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Biomedical subjects

R L McCann

Publications and source records attributed to R L McCann.

At least 55 records · Page 3Linked to original sources
PubMed1989

Prospective analysis of strategies for diagnosing renovascular hypertension.

Renovascular hypertension is a potentially curable form of high blood pressure. However, it is unclear how best to select patients who are likely to have renovascular hypertension, what diagnostic strategy to use in these selected patients, and how to predict the hemodynamic significance of a renal artery stenosis. We determined the prevalence of renovascular hypertension in adults who exhibited suggestive clinical features. In these clinically selected patients, we then determined the test characteristics of various diagnostic and potential screening tests. Renovascular hypertension was diagnosed if correction of renal artery stenosis resulted in decreased blood pressure. Of the 66 hypertensive adults evaluated, 11 (16.7%) had renovascular hypertension. Captopril-stimulated peripheral renin activity detected renovascular hypertension with 73% sensitivity, 72% specificity, 38% positive predictive value, and 92% negative predictive value. Less optimal combinations of sensitivity and specificity were found for differential glomerular filtration rate renography, differential effective renal plasma flow renography, and selective renal vein renin ratios, each performed after a single dose of captopril. Intravenous digital subtraction renal angiography detected all patients with renovascular hypertension and was normal in 71% of patients with essential hypertension. To evaluate potential screening tests for renovascular hypertension, we calculated predictive values applied to a low prevalence population. If the observed sensitivities and specificities apply to a population with 5% prevalence of renovascular hypertension, captopril-stimulated peripheral renin would have a positive predictive value of 12% and a negative predictive value of 98%. In 16 patients with known renal artery stenosis, neither the captopril-stimulated renal vein renin ratio nor captopril-stimulated differential renography accurately predicted blood pressure response to correction of the stenosis. We conclude that clinical criteria can identify a subgroup with 16.7% prevalence of renovascular hypertension. In this high prevalence group, intravenous digital subtraction renal angiography will identify virtually all patients with renovascular hypertension, and a normal study will be sufficient to exclude renovascular hypertension. In unselected hypertensive patients, screening with captopril-stimulated peripheral renin activity may be the most useful and efficient procedure for identification of patients with renovascular hypertension. Functional tests do not accurately predict the hemodynamic significance of a renal artery stenosis.

Adult↗
PubMed1989

Silent myocardial ischemia in patients undergoing peripheral vascular surgery: incidence and association with perioperative cardiac morbidity and mortality.

Atherosclerosis is a systemic disorder and coronary artery disease is highly prevalent in patients treated for lower-extremity obstructive vascular disease. Myocardial ischemia and infarction represent the most frequent and most clinically important complications of surgical procedures for lower-extremity revascularization. Despite attempts in several areas, no practical, sensitive, and specific method for identifying patients at highest risk for myocardial events postoperatively has been found before now. This study reports observations on a consecutive series of 50 patients who underwent continuous perioperative electrocardiographic monitoring with a microprocessor-based electrocardiographic ischemia monitor. Thirty-eight percent of the patients were found to have episodes of ischemia; most of these episodes were painless and would not otherwise have been recognized. Ischemia was most prominent in the postoperative rather than the preoperative or intraoperative phases. Tachycardia was often associated with ischemia. Significantly more cardiac-related morbidity and deaths occurred in patients who were documented to have silent myocardial ischemia. In fact, no cardiac events occurred in the 31 patients without ischemia (p less than 0.02). This type of ischemia monitoring represents a potential method for segregating patients at high risk for cardiac-related morbidity and death during lower-extremity revascularization.

Coronary Disease↗
PubMed1989

Resection of abdominal aortic aneurysm in patients with low ejection fractions.

