Partial Vascular Occlusion Research Articles

Acute gastric lesions induced by the administration of histamine to rats with partial vascular occlusion: evidence for the gastroprotective effect of prostaglandin

Histamine is not only a potent stimulator of gastric acid secretion, but it also plays a central role in gastroduodenal ulcerogenesis. In the present study we tested the effect of pre-treatment with exogenous prostaglandin E(2) (PGE(2)) in a new rat model of experimental gastric ulcers induced by combination of histamine and gastric ischemia. In male Wistar rats, a chronic ischemia of gastric mucosa was induced via the clamping of the left gastric artery and vein (L-AV) in combination with pylorus ligation. The following treatment groups of rats (6 rats/group) were investigated: 1) histamine alone (40 mg/kg twice s.c.); 2) vehicle (saline) followed 30 min later by gastric mucosal L-AV ischemia and pylorus ligation combined with histamine (40 mg/kg twice s.c.) and 3) PGE(2) (5 microg/kg i.g.) followed 30 min later by gastric mucosal L-AV ischemia combined with histamine (40 mg/kg twice s.c.) and pylorus ligation. At 4 hr after the clamping of L-AV and pylorus ligation, the area of gastric lesions and gastric acid secretion was determined. Histamine treatment failed to produce gastric lesions, but when it was combined with ischemia, the widespread gastric lesions in the corpus mucosa, but not in the antrum, were observed. This damaging effect and decrease in the GBF were significantly attenuated by pretreatment with PGE(2). The present study demonstrates that gastric hypersecretion induced by histamine in combination with gastric mucosal ischemia results in gastric lesions which progress into chronic gastric ulcers.

Resistance exercise effects on blood glutathione status and plasma protein carbonyls: influence of partial vascular occlusion

Seven weight-trained males performed both light resistance with partial occlusion (LRO: 30% 1 RM) and moderate resistance (MR: 70% 1 RM) to failure to ascertain whether blood protein carbonyls (PC) and glutathione status was altered compared to partial occlusion (PO) in a counterbalanced fashion. PO was identical in duration to the LRO session and all sessions were on separate days. PC did not differ for the three conditions at PRE (0.05 nM mg protein(-1)). PC significantly increased for PO and MR over time and was greater than the LRO treatment at POST (0.13 nM mg protein(-1)). The GSSG/TGSH ratio at PRE did not differ across treatments (8%) whereas the ratio at POST was significantly elevated for PO and MR treatments (17%). In contrast, no change occurred for the LRO session at any time. These results indicate that MR to failure and PO can significantly increase blood oxidative stress but LRO did not elicit oxidative stress.

Comparison of hormone responses following light resistance exercise with partial vascular occlusion and moderately difficult resistance exercise without occlusion

Previous studies of contracting muscle with low loading and partial vascular occlusion demonstrated hypertrophy and strength adaptations similar to and exceeding those observed with traditional moderate to high resistance (Shinohara M, Kouzaki M, Yoshihisa T, and Fukunaga T. Eur J Physiol 77: 189-191, 1998; Takarada Y, Takazawa H, Sato Y, Takebayashi S, Tanaka Y, and Ishii N. J Appl Physiol 88: 2097-2106, 2000; Takarada Y, Sato Y, and Ishii N. Eur J Physiol 86: 308-314, 2002). The purpose of the study was to determine the anabolic and catabolic hormone responses to light resistance exercise combined with partial vascular occlusion. Three experimental conditions of light resistance with partial occlusion (LRO), moderate resistance with no occlusion (MR), and partial occlusion without exercise (OO) were performed by eight healthy subjects [mean 21 yr (SD 1.8)]. Three sets of single-arm biceps curls and single-leg calf presses were completed to failure with 1-min interset rest periods. Workloads of 30 and 70% one repetition maximum for each exercise were lifted for the LRO and MR trials, respectively. Blood samples were taken preexercise, postexercise, and 15 min postexercise for each experimental condition. Lactate increased significantly in the LRO and MR trials and was not significantly different from each other at any time point. Growth hormone (GH) increased significantly by fourfold from pre- to postexercise in the LRO session but did not change significantly during this time period in the MR and OO trials (8.3 +/- 2.3 vs. 2.1 +/- 1.2 and 2.6 +/- 0.94 microg/l; respectively, P < 0.05). There were no changes in resting total testosterone [T; mean 15.7 +/- 1.6 (SE) nmol/l], free testosterone (FT; 54.1 +/- 4.5 pmol/l), or cortisol (267.6 +/- 22 nmol/l) across all trials and times. In conclusion, with similar lactate responses, light exercise combined with partial vascular occlusion elicits a greater GH response than moderate exercise without occlusion but does not affect T, FT, or cortisol.

