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Biomedical subjects

R D White

Publications and source records attributed to R D White.

At least 19 recordsLinked to original sources
PubMed1992

Cardiac tumors: diagnosis and management.

The first step towards the diagnosis of cardiac neoplasia is made when the clinician considers the diagnosis. While the classically described signs and symptoms of left-atrial myxomas are noteworthy, the vast majority of patients present with symptomatology that is less specific--either of a constitutional nature, or related to right- or left-sided congestion. Likewise, the physical examination may rarely disclose classic auscultatory signs, but is more likely to confirm the presence of the right- or left-sided congestion inferred from history. Peripheral, embolic, or vasculitis lesions should raise suspicion of the diagnosis. Nevertheless, the majority of patients will be diagnosed by the unexpected detection of a tumor at the time of echocardiography. Transthoracic echocardiography remains the procedure of choice in screening for cardiac neoplasia. It has excellent sensitivity for intracavitary and endocardial lesions. Myocardial lesions are also well imaged. Pericardial lesions, with or without extension into contiguous structures, are poorly visualized and, here, magnetic resonance imaging is unquestionably the superior investigative approach. Further, a limited degree of tissue characterization is possible with the latter technology. Transesophageal echocardiography is ideally suited for the examination of suspected tumors involving the atria, interatrial septum, superior vena cava, atrioventricular valves and, to a lesser extent, the ventricles. These three imaging modalities clearly complement one another and the choice of application will depend upon factors including the patient's transthoracic echogenicity, the availability of magnetic resonance imaging or transesophageal echocardiography, cost, and the physical status of the patient.

Angiocardiography↗
PubMed1992

The hemodynamics of vacuum constriction erections: assessment by color Doppler ultrasound.

Duplex ultrasound with pulsed Doppler and color flow sonography were used to image the penis and conduct blood flow velocity studies in 5 patients. Cavernous body cross sectional area, cavernous artery diameters and peak systolic velocities were measured in the flaccid shaft, after transient exposure to negative pressure in a vacuum constriction device, and with a vacuum constriction device band applied to the tumescent shaft. We found that exposure to vacuum transiently increased central cavernous arterial blood flow velocities compared to baseline values in all patients. After a trial of a vacuum constriction device and application of the constricting band cavernous body cross sectional areas doubled. Despite increased cavernous arterial diameters in 4 of 5 patients and increased blood flow in all patients after vacuum-induced tumescence alone, we could not visualize arterial inflow in the penile shaft once the constricting band was in place. Color Doppler ultrasound can detect cavernous artery systolic flow as low as 2 to 9 cm. per second. Our data suggest that the erectile state maintained distal to the vacuum constriction device band is low flow and relatively ischemic.

Aged↗
PubMed1992

Out-of-hospital pleomorphic ventricular tachycardia and resuscitation: association with acute myocardial ischemia and infarction.

Pleomorphic ventricular tachycardia is characterized by QRS complexes with repeated variation in polarity, amplitude, and regularity. When associated with prolongation of the QT interval, the term torsades de pointes is used to describe the arrhythmia. It usually is seen clinically in association with class IA antiarrhythmic drugs such as quinidine and procainamide, bradycardia, hypokalemia, and, much less often, other drugs and electrolyte disorders as well as a result of congenital and neurogenic causes. It also may accompany acute myocardial infarction or ischemia. We describe four patients in whom pleomorphic ventricular tachycardia was observed as the presenting rhythm or during the course of resuscitation in out-of-hospital cardiac arrest. In all four patients, acute myocardial ischemia appeared to be the provocative mechanism. Therapeutic implications include an awareness of the unusual behavior of this arrhythmia, especially its propensity to terminate spontaneously. Such awareness may prevent the delivery of unnecessary defibrillatory shocks.

Acute Disease↗
PubMed1992

Prehospital recognition of multifocal atrial tachycardia: association with acute myocardial infarction.

Patients with chronic obstructive pulmonary disease and acute decompensation commonly present with an irregularly irregular supraventricular tachycardia that is, in fact, multifocal atrial tachycardia, but frequently misdiagnosed as atrial fibrillation. To heighten awareness of this arrhythmia, its clinical and electrocardiographic presentations, and its potential therapeutic implications, two patients are reported who presented with multifocal atrial tachycardia during prehospital care. In these two patients the clinical substrate was not chronic obstructive pulmonary disease but instead acute myocardial infarction. By means of a high index of clinical suspicion and close scrutiny of an electrocardiogram, a diagnosis of multifocal atrial tachycardia can be established during prehospital management, and potentially ineffective therapeutic interventions can be avoided, both during prehospital care and in the emergency department.

Aged↗
PubMed1992

Protective effects of a novel perfluorochemical emulsion in photodynamic therapy.

