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At least 1,801 records · Page 100Linked to original sources
PubMed1994

Early recurrence of ST-segment elevation in patients with initial reperfusion during thrombolytic therapy: impact on in-hospital reinfarction and long-term vessel patency.

AIM: To investigate the frequency and prognostic impact of early recurrent ST-segment elevation after initial ST-segment resolution in patients with acute myocardial infarction who had been treated with intravenous thrombolysis. METHODS: Eighty-one patients with acute myocardial infarction underwent 24 h Holter monitoring of the infarct-related ST-segment elevation, at the initiation of thrombolytic therapy. Angiography was performed in 88% of the patients 9 +/- 4 days after infarction. RESULTS: Resolution of the ST-segment elevation during the first 4 h, suggestive of early reperfusion, occurred in 67 (83%) patients (group 1). Of these, 31 (46%) had subsequent re-elevations (group 1a), 26 during the first 4 h, and 20 later. Thirty-six (54%) patients had no recurrence of the ST-segment elevation (group 1b). During follow-up, patients in group 1a experienced more in-hospital reinfarctions (26 versus 6%, P = 0.04) and had a higher rate of occluded infarct-related vessels at angiography than patients in group 1b (40 versus 17%, P = 0.01). CONCLUSION: During the first 24 h after initiation of thrombolytic therapy, recurrences of ST-segment elevation are frequent in myocardial infarction patients with ECG signs of an initially reperfused infarct-related artery. Recurrence of ST-segment elevation indicates a higher risk of reinfarction during hospitalization and of long-term occlusion of the infarct artery.

Aged↗
PubMed1994

Word recognition with segmented-alternated CVC words: compact disc trials.

The Tonal and Speech Materials for Auditory Perceptual Assessment, Disc 1.0 audio compact disc contains a set of consonant, vowel-nucleus, consonant speech materials that have been segmented at the approximate phoneme boundaries so that the carrier phrase and consonant segments of a word can be presented to one ear and the carrier phrase and vowel segment of the word presented to the other ear. In this manner, consonant and vowel information are presented to different ears using a binaural fusion paradigm in which the temporal sequence of the word is maintained. The purpose of the compact disc trials was to document the recognition performance of 120 young adults with normal hearing under the following three conditions: (1) the consonant segments presented monaurally at 40, 50, and 60 dB HL; (2) the vowel segment of the words presented monaurally at 20, 30, and 40 dB HL; and (3) the binaural condition at 0 to 30 dB Hl in which the consonant segments were presented to one ear and the vowel segments were presented to the other ear. Recognition performance under the binaural fusion paradigm was identical to recognition performance on the same materials unaltered.

Adult↗
PubMed1994

[Significance of the persistence of ST segment elevation in anterior infarction].

OBJECTIVE: Persistent ST segmentary elevation in anterior myocardial infarction was classically attributed to ventricular aneurysm. This association is now considered controversial. We studied the association between this electrocardiographic finding and the left ventricular wall motion abnormalities and global function. DESIGN: Retrospective study. SETTING: Patients admitted to Hospital de Pulido Valente Coronary Care Unit in Lisbon with anterior myocardial infarction who were submitted to angiographic study. PATIENTS: 94 patients were included in the study. METHODS: The global ejection fraction, the regional wall motion abnormalities, the coronary artery disease extension, the patency and the proximal involvement of the left anterior descending artery were investigated. RESULTS: 56 of the 94 patients (60%) had persistent ST segment elevation and 38 (40%) had isoelectric ST segment. The ejection fraction was markedly depressed in the group with elevated ST segment (36.2 SD 17.6) in contrast with the group with isoelectric ST segment (49.3 SD 14.8) (p < 0.001). The group with persistent ST segment elevation had more advanced degrees of left ventricular asynergy (42/58-75%) than the group with isoelectric ST segment (12/38-32%) (p = 0.02). The other studied angiographic variables did not differ between the two groups. CONCLUSIONS: The group with persistent ST segment elevation was associated with advanced degrees of left ventricular asynergy and greater left ventricular function depression. The ventricular aneurysm was exclusive of the first group.

Adult↗
PubMed1994

Biochemical identification of transmembrane segments of the Ca(2+)-ATPase of sarcoplasmic reticulum.

