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Biomedical subjects

A J Dunning

Publications and source records attributed to A J Dunning.

At least 73 records · Page 4Linked to original sources
PubMed1987

Hemodynamics of nicardipine in coronary artery disease.

Calcium antagonists influence cardiovascular hemodynamics by 3 actions: peripheral arterial dilatation, coronary arterial dilatation and negative inotropic effect. The net hemodynamic effects vary depending on the relative strength of each action. Intravenous administration of the new compound nicardipine, a dihydropyridine derivative with calcium antagonist activity that is chemically related to nifedipine, induced a marked reduction of systemic vascular resistance in patients with and without beta blockade. This was accompanied by an increase in cardiac output and left ventricular ejection fraction. In addition, end-diastolic pressure, peak (+) dP/dt and dP/dt measured at a developed pressure of 40 mm Hg and normalized for this pressure remained unchanged. The time constant of isovolumetric pressure drop during the first 40 ms also decreased. Intravenous administration of nicardipine prevented a marked increase in end-diastolic pressure during exercise, and augmented left ventricular ejection fraction in chronic heart failure. At doses producing similar increases in coronary sinus blood flow, intracoronary administration of nicardipine, unlike nifedipine, has little effect on left ventricular contractility and end-diastolic pressure. Nicardipine is a powerful systemic vasodilator with minimal effects on myocardial inotropic state, even in patients with compromised left ventricular function and patients receiving beta blocker therapy.

Coronary Disease↗
PubMed1987

Transesophageal two-dimensional echocardiographic evaluation of biventricular dimension and function during positive end-expiratory pressure ventilation after coronary artery bypass grafting.

Transesophageal 2-dimensional echocardiography was performed in 21 patients soon after uncomplicated coronary artery bypass grafting to determine the mechanism of positive end-expiratory pressure (PEEP) ventilation-induced decreased cardiac output. End-diastolic and end-systolic short-axis area and percent area reduction of right and left ventricles were determined during 5-cm H2O stepwise increments of PEEP ventilation. Simultaneously, cardiac output and right- and left-sided hemodynamic values were determined. Cardiac output, mean arterial pressure and end-diastolic area of both ventricles gradually decreased, and right and left atrial and pulmonary arterial pressures (mainstem and capillary wedge) increased. Left ventricular end-systolic area did not change, whereas right ventricular area decreased. Percent area reduction of both ventricles decreased (p less than 0.01). Thus, decrease in cardiac output during PEEP ventilation is primarily caused by decrease of preload rather than compromised contractility.

Adult↗
PubMed1987

Diastolic flow characteristics of severely impaired left ventricles: a pulsed Doppler ultrasound study.

Left ventricular inflow was studied with pulsed Doppler echocardiography in 12 normals and 12 patients with a dilated left ventricle as a result of ischemic heart disease. To study the influence of left ventricular relaxation on both the transmitral and apical diastolic flow patterns, we applied range ambiguity. This provides simultaneous display of Doppler shifts obtained at different depths. The diastolic Doppler shift curves at the mitral valve and apical level in normals had the same time of onset, whereas there was an apparent time delay in the patients with heart disease (range 160-360 ms). This might be caused by absence of a normal apical wall motion in these patients.

Adult↗
PubMed1987

Signal processing in 2 dimensional Doppler echocardiography.

Blood flow recordings made by 2 dimensional Doppler echocardiography can sometimes be understood more easily than conventional Doppler recordings, because of the anatomical 2 dimensional presentation. In contrast, signal processing has become more complicated and requires more explanation. In 2 dimensional Doppler echocardiography the analog ultrasonic signal received by the transducer is converted into an audible signal, which next is digitized and analyzed for its mean frequency and variance. Data collection and processing require application of multigating and high speed frequency analysis, generally based upon autocorrelation. Some artifacts may be perceived, such as color reversal due to aliasing, deceptively colored tissue surfaces due to beam motion, and wall motion ghost signals due to multiple reflections. Color flow imaging is appropriate for a rapid scan of the heart cavities to detect and roughly evaluate flow abnormalities. Quantification is still accomplished by switching to conventional Doppler mode.

Echocardiography↗
PubMed1987

Influence of coronary artery bypass surgery on regional left ventricular wall motion: an intraoperative two-dimensional transesophageal echocardiographic study.

Two-dimensional transesophageal echocardiography was used to evaluate the effect of coronary revascularization on regional myocardial function in 30 patients. Cross-sections at the level of the papillary muscles were obtained 15 minutes after intubation, 15 minutes after sternal closure, and 6 and 12 hours later, in the intensive care unit. Regional myocardial function of eight segmental areas was obtained using a floating axis system. The segments were allocated to one of four conditions, depending on baseline regional area ejection fraction (RAEF): condition I) RAEF < 0%; condition II) RAEF = 0% to 25%; condition III) RAEF = 26% to 50%; or condition IV) RAEF > 50% (normal). Compared to baseline values (postinduction), RAEF changed after sternal closure in condition I from -10.4% +/- 5.4% to 17.6% +/- 10.3% (P < .01), in condition II from 14.3% +/- 6.1% to 30.7% +/- 7.8% (P < .01), and in condition III from 35.0% +/- 6.1% to 50.4% +/- 6.3% (P < .01). In condition IV there was no significant change in RAEF. Further improvement of RAEF in conditions I, II, and III was not seen in the intensive care unit. Thus, preoperative normal regional myocardial function was not affected by coronary revascularization, and dysfunctioning myocardium frequently improved immediately after revascularization.