Partial Vascular Occlusion Significantly Altered RPE, Pain, and Lactate during Resistance Exercise

Recent studies utilizing partial vascular occlusion during resistance exercise demonstrated that low workloads with partial occlusion resulted in local muscular ischemia and subsequent increase in muscle hypertrophy similar to moderate/ heavy loads. Perceptual responses to an ischemic environment are unknown. PURPOSE: The purpose of the present investigation was to employ partial occlusion and describe how peripheral manipulation of muscle oxygen delivery impacted RPE, pain, and lactate levels. METHODS: Three exercise conditions of light resistance with partial occlusion (LRO), moderate resistance with no occlusion (MR), and partial occlusion without exercise (OO) were performed by 7 subjects (21.7 ± .5 yrs) once a week for three weeks. Three sets of single-arm biceps curls and single-leg calf presses with partial vascular occlusion by an inflatable cuff placed proximal to the working muscle were completed to failure, with one-minute interset rest periods. Workloads approximating 30% and 70% 1-RM for each exercise were performed for the LRO and MR trials. RPE and pain changes were assessed on a 0–10 scale, immediately after each set. RPE and pain were determined when they became noticeably greater and when RPE and pain reached a 6. The RPE and pain level of 6 correlates with more rapid increases in effort sense and pain. Blood samples were taken pre, post, and 15 minutes post-exercise to determine lactate (Lac). RESULTS:MANOVAs with Bonferroni corrections were performed on RPE and pain and demonstrated that both noticeable differences and reaching a rating of 6 on RPE and pain were significantly different per trial and exercises (P's<.001). Univariate tests demonstrated that MR and LRO trials were different than the OO trial and that only between the MR and LRO conditions were the ratings of 6 for pain not significantly different. Lac changed significantly and to a similar extent for both the LRO and MR trials (P < .01). CONCLUSIONS: Thus, light exercise combined with partial vascular occlusion elicits similar RPE and pain response compared to a moderate resistance exercise trial.Table

Hormonal Responses to Resistance Exercise with Partial Vascular Occlusion

Hormonal Responses to Resistance Exercise with Partial Vascular Occlusion

Point: The muscle metaboreflex does restore blood flow to contracting muscles

Imposed reductions in oxygen delivery to active skeletal muscle during dynamic exercise in conscious dogs evoke a powerful pressor response, termed the muscle metaboreflex. During submaximal work rates, the major mechanism used by this reflex is to increase cardiac output (CO), which generates a

Clinicopathologic study after submacular removal of choroidal neovascular membranes treated with verteporfin ocular photodynamic therapy

PurposeTo report the clinicopathologic findings after submacular removal of choroidal neovascular membranes (CNV) treated with verteporfin ocular photodynamic therapy. DesignInterventional case series. MethodsRetrospective review of eight eyes of eight patients who underwent submacular surgery for CNV after having previously received verteporfin ocular photodynamic therapy for presumed ocular histoplasmosis (one patient), age-related macular degeneration ([AMD] three patients) pathologic myopia (two patients), punctate inner choroiditis (one patient), and idiopathic CNV (one patient). All cases had undergone ocular photodynamic therapy with verteporfin using standard protocols. Six of eight patients suffered a submacular hemorrhage after ocular photodynamic therapy, and two of eight patients refused further ocular photodynamic therapy. All patients subsequently had submacular surgery with removal of the CNV. One membrane was routinely processed, sectioned, and stained with hematoxylin and eosin. Five membranes were stained with toluidine blue for light microscopic examination. Semithin (1.0 μm) sections were cut and stained with uranyl acetate-lead citrate for transmission electron microscopy. ResultsChoroidal neovascular membranes were removed at 3 days (presumed ocular histoplasmosis), 29 days (punctate inner choroiditis), 63 days (AMD, pathologic myopia), 66 days (AMD), 107 days (pathologic myopia), 116 days (AMD), and 152 days (idiopathic) after verteporfin ocular photodynamic therapy. Histopathologic and ultrastructural examination showed areas of vascular occlusion at 3 days that were not seen at later time points. All specimens had patent CNV. There were signs of vascular damage with extravasated erythrocytes and fibrin, pigment clumping in cells, and inflammatory cells in all but the 3-day specimen. ConclusionsThis case series presents data only from patients who refused repeat treatment with ocular photodynamic therapy or who developed submacular hemorrhage after initial photodynamic therapy. Histopathologic evaluation of CNV 3 days after verteporfin ocular photodynamic therapy showed partial vascular occlusion that was not present in later specimens. These later specimens demonstrated evidence of vascular damage. Verteporfin ocular photodynamic therapy does not appear to lead to permanent and complete occlusion of the CNV. Thus, treatments that lead to permanent closure of CNV without damage to the retinal pigment epithelium and sensory retina are still needed.

