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Biomedical subjects

J Meyer

Publications and source records attributed to J Meyer.

At least 469 records · Page 26Linked to original sources
PubMed1995

The influence of tracheal pressure changes on the responses of the tympanal membrane and auditory receptors in the locust Locusta migratoria L.

In resting tethered locusts, the effect of slow changes in tracheal air pressure on peripheral auditory information processing was analysed. The tympanal membrane vibrations, the pressure inside the tracheal system and the summed activity of the auditory receptors were measured simultaneously. With the membrane in the resting position, laser vibrometry and Fast Fourier Transformation analysis of sound-induced membrane vibrations demonstrated characteristic power spectra at the attachment sites of the high-frequency and low-frequency receptors. The spectra were different above 9 kHz, but very similar in the range 2­9 kHz. During ventilation, tracheal pressure changed between -500 and 1500 Pa. This caused tympanal membrane peak-to-peak displacements in the range 70­90 µm outwards and 20­30 µm inwards, as measured by means of laser interferometry. For a quantitative analysis, sinusoidal tympanal membrane displacements with amplitudes such as those during natural ventilation could be induced by applying pressure to the tracheal system. There was a sigmoid relationship between the tracheal pressure and the corresponding membrane displacement. Outward displacements of the tympanal membrane at the attachment site of the elevated process (a-cells) attenuated sound-induced membrane vibrations in the ranges 2­10 kHz and 14­22 kHz and increased them in the ranges 10­14 kHz and 22­25 kHz. At the pyriform vesicle (d-cells), the vibration sensitivity was reduced in the frequency range 2­14 kHz. Sensitivity was enhanced in the range 14­25 kHz. As a consequence, the detection of acoustic signals was also influenced at the auditory receptor level. Tympanal membrane displacements during acoustic stimulation with 4 kHz sound pulses decreased the summed receptor response by approximately 15 dB. At 16 kHz, an increase of the response equivalent to 7 dB occurred. The effect on the response to white noise was intermediate.

Journal Article↗
PubMed1995

Objective Pulse-Synchronous "Essential" Tinnitus due to Narrowing of the Transverse Dural Venous Sinus.

Subjective tinnitus is a common problem with many etiologies. Objective tinnitus, in which the sound is perceived by both the patient and the examiner, is less common. Objective tinnitus of the vascular type, in which a pulse synchronous bruit is heard by an independent observer, is frequently related to an underlying arterial or arteriovenous malformation, most commonly a dural arteriovenous fistula (DAVF) involving the transverse and sigmoid sinuses. The remaining cases are usually termed "essential" vascular tinnitus, and are presumed to have a venous etiology. In these cases, the audible noise is generally assumed to be produced within the sino-jugular connection, or within an enlarged jugular bulb. We present four documented cases of objective pulse synchronous tinnitus due to focal narrowing (acquired and developmental) of the mid-portion of the transverse dural sinus. In all cases, a bruit was audible directly over a focal constriction in the sinus, demonstrated by cerebral angiography or direct catheter venography. In one case, selective venography revealed a distensible sinus narrowing, associated with a jet of contrast marking fast flow within a developmental sinus segmentation. In another case, a loud pulse synchronous bruit was heard directly over a focal transverse sinus stenosis, which was detected by angiography at the site of a vascular surgical clip. In this case, magnetic resonance (MR) falsely predicted sinus occlusion. In two other cases, an audible bruit was also heard directly overlying a narrowed transverse sinus, seen in the venous phase of angiography. Transverse sinus stenosis is an unappreciated cause of objective pulsatile tinnitus, and we believe that this mechanism may underlie many cases of "essential" or venous etiology tinnitus not otherwise anatomically explained. Non-invasive testing, computed tomography (CT) and MR and non-directed angiography may overlook it. Conventional catheter arteriography or venography should be performed in such cases, with attention to the dural sinuses, if other tests fail to define the anatomic basis of the audible bruit.

Journal Article↗
PubMed1995

[Reliability of digital transesophageal echocardiography in imaging the left coronary artery].

