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Biomedical subjects

M W Webster

Publications and source records attributed to M W Webster.

At least 91 records · Page 5Linked to original sources
PubMed1991

Alterations in erythrocyte rheology in patients with severe peripheral vascular disease: 1. Cell volume dependence of erythrocyte rigidity.

The erythrocyte rigidity of patients suffering from severe peripheral vascular disease (PVD) was measured by a filtration method using 3 microns pore size filters. Filtration pressures for both PVD patients and normal subjects showed a cell volume dependency, and patient filtration pressures were normalized to cell volume to evaluate intrinsic, ie, nonvolume dependent, abnormalities in erythrocyte deformability. A significant (p less than 0.001) increase in cell rigidity was found in 44 of 54 PVD patients in comparison with volume-matched normal controls. No significant difference was found between patient mean corpusculer hemoglobin (MCH) and normal MCH at any given mean corpuscular volume (MCV), indicating that observed increases in erythrocyte rigidity are not attributable to changes in patient MCH. Therefore, the mechanism of increase in erythrocyte rigidity for PVD patients still needs further investigation into such parameters as levels of adenosine triphosphate,2,3-DPG, and membrane fluidity (calcium- and/or protein-binding membrane, cholesterol and phospholipid content of membrane, etc), as well as other aspects of erythrocyte physiology.

Adult↗
PubMed1991

On the inheritance of abdominal aortic aneurysm.

To determine the mode of inheritance of abdominal aortic aneurysm, data on first-degree relatives of 91 probands were collected. Results of segregation analysis performed on these data are reported. Many models, including nongenetic and genetic models, were compared using likelihood methods. The nongenetic model was rejected; statistically significant evidence in favor of a genetic model was found. Among the many genetic models compared, the most parsimonious genetic model was that susceptibility to abdominal aortic aneurysm is determined by a recessive gene at an autosomal diallelic major locus. A multifactorial component in addition to the major locus does not increase the likelihood of the data significantly.

Adult↗
PubMed1990

A model of persistent partial hindlimb ischemia in the rabbit.

An animal model of resting limb ischemia in the rabbit was developed and studied. Anesthetized rabbits underwent unilateral common iliac artery (CIA) division, allowing comparisons between an experimental (ischemic) and the contralateral control limb in the same animal. The time course and severity of the ischemic insult were measured by quantitating muscle blood flow in seven muscle groups using 57Co-radiolabeled microspheres, limb femoral arteriovenous oxygen differences (AVDO2), and limb arterial pressure. Nine of 20 animals had objective evidence of functional limb impairment judged by abnormal resting posture and/or abnormal gait. Muscle blood flow in the experimental limbs became significantly less than blood flows of corresponding contralateral muscle groups (P less than 0.05) when measured at 1 week after CIA division. By 17 days, mean muscle blood flow had returned to within 82.5% of that of the control limb. AVDO2 increased from 4.8 +/- 0.99 to 8.13 +/- 2.26 ml O2/dl blood following CIA division and remained persistently greater than the control limb value until Day 31. Limb arterial pressure decreased markedly after CIA division and remained significantly depressed beyond 6 weeks when the study was terminated. The reasons for the differential time courses of these parameters of blood flow are discussed. Common iliac artery division in the rabbit appears to produce persistent, partial ischemia at least 17 days in duration, allowing in-depth study of the effects of persistent limb ischemia on muscle cell function in the laboratory setting, as well as permitting the assessment of various therapeutic manipulations for the treatment of prolonged muscle ischemia.

Animals↗
PubMed1990

Indirect revascularization of the lower extremity by means of microvascular free-muscle flap--a preliminary report.

We describe the treatment of a patient with end-stage peripheral vascular disease and ischemic ulceration of the lower extremity in whom an obliteration of the distal arterial bed precluded conventional arterial reconstruction. A nonhealing dorsal foot ulcer was debrided, and soft tissue reconstruction was accomplished by the free microsurgical transfer of a muscle flap to the distal lower extremity. Arterial inflow to this free flap was provided by a contralateral reversed saphenous vein graft from the proximal arterial tree of the leg. This procedure resulted in a healed wound, stable coverage, and limb salvage. The patient also noted complete relief of rest pain and improvement in his claudication symptoms. A follow-up arteriogram was done 2 months after surgery. Contrast injection directly into the artery of this flap showed new blood vessel growth from the muscle flap into the foot with anastomoses of these "new vessels" to the patient's native circulation. This experience suggests that limb salvage may be possible by the free microvascular transplantation of a muscle flap onto the limb in selected patients whose limbs are deemed "nonreconstructible."

