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Biomedical subjects

G Keren

Publications and source records attributed to G Keren.

At least 73 records · Page 4Linked to original sources
PubMed1995

Calculation of mean arterial pressure during exercise as a function of heart rate.

Mean arterial blood pressure (MAP) is a common characteristic of the cardiac cycle. Usually it is evaluated by assuming that the left ventricular ejection time (systole) constitutes a constant proportion of the cardiac cycle (i.e. 1/3), regardless of the heart rate (HR). However, elevation of HR during exercise results in a reduction of the duration of the ejection period and even a greater reduction of the ventricular filling period. Therefore, a constant diastole/systole proportion at various heart rates may be misleading. The purpose of this study was therefore to evaluate the accurate proportion of the systolic period from the cardiac cycle at different metabolic rates and calculate MAP accordingly. Twenty healthy subjects (age: 20-50 yr.) exercised at different work intensities on a cycle ergometer to elicit HR in the range of 55-180 bpm. During the ride the mitral and aortic flow velocity wave form were recorded by Doppler echocardiography; the mitral flow from the apical view and the aortic flow from the apical long axis view. Blood pressure was measured using a sphygmomanometer. The fraction of systole (St) from the heart cycle was related to HR and was described in mathematical terms as: St = 0.01exp(4.14-40.74/HR) MAP was then calculated from the diastolic blood pressure (dBP) and the pulse pressure (PP) adjusted for St as follows: MAP = dBP+St.PP; (mmHg) The use of the suggested model reduces errors in the evaluation of various cardiac parameters which are related to arterial pressure, such as peripheral resistance, especially under exercise-heat stress.

Adult↗
PubMed1994

Serum lipids and restenosis after successful percutaneous transluminal coronary angioplasty. Ichilov Magnesium Study Group.

The effects of plasma lipids on the clinical and angiographic parameters of 134 patients, in whom coronary angioplasty was performed in 157 vessels, were prospectively examined. During a 6-month follow-up, restenosis was detected angiographically in 39 patients (29%; 45 vessels). None of the clinical, biochemical, or angiographic variables examined was predictive of stenosis and the tendency of a vessel to restenose was not patient-dependent but rather lesion-related. However, restenosis developed in 31 of 102 vessels (30%) in patients with high-density lipoprotein (HDL) cholesterol < or = 40 mg/dl, compared with restenosis in 10 of 55 vessels (19%) in patients with HDL cholesterol > 40 mg/dl (p = 0.092). No significant differences were observed when restenosis rates were compared in patients with total cholesterol levels > 250 mg/dl or < 250 mg/dl; no differences were seen in low-density lipoprotein (LDL) cholesterol levels when comparing patients with > 160 mg/dl and < 160 mg/dl. In 117 patients (132 vessels), complete serial blood specimens were obtained until the concluding angiography at 6 months. During follow-up, both groups (those with and without restenosis) had almost similar findings. Triglycerides decreased equally in both groups, and total cholesterol increased mildly in those who had restenosis; HDL and LDL cholesterol levels increased significantly in each group. No significant differences were observed with respect to extent of these changes between the groups. Thus, although lipid levels at the time of angioplasty and at 6 months follow-up were not found to predict the occurrence of restenosis, the association of low high-density lipoprotein levels and the tendency for restenosis should not be overlooked.

Angioplasty, Balloon, Coronary↗
PubMed1994

Intravascular ultrasound characterization of thrombi of different composition.

An in vitro model was designed to test the hypothesis that thrombi of varying composition have different echogenic patterns. Thrombi were prepared in specially designed tubes, mounted on a holder that allows introduction of an intravascular ultrasound catheter rotated inside a subselective sheath. The thrombi were made by the addition of thrombin to whole blood, platelet-rich plasma, and to mixtures of whole blood and platelet-rich plasma with increasing concentration of whole blood relative to the volume of the mixture in the following ratios: 1:5, 2:5, 3:5 and 4:5. Sixty-six thrombi prepared from 11 blood samples of healthy subjects were studied and compared with control tubes filled with saline solution. Platelet-rich thrombi showed low echogenicity similar to saline solution. Whole blood thrombi appeared uniformly "speckled." Mixtures of whole blood and platelet-rich plasma showed a gradual increase in echogenicity with an increasing amount of whole blood in the mixture. Quantitative videodensitometry compared the gray scale intensity of each image relative to background saline. The mean value of echogenicity of platelet-rich thrombi was 0.9 +/- 1.2, and the mean value of whole blood thrombi was 13 +/- 5.3. Platelet-rich thrombi are echo-lucent, and the main echogenic reflectance of thrombi originates from red blood cells. The ultrasound intensity is in linear relation to the amount of red blood cells in the thrombus.

