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Biomedical subjects

J Rabin

Publications and source records attributed to J Rabin.

At least 19 recordsLinked to original sources
PubMed2001

Efficacy of a proximal occlusion catheter with reversal of flow in the prevention of embolic events during carotid artery stenting: an experimental analysis.

OBJECTIVE: The role of percutaneous angioplasty and stenting of carotid bifurcation lesions has been limited by its potential for producing embolic debris. We evaluated the efficacy of a proximal occlusion catheter (POC) in the prevention of embolic events during carotid artery stenting. In addition, pressure measurements relevant to the clinical application of this device were obtained from 10 patients undergoing carotid endarterectomy. METHODS: The POC is a guiding catheter with an occlusion balloon attached on the outside of the catheter at its distal end. Occlusion of the common carotid artery (CCA) was achieved by inflating the balloon while access to carotid bifurcation lesions was obtained through the inner lumen. The POC was inserted in the CCA of 10 dogs via the femoral artery. The side port of the POC was connected to a sheath placed in the femoral vein, thereby creating an external arteriovenous shunt. Ten artificial radiopaque particles simulating embolic particles and contrast agent were introduced in the CCA and monitored fluoroscopically. As a control, the same procedure was performed with a standard guiding catheter without an occlusion balloon. In 10 patients undergoing carotid endarterectomy, the internal carotid artery (ICA) and external carotid artery stump pressures and the pressure in the internal jugular vein were measured. RESULTS: Without the external arteriovenous shunt, in all animals there was prograde flow in the distal CCA despite CCA occlusion. This flow was derived from the thyroid artery. However, once the arteriovenous shunt was activated, reversal of flow in the distal CCA was achieved in each animal, and all the artificial particles were recovered from the side port of the POC. In the control group, each particle embolized to the brain (100%, P <.01). In the patients, the mean stump pressures in the ICA and external carotid artery and the jugular vein pressure were 51.8 +/- 14.2, 62.2 +/- 15.1, and 6.5 +/- 3.5 mm Hg, respectively. In each case, the jugular vein pressure was the lowest among the three. CONCLUSIONS: Obtaining proximal CCA control by inflating the POC does not sufficiently prevent embolization. However, reversal of flow in the ICA can always be created with the external shunt, which effectively prevents embolization. Thus, POC may markedly lower procedural stroke rates during carotid artery stenting. The ability of POC to prevent embolization before crossing the lesion with a guidewire may be an important advantage over other distal protection devices.

Angioplasty, Balloon↗
PubMed2000

Does the endovascular repair of aortoiliac aneurysms pose a radiation safety hazard to vascular surgeons?

OBJECTIVES: Endovascular aortoiliac aneurysm (EAIA) repair uses substantial fluoroscopic guidance that requires considerable radiation exposure. Doses were determined for a team of three vascular surgeons performing 47 consecutive EAIA repairs over a 1-year period to determine whether this exposure constitutes a radiation hazard. METHODS: Twenty-nine surgeon-made aortounifemoral devices and 18 bifurcated devices were used. Three surgeons wore dosimeters (1) on the waist, under a lead apron; (2) on the waist, outside a lead apron; (3) on the collar; and (4) on the left ring finger. Dosimeters were also placed around the operating table and room to evaluate the patient, other personnel, and ambient doses. Exposures were compared with standards of the International Commission on Radiological Protection (ICRP). RESULTS: Total fluoroscopy time was 30.9 hours (1852 minutes; mean, 39.4 minutes per case). Yearly total effective body doses for all surgeons (under lead) were below the 20 mSv/y occupational exposure limit of the ICRP. Outside lead doses for two surgeons approximated recommended limits. Lead aprons attenuated 85% to 91% of the dose. Ring doses and calculated eye doses were within the ICRP exposure limits. Patient skin doses averaged 360 mSv per case (range, 120-860 mSv). The ambient (> 3 m from the source) operating room dose was 1.06 mSv/y. CONCLUSIONS: Although the total effective body doses under lead fell within established ICRP occupational exposure limits, they are not negligible. Because radiation exposure is cumulative and endovascular procedures are becoming more common, individuals performing these procedures must carefully monitor their exposure. Our results indicate that a team of surgeons can perform 386 hours of fluoroscopy per year or 587 EAIA repairs per year and remain within occupational exposure limits. Individuals who perform these procedures should actively monitor their effective doses and educate personnel in methods for reducing exposure.