Does gender influence the strength and mechanisms of the muscle metaboreflex during dynamic exercise in dogs?

Ischemia of active skeletal muscle stimulates neuronal afferents within the muscle, which elicits a reflex increase in sympathetic nerve activity, systemic arterial pressure (SAP), and heart rate (HR), termed the muscle metaboreflex. We retrospectively investigated whether gender influences the activation of the muscle metaboreflex and the primary mechanisms used by this reflex, augmentation of cardiac output (CO) and peripheral vasoconstriction, using 15 female and 13 male chronically instrumented dogs exercising on a treadmill (3.2 km/h, 0% grade). Metaboreflex activation was achieved via progressive partial vascular occlusion of the terminal aorta during exercise. In both females and males, hindlimb ischemia elicited similar substantial increases in SAP (56.1 +/- 3.0 and 55.1 +/- 4.2 mmHg, respectively), HR (25.8 +/- 4.8 and 33.9 +/- 2.8 beats/min, respectively), and CO (1.39 +/- 0.3 and 1.64 +/- 0.2 liters, respectively) and a similar substantial decrease in renal vascular conductance (RVC; 42.7 +/- 4.9 and 42.9 +/- 5.3%, respectively). Both groups also demonstrated similar metaboreflex thresholds and sensitivities of SAP, HR, CO, and RVC. We conclude that the strength and mechanisms mediating the metaboreflex responses during dynamic exercise in dogs are not affected by gender.

Clinicopathologic effects of cryotherapy on hepatic vessels and bile ducts in a porcine model.

The proximity of a hepatic tumor to major vessels and bile ducts limits the use of cryotherapy because of the potential damage to these structures. However, the effects of cryotherapy on major hepatic vessels and bile ducts are not well understood. Nine pigs underwent laparotomy and intraoperative ultrasound to identify hepatic vessels larger than 5.0 mm. Cryotherapy consisting of two freeze-thaw cycles was performed, incorporating the identified vessel. In four pigs the Pringle maneuver was performed to determine the effects of partial vascular occlusion on the hepatic parenchyma and structures undergoing cryotherapy. The animals were sacrificed 30 days postoperatively, and the livers were processed for histologic examination. Eight of the nine livers had vessels larger than 5.0 mm incorporated into the iceball, with all vessels having evidence of infarction but remaining patent. All the livers had major bile ducts incorporated in the iceball, with eight having evidence of infarction. The Pringle maneuver had no real effect on the degree of vessel and bile duct infarction. There was no incidence of hepatic bleeding, liver fracture, bile leak, or hemobilia. Cryotherapy results in the infarction of major hepatic vessels and bile ducts but can be safely performed in the porcine model. Proximity of tumors to major vascular and biliary structures may not be a contraindication to the use of cryotherapy. Further studies are necessary to determine whether cryotherapy can be used in humans.

Muscle chemoreflex-induced increases in right atrial pressure.

When oxygen delivery to active muscle is too low for the ongoing rate of metabolism, metabolites accumulate and stimulate sensory nerves within the muscle leading to sympathetic activation (muscle chemoreflex). To date, studies on this reflex have focused primarily on its ability to increase arterial pressure or on the activity of the nerves that mediate this response. Clearly, a rise in cardiac output (CO) constitutes an important adjustment, because it increases the total blood flow available to be distributed among organs competing for flow. However, increments in heart rate and contractility provide limited means of raising CO because of the inverse relationship that exists between CO and right atrial pressure (RAP) in the intact circulation. Our goal was to test whether muscle chemoreflex activation, achieved via graded reductions in hindlimb blood flow by partial vascular occlusion, elicits peripheral vascular adjustments that raise RAP. In four conscious dogs exercising on a treadmill at 3.2 km/h 0% grade, RAP was well maintained during reflex activation despite increases in CO and arterial pressure that are expected to reduce RAP. Thus peripheral vascular adjustments elicited by the reflex successfully defend RAP in a setting where it would otherwise fall. To isolate the effects of the reflex on RAP, CO was maintained constant by ventricular pacing in conjunction with beta1-adrenergic blockade with atenolol. When the reflex was activated by reducing hindlimb blood flow from 0.6 to 0.3 l/min, RAP rose from 5.1 +/- 0.8 to 7.4 +/- 0.4 mmHg (P < 0.05) despite continued large (40 mmHg) increases in arterial pressure. During heavier exercise (6.4 km/h 10% grade) in five dogs with normal ventricular function, the reflex raised RAP from 5.7 +/- 0.9 to 6.6 +/- 0.8 mmHg (P < 0.05) despite increases in CO and arterial pressure. We conclude that the muscle chemoreflex is capable of eliciting substantial increases in RAP.