The effects of pre-injection of mice with a novel perfluorodecalin-based emulsion on the responses to photodynamic therapy (PDT) using the photosensitizer, metatetra (hydroxyphenyl) porphyrin (m-THPP), have been studied. Injection of emulsion after m-THPP and before illumination (activating wavelength 648 nm) protected skin against PDT-induced inflammatory effects, as reflected by decreases (P less than 0.05) in vascular permeability and oedema formation. However, there was no protection against epidermal cell loss. In contrast, injection of emulsion before sensitizer had no corresponding effect. A fall in mean dermal temperature of up to 6 degrees C occurred in mice injected with emulsion 1-2.5 h before illumination suggesting a decrease in skin blood flow which would reduce oedema formation. Possible mechanism(s) for this apparent protective effect are discussed.

Animals↗
PubMed1991

Single-lung transplantation with atrial septal defect repair for Eisenmenger's syndrome.

Heart-lung transplantation has been used successfully for patients with pulmonary vascular disease but its application has been very limited due to the scarcity of donors. We report a patient with Eisenmenger's syndrome who underwent right single-lung transplantation with closure of atrial septal defect; postoperative convalescence was uneventful. Serial magnetic resonance imaging examinations demonstrate improved right heart function.

Adult↗
PubMed1990

Perfluorochemicals and photodynamic therapy in mice.

The effects of pre-treatment with a novel PFC emulsion on PDT-induced tumor necrosis have been studied in mice. Injection of emulsion either 2.5 hr or 24 hr before PDT did not affect the depth of tumour necrosis. However, pre-treatment with the emulsion appeared to protect skin against photodynamic damage although the mechanism(s) and active principle(s) involved were not identified. These results suggest that there may be specific advantages in using emulsified PFCs in conjunction with PDT which may be independent of changes in tumour oxygenation.

Animals↗
PubMed1990

Induction of maternal toxicity in the rat by dermal application of retinoic acid and its effect on fetal outcome.

Time-mated Sprague-Dawley rats were administered all-trans-retinoic acid (RA) dermally on gestational days 11 through 14 at three dosage levels (25, 100, and 250 mg/kg body weight). Dams administered ethylenethiourea (ETU) dermally on gestational days 11 to 12 or RA orally on day 12 were used to indicate the strain's sensitivity to teratogenesis. The chemicals were dissolved in dimethylsulfoxide (DMSO) for dermal application or suspended in corn oil for treatment by gavage. The maternal weight gain, pup weight, number of resorptions and number of fetuses with gross malformations, and skeletal/organ-level anomalies were determined. Beginning with day 15, dams dermally treated with RA exhibited dermal lesions at the site of application, most dams showed vaginal bleeding by day 16, and approximately 20% did not survive to day 19. Relative to the DMSO control group, maternal weight gain in the dermal RA groups was decreased by approximately 50% at the lowest dose, with essentially no weight gain at the intermediate- and high-dose levels. The decrease in average fetal weight at the two higher doses was significant, whereas the resorption and malformation frequencies were not significantly increased by dermal treatment with RA. Without significantly affecting fetal weight or resorption frequency, dermal application of ETU significantly increased the frequency of skeletal anomalies, primarily tail defects. Oral administration of RA did not increase the malformation frequency nor produce significant maternal or fetotoxic effects. In summary, treatment of pregnant Sprague-Dawley rats by dermal application of RA dissolved in DMSO resulted in significant toxicity to the dam.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities, Drug-Induced↗
PubMed1990

Functional cardiovascular evaluation by magnetic resonance imaging.

The pursuit of capabilities for the evaluation of functional aspects of cardiovascular disease by MRI has resulted in the development and implementation of a number of interesting techniques that can be performed on a conventional scanner. Some currently available techniques emphasize the production of anatomically accurate images representing different phases of the cardiac cycle; others demonstrate physical changes within the acquired data that reflect motion, such as blood flow. Magnitude data from spin-echo and gradient-echo sequences can be used to produce dynamic images of the cardiovascular system. Phase data can be used to generate flow-based images reflecting the movement of blood protons. These techniques can be applied in the evaluation of ventricular function, valve function, or functional abnormalities in either congenital cardiovascular disease or great artery disease.

Cardiovascular Diseases↗
PubMed1979

An ultrasonic study of the thermotropic transition of dipalmitoyl phosphatidylcholine.

The acoustic absorption of sonicated and unsonicated suspensions of dipalmitoyl phosphatidylcholine has been studied as a function of temperature at frequencies between 0.6 and 4.0 MHz. The absorption at a fixed frequency passes through a maximum at a temperature which is dependent on the sample preparation and history and somewhat dependent on the frequency of observation, with sonicated vesicles exhibiting a temperature of maximum absorption 2--3 degrees C below that found for unsonicated dispersions. The temperature dependence of the absorption at fixed frequency suggests a cooperative process while the frequency dependence of the absorption at fixed temperature indicates that more than a single relaxation time is required to describe the acoustic absorption.

