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Biomedical subjects

R T Wall

Publications and source records attributed to R T Wall.

At least 19 recordsLinked to original sources
PubMed1992

Rapid reversible modulation of human motor outputs after transient deafferentation of the forearm: a study with transcranial magnetic stimulation.

Reorganization of corticospinal pathways after spinal cord injury and amputations leads to increased excitability of motor pathways targeting muscles proximal to the level of interruption of efferents from the CNS. To study the timing of these changes, we have recorded motor evoked potentials (MEPs) in the arm muscles of three normal subjects before, during, and after anesthetic block of the forearm and hand. The amplitudes of MEPs from biceps, which was the muscle immediately proximal to the block, gradually increased with anesthesia and then returned to preanesthesia levels within approximately 20 minutes after anesthesia was ended. MEPs from the contralateral arm were unaffected. Such rapid changes strongly suggest unmasking of preexisting synaptic connections, due to disinhibition at cortical or subcortical levels, as the mechanism underlying acute modulation of motor outputs.

Electromyography↗
PubMed1990

Surgical management of pheochromocytoma with the use of metyrosine.

Despite recommended preoperative preparation with alpha-adrenergic blockers, severe hemodynamic instability may occur during operations to resect pheochromocytoma. We combined the alpha-blocker phenoxybenzamine with the tyrosine hydroxylase inhibitor metyrosine in an attempt to better manage the hypertension of patients with pheochromocytoma undergoing surgical resection. This report reviews the cases of 25 consecutive patients undergoing surgery for known intra-abdominal pheochromocytoma. Each patient had elevated serum or urine levels of catecholamines or their metabolites. Nineteen patients were prepared before operation with phenoxybenzamine and metyrosine and six patients were given phenoxybenzamine alone. There were no significant differences in maximum, minimum, or mean blood pressure before or after tumor resection between patients who received metyrosine and those who did not. However careful review suggested that those who received metyrosine had more severe disease as judged by biochemical criteria. Study of selected patients matched for age and severity of disease suggested that the intraoperative blood pressure management of patients prepared with phenoxybenzamine and metyrosine was facilitated. In addition metyrosine-prepared patients lost less blood and required less volume replacement during surgery than did non-metyrosine-prepared patients. There were no apparent differences in postoperative fluid requirements. Although the study is not a prospective randomized trial, a retrospective review of patients managed with the combination of phenoxybenzamine and metyrosine suggests that surgery to resect pheochromocytoma can be better performed with both drugs than with phenoxybenzamine alone. The combination regimen appears to result in better blood pressure control, less blood loss, and the need for less intraoperative fluid replacement than does the traditional method of single-agent alpha-adrenergic blockade.

Adrenal Gland Neoplasms↗
PubMed1990

Multilayer model of photon diffusion in skin.

A diffusion model describing the propagation of photon flux in the epidermal, dermal, and subcutaneous tissue layers of the skin is presented. Assuming that the skin is illuminated by a collimated, finite-aperture source, we develop expressions relating photon flux density within the skin and intensities re-emitted from the skin surface to the optical properties of the individual layers. Model simulations show that the rate at which re-emitted intensities diminish with radial distance away from the source can provide information about absorption and scattering in underlying tissues. Re-emitted intensities measured from homogeneous and two-layer tissue phantoms compare favorably with model predictions. We demonstrate potential applications of the model by estimating the absorption (sigma a) and transport-corrected scattering (sigma's) coefficients of dermis and subcutis from intensities measured from intact skin and by predicting the magnitude of the optical-density variations measured by a photoplethysmograph.

Diffusion↗
PubMed1990

Use of analgesics in the elderly.