Angiography↗
PubMed1990

Hirudin, heparin, and placebo during deep arterial injury in the pig. The in vivo role of thrombin in platelet-mediated thrombosis.

Three dosages (0.3, 0.7, and 1.0 mg/kg) of recombinant hirudin, a specific inhibitor of thrombin, were compared with heparin (50 units/kg) and placebo for reducing thrombus formation in the carotid arteries of 50 pigs after deep injury by balloon dilatation. Each drug was administered as a bolus followed immediately by a continuous infusion of the same dose per hour. Major end points were quantitative indium-111-labeled platelet and iodine-125-labeled fibrinogen deposition and the incidence of mural thrombosis. This study showed that heparin, at a dose that prolonged the activated partial thromboplastin time (APTT) to twice the control time, did not prevent mural thrombosis or significantly reduce platelet deposition compared with placebo but did reduce fibrinogen deposition. Recombinant hirudin markedly reduced platelet and fibrinogen deposition in a dose-related manner and totally eliminated mural thrombosis at an APTT of two to three times that of control. Platelet deposition (x 10(6)/cm2, mean +/- SEM) in areas of deep arterial injury for the placebo, heparin, and 0.3, 0.7, and 1.0 mg/kg hirudin groups was 54 +/- 21, 33 +/- 9, 22 +/- 6, 8 +/- 1, and 7 +/- 1, respectively; electron microscopy showed a single layer (or less) of platelets at the two highest hirudin dosages. The incidence of macroscopic mural thrombosis was 76% with placebo, 57% with heparin, 46% with 0.3 mg/kg hirudin; there were no thrombi with 0.7 or 1.0 mg/kg hirudin (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Platelet inhibitor therapy. Agents and clinical implications.

Platelets are central to the pathophysiology of an array of vascular disorders. Current platelet-inhibitor drugs reduce platelet aggregation through one of three pathways but do not prevent initial platelet adhesion. The most extensive clinical experience is with aspirin, an irreversible inhibitor of cyclooxygenase. Aspirin is clinically effective and has few gastrointestinal side effects if used at a dosage of 150 to 300 mg per day. Large clinical trials have documented the benefits of aspirin in arterial thromboembolic disease. It is effective in the primary and secondary prevention of myocardial infarction, including patients with unstable angina; reduces the acute thrombotic complications of coronary angioplasty and revascularization surgery; and also reduces cerebral ischemic events in patients with cerebrovascular disease. Aspirin is less effective for thrombi arising from the venous system or intracardiac chambers, which respond well to anticoagulants. Dipyridamole and sulfinpyrazone are most effective at preventing thrombosis on prosthetic surfaces. Dipyridamole reduces emboli from mechanical prosthetic valves when combined with warfarin and, unlike aspirin plus warfarin, does not increase bleeding complications. Newer agents such as ticlopidine and the thrombin inhibitor, hirudin, appear promising but require further evaluation. Because thrombin plays a critical role in mechanisms of arterial thrombosis, its inhibition appears promising for future therapy.

Adult↗
PubMed1990

Clinical observations on the effect of carotid artery occlusion on cerebral blood flow mapped by xenon computed tomography and its correlation with carotid artery back pressure.

