Search PubMed⌕ Search

Biomedical subjects

R D White

Publications and source records attributed to R D White.

At least 145 records · Page 8Linked to original sources
PubMed1989

Effect of the manipulation of oxyhemoglobin status by BW12C on tumor thermosensitivity and on blood flow in tumor and normal tissues in mice.

The effect of 70 mgkg-1 BW12C 30 min before heating on the thermosensitivity of RIF-1 leg tumors was studied. This schedule is known to increase the hypoxic fraction by a factor of 5. Heating, using a combined radio-frequency and saline bath technique, was for 30 min at 43, 43.5, and 44 degrees C and response was assayed by clonogenic cell survival immediately and 24 hr after treatment. BW12C did not alter RIF-1 thermosensitivity. The effects of heat up to 44 degrees C on the oxygen saturation curves of normal and BW12C-modified blood were compared and P50s were shown to rise from 36 to 52 mm Hg and 6.5 to 8.0 mm Hg respectively, showing the latter to be relatively resistant to right-shifting by heat. 86Rb extraction studies on BW12C-treated unheated animals showed that blood flow in leg and flank tumours 60 min after BW12C was reduced to 64% and 34% of control values respectively, indicating a further mechanism for induction of tumour hypoxia by BW12C. Blood flow in leg muscle, liver, and spleen was unchanged but in kidney and lung was increased to 127% and 119% of control respectively 60 min after BW12C.

Aldehydes↗
PubMed1989

The automatic internal cardioverter defibrillator (AICD): description and guidelines for interaction during cardiac arrest.

The development and increasing use of the automatic implantable cardioverter defibrillator (AICD) represents a major therapeutic advance for management of recurrent ventricular tachycardia and ventricular fibrillation. However, the AICD sensing functions that determine appropriate energy discharge may complicate resuscitation from cardiac arrest. This care report illustrates a properly functioning AICD interfering with the resuscitation of a 67-year-old man. In the presence of persistent ventricular tachycardia and ventricular fibrillation or successful conversion to a supraventricular tachycardia with pulses that exceed the rate cutoff, it may be helpful to inactivate the AICD with a magnet to prevent unneeded discharges during resuscitation and stabilization.

Aged↗
PubMed1989

Perioperative cardiac pacing using an atrioventricular pacing pulmonary artery catheter.

An atrioventricular pacing thermodilution pulmonary artery catheter was evaluated in 40 patients undergoing cardiac surgery. The catheter was inserted in all study patients in a timely fashion without difficulty and functioned well during the perioperative period. Before the start of cardiopulmonary bypass, atrial capture was achieved in 98% of the patients (threshold mean 4.9 mA), ventricular capture in 100% (threshold mean 3.0 mA) and atrioventricular sequential (AVS) pacing in 98%. After cardiopulmonary bypass, atrial capture was achieved in 95% of the patients (threshold mean 5.2 mA), ventricular pacing in 100% (threshold mean 3.1 mA), and sequential pacing in 95%. In 27 patients in whom cardiac outputs were recorded, cardiac index increased an average of 45% (range 8% to 95%) with atrial or AVS pacing over ventricular pacing alone. In 11 patients, extended atrial pacing was used postoperatively, the longest for 93 hours. No major complications could be attributed to the study catheter. Minor complications included diaphragmatic stimulation in one patient and supraventricular tachycardia, possibly related to atrial pacing postoperatively, in one patient. These data suggest that this catheter/pacing system is effective and reliable for hemodynamic monitoring and temporary atrial or AVS pacing. In addition, the atrial pacing probe can be used perioperatively to record atrial electrograms to facilitate the diagnosis of supraventricular tachyarrhythmias.

Aged↗
PubMed1989

Magnetic resonance imaging of thoracic vascular disease.

