A comparison of CRT and digital stimulus delivery methods in the multifocal ERG

The purpose of this paper is to compare and evaluate the multifocal ERG response from raster based CRT and Digital Projection (LCD) stimulus delivery systems. A custom built p.c. based multifocal system was used to generate a 61 hexagonal element stimulus array. The stimulus was presented on a high luminance CRT display and on a back projected screen using a Digital polysilicon projection system. A fast response photodiode was used to analyse the stimulus pulse characteristics of both systems. A number of recordings were performed to assess the effect of stimulus delivery on a standard m-sequence response, inserted full-field filler response and on separation of onset and offset components. The pulse width for a CRT system is dependant on the type of phosphor and is typically 2 msec whereas the Digital Projection system produces a 13.3 msec pulse equivalent to the frame rate for the system. Slowing down the m-sequence by a factor of eight results in a pulse width of 106 msec which should enable the recovery of true offset responses. The CRT stimulus consists of a series of eight pulses of 2 msec duration each separated by 11.3 msec. First order responses are larger from the CRT system and second order responses larger from the Digital system. In conclusion, there are fundamental differences in the two delivery systems. The CRT system may have more potential in examining non-linear aspects of the multifocal response. Although both systems may be able to record offset responses, the Digital system will generate true offset responses whereas the CRT system may not allow true separation of these components.

The impact of fixation on the multifocal electroretinogram

There are a number of variables which can influence the quality of multifocal ERG waveforms. In common with visual field measurements, fixation quality may be an important parameter on the integrity of the acquired data. A low cost, fixation-monitoring device was used to assess fixation quality on a group of normal volunteers. Data was successfully acquired while five subjects viewed a fixation target for a period of time equal to that of a single multifocal recording segment. The target was presented on a stationary grey background and as the central fixation mark on a 61-element multifocal flicker stimulus. The results show no significant difference with or without the flickering pattern. The percentage of samples falling within 1.2 degrees of the point of fixation was 51%. This suggests that fixation quality is adequate for scaled stimuli where the central element subtends 2.4 degrees. High resolution stimuli of less than 2.4 degrees may be more susceptible to fixation fluctuations during the recording process.

Technical aspects of multifocal ERG recording

There are a wide range of variables which can influence the quality of the multifocal response. It is possible to place these variables into one of four categories. First, the method of stimulus delivery will determine the field of view, interference levels and the duration of on-state stimulation. Second, data acquisition variables such as electrode type and placement, amplifier specifications and filter bandwidth settings will have a direct impact on waveform shape and on the topographic distribution of signal amplitudes. Third, patient variables such as fixation, pupil dilation and refractive error will also contribute to the multifocal response. Fourth, there are many measurements that can be taken from multifocal recordings. In addition to standard amplitude and implicit time measures (the implicit time measure in the multifocal response is becoming increasingly important particularly in early stages of disease processes), the scalar product measure provides information on waveform shape. The conventional impulse and higher order responses will be different for different modes of stimulation such as Cathode Ray Tube (CRT) and Liquid Crystal Display (LCD) systems and latency shifts will be introduced if not corrected in software. Procedures which could lead to misleading interpretation include artefact rejection, averaging with neighbours and summing of responses. These procedures should be handled with caution.

Spatial localization in esotropia: does extraretinal eye position information change?

PURPOSE

To investigate the accuracy of spatial localization in children with a specific type of convergent strabismus, fully accommodative esotropia.

METHODS

Two groups of children, with right and left fully accommodative esotropia, respectively, pointed at targets located centrally and eccentrically on a computer touchscreen without being able to see their hands. The size and the direction of the horizontal pointing responses were recorded under two conditions: when their eyes were aligned (wearing spectacles) and when they were squinting (not wearing spectacles). A group of children without strabismus but with hypermetropia were assessed as controls.

RESULTS

For both fully accommodative groups, the pointing responses to the central target shifted in the direction of the nonsquinting eye when deviations were manifest. No difference was found for the eccentric targets. No difference was found for the hypermetropia group with any target.

