Biomedical subjects

D J Donohue

Publications and source records attributed to D J Donohue.

7 recordsLinked to original sources

PubMed1996

A numerical test of the normal incidence uniaxial model of corneal birefringence.

The suggestion that the central cornea can be modeled as a uniaxial birefringent material with its optic axis normal to the surface is explicitly tested by numerical calculations. A theoretical framework is presented to model the corneal stroma as a series of stacked, uniaxial birefringent layers (lamellae). Calculations are then made of the transmission of normally incident, linearly polarized light through model systems having various azimuthal orientations of the layers, motivated by the suggestion of an overall "random" organization of the stromal lamellae. It is concluded that the uniaxial description, and the assumptions upon which that description is based, do not hold for the cornea. In particular, the calculations are in agreement with recent experiments in which one always observes a non-zero cross-polarized transmission (hence birefringence) at normal incidence.

Animals↗

PubMed1995

Numerical modeling of the cornea's lamellar structure and birefringence properties.

A model of the cornea's lamellar structure is proposed that is capable of explaining experimental results obtained for the transmission of normal-incidence polarized light through rabbit and bovine cornea. The model consists of a large number of planar lamellae, each approximated as a uniaxial birefringent layer, stacked one upon another with various angular orientations. Polarized light transmission through the composite system is modeled theoretically by use of the Jones matrix formalism. The light transmission is calculated numerically for a large number of model lamellae arrangements, each generated from a statistical description, and histograms are constructed of various properties of the light transmission, including the minimum and maximum cross-polarized output intensities. It is demonstrated that various structural and optical parameters of the lamellae arrangements of actual corneas may be estimated by comparison of the calculations with detailed experimental data. Certain characteristics of the histograms are identified that permit a clear distinction between random and partially ordered systems. Comparisons with previously published experimental data provide strong evidence that the lamellae orientations are not entirely random, but rather a significant fraction are oriented in a fixed, preferred direction.

Animals↗

PubMed1989

Asymptomatic left main coronary artery disease and silent myocardial ischemia.

Gathering data on the prognosis, detection, and natural history of asymptomatic left main coronary artery disease with silent myocardial ischemia is difficult. Epidemiologic studies of unexpected death and postmortem studies on silent myocardial infarction suggest this entity to be common. We reviewed 89 consecutive patients with left main coronary artery disease (LMD), defined as 50% or greater reduction of luminal diameter. Of this group, 10 patients (11%) were asymptomatic (ALMD) and 79 patients (88%) were symptomatic (SLMD). All 10 ALMD patients were men, with a mean age of 53 years (range 40 to 65). Treadmill tests (TMT) were performed for: ECG abnormalities six; pre-jogging evaluation two; risk factor evaluation two. The TMT within 9 minutes showed 2 mm or greater ST depression in seven (70%) and 1 to 2 mm in three (30%). Similar TMT results were obtained in the SLMD group, although two patients had negative responses. The degree of stenosis of the left main coronary artery and the frequency of three-vessel disease were similar in both groups. The ejection fraction (EF) and contractile pattern of the left ventricle (LV) were normal in all 10 ALMD patients, but the left ventricular end-diastolic pressure (LVEDP) was abnormal in three (70%). In the SLMD group, 51 (64%) had an abnormal ejection fraction, 50 (65%) had wall motion abnormalities, and 25 (32%) had an abnormal LVEDP.

Adult↗

PubMed1984

Effects of nadolol on the spontaneous and exercise-provoked heart rate of patients with chronic atrial fibrillation receiving stable dosages of digoxin.

Nadolol, a long-acting beta-adrenergic-blocking agent, was evaluated in 20 patients with chronic atrial fibrillation by means of a randomized, double-blind, crossover study. Patients were required either to demonstrate resting heart rates in excess of 80 bpm or to show a rate of 120 bpm or an increment of greater than 50 bpm during mild treadmill exercise provocation (3 minutes, 1.75 mph, 10% grade). With placebo the group averaged a heart rate of 92 +/- 19 bpm, determined by 24 hours of ambulatory ECG recordings; this rate was significantly reduced to 73 +/- 16 bpm (p less than 0.001) with nadolol (mean dosage, 87 +/- 43 mg/day). During standardized exercise testing, heart rates increased to 153 +/- 26 bpm with placebo and to 111 +/- 24 bpm with nadolol (p less than 0.001), representing 65% and 52% increments, respectively. Digoxin blood levels averaged 0.8 +/- 0.5 ng/ml with placebo and were similar with nadolol (0.9 +/- 0.4; p = NS). Total exercise time on a modified Bruce treadmill protocol was 466 +/- 143 seconds with placebo and was significantly decreased by nadolol (380 +/- 143; p less than 0.01). During initial dose titration with nadolol, one patient was dropped from study for intolerable fatigue and one for worsened claudication. No patients were dropped from the double-blind treatment periods, although two patients receiving nadolol and one patient receiving placebo complained of moderate fatigue. We conclude that nadolol is a safe and effective agent for the control of spontaneous and exercise-provoked heart rates in patients with chronic atrial fibrillation who were already receiving digoxin treatment.

Adrenergic beta-Antagonists↗

PubMed1983

A new oral slow release form of isosorbide dinitrate. Effect on the hemodynamics and exercise capacity of patients with angina.

To assess the bioavailability of a new oral and slow release form of isosorbide dinitrate (ISDN-SR), we evaluated 12 patients with confirmed coronary artery disease, chronic stable angina pectoris and abnormal maximal exercise tests (angina-limited and associated with greater than or equal to 0.1 mV ST displacement). Each patient was known to have an increased exercise time after 0.4 mg of sublingual nitroglycerin. Patient responses to exercise on the treadmill at two, four, six, and eight hours after the double-blind administration of 40 mg of ISDN-SR were compared to an identical placebo. It is concluded that 40 mg of this slow release form of isosorbide dinitrate is bioavailable for at least eight hours as demonstrated by significantly improved exercise capacity of the majority (64 percent) of angina patients in this study, each of whom demonstrated anginal limitation to exercise and favorable responses to 0.4 mg of sublingual nitroglycerin.

Administration, Oral↗

PubMed1981

ST-segment elevation with elective DC cardioversion.

Elective direct-current cardioversion was performed in three patients with atrial fibrillation. Transient ST-segment elevation on monitored leads, lasting seconds, was recorded after cardioversion in all three patients. LDH, CPK isoenzymes, and myocardial scintigraphy did not reveal myocardial damage. Elective cardioversion should be performed with caution, for the potential for cardiac damage cannot be ignored.

Adult↗

PubMed1980

Björk-Shiley mitral valvular dehiscence. Documented by radiography, echocardiography, fluoroscopy, and cineangiography.

This case report presents combined radiographic, echocardiographic, fluoroscopic, and cineangiographic findings of the dehiscence of a Bjork-Shiley mitral prosthetic valve. The valvular dehiscence was confirmed at surgery. A distinct rounding of the opening phase of the valve was recorded on the echocardiogram. Other clinical evidence, documenting the severe valvular dehiscence, is reported in detail. Non-invasive procedures are therefore invaluable in recording prosthetic valvular dysfunction.

Adult↗