Magnetic resonance imaging (MRI) appears to provide at least as much diagnostic information as angiography in the evaluation of acquired and congenital forms of disease of the great arteries. Since it can also be used to assess the tissues adjacent to the great arteries, MRI often provides a distinct diagnostic advantage over angiography. In addition, the recently introduced dynamic MRI techniques may provide valuable information regarding hemodynamic abnormalities associated with diseases of the thoracic aorta and the pulmonary arterial system.

Humans↗
PubMed1989

Influence of bovine intestinal fluid on the expression of K99 pili by Escherichia coli.

A study was conducted to determine whether intestinal fluid collected from various portions of bovine intestine differed in its effect on production of K99 pili by Escherichia coli. The small and large intestines of 7 calves, euthanatized 4 hours after a final feeding of milk, were divided into 6 to 9 segments from which intraluminal fluids were collected. Depending on the amount of fluid collected, up to 20 E coli strains that express K99 pili were grown on media prepared from the content of each specimen and then were tested for K99 pilus expression. In general, intestinal fluid from the most proximal small intestinal segments were more suppressive to K99 pilus expression than was fluid from more distal segments of small intestine. Only about 20% of the E coli test strains expressed K99 pili when grown on medium prepared from proximal small intestinal segmental fluid, whereas greater than 90% did when grown on medium prepared from distal small intestinal segmental fluid. Fluid from the large intestine varied considerably from calf to calf in its effect on K99 pilus expression. A correlation was found between K99 pilus expression and pH of the intestinal fluid, with the lower pH values (characteristic of proximal intestinal segmental fluid) being suppressive. The correlation between K99 pilus production and the pH of the medium was verified, using defined laboratory media adjusted to various pH values. Strains of E coli grown in medium at or below pH 5.5 failed to express K99 pili, whereas the same strains when grown in medium at or above pH 6.5 expressed K99 pili in abundance.

Amino Acids↗
PubMed1988

Evaluation of a QRS scoring system for estimating myocardial infarct size. VI: Identification of screening criteria for non-acute myocardial infarcts.

Each of the 54 criteria in the Selvester 32-point QRS scoring system for estimation of myocardial infarct (MI) size has attained greater than or equal to 95% specificity in normal subjects. This study was performed to identify a subset of those criteria with cumulative specificity greater than or equal to 95% and maximal sensitivity for use in screening for the presence of non-acute MI. Coronary angiography and left ventriculography were used to identify 500 normal subjects, 60 patients with isolated anterior MI and 62 patients with isolated inferior MI. Patients with the QRS confounding factors of ventricular hypertrophy, fascicular block or bundle branch block on their electrocardiogram were not included. Using stepwise logistic regression analysis, the screening criteria identified were: (1) Q greater than or equal to 30 ms in aVF, (2) R less than or equal to 10 ms and less than or equal to 0.1 mV in V2 and (3) R greater than or equal to 40 ms in V1. Cumulatively, these 3 screening criteria achieved 84% and 77% sensitivities for inferior and anterior MI groups, respectively. Thus, a set of 3 criteria from the Selvester QRS scoring system is capable of identifying single non-acute anterior or inferior MI in 80% of patients, and falsely indicating presence of MI in only 5% of normal subjects.

Adult↗
PubMed1988

Characterization of high-energy phosphate compounds during reperfusion of the irreversibly injured myocardium using 31P MRS.

Phosphorus-31 magnetic resonance spectroscopy (MRS) was used to monitor regional changes in high-energy phosphorus compounds and intracellular pH during 60 min of acute regional ischemia (acute occlusion of left anterior descending artery) and reperfusion in open-chest cats using a 1.2-cm two-turn coil sutured to the myocardium. During the 60-min ischemic phase, phosphocreatine (PCr) intensity was reduced to 47 +/- 4.9% (mean +/- SE) of control (p less than 0.01) by 15 min postocclusion while adenosine triphosphate (ATP) intensity decreased more slowly with the decrease (66 +/- 5.6%) achieving significance (p less than 0.05) only at 60 min postocclusion. Inorganic phosphate (Pi) increased to a maximum of 397 +/- 42% of control (p less than 0.01) while the pH decreased progressively from 7.36 +/- 0.02 to 6.02 +/- 0.14 (p less than 0.01). After release of occlusion PCr intensity recovered to 86 +/- 12% of the initial control value at 15 min postreperfusion but showed a subsequent downward trend to 79 +/- 8.8%. The ATP did not recover but tended to decline further during reperfusion. The Pi intensity decreased to 260 +/- 38% of control while the pH increased to 7.01 +/- 0.23 by 15 min postreperfusion. Thus, the reperfused irreversibly injured myocardium is characterized by persistent depletion of PCr and ATP and elevation of Pi. Phosphorus-31 MRS provides a nondestructive method for characterizing the reperfused irreversibly damaged myocardium.

