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Biomedical subjects

J Meyer

Publications and source records attributed to J Meyer.

At least 541 records · Page 30Linked to original sources
PubMed1993

Variations in acoustical beam properties of intracoronary Doppler catheters.

The limitations of coronary angiography in assessing the functional significance of coronary obstructions is well known. While the critical variable of coronary blood flow cannot be readily measured, intraluminal Doppler sonography offers useful related functional information on blood flow velocity. In order to fully evaluate Doppler signals it is essential to have exact knowledge of the transducer transmission characteristics and of the ultrasound beam topology. In an experimental set-up, the transmitter-receiver characteristics of five commonly used Doppler catheters were investigated. In comparing the beam characteristics we found inhomogeneities in the lateral beam spread. At a penetration depth of 3.0 mm the beam shape varied from a minimum of 1.25 mm up to a maximum of 3.5 mm. The mean was 2.25 mm. The different beam profiles of the investigated Doppler transducers cause an error in measuring the blood flow velocity. The blood flow velocity tends to be underestimated the more the vessel diameter and the blood flow velocity increase. Contrary to transducer design optimized for imaging, for spectral analysis of the Doppler signal it would be advantageous to have as broad a beam as possible in order to illuminate the entire vessel lumen.

Angioplasty, Balloon, Coronary↗
PubMed1993

Miniaturized pressure-guide-wire: evaluation in vitro and in isolated hearts.

UNLABELLED: The present study focused on the accuracy and reproducability of measurements performed with a miniaturized pressure guidewire system (PGWS) under standardized in vitro conditions and in an isolated pig heart model. We used a pressure guide wire system provided by Pressure Guide, Radi Medical Systems, Uppsala, Sweden. Pressures were recorded by a fiber optic pressure sensor located laterally and 3 cm from the distal end. The basic principle is that the element modulates an optical reflection by pressure induced elastic movements. The light source is an emitting diode in the control unit. The PGWS replaces a standard 0.018 in. guidewire. The PGWS was introduced through a Y-adapter in a recirculating perfusion model, consisting of tubing with internal diameters from 1.00 to 4.00 mm. Different perfusion pressures (range 20-140 mm Hg) were generated by a pressure controlled roller pump. RESULTS: Different lumen sizes from 1 to 4 mm had no influence on the measurements. a) In a range from 20 to 140 mm Hg no significant differences were found between the perfusion pressure and the pressures obtained by the PGWS, resulting in an r-value of 0.99 and an equation of y = 1.04x + 1.9. b) In pressure measurements proximal and distal of an artificial stenoses resulting in gradients from 0 to 100 mm Hg, the PGWS correctly identified the pressure difference with an equally high accuracy, 1, 2, and 3 cm behind the stenoses.(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Balloon, Coronary↗
PubMed1993

Diagnosis of papillary muscle rupture after acute myocardial infarction by transthoracic and transesophageal echocardiography.

The sensitivity of transthoracic echocardiography to visualize the structural abnormality of papillary muscle rupture (PMR) after acute myocardial infarction can be anticipated to average about 50%; therefore, we evaluated five patients exhibiting the condition with both transthoracic and transesophageal echocardiography. The use of the two imaging techniques resulted in the fact that no instance of PMR was missed. Using transthoracic echocardiography in two patients and transesophageal echocardiography in four, the ruptured papillary muscle was visualized directly. Mitral insufficiency as an indirect sign was observed in all patients. In one patient the papillary muscle rupture developed in a mitral valve previously affected by endocarditis. All patients underwent mitral valve replacement and coronary artery bypass grafting. The diagnosis was confirmed at surgery in all patients. Four patients died in hospital, the fifth 5 months later. We recommended that transesophageal echocardiography be performed in patients with suspected PMR if transthoracic echocardiography does not provide an unequivocal diagnosis.

Aged↗
PubMed1993

Burst-promoting activity in the serum of patients with chronic renal failure undergoing long-term hemodialysis.

