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Biomedical subjects

S Chavez

Publications and source records attributed to S Chavez.

10 recordsLinked to original sources
PubMed2000

A fast implementation of the minimum spanning tree method for phase unwrapping.

A new implementation of the minimum spanning tree (MST) phase unwrapping method is presented. The time complexity of the MST method is reduced from O(n2) to O(n log2 n), where n is the number of pixels in the phase map. Typical 256 x 256 phase maps from magnetic resonance imaging can be unwrapped in seconds, compared with tens of minutes with the O(n2) implementation. This makes the pixel-level MST method time efficient and practically attractive. Index Terms-Image processing, magnetic resonance imaging, medical imaging, phase unwrapping.

Humans↗
PubMed2000

Information systems disaster planning in the patient care environment.

This article focuses on preparedness planning for the nurse manager in the event of a network failure of a hospital clinical information system. The evolution of health care information systems is discussed. A 4-step preparation model is discussed to aid the nurse manager in preparing for network failure.

Disaster Planning↗
PubMed1998

Laser in situ keratomileusis for simple myopic, mixed, and simple hyperopic astigmatism.

PURPOSE: To summarize initial results of astigmatic laser in situ keratomileusis (LASIK) for 41 eyes of 26 patients using the EC-5000 Nidek system and assess its safety, efficacy and predictability. METHODS: The EC-5000 Nidek excimer laser was used to correct simple myopic, mixed, and simple hyperopic astigmatism with manifest cylinder from 2.00 to 6.50 D. Ablation zone diameters were 6.5 mm (steep meridian ablation) to 7.5 mm (flat meridian ablation) with a repetition rate of 40-41 Hz. In eyes with simple myopic and mixed astigmatism, ablation was performed in both meridians; in eyes with simple hyperopic astigmatism, ablation was performed in the flat meridian alone. Follow-up was 3 months in all eyes. RESULTS: Uncorrected visual acuity was 20/40 or better in 85% of the eyes. Uncorrected visual acuity was equal to the preoperative spectacle-corrected visual acuity in 63% of the eyes. Intended cylinder correction was within 1.00 D in 95% of eyes. No eyes lost lines of spectacle-corrected visual acuity. CONCLUSION: LASIK using the EC-5000 excimer laser appears to effective in the treatment of simple myopic, mixed, and simple hyperopic astigmatism, with favorable results as compared to those previously described for astigmatic keratotomy.

Astigmatism↗
PubMed1997

Interview with a perioperative burn nurse.

This is an interview with a staff nurse who is presently working in the operating room (OR) with burn patients. Special knowledge and techniques specific to the OR are discussed. Personal thought on possible research and the future role of perioperative nurses in caring for the burn patient are also addressed.

Burns↗
PubMed1996

Interaction of steroid hormone receptors with transcription factors involves chromatin remodelling.

The mechanism by which steroid hormones modulate promoter utilization is not clear. Evidence from transfection studies and cell-free assays points to an interaction of the hormone receptors with general transcription factors, as well as with sequence-specific transcription factors. Moreover co-activators or transcription intermediary factors, have been identified which could mediate some of the transcriptional effects of the hormone-receptor complex. However, in addition to this interaction of receptors with proteins directly involved in transcription, a participation of chromatin structure in gene regulation by steroid hormones is becoming increasingly evident. In the case of the MMTV promoter, the nucleosomal organization seems to be responsible for transcriptional repression prior to hormonal stimulation. This effect is due to occlusion by a nucleosome positioned on the MMTV promoter sequences in such a way that essential transcription factors cannot access their recognition sites. Following hormone induction, a remodelling of the nucleosome structure takes place which enables a whole complement of sequence specific transcription factors to assemble on the promoter. Since a complete occupancy of binding sites does not take place when the promoter is present as naked DNA, the nucleosomal organization appears to be required for the proper synergism between transcription factors following hormonal induction. According to this model, the positioning of a nucleosome sets the stage for constitutive repression and hormone induction of the MMTV promoter.

Amino Acid Sequence↗
PubMed1996

Analysis of astigmatic keratotomy with a 5.0-mm optical clear zone.