Animals↗
PubMed1988

Segmental evaluation of left ventricular wall motion after myocardial infarction: magnetic resonance imaging versus echocardiography.

To assess relative capabilities of magnetic resonance (MR) imaging and two-dimensional echocardiography (2DE) for evaluating regional contractile dysfunction in the left ventricle after a myocardial infarction, results from 22 concurrent MR (orthogonal-transaxial, ECG-gated, multiphasic, single-spin echo) and 2DE examinations were compared. By means of the same 11-segment LV description, MR and 2DE examinations were independently scored segment by segment for residual wall motion (point scores: 2 = normal, 1 = hypokinesia, 0 = akinesia, and -1 = dyskinesia). Significant correlation between MR and 2DE scoring was found throughout most of the left anterior descending (LAD) distribution, but right coronary artery (RCA) distribution (i.e., middle-posterior segment not well seen) could not be fully evaluated by MR imaging. When cumulative scores for the 10 segments mutually evaluated were used to derive measures of global residual LV function (i.e., score quotient [SQ] = accumulated points divided by 20 total possible points), MR SQ correlated well overall with both 2DE SQ (r = 0.82; p less than 0.05) and ejection fraction (EF) from ventriculography (r = 0.86, p less than 0.05 vs r = 0.88, p less than 0.05 for 2DE SQ compared with EF). MR evaluation of segmental wall motion was relatively stronger in the LAD distribution (MR SQ compared with 2DE SQ: r = 0.86, p less than 0.05; MR SQ compared with EF: r = 0.96, p less than 0.05) than in the RCA distribution (r = 0.06, p greater than or equal to 0.05 and r = 0.62, p greater than or equal to 0.05, respectively). For 2DE, regional variations were not as evident (2DE SQ compared with EF: r = 0.90, p less than 0.05 for LAD and r = 0.81, p less than 0.05 for RCA). For segmental evaluation of wall motion after myocardial infarction, MR imaging (transaxial, multiphasic) appears to be comparable to 2DE overall but superior in LAD distribution and inferior in RCA distribution.

Adult↗
PubMed1988

Estimation of the functional and anatomic extent of myocardial infarction using magnetic resonance imaging.

This study assesses magnetic resonance (MR) imaging for the evaluation of both the functional and anatomic extent of damage to the left ventricle (LV) from myocardial infarction (MI). This was accomplished by blinded region-of-interest analysis of 36 MR examinations (orthogonal-transaxial, electrocardiographically-gated, multiphasic, single spin-echo) for determination of ejection fraction (EF) and relative MI volume (i.e., percent of total LV myocardial volume). Comparison of the results was then made with a measure of global residual LV function (i.e., score quotient or SQ) derived from segmental scoring of LV wall motion on a two-dimensional echocardiogram (Echo) and with an EF value from a left ventriculogram (LVG), both performed relatively concurrently with MR. Significant (p less than 0.01) overall correlations were noted between MR-EF and both Echo-SQ (r = 0.56) and LVG-EF (r = 0.78), and these relationships were relatively stronger when MI was located in the right coronary artery (RCA) than when it was found in the left anterior descending (LAD) distribution (e.g., MR-EF compared with LVG-EF: r = 0.87, p less than 0.05 for RCA; and r = 0.48, p = NS for LAD). The best expression of relative MI volume appeared to be based upon absolute volume of regionally-thinned LV wall multiplied by a correction factor for its residual contractility and then the addition of a volume correcting for the amount of regional wall thinning by necrosis (i.e., "total-Fxn" MI volume).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

New perspectives on rural EMT defibrillation.

