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Biomedical subjects

J Meyer

Publications and source records attributed to J Meyer.

At least 289 records · Page 16Linked to original sources
PubMed1998

Paroxysmal atrial fibrillation and high degree AV block: use of single-lead VDDR pacing with mode switching.

Dual chamber rate responsive pacing incorporating a mode switching option is increasingly used in patients with chronic paroxysmal atrial fibrillation and high degree AV block. Single-lead VDDR pacemakers have rarely used for this indication. The purpose of this study was to determine their reliability of atrial sensing during atrial fibrillation, the percentage of atrial synchronous ventricular pacing, and the behavior of the sinus rate outside the phases of atrial fibrillation. We studied ten patients with a single-lead VDDR pacemaker implanted for this indication. Follow-up visits were performed at predischarge and after 1, 3, 6, 12, 18, and 24 months. During the mean follow-up period of 18.9 +/- 6.9 months, the atrial sensing thresholds in sinus rhythm remained stable. Atrial synchronous ventricular stimulation was achieved in 68.7 +/- 31.2% (median 82.5%) of the whole follow-up time. All patients showed an adequate atrial rate response during sinus rhythm. Atrial fibrillation was detected by the pacemakers in 24.0 +/- 29.8% of time. In 3 of 10 patients the duration of atrial fibrillation showed a steady increase from visit to visit. The sensed amplitudes of atrial fibrillation ranged from 0.1-1.0 mV. A programmed atrial sensitivity of 0.1 mV was necessary to achieve complete sensing of atrial fibrillation. None of the patients experienced tachycardias with optimized pacemaker programming. Single-lead VDDR pacing incorporating a mode-switching option is useful in patients with high degree AV block and paroxysmal atrial fibrillation, since it provides atrial synchronous ventricular pacing in more than two-thirds of follow-up time. In a subgroup of patients, a progressive increase of the time during atrial fibrillation was demonstrated. A reliable detection of paroxysmal atrial fibrillation requires the programming of the atrial sensitivity to its most sensitive value.

Atrial Fibrillation↗
PubMed1998

Pacemaker therapy in premature children with high degree AV block.

The smallest pacemaker pulse generator and a steroid-eluting bipolar epicardial lead were implanted in two premature children with symptomatic AV block. Stable capture threshold and high amplitude evoked response electrogram resulted in normal function of the pacemaker Autocapture algorithm, which adjusts output 0.3 V above the measured capture threshold. Autocapture had previously been used only with endocardial leads. Longer-term observation is required.

Electrodes, Implanted↗
PubMed1998

How reliable is atrial sensing in single-lead VDD pacing: comparison of three systems.

UNLABELLED: This study evaluated the reliability of atrial sensing, expressed as AV synchronous stimulation, in three VDD systems with the atrial sensitivity (AS) programmed to a conventional value with a 2:1 safety margin compared to most-sensitive values. We studied 34 sex- and age-matched patients with 3 VDD systems: 14 with Unity 292-07, 10 with Saphir 600, and 10 with Thera VDD (5 model 8948 and 5 model 8968i). Two 24-hour Holters were performed on consecutive days. The AS was programmed in a randomized order to its most-sensitive value or to a 2:1 safety margin. All other parameters were programmed identically. The patients underwent a myopotential oversensing test and a daily life activity protocol. A beat-to-beat analysis of the Holters was performed to determine AV synchrony. For the entire group AV synchrony with conventional AS was 98.63% +/- 2.57%, compared to 99.80% +/- 0.43% with most-sensitive values (p = 0.002). There was no difference between the three systems with conventional AS. With the most-sensitive AS, AV synchrony was: Unity 99.99% +/- 0.03%, Saphir 99.42% +/- 0.60% (P = 0.002), Thera 99.81% +/- 0.35% (ns). In the Saphir system with an atrial blanking period of 150 ms, ventricular far-field sensing could be demonstrated in 5 of 10 patients. This reduced the percentage of AV synchrony due to an unwanted mode-switch to a nontracking mode. Myopotential oversensing was not detected in any patient. CONCLUSION: The VDD systems tested under identical conditions showed reliable P wave sensing at the most-sensitive atrial sensing setting without myopotential oversensing. Ventricular far-field sensing reduced AV synchrony and must be avoided by appropriate refractory periods.

Aged↗
PubMed1998

First experience with an automatic sensing algorithm in single-lead VDD stimulation.

