Biomedical subjects
M E Ring
Publications and source records attributed to M E Ring.
Attenuation of pulsus alternans during coronary angiography.
Following coronary angiography in a patient with cardiomyopathy and pulsus alternans, we observed a transient but marked attenuation of the alternation in pulse pressure associated with an elevation in pulmonary artery pressure. Attenuation of pulsus alternans has been rarely reported and may represent further deterioration of ventricular function.
Early life of Nathan Cooley Keep, monumental figure in American dentistry.
Explore the source record for details and available documents.
How to rush a dying patient out of the office!
Explore the source record for details and available documents.
Catheter ablation of the ventricular septum with radiofrequency energy.
The safety and feasibility of performing catheter ablation of the ventricular septum with radiofrequency energy was assessed in a closed-chest canine model. Radiofrequency energy (750 kHz) was delivered in a bipolar manner via the distal electrodes of two quadripolar catheters positioned across the ventricular septum in 10 dogs at two sites. Each site received from 159 to 823 joules of delivered energy over one to three applications. Four additional dogs underwent unipolar radiofrequency ablation with 331 to 767 joules of delivered energy to each septal site. No significant acute or latent arrhythmias were noted. Dogs were killed at 1 day, and at 1, 2, and 4 weeks after the procedure. Out of a possible 40 potential ablation sites on each side of the septum after bipolar ablation, 21 (53%) discrete endocardial lesions were identified, ranging in size from 4 x 3 x 1.5 to 10 x 8 x 4 mm. When 352 joules or more delivered energy was applied per site, lesions were located at 18 of 28 (64%) possible sites. After unipolar radiofrequency ablation, similarly sized lesions were identified at 15 of 16 (94%) ablation sites. Histologic examination demonstrated well-delineated round or ovoid-shaped lesions with microscopic thrombi overlying two lesions. In conclusion, catheter ablation of the ventricular septum with radiofrequency energy appears capable of safely producing discrete areas of necrosis and may provide an alternative to direct current (DC) energy for catheter ablation of ventricular tachycardia originating from the septum.
Determinants of impedance rise during catheter ablation of bovine myocardium with radiofrequency energy.
Recently, radiofrequency (RF) energy has been used as an alternative energy source to direct-current (DC) electricity for catheter ablation of recurrent tachyarrhythmias. Since delivered energy is inversely related to impedance, factors that cause impedance rise during catheter ablation impede the ability to ablate tissue. To elucidate some of the factors responsible for impedance rise during RF (750 kHz) catheter ablation using a constant voltage RF generator, the effects of the following variables on impedance were studied in an in vitro bovine heart model: power setting (10-70 W), pulse duration (10-60 sec), catheter contact pressure (5-120 gm), repeated applications (2-4), and immersion media (saline vs citrated blood). Baseline impedance in blood was twice that of saline (190 vs 80 ohm) and rises in impedances occurred more rapidly in blood for the same energy settings. Increased power settings (greater than or equal to 30 W) and pulse duration (greater than or equal to 30 sec at 20 W) were associated with impedance rises in blood medium. Typically, impedance rises in blood were associated with blood coagulum on the catheter electrodes. Impedance rises in both saline and blood media were also associated with tissue charring and endocardial surface disruption. Once a rise in impedance occurred at the ablation site, repeated applications to the same site resulted in a more rapid rise in impedance. Catheter contact pressure of 80 gm or more also resulted in rapid impedance rise. These data suggest that factors other than set power and duration may also contribute to impedance rises during RF ablation. These findings may have important clinical implications in performing catheter ablation with RF energy.
Hemostatic markers in acute stroke.