The perioperative and long-term survival of patients who undergo resection of abdominal aortic aneurysm is often determined by coexisting cardiac disease. This study evaluates the influence of left ventricular ejection fraction on both perioperative and long-term morbidity and mortality. Preoperative ejection fraction was measured in 104 of 208 patients undergoing elective abdominal aortic aneurysm resection. Nineteen patients were found to have ejection fractions less than 0.35, and this group was compared to 85 patients with ejection fractions greater than 0.35. The two groups did not differ significantly in terms of age, sex, preoperative renal function, or smoking status. The groups were significantly different with respect to the prevalence of prior myocardial infarction (79% of the low ejection fraction group vs 31% of the high ejection fraction group) and symptoms equivalent to New York Heart Association class II or greater (47% of the low ejection fraction group vs 24% of the high ejection fraction group) but not prior myocardial revascularization procedure (42% of the low ejection fraction group vs 31% of the high ejection fraction group). Surgical factors including aneurysm size, duration of aortic cross-clamping, and extent of arterial replacement did not differ significantly between the two groups. The perioperative mortality was not significantly different (low ejection fraction, 5%; high ejection fraction, 2%). The cumulative life-table survival of the two groups was not statistically different. Two patients in the low ejection fraction group died in the follow-up period, yielding a 4-year actuarial survival of 0.74. This is compared to 10 deaths and actuarial survival of 0.63 (p = NS) in the high ejection fraction group. We conclude that patients should not be denied aneurysm resection solely on the basis of left ventricular ejection fraction.

Aged↗
PubMed1989

Traumatic false aneurysm of the common carotid artery presenting as a mediastinal mass: a case report.

A 42-year-old man came to another institution with chest pain and a cough and was found to have a 15 cm mass on the left side of his chest. Carcinoma was suspected but not proved, and a course of chemotherapy was administered. Two years later he was referred to Duke University Medical Center after he experienced a thromboembolic event in his left upper extremity. A CT scan and angiogram of the chest showed a large false aneurysm located 5 cm from the origin of the left common carotid artery and filling the anterior mediastinum. Additional history was obtained of multiple stab wounds to the left side of the chest 7 years before admission. The aneurysm was treated with sequential saphenous vein bypass grafting of right common carotid to left common carotid to left subclavian artery, followed by aneurysm thrombosis induced with wire coils. The differential diagnosis of a chest mass should include aneurysms of the great vessels.

Adult↗
PubMed1988

Prospective evaluation of a Dacron cuffed hemodialysis catheter for prolonged use.

Double lumen subclavian venous hemodialysis catheters are in wide use in the United States to provide temporary vascular access. The disadvantages of these catheters include a high infection rate and short use-life (2 to 3 weeks). We evaluated a felt cuffed tunnelled jugular venous hemodialysis catheter (PermCath) to determine its ability to overcome these shortcomings and compared it with standard noncuffed double lumen dialysis catheters. Eighty PermCaths were inserted during this prospective study in patients needing temporary vascular access in excess of 1 month. Median use-life of these catheters was 8 weeks with a use range of 3 weeks to 5.4 months. Only four functioning catheters failed before elective removal. Despite the prolonged use-life there was only one episode of catheter mediated bacteremia. Seven catheters (9%) failed to function immediately after insertion. These failures were caused by catheter kinking in the region of the felt cuff. Thrombosis of the catheter lumen was the most frequent complication (137 episodes) but resolved in over 95% of the instances with urokinase instillation. Exit site infections (23 instances) were successfully treated conservatively. We conclude that the PermCath (Quinton Instrument Co, Seattle) is a safe and reliable new device with a low complication rate and a longer use-life than standard subclavian dialysis catheters. This longer use-life allows more time for maturation of primary arteriovenous (AV) fistulas and Tenckhoff peritoneal dialysis catheters, and provides time for the healing of infected vascular access grafts. Its primary disadvantage is the need for surgical insertion.

Adolescent↗
PubMed1988

Surgical renal artery reconstruction after percutaneous transluminal angioplasty.

Percutaneous transluminal renal angioplasty (PTRA) is a controversial treatment for renal artery stenosis. This article discusses whether or not a prior attempt at PTRA compromises a subsequent elective or emergent surgical revascularization. Thirteen patients had surgical renal artery reconstruction after one or more PTRAs. Eight of the patients were treated because of atherosclerotic renal artery disease whereas five had a form of fibromuscular dysplasia. Five patients had renal artery injury directly related to the angioplasty. Four of these kidneys were saved. Eight patients were treated from 6 to 920 days after PTRA because of recurrent stenosis or occlusion of the renal artery. Only one of these kidneys was lost, an attempt at revascularization of a small kidney that failed to resume function. A prior attempt at PTRA did not compromise the ability of subsequent surgical revascularization to ameliorate hypertension. We conclude that surgical renal revascularization is not made less likely to succeed by a previous attempt at PTRA; even if the renal artery is thrombosed or perforated during the procedure, a reasonable chance of renal salvage is obtained by immediate surgical revascularization.