Xenon computed tomographic cerebral blood flow mapping was correlated with internal carotid artery stump pressures and clinical neurologic assessment during temporary internal carotid artery occlusion. One hundred fourteen patients with skull base tumors or intracranial aneurysms potentially requiring carotid resection or ligation underwent angiography, xenon CT cerebral blood flow mapping, and internal carotid artery blood pressure monitoring. The internal carotid artery was then temporarily occluded with a balloon catheter, stump pressure was measured through the catheter, and the xenon CT cerebral blood flow mapping was repeated. Adequate xenon CT cerebral blood flow was defined as greater than 30 cc/100 gm/min. All patients had normal xenon CT cerebral blood flow before internal carotid artery occlusion. During internal carotid artery occlusion, xenon CT cerebral blood flow was found to be normal (group I, 40 patients), globally reduced but still within the normal range (group II, 50 patients), or low in the distribution of the ipsilateral middle cerebral artery (group III, 13 patients). With balloon occlusion, an immediate neurologic deficit developed in 11 patients (9%) requiring deflation of the balloon preceding xenon CT cerebral blood flow measurement (group IV). In group I internal carotid artery blood pressure was 128 mm Hg. (range 85 to 171 mm Hg) with stump pressure 86 mm Hg (range 46 to 125 mm Hg). In group II internal carotid artery blood pressure was 130 mm Hg. (range 78 to 199 mm Hg), with stump pressure 86 mm Hg (range 31 to 150 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Effect of reducing atrial pressure on atrial natriuretic factor and vasoactive hormones in congestive heart failure secondary to ischemic and nonischemic dilated cardiomyopathy.

The effect of an acute and sustained reduction in atrial pressure on atrial natriuretic factor (ANF) and vasoactive hormone secretion was studied in 9 patients with congestive heart failure (CHF). Intravenous nitroglycerin was titrated to reduce the pulmonary artery wedge pressure by 30 to 50% and maintain this reduction for 4 hours. After 60 minutes of nitroglycerin administration, the mean decrement in wedge pressure was 10.0 +/- 1.7 (standard error) mm Hg (35%) and plasma ANF was 65.3 +/- 13.9 pmol/liter (35%). The initial decrease, sustained reduction and later increase in plasma ANF levels closely paralleled the changes in pulmonary arterial wedge (r = 0.94, p less than 0.0001) and right atrial pressures (r = 0.91, p less than 0.0001) during and immediately after the nitroglycerin infusion. Plasma aldosterone and cortisol levels increased during the first 2 hours of the nitroglycerin infusion, but there was little change in plasma norepinephrine or plasma renin activity. Although levels were elevated in CHF, plasma ANF still responded rapidly to changes in atrial pressure. A sustained reduction in pressure produced a sustained reduction in ANF levels. These findings provide further support for a regulatory role of ANF, even in chronic CHF.

Aged↗
PubMed1989

Inflammatory aneurysms of the abdominal aorta.

Inflammatory aneurysms of the abdominal aorta (IAAAs) have distinctive clinical and physical characteristics that separate them from typical atherosclerotic aneurysms. They were identified in 19 (7.2%) of 265 patients undergoing abdominal aortic aneurysm repair. Symptoms were present in 12 (63%) of 19, with one patient presenting with rupture, and multiple symptoms were present in six (32%). Intraoperatively, all aneurysms exhibited dense periaortic inflammation. Adjacent structures most frequently involved were the duodenum in 15 (79%) of 19 patients, the left renal vein in six (32%) of 19, and the ureter in five (26%) of 19. Seventeen (94%) of the 18 patients who underwent elective aneurysm resection survived. The involvement of retroperitoneal structures varied in number and severity, demonstrating that a wide spectrum of inflammation is present in IAAAs, making diagnosis and definition difficult.

Aged↗
PubMed1988

Patent foramen ovale in young stroke patients.

The prevalence of patent foramen ovale in patients presenting with non-haemorrhagic stroke or transient ischaemic attacks under the age of 40 years was determined by contrast echocardiography. Studies were performed at rest and with a Valsalva manoeuvre in 40 stroke patients and in an age and sex matched control group. Right-to-left shunting was found in 20 (50%) of the stroke patients and 6 (15%) of the controls (p less than 0.001). Paradoxical embolism through a patent foramen ovale may be an under-recognised cause of stroke in young adults.

Acute Disease↗
PubMed1988

Chronic contained rupture of an abdominal aortic aneurysm presenting as a lower extremity neuropathy.

