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Biomedical subjects

D T Mason

Publications and source records attributed to D T Mason.

At least 37 records · Page 2Linked to original sources
PubMed1990

Cardiac surgery in patients over the age of 80 years.

The risk-benefit relationship of open heart surgery in octogenarians is not well established. Eighty consecutive patients over the age of 80 who underwent cardiac operations under cardiopulmonary bypass were evaluated. Twenty-five patients were in functional class IV, 42 in class III, and 13 in class II. Forty-four patients had only coronary artery bypass grafts (CABG), 12 only aortic valve replacement (AVR), 6 only mitral valve replacement (MVR), 12 CABG and AVR, 4 CABG and MVR, 1 CABG and aneurysmectomy, and 1 had resection of left atrial myxoma. Operative mortality (within 30 days) was 12.5% for the group. Mortality was related to bleeding, left ventricular failure, primary ventricular fibrillation, pulmonary failure, and renal failure. Mortality was higher in patients with (1) advanced functional class, (2) mitral valve replacement, (3) postoperative hemorrhage, and (4) associated pulmonary disease. While a generally conservative approach is recommended for octogenarian patients, many with life-threatening cardiac disease, especially those free of major multisystem illnesses, should not be denied the benefit of surgical treatment.

Aged↗
PubMed1989

Influence of positive inotropic agents on intracellular calcium transients. Part I. Normal rat heart.

This study, which was designed to evaluate the effects of positive inotropic agents on intracellular calcium transients ([Ca2+]i), is the first to analyze calcium transients in the whole heart. The positive inotropic agents that augment intracellular cyclic adenosine monophosphate (cAMP) (dibutyryl cAMP, amrinone, and isoproterenol) caused an increase in developed pressure and [Ca2+]i transients and a decrease in diastolic [Ca2+]i. On the other hand, the glycoside digoxin and the alpha-adrenoceptor agents, phenylephrine and dobutamine, also caused an increase in [Ca2+]i transients and developed pressure. However, unlike the agents that increase [cAMP]i, they induced an elevation in diastolic [Ca2+]i. With all the positive inotropic agents, developed pressure increased commensurately with the percentage changes in amplitude of the [Ca2+]i transients.

Animals↗
PubMed1989

Influence of positive inotropic agents on intracellular calcium transients. Part II. Cardiomyopathic hamster hearts.

To study the mechanism of dobutamine on end-stage heart failure, we assessed hemodynamic responses, high-energy phosphates (31P-NMR), and free intracellular calcium ([Ca2+]i) transients (surface fluorometry) during perfusion with 10(-6) mol/L dobutamine in Syrian cardiomyopathic hamsters with severe heart failure. These results were compared to perfusion of the heart with 10(-6) mol/L norepinephrine and 10(-6) mol/L isoproterenol. With the positive inotropic agents the rate-pressure product increased immediately (p less than 0.01 with dobutamine, norepinephrine; p less than 0.003 with isoproterenol); after 10 to 15 minutes of perfusion the rate-pressure product remained relatively stable with norepinephrine and isoproterenol but decreased with dobutamine (p = NS vs control values). [Ca2+]i-transients increased significantly in all groups. The end-diastolic [Ca2+]i decreased continuously with norepinephrine and isoproterenol (p less than 0.008; p less than 0.005) but increased during dobutamine by 19%. Alterations in coronary flow, pHi, high-energy phosphates, and the phosphorylation potential were not significantly different among the three catecholamines. In conclusion, in contrast to norepinephrine and isoproterenol, dobutamine depressed myocardial performance and increased end-diastolic [Ca2+]i in late heart failure.

Animals↗
PubMed1988

Hazards of angioscopic examination: documentation of damage to the arterial intima.

The fiberoptic scope is increasingly used in the coronary and peripheral arteries to quantitate the degree and type of arterial obstructive disease and to inspect the results of procedures such as bypass grafting and laser irradiation of obstructive lesions. Since little is known about this instrument's potential complications, we passed a variety of fiberoptic scopes (1.8 to 3.6 mm outer diameter) in fresh postmortem pig coronary arteries and live monkey and canine peripheral arteries, and observed the intraluminal anatomy through the angioscope. No perforations were created, but ridges rising from the vascular luminal surface, avulsion of the endothelial lining, and small flaps attached at one end to the vessel wall were observed. Histologically, subintimal and medial tears were evident. Inserting large diameter scopes or making frequent passes (10 to 100) in coronary arteries increased intravascular injury. The use of small diameter flexible scopes or infrequent passes (less than 10) in the larger iliac and femoral arteries of live monkeys and dogs resulted in a lower frequency of myointimal sloughing or flap formation. Current fiberoptic scopes are not ideal angioscopes; they have a rigid tip, cannot be steered adequately, and are relatively stiff, resulting in a high probability of intraluminal injury, especially when used in small tortuous arteries. To decrease the risk of such injury, we recommend gentle manipulations while passing the scope and use of the smallest diameter scope possible. We further suggest limited use of the fiberscope, or at least limiting the number of passes in small vessels such as coronary arteries.