The transmembrane segments of sarcoplasmic reticulum Ca(2+)-ATPase were determined by trypsinization of cytoplasmic side-out intact sarcoplasmic reticulum vesicles. The membrane portion of tryptic digest comprising the transmembrane fragments, joined by the intravesicular segments, was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after labeling with fluorescein 5-maleimide in the presence of sodium dodecyl sulfate. In this way, seven fluorescent bands of tryptic fragments below 11 kDa were observed which were derived from 4 pairs of membrane spanning segments and one hydrophobic sequence at the C-terminal end. Two peptides of 10.8 and 10.6 kDa had the identical N-terminal sequence beginning at Glu826, representing the transmembrane segments M7 and M8 and their connecting loop. A band at 8.1 kDa contained one peptide beginning at Tyr36 (M1/loop/M2). A 7.7-kDa peptide starting at Leu253 (M3/loop/M4) and a 7.3-kDa peptide beginning at Ala752 (M5/loop/M6) were also observed. A band at 6.7 kDa contained two peptides, one beginning at Ser48 (M1/loop/M2) and another beginning at Tyr763 (M5/loop/M6). In addition, a 4-kDa peptide beginning at Met925 was observed. The size of this peptide did not allow for a complete pair of transmembrane segments, but this peptide could have been derived from trypsinolysis between the last pair of membrane spanning segments. These data therefore provide biochemical evidence for at least 8 transmembrane segments and perhaps two more at the C-terminal end of the enzyme.

Amino Acid Sequence↗
PubMed1994

[Single segment internal fixator device in treatment of thoracolumbar vertebral fractures].

Treatment of vertebral fractures by the fixed-angle system of the internal fixator allows fusion over a short area and is the form of treatment now in general use. A bisegmental construction is usual, which means that reduction and relief of the injured vertebral body is achieved indirectly by means of two intact vertebrae immediately adjacent on either side. As a result, both segments stiffen up or are permanently damaged in their function. We report on the possibility of single-segment fixation. The principle is the fusion of the injured segment itself only, i.e., the vertebra actually injured and the vertebra adjacent to the injured segment. Unnecessary fixation of a second healthy segment can thus be avoided. The characteristics of the fracture type in which single-segment stabilization is possible are explained. In a small study of the technique, we used the new AO classification of vertebral fractures of the thoracolumbar spine. The operation technique differs in some details from that applied with a multisegmental internal fixator. For example, the pedicle screws occasionally need to be inserted extremely close to the end-plates if the remaining part of the vertebral body has been destroyed and therefore cannot provide stability. Contraindications are broken pedicles and complete burst fractures of the body. With due consideration for these limitations fractures in all three main groups of the AO classification can, in principle, be stabilized in a single segment. In the years 1988-1990, 14 patients were operated on in this way (12 acute injuries, 2 secondary operations).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1997

A prospective study of S-T segment depression in the electrocardiogram and mortality in the population.

A prospective study was carried out of all degrees of horizontal or descending depression of the S-T segment in the electrocardiogram (more than 1 mm or 0.1 mV, 0.5-0.9 mm or 0.05-0.05 mV and up to 0.5 mm or 0.05 mV) in a sample of 2414 subjects of both sexes, aged 35-54 years, (1326 females and 1088 males) in six Croatian regions on three occasions during a 13-year period: 1969, 1972 and 1982, according to the Minnesota code. S-T segment depression in the ECG was found during the first examination in 10.69% of females and 4.13% of males; during the second examination in 12.66% females and 6.24% males, and in the third examination in 19.06% females and 12.12% males. S-T segment depression of up to 0.5 mm was dominant and twice as frequent in females than in males, and the difference was significant. S-T segment in the ECG was also analyzed in a sample of 239 subjects (141 males and 98 females) who died during the period between the second and third examination, and for whom ECGs had been recorded in 1969 and 1972. In the group of females who died during the period between the first and second examination, 16.32% had all degrees of S-T segment depression, while in the group of surviving females this amounted to 10.6%. In the group of deceased males this finding was found in 4.24% of deceased and 4.13% of surviving males. In the group of females who died between the second and third examination, S-T segment depression was found in 18.36% of deceased and 12.66% of surviving females, and 10.62% in deceased males and 6.24% in surviving males (depression of 1 mm or deeper and 0.5-0.9 mm was found in 7.08% of deceased and 1.28% surviving males). The relative risk of mortality in middle-aged females with S-T segment depression of 0.5 mm or deeper, was 3.65 times higher than in females without such ECG changes, while the relative risk of mortality in males of the same age with the same finding was 5.85 times higher than in those without such ECG changes.

