine pools was seen. These findings might indicate a damage of the mitochondria and the cellular membranes in skeletal muscle after temporary arterial occlusion.