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Biomedical subjects

R Davidoff

Publications and source records attributed to R Davidoff.

51 records · Page 3Linked to original sources
PubMed1990

Quantification of jet flow by momentum analysis. An in vitro color Doppler flow study.

Previous investigations have shown that the size of a regurgitant jet as assessed by color Doppler flow mapping is independently affected by the flow rate and velocity (or driving pressure) of the jet. Fluid dynamics theory predicts that jet momentum (given by the orifice flow rate multiplied by velocity) should best predict the appearance of the jet in the receiving chamber and also that this momentum should remain constant throughout the jet. To test this hypothesis, we measured jet area versus driving pressure, flow rate, velocity, orifice area, and momentum and showed that momentum is the optimal jet parameter: jet area = 1.25 (momentum).28, r = 0.989, p less than 0.0001. However, the very curvilinear nature of this function indicated that chamber constraint strongly affected jet area, which limited the ability to predict jet momentum from observed jet area. To circumvent this limitation, we analyzed the velocities per se within the Doppler flow map. For jets formed by 1-81-mm Hg driving pressure through 0.005-0.5-cm2 orifices, the velocity distribution confirmed the fluid dynamic prediction: Gaussian (bell-shaped) profiles across the jet at each level with the centerline velocity decaying inversely with distance from the orifice. Furthermore, momentum was calculated directly from the flow maps, which was relatively constant within the jet and in good agreement with the known jet momentum at the orifice (r = 0.99). Finally, the measured momentum was divided by orifice velocity to yield an accurate estimate of the orifice flow rate (r = 0.99). Momentum was also divided by the square of velocity to yield effective orifice area (r = 0.84). We conclude that momentum is the single jet parameter that best predicts the color area displayed by Doppler flow mapping. Momentum can be measured directly from the velocities within the flow map, and when combined with orifice velocity, momentum provides an accurate estimate of flow rate and orifice area.

Animals↗
PubMed1989

Evolution of the temporal contraction sequence after acute experimental myocardial infarction.

The effect of infarct maturation on the temporal sequence of contraction within infarct zones has not previously been described. Accordingly, the time-varying pattern of contraction within ischemic/infarct zones was studied with use of cross-sectional echocardiography in 17 dogs at 10 min to 6 weeks after acute experimental myocardial infarction. Left ventricular short-axis images were digitized from end-diastole to end-systole and endocardial fractional radial change along 36 evenly spaced rays was calculated. The circumferential extent of dyskinesia and the number of rays that exhibited maximal dyskinesia were determined for each decile of the normalized contraction sequence. Between 10 min and 1 week after infarction, the greatest circumferential extent of dyskinesia occurred between the 3rd and 4th deciles of the normalized contraction sequence. However, as the infarct matured, the greatest spatial expanse of dyskinesia was noted to occur progressively earlier in the contraction sequence (second decile at 6 weeks), and the extent of mid- to late-systolic dyskinesia decreased markedly. Whereas end-systolic dyskinesia was present in 30% to 50% of ischemic/infarct zone rays from 10 min to 48 h, end-systolic dyskinesia was no longer observed at 6 weeks. Similarly, the maximal amplitude of dyskinesia was most commonly observed during midsystole from 10 min to 48 h, but occurred progressively earlier as the infarct matured, falling during the first decile at 6 weeks after infarction. These data suggest that maximal circumferential extent and amplitude of dyskinesia occur progressively earlier in the systolic contraction sequence as the infarct matures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Programmed ventricular stimulation in patients with left ventricular dysfunction and ventricular tachycardia: effects of acute hemodynamic improvement due to nitroprusside.

To assess the electrophysiologic effects of acute hemodynamic improvement in patients with left ventricular systolic dysfunction, 12 patients with a left ventricular ejection fraction less than 0.40 and a history of sustained monomorphic ventricular tachycardia were studied. All patients had underlying coronary artery disease. Patients underwent programmed cardiac stimulation in random order during a baseline period and with nitroprusside infusion. Mean pulmonary capillary wedge pressure decreased from 20 +/- 8 mm Hg at baseline study to 8 +/- 3 mm Hg during nitroprusside infusion (p less than 0.0001). Pulmonary artery, right atrial and systemic arterial pressures also decreased with nitroprusside (p less than 0.01). Cardiac output did not change. Left ventricular dimensions, determined by two-dimensional echocardiography, decreased significantly during nitroprusside infusion. The right ventricular effective refractory period, measured during ventricular drive trains at cycle lengths of 400 and 600 ms, were similar during baseline and nitroprusside periods (271 +/- 30 versus 274 +/- 31 ms at 600 ms, and 249 +/- 25 versus 246 +/- 18 ms at 400 ms). In 2 patients no ventricular arrhythmias were induced during either study period; in the other 10, ventricular tachyarrhythmias were induced during both periods. The mean number of extrastimuli required to induce a ventricular tachyarrhythmia was similar during the baseline period (1.8 +/- 0.6) and during nitroprusside infusion (1.9 +/- 0.7). As well, the mean cycle length of ventricular tachycardia induced was similar during the baseline period (347 +/- 61 ms) and during nitroprusside infusion (342 +/- 70 ms).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Pulmonary arterial thrombosis in secundum atrial septal defect.