Adult↗
PubMed1997

Segmented three-dimensional echo-planar flow imaging of the cervical carotid arteries.

PURPOSE: To implement and assess the application of segmented three-dimensional echo-planar MR imaging time-of-flight flow sequences for studying the anatomy of the cervical carotid arteries at 1.5 T. METHODS: The 3-D echo-planar sequences were segmented along the in-plane phase-encoding direction. Echo train lengths (ETLs) of 3 and 5 and signal bandwidths of +/-25, +/-33, and +/-50 KHz were tested along with a conventional (ETL = 1) 3-D MR flow study in six healthy volunteers and in five patients with known arteriosclerotic disease involving the carotid bifurcation as confirmed by conventional angiography. The volunteer data were used to rank the techniques with respect to vessel dimension, vessel/background contrast, and quality by four trained neuroradiologists. For the patient studies, the percentage of stenoses was measured for all MR studies and compared against the conventional angiographic data using the criteria of the North American Symptomatic Carotid Endarterectomy Trial. RESULTS: Using Wilcoxon's test statistic and a significance level of .05, we found that the conventional MR flow examination was better than the segmented techniques and that the segmented techniques with ETL of 3 were superior to their counterparts with ETL of 5. For the ETL of 3 techniques, the high-bandwidth studies were inferior to their lower bandwidth counterparts; however, there was no significant difference between the performance of the medium- and low-bandwidth sequences. The patient data revealed that the segmented techniques consistently overestimated the severity of stenosis; however, in no instance did any of the segmented examinations erroneously indicate the presence of disease. CONCLUSIONS: The reduction in acquisition time and the zero false-positive rate we obtained suggest that segmented 3-D echo-planar MR flow techniques may be used as a screening/locating study for cervical carotid artery disease.

Adult↗
PubMed1998

Mechanical correlations derived from segmental histologic study of the equine superficial digital flexor tendon, from foal to adult.

OBJECTIVE: To assess histologic variations of the equine superficial digital flexor tendon (SDFT) according to site and to horse age and activity, and to correlate these data with reported segmental mechanical results. SAMPLE POPULATION: Superficial digital flexor tendons isolated from 42 horses 0.5 hour to 23 years old. PROCEDURE: 7 segments of each SDFT were delimited and submitted for conventional histologic examination. Each segment was examined and graded for fiber undulation, cellularity, number and size of interfascicular connective spaces (ICS), presence or absence of focal and diffuse chondroid metaplasia, and differentiation of the dorsal (DB) and palmar (PB) borders of the tendon. RESULTS: Fiber undulation and cellularity significantly decreased with age. The proximal and middle metacarpal segment fibers were significantly less undulated and their ICS were smaller than those of the other segments, especially in old horses. Focal chondroid metaplasia developed from 5 years onward, mainly in the sesamoidean segments. Diffuse chondroid metaplasia was characteristic of the digital region in horses > 6 years old. The DB of the metacarpodigital region tended to differentiate into fibrocartilage in association with age. The PB was generally differentiated as nonfascicular dense connective tissue. Activity induced a decrease in the number and size of the ICS. CONCLUSIONS: The lesser undulation of the proximal and middle metacarpal segments fibers can be correlated to their mechanical behavior (stress-strain curve) and relative weakness within the SDFT. Focal chondroid metaplasia and fibrocartilage on the DB are normal features, related to the compression stresses undergone by the sesamoidean region of the tendon.

Aging↗
PubMed1999

Collective Adaptation: The Exchange of Coding Segments.