Animals↗
PubMed1987

Pharmacokinetics of moricizine HCl.

Moricizine HCl is a phenothiazine derivative with antiarrhythmic properties. It was developed in the USSR and is now undergoing clinical evaluation. Although preliminary work has shown moricizine HCl to be effective in treating both atrial and ventricular arrhythmias, little is known of its pharmacokinetics. There is a 4-fold variability in range for its elimination half-life and in volumes of distribution and clearance. There is a linear relation for peak plasma levels and area under the plasma concentration/time curve with regard to single-dose administration of moricizine HCl. The bioavailability of moricizine HCl connotes extensive first-pass effect, or presystemic metabolism. Very little of moricizine is excreted unchanged; it is extensively metabolized to certain compounds that are present in plasma for extended periods. Moricizine is extensively (92% to 95%) bound to plasma protein. Its coadministration with cimetidine leads to additive systemic effects; however, there is no evidence of alterations in steady-state levels when moricizine HCl is coadministered with digoxin. Because moricizine is a drug with active metabolites, its concentration/effect profile is complex; this poses a challenge for accurate dose titration. This may, however, be a helpful challenge in that the metabolites may one day prove useful in therapy. This surmise warrants further study.

Anti-Arrhythmia Agents↗
PubMed1987

Efficacy and tolerance of Ethmozine (moricizine HCl) in placebo-controlled trials.

To investigate the tolerance and efficacy of moricizine HCl, single-blind placebo-controlled trials were conducted. The early protocols involved patients hospitalized for 14 days, and daily Holter monitoring was used to document efficacy and the degree of spontaneous variability of ventricular premature complexes (VPCs). Moricizine HCl was given orally from 2.9 to 15.3 mg/kg 3 times daily. Patients with lethal ventricular arrhythmias were excluded. Additional outpatient trials were conducted to define long-term efficacy and safety. A dose-response relation between moricizine HCl and the percentage of reduction in frequency of benign or potentially lethal ventricular arrhythmias was documented. Eighty-five percent of patients achieved a reduction in VPCs greater than 75% with daily dosages ranging from 10.1 to 15 mg/kg. This corresponded to a 95% decrease in mean frequency of VPCs. Long-term studies demonstrated no evidence of compromise in left ventricular function, and the proarrhythmic rate was only 2%. Symptomatic side effects were mild and usually well tolerated. Nausea, the most common, occurred in 11% of patients and dizziness in 9%. These results indicate that moricizine HCl is an effective and well-tolerated antiarrhythmic agent.

Anti-Arrhythmia Agents↗
PubMed1987

Antihypertensive therapy and the concept of total cardiovascular protection.

Drug-induced reduction of elevated blood pressure decreases cardiovascular mortality and morbidity in patients with moderate and severe hypertension. Furthermore, antihypertensive drug studies in mild hypertensive subjects (diastolic blood pressure 90 to 104 mm Hg) have shown protection against stroke, left ventricular hypertrophy, congestive heart failure and progression of renal damage, as well as improved patient longevity. The Hypertension Detection and Follow-up Program trial, recently carried out in the U.S., documented reduced coronary artery disease events (fatal and nonfatal) in special drug-treated patients with mild hypertension. From the standpoint of practical management and considering the ubiquity of essential hypertension, a modified stepped-care regimen advocating initial drug therapy with a beta blocker and addition of low-dose thiazide diuretic when necessary constitutes a judicious approach for widespread application. Although there are 8 orally active beta blockers currently approved in the U.S. for clinical use in systemic hypertension, only acebutolol possesses all of the salutary pharmacologic properties of cardioselectivity, intrinsic sympathomimetic activity and hydrophilicity, thereby making this compound an effective and safe beta-blocking agent for first-order management of a broad segment of the hypertensive population.

Acebutolol↗