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Biomedical subjects

D T Mason

Publications and source records attributed to D T Mason.

At least 73 records · Page 4Linked to original sources
PubMed1985

A cooperative multicenter study of captopril in congestive heart failure: hemodynamic effects and long-term response.

The acute hemodynamic effects, long-term clinical efficacy, and safety of the oral angiotensin-converting enzyme inhibitor, captopril, were assessed in a multicenter cooperative study of 124 patients with heart failure resistant to digitalis and diuretics. The cardiac status of most patients was deteriorating prior to the study. Favorable acute hemodynamic effects consistently occurred with captopril. Maximal mean percentage increases in cardiac index, stroke index, and stroke work index were, respectively, 35%, 44%, and 34%. Systemic and pulmonary vascular resistances were each decreased by approximately 40%, as were the filling pressures of the right and left heart. Infusion of nitroprusside in some of the same patients to an end point of a pulmonary capillary wedge pressure of 12 to 18 mm Hg (equivalent to that after captopril) revealed no significant difference in the effect of either drug on the other hemodynamic parameters. Recatheterization after 8 weeks of captopril therapy revealed sustained hemodynamic changes. Significant and sustained improvements in clinical status were observed in most patients as measured by changes in New York Heart Association (NYHA) functional classification and exercise tolerance times. Seventy-nine percent of patients for whom there were adequate NYHA class data improved. Twenty percent remained unchanged and 1% deteriorated. Those patients who had both pretreatment and post-treatment exercise stress testing exhibited a highly significant mean increase in exercise tolerance times of 34% (317 +/- 32 seconds pretreatment to 425 +/- 34 seconds, final measurement). There was no evidence of tachyphylaxis over an 18-month period.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Laser therapy of coronary artery obstructions.

Laser energies can be transmitted through flexible optical fiber to vaporize and penetrate coronary atherosclerotic and thrombotic obstructions. There are risks and complications involved in this therapy, however, including perforation, aneurysm formation, and thromboembolic risks, and further research is needed to render the laser recanalization procedure safe.

Angioplasty, Balloon↗
PubMed1984

Acute and chronic complications of laser angioplasty: vascular wall damage and formation of aneurysms in the atherosclerotic rabbit.

Acute and chronic vascular responses to laser exposure in atherosclerotic rabbits were studied. In 7 rabbits fed an atherogenic diet for 3 to 5 months before the study to induce aortic atherosclerosis, a flexible quartz fiber, 400 micron core diameter, attached to an argon ion laser was passed anterogradely or retrogradely to the atherosclerotic ascending aorta. The laser was turned on using power intensities of 1 to 2 W for 3 seconds. After laser treatment, the aortas were studied acutely in 3 rabbits and chronically in 4 rabbits after recovery for 1 to 14 days. In 2 rabbits studied acutely, the argon laser produced a vaporized crater within the atherosclerotic plaque at the endothelial surface; however, in 1 there was also vascular damage extending deep into the medial layer. In addition, aortic aneurysm with muscular wall damage occurred in 2 of the 4 animals studied chronically. Thus, vascular complications may arise when catheter laser angioplasty is randomly applied without visualizing specific plaque targets or without using safe dose increments of power intensities and durations of exposure. This study suggests caution in the clinical use of intensive phototherapy to cardiovascular lesions and stresses the need for further understanding of laser vascular consequences before application of laser angioplasty in patients.

Animals↗
PubMed1984

Intraoperative use of dual fiberoptic catheter for simultaneous in vivo visualization and laser vaporization of peripheral atherosclerotic obstructive disease.

Since laser energy has been shown to produce controlled thermal injury to atherosclerotic plaques from postmortem human hearts, a 3-mm diameter fiberoptic catheter was devised and tested for use in peripheral vessels. The catheter has channels for viewing, laser delivery, and suction/flushing. In five femoral or carotid arteries from three dogs implanted with near-total human atherosclerotic obstructions, the fiberoptic catheter was capable of viewing and targeting the atherosclerotic plaque for laser irradiation. The plaque was vaporized using 5 watts with time exposures lasting from 2 to 5 sec from an argon-ion laser. In three other animals each implanted with a 3- to 4-cm long segment of human cadaver atherosclerotic vessel, the fiberoptic catheter clearly visualized the internal diseased vascular wall. Thus, this investigation provides the initial demonstration and practicality of applying a flexible dual fiberoptic catheter for simultaneous in vivo visualization and laser vaporization of peripheral atherosclerotic disease.

Animals↗
PubMed1984

Electrocardiographic diagnosis of left ventricular hypertrophy in the presence of left bundle branch block.