Coding segments are those subsegments of the chromosome that contribute positively to the fitness evaluation of the chromosome. Clique detection is a NP-complete problem in which we can detect such coding segments. We extract coding segments from chromosomes, and we investigate the duplication of coding segments inside the chromosome and the collection of coding segments outside of the chromosome. We find that duplication of coding segments inside the chromosomes provides a back-up mechanism for the search heuristics. We further find local search in a collective memory of coding segments outside of the chromosome, collective adaptation, enables the search heuristic to represent partial solutions that are larger than realistic chromosomes lengths and to express the solution outside of the chromosome.

Journal Article↗
PubMed2001

Real-time optical coherence tomography of the anterior segment at 1310 nm.

BACKGROUND: Recent advances in high-speed scanning technology have enabled a new generation of optical coherence tomographic (OCT) systems to perform imaging at video rate. Here, a handheld OCT probe capable of imaging the anterior segment of the eye at high frame rates is demonstrated for the first time. OBJECTIVE: To demonstrate real-time OCT imaging of anterior segment structures. DESIGN: Survey of anterior segment structures in normal human subjects. SETTING: Laboratory. MAIN OUTCOME MEASURES: Achieving real-time imaging of the anterior segment, satisfactory image quality, and convenience of a handheld probe. RESULTS: Optical coherence tomographic imaging of the anterior segment of the eyes of human subjects was performed using 1310-nm wavelength light with an image rate of 8 frames per second. Imaging trials demonstrated clear resolution of corneal epithelium and stroma, sclerocorneal junction, sclera, iris pigment epithelium and stroma, and anterior lens capsule. The anterior chamber angle was clearly visualized. Limited imaging of the ciliary body was performed. Real-time imaging of pupillary constriction in response to light stimulus was also performed. CONCLUSION: High-speed OCT at 1310-nm wavelength is a potentially useful technique for noninvasive assessment of anterior segment structures. CLINICAL RELEVANCE: Our results suggest that real-time OCT has potential applications in glaucoma evaluation and refractive surgery.

Anterior Chamber↗
PubMed1997

Evidence from normal and degenerating photoreceptors that two outer segment integral membrane proteins have separate transport pathways.

Detachment of the neural retina from the retinal pigment epithelium induces photoreceptor degeneration. We studied the effects of this degeneration on the localization of two photoreceptor outer segment-specific integral membrane proteins, opsin and peripherin/rds, in rod photoreceptors. Results from laser scanning confocal microscopic and electron microscopic immunolocalization demonstrate that these two proteins, normally targeted to the newly-forming discs of the outer segments, accumulate in different sub-cellular compartments during photoreceptor degeneration: opsin immunolabeling increases throughout the photoreceptor cell's plasma membrane, while peripherin/rds immunolabeling occurs within cytoplasmic vesicles. The simplest hypothesis to explain our results is that these proteins are transported in different post-Golgi transport vesicles and separately inserted into the plasma membrane. More complex mechanisms involve having the two co-transported and then opsin finds its way into the plasma membrane but peripherin/rds does not, remaining behind in vesicles. Alternatively, both insert into the plasma membrane but peripherin/rds is recycled into cytoplasmic vesicles. We believe the data most strongly supports the first possibility. Although the transport pathways for these proteins have not been fully characterized, the presence of peripherin/rds-positive vesicles adjacent to the striated rootlet suggests a transport role for this cytoskeletal element. The accumulation of these proteins in photoreceptors with degenerated outer segments may also indicate that their rate of synthesis has exceeded the combined rates of their incorporation into newly forming outer segment disc membranes and their degradation. The accumulation may also provide a mechanism for rapid recovery of the outer segment following retinal reattachment and return of the photoreceptor cell to an environment favorable to outer segment regeneration.

Animals↗
PubMed1986

Increased phagocytosis of outer segments in the presence of serum by cultured normal, but not dystrophic, rat retinal pigment epithelium.