Anemia in patients with chronic renal failure (CRF) is multifactorial, and while the majority will respond to the paternal administration of recombinant human erythropoietin (r-HuEPO), a role for coexistent plasma inhibitors and stimulators, such as burst-promoting activity (BPA), remains controversial. To evaluate the latter possibility, eight individuals with CRF on long-term hemodialysis, were studied before (mean hemoglobin 58.4 +/- 8.0 g/l and after 12 weeks of r-HuEPO therapy (mean hemoglobin 100.4 +/- 18.3 g/l). In vitro erythroid cultures using erythroid burst forming unit (BFU-E) and erythroid colony forming unit (CFU-E) assays were performed, plating 5 x 10(4) bone marrow mononuclear cells and comparing growth in heat-inactivated autologous serum with AB serum. Using Step III sheep erythropoietin (Connaught Laboratories, Willowdale, Ontario, Canada) (n = 4), mean BFU-E pre-therapy were 89.7 +/- 75.1, CFU-E were 418.5 +/- 150.6, whereas the corresponding figures in AB serum were 2.5 +/- 2.9 and 197 +/- 94.19, p = 0.1, p = 0.01, respectively. Similarly, with r-HuEPO (EPOCONN: Connaught Laboratories, Willowdale, Ontario, Canada) (n = 4), mean BFU-E were 145.25 +/- 103.3 in autologous serum and 31.0 +/- 56.75 in AB serum (p = 0.04). As controls, erythroid progenitors from two normal donors yielded 69 and 61 BFU-E colonies in autologous serum and 103 and 42 in AB serum; the corresponding CFU-E were 52 and 235 versus 136 and 137.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Intraoral galvanic corrosion: literature review and case report.

This article reviewed the dental history of a patient with symptomatic electro-chemical reactions after the occlusal relationship of an existing complete gold crown and silver amalgam restoration was changed. A literature review of oral galvanism is presented with diagnostic techniques and treatment options.

Composite Resins↗
PubMed1993

Long-term follow-up of global and regional left ventricular function by two-dimensional echocardiography after thrombolytic therapy in acute myocardial infarction.

In order to evaluate changes in left ventricular volumes and regional left ventricular function after thrombolytic therapy in acute myocardial infarction serial two-dimensional echocardiography was performed during a follow-up of 2 years in 206 consecutive patients treated with streptokinase and adjunctive angioplasty in a randomized group of patients. Unexpected progressive left ventricular enlargement was detected both with and without angioplasty. In anterior wall infarction, end-diastolic volume index increased from 55 +/- 14 to 91 +/- 28 ml/m2 (+65%, P < 0.01) and end-systolic volume index increased from 31 +/- 11 to 55 +/- 23 ml/m2 (+79%, P < 0.01), whereas ejection fraction decreased from 45 +/- 9 to 41 +/- 7% (-9%, P = NS). Averaged regional anterior wall motion improved during the first 4 weeks (11 +/- 10 to 16 +/- 12%), but subsequently deteriorated (16 +/- 12 to 10 +/- 6, P < 0.05). The number of segments with pathological wall motion increased. Similar volumetric and regional wall motion data were demonstrated in inferior wall infarction. We believe this reflects a chronic ventricular remodelling phenomenon. This process takes place predominantly during the first 3 months, but continues over the whole follow-up period. Forty percent of the patients suffered symptoms of heart failure on long-term follow-up. Attenuation of progressive ventricular enlargement remains a therapeutic challenge in the long-term care of these patients. Angiotensin-converting enzyme inhibitors are promising agents in this regard.

Adult↗
PubMed1993

Exercise echocardiography for the evaluation of patients after nonsurgical coronary artery revascularization.

