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Biomedical subjects

D T Mason

Publications and source records attributed to D T Mason.

At least 325 records · Page 18Linked to original sources
PubMed1975

Purification and characterization of cardiac tropomyosins.

A new procedure was developed to purify tropomyosin. The procedure was an adaptation of that described for purification of myosin. By eliminating troponin before precipitating with (NH4)2 SO4, it was possible to obtain pure tropomyosin from the same preparation from which myosin was purified. When tropomyosin was subjected to isoelectrofocusing two tropomyosins were present, having similar isoelectric points of pH 5.4 and 5.6; two tropomyosin subunits were resolved in the presence of 6 M urea. The two subunits had very similar isoelectric points, pH 4.7 and 5.0. According to Ouchterlony analyses the tropomyosins from canine skeletal and cardiac tissue were immunologically identical when incubated with goat gammaG antitropomyosin (cardiac).

Amino Acids↗
PubMed1975

Plasma lipid changes in young adult couples consuming polyunsaturated meats and dairy products.

Twenty-five young couples consumed either a saturated or polyunsaturated fat diet for a 20-week period. The polyunsaturated beef, lamb and dairy products, high in linoleic acid, were produced by feeding ruminant animals "protected lipid" feeds which prevent hydrogenation of fats in the rumen. The experimental design provided for four dietary groups: A) saturated diet for 20 weeks; B) polyunsaturated diet for 20 weeks; C) saturated diet for 10 weeks then polyunsaturated diet for 10 weeks; and D) polyunsaturated for 10 weeks then saturated diet for 10 weeks. Polyunsaturated-to-saturated ratios (linoleic: total saturated fatty acids) for the diets were: prestudy, 0.43-0.56; saturated 0.11-0.14; polyunsaturated, 0.56-0.62. Factors other than diet that appeared to affect cholesterol responses were carefully considered. During the initial 3 weeks (regimentation period) plasma cholesterol concentration decreased in all groups irrespective of diet. This was followed by two experimental periods in which the effects of the prescribed diets were readily apparent (response periods I and II). The final 4 weeks of the study were characterized by diminishing compliance with the dietary discipline (abatement period). Subjects in each group (A,B,C,D) were subdivided into high and low on a basis of each group's initial median cholesterol level. Those in the high subgroups were very responsive to dietary changes whereas those in the low subgroups were not. Combined responses of high subjects were: polyunsaturated diet, -10.7 mg/dl (P less than 0.025), saturated diet, d8 mg/dl (P less than 0.05). Combined difference between saturated and polyunsaturated diets was 18.5 mg/dl or approximately a 10% cholesterol difference between the experimental polyunsaturated and saturated diets.

Adult↗
PubMed1975

Effects of chronic graded ethanol consumption on the metabolism, ultrastructure, and mechanical function of the rat heart.

Three sequential sets of ethanolic rats (E) and their matched controls (C) were fed regular chow containing standard vitamins with the ethanol group in each series also receiving a progressively greater alcohol intake for 3 to 6 months: E1 5%, E2 10%, and E3 25% ethanol. Electron microscopy showed swelling of mitochondria, transverse tubules and sarcoplasmic reticulum, dehiscence of intercalated discs and disintegration of myofibrils scattered throughout the ventricular myocardium in E1 and E2 as early as 7 wk after beginning 5% ethanol; in addition, there were clumping of mitochondria and supercontraction of myofibrils in E3. Concomitant with substructural abnormalities in E3, there were slight but significant depressions of cardiac myofibrillar ATPase activity and mitochondrial function. Cardiac catecholamines, hydroxyproline, and total bound glycerol were unchanged. Alteration of isometric contraction of isolated, supported left ventricular papillary muscles occurred initially in E2 and was clearly evident in E3 by significant reduction of duration of systolic active state (time from onset to peak tension), while total tension generated and peak rate of tension rise were not yet disturbed. Extra vitamin supplementation in additional rats drinking 25% ethanol minimally lessened decline in myofibrillar ATPase activity, but otherwise provided no protection. Thus, chronic daily ingestion of graded quantities of ethanol representing 10 to 30% of total calories in well-nourished animals exerted toxic effects on microstructure, metabolism and mechanics of the ventricle. These alterations are postulated to be pertinent to early pathogenesis of clinical alcoholic cardiomyopathy.

Adenosine Triphosphatases↗
PubMed1975

Evaluation of arrhythmias in the late hospital phase of acute myocardial infarction compared to coronary care unit ectopy.

