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Biomedical subjects

K G Morris

Publications and source records attributed to K G Morris.

64 records · Page 4Linked to original sources
PubMed1983

Comparison of high-dose and medium-dose propranolol in the relief of exercise-induced myocardial ischemia.

The effects of medium-dose (160 mg/day) and high-dose (480 mg/day) oral propranolol were compared in 22 patients who had typical angina pectoris and objective evidence of myocardial ischemia during exercise. Left ventricular (LV) ejection fraction (EF) and wall motion score (WMS) (an index of regional LV dysfunction) were assessed by radionuclide angiography both at rest and during exercise to the pretreatment maximum work load. Functional class improved in 11 of the 22 patients during medium-dose propranolol therapy. Medium-dose propranolol reduced mean resting heart rate from 71 to 55 beats/min, exercise heart rate from 122 to 93 beats/min, and exercise systolic blood pressure from 183 to 162 mm Hg (p less than 0.001 for each). The incidences of exercise-induced chest pain and S-T segment depression were reduced from 19 to 9 patients (p less than 0.001), and from 20 to 10 patients (p = 0.002), respectively. Medium-dose propranolol had no effect on mean EF or WMS at rest, but improved function in ischemic regions during exercise; WMS decreased (p = 0.001), and mean exercise EF increased from 0.51 to 0.56 (p = 0.025). Compared with the medium dose, high-dose propranolol improved functional class in 3 additional patients, and further reduced mean resting heart rate (from 55 to 52 beats/min, p = 0.001) and mean exercise heart rate (from 93 to 86 beats/min, p = 0.001). Exercise-induced chest pain and S-T segment depression were abolished in a further 7 and 6 patients, respectively. Exercise EF and WMS improved further in several patients, but the changes were not statistically significant for the group (p = 0.095 and 0.082, respectively). Thus, in patients with coronary artery disease and exercise-induced ischemia, propranolol reduced heart rate and blood pressure and the incidence of exercise-induced chest pain, electrocardiographic changes, and ischemic LV dysfunction. Although most of these effects were seen with medium-dose propranolol, higher doses provided additional relief of chest pain and S-T segment depression, and further improved global and regional LV function in several patients.

Angina Pectoris↗
PubMed1983

Effect of rate-dependent left bundle branch block on global and regional left ventricular function.

Seven subjects with rate-dependent left bundle branch block (RDLBBB) and 13 subjects with normal conduction (control group) underwent upright bicycle exercise radionuclide angiography to determine the effects of the development of RDLBBB on global and regional left ventricular function. Six of the seven subjects with RDLBBB had atypical chest pain syndromes; none had evidence of cardiac disease based on clinical examination and either normal cardiac catheterization or exercise thallium-201 scintigraphy. Radionuclide angiograms were recorded at rest and immediately before and after RDLBBB in the test group, and at rest and during intermediate and maximal exercise in the control group. The development of RDLBBB was associated with an abrupt decrease in left ventricular ejection fraction (LVEF) in six of seven patients (mean decrease 6 +/- 5%) and no overall increase in LVEF between rest and maximal exercise (65 +/- 9% and 65 +/- 12%, respectively). In contrast, LVEF in the control group was 62 +/- 8% at rest and increased to 72 +/- 8% at intermediate and 78 +/- 7% at maximal exercise. The onset of RDLBBB was associated with the development of asynchronous left ventricular contraction in each patient and hypokinesis in four of seven patients. All patients in the control group had normal wall motion at rest and exercise. These data indicate that the development of RDLBBB is associated with changes in global and regional ventricular function that may be confused with development of left ventricular ischemia during exercise.

Adult↗
PubMed1982

A QRS scoring system for assessing left ventricular function after myocardial infarction.

A QRS scoring system for estimating the size of a myocardial infarct was evaluated in 55 patients who did not have left ventricular hypertrophy or conduction abnormalities. Serial 12-lead surface electrocardiograms were scored according to a 29-point system based on the duration of Q and R waves and on the ratios of R-to-Q amplitude and R-to-S amplitude. The scores were proportional to the severity of wall-motion abnormalities, which was determined by radionuclide blood-pool scanning and which correlated inversely with the radionuclide-determined left ventricular ejection fraction (LVEF). A score less than 3 was 93 per cent sensitive and 88 per cent specific for both severe regional dyssynergy and major depression of the global LVEF. The following equation was used to estimate the LVEF from the QRS score: LVEF (%) = 60 - (3 x QRS score). After acute myocardial infarction, an electrocardiogram can provide important indirect quantitative information about left ventricular function.

Electrocardiography↗
PubMed1982

Hemodynamic effects of the antiarrhythmic drug pirmenol.