OBJECTIVES: The purpose of this study was to demonstrate the accuracy of stress echocardiography for detecting the progression of coronary artery disease after nonsurgical revascularization. BACKGROUND: The expanding role of nonsurgical coronary revascularization procedures mandates the development of sensitive noninvasive techniques for the detection of recurrent ischemia. METHODS: Bicycle stress echocardiography was performed in a series of 86 patients 6.5 +/- 1.3 months after a revascularization procedure. Seven patients were excluded from analysis because of poor echocardiographic image quality. RESULTS: Digital analysis achieved a sensitivity of 83% for the entire group and a specificity of 85% for stress echocardiographic detection of significant coronary artery disease. Sensitivity was greater in patients with (88%) than in those without (75%) prior myocardial infarction, but this difference did not reach statistical significance. Additional analysis using an increase in end-systolic volume index or a decrease in ejection fraction during stress as an additional marker for ischemia tended to enhance sensitivity (90% for the entire group and 93% for the subgroup with prior myocardial infarction). CONCLUSIONS: Stress echocardiography is a useful and sensitive method for the follow-up of patients undergoing nonsurgical revascularization procedures. The addition of volume determination to routine wall motion analysis may be helpful in patients with prior infarction who have scar tissue that may be difficult to distinguish from an adjacent exercise-induced wall motion abnormality.

Angioplasty, Balloon, Coronary↗
PubMed1993

Quantitative analysis of elastic recoil after balloon angioplasty and after intracoronary implantation of balloon-expandable Palmaz-Schatz stents.

OBJECTIVES: The purpose of this study was to measure elastic recoil from sequential angiograms after balloon angioplasty and after implantation of a balloon-expandable Palmaz-Schatz stent in the same patient, and to compare the results with the late angiographic outcome. BACKGROUND: The immediate result of coronary balloon angioplasty is influenced by plastic deformation, primarily of the atherosclerotic plaque, and by elastic recoil, primarily of the less or nondiseased vessel circumference. METHODS: The extent of elastic recoil was measured quantitatively as the difference between maximal balloon size and the resulting vessel diameter or cross-sectional area. RESULTS: Analysis was performed in 60 patients who received a single stent for late restenosis after initially successful coronary balloon angioplasty. Minimal lumen diameter (minimal cross-sectional area) was 0.98 +/- 0.43 mm (0.97 +/- 0.67 mm2) before balloon angioplasty, 2.06 +/- 0.36 mm (3.68 +/- 1.17 mm2) after angioplasty (both p < 0.001 vs. values before angioplasty) and 2.98 +/- 0.26 mm (7.12 +/- 1.28 mm2) after stenting (both p < 0.001 vs. postangioplasty results). No significant changes in vessel reference diameters or areas were measured. Mean balloon/artery ratios were similar in both procedures, ranging from 0.93 to 0.96. The calculated mean elastic recoil was 0.98 +/- 0.50 mm in diameter (31%) and 3.67 +/- 2.05 mm2 in area (48%) after balloon angioplasty compared with 0.10 +/- 0.07 mm (3.5%) and 0.38 +/- 0.36 mm2 (5.1%) after stenting. Increasing balloon sizes induced increased vessel stretch, which was followed by increased elastic recoil in the angioplasty group in contrast to the stenting group. Short, noncalcified and eccentric lesions tend to be associated with increased recoil after balloon angioplasty. Overdilation or underdilation in one of the procedures, changes in postprocedural vasomotion or postprocedural thrombus formation was not responsible for this outcome. After 6 months mean minimal lumen diameter was 2.39 +/- 0.58 mm, suggesting a mean hyperplasia of 0.59 +/- 0.51 mm. Twelve patients (20%) had a follow-up diameter that was equal to or less than the mean postangioplasty result and eight patients (14%) had a diameter stenosis of > 50%. CONCLUSIONS: The implantation of a Palmaz-Schatz stent almost completely eliminates the decrease in vessel dimensions caused by elastic recoil and therefore diminishes the impact of hyperplasia and reduces the rate of restenosis.

Adult↗
PubMed1993

Genetic contribution to risk of smoking initiation: comparisons across birth cohorts and across cultures.