In recent years, several studies have produced contradictory data regarding the impact of emergency medical technicians trained in defibrillation on hospital admission and dismissal survival rates in rural areas. Fourteen communities (service area populations, 4,000 to 36,000) in rural south-eastern Minnesota participated in a two-year crossover study to further define the factors necessary for success. Automatic external defibrillators were used to defibrillate and record patient rhythms in the treatment group and to only record in the control group. Although six of 36 patients (17%) in ventricular fibrillation who experienced a witnessed arrest survived in communities using automatic external defibrillators, compared with one of 27 (4%) in the control group, five of the six survivors were from a single large community with a 911 system, full-time emergency medical technicians, police first-responders, and a well-equipped emergency facility. Our data suggest that certain prerequisites, especially CPR prior to ambulance arrival and collapse to defibrillation times of less than ten minutes, are clearly essential to produce significant benefits from emergency medical technicians trained in defibrillation in rural communities.

Aged↗
PubMed1988

Aortic dissection: sensitivity and specificity of MR imaging.

Gated transverse magnetic resonance (MR) images of 54 patients (35 male, 19 female; aged 16-90 years) with suspected or known aortic dissection were reviewed by three cardiac radiologists without knowledge of clinical details. The reviewers independently determined the presence or absence and the type of aortic dissection. A confidence level was assigned for each diagnosis, and receiver operating characteristic curves were generated. The reviewer with extensive MR experience correctly identified 96% of the proved aortic dissections and all of the normal cases; the reviewer with moderate experience identified 96% and 84%, respectively; and the reviewer with minimal experience, 78% and 94%. The sensitivity at a specificity level of 90% was determined for each reviewer (100%, 96%, and 83%, respectively). MR imaging is highly sensitive and specific in the diagnosis of aortic dissection but does require considerable experience because of the need to recognize flow artifacts.

Adolescent↗
PubMed1988

Mitral or aortic regurgitation: quantification of regurgitant volumes with cine MR imaging.

A new, rapid magnetic resonance (MR) imaging method, cine MR imaging, was used to determine the regurgitant fraction (RF) in patients with left-sided regurgitant lesions. Right and left ventricular stroke volumes were determined with cine MR imaging and a modified Simpson formula in ten healthy volunteers and 23 patients known to have either predominant mitral (n = 17) or aortic (n = 6) regurgitation. RFs evaluated at cine MR imaging were compared in healthy persons and patients with mild, moderate, or severe regurgitation demonstrated at angiography (n = 10) and Doppler echocardiography (n = 13). Cine MR imaging depicted regurgitant blood flow in all 29 regurgitant lesions in 23 patients as areas of low signal intensity within the regurgitant chamber. The RF was 4% +/- 7% in healthy subjects and 12% +/- 12% in those with mild, 35% +/- 14% in those with moderate, and 63% +/- 5% in those with severe regurgitation. The RFs determined by two observers were similar.

Adult↗
PubMed1988

MR imaging of the aorta after surgery for aortic dissection.

MR imaging is known to be an effective technique for the noninvasive diagnosis of thoracic aortic disease, but it has not been used to monitor the appearance of the aorta or the fate of the false lumen after surgery for aortic dissection. This study describes our initial experience with postsurgical MR imaging of aortic dissection (nine type A and two type B) to evaluate prognostically important features, including the status of residual false lumen. The most notable findings were (1) aneurysmal dilatation beyond the interposed graft (11/11 cases), (2) residual intimal flap (10/11 cases) with at least partial patency of the false lumen (10/10 cases), and (3) origin of a visceral vessel from the false lumen in persistently dissected abdominal aorta (6/9 cases). Evaluation of residual false lumen by double-spin-echo-intensity and phase-display techniques showed evidence of slow blood flow with variable amounts of thrombus in eight of 10 cases. Differentiation between signal within the false lumen due to slow flow and signal due to thrombus was facilitated by phase display. MR imaging can be used for noninvasive monitoring of the aorta after surgical repair of aortic dissection. Since the false lumen usually remains patent after surgical repair, such follow-up of its status seems necessary for identifying potential complications of the original dissection and/or the therapy.