Aortic Aneurysm↗
PubMed1997

The neural substrates of religious experience.

Religious experience is brain-based, like all human experience. Clues to the neural substrates of religious-numinous experience may be gleaned from temporolimbic epilepsy, near-death experiences, and hallucinogen ingestion. These brain disorders and conditions may produce depersonalization, derealization, ecstasy, a sense of timelessness and spacelessness, and other experiences that foster religious-numinous interpretation. Religious delusions are an important subtype of delusional experience in schizophrenia, and mood-congruent religious delusions are a feature of mania and depression. The authors suggest a limbic marker hypothesis for religious-mystical experience. The temporolimbic system tags certain encounters with external or internal stimuli as depersonalized, derealized, crucially important, harmonious, and/or joyous, prompting comprehension of these experiences within a religious framework.

Epilepsy↗
PubMed1996

Measuring resolution in the contrast domain: the small letter contrast test.

BACKGROUND: Recent evidence suggests that small letter contrast sensitivity (CS) is more sensitive than visual acuity (VA) to defocus, luminance, binocular enhancement, and visual differences among pilot trainees. It would be valuable to make this test available for general use. We developed a hard copy (letter chart) version called the Small Letter Contrast Test (SLCT) and evaluated its sensitivity and reliability in comparison to standard vision tests. METHODS: The SLCT has 14 lines of letters with 10 letters per line. The letters are of constant size (20/25 or 4/5 at 4 m), but vary in contrast by line in 0.1 log steps (0.01 log units per letter). Normal room illumination is used. The SLCT was evaluated in 16 subjects under various conditions (spherical and astigmatic blur, low luminance, 2 eyes vs. 1 eye) to determine test sensitivity and reliability, and in patients with clinical conditions. Scores were compared to those obtained with standard tests of VA (Bailey-Lovie) and CS (Pelli-Robson). RESULTS: SLCT scores were similar to previous measures, and retest reliability was one line. The SLCT was more sensitive than VA to spherical and astigmatic blur, low luminance, and vision with two eyes vs. one eye. Greater sensitivity of the SLCT endured despite correction for variability. The SLCT was more sensitive than standard tests to visual loss from early cataract, keratoconus, corneal infiltrates, edema, and amblyopia. CONCLUSIONS: The SLCT is a sensitive, adjunctive test, which complements existing measures of VA. It can reveal subtle visual deficits that may be undetected by standard clinical techniques. The SLCT should prove useful for monitoring vision in refractive surgery, corneal and macular edema, optic neuritis, and for selection and evaluation of candidates for occupations requiring unique visual abilities like aviation.

Contrast Sensitivity↗
PubMed1996

A comparison between phosphors for aviator's night vision imaging system.

BACKGROUND: The visual display on night vision goggles (NVG's) is green and isochromatic (P22 phosphor). Future systems are expected to use a P43 phosphor which has a narrower visible spectrum and is yellowish green, while the P22 is deeper green. In transitioning to the P43, some NVG's may have P22 and P43 phosphors paired in the same NVG. The purpose of this study was to evaluate the suitability of the P43 phosphor and the effect of mixing phosphors in the same NVG. METHODS: We tested three systems: one with P22 phosphors in both tubes (P22), one with P43 in both tubes (P43), and one with P22 in the right and P43 in the left tube (mixed). Visual acuity (VA), contrast sensitivity (CS), flicker sensitivity, and dynamic CS were measured in six subjects with measures repeated across the three systems (P22, P43 and mixed). RESULTS: There was no difference between systems in VA or CS across a range of simulated night sky conditions. There also was no difference between systems in sensitivity to flicker. Performance on dynamic CS was slightly better with the P43 display, which may relate to the faster decay time of this phosphor. CONCLUSIONS: These results provide no contraindication for using the P43 phosphor in NVG's (paired or unpaired), but it would be prudent to minimize mixing of phosphors in the same NVG. Additional factors that may affect performance with different color displays are discussed.

Adult↗
PubMed1996

Differences in apparent contrast in yellow and white light.