Self-report data on smoking initiation (whether the respondent admitted ever having smoked) were obtained from three large adult twin samples (Australia, N = 3,808 pairs; Virginia, N = 2,145 pairs; AARP, N = 3,620 pairs). Data were broken down into birth cohorts, and genetic models were fitted to test whether the decline, in more recent birth cohorts, in the percentage of individuals becoming smokers has led to a change in the relative contributions of genes and environment to risk of becoming a smoker. Despite a marked change in the proportion of male respondents who reported ever having smoked, we found no evidence for cohort differences in genetic and environmental effects (no Genotype x Cohort interaction). Significant differences in genetic and environmental parameters were found between sexes, and between the Australian and the two U.S. samples. In the U.S. samples, estimates of the genetic contribution to risk of becoming a smoker were 60% in men, 51% in women. In the Australian sample, heritability estimates were 33% in men, but 67% in women. Significant shared environmental effects on smoking initiation also were found, accounting for 23% of the variance in U.S. men, 28% of the variance in U.S. women, 39% of the variance in Australian men, and 15% of the variance in Australian women. In models that allowed for the environmental impact of cotwin smoking on a twin's risk of smoking initiation, estimates of the direct genetic contribution to risk of smoking initiation were comparable or higher (49-58% in U.S. women and 71% in Australian women; 58-61% in U.S. men, and 37% in Australian men).

Adult↗
PubMed1993

Genetic diversity among Borrelia burgdorferi isolates: more than three genospecies?

In order to assess the genetic relationships among isolates of Borrelia burgdorferi, we have determined chromosomal DNA restriction fragment length polymorphisms (RFLP) of 27 isolates. Using five restriction enzymes and seven DNA probes, we recorded 246 different hybridizing bands. The resulting matrix was subjected to factorial correspondence analysis and to phylogenetic analysis using a parsimony program. These analyses demonstrate two closely related genospecies and three individual strains. RFLP variations among these three strains are much more pronounced than among the members of the other two genospecies. This may indicate the existence of more than three genospecies. Plasmid analysis did not contribute significantly to the genotypic differentiation.

Borrelia burgdorferi Group↗
PubMed1993

Lowest excited triplet states of hypericin and isohypericin.

The fluorescence and phosphorescence of hypericin and isohypericin were studied in an ethanol matrix at 1.2 K. The prompt fluorescence spectra are mirror images of the absorption around the 0-0 transition, as expected. The 0-0 vibronic lines of the phosphorescence are found at 13,190 and 13,622 cm-1, and the phosphorescence decay times are 2.79 and 6.6 ms at 1.2 K for hypericin and isohypericin respectively. The fluorescence excitation spectrum of isohypericin reveals a small trace of a different pigment, possibly a tautomeric form of isohypericin. The decay of the phosphorescence of isohypericin is biexponential. The slow component is attributed to an unknown contaminant with a high quantum yield of phosphorescence.

Anthracenes↗
PubMed1993

Subacute thrombotic complications after intracoronary implantation of Palmaz-Schatz stents.

Despite excellent results as a bail-out procedure for the management of abrupt closure after balloon angioplasty and the potential beneficial effects on restenosis after angioplasty, intracoronary stenting is limited, especially by subacute stent thrombosis. In 100 consecutive patients with intracoronary implantation of 118 Palmaz-Schatz stents, 10 patients (10%) developed subacute stent thrombosis during their hospital course 3 to 9 days after implantation. Therapy included intravenous thrombolysis, mechanical recanalization by balloon angioplasty, and emergency bypass surgery. Although successful recanalization was maintained in eight of nine nonsurgically treated patients within 2 hours after the onset of symptoms, seven patients developed myocardial infarction, with two patients having Q wave myocardial infarction and five patients having non-Q wave myocardial infarction. By univariate analysis, several variables could be identified as risk factors for the development of subacute stent thrombosis: bail-out implantations (odds ratio: 6.42; 95% confidence interval: 1.53 to 26.38; p = 0.007), unstable angina (12.32; 1.50 to 101.37; p = 0.006), long (5.44; 1.31 to 22.65; p = 0.015) and complex (type C) lesions (8.17; 1.93 to 34.50; p = 0.002) with large plaque areas (9.85; 1.96 to 44.51; p = 0.002), symptomatic postangioplasty dissections (4.36; 1.10 to 16.90; p = 0.029), incomplete wrapping of the dissection after stenting (6.50; 1.10 to 42.30; p = 0.039), and vessel irregularities distal to the stented segment (21.70; 4.12 to 113.18; p < 0.001). These variables, except the variable large plaque area, were confirmed as independent predictors of subacute stent thrombosis by a stepwise multivariate logistic regression analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Genotypic and phenotypic diversity among nine Swiss isolates of Borrelia burgdorferi.