Basic and clinical research on the pathophysiology, neurophysiology, biochemistry, and psychology of pain and its management has enhanced our understanding of this complex field. Clinical applications of new knowledge have led to the development of more effective analgesics and better modes of administration in concert with improved technology. However, applications to pain problems unique to the elderly require greater attention. Unfortunately, state-of-the-art analgesic care is not widespread. Barriers exist in knowledge, skills, and attitudes among health care providers. To provide optimal analgesic care, management of each patient should be individualized. The prescribing of standard doses of analgesics should be condemned. An understanding of the various pain problems (acute and chronic) that afflict the elderly, the effects of aging on the pharmacokinetics and pharmacodynamics of analgesics, and the role of specific analgesics for specific pain states is necessary. In addition to analgesics, nonpharmacologic methods of pain control should be utilized. If needed, consultations or referrals to pain clinics or pain centers which provide expert evaluation, recommendations, and/or treatment are available.

Aged↗
PubMed1987

Fentanyl and diazepam for analgesia and sedation during radiologic special procedures.

Fentanyl is a synthetic narcotic which, when administered intravenously, has a rapid onset and short duration of action. It produces less cardiovascular depression than either meperidine or morphine. Experience with 100 examinations performed using intravenous fentanyl and diazepam for analgesia and sedation in adults is reviewed. There were no complications, and effective analgesia was obtained in all cases. Fentanyl has distinct pharmacologic advantages over both morphine and meperidine for use in radiologic special procedures.

Adolescent↗
PubMed1986

Plasma concentrations of sodium cromoglycate given by nebulisation and metered dose inhalers in patients with exercise-induced asthma: relationship to protective effect.

Plasma sodium cromoglycate (SCG) concentrations were measured in 11 patients at regular intervals before and after exercise in a double-blind study to assess the protective effect in exercise-induced asthma (EIA) of 2, 10 and 20 mg SCG aerosol and placebo, and (on an open basis) nebulised SCG (10 g l-1). There was a dose related increase in plasma concentration and AUC (0-1 h) with the aerosol formulations; values with nebulised SCG were significantly higher than with any aerosol dose. Protection from EIA increased to a maximum of 66% at plasma concentrations of 4 ng ml-1 and above. Thus measurement of plasma concentration can allow a comparison to be made between the protective effects of SCG following different methods of inhalation. It is important to note, however, that plasma concentration per se is almost certainly not related directly to protective effect.

Adult↗
PubMed1986

Dose-duration effect of sodium cromoglycate aerosol in exercise-induced asthma.

The dose-duration effect of sodium cromoglycate given by metered dose aerosol was studied in nine patients with exercise-induced asthma. Exercise tests were carried out at 15, 135 and 255 min after placebo, sodium cromoglycate 2 mg, 10 mg and 20 mg. The protective effect and the duration of action were dose-related. The new metered dose aerosol delivering 5 mg of sodium cromoglycate per actuation allows greater flexibility in adjusting the dosage and frequency of administration for individual patients.

Administration, Inhalation↗
PubMed1985

Dose-response effect of sodium cromoglycate pressurised aerosol in exercise induced asthma.

The effects of 2, 10, and 20 mg of sodium cromoglycate delivered by aerosol were compared with those of placebo in a double blind study in 11 patients with extrinsic and exercise induced asthma. The effect of nebulised sodium cromoglycate delivered through a Wright nebuliser (estimated dose 12 mg) was also studied. Patients exercised on a treadmill for six to eight minutes at submaximal work loads on five days, 30 minutes after inhaling placebo or sodium cromoglycate. The FEV1 was recorded before treatment, before exercise, and up to 30 minutes after exercise. Mean baseline values of FEV1 before and after placebo or sodium cromoglycate did not differ significantly on the five days. After exercise the mean (SEM) maximal percentage fall in FEV1 after placebo; 12 mg sodium cromoglycate nebuliser solution; and 2, 10, and 20 mg sodium cromoglycate aerosol were 31.1 (3.8); 9.4 (2.1); and 19.4 (4.6), 13.7 (3.5), and 9.4 (1.9). Sodium cromoglycate inhibited exercise induced asthma at all doses used; the protective effect of the aerosol increased from 2 to 20 mg. The protective effect of 20 mg sodium cromoglycate aerosol was similar to that seen with 12 mg nebulised solution. Our results suggest that the effect of sodium cromoglycate aerosol in exercise induced asthma is dose related.