CONCLUSIONS

These results are consistent with an alteration in the extraretinal eye position information (efference copy, extraocular muscle proprioception, or both) that is used in spatial localization.

Use of complementary medicine by adult patients participating in cancer clinical trials

PURPOSE/OBJECTIVES

To document the prevalence, demographic correlates, patterns of use, and beliefs about complementary and alternative medicine (CAM) therapies of adult patients enrolled in National Cancer Institute (NCI) clinical trials.

DESIGN

Prospective, cross-sectional, descriptive survey.

SETTING

W.G. Magnuson Clinical Center of the National Institutes of Health in Bethesda, MD.

SAMPLE

Convenience sample of 100 English-speaking, adult patients with cancer admitted to intramural clinical trials.

METHODS

A standardized, 99-item questionnaire assessing use of CAM therapies pre- and postcancer diagnosis was administered by face-to-face interview.

MAIN RESEARCH VARIABLES

Use of CAM therapies, beliefs, communication with physician.

FINDINGS

63% used at least one CAM therapy, with an average use of two therapies per patient. Men were significantly less likely to use a therapy than women; women were more likely to use numerous therapies. Cancer diagnosis seems to have had no influence overall on the frequency of use of CAM therapies. The major reasons stated for CAM use were for treatment-related medical conditions as well as depression, anxiety, and insomnia. The most frequently reported therapies were spiritual, relaxation, imagery, exercise, lifestyle diet (e.g., macrobiotic, vegetarian), and nutritional supplementation. Patients unanimously believed that these complementary therapies helped to improve their quality of life through more effective coping with stress, decreasing the discomforts of treatment and illness, and giving them a sense of control.

CONCLUSIONS

Patients with cancer use various complementary therapies to cope with their disease and the rigors of clinical trials. Women and those with higher educational backgrounds were more frequent users.

IMPLICATIONS FOR NURSING PRACTICE

Nurses who provide care to subjects of biomedical research have an opportunity and responsibility regarding their patients' use of CAM therapies. Nurses may use in-house resources to help evaluate subjects' use of a CAM modality or to provide quality-of-life therapies such as relaxation, imagery, or healing touch. Discussing these health practices in a nonjudgmental manner adds to the assessment of patients' coping skills and ability to make decisions about their health care.

Ozone exposure: a case report and discussion

A 45-year-old man working with ozone presents with evidence of sinusitis, mucus membrane irritation, sleep disturbance and shortness of breath. Naturally occurring or manmade, ozone may damage pulmonary alveolar type I cells at significant exposure levels. EPA and OSHA regulate exposure concentrations. Studies show dose responses with exposures. Supporting epidemiological studies are reviewed briefly. Limiting potential for excess exposure is key to prevention. Recognition of ozone as a potential exposure in the Oklahoma workplace is key to symptom management.

Three-dimensional electromagnetic model of the human eye: advances towards the optimisation of electroretinographic signal detection

Classical electromagnetic theory is used to examine the topographical variation in electrical potentials over the corneal surface resulting from specific retinal stimuli. Results from a three-dimensional mathematical model show that over 97% of calculated electromagnetic field potentials lie within 3% of previous analytical model data for an axially symmetric case. Maps of corneal potentials are produced that are shown to be characteristic of specific retinal stimuli and location. The maximum variation in corneal potential for a full field global stimulus is found to be approximately 1%. This is considered encouraging, as current electrophysiology techniques measure ocular potentials from a single corneal or scleral site, the position of which is often difficult to localise and reproduce. The model is used to simulate both central and peripheral stimuli and scotoma conditions. A 20 degrees central scotoma simulation shows an overall reduction in central corneal potential of only 3%, whereas peripheral stimuli are found to cause up to 10% variations in this potential. There is therefore a possibility that a single recording site for multifocal retinal stimulation is not ideal. These data may be used to suggest more appropriate electrode recording positions for maximum signal recovery, not least in optimising signal detection for multi-focal electroretinography stimulation.