We examined the hemodynamic effects of pirmenol, a new antiarrhythmic drug, for the first time in man. Right and left heart pressures, Fick cardiac output, and radionuclide ejection fraction were measured before and during infusion of pirmenol in 10 patients with coronary artery disease who were undergoing routine diagnostic cardiac catheterization. Pirmenol was given as a 50-mg IV injection over 2 min followed by a constant infusion of 2.5 mg/min for up to 36 min. Plasma pirmenol levels were within or near the previously determined therapeutic range in all patients. There were no significant changes in systolic blood pressure or cardiac output. Diastolic blood pressure rose from a mean (+/- SD) 78 +/- 7 during the control period to 82 +/- 6 during the infusion, heart rate rose from 66 +/- 6 during the control period to 75 +/- 7 during infusion and ejection fraction fell from 60 +/- 8 during control to 55 +/- 12 during infusion. Although the left ventricular end-diastolic pressure rose from 6 +/- 2 during control to 8 +/- 3 during the infusion, the left ventricular stroke work index fell and the left ventricular work index per minute did not change. The fall in ejection fraction did not correlate with the control ejection fraction, plasma pirmenol levels, or the change in heart rate. The decline in ejection fraction and the failure of the left ventricular work index per minute to rise despite a small rise in left ventricular end-diastolic pressure may indicate a potential myocardial depressant effect of pirmenol.

Anti-Arrhythmia Agents↗
PubMed1982

Subvalvular thrombotic obstruction of an aortic porcine heterograft.

A 48-year-old man had angina pectoris and symptoms of heart failure. Cardiac catheterization showed severe aortic stenosis and regurgitation, and he underwent aortic valve replacement in 1976 with a 23-mm Carpentier-Edwards aortic porcine heterograft. Initially there was symptomatic improvement, but one year later the patient had the onset of dyspnea and exertional chest pain that became progressively more severe over the next three years. Repeat cardiac catheterization was performed 45 months after valve implantation, and a 76 mm Hg peak to peak and a 44 mm Hg mean systolic gradient across the aortic bioprosthesis were recorded. The porcine heterograft was surgically explanted and found to be obstructed by a subvalvular thrombus that appeared to arise from the junction of the aortic and mitral valve annuli.

Aortic Valve↗
PubMed1982

Criteria for early discharge after acute myocardial infarction: validation in a community hospital.

All patients admitted to a community hospital coronary care unit during an 18-month-period were studied to validate previously reported criteria for early hospital discharge after myocardial infarction. Factors present during the first four hospital days, which predict subsequent complications requiring urgent medical attention, were classified as either urgent or prognostic. Patients whose initial four days were marked by either no complications (81 patients) or prognostic complications (51 patients) are described. Only one patient in the group of 81 patients had a subsequent urgent complication. Four of 55 patients had late urgent complications. Persistent sinus tachycardia occurred during the first four days in all four of these 55 patients. Early hospital discharge would be feasible in the group with neither urgent nor prognostic complications. Further study of persistent sinus tachycardia is required to improve its predictive ability.

Arrhythmias, Cardiac↗
PubMed1980

Comparison of multigated radionuclide angiography with ultrasonic sonomicrometry over a wide range of ventricular function in the conscious dog.

This study compared the noninvasive assessment of left ventricular function with radionuclide angiography with that obtained with ultrasonic sonomicrometry. Left ventricular ejection fraction and rate of ventricular ejection (dV/dt) were measured with both techniques over a wide range of ventricular function. Six dogs were prepared with epicardial crystals across the major and minor axes of the left ventricle, paired transmural wall thickness crystals and a left ventricular catheter. The animals were studied while awake after they had recovered from operation. Left ventricular volume was calculated from the ultrasonic sonomicrometric dimension measurements and the equation for a prolate ellipsoid; dV/dt was calculated from the stroke volume and ejection time. Radionuclide angiograms were performed using technetium-99m--labeled red blood cells and an Anger camera with a converging collimator interfaced to a computer programmed for multigated acquisition. A wide range of ventricular function was produced with sequential infusion of isoproterenol, propranolol, phenylephrine and sodium thiamylal. Ejection fraction and dV/dt were measured simultaneously during each intervention using the time-activity curves of the multigated radionuclide angiogram and ultrasonic sonomicrometric dimensions. Regression analyses demonstrated a close correlation between the simultaneous measurements of ejection fraction (r values ranged from 0.95 to 0.99) and dV/dt (r values ranged from 0.87 to 0.99). These data indicate that noninvasive multigated radionuclide angiography accurately assesses changes in ejection fraction and dV/dt over a wide range of ventricular function.

Animals↗
PubMed1980

Calcium augments hypoxic vasoconstriction in lungs from high-altitude rats.

Isolated lungs from high-altitude rats compared with those from low-altitude rats have blunted hypoxic pressor responses. Because calcium is essential for the hypoxic pressor response and has been shown to be altered in the pulmonary arterial smooth muscle during high-altitude exposure, we wondered whether altered calcium metabolism might account for the blunted response. We attempted to unmask differences between high- and low-altitude rat lungs by altering extracellular calcium. The addition of calcium to the blood perfusate augmented the hypoxic pressure response of high-altitude lungs and depressed that of low-altitude lungs. Calcium addition did not affect pressor responses to angiotensin II, but slowed vasodilation after both angiotensin injection and removal of the hypoxic stimulus. The maximal KCl-induced contraction was blunted in rings of main pulmonary artery from high-altitude rats, but augmented in their aortic rings. Submaximally constricted (40 mM KCl) pulmonary arteries from low- but not high-altitude rats further constricted with calcium addition. Aortic rings exhibited an inverse behavior. Thus, calcium addition augmented the blunted vasopressor response in high-altitude rats lungs, possibly by an effect on lung arteries. The aorta and main pulmonary artery differ in calcium handling.

Adaptation, Physiological↗