The presence of left bundle branch block (LBBB) on 12-lead ECG may obscure the diagnosis of other ECG abnormalities including left ventricular hypertrophy (LVH). We retrospectively reviewed ECGs of patients with LBBB and LVH as determined by echocardiography to evaluate several ECG parameters as predictors of LVH. ECG evaluation included precordial voltage as measured by the sum of the S wave in leads V1 or V2 plus R wave in lead V6, QRS duration, mean frontal plane QRS axis, R wave amplitude in lead aVL, intrinsicoid deflection, and the presence or absence of criteria for left atrial enlargement. In the presence of LBBB and LVH, precordial voltage was significantly greater (p less than 0.001), QRS duration more prolonged (p less than 0.001), and left atrial enlargement more frequently present (p less than 0.001) than when LVH was not present. There was no difference in limb lead voltage, intrinsicoid deflection, or mean frontal plane QRS axis. Furthermore, the criterion of SV2 + RV6 greater than 4.5 mV demonstrated a sensitivity of 86% and a specificity of 100%. We conclude that a voltage criterion of SV2 + RV6 greater than 4.5 mV is diagnostic of LVH in the presence of LBBB; furthermore, QRS duration of greater than 160 msec plus left atrial enlargement strongly supports the diagnosis of LVH.

Bundle-Branch Block↗
PubMed1984

Arrhythmias in patients with mitral valve prolapse. Types, evaluation, and therapy.

A wide spectrum of cardiac rhythm and conduction disorders occur in patients with all types of valvular heart disease. However, certain types of valvular disease have a special predilection for arrhythmias, including atrial and ventricular tachyarrhythmias as well as bradyarrhythmias, inherent to the etiology of the condition itself. Most notable in this regard is mitral valve prolapse, in which cardiac dysrhythmia is now recognized as the complication of highest frequency. The principal purpose of this article is the delineation of the characteristics and management of rhythm disorders in the mitral valve prolapse syndrome.

Adult↗
PubMed1984

Dissolution of pulmonary carcinoma via argon-laser bronchoscopy. First clinical use of fiberoptic metal cautery cap heated by laser radiation.

A 60-year-old man with nonresectable lung cancer underwent bronchoscopy which revealed a large squamous cell tumor mass narrowing the free airway to the left lung. A flexible quartz fiber connected to an argon ion laser was then inserted through a hollow channel of the fiberoptic bronchoscope. The laser was activated to heat the metal cap on the distal tip of the fiber to thermally dissolve the mass and relieve airway obstruction.

Argon↗
PubMed1984

Effects of laser radiation on the morphology of human coronary atherosclerotic disease.

Laser energy delivered through optical fibers can produce potent controlled thermal dissolution of human coronary obstructive disease, thus widening the stenotic vascular lumen. The ease of vaporization and penetration depends not only on the physical properties of the laser beam but also on the physical characteristics of the atherosclerotic plaque. Lipid-laden plaques are more easily vaporized compared with plaques that are heavily calcified. In atherosclerotic animal models studied in vivo, laser radiation produced a charred lining around the evacuated area and rapid regeneration of a new endothelial lining. After several weeks, the laser-induced crater was still evident, and thrombogenesis was not a significant complication. Focal aneurysmal dilatation may develop when there is thermal injury of the medial layer, and acute perforation can occur if severe laser burn is extended beyond the adventitial layer. Further technical advances and achievements are needed before laser recanalization becomes a clinical reality.

Animals↗
PubMed1983

Effects of laser irradiation on human thrombus: demonstration of a linear dissolution-dose relation between clot length and energy density.

Because vascular thrombosis often accompanies arteriosclerotic disease in occluding blood vessels, the dissolution properties of laser irradiation were investigated and the energies needed to penetrate different lengths of thrombus were quantitated. Spectrophotometric studies show that the blood clot due to the presence of hemoglobin is well absorbed by argon laser energies, which emit blue-green wavelengths between 454 and 514 nm. Thus, laser energies transmitted directly from an argon-ion source produced vaporization and penetration of human thrombus in a linear dose-response fashion; the longer the thrombus, the greater the power intensity or time exposure necessary to penetrate the clot.

Dose-Response Relationship, Radiation↗
PubMed1983

Antianginal efficacy and improved exercise performance with timolol. Twice-daily beta blockade in ischemic heart disease.

