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Biomedical subjects

R D White

Publications and source records attributed to R D White.

At least 109 records · Page 6Linked to original sources
PubMed1993

Toxicity evaluations of L-cysteine and Procysteine, a cysteine prodrug, given once intravenously to neonatal rats.

Decreased enzymatic production of cysteine in premature and newborn infants may limit the synthesis of glutathione. Unfortunately, cysteine supplementation is limited by associated toxicity and product instability. Procysteine (L-2-oxothiazolidine-4-carboxylate) is a prodrug of cysteine that is inert until metabolized to cysteine intracellularly, thus stimulating glutathione synthesis. The potential toxicities of cysteine and Procysteine were compared in two studies with neonatal rats (10 per group; 3 +/- 1 days of age) after a single intravenous administration. In one study, acute high dosage survivorship was compared for approximately equimolar cysteine dosages of L-cysteine and Procysteine. Mortality at 7 days after single intravenous dosages of L-cysteine at 1.52 or 1.14 g/kg or Procysteine at 1.80 or 1.35 g/kg was 80, 50, 10 and 0%, respectively. Clinical pathology parameters and body and organ weights were compared in a second study, following a moderate dosage of Procysteine or equimolar or lower dosages of L-cysteine. No differences were observed in clinical pathology parameters nor body or organ weights at 14 days following single intravenous dosages of L-cysteine at 369, 185 or 37 mg/kg or Procysteine at 450 mg/kg. Also, Procysteine solutions were considerably more stable than L-cysteine solutions (months vs. hours, respectively). These studies indicated that cysteine supplementation in infants may be enhanced by Procysteine administration.

Animals↗
PubMed1993

Differentiation of constrictive pericarditis from restrictive cardiomyopathy by Doppler transesophageal echocardiographic measurements of respiratory variations in pulmonary venous flow.

OBJECTIVES: The purpose of this study was to test the utility of measuring respiratory variation in pulmonary venous flow by transesophageal echocardiography. BACKGROUND: Respiratory variation of atrioventricular and central venous flow velocities by Doppler echocardiography has been used to differentiate constrictive pericarditis from restrictive cardiomyopathy. METHODS: We performed pulsed wave Doppler transesophageal echocardiography of the left or right pulmonary veins in 31 patients with diastolic dysfunction. Fourteen patients had constrictive pericarditis, and 17 had restrictive cardiomyopathy. We measured the pulmonary venous peak systolic and diastolic flow velocities and the systolic/diastolic flow ratio with transesophageal echocardiography during expiration and inspiration. The percent change in Doppler flow velocity from expiration to inspiration (%E) was calculated. RESULTS: Pulmonary venous peak systolic flow in both inspiration and expiration was greater in constrictive pericarditis than in restrictive cardiomyopathy. The %E for peak systolic flow tended to be higher in constrictive pericarditis (19% vs. 10%, p = 0.09). In contrast, pulmonary venous peak diastolic flow during inspiration was lower in constrictive pericarditis than in restrictive cardiomyopathy. The %E for peak diastolic flow was larger in constrictive pericarditis (29% vs. 16%, p = 0.008). The pulmonary venous systolic/diastolic flow ratio was greater in constrictive pericarditis in both inspiration and expiration. The combination of pulmonary venous systolic/diastolic flow ratio > or = 0.65 in inspiration and a %E for peak diastolic flow > or = 40% correctly classified 86% of patients with constrictive pericarditis. CONCLUSIONS: The relatively larger pulmonary venous systolic/diastolic flow ratio and greater respiratory variation in pulmonary venous systolic, and especially diastolic, flow velocities by transesophageal echocardiography can be useful signs in distinguishing constrictive pericarditis from restrictive cardiomyopathy.

Blood Flow Velocity↗
PubMed1993

Comparison of axillary artery or brachial artery pressure with aortic pressure after cardiopulmonary bypass using a long radial artery catheter.

Arterial pressure measured in a peripheral artery may significantly underestimate central arterial pressure after discontinuation of cardiopulmonary bypass (CPB). Arterial pressure measured with a 50 cm radial artery catheter advanced into the brachial or axillary artery was compared to ascending aortic pressure in 31 patients before and after discontinuation of CPB. The radial artery catheter extended proximally into the brachial artery in 8/31 patients, and into the axillary artery in 23/31 patients. The patient's age, pre-CPB cardiac ejection fraction, and surgical procedures were similar in both groups. The systolic arterial pressure measured in the ascending aorta was found to be significantly different from that in the axillary artery after CPB, whereas the mean and diastolic pressures were not. The average aorta-to-axillary artery systolic pressure gradient was -3.0 +/- 4.0 mmHg, with no patient having a gradient greater than 10 mmHg. The systolic and mean arterial pressures measured in the ascending aorta were found to be significantly different from that in the brachial artery after discontinuation of CPB, whereas the diastolic pressure was not. The average aorta-to-brachial artery systolic pressure gradient was 6.9 +/- 6.9 mmHg, with 3/8 patients having a gradient greater than 10 mmHg. Long radial artery catheters, placed using the Seldinger technique, provide an accurate estimate of central aortic pressure after CPB when they are advanced into the axillary artery. Sites more distal than the axillary artery may result in significant underestimation of the central aortic pressure in these patients.