The purpose of this study was to investigate suprathreshold contrast perception in white and yellow light. The contrast of black-on-white letters was adjusted to match the perceived contrast of yellow-on-yellow letters presented simultaneously on a video display. At lower contrasts (7-15%), the apparent contrast of yellow letters was slightly enhanced compared to black-on-white letters (mean enhancement = 23%), but this effect diminished with increasing contrast. The slight enhancement in yellow light was independent of letter size, and could not be explained by luminance differences between yellow and white displays. This effect may relate to the subjective improvement often reported when wearing yellow (blue-blocking) lenses.

Adult↗
PubMed1996

Correction of subtle refractive error in aviators.

Optimal visual acuity is a requirement for piloting aircraft in military and civilian settings. While acuity can be corrected with glasses, spectacle wear can limit or even prohibit use of certain devices such as night vision goggles, helmet mounted displays, and/or chemical protective masks. Although current Army policy is directed toward selection of pilots who do not require spectacle correction for acceptable vision, refractive error can become manifest over time, making optical correction necessary. In such cases, contact lenses have been used quite successfully. Another approach is to neglect small amounts of refractive error, provided that vision is at least 20/20 without correction. This report describes visual findings in an aviator who was fitted with a contact lens to correct moderate astigmatism in one eye, while the other eye, with lesser refractive error, was left uncorrected. Advanced methods of testing visual resolution, including high and low contrast visual acuity and small letter contrast sensitivity, were used to compare vision achieved with full spectacle correction to that attained with the habitual, contact lens correction. Although the patient was pleased with his habitual correction, vision was significantly better with full spectacle correction, particularly on the small letter contrast test. Implications of these findings are considered.

Adult↗
PubMed1996

Cone-specific measures of human color vision.

PURPOSE: To describe a new test of color vision (cone-specific contrast sensitivity) and to evaluate its sensitivity in comparison to standard clinical tests. METHODS: Cone-specific colored letter charts were generated by computer and displayed on a color monitor. Each chart consists of colored letters that are most visible at the top but that gradually fade into a gray background. Cone contrast varies systematically on each chart so that letters are visible to only one cone type (L, M, or S cone). Cone-specific letter contrast sensitivity was measured in 30 color normals and 13 subjects with hereditary color deficiency. Values were compared to standard measures of color vision. RESULTS: In color normals, mean log contrast sensitivity was approximately the same on L-cone (1.84 +/- 0.08 log contrast sensitivity) and M-cone (1.87 +/- 0.08) tests but was reduced on the S-cone test (0.89 +/- 0.15) because of the fewer number of S-cones in the human retina. Subjects with red color deficiency showed significantly reduced contrast sensitivity on the L-cone test but normal performance on M- and S-cone tests. Subjects with green color deficiency showed decreased contrast sensitivity limited to the M-cone test. When standardized relative to variability, cone contrast sensitivity identified color deficiency unequivocally in all subjects, whereas FM 100 hue error scores detected 9 of 13 subjects with color deficiency. CONCLUSIONS: Cone-specific contrast sensitivity provides a quantitative measure of normal color vision and indicates both type and severity of color deficiency. It is useful for diagnosing hereditary color deficiency and for monitoring early color vision loss in ocular and systemic disease.

Adult↗
PubMed1995

Time-limited visual resolution in pilot trainees.

Superior vision is needed for piloting aircraft in military and civilian environments. Although visual evaluations of potential pilots typically are conducted with no limit on viewing time, aviation and related occupations require superior vision under time-limited viewing conditions, and assessment of this capability is needed. The purpose of this study was to evaluate time-limited visual resolution in pilot trainees. A forced-choice letter recognition task was used to measure visual acuity (VA) and small letter contrast sensitivity (SLCS) in 37 trainees who had satisfied all vision requirements for pilot training. VA and SLCS were highly correlated (r = 0.76), indicating that the two tests measure similar aspects of visual resolution. However, although VA scores were distributed across 0.16 log units (two lines of letters on a VA chart). SLCS scores varied across 0.35 log units, which is nearly four lines on the SLCS chart. The variation in SLCS performance could be explained, in part, by subtle refractive error in pilot trainees. The results exemplify differences in performance among visually qualified trainees, and underscore the need for proper refractive correction. SLCS is a useful screening test for identifying subtle changes in vision that herald the need for optical or medical intervention.