Adult↗
PubMed1986

Incidence, timing and prognostic value of left ventricular aneurysm formation after myocardial infarction: a prospective, serial echocardiographic study of 158 patients.

Serial 2-dimensional echocardiography was performed prospectively in 158 consecutive patients with first acute myocardial infarction (AMI) to determine the incidence of left ventricular (LV) aneurysm formation and the time course required for, and the clinical significance of, onset of LV aneurysm formation. Studies were performed throughout the first 5 days and after 3 months and 1 year. LV aneurysm was defined as an abnormal bulge in the LV contour during both systole and diastole. Eighty-four patients had anterior, 68 posterior and 6 anteroposterior AMI defined echocardiographically. During the study period, LV aneurysm was found in 35 of 158 patients (22%): in anterior AMI in 27, in posterior AMI in 6 and in anteroposterior AMI in 2. No new aneurysm developed after 3 months. Early aneurysm formation, during the first 5 days after AMI, was seen in 15 patients with anterior infarction. Twelve of these 15 (80%) died within 1 year (10 within 3 months), in contrast to 5 (25%) of the remaining 20 patients with LV aneurysm (p less than 0.05). Dyskinesia of the anterior wall in the acute stage usually resulted in aneurysm formation. Thus, LV aneurysm formation is seen in 22% of mostly anterior AMI and occurs within 3 months after AMI. Early aneurysm formation is associated with a high 3-month (67%) and 1-year (80%) mortality rate.

Echocardiography↗
PubMed1986

Two-dimensional echocardiography during percutaneous transluminal coronary angioplasty.

In order to study myocardial and clinical events during transient coronary occlusion in humans, two-dimensional echocardiography was continuously performed in 15 patients undergoing 49 balloon inflations during percutaneous transluminal coronary angioplasty (PTCA). Transient segmental asynergy developed in all patients 8 +/- 3 seconds after balloon inflation and returned to baseline 19 +/- 8 seconds after balloon deflation. Segmental dyskinesis was seen in only 8 of 11 patients undergoing PTCA of the left anterior descending artery (LAD). A wall motion score, based on degree of asynergy of 13 segments of the left ventricle, was significantly higher during LAD than during right coronary artery inflation (7.9 +/- 1.3 vs 4.0 +/- 1.4, p less than 0.01). Left ventricular size index increased significantly during balloon inflation, from 179 +/- 9 to 196 +/- 10 mm (p less than 0.01). Four patients developed transient ST segment changes in the extremity leads of the ECG and five patients had angina pectoris. The very first sign of ischemia in three patients, who developed all of these symptoms together, was consistently asynergy, followed by ECG changes, and last, angina pectoris. Thus during PTCA, transient asynergy and left ventricular dilatation develop, which are often clinically silent.

Angina Pectoris↗
PubMed1986

Ambulatory ECG recording during competitive parachute jumping in apparently healthy young men: more evidence for intermittent vagal dominance during enhanced sympathetic activity.

Using two-channel 24-hour ambulatory ECG recording we studied seven healthy young men during one day of parachute jumping competition (day 1), as compared to one control day (day 2). A symptom limited exercise test was also performed on day 2. Maximal heart rates attained during exercise testing were of the same order as during parachute jumping. In the phases just prior to 'exit', short periods of striking sinus arrhythmia with slow atrial rhythm were present in 3 subjects. Only one of these had slow atrial rhythm during the control day. Atrial and ventricular premature complexes, when present, disappeared with higher heart rates under all circumstances. No AV conduction disturbances were found.

Adult↗
PubMed1986

Short and long term predictive value of admission wall motion score in acute myocardial infarction. A cross sectional echocardiographic study of 345 patients.

A score of left ventricular segmental wall motion was used as a convenient rapid way to assess overall left ventricular function in acute myocardial infarction. Its success in risk stratification at admission was assessed by a blind review of cross sectional echocardiographic tape recordings from multiple acoustic windows. Sixty nine (20%) of the 345 patients died during hospital stay or within a one year follow up. The mean (SD) wall motion score in those who died was significantly higher than in those who survived (16.2 (5.9) vs 5.7 (3.9)). There were no differences between the group that died in hospital within three months of discharge and the group that died between three months and one year after discharge. Among the 31 patients who died in hospital, however, wall motion score was highest in 15 patients dying of cardiogenic shock (19.2 (4.2)). In 16 patients with lethal ruptures it was 13.5 (6.1). The nine patients with free wall ruptures had higher wall motion scores than those with ventricular septal rupture or papillary muscle rupture (15.7 (6.9) vs 8.5 (5.3)). Eight (3.3%) of 245 patients with a score less than 10 died, compared with 61 (61%) of 100 scoring greater than or equal to 10. The sensitivity of a score of greater than or equal to 10 in predicting death within one year was 88%, the specificity was 86%, the positive predictive value was 61%, and the negative predictive value was 97%.

Aged↗