Nine strains of Borrelia burgdorferi isolated from ticks in the canton of Valais (Switzerland) were characterized genotypically by determining restriction fragment length polymorphisms (RFLP) and plasmid profiles. The strains were also compared with respect to presence and electrophoretic mobility of the outer surface proteins OspA and OspB, and immunoreactivity of OspA and a 12 kD antigen. By both approaches, three different patterns were observed resulting in identical grouping of the strains. However, RFLP's allowed determination of relationships among strains within a group and have shown that geographic distribution does not correlate with genotype.

Animals↗
PubMed1993

[Magnetic resonance tomography of chronic aortic dissection].

17 patients with chronic aortic dissection were examined by MRI. In 12 patients, comparison between gradient echo sequences and SE sequences was possible. Gradient echo sequences, unlike SE sequences, permitted evaluation of flow in the true and false lumen, reliable differentiation between thrombus and flowing blood and clear delineation of the intimal flap. An additional comparison between transoesophageal ultrasound and MRT in 15 patients showed significant advantages in favour of MRI. In three patients MRI was able to detect more proximal origins of the dissection. Moreover, MRI allowed evaluation of the major aortic branches and their relation to the dissection; this was not possible with ultrasound. MRI plays an important role in the follow-up of chronic aortic dissections.

Adult↗
PubMed1993

Effective pulmonary capillary pressure in experimental myocardial ischaemia.

Effective pulmonary capillary pressure and extravascular lung water were investigated in dogs (n = 9) with normal heart function and after development of acute myocardial ischaemia. During control, no impairment of cardiopulmonary performance was observed. Extravascular lung water was in the normal range (8.1 +/- 2.8 ml.kg-1) and the effective pulmonary capillary pressure accounted for 1.36 +/- 0.53 kPa (10.2 +/- 4 mmHg). No correlation between extravascular lung water and effective pulmonary capillary pressure was observed (r2 = 0.347, P = 0.06). Arterial (RPA) and venous pulmonary resistance (RPV) were 70 +/- 15% and 30 +/- 6%, respectively. Acute myocardial ischaemia was induced by one stage occlusion of the left anterior descending (LAD) coronary artery; measurements during the ischaemia phase were performed 60 min following LAD occlusion. Myocardial ischaemia resulted in moderate changes of cardiac output, heart rate and left ventricular end-diastolic pressure. Oxygenation deteriorated, but no hypoxaemia occurred in any animal and CO2 elimination remained unchanged. Extravascular lung water was elevated (16.5 +/- 7.9 ml.kg-1, P < or = 0.01), and effective pulmonary capillary pressure was higher when compared with the control state (2.32 +/- 1.05 kPa (17.4 +/- 7.9 mmHg), P < or = 0.01). There was a significant correlation between both parameters (r2 = 0.528, P < or = 0.05). Longitudinal distribution of pulmonary vascular resistance was altered, and RPA decreased to 60 +/- 13% (P < or = 0.05), while RPV increased to 40 +/- 8% (P < or = 0.05). It is concluded that development of lung oedema is related to elevated effective pulmonary capillary pressure in dogs with acute myocardial ischaemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The effect of taprostene in patients with acute myocardial infarction treated with thrombolytic therapy: results of the START study. Saruplase Taprostene Acute Reocclusion Trial.