PURPOSE: To investigate the surgically induced refractive change after astigmatic keratotomy with a 5.0-mm optical clear zone in patients with severe naturally occurring astigmatism. METHODS: We analyzed surgically induced refractive change in 40 consecutive eyes undergoing astigmatic keratotomy with a 5.0-mm optical clear zone. The surgically induced refractive change was calculated according to the method of Holladay, Cravy, and Koch with some modifications. Eyes were divided into two groups: Group I included eyes with mixed astigmatism and a maximum preoperative spherical equivalent of +1.25 diopters that underwent arcuate keratotomy, and Group II included eyes with compound myopic or simple myopic astigmatism (maximum preoperative spherical equivalent of -3.00 diopters) or mixed astigmatism with low minus spherical equivalent that underwent four-incision radial keratotomy and arcuate keratotomy. RESULTS: After refractive surgery, all eyes experienced a reduction of astigmatism when examined three months or more after surgery. Only one eye from each group was overcorrected. The magnitude of refractive astigmatism of surgically induced refractive change was 3.25 +/- 0.90 diopters for eyes in Group I and 3.25 +/- 0.80 diopters for eyes in Group II. There was minimal axis deviation. Eyes in Group I had more flattening with the wound than steepening against the wound, with a coupling ratio of -0.86 +/- 0.36, whereas in Group II, there was flattening both with the wound and against the wound. The net effect of surgery (sum of the primary and secondary effects) was more flattening than steepening in Group I eyes, and flattening of the circumference of the eye in Group II. A decrease of one line of best-corrected visual acuity was observed in one (6.6%) of 15 eyes in Group I and in two (8%) of 25 eyes in Group II. CONCLUSIONS: A 5.0-mm optical clear zone arcuate keratotomy is an effective method for correcting moderate to severe naturally occurring astigmatism. Further investigation of this optical clear zone size on glare and contrast sensitivity testing is necessary and is underway.

Adult↗
PubMed1994

Light-regulated promoters from Synechocystis PCC6803 share a consensus motif involved in photoregulation.

A library of Synechocystis PCC6803 (S.6803) DNA cloned in front of the promoterless cat reporter gene of the plasmid pFF11 was used to transform S.6803 to high light-dependent resistance to chloramphenicol. In five clones harbouring a stably replicating pFF11-derived plasmid, this phenotype occurred independently of the photosystem II electron transport and resulted from the correlated increase of CAT activity level and cat mRNA accumulation. The five promoter inserts contained no Escherichia coli sigma 70 promoter element, in agreement with their lack of activity in this organism, but shared two conserved motifs. Two secondary mutations, which restored light-regulated promoter activity to an inactive mutant of the smallest insert, mapped within one of the common motifs, emphasizing the probable involvement of this element in photoregulation.

Base Sequence↗
PubMed1994

Influences of renal nerves and pregnancy on renin secretion in sheep.

To investigate the role of the renal nerves in the control of renin secretion during pregnancy, we prepared sheep with one denervated kidney, bilateral renal vein catheters, and an inflatable aortic occluder. The renin secretory responses to step reductions of renal perfusion pressure (RPP) of the innervated and denervated kidneys were compared in eight nonpregnant and nine pregnant (115-130 days gestation) sheep in a normal conscious state. Nonpregnant sheep had average basal levels of mean arterial pressure (MAP) of 91 +/- 3 mmHg, plasma renin activities (PRA) of 2.3 +/- 0.4 ng ANG I.ml-1.3 h-1, and plasma angiotensin (ANG) concentrations of 8.4 +/- 1.1 pg/ml. Pregnant sheep had reduced levels (P < 0.01) of MAP (76 +/- 3 mmHg) but elevated levels of PRA (3.8 +/- 0.4 ng ANG I.ml-1.h 3-1; P < 0.5) and ANG II (12.0 +/- 1.6 pg/ml; P = 0.08). Four successively reduced levels of RPP were observed for 15 min each in both groups of sheep. In both groups, RPP was reduced to a final level of 51 +/- 2 mmHg. The renal venous-arterial difference of PRA (v-aPRA) from the innervated kidneys was increased as RPP was reduced. However, there was little response of v-aPRA to RPP in denervated kidneys. In nonpregnant sheep, the relationship between RPP and renin secretion rate was characterized by an initially slow phase, over which small reductions of RPP resulted in small increases in renin secretion. As RPP fell, this relationship became progressively steeper in nonpregnant ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMedDate not supplied

Hyperopic shift and myopic regression in a patient 7 years after bilateral refractive keratotomy.

PURPOSE/METHODS: To report a patient who developed hyperopic progression in one eye and myopic regression in the other eye following bilateral, non-simultaneous refractive keratotomy. RESULTS: Uncorrected visual acuity improved to 20/25 and 20/25-2 in the right and left eyes, respectively, 3 months following refractive keratotomy (one procedure in the right eye, two procedures in the left eye). The visual acuity was not stable over time and almost 8 years after surgery, uncorrected distance visual acuity was 20/40- and 20/200. The spherical equivalent refraction of the right eye progressed from -0.50 diopter (D) 3 months after surgery to +1.25 D several years later. The left eye regressed from a spherical equivalent refraction of -0.75 D 3 months after the second surgery to -2.50 D more than 7 years postoperatively. Slit-lamp microscopy disclosed deeper, opaque incisions in the hyperopic eye, and shallower and more transparent incisions in the myopic eye. CONCLUSIONS: The shift toward hyperopia and myopia in an individual suggest that instability of the radial keratotomy wound may be related to local wound healing events that are, in part, related to incision depth.

Adult↗