Nineteen adolescent or adult patients with secundum atrial septal defect (ASD) underwent pulmonary arteriography to evaluate the presence of proximal pulmonary arterial (PA) thrombosis. This procedure demonstrated proximal PA thrombosis in 8 patients (group 2). These patients had a distinctive hemodynamic profile, consisting primarily of significant PA hypertension. None of the 11 patients with normal angiograms (group 1) had severe PA hypertension (p less than 0.0001). Proximal PA thrombosis appears to be the major factor in the development and progression of PA hypertension in adult patients with ostium secundum ASD. Pulmonary angiography should be undertaken in all adult patients with ostium secundum ASD who have at least moderate PA hypertension. Long-term anticoagulation is advocated for patients with PA thrombosis irrespective of a decision for surgical intervention.

Adolescent↗
PubMed1985

Persistent ST-segment elevation in patients with anterior myocardial infarctions. Evaluation by exercise electrocardiography, echocardiography and Holter monitoring.

One hundred and seventy patients who suffered an acute myocardial infarction (MI) were followed up at 3-monthly intervals by a full clinical evaluation, exercise electrocardiography and ambulatory Holter monitoring. Fifty-eight patients (34%) had anterior MIs, and of these 23 (40%) had persistent ST-segment elevation over the infarct zone, reflected by leads presenting with Q-S configuration. Fifteen (65,2%) of the latter demonstrated further ST-segment elevation during exercise. They were further investigated by cross-sectional echocardiography. Left ventricular (LV) dysfunction was diagnosed in 87% of patients with persistent ST-segment elevation, and in 93% of the patients with additional exercise-induced ST-segment elevation. Organized thrombi occurred in 2 patients (8,7%) and 1 experienced a transient ischaemic attack. Ventricular arrhythmias occurred frequently (ventricular ectopy--91,3%, ventricular tachycardia--17,4%, and couplets--47,8%). Death occurred in 3 patients (13,1%) and 1 patient (4,3%) had a second MI over a mean follow-up period of 83,6 months. This study suggests that persistent ST-segment elevation on the resting ECG of patients with anterior MIs is a reliable indicator of LV wall motion abnormalities, and that this correlation further increases if it is associated with exercise-induced ST-segment elevation. Furthermore, the role of echocardiography as a diagnostic tool in evaluating LV function is stressed. The prognosis of patients with post-infarction LV dysfunction is notably poor and may be the result of frequent complex ventricular arrhythmias.

Arrhythmias, Cardiac↗
PubMed1982

The natural history of the Q wave in inferoposterior myocardial infarction.

One hundred and twenty-five patients who had suffered transmural inferior myocardial infarctions were followed up for a mean period of 55 months. On electrocardiography the area under the pathological Q waves in the inferior leads was measured serially. Eighty-one patients (65%) showed a highly significant time-related diminution in Q-wave area. The ECGs of 17 subjects (14%) became normal and there was no electrocardiographic evidence of the previous myocardial infarction. The Q waves of the remaining 44 subjects (35%) remained constant or increased. A discussion of the possible mechanisms of changes in Q-wave size follows.

Adult↗
PubMed1982

Correlation of ventricular ectopic activity and exercise-related ST-segment changes.

Same-day exercise electrocardiography and ambulatory electrocardiographic (Holter) monitoring were performed on 167 patients, all of whom had suffered myocardial infarctions over the past 12 years. A significant correlation (P less than 0,0001) was found when comparing exercise testing for ischaemic ST-segment changes and the number of complexity of ventricular arrhythmias found on Holter monitoring. Two different methods of arrhythmia classification were used and the results were similar. The value of simultaneous Holter monitoring and exercise electrocardiography to detect 'late' exercise-related ventricular arrhythmias was not found to be sufficient to warrant their widespread simultaneous use.

Adult↗
PubMed1982

Lack of correlation between the clinical assessment of cardiovascular status and exercise electrocardiography.

One hundred and seventy-one patients who had had a myocardial infarction were evaluated at the Institute for Aviation Medicine, Pretoria. Patients were graded according to the New York City Heart Association classification of cardiac functional capacity and then subjected to exercise electrocardiography. Only 20% of the 74 patients whose exercise electrocardiograms revealed ischaemic heart disease felt that their cardiovascular function was limiting their daily activity. This lack of correlation between the two forms of assessment was highly significant (P less than 0,0001). It is therefore concluded that clinical evaluation of an individual with known ischaemic heart disease may be misleading.

Adult↗
PubMed1982

Beta adrenergic blocking agents to control hypertension in aviation personnel.

Beta adrenergic receptor blocking agents were used in the treatment of 15 hypertensive aircrew who had failed to respond to thiazide diuretics. Atenolol (Tenormin) resulted in adequate control of blood pressure in all subjects. Side effects were minimal and insignificant. It is recommended that a cardio-selective, water-soluble beta blocker, such as atenolol, be made available to selected hypertensive aircrew.