Fifty consecutive patients (mean age 56 years) were examined to evaluate the reliability of transesophageal echocardiography in the evaluation of the left proximal coronary artery. Results of 28 cases were compared to selective coronary angiography. Echocardiography was able to visualize the left main artery for the length of 1.0 +/- 0.6 cm in all patients (100%), the left circumflex artery for maximal 3.1 +/- 1.4 cm in 86% and the left anterior descending artery as long as 2.3 +/- 0.9 cm in 58%. The intraluminal diameter of the most proximal localized segments measured by echocardiography and angiography in the LAO and RAO-projection was in terms of the left main artery 4.1 +/- 0.9 mm, 4.1 +/- 0.9 mm and 4.0 +/- 0.9 mm (n.s.), of the left circumflex artery 2.8 +/- 0.5 mm, 3.3 +/- 0.8 mm and 3.3 +/- 0.9 mm (n.s.) and of the left anterior descending artery 3.0 +/- 0.8 mm, 3.4 +/- 0.7 mm, and 3.6 +/- 1.0 mm (n.s.). In respect of detection of coronary artery stenoses in correspondence to the coronary angiogram sensitivity was 81%, specificity 93% and positive predictive accuracy 86%. Quantitative analyses of the coronary anatomy and the correlation to angiography could contribute to the validation of transoesophageal echocardiography.

Adult↗
PubMed1995

Use of nitric oxide synthase inhibitors in animal models of sepsis.

Sepsis, as a general inflammatory process, affects the whole organism, mainly because of the intense vasodilation and reduced perfusion pressures associated with it. The high mortality rates seen with sepsis are correlated with a reduction in mean arterial pressure. Therefore, the restoration of adequate arterial pressures is imperative. Nitric oxide (NO.) is at least partly responsible for the vasodilation. Inhibition of nitric oxide synthase (NOS) is, therefore, a logical approach for the treatment of sepsis. As with any other vasoconstrictive drug, NOS inhibitors are clinically indicated only in hyperdynamic sepsis. In animal models, their administration leads to an immediate restoration of blood pressure, accompanied by improved myocardial, pulmonary, and renal function. An increase in oxygen extraction prevents oxygen consumption from decreasing, despite a marked reduction in cardiac output to normal concentrations. In sepsis, virtually all regional blood flows are increased. In our experiments, no organ systems showed a reduction below preseptic baseline values when NOS inhibitors were administered. Furthermore, NOS inhibition did not cause an increase in lactate concentrations, indicating adequate nutritive organ blood flow. Consequently, NOS inhibitors seem to be beneficial and safe when administered under the right circumstances and in a controlled fashion.

Amino Acid Oxidoreductases↗
PubMed1995

[Trans-thoracic 3D echocardiography reconstruction for left ventricular volume determination].

2D-echocardiography is a safe and inexpensive method for accurate left ventricular volume quantification. However, accuracy of measurements is limited by the requirement of geometric assumptions and volume computation algorithms. Reproducibility is diminished by erroneous image plane positioning, which is due to the necessity of standardized reference images. The degree of variation can influence clinical decision making. 3D-echocardiography has overcome those problems. Volume quantitation is performed without the need of geometric assumptions, computation algorithms or reference images. The shape of a ventricle is defined by acquired data, not by calculated data. Since the recent development of sophisticated hardware- and software techniques the method can be utilized under clinical circumstances. For data acquisition tomographic planes are acquired either in a random or in a sequential order. For random acquisition the transducer is positioned at various acoustic windows at the thoracic wall and spatial orientation of the corresponding plane is localized by a spark gap device. By this way various, non-parallel cross-sectional images of the left ventricle are acquired. The spatial position of the planes is displayed by lines in a parasternal longitudinal view, each representing a "line of intersection". When tomographic planes are acquired in a sequential manner, mostly rotational scanning is utilized. Here, multiple apical views of the left ventricle are acquired during ECG- and respiration gated rotation of the transducer over a span of 180 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1995

[Reconstruction methods for 3D imaging and quantification of intracoronary ultrasound cross-sectional images using biplanar fluoroscopy. Initial experiences in vitro and in vivo].