Outbreak of sterile peritonitis among continuous cycling peritoneal dialysis patients

BACKGROUND

Approximately 30,000 patients receive peritoneal dialysis in the United States. In August 1996, several dialysis centers from different states reported sterile peritonitis among CCPD patients using sterile peritoneal dialysis solution (PDS) from a single manufacturer. The manufacturer recalled 53 lots of PDS that had passed established industry guidelines and Food and Drug Administration (FDA) approved quality control tests [including endotoxin levels <0.5 endotoxin units (EU)/ml], but had pre-sterilization bacterial colony counts >1 cfu/ml.

METHODS

At one outpatient dialysis center, Hospital of the University of Pennsylvania (HUP), we conducted a retrospective cohort study of all CCPD patients treated during July 15 to August 30, 1996. A case-patient was defined as any HUP patient with culture-negative peritoneal fluid with a white blood cell count >100/mm3, cloudy peritoneal fluid, and/or abdominal pain. PDS and tubing were cultured for bacteria and assayed for endotoxin.

RESULTS

Overall, 14 of 28 patients had sterile peritonitis. The only risk factor identified was exposure to > or =1 lot of recalled PDS (14 of 22 vs. 0/6, P = 0.02); the more recalled lots received, the higher the attack rate (P = 0.0001). Five of 47 PDS bags had detectable endotoxin; recalled lots were more likely to have measurable endotoxin than nonrecalled lots (5/19 vs. 0/17, P = 0.05). When case-patients resumed CCPD using PDS from non-recalled lots, no further cases were reported.

CONCLUSIONS

Our results suggest that this outbreak was caused by intrinsic PDS contamination with endotoxin. Pre-sterilization colony counts may be an important quality control indicator for CCPD fluids in conjunction with endotoxin levels.

Can Ringer's lactate be used safely with blood transfusions?

BACKGROUND

Blood bank recommendations specify that Ringer's lactate solution (LR) should be avoided while transfusing blood. However, there are few studies either evaluating or quantifying increased coagulation during rapid infusion of LR and blood.

DESIGN AND METHODS

Whole blood (WB, n = 25) and packed red blood cells (PRBC, n = 26) were rapidly admixed with normal saline (NS), Lactate solution and LR with 1 g (LR-1), 2 g (LR-2), and 5 g (LR-5) CaCl2/L solutions for assessment of infusion time, filter weight, and clot formation.

RESULTS

No significant differences in infusion time or filter weight using WB or PRBC with NS or LR were seen. No significant difference in clot formation between NS and LR with WB or PRBC was found, but the presence of visible clot was increased in the LR-5 group (P = 0.013, WB, and P = 0.002, PRBC).

CONCLUSION

A comparison of LR and NS with rapid infusion rates of blood showed no significant difference between infusion time, filter weight and clot formation. Blood bank guidelines should be revised to allow the use of LR in the rapid transfusion of PRBC.

Effect of Implanted Insulin Pumpson Fluorescein Transcapillary Escape Timein Type 1 Diabetes Mellitus

OBJECTIVE

To determine whether significant increases in fluorescein transcapillary escape time (FTET) would occur after treatment of patients with type 1 diabetes with insulin delivered intraperitoneally by a surgically implanted pump.

METHODS

Nine patients with type 1 diabetes who were otherwise healthy and had received surgically implanted insulin pumps on a study protocol were recruited to have three measurements of FTET and glycosylated hemoglobin during an 18-month period. Serum fluorescein-albumin binding was measured at the time of the final test. Control FTETs were measured in 46 patients with type 1 diabetes who did not have insulin pumps and in 15 adults without diabetes.