Aircraft↗
PubMed1995

Small letter contrast sensitivity: an alternative measure of visual resolution for aviation candidates.

Exceptional vision is needed to maintain high levels of aviation performance. Current standards for helicopter pilot training include superior visual acuity with minimal refractive error. Despite these demanding criteria, it is likely that visual ability varies among those who meet the standards for pilot training. A more complete knowledge of visual capabilities in these individuals will allow us to better correlate vision with performance and to develop more incisive criteria for selection. The purpose of this study was to investigate an alternative test of visual resolution for aviation candidates using small letter contrast sensitivity (SLCS). Computer-generated letter charts were used to measure visual acuity (VA) and SLCS in 16 candidates who had satisfied military vision standards for pilot training. The acuity and contrast charts varied, by line, in equal log steps such that the letter recognition task was comparable for the two types of measurement. VA and SLCS were highly correlated in these subjects, indicating that the two tests measure similar aspects of visual resolution. Scores were distributed across two lines on the acuity chart, but across four lines on the contrast chart, suggesting that SLCS offers a more discriminating test of resolution. This assumption was confirmed in that SLCS was more highly correlated with small amounts of refractive error in the candidates tested. SLCS offers a sensitive, adjunctive measure of visual resolution which may be useful for identifying the unique visual abilities required for aviation.

Analysis of Variance↗
PubMed1995

Two eyes are better than one: binocular enhancement in the contrast domain.

The purpose of this study was to compare the improvement in visual acuity (VA) with the improvement in contrast sensitivity (CS) with two eyes as compared with one. Computer generated letter charts were used to measure VA and small letter CS (20/25 Snellen equivalent) in 13 emmetropic subjects. Letter size (for VA) and contrast (for CS) were varied in equal log steps making the task comparable for the two types of measurement. VA improved by an average of 10% (2-3 letters), while CS improved by an average of 40% (1 1/2 lines) when tested with two eyes as compared with one. Greater sensitivity in the contrast domain prevailed even when expressed relative to variability. Using this approach, binocular enhancement was identified in 8/13 subjects with CS, but in only 4/13 subjects with VA. Binocular enhancement of letter recognition occurs in both size and contrast domains. However, the effect is 4x greater when small letters are varied in contrast rather than size. Potential applications are considered.

Adult↗
PubMed1994

Transgenic mouse brain histopathology resembles early Alzheimer's disease.

Transgenic mice expressing the 751-amino acid form of the human amyloid precursor protein develop extracellular beta-amyloid protein (A beta)-immunoreactive deposits that increase in frequency with age. Here we show that the appearance and histological profile of deposits in the transgenic mice closely resemble those of preamyloid deposits in the brains of young adults with Down's syndrome, who presumably have the pathology of early-stage Alzheimer's disease. Specific monoclonal antibodies reveal that material in the deposits has the free carboxyl terminus of A beta 1-42, and that the deposits contain material which, by immunohistochemical analysis, apparently originates from the human beta-amyloid precursor protein (beta PP) transgene. In rare cases, the transgenic mouse brains contain several different histopathological characteristics of Alzheimer lesions. These features include dense A beta immunoreactivity which co-localizes with gliosis and with Alz50-immunoreactive structures resembling swollen boutons of dystrophic neurites. These observations demonstrate that the murine brain is capable of reproducing several typical features of Alzheimer histopathology.

Alzheimer Disease↗
PubMed1994

Visual evoked potentials in three-dimensional color space: correlates of spatio-chromatic processing.