In this investigation, we studied the feasibility of 3D-reconstruction from 2D cross-sectional intracoronary ultrasound images. A computer-aided, automated 3D-reconstruction was used to generate cylindrical and sagittal format of vessels in vitro (n = 9) and in vivo (n = 48). Ultrasound 2D-images were acquired with a 20 MHz mechanical intracoronary ultrasound catheter (Boston Scientific). A slow pullback (about 1 mm/s) of the catheter was performed during continuous recording of the ultrasound images. The recorded 2D-images were then fed to an image processing computer. Correction and scaling of the axial vessel dimensions was performed by the assessment of the catheter position in the simultaneously recorded biplane fluoroscopy. Digitized data were then processed to 3D-images with use of voxel space modeling. The 3D-views from any plane can be reconstructed. The in-vitro study demonstrated that the reconstructed images were able to correctly portray the pathological changes of the vessel wall in all specimen as proved by pathologic examination. In the in-vivo study, 3D-reconstruction provided not only a spatial visualization of the coronary arterial disorders (such as coronary aneurysm, coronary dissection, spontaneous plaque rupture etc.) but also provides the potential to quantify the mass of lesions. By combining sagittal and cylindrical views, 3D-reconstruction enables longitudinal and orthogonal imaging of the both the vessel lumen and vessel wall, therefore, it has the advantage of cross-sectional viewing as obtained from intracoronary ultrasound and the longitudinal viewing as derived from coronary angiography. These preliminary results of the study indicate that 3D-reconstruction of coronary segments is a promising technique for studying coronary artery disease. Analysis can be based not only on single or multiple cross-sectional images but also on vessel segments facilitating serial studies as for instance studies assessing the progression and regression of atherosclerosis.

Aortic Dissection↗
PubMed1995

[Experimental ultrasound angioplasty: in vitro resolution of thrombi].

A new ultrasonic angioplasty ablation catheter connected to a 19.5 kHz. 25 W transducer was tested in vitro for its ability to disrupt 12-h. 24-h, and 5-day-old whole blood thrombi (n = 45.697 mg +/- 223 mg) and fibrin thrombi (n = 45.338 mg +/- 133 mg), as well as 5-day-old cadaver thrombi (n = 8.270 mg +/- 71 mg) within 10 min. Five of each age were used as control thrombi in which the catheter was moved back and forth without ultrasound emission. The size of ablated thrombus particles was measured by a laser device. The power output at the end of the catheter was assessed calorimetrically. The loss of weight of whole blood thrombi was between 429 (74%) and 524 mg (91%) (p < 0.01, whole blood thrombi vs. control thrombi) and between 302 (85%) and 314 mg (95%) (p < 0.05) for fibrin thrombi, respectively. Thrombus age did not prove to be a highly significant influencing factor. The disruption rate for whole blood thrombi was 0.75 to 1.05 mg/s and for fibrin thrombi 0.69 to 0.7 mg/s. It was only 0.09 mg/s for the cadaver thrombi. 93% of all particles ablated from whole blood thrombus ranged between 0-5 micron, less than 0.2% between 30-150 microns. For fibrin thrombi 69% of all particles were < 10 microns (25% between 10-20 microns). Only 0.02% ranged between 300-600 microns, which was similar for cadaver thrombi. The mean measured power output at the catheter tip was 5.9 W compared to the power output of 25 W at the ultrasound generator.(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Balloon↗
PubMed1995

[Atrial sensing by a new VDD pacemaker].