Adrenergic beta-Antagonists↗
PubMed1982

Postexercise blood pressure as a predictor of hypertension.

A study on 721 healthy male aircrew assessed whether the blood pressure response to exercise could be used to predict the development of hypertension. A positive blood pressure response to exercise, recorded 30 s after the completion of exercise, was defined as a systolic blood pressure of 200 torr or more (systolic test) or a raised diastolic blood pressure (diastolic test). While 236 (32.7%) became hypertensive with a blood pressure greater than 149/90 torr, 17% of these had shown a positive systolic response and 17% a positive diastolic response. The other 485 individuals (67.3%) remained normotensive throughout the mean follow-up period of 68 months (range 12-170 months). Of this group, 88% never manifested a positive systolic or diastolic response to exercise. Although 5% of the normotensive subjects manifested a positive systolic response to exercise, and 12% manifested a positive diastolic response to exercise, a longer period of follow-up may reduce this figure. It is concluded that exercise related blood pressure is a useful test in predicting the development of essential hypertension.

Adult↗
PubMed1981

The Wolff-Parkinson-White pattern in health aircrew.

The Wolff-Parkinson-White syndrome has been studied in a group of healthy aviation personnel over the past 15 years. The incidence of this electrocardiographic pattern has been determined in 22,500 healthy individuals and found to be 0.25%. The prevalence of documented tachyarrhythmias in this group of individuals was found to be only 1.8% while in a group of referred patients the prevalence was 20%. The limitations of the widely accepted classification into Type A and Type B patterns was borne out by our inability to categorize 45% of subjects with the WPW pattern. Q waves as QS or QR complexes in the inferior limb leads were found in 16.7% of subjects, but in all there was Q wave-T wave vector discordance. The limited value of stress testing in these individuals was reflected by 30% of our patients who demonstrated false positive signs of ischaemic heart disease. A discussion of the incidence, classification, differential diagnosis, mechanism of tachyarrhythmias, associated cardiovascular anomalies, and treatment follows.

Adolescent↗
PubMedDate not supplied

Right ventricular thrombus: an unusual manifestation of Behçet's disease.

Behcet's disease is a chronic multisystem illness in which cardiac involvement is a rare manifestation. In this unusual case a young man had symptoms that primarily related to recurrent right ventricular thrombi and pulmonary thromboemboli. Transesophageal echocardiography was useful in documenting the presence of intracardiac thrombus and establishing the diagnosis.

Adult↗
PubMedDate not supplied

Moderate-high intensity exercise training after myocardial infarction: effect on left ventricular remodeling.

BACKGROUND: Regular exercise increases exercise capacity and physical fitness, but questions remain about the effects of exercise on left ventricle (LV) remodeling after myocardial infarction. This study investigated the effects of moderate to high intensity exercise training on LV remodeling after a first myocardial infarction. METHODS: An exercise group of 68 patients in cardiac rehabilitation after a first myocardial infarction had an initial echocardiogram and exercise stress test. Thirty patients completed the 12 weeks of training and had echocardiograms suitable for quantitative analysis. Follow-up echocardiograms and exercise tests were performed. A carefully matched control group of 30 patients with echocardiograms at fixed intervals after myocardial infarction and no formal exercise training were also studied. LV size was expressed as the endocardial surface area-to-body surface area (ESAi), whereas infarct size was characterized by the percent abnormal wall motion (%AWM) by echocardiography using an endocardial surface area mapping technique. Indices of LV shape (sphericity) were also assessed. RESULTS: In the exercise group, no significant changes were seen in ESAi (57.95 +/- 13.1 vs 57.80 +/- 12.04 cm2/m2) or in %AWM (19.33 +/- 15.27 vs 20.11 +/- 15.95) from the initial to the final echo. The indices of sphericity were also unchanged. None of these parameters changed in the control group. Within each group was found heterogeneity in LV remodeling. Multivariate regression analysis revealed initial ESAi and initial %AWM to predict change in ESAi over time. CONCLUSIONS: In this study of patients with predominately small infarcts, exercise training did not adversely affect LV remodeling after myocardial infarction. Remodeling is heterogeneous and appears related to infarct and LV size.

Aged↗
PubMedDate not supplied

Grand mal epilepsy as recorded during dynamic electrocardiography.

A patient with diagnosed epilepsy was followed at a post-myocardial infarction clinic with routine ambulatory electrocardiographic monitoring. On one particular occasion while being monitored, he manifested an epileptic seizure. The features and duration of the seizure were reflected in the electrocardiographic recording. Cardiac arrhythmias may result in epileptiform seizures which may be mediated either through vagomedullary reticular pathways or through cerebral hypoxia as a result of the hemodynamic disturbance. The apparent epilepsy may vary from confused behavior to a generalized seizure and may thus mimic true cryptogenic epilepsy. The following case concerns a post-myocardial infarction patient with diagnosed epilepsy who sustained a seizure which was documented by an ambulatory electrocardiographic recorder.

Aged↗