RESULTS

In the implanted insulin pump group, 50% of the FTETs were below normal, but no significant longitudinal change in FTETs was noted in eight of the nine study patients. The mean FTETs in the implanted insulin pump group were significantly higher than those of the control patients with diabetes but without insulin pumps (mean, 88 versus 62 seconds; P<0.05) but significantly lower than those of the control subjects without diabetes (88 versus 163 seconds; P<0.001). Four of the nine patients with implanted insulin pumps had normal FTETs on all three studies. This subgroup had used insulin pumps (external + implanted) for significantly longer periods (6.2 versus 2.6 years; P<0.05) than the other five patients. These differences within the implanted pump group did not correlate with differences in glycosylated hemoglobin values or fluorescein-albumin binding; however, the glycosylated hemoglobin levels before insulin pump implantation were significantly lower than those of the other five patients. Three patients with onset of type 1 diabetes before age 10 years had the lowest FTETs.

CONCLUSION

Implanted insulin pumps did not alter FTETs between 6 months and 32 months after pump implantation. Total time on insulin pumps (external and implanted) is associated with normal FTET, and onset of diabetes before age 10 years is associated with abnormal FTET.

Comparison of repeatability of the multifocal electroretinogram and Humphrey perimeter

Functional mapping of the retina by multifocal electroretinographic recordings is now possible. We compared the normal range, repeatability and response topography of this new technique with conventional static Humphrey perimetry to assess its suitability in clinical practice. The multifocal technique was performed on 60 age-matched controls. Measures of repeatability and reproducibility were obtained. Results were then compared with those obtained from a customized perimetry test. In both tests the coefficients of repeatability were found to decrease with eccentricity. The inherent measurement variation between techniques was comparable. Overall system variation indicates that the technique could be a useful tool at the clinical level.

The effect of filter bandwidth on the multifocal electroretinogram

The effect of filter bandwith on the multifocal electroretinogram was assessed by means of theoretical calculation, electronic simulation and real multifocal electroretinogram recordings. Waveform distortion by high-pass filtering on simulated square waves, normal electroretinogram waveforms and negative electroretinogram waveforms was demonstrated. The theory of the effect of differentiation on electroretinogram waveform shape by electronic filtering indicates that little effect would be observed by changing the input filter cut-off for normal electroretinographic waveform shapes. However, negative electroretinogram waveforms are differentiated when the high-pass filter setting is increased. The differentiation effect artificially recreates a positive component that could be mistaken as a b-wave component. To eliminate this effect when recording multifocal electroretinograms, a high-pass filter setting of less than 1 Hz should be used to preserve the true electroretinographic waveform shape.

Hyperactivation of the folded gastrulation pathway induces specific cell shape changes

During Drosophila gastrulation, mesodermal precursors are brought into the interior of the embryo by formation of the ventral furrow. The first steps of ventral furrow formation involve a flattening of the apical surface of the presumptive mesodermal cells and a constriction of their apical diameters. In embryos mutant for folded gastrulation (fog), these cell shape changes occur but the timing and synchrony of the constrictions are abnormal. A similar phenotype is seen in a maternal effect mutant, concertina (cta). fog encodes a putative secreted protein whereas cta encodes an (alpha)-subunit of a heterotrimeric G protein. We have proposed that localized expression of the fog signaling protein induces apical constriction by interacting with a receptor whose downstream cellular effects are mediated by the cta G(alpha)protein. &lt;P&gt; In order to test this model, we have ectopically expressed fog at the blastoderm stage using an inducible promoter. In addition, we have examined the constitutive activation of cta protein by blocking GTP hydrolysis using both in vitro synthesized mutant alleles and cholera toxin treatment. Activation of the fog/cta pathway by any of these procedures results in ectopic cell shape changes in the gastrula. Uniform fog expression rescues the gastrulation defects of fog null embryos but not cta mutant embryos, arguing that cta functions downstream of fog expression. The normal location of the ventral furrow in embryos with uniformly expressed fog suggests the existence of a fog-independent pathway determining mesoderm-specific cell behaviors and invagination. Epistasis experiments indicate that this pathway requires snail but not twist expression.