Adult↗
PubMed1994

Effect of magnesium on restenosis after percutaneous transluminal coronary angioplasty: a clinical and angiographic evaluation in a randomized patient population. A pilot study. The Ichilov Magnesium Study Group.

Restenosis is a major clinical problem following successful percutaneous transluminal coronary angioplasty. Since magnesium has vasodilator and antithrombotic effects, this study was designed to evaluate its potential to decrease the rate of restenosis. In an open-labelled, randomized controlled study, 148 patients underwent successful coronary angioplasty. Ninety-eight patients were treated with 46-52 mmol/18-20 h intravenous magnesium sulphate (groups M1 and M2), and 49 of them continued with oral supplements of magnesium hydroxide 600 mg.day-1 (group M2). The other 50 patients served as controls (group C). Coronary angiography was performed before, immediately after and at 6 months follow-up or earlier if clinically indicated. Clinical, laboratory, ergometric and radionuclide evaluations were also carried out. One hundred and thirty-nine patients (94%) with 163 dilated segments completed the study. Intravenous magnesium was well tolerated. The cross-sectional area at the site of angioplasty increased by 3.55 +/- 2.01 mm2 in groups M1 and M2 compared with an increase of 2.90 +/- 1.63 mm2 in the control group, (P = 0.03). A trend towards a lower rate of restenosis (> 50% reduction in luminal diameter) was noticed in the magnesium groups (28/110, 25%) compared with the control group (20/53, 38%) P = 0.10. Oral administration of magnesium was well tolerated, did not have an additive effect on restenosis, but an improved clinical course was noted. It is concluded that intravenous administration of magnesium in patients undergoing coronary angioplasty is feasible and safe and that the beneficial trend of magnesium to prevent acute recoil and late (within 6 months) restenosis is encouraging and should promote further investigation in a larger patient population.

Administration, Oral↗
PubMed1994

Detection of restenosis following percutaneous coronary angioplasty in single-vessel coronary artery disease: the value of clinical assessment and exercise tolerance testing.

Chest pain and submaximal exercise testing were prospectively assessed over a 6-month period, for detecting the evolution of restenosis in patients undergoing percutaneous coronary angioplasty, following either acute myocardial infarction or treatment of an anginal syndrome. Seventy-eight patients with one-vessel coronary artery disease underwent a modified treadmill exercise test at the 1-week, 3-month and 6-month follow-up after angioplasty, when a final angiogram was also performed. Forty-four patients (group A) were examined after myocardial infarction; in 34 patients (group B) angioplasty was done for incapacitating angina. Both groups showed similar results with low sensitivity and relatively moderate specificity of both chest pain and exercise tests; this was also the case for the time of restenosis to occur. It is thus concluded that the parameters examined are somewhat limited markers of restenosis following coronary angioplasty.

Adult↗
PubMed1994

Percutaneous transluminal coronary angioplasty in elderly patients.