To evaluate the prevalence and nature of arrhythmias during the entire three-week period in hospital after myocardial infarction, the results of coronary care unit monitoring (initial 3 to 5 days) were compared with continuous 8-hour portable monitoring during the ambulatory phase (second and third weeks) in 83 consecutive survivors. Arrhythmias were detected in 84.3 per cent (70/83) of patients while in the coronary care unit and in 85.5 per cent (71/83) during hospital stay after the coronary care unit. Ventricular ectopic depolarizations were classified as complicated (multifocal, paired, R on T, or five or more a minute) or uncomplicated. Importantly, the high frequency of complicated ventricular extrasystoles and tachycardia persisted during the entire period in hospital (early 34.9% and late 42.5% of all patients). However, only 16.9 per cent (14/83)had these ventricular arrhythmias during both coronary care unit and ward monitoring. Thus, the absence of complicated ventricular ectopic depolarization and ventricular tachycardia in the coronary care unit did not exclude their subsequent occurrence in the majority of the large number of patients with late hospital complicated ventricular ectopy.

Adult↗
PubMed1975

Cardiac glycogen in long-evans rats: diurnal pattern and response to exercise.

The 24-h pattern of cardiac glycogen was determined in normally active, caged male Long-Evans rats. Relatively small fluctuation was observed during a 24-h cycle with maximal difference between mean values ranging from 3.41 +/- 0.28 (dark room) to 5.15 +/- 0.19 (light room) mg glycogen/g wet wt heart, suggesting that the substantial diurnal variation of cardiac glycogen reported in Wistar rats is not a universally observed phenomenon. Cardiac glycogen during and following a single bout of moderate running was compared to a bout of strenuous running in fed male Long-Evans rats. Moderate continuous running at 20 m/min for 30 min did not decrease cardiac glycogen below the average control level (4.09 +/- 0.10 mg glycogen/g heart) but did cause a short period of supercompensation, which reached a peak of 6.27 +/- 0.19 mg/g heart at 2 h postexercise. Strenuous running in bouts at 30 m/min over a 2-h period for a distance of 1,413 m caused a significant decrease in cardiac glycogen to 2.66 +/- 0.20 mg/g heart followed by an extended period of supercompensation, which reached a peak of 9.01 +/- 1.41 mg/g heart at 4 h postexercise and remained significantly elevated during the next 13 h. Thus, the severity of exercise in normal, fed rats determines not only the extent of cardiac depletion, but also the supercompensation pattern of glycogen repletion following exercise.

Animals↗
PubMed1975

Echographic assessment of atrial transport, mitral movement, and ventricular performance following electroversion of supraventricular arrhythmias.

Controversy attends the extent and temporal sequence of improvements in hemodynamic function resulting from the return of atrial contraction following cardioversion of supraventricular arrhythmias. Thus, mitral, left atrial (LA) and left ventricular (LV) echograms were obtained before and one hour after conversion of supraventricular arrhythmias to normal sinus rhythm by direct current countershock in patients with chronic coronary disease or cardiomyopathies without valvular dysfunction. The duration of the rhythm disturbance varied from one day to five years in 22 patients and was indeterminate in 13. Atrial systole immediately produced prominent mitral "A" waves with anterior valve excursion of 7.5 mm (range 3 to 12) in 33 of the 35 patients (94%). The two patients with atrial electromechanical dissociation reverted to atrial fibrillation within one week. Cardioversion caused a decline in LA diameter (3.5 to 3.2 cm, P less than .001) and a rise in LV end-diastolic dimension (5.2 to 5.5 cm, P less than .001) while LV end-systolic dimension was unchanged (4.2 cm). Thereby stroke volume rose. Heart rate fell an average of 16 beats/min. Depressed cardiac output was improved + 0.84 L/min/m-2. Thus, in the majority of patients with acute or chronic supraventricular arrhythmias without mitral valve disease, cardioversion promptly restores effective atrial contraction, decreases LA size, and results in substantial hemodynamic benefit.

Adult↗
PubMed1975

Clinical use of sodium nitroprusside in chronic ischemic heart disease. Effects on peripheral vascular resistance and venous tone and on ventricular volume, pump and mechanical performance.