Adult↗
PubMed1988

Quantification of regional myocardial function by rapid cine MR imaging.

The capability of rapid (cine) MR imaging to quantitate left ventricular function was assessed in 13 normal subjects and in 15 patients with ischemic heart disease and regional wall-motion abnormalities proved by echocardiography and/or by contrast ventriculography. Fifteen to 20 MR images/cardiac cycle were acquired by using partial flip angles, short repetition times, and gradient-refocused echoes. Regional wall motion was assessed qualitatively in the equatorial left ventricular section by using the cine display and quantitatively by measuring myocardial thickness at end-diastole and at end-systole in six left ventricular segments in this plane. In normal volunteers wall motion was normal in all segments. Heterogeneity of systolic wall thickening was observed in normal subjects, ranging from 33% +/- 17% in the posteroseptal segment to 66% +/- 29% in the posterior segment. Overall systolic wall thickening was 48% +/- 28%. From the cinematic display of MR images, abnormal wall motion was observed in 40 of 90 segments in patients with ischemic heart disease, which correlated well with results of echocardiography or contrast ventriculography. Twenty-one segments were hypokinetic, 15 were akinetic, and four were dyskinetic. In patients with ischemic heart disease, percentage systolic wall thickening was 43% +/- 31% in the segments with normal wall motion, 6% +/- 18% in hypokinetic segments, -4% +/- 24% in akinetic segments, and -13% +/- 25% in dyskinetic zones. Absolute systolic wall thickening was less than 2 mm in 31 of 40 abnormal segments and was greater than 2 mm in only three. Rapid acquisition, improved temporal resolution, and the capacity for cine display make this new MR technique potentially useful not only for qualitative assessment of cardiac wall motion, but also for quantification of regional myocardial function.

Adult↗
PubMed1988

Coronary artery bypass grafts: evaluation of patency with cine MR imaging.

This report describes our first experiences in using cine MR imaging to assess the status of a coronary artery bypass graft (CABG). This technique uses a low flip angle, a fast repetition rate, and gradient-refocused echoes to produce images in which the signal of flowing blood within even small vascular structures (e.g., CABGs) is enhanced. Twenty-eight CABGs were evaluated by using both cine MR imaging and coronary angiography (as "gold standard"), and the MR images were interpreted blindly for determination of patency or occlusion of the CABGs. The sensitivity of cine MR imaging for determination of CABG patency was 93%, the specificity was 86%, and the overall predictive accuracy was 89%. Because cine MR imaging facilitates the identification of patent vascular structures by enhancing the signal intensity of flowing blood, this technique seems particularly attractive for noninvasively determining CABG patency.

Adult↗
PubMed1988

The ultrasound appearance of radiation-induced hepatic injury. Correlation with computed tomography and magnetic resonance imaging.

The ultrasound findings in three cases of radiation-induced hepatic injury are described and compared with computed tomography and magnetic resonance imaging findings. Fatty infiltration of the liver was present in two of the cases in which concurrent chemotherapy was being administered. On ultrasound B-scans, the regions of radiation injury were hypoechoic relative to the remainder of the liver. This finding was more obvious in the patients with fatty livers. CT scans on the patients with fatty infiltrated livers showed higher attenuation in the irradiated region than in unexposed liver. In the patient where no fatty infiltration was present, the radiated section of liver had lower attenuation consistent with previous reports. Magnetic resonance imaging showed decreased signal in the exposed areas on T1 weighted images.

Child, Preschool↗