UNLABELLED: An "Autosensing" algorithm available in SSI(R) and DDR(R) pacemakers automatically adapts the device's sensitivity to changing intracardiac signals. The atrial sensing function of this algorithm was tested for the first time with a VDD pacing system in which large variations of the atrial signal may occur because the atrial electrodes float in the atrial blood pool. METHODS: 15 patients with a VDD pacing system were studied (Unity 292-07, lead 425; Sulzer Intermedics). The atrial sensing threshold was measured, and the atrial sensitivity was programmed with a 2:1 safety margin. The autosensing algorithm and sensitivity profile were temporarily activated, and an ambulatory ECG with continuous marker annotation was recorded. All patients underwent a 30-minute daily life activities protocol. A beat-to-beat analysis of the ambulatory ECG was correlated with the changes in atrial sensitivity. RESULTS: The algorithm changed the baseline sensitivity from 0.57 +/- 0.23 mV during the test to 0.39 +/- 0.20 mV after the final rest period (P < 0.05). During the test 12.6 +/- 10.2 adaptations of the sensitivity occurred (range 0-33). In eight patients atrial undersensing occurred in 4.4% +/- 7.5% of the cycles (4-458 unsensed P waves). In these patients, the algorithm continuously adjusted the sensitivity towards more sensitive values, operating 19.1 +/- 18.3 changes compared with 5.4 +/- 7.3 changes in patients without undersensing (P = 0.009). Oversensing did not occur. CONCLUSION: The autosensing algorithm effectively optimized atrial sensitivity in VDD pacing. In patients with atrial undersensing the algorithm continuously remained near the most sensitive settings, thus reacting as intended. A faster sensitivity adjustment of the system would be desirable.

Activities of Daily Living↗
PubMed1998

Is atrial sensing of ventricular far-field signals important in single-lead VDD pacing?

UNLABELLED: In single-lead VDD pacing the atrial sensitivity frequently is programmed to sensitive values. Atrial sensing of ventricular far-field signals should be reduced by differential atrial sensing. The aim of the study was to evaluate the effectiveness of this approach. METHODS: The study included 10 patients with a single-lead VDD pacemaker (Thera 8948, Lead 5032). The atrial sensitivity was set to its most sensitive value of 0.18 mV and the telemetered intraatrial EGM was continuously recorded. After atrial tracked ventricular pacing, VVI pacing was performed with pacing rates from 100 to 160 beats/min in steps of 10 beats/min and up to 165 beats/min. The peak-to-peak amplitudes of P waves (P) and ventricular far-field signals (VFFS) were measured from the recordings. The ratio P/VFFS that defines the atrial signal-to-noise ratio was calculated, and the time from stimulus to maximum of the far-field signals amplitude (Tmax) was measured. RESULTS: P measured 0.98 +/- 0.76 mV. A VFFS was visible in the atrial channel in all patients with an amplitude of 0.45 +/- 0.25 mV (range 0.01-1.0 mV), independent of the pacing rate. The ratio P/VFFS was 3.9 +/- 4.2 (range 0.9-21.0). Tmax measured 99.4 +/- 15.2 ms during sinus rhythm. A rate dependent shortening of Tmax to 92.7 +/- 11.2 ms at 140 beats/min was observed (P = 0.001). At rates above 140 beats/min no further shortening occurred. CONCLUSION: Ventricular far-field signals are measurable in the atrial channel of VDD systems and may reach considerable amplitudes, which are not rate dependent. Although differential sensing provides favorable P waves to ventricular far-field signal ratios, refractory periods are needed to avoid far-field sensing. The rate dependent shortening of the ventricular signal can be detected in the atrial channel in VDD pacing.

Aged↗
PubMed1998

Host cis-mediated extinction of a retrovirus permissive for expression in embryonal stem cells during differentiation.

The use of retroviral vectors for gene transfer into animals has been severely hampered by the lack of provirus transcription in the early embryo and embryonic stem (ES) cells. This primary block in provirus expression is maintained in differentiated cells by a cis-acting mechanism that is not well characterized. Retroviral vectors based on the murine embryonal stem cell virus (MESV), which overcome the transcriptional block in ES cells, were constructed to investigate this secondary mechanism. These vectors transferred G418 resistance to ES cells with the same efficiency as to fibroblasts, but overall transcript levels were greatly reduced. A mosaic but stable expression pattern was observed when single cells from G418-resistant clones were replated in G418 or assayed for expression of LacZ or interleukin-3. The expression levels in independent clones were variable and correlated inversely with methylation. However, a second, more pronounced, block to transcription was found upon differentiation induction. Differentiation of the infected ES cells to cells permissive for retroviral expression resulted in repression and complete extinction of provirus expression. Extinction was not accompanied by increased levels of methylation. Provirus expression is thus regulated by two independent cis-acting mechanisms: (i) partial repression in the undifferentiated state, accompanied by increased methylation but compatible with long-term, low expression of retroviral genes, and (ii) total repression and extinction during early stages of differentiation, apparently independent of changes in methylation. These results indicate a time window early during the transition from an undifferentiated to a differentiated stage in which provirus expression is silenced. The mechanisms are presently unknown, but elucidation of these events will have an important impact on vector development for targeting stem cells and for gene therapy.