Although hemodynamic benefit has been shown with sodium nitroprusside (NP) in acute coronary pump failure, complete understanding of the mechanisms of action of the agent on the cardiocirculation and its value in chronic ventricular dysfunction are lacking. This investigation evaluates the effects of NP on the systemic and regional arterial and venous beds and on cardiac dynamics, ventricular volumes, contractile state and myocardial energetics in long-standing congestive heart failure. Twelve patients with chronic coronary pump dysfunction received NP infusion to lower systolic pressure to 95-105 mm Hg. Left ventricular (LV) function was assessed directly by angiographic volumes and high fidelity pressure, and peripheral circulatory dynamics were determined simultaneously by forearm arterial and venous plethysmography. NP reduced mean arterial pressure (MAP) from 88.2 to 73.4 mm Hg (P less than 0.05) and significantly (P less than 0.05) enhanced the variables of LV performance: LV end-diastolic pressure (EDP) diminished from 18.5 to 9.9 mm Hg; ejection fraction rose from 0.47 to 0.55; percent of LV segmental shortening increased; and isovolumic and ejection indices of contractility improved. Concomitantly, NP reduced the indices of myocardial oxygen demands of ventricular tension time index and LVED volume index. These salutary effects on LV performance and energetics occurred secondary to peripheral arterial and venous dilation (P less than 0.05) produced by NP: total systemic vascular resistance was lowered from 1590 to 1310 dynes sec cm--5; forearm vascular resistance diminished from 46 to 37 mm Hg/ml/100 gm/min; and forearm venous tone fell from 14.2 to 10.1 mm Hg/cc. Depressed stroke index (SI) and cardiac index (CI) increased (P less than 0.05) with NP: despite the fall in LVEDP, when ventricular filling pressures with the agent were at levels slightly above normal. Dextran infusion given with NP to restore LVEDP to moderately elevated values increased SI and CI (P less than 0.05) when NP alone produced no change in stroke output. Thus, the peripheral vasodilator properties of nitroprusside improve LV function by reducing impedance to ventricular ejection, while MVO2 is diminished by decreasing LV preload and afterload through relaxing actions

Adult↗
PubMed1975

Hemodynamic effects of nitroglycerin in acute myocardial infarction.

Nitroglycerin (NTG) has recently been suggested to decrease myocardial ischemia and enhance cardiac pump function during acute myocardial infarction (AMI). To evaluate the sublingual agnet in this condition, the hemodynamic effects of 0.4 mg NTG administered to 16 supine patients during the first 72 hours of AMI were determined serially 5, 10 to 15, and 20 to 30 minutes post-NTG. Data were evaluated for the entire group, as well as for six patients with normal pulmonary artery wedge pressure (PAW) (less than or equal to 12 mm Hg; mean 7) who formed group I and for ten patients with elevated PAW (greater than 12 MM Hg; mean 19) who comprised group II. In the 16 patients, NTG resulted in significant decreases in PAW (14 TO 7 MM Hg; P less than .01), mean systemic arterial pressure (MAP) (95 TO 82 MM Hg; P less than .01), cardiac index (CI) (1.79 TO 1.46 L/min/m-2; P less than .02), stroke index (SI) (24 TO 18 CC/M-2; P less than .01) and stroke work index (SWI) (27 TO 20 GM TIMES M/M-2; P less than .01). These alterations were significant in both subgroups, with the decline in PAW greater (P less than .05), while there was no change in group II. There was no significant change in total peripheral vascular resistance (TPVR) for the entire group or in the two subgroups. This study demonstrates that, regardless of initial left ventricular filling pressure, sublingual NTG given in the acute phase of AMI results in rapid fall in PAW, concomitant with decreases in systemic blood pressure, cardiac output and SWI, without changes in TPVR and with little or no effect on heart rate. Since TPVR was unaltered, the decline in MAP was due to fall in cardiac output. Thus, the principal action of sublingual NTG in AMI appears to be systemic venodilation with consequent reduction of ventricular preload. This effect is translated into decline ofpump output even in patients with high initial filling pressures. Although NTG may rapidly relieve pulmonary congestion and lower myocardial oxygen consumption, use of the agent sublingually is limited in AMI because these salutary effects are accomppanied by potentially deleterious fall in cardiac output and systemic blood pressure.

Aged↗
PubMed1975

Lack of sensing by demand pacemakers due to intraventricular conduction defects.