Rupture of an abdominal aortic aneurysm often presents with a pulsatile abdominal mass, abdominal pain, and hypotension. Recent clinical reports describe patients with less apparent clinical signs and symptoms who were found later in their evaluation to have a contained rupture of an abdominal aortic aneurysm. Even more unusual is a chronic contained rupture of an abdominal aortic aneurysm. Our patient had a chronic contained rupture of an abdominal aortic aneurysm that presented with erosion into the lumbar vertebral bodies and subsequent lumbar neuropathy. CT scan confirmed the contained rupture of the aortic aneurysm and the patient underwent successful repair of his aortic aneurysm. Our report discusses the significance of atypical presentations of abdominal aortic aneurysm rupture and the importance of prompt diagnosis and definitive repair.

Aged↗
PubMed1988

Upper gastrointestinal endoscopy after cardiac transplantation.

Three hundred four patients have undergone cardiac transplantation at the University of Pittsburgh since 1980. Twenty patients have required 27 upper gastrointestinal (GI) endoscopic procedures. After heart transplantation the primary indications for endoscopy were epigastric pain (six patients with gastritis, one with multiple shallow gastric ulcers, and one with normal test results), mild upper GI bleeding (four patients with esophagitis, two with gastritis, and two with multiple shallow gastric ulcers), dysphagia and odynophagia (two patients with esophagitis), persistent nausea and vomiting (one with normal test results), lower GI bleeding (one with normal test results), and routine follow-up (one with normal test results). After heart-lung transplantation the primary indications for the endoscopy were massive upper GI bleeding (three patients with actively bleeding duodenal ulcers), dysphagia and odynophagia (one patient with esophagitis), mild upper GI bleeding (one patient with gastritis), and routine follow-up (one patient with normal test results). No complications resulted from endoscopy. The procedures were performed in the GI suite without cardiac monitoring. Prophylactic antibiotics were not routinely administered. No patient had a fungal infection of the upper GI tract--a finding attributed to the prophylactic use of nystatin in all patients. Opportunistic viral infections were identified histologically in six patients, including two patients with actively bleeding duodenal ulcers. The possibility of opportunistic viral infections in this immunosuppressed group required aggressive diagnostic techniques, including endoscopy and biopsy, which can be safely performed after cardiac transplantation.

Adult↗
PubMed1988

Transcutaneous oxygen measurements in lower extremity ischemia: effects of position, oxygen inhalation, and arterial reconstruction.

Transcutaneous oxygen tension (TcPO2) measurement has been successfully applied to the diagnosis and monitoring of patients with peripheral arterial insufficiency. This study was performed to assess the effects of changes in limb position, oxygen inhalation, and arterial reconstruction on TcPO2 values in patients with peripheral vascular disease. In addition, a TcPO2 index (foot TcPO2/chest TcPO2) was compared with the Doppler-derived ankle-to-brachial index (ABI) to determine which was the more effective monitor of the response to revascularization. Foot TcPO2 values of 22 patients with claudication or rest pain were measured before and after vascular reconstruction. TcPO2 increased after revascularization in both groups regardless of limb position or oxygen (O2) administration. The dependent position and O2 inhalation had an additive effect on TcPO2. Preoperative TcPO2 values in patients with rest pain showed the greatest response to the dependent position, increasing from 14 mm Hg to 33 mm Hg at room air and from 21 mm Hg to 53 mm Hg with O2 inhalation. TcPO2 in both patient groups was remarkably enhanced by O2 administration after revascularization. Postoperative supine TcPO2 values measured at room air increased from 50 mm Hg to 124 mm Hg (148%) in patients with claudication and from 40 mm Hg to 109 mm Hg (173%) in patients with rest pain after O2 inhalation. Comparison of the TcPO2 index with the ABI showed that absolute and normalized TcPO2 values are equally effective in monitoring peripheral arterial insufficiency. This study suggests that placing the limb in the dependent position and administering O2 may augment TcPO2 to levels where symptoms may resolve. The response of TcPO2 to O2 inhalation may be an indicator that reflects the response to revascularization.

Arterial Occlusive Diseases↗
PubMed1987

Myocardial function in alcoholic cardiac beriberi.

A case of alcoholic beriberi is described. Left ventricular systolic function as measured by the radionuclide ejection fraction showed an abnormal fall with exercise. Subsequent return to normal with the administration of thiamine suggests myocardial involvement in the condition.

Adult↗