Animals↗
PubMed1998

Clinical and morphological characteristics in Streptococcus bovis endocarditis: a comparison with other causative microorganisms in 177 cases.

AIM: To compare the clinical and morphological characteristics of patients with Streptococcus bovis endocarditis with those of patients with endocarditis caused by other microorganisms. METHODS: 177 consecutive patients (Streptococcus bovis, 22; other streptococci, 94; staphylococci, 44; other, 17) with definite infective endocarditis according to the Duke criteria were included. All patients underwent transthoracic and transoesophageal echocardiography. In 88 patients, findings from surgery/necropsy were obtained. RESULTS: S bovis endocarditis was associated with older patients, with a higher mortality (p = 0.04), and with a higher rate of cardiac surgery (p < 0.001) than other microorganisms, although embolic events were observed less often (p = 0.02). Pathological gastrointestinal lesions were detected in 45% of the patients. Multiple valves were affected in 68% of the patients with S bovis endocarditis and in 20% of those with other organisms (p < 0.001). Moderate or severe regurgitation occurred more often in S bovis endocarditis than with other microorganisms (p = 0.05). When surgery or necropsy was performed, infectious myocardial infiltration of the left ventricle was confirmed histopathologically in 36% of the patients with S bovis endocarditis and in 10% of those with other organisms (p = 0.002). CONCLUSIONS: S bovis endocarditis is a severe illness because of the more common involvement of multiple valves, and of the frequent occurrence of haemodynamically relevant valvar regurgitation and infectious myocardial infiltration.

Adult↗
PubMed1998

Brief, intermittent hypoxia restricts fetal growth in Sprague-Dawley rats.

This study was conducted to determine whether brief, intermittent exposure to hypoxia with little change in nutrient intake would affect fetal growth. Pregnant rats were exposed to 1 or 2 h of hypoxia (FiO2 = 0.09-0.095) from days 15 to 19 of gestation. Exposure to 1 h of hypoxia decreased fetal body weight and length, liver weight and increased the brain/liver weight ratio (p < 0.05) as compared to controls. Two hours of hypoxia decreased fetal body weight and length, and heart, lung, kidney, gut, brain and liver weights (p < 0.01), but did not affect the brain/liver weight ratio. Two hours of hypoxia decreased maternal food intake and weight gain (p < 0.05), but fetal growth was not significantly altered in pair-fed controls. These data demonstrate that brief, intermittent periods of intrauterine hypoxia have significant effects on fetal growth.

Animals↗
PubMed1998

Endogenous nitric oxide and the pulmonary microvasculature in healthy sheep and during systemic inflammation.

Nitric oxide (NO) influences microvascular integrity. NO synthase inhibitors are regarded as therapeutic options, but their impact on the pulmonary microvasculature is not well defined. We studied the microvascular effects of the nonselective NO synthase inhibitor N(omega)-nitro L-arginine methylester (L-NAME) in healthy sheep and during systemic inflammation. Permeability analysis was performed in 30 adult ewes with chronic lung lymph fistulas and pulmonary venous occluders. Experiment 1: 20 sheep received Escherichia coli endotoxin (lipopolysaccharide, 10 ng/kg/min) for 32 h. After 24 h of endotoxemia, 10 sheep were given L-NAME (25 mg/kg), and 10 sheep received NaCl 0.9%. Experiment 2: six sheep were treated with L-NAME (25 mg/kg), and four animals received NaCl 0.9%. Endotoxin induced a phasic pulmonary microvascular response with early transiently increased endothelial permeability at 4 h and late normalization of microvascular integrity to large molecules after 24 h. At that time systemic vasodilation had occurred. L-NAME raised pulmonary artery pressure and pulmonary vascular resistance index without signs of increased permeability in either experiment. NO is involved in vascular tone in healthy sheep and during systemic inflammation, but it does not seem to play a role in the integrity of the pulmonary microvascular barrier function to large molecules.

Animals↗
PubMed1998

The perception of risk messages regarding electromagnetic fields: extending the extended parallel process model to an unknown risk.