Muscle metaboreflex increases ventricular performance in conscious dogs.

Ischemia of active skeletal muscle stimulates neuronal afferents within the muscle, which elicits a reflex increase in systemic arterial pressure (SAP), heart rate (HR), and cardiac output (CO) termed the muscle metaboreflex. We investigated whether activation of the muscle metaboreflex elicits increases in ventricular performance using conscious, chronically instrumented dogs trained to run on a treadmill (3.2 km/h, 0% grade). The muscle metaboreflex was activated via progressive partial vascular occlusion of the terminal aorta during control experiments and with HR maintained constant via a pacemaker connected to ventricular electrodes (225 beats/min). In control experiments, hindlimb ischemia elicited substantial increases in SAP, HR, and CO (+53.9 +/- 4.3 mmHg, +32.4 +/- 4.5 beats/min, and +1.57 +/- 0.22 l/min, respectively; all changes P < 0.05), whereas stroke volume (SV) remained unchanged with reflex activation (control 45.9 +/- 2.3 vs. 46.1 +/- 2.4 ml, P > 0.05). During metaboreflex activation at constant HR, SV significantly increased such that the increases in CO and SAP were not significantly different from control experiments (+1.77 +/- 0.56 l/min and +57.4 +/- 3.8 mmHg, P > 0.05 vs. control experiments). No significant change in central venous pressure occurred in either experiment, indicating no Frank-Starling effect on SV. We conclude that muscle metaboreflex-induced increases in ventricular contractility act to sustain SV despite decreases in ventricular filling time due to the tachycardia such that the sustained SV coupled with the tachycardia elicits substantial increases in CO that contribute importantly to the reflex increase in SAP.

The clinical implications of hypophosphatemia following major hepatic resection or cryosurgery.

To determine the incidence and predisposing factors leading to postoperative hypophosphatemia after major hepatic surgery and the consequences of this electrolyte abnormality. A retrospective study. A university tertiary care referral center. Thirty-five consecutive patients undergoing either major hepatic resections or cryosurgery from July 1994 through January 1997 were retrospectively reviewed for the occurrence of hypophosphatemia and postoperative complications. Prolonged ventilatory support, intensive care unit and hospital stays, and the incidence of postoperative complications. The overall incidence of hypophosphatemia in our series was 21 (67%) of 35 with a mortality rate of 1 (2.8%) in 35. Mean operative time, estimated blood loss, partial vascular occlusion time, and transfusion requirements were similar between the hypophosphatemic and the nonhypophosphatemic groups. The presence of postoperative complications was significantly greater in the hypophosphatemic group (17 [80%] of 21) vs the nonhypophosphatemic group (4 [28%] of 14) (P<.05). The incidence of antacid use in the hypophosphatemic group (14 [66%] of 21) was significantly higher than the use in the nonhypophosphatemic group (2 [14%] of 14) (P<.05). Hypophosphatemia commonly occurs in major hepatic procedures. The presence of moderate hypophosphatemia is associated with the use of antacid therapy but no other perioperative or operative variables. The occurrence of hypophosphatemia correlates with an increased incidence of postoperative complications. Awareness of this entity can direct aggressive replacement of phosphates and avert the occurrence of severe hypophosphatemia and associated complications.