Adult↗
PubMed1983

Intensive plasmapheresis in the treatment of diabetic retinopathy.

Two insulin-dependent diabetic patients with advanced nonproliferative and early proliferative retinopathy showed regression of diabetic retinopathy after three weeks of intensive plasmapheresis. Because of the sudden unexplained death in one patient, the study was stopped. However, these observations in this pilot study suggest that factors mediated through plasma contribute to the pathogenesis of diabetic microangiopathy.

Adult↗
PubMed1983

Complications of therapeutic apheresis, including a fatal case with pulmonary vascular occlusion.

A high incidence of anaphylactic reactions has been observed in patients undergoing therapeutic plasma exchange. In three of 22 patients who underwent multiple exchanges, urticaria, bronchospasm, and hypotension developed during a course of plasma exchange that responded to treatment with steroids, antihistamines, and epinephrine. Fatal pulmonary microvascular occlusion with platelets and granulocytes developed in an additional patient eight hours following an apheresis procedure involving albumin replacement. The mechanism for the latter complication is not known but did not appear to invoke complement activation. This unexpectedly high risk of potentially fatal complications must be considered when a course of therapeutic apheresis, particularly involving treatment of a chronic disease, is planned.

Adult↗
PubMed1983

Binding of plasma fibronectin to monolayer human endothelium.

Interaction of exogenous plasma fibronectin with endothelium was examined using monolayer cultures of human umbilical vein endothelial cells. Plasma fibronectin was purified on gelatin-sepharose with 1 M arginine elution and iodinated with 125I by the solid phase glycoluril method. Endothelial monolayers were incubated with 0.5 to 15.0 mg/l (125I)fibronectin. Specificity of binding was 50 to 60% as determined by competition with 50-fold excess nonlabeled fibronectin. Binding reached maximal levels within 1 hour and without saturation over the concentration range. The bound glycoprotein showed minimal dissociation during subsequent incubation in media free of fibronectin.

Cells, Cultured↗
PubMed1981

Clinical use of beta-thromboglobulin levels in diagnosing and treating consumptive and immune thrombocytopenia.

Plasma beta-thromboglobulin (beta-TG), a platelet-specific protein, is a marker of intravascular platelet degranulation. We measured plasma beta-thromboglobulin by radioimmunoassay in 13 patients with thrombocytopenia of various etiologies to determine whether or not the test is clinically useful in the differential diagnosis of thrombocytopenia. Four patients with intravascular platelet consumption (three with thrombotic thrombocytopenic purpura and one with vasculitis) had significantly higher plasma beta-thromboglobulin levels than four patients with extravascular platelet destruction due to idiopathic thrombocytopenic purpura. Five patients with thrombocytopenia and decreased numbers of megakaryocytes in the bone marrow also had beta-thromboglobulin levels that were not elevated. Two patients with thrombotic thrombocytopenic purpura achieved clinical remission associated with a decrease in beta-TG level to the normal range. Plasma beta-thromboglobulin determination can be useful in determining the mechanism of thrombocytopenia when bone marrow examination demonstrates adequate megakaryocyte numbers.

Beta-Globulins↗
PubMed1981

Thrombotic thrombocytopenic purpura: prolonged coma with recovery of neurologic function with intensive plasma exchange.

A 45-year-old-woman was presented with fever, microangiopathic hemolytic anemia, thrombocytopenia, purpura, and mental status changes. She was diagnosed as having thrombotic thrombocytopenic purpura (TPP). She was treated with daily plasma exchange and antiplatelet drugs, steroids, and vincristine. This patient had a remarkable course with 18 days of coma on full therapy followed by essentially complete recovery coincident with an increase of the plasma exchange dose to two plasma volumes processed per procedure. The patient has remained well with discontinuation of plasma exchange. We conclude that prolonged coma without evidence of major central nervous system structural lesions in TTP should be treated vigorously and continuously with plasma exchange.

Aspirin↗