The Extended Parallel Process Model (EPPM) was developed as a model to assist in the development of effective risk communication messages, specifically messages that elicit adaptive behavioral responses. It has shown to be effective in several settings invoking clearly delineated dangers (e.g., safety belt usage, condom usage).Unfortunately, communicating risk messages is not always so straightforward. One increasing concern in the risk communication field is the controversy over electromagnetic fields (EMFs) and the uncertain hazards they present to individuals. The purpose of this study is to test the EPPM with this unknown risk and to explore which type of risk message may motivate adaptive behavioral responses. In accordance with the EPPM model, 251 participants received either a low- or high-threat risk message and a list of control measures they could use to reduce their exposure to EMFs. Results suggest that the EPPM model can be extended to an unknown risk.

Journal Article↗
PubMed1998

Models for the longitudinal genetic analysis of same-age twins: application to HDL cholesterol.

Models are presented for the analysis of longitudinal data from same-age twins which permit the exploration of a remarkably diverse array of alternative explanations for continuity and change during development. Data of this type permit the detection of new sources of genetic or environmental covariation during development that are not expressed at earlier ages and, because they include the effects of age-specific genes, the resulting heritability estimates are more reliable than those obtained from relatives who differ in age. The proposed models were applied to measurements of HDL cholesterol obtained on 81 pairs of monozygotic (MZ) twins and 69 dizygotic (DZ) pairs at 11, 12.5 and 14 years of age. All three MZ co-twin correlations were substantially higher than the self correlations across occasions, suggesting that new sources of genetic or environmental covariation must be expressed during early adolescence. This interpretation was confirmed by analysis of the full covariance matrices which showed that only models which assumed the expression of new or age-specific genes could explain the observed pattern of covariation. Because they include the effects of age-specific genes, the resulting heritabilities (0.80-0.83) were substantially higher than many previous estimates.

Adolescent↗
PubMed1998

Patient choice in diabetes education curriculum. Nutritional versus standard content for type 2 diabetes.

OBJECTIVE: To examine the effects of patient choice between two education curriculums that emphasized either the standard or nutritional management of type 2 diabetes on class attendance and other outcomes among a mostly Hispanic patient population. RESEARCH DESIGN AND METHODS: A total of 596 patients with type 2 diabetes were randomly assigned to either a choice or no choice condition. Patients in the choice condition were allowed to choose their curriculum, while patients in the no choice condition were randomly assigned to one of the two curriculums. Outcomes were assessed at baseline and at a 6-month follow-up. RESULTS: When given a choice, patients chose the nutrition curriculum almost four times more frequently than the standard curriculum. Contrary to our hypothesis, however, patients who had a choice did not significantly increase their attendance rates or demonstrate improvements in other diabetes outcomes compared with patients who were randomly assigned to the two curriculums. Patients in the nutrition curriculum had significantly lower serum cholesterol at a 6-month follow-up, whereas patients in the standard curriculum had significant improvements in glycemic control. Of the randomized patients, 30% never attended any classes; the most frequently cited reasons for nonattendance were socioeconomic. Hispanic patients, however, were just as likely as non-Hispanic patients to attend classes and participate at the follow-up. Patients who attended all five classes of either curriculum significantly increased their diabetes knowledge, gained less weight, and reported improved physical functioning compared with patients who did not attend any classes. CONCLUSIONS: Although providing patients with a choice in curriculums at the introductory level did not improve outcomes, differential improvements were noted between patients who attended curriculums with different content emphasis. We suggest that diabetes education programs should provide the opportunity for long-term, repetitive contacts to expand on the modest gains achieved at the introductory level, as well as provide more options to match individual needs and interests and to address socioeconomic barriers to participation.

Adult↗
PubMed1998

Clinical profile of saruplase: angiographic findings.

Saruplase is a relatively new fibrinolytic drug. Dose finding studies indicated that 70-80 mg saruplase given intravenously results in a high perfusion rate. With a 20 mg bolus followed by a 60 mg infusion over 1 h, a rapid and complete restoration of blood flow can be achieved in a fairly high number of patients. This dose regimen was used in subsequent studies comparing saruplase with other thrombolytic agents. The PRIMI (Pro-urokinase In Myocardial Infarction) study compared saruplase with streptokinase. Early patency rate at 60 min (TIMI grade 2 and 3 flow) was significantly higher with saruplase (71.8%) than with streptokinase (48.0%). In the SESAM (Study in Europe with Saruplase and Alteplase in Myocardial Infarction) study comparing saruplase with alteplase, at 60 min patency rate was 79.9% versus 75.3%, respectively, and at 90 min the rate was 79.9% versus 81.4%, respectively. In the LIMITS (Liquemin in Myocardial Infarction during Thrombolysis with Saruplase) study a heparin bolus of 5000 IU was shown to have an important impact on patency rate. Both heparin and acetylsalicylic acid are recommended as adjunctive therapy before fibrinolysis with saruplase. The reocclusion rates within 24-40 h were between 0.9% and 2.4% in the saruplase studies. There is some variation in estimating whether patency rates are higher with anterior or with inferior infarctions. Saruplase appears to be equally effective in the treatment of infarction in both locations.