Substance use and risky sexual behavior in female adolescents

The purpose of this study was to elucidate the etiological pathways towards substance use and risky sexual behavior in female adolescent substance abusers. The study had three aims: (1) to determine the relations between behavioral dysregulation, negative affectivity, and childhood victimization with substance use and risky sexual behavior, (2) to determine whether these relations are mediated by internalizing symptomatology, antisocial behavior, and affiliating with an adult boyfriend; and (3) to determine whether age of menarche moderates the relation between the mediating variables and substance use and risky sexual behavior. Multiple behavioral, psychiatric interview, and self-report measures were used to index behavioral dysregulation, negative affectivity, childhood victimization, internalizing symptomatology, antisocial behavior, affiliation with adult boyfriends, substance use, and risky sexual behavior in 125 substance abusing female adolescents and 78 controls between the ages of 14-18 years. Structural equation modeling was used to determine the etiological pathways. Results indicated that behavioral dysregulation, negative affectivity, and childhood victimization were related to substance use and risky sexual behavior. Age of menarche was significantly correlated with affiliation with an older boyfriend and risky sexual behavior. Antisocial behavior mediated the associations between behavioral dysregulation, negative affectivity and childhood victimization with substance use and risky sexual behavior. Affiliation with an adult boyfriend was directly associated with substance use involvement and accounted for the relationship between chronological age and risky sexual behavior. Finally, late menarche enhanced the association between internalizing symptomatology and substance use involvement. The results highlight the importance of behavioral dysregulation, negative affectivity, and childhood victimization in predicting substance use and risky sexual behavior, as well as the finding that antisocial behavior and affiliation with an adult boyfriend may be etiologically important in predicting these outcomes. Therefore, from a prevention and treatment standpoint, behavioral and affective dysregulation, childhood victimization as well as antisocial behavior may serve as clinical 'gateways' for altering the developmental trajectory toward substance use and risky sexual behavior in high risk and substance abusing youth. For example, reducing dysregulation through behavior modification procedures that have been developed for conduct disordered children would appear to be a heuristic avenue of investigation emanating from the results obtained in this study.

Functional imaging of the retina using the multifocal electroretinograph: a control study

BACKGROUND

A new technique exists that enables functional mapping of the retina. A control population was examined to obtain normative values and to assess the reproducibility of this new test.

METHODS

Twenty healthy volunteers were tested using a 61 hexagonal array stimulus with a 14 minute recording period. Median 5th and 95th percentiles were determined for implicit times and amplitude measures for the 61 test areas. Repeat measurements were performed on 10 individuals. Wilcoxon and Bland and Altman techniques were used to quantify reproducibility of the test.

RESULTS

The implicit time of the wave-form components was not found to vary over the retina (peak or b-wave component, 35.52 (1.4) ms; trough or a-wave component, 17.76 (0.8) ms). Reproducibility was found to decrease with eccentricity (coefficient of repeatability 17.4% for the central area increasing to 30.3% for the peripheral ring).

CONCLUSIONS

The findings suggest that reproducibility, although variable with eccentricity, is comparable with conventional electrophysiology. These limits of variation were used to assign confidence intervals to individual retinal areas and will be used (future work) in the examination of diseased states.

Crossed polarising filters to measure relative afferent pupillary defects: reproducibility, correlation with neutral density filters and use in central retinal vein occlusion

Measurement of a relative afferent pupillary defect (RAPD) can be carried out by attenuation of light received by the normal eye during the swinging flashlight test. Such measurements may be useful in the management of central retinal vein occlusion (CRVO). In this study a method employing cross polarised filters (CPFs) was tested for reproducibility. In addition the pattern of attenuation of light was compared with that by neutral density filters (NDFs). Finally, the method was used to investigate 74 patients with CRVO. The method was reproducible (8.7% variation) and showed exponential attenuation of light (in contrast to linear attenuation by the NDFs). In unilateral CRVO a sensitivity of 71% and specificity of 69% for the risk of iris neovascularisation was determined by the presence of RAPD requiring 20 degrees of rotation of the CPFs. It is concluded that CPFs provide a useful alternative to NDFs for the measurement of RAPD and have some advantages. They can be employed in the clinical management of patients with CRVO.