Angioplasty, Balloon↗
PubMed1988

Functional abnormalities of experimental autogenous vein graft neoendothelium.

When a vein is grafted into the arterial circulation, the endothelium of the graft is damaged. Regeneration of an intact neoendothelium occurs, but the functional properties of this surface have not been clarified. In this study, the functional integrity of the neoendothelium of veins grafted into the carotid artery of the rabbit was assessed through the use of acetylcholine and histamine to stimulate the production of the important endothelium-derived relaxing factor (EDRF). Control veins, precontracted with norepinephrine [10(-5) M], relaxed after exposure to acetylcholine [( 10(-7) M], 42.4% +/- 6.4%, p = 0.008) and histamine [( 10(-6) M], 30.6% +/- 4.3%, p = 0.03). This relaxation response was abolished after mechanical removal of the endothelium. By contrast, neither acetylcholine nor histamine caused an endothelium-dependent relaxation in the vein grafts, even though scanning electron microscopy demonstrated the presence of a morphologically intact endothelium. However, addition of stabilized EDRF purified from cultured endothelial cells induced relaxation of the vein grafts (35.8% +/- 3.6%, p = 0.002). These data indicate that vein graft endothelium is unable to produce EDRF in response to exposure to acetylcholine or histamine. The inability to produce this potent smooth muscle cell relaxing factor and anti-aggregatory substance may be a predisposition to vein graft failure.

Acetylcholine↗
PubMed1988

Comparison of intravenous digital subtraction angiography and conventional arteriography in defining renal anatomy.

Intravenous digital subtraction renal angiography (IV-DSRA) is frequently used in the preoperative evaluation of living-related (LR) kidney donors. However, the true accuracy of IV-DSRA in the donor population is difficult to assess since abnormalities of the kidney and its circulation are uncommon in this group. Therefore, we evaluated IV-DSRA in a group of patients more likely to have anomalies and abnormalities that would affect LR donor selection, donor nephrectomy, and subsequent transplantation. Hypertensive adults being evaluated for renovascular hypertension had IV-DSRA and conventional renal arteriograms, which were interpreted independently. We determined the accuracy of IV-DSRA, compared with conventional arteriography, in detecting multiple renal arteries, renal artery stenosis, fibromuscular dysplasia, and abnormal renal parenchyma. Technically unsatisfactory studies were excluded from analysis. Of 59 patients evaluated, 37 had abnormalities or anomalies. IV-DSRA failed to detect 28 of 50 findings in these 37 patients. In 21 patients with multiple renal arteries, IV-DSRA underestimated the number of main renal arteries in 8. Significant renal artery stenosis, present in 16 patients, was undetected by IV-DSRA in 3 of these patients. Mild fibromuscular dysplasia was not detected by IV-DSRA in any of the 5 patients with this condition, and abnormalities of renal parenchyma were not detected in 6 of the 8 patients with scarred or cystic kidneys. When compared with conventional renal arteriography in a hypertensive population, the IV-DSRA does not accurately detect abnormalities of the kidney and its circulation. If these data are confirmed in nonhypertensive subjects, preoperative evaluation of LR kidney donors using IV-DSRA alone may fail to detect potentially important anatomic abnormalities.

Adult↗
PubMed1988

Peripheral artery atherectomy: description of technique and report of initial results.