Effects of U-74389G, a novel 21-aminosteroid, on small intestinal ischemia and reperfusion injury in horses

Abstract Objective To determine the effects of the 21-amino-steroid, U-74389G, on reperfusion of the equine jejunum, using total (TVO) and partial (PVO) vascular occlusion during the ischemic period. Design TVO: 16 healthy horses were randomly allotted to 3 groups—4 horses received the vehicle alone, 6 horses received a low dosage (3 mg/kg of body weight), and 6 horses a high dosage (10 mg/kg) of U-74389G. PVO: 10 healthy horses were randomly allotted to 2 groups—5 horses received the vehicle alone, and 5 horses received the low dosage (3 mg/kg) of U-74389G. Procedure TVO was induced for 1 hour followed by 2 hours of reperfusion. During PVO, blood flow was reduced to 20% of baseline for 2 hours, followed by 2 hours of reperfusion. For both models, either the vehicle alone or the drug was given 15 minutes prior to reperfusion. Samples were obtained before, during, and after ischemia for determination of myeloperoxidase (MPO) activity, malondealdehyde (MDA) concentration, concentration of conjugated dienes (PVO experiment only), and morphometric analysis. Results TVO: tissue concentration of MDA and MPO activity were not altered in any group by ischemia or reperfusion. During ischemia, mucosal volume and surface area were reduced. After reperfusion, no further reduction occurred. After initial decrease in submucosal volume during ischemia, there was a significant increase after reperfusion in the vehicle-only group (P &lt; 0.05). PVO: there were no alterations in the concentration of either MDA or conjugated dienes. There was a significant increase in the activity of MPO during ischemia and reperfusion (P&lt; 0.05). These effects were similar for the vehicle-only and drug groups. During ischemia, there was a significant decrease in mucosal surface area and volume (P&lt; 0.05), that was continued during reperfusion for the vehicle-only group (P&lt; 0.05). Submucosal volume increased during reperfusion (P&lt; 0.05). Serosal volume was increased during ischemia and reperfusion. Conclusions and Clinical Relevance Reduced blood flow during ischemia (PVO group) caused continued loss in mucosal volume and surface area during reperfusion. At the dosage given, the 21-aminosteroid, U-74389G, was not effective in preventing continued reduction in mucosal volume and surface area after restoration of blood supply in the horses subjected to reduced blood flow. (Am J Vet Res 1996; 57:762–770)

Is the muscle metaboreflex important in control of blood flow to ischemic active skeletal muscle in dogs?

Ischemia of active skeletal muscle induces a reflex increase in sympathetic activity, heart rate, cardiac output, and arterial pressure, termed the muscle metaboreflex. Whether this pressor response contributes importantly in the regulation of blood flow to the ischemic active skeletal muscle is not well understood. If the pressor response is achieved without substantial vasoconstriction in the ischemic muscle, this increase in arterial pressure would act to improve muscle blood flow. Dogs performed treadmill exercise at mild (3.2 km/h, 0% grade) and moderate (6.4 km/h, 10% grade) workloads. During each workload, resistance to blood flow in the hindlimbs (Rh) was increased via graded partial inflation of a vascular occluder implanted on the terminal aorta. The closed-loop gain of the muscle metaboreflex (Gcl) was calculated, based on the steady-state changes in terminal aortic blood flow (TAQ). If no pressor response occurred, then TAQ should decrease in proportion to the increase in total Rh (the sum of resistance due to partial vascular occlusion and hindlimb vascular resistance); i.e., no reflex restoration of hindlimb blood flow would occur. However, with a reflex increase in systemic arterial pressure, TAQ could rise above the level predicted on the basis of the increase in Rh. We observed that with the initial increase in Rh during mild exercise, Gcl was not significantly different from zero (P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Translocation and Its Relationship to Visceral Blood Flow, Gut Mucosal Ornithine Decarboxylase Activity, and DNA in Pigs

The relationship of bacterial translocation to gut blood flow and mucosal integrity was studied in pigs. Three groups of miniature pigs were studied: sham injured (controls) (n = 7), 50% mechanical reduction in blood flow to the superior mesenteric artery (SMA) and celiac artery (CA) (n = 6), and a 40% third-degree cutaneous flame burn (n = 9). Forty-eight hours after injury, animals were killed and organ samples obtained for analysis. Bacteria of the same biotype as that found in the intestinal lumen were present in the mesenteric lymph nodes (MLN) of 9 of 9 burned pigs and 5 of 6 pigs undergoing partial vascular occlusion. The DNA content and ornithine decarboxylase (ODC) activity were increased in the colon mucosa of animals from both the reduced-flow and burn-injured groups compared with control animals. Decreased blood flow to the gut may contribute to the development of bacterial translocation. In addition, intestinal regenerative capacity remains intact 48 hours after injury.