VDD stimulation is an alternative to DDD pacing due to the possibility of p-wave synchronous ventricular pacing without the need of an atrial lead. Mainly, the reliability of the system depends on the atrial sensing. In 22 patients the intraoperative atrial amplitude and, postoperatively, the atrial sensing threshold were measured. Furthermore, the stability of the atrial sensing threshold during follow-up was proven. The mean atrial amplitude was intraoperative by 2.4 +/- 1.2 (1.0-6.8) mV. The measurement of the atrial sensing threshold in the first 5 postoperative days showed a mean value of 1.02 +/- 0.49 (0.3-1.6) mV. The measurements of the mean atrial sensing threshold after 30, 90, and 180 days showed no statistical differences. Intraindividual variance was shown in 17/20 patients (0.55 +/- 0,42; 0.15-1.05 mV). Seventeen of the 22 patients were programmed with an atrial sensing threshold of 0.3 mV. In five patients the atrial sensing threshold was programmed at less than 0.3 mV in order to reach a twofold atrial sensitivity. Despite a programmed atrial sensitivity of 0.1 mV and isometric conditions no atrial oversensing occurred. The postoperative atrial sensing thresholds of the VDD system investigated were significantly lower than the intraoperatively measured atrial amplitudes. The mean atrial sensing threshold did not change during the follow-up period. The variation which did occur was within individual variation at different return visits.

Aged↗
PubMed1995

[PTCA-induced myocardial ischemia for detection salvaged myocardium after thrombolytic therapy of acute myocardial infarct].

In 43 patients (ages 55.8 +/- 9.0 years) with myocardial infarction treated with thrombolytic therapy presenting with one-vessel coronary artery disease, the monitoring-ECGs during PTCA (17.0 +/- 12.7 days after infarct) were analyzed. Patients with ST-segment deviations > or = 0.1 mV (group A, n = 33) were compared with those < 0.1 mV (group B, n = 10). To answer the question, if these ischemic signs might be interpreted as salvaged myocardium, parameters of infarct size were evaluated. The maximal CK-activity in group A was 867 +/- 567 IU/l, in group B 1452 +/- 992 IU/l (p < 0.05), whereas the maximal GOT-activity was 113 +/- 69 IU/l and 174 +/- 102 UI/l (p < 0.05). The number of pathologic segments of the ventriculographies in the acute phase were 9 +/- 2 and 14 +/- 3 (p < 0.05), shortly after PTCA, 12 +/- 2 and 16 +/- 2 (p = 0.06), and after 6 months, 11 +/- 4 and 13 +/- 1 (N.S.). At the same time points EDV was analyzed in both groups and revealed the following: 103 +/- 20 ml, 98 +/- 21 ml, 104 +/- 23 ml and 103 +/- 25 ml (N.S.), 101 +/- 21 ml (N.S.), 116 +/- 46 ml (N.S.).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

[Subgingival plaque due to gingivitis and inactive periodontitis sites in the adult periodontitis patient].

There are several discrepancies with respect to the composition of subgingival plaque in gingivitis and in inactive adult periodontitis (AP). In this study we compared subgingival plaque samples taken from gingivitis sites to those from inactive periodontitis sites of the same patients. Of 44 patients plaque samples from 86 gingivitis sites and 92 periodontitis sites were analysed. Darkfield microscopy showed a higher proportion of spirochetes and mobile rods in the periodontitis sites. Analysis of cultures revealed a higher and statistically significant number of anaerobes in the periodontitis sites (1.7 x 10(7) vs 3 x 10(6), p = 0.006). The following bacterial species were isolated more frequently from periodontitis sites than from gingivitis sites: Actinobacillus actinomycetemcomitans (18% vs 10%), as well as the black-pigmented Prevotella intermedia (68% vs 48%) and Porphyromonas gingivalis (48% vs 28%). On the one hand, these small differences in the bacteriological parameters can be explained by the fact that both gingivitis and periodontitis plaque samples were taken from the same periodontitis patients. An infection of the gingivitis sites from the parodontitis sites within the same patient could not be excluded. On the other hand, the mean probing depth of the gingivitis sites was relatively high, 3.6 mm (measuring point interdental plus pseudo-pocket) which may favor the growth of anaerobic bacteria.

Adult↗
PubMed1995

[Cardiovascular parameters in transient hypothyroidism].