Aspirin↗
PubMed1998

Blocking of classical complement pathway inhibits endothelial adhesion molecule expression and preserves ischemic myocardium from reperfusion injury.

Myocardial injury after ischemia (I) and reperfusion (R) is related to leukocyte activation with subsequent release of cytokines and oxygen-derived free radicals as well as complement activation. In our study, the cardioprotective effects of exogenous C1 esterase inhibitor (C1 INH) were examined in a rat model of myocardial I + R (i.e., 20 min + 24 hr or 48 hr). The C1 INH (10, 50 and 100 U/kg) administered 2 min before reperfusion significantly attenuated myocardial injury after 24 hr of R compared to vehicle treated rats (P < .001). Further, cardiac myeloperoxidase activity (i.e., a marker of PMN [polymorphonuclear leukocyte] accumulation) in the ischemic area was significantly reduced after C1 INH treatment compared to vehicle treated animals (0.81 +/- 0.1, 0.34 +/- 0.13, 0.13 +/- 0.1 vs. 1.44 +/- 0.3 U/100 mg tissue, P < .001). In addition, C1 INH (100 U/kg) significantly attenuated myocardial injury and neutrophil infiltration even after 48 hr of reperfusion compared to vehicle treatment. Immunohistochemical analysis of ischemic-reperfused myocardial tissue demonstrated activation of classical complement pathway by deposition of C1q on cardiac myocytes and cardiac vessels. In addition, expression of the endothelial adhesion molecules P-selectin and intercellular adhesion molecule 1 (ICAM-1) was observed after reperfusion of the ischemic myocardium. In this regard, C1 INH administration abolished expression of P-selectin and ICAM-1 on the cardiac vasculature after myocardial ischemia and reperfusion. Blocking the classical complement pathway by exogenous C1 INH appears to be an effective means to preserve ischemic myocardium from injury after 24 and 48 hr of reperfusion. The mechanisms of this cardioprotective effect appears to be due to blocking of complement activation and reduced endothelial adhesion molecule expression with subsequent reduced PMN-endothelium interaction, resulting in diminished cardiac necrosis.

Animals↗
PubMed1998

Gastrografin as a gastrointestinal contrast agent in the Greek tortoise (Testudo hermanni).

Eighteen Greek tortoises (Testudo hermanni), divided into three groups, were kept at three different average ambient temperatures. Gastrografin was administered to all individuals by orogastric tube at a dosage of 1 ml/130 g body weight. The partial and total transit times were recorded by means of radiographs taken immediately postadministration and at 20, 40, 60, 90, 120, and 150 min and 3, 4, 6, 8, 12, 24, 48, 72, and 96 hr postadministration. Mean total transit times were 2.6 hr (range 1.5-4.0 hr) at 30.6 degrees C, 6.6 hr (range 3.0-8.0 hr) at 21.5 degrees C, and 17.3 hr (range 8.0-24.0 hr) at 15.2 degrees C. These transit times allow a radiologic diagnosis within a relatively short period, especially compared with contrast studies performed with barium sulfate. The visualization of the intestinal tract is good with Gastrografin; however, intestinal mucosal detail was not completely satisfactory.

Animals↗
PubMed1998

Genetic and environmental influences on subtypes of conduct disorder behavior in boys.

Oppositional and conduct disorders are a heterogeneous collection of disruptive behaviors associated with diverse risk factors and varying outcomes. Data from males in the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) are used to explore the relative importance of genetic and environmental influences on four previously described disruptive subtypes: property violations, status violations, oppositional behavior, and aggression. Striking differences between results according to mother and child ratings are found, indicating the need to consider carefully the origin of rater differences. Child ratings indicate support for a general genetic liability, with greatest influence on property violations, oppositional behavior and aggression. Maternal ratings suggest that the genetic factors influencing conduct disorder behavior are more specific to the behavioral area, with the stronger genetic influence on property violations and aggression.

Adolescent↗