Cultured normal rat retinal pigment epithelium (PE) ingested six times more rod outer segments in the presence of 20% fetal bovine serum than in serum-free medium. PE cultured from Royal College of Surgeons (RCS) rats with hereditary retinal dystrophy, known to have a defect in vivo in the phagocytosis of shed outer segment tips, ingested amounts of outer segments comparable to normal PE in serum-free medium but did not show an increase in the presence of serum. In both strains of rat PE phagocytosis of latex spheres was similar in the absence of serum and was six-fold higher in the presence of serum, showing that the RCS phagocytic deficiency for outer segments in vitro is not due to a general defect in the phagocytic capacity of the cell. Increased phagocytosis of outer segments by normal PE was observed in the presence of the high molecular weight fraction of ultrafiltered serum but was not seen with serum that was heated at 93 degrees C or precipitated with 5% trichloroacetic acid. Bovine serum albumin had no effect on phagocytosis. These results are consistent with the idea that the phagocytosis of outer segments by cultured normal rat PE, but not by cultured RCS rat PE, is increased in the presence of a specific protein or other macromolecular component of fetal bovine serum.

Animals↗
PubMed1994

Photoreceptor outer segment development in Xenopus laevis: influence of the pigment epithelium.

Opsin gene expression, synthesis, and photoreceptor outer segment morphology were evaluated during retinal development in Xenopus laevis. Retinal rudiments were harvested during in vivo development from embryonic stages 31 through 46 or were allowed to develop in vitro after removal from stage 33/34 embryos for 1, 2, or 3 days either with or without an investing pigment epithelium. Opsin mRNA was detected at stage 33/34 and the transcript level increased until stage 40 and remained at this level through stage 46. Opsin was first detected at stage 37/38 and progressively increased through stage 46. Rudimentary photoreceptor outer segment membranes occasionally appeared as early as stage 33/34 and they gradually increased in length, forming well-defined stacks of collapsed membranous saccules (discs) during in vivo development. The maturation of eye rudiments in culture was followed to determine how closely in vivo and in vitro development compare and to examine the ability of photoreceptors to differentiate when maintained in the absence of an overlying pigment epithelium (PE) layer. With the PE present, opsin mRNA as well as opsin content steadily increased over the entire culture period. After 1 day of culture, short cilia with minimal amounts of outer segment membranous material were present. By Day 3, the degree of outer segment differentiation corresponded morphologically to approximately stage 43 of in vivo development. When cultured in the absence of an investing PE, the opsin mRNA level increased minimally during the 3 days in culture. Opsin content increased, yet the relative amount was approximately 50% less than that present in retinas developing in the presence of the PE. Membranous material was elaborated; however, the outer segments appeared to be highly disorganized and formed whorl-like structures rather than the normal stacked disc morphology. These results suggest that the PE may be involved in regulating opsin at the transcriptional and/or translational levels and also participates in the organization of rod outer segment membranes.

Animals↗
PubMed1998

The role of taurine in osmotic, mechanical, and chemical protection of the retinal rod outer segments.

The ability of the photoreceptor cell to resist osmotic stress was examined by incubating isolated frog retina in medium of varying osmolality. An electron microscopic analysis of the rod outer segment following a severe hypoosmotic insult revealed connections between adjacent disks and between disk rims and the plasma membrane, which presumably provide mechanical stability to the rod outer segment. One surprising result was the extent of the damage incurred by the electrical signaling pathway of the photoreceptor cells subjected to a 50 mOsm insult; only the distal P111 component of the ERG remained unaffected. Thus, the rod outer segment is particularly resistant to osmotic-induced injury, presumably because of the effective osmoregulatory actions of taurine. Incubation of retina with tauret, retinylidentaurine, uncovered rose-like hexagonal structures on the surface of the rod outer segment. These structures purportedly consist of connections between disk rims and the plasma membrane of the rod outer segments. Based on the influence of tauret, it is likely that the calcium dependence of these channels is selective for retinoids. These data are discussed relative to taurine's role in the process of rhodopsin regeneration and in the protection of the rod outer segments against osmotic, mechanical and light induced damage.

Animals↗
PubMed1983

Histo- and cytochemical demonstration of guanosine triphosphatase activity in the outer segments of rods in the rat retina by means of a newly developed method.