Cardiovascular manifestations are a frequent finding in hypothyroidism. Thus, blood-pressure measurements, longtime electrographic monitoring, and spiroergometry were examined in 20 patients with transitory hypothyroidism. In the patients with thyroid carcinoma, total thyroidectomy was performed. Measurements were made in hypothyroidism and after TSH-suppression with L-thyroxine. Thirty-five patients in whom intracardiac catheter examination ruled out cardiopulmonary disease served as controls. Cardiopulmonary exercise was done by bicycle exercise testing. In transitory hypothyroidism an increase of diastolic blood pressure was found at rest (p = 0.02) and during exercise (p = 0.002), which was reversible after T4-therapy. Compared to the controls diastolic blood pressure in hypothyroidism was increased at rest (p = 0.014) and during exercise (p = 0.005). ECG-monitoring showed a day-night difference in heart rate in hypothyroid patients and after therapy. The mean heart rate (74 vs. 88 beats per minute; p = 0.0006), the minimal (p = 0.0062) and the maximal heart rate (p = 0.0016) during the day were decreased in hypothyroidism compared to euthyroidism. There were no atrioventricular blocks in transitory hypothyroidism and no increase of ventricular or supraventricular premature beats after high-dose T4-treatment. Spiroergometry showed no change in ventilation and an increased growth in heart rate (p = 0.021) associated with good working capacity in hypothyroid patients. Heart rate at rest (p = 0.004) and at the anaerobic threshold (p = 0.03) were decreased in transitory hypothyroidism.

Adult↗
PubMed1995

Microscopic evaluation of an occluded intracoronary Palmaz-Schatz stent removed before coronary artery bypass grafting.

Intracoronary implantation of stent devices is a new interventional technique with a promising role in the treatment of acute coronary occlusions caused by intimal dissection and suboptimal results of percutaneous transluminal coronary angioplasty. However, the prolonged presence of stent material embedded in the arterial wall may generate unknown late consequences. Major complications consist of subacute to chronic occlusion and restenosis. To elucidate the underlying cause we removed an angiographically occluded intracoronary artery Palmaz-Schatz stent before coronary artery bypass grafting. Scanning electron microscopy showed thorough coating of the metal struts of the stent by normal neoendothelial cells. Side branches arising at the level of the stent were patent. According the specific angiographic feature thrombotic occlusion originated distally of the stent.

Aged↗
PubMed1994

[Tumor-induced anemia and markers of inflammation].

Anemia of cancer patients is multifactorial but often resembles anemia of chronic inflammatory disorders. We investigated the possibility of measurably increased parameters of inflammation in the serum of cancer patients and examined the correlation of hemoglobin levels, serum iron, and markers of inflammatory response in 201 cancer patients. Serum levels of CRP, ferritin, s-IL-2R, neopterin levels and TNF were assayed with ELISA tests. Statistically significant correlations were found between hemoglobin levels, CRP (Pearson's R = -0.451; p < 0.0001), serum iron (R = 0.326) and ferritin levels (R = -0.449). No significant correlations were seen between hemoglobin levels and neopterin or s-IL-2R. The correlation between hemoglobin levels in cancer patients and elevated markers of inflammatory responses, such as CRP, suggest that cytokines involved in the inflammatory responses may be at least partially responsible, directly or indirectly, for anemia in cancer patients.

Adult↗
PubMed1994

Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9.

A human autosomal XY sex reversal locus, SRA1, associated with the skeletal malformation syndrome campomelic dysplasia (CMPD1), has been placed at distal 17q. The SOX9 gene, a positional candidate from the chromosomal location and expression pattern reported for mouse Sox9, was isolated and characterized. SOX9 encodes a putative transcription factor structurally related to the testis-determining factor SRY and is expressed in many adult tissues, and in fetal testis and skeletal tissue. Inactivating mutations on one SOX9 allele identified in nontranslocation CMPD1-SRA1 cases point to haploinsufficiency for SOX9 as the cause for both campomelic dysplasia and autosomal XY sex reversal. The 17q breakpoints in three CMPD1 translocation cases map 50 kb or more from SOX9.