Baroreflex attenuates pressor response to graded muscle ischemia in exercising dogs

Graded reductions in hindlimb perfusion in dogs exercising at 2 miles/h (0% grade) elicited reflex pressor responses by what is referred to as the "muscle chemoreflex." To determine the extent to which arterial baroreceptor reflexes oppose the muscle chemoreflex, we elicited pressor responses to muscle ischemia before and after chronic surgical denervation of the arterial baroreceptors. The muscle chemoreflex showed a threshold beyond which systemic pressure rose approximately 3 mmHg for each 1-mmHg decrease in hindlimb perfusion pressure when the arterial baroreceptors were intact. Arterial baroreceptor denervation approximately doubled the pressor responses, i.e., systemic pressure rose by approximately 6 mmHg for each 1-mmHg fall in hindlimb perfusion pressure, without alteration in threshold. We conclude that during mild dynamic exercise, the arterial baroreflexes oppose the pressor response to graded reductions in hindlimb perfusion, reducing it by approximately 50%. When unopposed by the arterial baroreflexes the muscle chemoreflex exhibits a gain (ratio of change in systemic pressure to change in hindlimb perfusion pressure) of approximately -6; thus this reflex can correct by 85% the decrease in muscle perfusion pressure caused by partial vascular occlusion.

Reflex stimulation of sympathetic outflow during rhythmic exercise in humans

The aim of this study was to determine whether a chemically generated reflex arising in nonischemic skeletal muscle normally increases sympathetic outflow during rhythmic exercise. To accomplish this aim, we recorded muscle sympathetic nerve activity (MSNA, peroneal nerve) in conscious humans during exercise interventions designed to alter the relationship between muscle blood flow and metabolic demand. Under normal conditions, MSNA increased during moderate but not during mild levels of rhythmic handgrip (0.67 Hz) and one-arm cycling (0.83 Hz). MSNA remained elevated when the moderate level of rhythmic handgrip was followed by forearm vascular occlusion, a maneuver that sustains muscle chemoreflex stimulation. Complete arm vascular occlusion was needed to increase MSNA during mild arm cycling, whereas even partial vascular occlusion greatly amplified the stimulation of MSNA normally produced by the moderate level of arm cycling. We conclude that a chemically generated reflex arising in nonischemic working muscle plays an important role in the normal activation of sympathetic discharge to nonexercising leg muscles during moderate but not during mild levels of rhythmic arm exercise.

Will emergency coronary bypass grafting after failed elective percutaneous transluminal coronary angioplasty prevent myocardial infarction?

An emergency aorto-coronary bypass grafting operation was performed within 12 hours after the development of acute myocardial ischemia due to partial or complete vascular occlusion in 34 of 950 (3.6%) patients who had received elective percutaneous transluminal coronary angioplasty (PTCA). Of the 34 patients, three (= 8.8%) died postoperatively in irreversible cardiogenic shock. Half of the surviving patients developed a Q-wave infarction after the operation, whereas the other half remained without transmural infarct. With comparable clinical data and times of operation up to placement of the aorto-coronary bypass vessel, an adequate residual perfusion must still have been present in the cases with non Q-wave infarction. Since in many cases a myocardial necrosis is unavoidable despite relatively early operative revascularization, the decisive role will be played by the remaining perfusion of the vessel concerned and any collaterals. It follows that treatment of an early PTCA complication, occurring in the catheter laboratory, ought to be the earliest possible aorto-coronary bypass operation unless available cardiological methods can reliably assure reperfusion. Treatment of a PTCA complication occurring later, however, e.g. after hours in the intensive-care unit, should be a repeat PTCA attempt: surgery at this stage will not prevent the transmural infarction but will increase risk of lethal complications.

Intravascular signal in MR imaging: use of phase display for differentiation of blood-flow signal from intraluminal disease.

Intravascular signal from flowing blood is frequently observed on magnetic resonance (MR) images and may be indistinguishable from partial or complete vascular occlusion caused by thrombus or tumor. With a phase-display reconstruction method, qualitative assessment of large-vessel patency within the abdomen was undertaken in 15 healthy subjects and 12 patients with angiographically or surgically documented intravascular thrombus or tumor. Computed tomographic (CT) scans were available in all patients for correlation. MR studies were performed with a multisection spin-echo pulse sequence and two-dimensional Fourier transform spatial encoding. Data acquired from a single sequence was reconstituted in two ways to provide both routine anatomic images and a pictorial representation of large-vessel flow on a phase-sensitive image. With this method, reliable and easy differentiation of intraluminal thrombus and tumor from blood flow signal within large vessels was achieved. Information from these phase-display images compared favorably with findings from angiography and contrast-enhanced CT in the determination of luminal patency and obstruction.