Aged↗
PubMed1993

Maintenance of defibrillators in a state of readiness.

Since 1984, the US Food and Drug Administration (FDA) has utilized the Medical Device Reporting system as a mechanism for reporting adverse incidents associated with the use of medical devices, including external defibrillators. The frequency and content of these reports prompted an FDA-conducted five-state study of defibrillator-user training and maintenance practices for both devices and batteries. The study also included inspection and testing of defibrillators and batteries to assess their state of maintenance. A detailed review of the reports and of the five-state data confirmed that in the majority of cases, adverse incidents were related to improper defibrillator operation and maintenance, prompting the FDA Center for Devices and Radiological Health to launch an educational effort directed toward those who operate and maintain defibrillators. Proper maintenance of batteries (both nickel-cadmium and sealed lead-acid) was a major component of the educational thrust, because battery failure was identified as a recurrent and preventable problem. In an effort to correct the diverse types of incidents being reported, checklists were developed by the FDA for both manual and automated defibrillators. The checklists are designed to cover the spectrum of reported problems related to both device and user. The advent of more stringent FDA adverse incident-reporting regulations, coupled with increased use of defibrillators in diverse settings with varying usage frequencies, would seem to give a major impetus to the regular use of these checklists wherever defibrillators are employed.

Electric Countershock↗
PubMed1993

Cardiac radiology. A survey of its current status.

RATIONALE AND OBJECTIVES: A number of pressures have taken their toll on cardiovascular (CV) imaging in radiology. We conducted a survey to develop accurate information about the current status of cardiac radiology (CR) that might guide future responses and initiatives. METHODS: To assess the current status of CR, a survey form was sent to all 117 active radiologist members of the North American Society for Cardiac Imaging (N = 72) and/or the Council on Cardiovascular Radiology of the American Heart Association (N = 98). The topics of inquiry included 1) present CR staffing; 2) specific adult and pediatric CR activities (cardiac plain-film interpretation, cardio-angiography (CA), echocardiography, nuclear cardiology (NC), and CV magnetic resonance imaging (MRI); 3) CR instruction of radiology residents; and 4) CR fellowship activities. RESULTS: The survey was concluded with 64 (55%) individual responses from 58 (67%) different centers with CR groups. An overall need for CR staff (average unfilled positions/center = 0.4) was indicated. Regarding CR activities, the following were reported: 1) universal cardiac plain-film interpretation by radiologists, with most CR groups involved (adult, 64%; pediatric, 64%); 2) moderate CR contributions to CA (adult, 62%; pediatric, 57%), of which cine interpretation was the most common form (79% and 85%, respectively); 3) rare CR involvement in echocardiography (adult, 9%; pediatric, 6%); 4) low-level CR involvement in NC (adult, 16%; pediatric, 17%), but high level when combined with that of nuclear medicine (93% and 91%, respectively); and 5) almost universal radiology responsibility for CV MRI (adult, 96%; pediatric, 96%), with extensive CR involvement (77% and 82%, respectively). Of 46 reporting academic centers, most (76%) required CR training of residents; a smaller proportion (33%) of all centers offered CR fellowships. CONCLUSIONS: Because of the insights gained from this survey, recommendations can be better made to strengthen CR based on a foundation in plain-film interpretation, computed tomography, NC, and MRI.

Adult↗
PubMed1993

Initial experience with the maze procedure for atrial fibrillation.

From January 1991 until May 1992, a total of 14 patients (mean age 48 years) underwent the maze procedure for refractory atrial fibrillation (mean duration, 7 years; mean number of antiarrhythmic medications, six). Three patients had had embolic events, one patient had had a cardiac arrest from flecainide, one had pulmonary fibrosis from amiodarone, and six of ten who were employed were temporarily disabled. Two patients underwent successful mitral valve repair in which the maze procedure was added as a secondary goal of the operation. Postoperative fluid retention was a problem in five patients (36%). Six patients (43%) were temporarily treated with an antiarrhythmic medication. Two patients (14%) with preoperative sick sinus syndrome required pacemakers. One patient was discharged from the hospital but died suddenly less than 1 month after the operation (7% operative mortality) of hyperkalemia caused by acute renal failure. All patients beyond 3 postoperative months (100% "cure") are receiving no antiarrhythmic medications, have sinus rhythm, or have p-wave tracking with ventricular pacing. Atrial contraction has been documented by cinegraphic magnetic resonance imaging studies and by Doppler echocardiography performed when sinus rhythm had resumed. The maze procedure is an extensive operation but is indicated for selected patients who have the severe sequelae of atrial fibrillation.

Adult↗
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↗