Percutaneous transluminal atherectomy has been developed for treatment of peripheral artery stenoses. The atherectomy catheter is inserted through a sheath, and the resection window of the catheter is positioned adjacent to the vascular stenosis. The balloon is inflated, and the motor-driven cutting blade advanced. The balloon is then deflated, the catheter withdrawn, and the atheromatous material, which resembles the resected material of an endarterectomy, removed from the catheter. This process is repeated until the resection provides an adequate lumen. To date, 12 arterial lesions (three common iliac, two external iliac, four superficial femoral, and three popliteal artery) in ten patients have been resected with excellent angiographic results. The conditions of seven patients who underwent atherectomy for relief from claudication were improved by the criteria of ankle/arm ratios and/or claudication distance. Three patients successfully underwent atherectomy for limb salvage. More data on long-term patency and restenosis rates are needed before the ultimate role of atherectomy in the management of peripheral artery disease can be determined.

Adult↗
PubMed1988

A neutrophil derived factor(s) stimulates [3H]thymidine incorporation by vascular smooth muscle cells in vitro.

There is increasing evidence for the involvement of inflammatory cells in the development of intimal hyperplasia. This study examines the effect of human neutrophils on the incorporation of [3H]-thymidine into acid precipitable materials (DNA) in cultured rabbit vascular smooth muscle cells. Co-culture of intact neutrophils and vascular smooth muscle cells caused [3H]-thymidine incorporation by these cells to increase 209 +/- 22% (mean +/- SEM) of control. Sonication of the neutrophils abolished this effect (117 +/- 10%). Neutrophil conditioned medium prepared in the presence or absence of fetal calf serum had a similar effect on [3H]-thymidine incorporation by vascular smooth muscle cells (204 +/- 20% and 172 +/- 17% respectively). Stimulation of neutrophils with either Concanavalin A or serum-activated zymosan failed to increase production of the factor(s). The neutrophil derived factor(s) prepared in minimal essential medium was partially stable at 56 degrees C, but inactivated by boiling. Dialysis (pore size 12,000-14,000) did not remove the factor(s). Cyclooxygenase inhibition with indomethacin did not inhibit production of the factor(s) by neutrophils, but indomethacin caused an increase in [3H]-thymidine incorporation by vascular smooth muscle cells (181 +/- 11%). Indomethacin together with intact neutrophils had an additive effect on [3H]-thymidine incorporation (273 +/- 42%) into cellular DNA. These data show that neutrophils produce a factor(s) that stimulates [3H]-thymidine incorporation into DNA by vascular smooth muscle cells and suggests that vascular smooth muscle proliferation and intimal hyperplasia may be initiated by neutrophils adherent to sites of endothelial injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Mast cell infiltration: a possible mechanism for vein graft vasospasm.

Mast cell infiltration of the arterial wall has been demonstrated in atherosclerotic vessels and implicated in coronary artery spasm. Spasm of vein bypass grafts has also been reported. In this study we performed vein bypass grafting of the carotid arteries in rabbits and examined the grafts for the presence of mast cells. We also determined vein graft vasoreactivity to histamine, to assess whether mediators of mast cells may have a functional role in vivo. In the control veins no mast cells were identified in 80 high-power fields (400X). In the vein bypass grafts an average of 2.6 +/- 0.8 (p = 0.01) mast cells were identified in the same number of high-power fields. Isometric tension studies of control vein and vein bypass grafts treated with histamine resulted in sigmoid dose-response curves. The ED50 for control vein was 4.69 +/- 0.63 X 10(-5) mol/L. Compared with control vein, the vein bypass grafts showed a rightward shift in the dose-response curve to histamine (ED50 11.6 +/- 1.7 X 10(-5) mol/L, p = 0.01). The histaminergic response in both vessels was blocked by the H1 receptor antagonist pyrilamine (10(-7) mol/L) and was not altered by the H2 receptor antagonist cimetidine (10(-5) mol/L). The decreased sensitivity of vein bypass grafts to histamine suggests receptor down-regulation and is possibly the result of increased histamine in the vein bypass grafts. The presence of mast cells and histamine receptors, as well as altered histamine sensitivity, in vein bypass grafts suggests that infiltration by these cells may contribute to vein bypass graft vasospasm.

Animals↗
PubMed1987

Evidence for the involvement of platelet glycoproteins other than GP Ib in heparin-associated thrombocytopenia and thrombosis.