A previously unrecognized form of failure of normally functioning noncompetitive R-inhibited or R-triggered pacemakers to sense is described in 30 patients. The failure was produced by the delayed arrival of ventricular depolarization due to intraventricular conduction disturbances at the site of pacemaker sensing electrodes. These patinets with late activation of the right ventricle exhibited right bundle branch block (RBBB) during conducted sinus beats or had ectopic beats arising from the left ventricle. In both these situations, several late occurring QRS complexes were not sensed by the pacemaker electrodes in the right ventricular apex (RVA) and thereby the R-inhibited pacemaker spike discharged into the initial portion of the QRS complex. Activation of the RVA was delayed up to 65 msec in sinus beats with RBBB and even longer in premature beats arising from the left ventricle. The depolarization front of such beats reached the myocardium around the right ventricular pacemaker electrodes late in the QRS and thereby were not sensed up to 65 msec after the QRS onset as seen on the surface electrocardiogram (ECG). It was found in this study that if the inscription of such QRS complexes began up to 65 msec before the next due pacemaker impulse, these complexes were not sensed, allowing discharge of normally functioning R-inhibited pacemakers within the QRS which mimicked pacemaker malfunction. Failure to sense due to this phenomenon was observed in patients with noncompetitive pacemakers, both R-inhibited and R-triggered; temporary and permanent; with unipolar as well as bipolar electrodes. Similarly, patients with left ventricular epicardial electrodes and left bundle branch block in sinus beats also exhibited this phenomenon. Complete evaluation proved that pacemaker function was normal in the entire patient group. Recognition that failure to sense was the result of intraventricular conduction disorder prevented the untimely replacement of the pulse generator. This phenomenon of nonsensing by noncompetitive pacemakers should be considered in the presence of wide QRS complexes before the pacemaker is concluded to be malfunctioning.

Aged↗
PubMed1975

Noninvasive detection of regional myocardial ischemia using rubidium-81 and the scintillation camera: comparison with stress electrocardiography in patients with arteriographically documented coronary stenosis.

The sensitivity of rest and stress myocardial perfusion studies using scintillation camera imaging of intravenously administered rubidium-81 (81Rb) in the detection of myocardial ischemia was compared to that of stress electrocardiography by relating results in 40 patients to the degree of stenosis delineated by coronary arteriography. Of 33 patients with greater than 75% stenosis of at least one of the three major coronary vessels (significant stenosis), rest and stress 81Rb imaging detected ventricular ischemia in 29 (88%) whereas simultaneous stress electrocardiography was positive (1 mm or greater horizontal ST-segment depression) in only 19 (58%) of the same patients. Five of the 29 patients who developed stress-induced scintigraphic evidence of ischemia did not develop angina or a positive electrocardiogram with stress. In 31 of the 33 patients with significant coronary stenosis, either the stress scintigram or the stress electrocardiogram was positive. In seven patients with less than 50% narrowing of a major coronary vessel on coronary arteriography, the stress scinitigrams were negative, whereas the stress electrocardiograms were positive in the two of these patients with the syndrome of angina with normal coronary arteriograms. It is concluded that high resolution images of the myocardium can be obtained with 81Rb using the scintillation camera with special shielding, and that rest and stress 81Rb scintigraphy appears to provide greater sensitivity and specificity when compared to stress electrocardiography in the nininvasive identification of significant coronary stenosis.

Coronary Angiography↗
PubMed1975

Echography and phonography of acute aortic regurgitation in bacterial endocarditis.

Since management of acute aortic regurgitation in bacterial endocarditis is enhanced by early recognition, echocardiography and phonocardiography were evaluated in three such cases documented by catheterization and surgery without positive blood cultures and compared to echophonograms of 34 patients with aortic regurgitation of other origins. Endocarditis manifested distinctive, thickened, irregular aortic leaflet echoes with normal systolic excursion and mitral echopreclosure with anterior leaflet fluttering. Mitral preclosure resulted in mid- or end-diastolic crescendo murmur accompanied by soft first heart sound. Aortic echograms in nonendocarditis showed either widened root, diminished leaflet excursion, absence of irregular valvular thickening, or normal leaflets, all without mitral preclosure. This study shows specific echophonographic findings of aortic regurgitation due to endocarditis that enable diagnosis of this condition in the absence of positive blood cultures.

Acute Disease↗
PubMed1975

Effects of hemodynamic overload on canine myocardial myosin.

After mild banding of pulmonary artery in dogs there was a rapid elevation in protein and RNA synthesis, followed by an elevation in myosin content and myosin ATPase activity. There was an increase in myosin ATPase activity when K+ or Ca++ was used as activator effector but not with the cations, Mn++ or NH4+. Concomitant with an increase in myosin ATPase activity there was a decrease in one of the C1 light chain components, previously named C1d.

Adenosine Triphosphatases↗