Fifty-six patients aged 75 years and older underwent percutaneous transluminal coronary angioplasty (PTCA) at our institution from 1984 to 1991. The average age was 76.7 +/- 1.5 years, and 84% of the patients were males. Single-vessel disease occurred in 21 patients, double-vessel disease in 16, and three-vessel disease in 19 patients. The mean left ventricular ejection fraction was 57 +/- 5%, and 8 patients had an ejection fraction of < 40%. The anginal functional class was I in 1 patient, II in 3, III in 6, and IV in 46 patients. Single-vessel PTCA was attempted in 43 patients, two-vessel PTCA in 8, and three-vessel PTCA in 5 patients. Revascularization was complete in 35% of the patients, incomplete in 57, and no revascularization was obtained in 8% of the patients. Ninety-one percent of the patients had a successful procedure. In 5 patients there was severe dissection, 1 patient died, 1 patient had an acute myocardial infarction, and 1 patient had emergency bypass surgery. Long-term follow-up (6-96 months, mean 21 +/- 4) in the 51 successfully treated patients revealed late cardiac death in 1 patient, repeated PTCA for restenosis in 9, and coronary bypass surgery in 2 patients. Twenty-two patients were asymptomatic, 12 had improved symptoms, and 5 remained symptomatic. PTCA appears to be a safe and effective treatment in elderly patients with one- and two-vessel disease, with excellent long-term results. Age is not a contraindication to PTCA. The results in elderly patients with three-vessel disease are less encouraging.

Aged↗
PubMed1994

Acute mastoiditis--revisited.

The clinical course and causative organisms were studied in 18 patients with acute mastoiditis, 13 of whom (72%) had no previous history of middle ear disease. Their age ranged from 5 months to 21 years, and duration of middle ear symptoms immediately prior to admission ranged from 1 to 45 days (average 9.7 days). None had undergone a myringotomy prior to admission, while 13 (72%) had been receiving antibiotic treatment for acute otitis media. Three were admitted with intracranial complications. Bacteria were isolated in 10 of the 16 patients in whom samples were available for bacterial culture, and included Streptococcus pneumonia (2), Streptococcus pyogenes (2), Staphylococcus aureus (2), Staphlococcus coagulase negative (2), Klebsiella pneumonia (1), and Pseudomonas aeruginosa (1). Of the 17 patients treated by us, 11 received surgery. Acute otitis media, secretory otitis media, acute mastoiditis, subacute mastoiditis and masked mastoiditis create a continuum. Antibiotic treatment for acute otitis media cannot be considered as an absolute safeguard against acute mastoiditis. When antibiotics are prescribed for acute mastoiditis before culture result is available, an anti-staphylococcal agent should be included. At least some patients with acute mastoiditis develop a primary infection of the bony framework of the middle ear cleft. The prevalence of the intracranial complications in acute mastoiditis is still high and may appear soon after or concomitant with the first sign of acute mastioditis.

Acute Disease↗
PubMed1994

One-year clinical and echocardiographic follow-up of patients with congestive cardiomyopathy treated with captopril compared to placebo.

The beneficial hemodynamic and clinical effects of angiotensin-converting enzyme (ACE) inhibition in patients with severe congestive heart failure has recently been documented in large-scale studies. This mode of therapy when added to digitalis and diuretics improves survival. To evaluate the clinical effect and the changes in cardiac dimensions of captopril compared to placebo we followed 50 patients with severe congestive heart failure over 1 year using echo-Doppler cardiography. After randomization, 25 patients were started on captopril and 25 patients on placebo. At baseline and at 6 and 12 months, each patient underwent exercise tolerance test, radionuclide angiography to estimate left and right ventricular ejection fraction, M mode and two-dimensional echocardiography and Doppler cardiography to calculate cardiac dimensions and stroke volumes. During follow-up two patients in the captopril group and four in the placebo group died. Due to clinical deterioration nine patients in the placebo group had to be started on open-label captopril. Treatment with captopril was associated with a more significant improvement in functional class and exercise duration compared to placebo. Forward stroke volume estimated from Doppler echocardiography increased significantly by captopril from 47 +/- 3 to 55 +/- 3 ml and decreased in the placebo-treated patients from 49 +/- 5 to 44 +/- 4 ml. This improvement was associated with a trend towards reduced heart rate by captopril. Left ventricular end diastolic volume tended to increase in the placebo group and did not change in the captopril group. Calculated mitral regurgitant volume at 6 and 12 months tended to be lower in the captopril-treated patients. Thus captopril therapy proved efficacious in patients with severe congestive heart failure and resulted in increased forward stroke volume; it may have a beneficial effect on cardiac dimensions and on mitral regurgitation.

Analysis of Variance↗
PubMed1992

Failure or success of complex catheter-based interventional procedures assessed by intravascular ultrasound.