Heparin-associated thrombocytopenia and thrombosis (HATT) is a potentially fatal complication of heparin therapy which is characterized by a progressive fall in the platelet count associated with arterial or venous thrombosis. The etiology is consistent with the development an antibody which, in the presence of heparin, induces intravascular platelet aggregation. Biochemical analysis has demonstrated that the platelet membrane glycoprotein (GP) Ib binds heparin. Recent studies have shown that polyclonal antisera or monoclonal antibodies to GP Ib can inhibit platelet aggregation induced by HATT plasma in the presence of heparin implicating GP Ib as the site of heparin-antibody interaction. The Bernard-Soulier syndrome (BSS) is an inherited bleeding disorder in which the platelets fail to adhere to exposed subendothelium due to a deficiency of GP Ib. We have used the platelets from a patient with documented BSS to further investigate the role of GP Ib in the heparin- dependent platelet aggregation induced by the plasma of three patients with HATT. We have shown that platelet aggregation by HATT plasma in the presence of heparin occurred as readily with BSS platelets as with normal donor platelets. These results indicate that glycoprotein Ib cannot be the only site of platelet-heparin-antibody interactions.

Bernard-Soulier Syndrome↗
PubMed1987

Digital intravenous subtraction angiography in the evaluation of reconstructed renal arteries.

Digital intravenous subtraction angiography (DISA) was used to evaluate 28 patients who had undergone renal artery reconstruction either as part of a renal transplant procedure or for treatment of renovascular hypertension. Satisfactory visualization of the renal artery was obtained in 26 cases, and the clinical questions were adequately answered in these cases. The findings included a variety of possible outcomes and demonstrate the adequacy of DISA as a means of evaluating the results of renal artery surgery. Technical and anatomic factors affecting the quality of the examination are discussed. The cases also illustrate the critical importance of thorough familiarity with the surgical procedures in general and of mutual discussion between surgeon and radiologist in optimizing the DISA examination in a given patient.

Adult↗
PubMed1987

Association of polymorphonuclear leukocytes with sites of aortic catheter-induced injury in rabbits.

The kinetics of the association of polymorphonuclear leukocytes (PMNs) with arterial balloon catheter-induced injury have been examined. An average of 6 X 10(7) PMNs were isolated from 20 ml of blood and labelled with 111In-oxine for reinfusion into the donor rabbit. The cells remained viable as demonstrated by both in vitro and in vivo tests of cell function. The abdominal aorta of rabbits was denuded of endothelium and immediately, 24 h, or 5 weeks later, exposed to autologous radiolabelled PMNs for 1 h. The presence of PMNs at sites of denudation was demonstrated by detection of the radioactive label and was confirmed by light and electron microscopy after 24 h, but not at 5 weeks. Immediately following denudation radioactivity was 2.44 +/- 0.33 times control (P = 0.006); 2.52 +/- 0.18 at 24 h (P = 0.005); and 1.88 +/- 0.32 times control at 5 weeks (P = 0.045). The presence of PMNs, or their products, 5 weeks after denudation suggests a more complex role of PMNs and possibly a direct involvement in the long term changes resulting from arterial balloon catheter injury.

Animals↗
PubMed1987

Management of patients with heparin-associated thrombocytopenia and thrombosis requiring cardiac surgery.

Heparin-associated thrombocytopenia and thrombosis (HATT) is a serious complication of heparin therapy that results in intravascular platelet aggregation with arterial or venous thrombosis. Platelet aggregation to heparin in vitro is used to confirm the diagnosis. Cessation of heparin therapy with avoidance of reexposure to heparin is an important principle in the management of HATT. However, certain patients with HATT may require reexposure to heparin for emergency cardiac operations requiring cardiopulmonary bypass while still demonstrating positive in vitro platelet aggregation with heparin. The present report describes the management of 2 such patients. In each patient aspirin was shown to inhibit platelet aggregation to heparin in vitro; therefore, aspirin and dipyridamole were administered to each patient before heparin reexposure and continued throughout the perioperative period. Cardiopulmonary bypass with full heparinization was achieved without thrombotic or hemorrhagic complications in both patients. Despite the presence of a heparin-dependent platelet-aggregating factor in the plasma of these 2 patients, inhibition of platelet aggregation with aspirin and dipyridamole allowed uneventful reexposure to heparin.

Adult↗