Visual evoked potentials (VEPs) were measured for sinusoidal gratings with spatio-chromatic modulation defined in a three-dimensional color space. The spatio-chromatic modulation of the gratings can be decomposed into contributions from an achromatic luminance varying component, an isoluminant component which modulates only the activities of L cones and M cones, and an isoluminant component corresponding to modulation of only S-cone activity. The emphasis of this report is the nature of VEPs resulting from isoluminant spatio-chromatic modulation. The VEP response was characterized along a number of spatial, temporal, and chromatic stimulus dimensions: contrast, spatial frequency, chromaticity in the isoluminant plane, chrominance/luminance ratio, orientation, and temporal frequency. Isoluminant VEPs resulting from stimuli modulating L and M cones are compared with those from S-cone modulation. When appropriate spatiotemporal conditions are employed, both types produce robust VEPs; however, the S-pathway VEPs show considerably longer latencies than do those from LM-pathway activation. The VEP results are compared to psychophysical and single unit electrophysiological observations. VEP latencies exhibit the lowpass character of psychophysical chromatic contrast sensitivity functions but VEP amplitudes show bandpass tuning along both the S and LM axes. An oblique effect, i.e. shorter latencies for horizontal and vertical gratings than for diagonal, is observed in the isoluminant VEP. S-pathway VEPs are used to demonstrate an electophysiological correlate of transient tritanopia. Normative amplitude and latency data for VEPs from selectivity stimulated chromatic mechanisms provide a baseline for clinical electrodiagnostic applications.

Adaptation, Ocular↗
PubMed1994

Association of an estrogen receptor variant with increased height in women.

There is an association between a B region allele (here called the B' allele) of the estrogen receptor (ER) and a history of spontaneous abortion in women with ER positive breast cancer, but no such association for women with ER negative tumors or women without breast cancer. In this study we compared the heights of women carrying the B and B' alleles. The B' allele was identified by polymerase chain reaction to amplify genomic DNA around the polymorphic region of the ER gene, followed by allele specific oligonucleotide hybridization. This analysis used DNA obtained from blood lymphocytes. Women carrying the B' allele were significantly taller than those carrying the wild type allele (B allele). Multiple linear regression also demonstrated that this association remained (p = 0.017), controlling for the effects of age and race. Since the B' ER allele results from a silent mutation, a second mutation, segregating with it, no doubt plays a role in producing the high incidence of spontaneous abortion we reported previously and the height difference we report here. This second mutation might lie within the estrogen receptor itself or within one of the genes nearby.

Adolescent↗
PubMed1994

Luminance effects on visual acuity and small letter contrast sensitivity.

The purpose of this study was to evaluate the effects of luminance on visual acuity (VA) and small letter contrast sensitivity (SLCS). Computer-generated letter charts were used to measure VA and SLCS [6/7.5 (20/25) Snellen equivalent] as a function of stimulus luminance. Letter size (VA) and contrast (SLCS) were varied in equal logarithmic steps, making the task and scoring procedure comparable for the two types of measurement. Both VA and SLCS decreased with decreasing luminance, but the effect was far greater in the contrast domain. Reducing luminance from 116 cd/m2 to 0.23 cd/m2 produced a 3 x reduction in VA, but a 17 x reduction in SLCS. The greater sensitivity of SLCS to luminance endured even after correction for greater measurement variability. SLCS is a sensitive approach for detecting resolution loss undisclosed by standard measures of VA. It may be useful for monitoring visual loss from light attenuation in early cataracts, and for detecting subtle resolution loss from neural or pathologic factors in ocular and neuro-ophthalmologic disease.

Adult↗
PubMed1994

Switching from forward-looking infrared to night vision goggles: transitory effects on visual resolution.

Helmet-mounted displays under development for rotary- and fixed-wing aircraft will allow the user to switch electronically between forward-looking infrared (FLIR) and night vision goggle (NVG) sensors. These sensor transitions potentially involve large changes in display luminance which could transiently impair visual resolution and performance. The purpose of this study was to identify the display luminances which produce a transient reduction in vision when switching from a higher luminance (i.e., FLIR) to a lower luminance (i.e., NVG) display. A letter recognition task was used to assess the effect of luminance adaptation on visual resolution in five subjects. A significant reduction in letter recognition was observed in the first second after switching from simulated FLIR to simulated NVG's when the FLIR luminance was > or = 10 fL. By varying letter size, contrast, and exposure time, the magnitude and duration of visual loss after switching from a bright (49.2 fL) FLIR display were determined. The visual loss lasted up to 4 s, and included a 2x reduction in visual acuity, and a 3x reduction in contrast sensitivity. Large differences in sensor display luminance should be avoided to maintain high levels of visual performance and aviation safety. Design features or training may be necessary to achieve a proper balance between FLIR and NVG luminances which optimize performance and safety without sacrificing the quality of the sensor image.

Adult↗