Antianginal efficacy and improved exercise performance with timolol, a new beta-adrenergic blocking agent, was assessed in 23 patients with chronic stable angina pectoris in an 11-week double-blind, placebo-controlled study. Twenty-two of the 23 subjects completed the open-label phase of this investigation (weeks 0 to 6) while receiving 10 to 30 mg of timolol twice daily to optimize exercise capacity. Weekly anginal episodes and nitroglycerin consumption declined from 8.9 +/- 9.1 episodes/week and 8.1 +/- 10.6 tablets/week, respectively, with placebo to 2.7 +/- 5.2 episodes/week and 2.6 +/- 6.0 tablets/week with optimal timolol dose (p less than 0.05). Resting heart rate (HR) and systolic blood pressure (SBP) also decreased from 75.2 +/- 14.0 beats/min and 139.1 +/- 15.7 mm Hg with placebo to 55.1 +/- 8.9 beats/min and 130.5 +/- 15.9 mm Hg with timolol (p less than 0.05). Peak exercise HR, peak exercise SBP, and peak exercise double product (HR X SBP) were significantly (p less than 0.05) reduced when evaluated 12 to 13 hours after administration of timolol compared with placebo (101.5 +/- 21.1 beats/min verus 193.3 +/- 96.2 beats/min, 161.5 +/- 26.7 mm Hg versus 175.6 + 20.8 mm Hg, and 16.6 +/- 5.1 X 10(-3) versus 21.7 +/- 5.4 X 10(-3), respectively). Exercise duration was prolonged from 263.3 +/- 90.2 seconds to 330.3 +/- 73.9 seconds (p less than 0.05), while time to onset of 1 mm S-T segment depression was delayed in 15 patients from 231.8 +/- 86.4 seconds to 298.7 +/- 68.4 seconds (p less than 0.05). During the double-blind phase (weeks 7 to 10), 8 subjects received timolol and 11 patients received placebo. Nitroglycerin consumption at weeks 8 and 10 and anginal frequency at week 8 were unchanged compared with initial placebo treatment. Resting HR, peak exercise HR, and peak exercise double product were significantly attenuated at weeks 8 and 10 in timolol patients compared with their initial placebo exposure. However, these variables were unchanged in placebo subjects compared with their initial placebo therapy. Exercise duration was again prolonged at week 8 in timolol subjects compared with initial placebo results (315.1 +/- 61.2 seconds versus 261.3 +/- 68.8 seconds, p less than 0.05), but not at week 10. Placebo patients demonstrated no difference at week 8 or 10 in exercise performance compared with initial placebo treatment. Timolol twice daily, therefore, is potentially useful in some patients with angina pectoris. Other patients may, however, require a shorter dose interval for optimal angina control and maximal improvement in exercise capacity.

Administration, Oral↗
PubMed1983

Effects of laser irradiation on human erythrocytes: considerations concerning clinical laser angioplasty.

Recent studies demonstrate the potential use of laser to vaporize human coronary atherosclerotic plaques. The laser energy is transmitted through flexible quartz fiber and discharged intravascularly. Since red blood cells could be exposed to intense heat, we examined effects of laser irradiation on human erythrocytes. Blood was obtained and placed in 5 ethylene diaminetetracidic acid (EDTA) vials for each normal donor. A flexible 400 microns diameter core quartz fiber coupled to an argon-ion laser source was positioned 1 cm above the surface of 1.5 ml blood. Four vials were exposed to 5 W laser beam for 5, 10, 15, or 20 s; the remaining vial was left untreated. Packed cell volume fell primarily during the first 5 s of laser exposure (p less than 0.01) and plateaued beyond 5 s. Plasma hemoglobin (Hgb) rose progressively with each increased duration of exposure (p less than 0.01). This study indicates that lysis of erythrocytes occurs in cells exposed directly to the laser beam. However, beyond the direct beam, damage to red cell membrane took place as evident by progressive Hgb leakage into plasma despite no further cell lysis. These observations require consideration during clinical laser angioplasty.

Erythrocyte Indices↗
PubMed1983

Laser irradiation of congenital heart disease: potential for palliation and correction of intracardiac and intravascular defects.

We examined the potential for laser irradiation of congenital heart defects, with the use of postmortem hearts and an argon ion laser with a flexible quartz fiber. Atrial septectomy was performed in five newborn hearts. Obstructive lesions were relieved by laser irradiation in valvular pulmonic and aortic stenosis, dysplastic pulmonary valve, pulmonary atresia, and coarctation of the aorta. To demonstrate the efficacy of in vivo cardiac laser surgery, atrial septectomy was also performed in an anesthetized dog model, under echocardiographic visualization, without change in heart rate or blood pressure. Our results demonstrate the feasibility of intracardiac and intravascular laser irradiation for palliation and repair of selected congenital heart diseases.

Animals↗
PubMed1983

Reduction of ventricular ectopic beats with oral acebutolol: a double-blind, randomized crossover study.

The antiarrhythmic efficacy of oral acebutolol, a new cardioselective beta-blocking agent, was assessed in a randomized double-blind, placebo-controlled study. Twenty-five patients with greater than or equal to 30 ventricular ectopic beats (VEB) per hour on three control ambulatory monitorings were studied. Mean VEB reduction from the control period was 35% with placebo and 45% and 50% with the use of acebutolol 200 mg and 400 mg, respectively. Eleven patients had greater than or equal to 70% reduction in VEB with acebutolol and nine of them had greater than or equal to 90 VEB reduction. Among these 11 patients, the mean VEB suppression was 51% after placebo but significantly higher following the two doses of acebutolol at 71% (p less than 0.05) and 86% (p less than 0.01). The mean reduction of paired VEB compared to placebo was 71% (p less than 0.05) and 75% (p less than 0.01) following 200 mg and 400 mg of acebutolol and only 49% after placebo. Complete suppression of paroxysmal ventricular tachycardia was also noted in five patients. Mean PR interval only increased slightly when patients took 400 mg of acebutolol, but there was no significant change in either the QRS or QTc intervals. A significant decrease in heart rate from that during control periods was noted after acebutolol. No significant adverse reactions were noted during the study. Acebutolol appears to be an effective and well-tolerated antiarrhythmic agent in the treatment of VEB and higher grades of ventricular ectopy.

Acebutolol↗