Amino Acid Sequence↗
PubMed1994

Mutated forms of the [2Fe-2S] ferredoxin from Clostridium pasteurianum with noncysteinyl ligands to the iron-sulfur cluster.

The [2Fe-2S] ferredoxin from Clostridium pasteurianum is unique among ferredoxins, both by its sequence and by the distribution of its cysteine residues (in positions 11, 14, 24, 56, 60). Thus, no homologous sequences are available to infer, by comparison, the identity of the ligands of the iron-sulfur cluster. Therefore, in order to obtain information on the latter point, a combination of site-directed mutagenesis and UV-vis, EPR, and resonance Raman spectroscopy has been implemented. All of the cysteine residues have individually been replaced by serine and two of them by alanine. Cysteine 14 could be replaced by either serine or alanine without any modification of the spectroscopic properties of the protein and was therefore dismissed as a ligand of the [2Fe-2S] cluster. The C56S, and C60S-mutated proteins were both found to display UV-vis, EPR, and resonance Raman spectra consistent with serine-coordinated [2Fe-2S] clusters. The C11S-mutated protein was considerably less stable than the wild type ferredoxin. This observation, together with the hypsochromic shifts of UV-visible absorption features upon cysteine 11-->serine mutation, suggested cysteine 11 to be a ligand of the [2Fe-2S] cluster. Cysteine 24 could be replaced by either serine or alanine without decreasing the stability of the protein and without dramatically changing its spectroscopic properties. Thus, either cysteine 24 is not a ligand of the [2Fe-2S] cluster or it is replaced by another ligand in the C24A mutated protein. A [2Fe-2S] cluster was also assembled in the C14A/C24A doubly mutated protein, i.e., in a polypeptide chain containing only three cysteine residues.2+ off

Alanine↗
PubMed1994

Refined crystal structure of the 2[4Fe-4S] ferredoxin from Clostridium acidurici at 1.84 A resolution.

The crystal structure of the 2[4Fe-4S] ferredoxin from Clostridium acidurici has been determined at a resolution of 1.84 A and refined to an R-factor of 0.169. Crystals belong to space group P4(3)2(1)2 with unit cell dimensions a = b = 34.44 A and c = 74.78 A. The structure was determined by molecular replacement using the previously published model of an homologous ferredoxin and refined by molecular dynamics techniques. The model contains the protein and 46 water molecules. Only two amino acid residues, Asp27 and Asp28, are poorly defined in the electron density maps. The molecule has an overall chain fold similar to that of other [4Fe-4S] bacterial ferredoxins of known structure. The two [4Fe-4S] clusters display similar bond distances and angles. In both of them the co-ordination of one iron atom (bound to Cys11 and Cys40) is slightly distorted as compared with that of the other iron atoms. A core of hydrophobic residues and a few water molecules contribute to the stability of the structure. The [4Fe-4S] clusters interact with the polypeptide chain through eight hydrogen bonds each, in addition to the covalent Fe-Scys bonds. The ferredoxin from Clostridium acidurici is the most typical clostridial ferredoxin crystallized so far and the biological implications of the newly determined structure are discussed.

Amino Acid Sequence↗
PubMed1994

Activation of specific cortical regions by apomorphine: an [15O]H2O PET study in humans.

The purpose of this study was to investigate the functional effects of apomorphine, a non-selective dopamine agonist, on regional neuronal activity using regional cerebral blood flow, measured using [15O]H2O and positron emission tomography (PET), as an index. Eight normal volunteers were scanned twice before and twice after receiving 10 micrograms/kg subcutaneous apomorphine. Apomorphine produced the expected side-effects and endocrine response. Analysis of the PET scans revealed that apomorphine increased regional cerebral blood flow (rCBF), presumably reflecting a change in neuronal activity, in the anterior cingulate, ventral motor cortex and the dorsolateral prefrontal cortex along with a decrease in rCBF in the retrosplenial cingulate region. These regions form a functional network of brain regions modulated by the dopaminergic system.

Adult↗