To assess the time course of thrombosis and fibrinolysis after acute stroke, we measured concentrations of fibrinopeptide A (FpA), B-beta 1-42 peptide (B-beta 1-42), B-beta 15-42 peptide (B-beta 15-42), and crosslinked D-dimer (XDP) in 31 patients at varying times following acute ischemic stroke and in 13 neurologically stable patients with chronic strokes. FpA levels were markedly elevated during the first week after stroke and declined slowly during the first month. Mean FpA levels were not significantly elevated in chronic stroke patients. Mean XDP levels were slightly elevated during the first week and increased during the next 2 weeks after stroke. B-beta 1-42 and B-beta 15-42 levels were not elevated at any time following acute stroke. Our data suggest that fibrin formation greatly exceeds endogenous fibrinolysis during the acute phase of ischemic stroke. Endogenous fibrinolysis develops slowly following stroke. Prolonged elevation of FpA concentration suggests that thrombin activity and fibrin formation continue for up to 4 weeks in some patients with ischemic stroke.
Oddments in dental history: maxillo-facial prosthetics over a century ago.
Explore the source record for details and available documents.
Fibrin metabolism in patients with acute myocardial infarction during and after treatment with tissue-type plasminogen activator.
In order to define some of the determinants of successful thrombolysis and reocclusion during fibrinolytic therapy for acute myocardial infarction (AMI), specific molecular markers of fibrin metabolism were serially measured in 15 patients with AMI treated with tissue-type plasminogen activator (t-PA). Fibrin formation was assessed by measurement of fibrinopeptide A (FpA) and fibrinolysis by assay of B-beta peptides 1-42 and 15-42 and crosslinked fibrin degradation products (XDP). At baseline, FpA levels were high while markers of fibrinolysis were near normal. Following a 90-minute infusion of t-PA (0.5-1.1 mg kg-1 hr-1), all markers of fibrinolysis increased. Levels of FpA remained elevated despite heparin at the initiation of cardiac catheterization. None of these markers discriminated between patients with successful reperfusion from those without. At 4 hours, B-beta 15-42 peptide and XDP levels remained elevated suggesting persistence of fibrinolysis beyond the short circulatory half-life of t-PA. FpA levels at 4 hours were lower in patients who underwent acute coronary angioplasty compared to those who received additional low dose t-PA (12.3 +/- 4.5 vs. 30.4 +/- 5.5 ng/ml, p less than 0.05). By 48 hours, markers of fibrinolysis had returned toward normal except in 2 patients with persistently elevated B-beta 15-42 peptide levels who suffered reocclusion on days 5 and 6 (75 and 44 vs. 29 +/- 3 nM, p less than 0.005). In conclusion, molecular markers of fibrin metabolism during fibrinolytic therapy may provide clinically relevant data.
Platelet activity during acute myocardial infarction treated with tissue plasminogen activator.
Explore the source record for details and available documents.
The true discoverer of the dental air turbine handpiece, Sir John Walsh of New Zealand.
Explore the source record for details and available documents.
Oddments in dental history: Jack London as dentist.
Explore the source record for details and available documents.
The development of the dental drill.
Explore the source record for details and available documents.
On use of composites.
Explore the source record for details and available documents.
Spontaneous termination from prolonged ventricular fibrillation.
Explore the source record for details and available documents.
Antiplatelet effects of oral diltiazem, propranolol, and their combination.
1. The antiplatelet effects of a single oral dose of the calcium entry blocker diltiazem (60 mg), the beta-adrenoceptor blocker propranolol (40 mg), and their combination were studied in five healthy subjects. 2. Platelet aggregation and ATP release induced by adrenaline and ADP and ADP induced platelet thromboxane A2 generation were significantly inhibited (P less than 0.05) by either diltiazem or propranolol, although propranolol tended to have greater inhibitory effects on platelet function than diltiazem that did not reach statistical significance. 3. Combination therapy resulted in additive antiplatelet effects that were significantly (P less than 0.05) greater than either drug alone. 4. These data indicate that combined administration of a calcium entry blocker and a beta-adrenoceptor blocker results in additive inhibitory effects on platelet function. These effects may mediate part of the therapeutic efficacy of combination therapy in patients with coronary artery disease.
The true discoverer of the dental air turbine handpiece, Sir John Walsh of New Zealand.
Explore the source record for details and available documents.
Oddments in dental history: a warning about unskilled extractionists in 19th century England.
Explore the source record for details and available documents.