Liposomes↗
PubMed1979

Anesthetic considerations for aortocoronary bypass graft surgery.

Between 1964 and 1978, aortocoronary bypass graft procedures were performed in more than 300,000 patients, and the number seems to increase every year. Nevertheless, the procedure itself can result in perioperative myocardial infarction leading to death. Greater understanding of and constant attention to the myocardial oxygen (O2) supply and demand may reduce the incidence of perioperative myocardial infarction. Some of the factors influencing supply and demand can be controlled pharmacologically. Drugs such as nitroglycerin, nitroprusside, and propranolol can reduce the myocardial O2 demand. Unfortunately, there are few data to elucidate the relationship between myocardial O2 demand and supply as influenced by anesthetic drugs, especially in patients with myocardial ischemia. However, enthusiasm for aortocoronary bypass graft operations has given enormous impetus to laboratory and clinical studies of this subject. Recent developments in anesthetic management afford better means for protection of the ischemic myocardium during and after operation.

Adjuvants, Anesthesia↗
PubMed1979

[3H]gamma-Aminobutyric acid uptake into neuroglial cells of rat superior cervical sympathetic ganglia.

1. The influx of [3H]gamma-aminobutyric acid ([3H]GABA) into isolated rat superior cervical ganglia has been measured by radioassay, supplemented by autoradiography. Ganglia were incubated in oxygenated Krebs solution at 25 degrees C, containing 10 microM-amino-oxyacetic acid. Under these conditions more than 95% of accumulated tritium was unmetabolized [3H]GABA. 2. Ganglionic radioactivity increased linearly with incubation time, to yield an intracellular fluid/extracellular fluid concentration ratio (Ci/Co) of about 200 after 6 hr in 0.5 microM-external [3H]GABA. 3. Uptake showed saturation with an apparent transport constant (KT) of 6.8 microM and maximum influx velocity (Jmaxi) of 7 mumole 1. cell fluid-1- min-1. 4. The influx rate at Co = 0.5 microM was unaltered by raising intracellular GABA from 0.2 to 1 mM. 5. Influx velocity increased with temperature (5--35 degrees C) in a monotonic manner with an apparent activation energy of 14 kcal mole-1. 6. Concentrative uptake was depressed by reducing external [Na+] with ouabain, by raising [K+]o above 20 mM, or by removing external Cl-. Uptake was not particularly sensitive to Ca2+ or Mg2+ ions. 7. Utake of [3H]GABA (0.5 microM) was inhibited by beta-guanidinopropionic acid (apparent KI, 28 microM), beta-alanine (KI, 55 microM), gamma-amino-beta-hydroxybutyric acid (KI, 220 microM), beta-amino-n-butyric acid (KI, 708 microM), 3-aminopropanesulphonic acid (KI, 832 microM) and taurine (KI greater than 1 mM). Uptake was not depressed by 1 mM-glycine, alpha-alanine, leucine, serine, methionine or alpha-amino-iso-butyric acid. 8. Radioactively labelled methionine, leucine, glycine, serine, beta-alanine and taurine (concentrations less than or equal to 5 microM) were also taken up by ganglia. Of these, only uptake of beta-alanine and taurine were significantly depressed by 1 mM-GABA. 9. Autoradiographs confirmed that [3H]GABA and [3H] beta-alanine were taken up predominantly into extraneuronal sites (presumed to be neuroglial cells). Methionine, leucine, glycine and serine showed preferential accumulation in neurones. Neuronal uptake of leucine was not prevented by inhibiting protein synthesis. 10. Calculations of net fluxes from unidirectional tracer fluxes suggest that the sympathetic glial cells are capable of promoting net uptake of GABA at external concentrations above 1 microM.

Amino Acids↗
PubMed1979

Comparison of capillary ear blood and arterial blood to validate capillary sampling as an accurate assay of blood gas in swine.

Capillary sampling in swine can be performed as an accurate assay of arterial blood gases. Studies with swine provided results similar to, or slightly more favorable than, those reported for human beings, depending upon which cutaneous technique was used on human beings. On the basis of free flow or arterilization of the cutaneous sample and of the correlation between capillary and arterial pH, CO2 partial pressure (PCO2), and O2 partial pressure (PO2) values, the capillary sampling technique of complete incisement of a 2-mm section from the tip of the warmed porcine ear could be a substitution technique for arterial blood sampling. Free flow with this technique was maximized and high correlation coefficients (r) for pH (r = 0.96), PCO2 (r = 0.82), and PO2 (r = 0.90) capillary-arterial values (n = 37) were obtained.

Animals↗