Intravascular ultrasound provides high resolution cross-sectional images of vessel walls and may help to characterize atherosclerotic plaque morphology subtypes. This new imaging modality may have an important role in assessing the results of standard and investigational interventional therapeutic procedures. Four case histories of patients with coronary artery disease treated with different catheter-based therapies are presented. In each case, intravascular ultrasound added diagnostic information unobtainable from standard radiographic imaging techniques. These cases, involving PTCA (balloon dilatation), directional coronary atherectomy, high-speed rotational ablation, and balloon-expandable stent implantation, each represent an interesting example of procedure success or failure that could not be fully discerned without the use of intravascular ultrasound. Specifically, the distribution of intramural dissection, the presence and magnitude of intracoronary calcification, and morphologic patterns of intimal hyperplasia leading to restenosis, were accurately identified by ultrasound images. Thus intracoronary ultrasound imaging significantly enhances the understanding of failure modes, success, and complications after therapeutic interventions in patients with complex coronary disease.

Aged↗
PubMed1992

Atherosclerotic saphenous vein grafts treated with different interventional procedures assessed by intravascular ultrasound.

Intravascular ultrasound imaging of saphenous vein grafts may enhance the angiographic interpretation of results following transcatheter interventions. We used intravascular ultrasound to study 18 patients with stenotic vein grafts following balloon angioplasty, atherectomy, or stent placement. In real-time imaging the three-layer appearance was rarely seen, calcification was infrequent (11% of patients), and atheroma were usually mildly echogenic ("soft"). Despite excellent angiographic results (reduction in percent diameter stenosis from 90 +/- 8% to 17 +/- 8%) and concordant improvement in lumen area by ultrasound regardless of the intervention, there was usually significant retained atheroma at the treatment site. Following balloon angioplasty, ultrasound showed multiple superficial fissures and fractures without discrete dissections. Atherectomy caused a smooth lumen surface without deep dissections or resections, but significant retained atheroma was observed with each one of the atherectomy procedures. Endovascular stents were concentric in the vein with reflective struts above compressed atheroma and an outer echogenic adventitia. Stent expansion was asymmetric axially and longitudinally and evidence of stent recoil was present. Thus intravascular ultrasound may be an important adjunct to angiography in characterizing postintervention results in saphenous vein grafts.

Aged↗
PubMed1992

Arterial responses to balloon coronary angioplasty: an intravascular ultrasound study.

OBJECTIVES: The purpose of this study was to examine the coronary artery response to percutaneous transluminal coronary angioplasty by using intravascular ultrasound. BACKGROUND: The immediate effects of coronary angioplasty on arterial wall geometry and surface appearance are understood poorly. Most of the available data are derived from small necropsy series, inferred from animal models or extrapolated from in vitro studies. High frequency intravascular ultrasound provides transmural images of coronary arteries in vivo. METHODS: We used intravascular ultrasound to study 29 patients before or after, or both, successful coronary angioplasty. RESULTS: The angiographic diameter narrowing was 72 +/- 13% before and improved to 19 +/- 11% after angioplasty. Calcium was visualized in 7 (24%) of the 29 angioplasty sites by fluoroscopy versus 15 (52%) of sites by intravascular ultrasound (p = 0.022). Arterial dissection after angioplasty was observed in 8 (27%) of cases by contrast angiography versus 24 (83%) by intravascular ultrasound (p less than 0.001). Intravascular ultrasound detected extensive dissection at the angioplasty site in 11 (73%) of the 15 calcified plaques and in only 3 (21%) of the 14 noncalcified plaques (p = 0.024). Arterial expansion (defined as the area within the external elastic membrane at the angioplasty site greater than that of the proximal reference segment) occurred in 29% of calcified plaques compared with 86% of noncalcified plaques (p = 0.007). CONCLUSIONS: Intravascular ultrasound is more sensitive than angiography for identifying arterial calcium and dissection at the site of angioplasty. At the site of angioplasty, arterial dissection occurred more frequently in calcified plaques whereas arterial expansion occurred more frequently in noncalcified plaques. Successful angioplasty causes a continuum of arterial responses that vary importantly with plaque composition.

Angioplasty, Balloon, Coronary↗