Guanosine triphosphatase (GTPase) activity was studied histo- and cytochemically in the rod outer segments of the rat retina by means of a newly developed method. Differences in the distribution pattern of the enzyme activity exist within the outer segment: the activity is more intense at the tip of the rod outer segments near the pigment epithelium than in their proximal portion. Ultracytochemically, the new procedure reveals the reaction product of GTPase activity partly (i) on the extradisk membrane side and (ii) on the disk membranes. This result is in contrast to the cytochemical localization of guanylate cyclase (GCLase), an enzyme also localized at the tip of the rod outer segments: GCLase activity is restricted to the intradisk membrane area of the rod outer segments. The functional role of GTPase activity in the outer segments of rods is discussed.

Animals↗
PubMed1982

Use of a density modification technique for isolation of the plasma membrane of rod outer segments.

The external surface of rod outer segments contains receptors for the Jack Bean lectin, concanavalin A. Using isolated intact bovine rod outer segments, we have modified the density of the outer segment plasma membranes by means of polystyrene beads carrying covalently linked concanavalin A. After hypotonic lysis the bulk of the disk membranes can be removed and a plasma membrane fraction is isolated. The plasma membrane preparation contains 1.5% of total outer segment rhodopsin and 2.7% of total outer segment protein. it shows very little contamination with inner segment plasma membrane. Contamination with disk membranes appears to be low as well. Fatty acid analysis reveals that the plasma membranes are more saturated than the highly unsaturated disk membranes. Gel electrophoresis shows the presence of at least six additional polypeptides besides besides rhodopsin.

Animals↗
PubMed1982

Sterol composition of bovine retinal rod outer segment membranes and whole retinas.

The sterol composition of bovine retinal rod outer segment membranes and whole retinas was studied by detailed chromatographic analyses. Cholesterol represented at least 98% of the total 3 beta-monohydroxy sterols of rod outer segment membranes, accounting for 1.68 +/- 0.15% of the dry weight. Whole retinas contained 1.76 +/- 0.29% cholesterol by dry weight, representing at least 99% of the total 3 beta-monohydroxy sterols. Trace amounts of a component having the chromatographic properties of 5 alpha-cholestan-3 beta-ol were found in rod outer segment membranes and whole retinas. Very small amounts of a component having the chromatographic properties of 5 alpha-cholest-7-en-3 beta-ol were found in whole retinas, but not in rod outer segment membranes. The molar ratio of cholesterol to rhodopsin in bovine rod outer segment membranes was approximately 4.7. Cholesterol accounted for only 5-7 mol% of total rod outer segment membrane lipids.

Animals↗
PubMed1986

Phosphatidate phosphatase activity in isolated rod outer segment from bovine retina.

Phosphatidate phosphohydrolase (EC 3.1.3.4) was detected in isolated bovine rod outer segments and its properties investigated. The enzyme activity was assayed using aqueously dispersed 1,2-diacyl-sn-[2-3H]glycerol 3-phosphate as substrate. The phosphatidic acid concentration was optimal at 1 mM and the estimated Km value was 6.7 X 10(-4) M. The activity was linear for 60 min with a protein concentration of 0.3 mg. A clear pH optimum was observed at 7.5. When the enzyme activity was measured using a substrate phosphatidic acid containing 15% lyso compound, the production of diacylglycerols was inhibited by about 70-75% at all concentrations studied. In rod outer segment preparations containing 0.2 mM Mg2+, further additions of the ion (0.2-2.5 mM) only produced a slight inhibition of the activity at 2.5 mM. F- (50 mM), Ca2+ (1 mM) and EDTA (50 mM) inhibited the dephosphorylation of the substrate by 80, 10 and 70%, respectively. The aqueously dispersed phosphatidic acid-dependent activity present in rod outer segments was stimulated by Triton X-100 and taurocholate. Similar values were observed in the enzyme activity of entire rod outer segments and in that of disks obtained from them, showing the enzyme to be associated with disk membrane. The [3H]diacylglycerol production from [3H]phosphatidic acid was analyzed in synaptosomal-mitochondrial and microsomal fractions and in a crude pigment epithelium preparation. The degree of dephosphorylation of phosphatidic acid in these subcellular fractions was as follows: microsomes greater than synaptosomal-mitochondrial fraction greater than rod outer segment greater than crude pigment epithelium. The present report is the first evidence of phosphatidic acid phosphohydrolase activity associated with rod outer segment membranes.

Animals↗

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