Taprostene is a prostacyclin analogue that inhibits platelet aggregation and thus might be a useful adjuvant to thrombolytic agents in acute myocardial infarction. In a placebo-controlled dose rising study, taprostene or placebo was intravenously infused in 80 patients treated with the thrombolytic agent saruplase (rscu-PA) for acute myocardial infarction. Three doses of taprostene were used: 6.25; 12.5; or 25.0 ng.kg-1 x min-1. Taprostene or placebo was infused for 48 h, followed by a 24 h tapering period. All 80 patients had short symptom-to-treatment delay and marked ST segment elevation. Patency at 90 min was documented in 58/78 patients (two patients had no angiography). Success rate varied from 67-82% in the four treatment arms (P = 0.33). Patency after rescue PTCA was seen in 10 out of 13 patients. Of the 58 patients having a patent artery at 90 min, none of the 43 taprostene patients and one of the 15 placebo patients had a re-occluded artery at the second angiography at 32-48 h (5/58 patients had no recatheterization). Conversely, of nine patients who had successful rescue PTCA, three of four placebo patients had a re-occluded artery at the second angiography compared to one of five taprostene patients (one placebo patient had no recatheterization) (P = 0.33). Safety evaluation revealed no major difference between the placebo plus saruplase and the taprostene plus saruplase groups. Taprostene was well tolerated up to 25 ng.kg-1 x min-1. Although taprostene did not affect 90 min patency, there was a trend to better maintenance of patency after rescue PTCA.

Angioplasty, Balloon, Coronary↗
PubMed1993

Heparin in experimental hyperdynamic sepsis.

OBJECTIVE: To evaluate the hypothesis that heparin administration increases cardiac output and improves oxygenation in experimental hyperdynamic sepsis in sheep. DESIGN: Prospective trial. SETTING: Laboratory at a large university-affiliated medical center. SUBJECTS: A total of 14 sheep weighing 28 to 44 kg. INTERVENTIONS: All 14 chronically instrumented sheep received a continuous infusion of Escherichia coli endotoxin (10 ng/kg/min) over 24 hrs. Seven sheep received a fixed bolus of beef lung heparin (5000 units) every 4 hrs intravenously. The other seven sheep served as controls. MEASUREMENTS AND MAIN RESULTS: The heparinized animals showed a triphasic cardiovascular response. Cardiac index increased (p < .05), and systemic vascular resistance index decreased (p < .05) at 2 hrs after the start of the endotoxin infusion (early phase, 0 to 2 hrs). Both variables returned to approximately baseline levels at 4 hrs (second period, 2 to 4 hrs). A hyperdynamic state (in terms of an increased cardiac index), a decreased systemic vascular resistance index, and a decreased mean arterial pressure (MAP) (p < .05 for all) was observed in the third phase (8 to 24 hrs). In the control group, cardiac index, systemic vascular resistance index, and MAP showed no changes in the first period, but a slight decrease in cardiac index and a slight increase in systemic vascular resistance index in the second period. The onset of the hyperdynamic state was less pronounced in the control group and cardiac index was lower (p < .05); likewise, systemic vascular resistance index was increased (p < .05) when compared with heparinized animals. Both groups developed pulmonary hypertension during the endotoxin infusion. The gas exchange in the heparin group was significantly impaired in the first and second periods, but returned to baseline levels in the hyperdynamic phase, whereas the oxygenation of the nonheparinized animals showed only minor changes in the first and second phases, but deteriorated significantly during the third phase of endotoxemia. CONCLUSIONS: In this experimental model of hyperdynamic sepsis, heparin significantly influenced the cardiopulmonary performance. Heparin preserved gas exchange and increased cardiac output but lowered systemic vascular resistance and MAP in the hyperdynamic state.

Animals↗