1,721,016 research outputs found
Aligning scan locations from consecutive spectral-domain optical coherence tomography examinations : a comparison among different strategies
No full textPURPOSE: We compared intrasession repeatability values produced by different spectral-domain optical coherence tomography (SD-OCT) instruments when measuring macular retinal thickness from consecutive examinations.
METHODS: A total of 40 eyes from 23 healthy subjects and 47 eyes from 42 patients with macular edema were enrolled in the study. Subjects underwent two consecutive SD-OCT examinations using three instruments: spectralis HRA+OCT, Cirrus, and RS 3000. For the second SD-OCT examination, the scan location was aligned to the baseline exam using different strategies: RS 3000 eye-tracking (pre-acquisition), Spectralis follow-up (during acquisition), Cirrus fovea finding (postacquisition), and Cirrus macular change analysis (postacquisition). Macular retinal thickness values from the consecutive examinations were evaluated to assess repeatability of the measurements.
RESULTS: In healthy subjects all of the strategies used for scan location alignment for the second examination provided good repeatability. For instance, intraclass correlation coefficients (ICC) from the central subfield were between 0.88 (RS 3000 eye-tracking) and 0.99 (Spectralis follow-up). In subjects affected by macular edema, the results were excellent. Cirrus macular change analysis and Spectralis follow-up produced ICC values equaled 1.00 in the central subfield. Cirrus fovea finding and RS 3000 eye-tracking produced slightly lower ICC values (0.98 and 0.99, respectively) in the central subfield.
CONCLUSIONS: All of the strategies for aligning consecutive SD-OCT scan locations produced repeatable retinal thickness values. The best results were obtained using the Spectralis with follow-up and Cirrus with macular change analysis
Cerebral CO2 vasoreactivity evaluation by transcranial Doppler ultrasound technique: a standardized methodology
No full textObjective: In normal subjects
cerebral CO2 vasoreactivity is
measured during spontaneous hyperventilation,
breathholding, or
adding CO2 to inspiratory gases.
The correlation between CO2 and
cerebral blood flow may, however,
be invalidated by the effects of a
modified respiratory pattern on venous
return, sympathovagal balance,
and cathecolamine release.
Moreover, the duration of the test,
usually not considered, may play an
important role. This may justify the
scattering of values found in literature.
We evaluated a new standardized
method for overcoming these
confounding factors.
Design: Experimental.
Participants: Twenty-one healthy
volunteers.
Methods: Subjects were connected
through a mouthpiece to a mechanical
ventilator set in the intermittent
positive pressure ventilation mode.
The ventilator was fed by two 40-l
tanks, one of which contained 5%
CO2. The inspiratory CO2 concentration
was varied at fixed time intervals
from 0% to 5% without
modifying ventilator settings. Endtidal
CO2 was measured at the mouthpiece. Mean blood velocity
(Vm) and pulsatility index (PI) in the
middle cerebral artery were measured
by means of transcranial
Doppler ultrasound.
Results: The test was easily applicable
and well tolerated. No hemodynamic
alterations were observed
during the tests. The correlation
between CO2 and Vm was always
linear and highly significant
(R2 > 0.8, p < 0.0001). A low intersubject
variability was observed. No
difference was found between the
two hemispheres, nor between the
sexes.
Conclusions: The strict standardization
of the technique, avoiding
hemodynamic interference, may explain
the low intersubject variability.
The value of this technique in ventilated
neurosurgical patients is still
speculative, but it might allow the
collecting of valuable data together
with a reduction in exposure to CO2,
and hence cerebral blood flow modifications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Long-term respiratory support and risk of pneumonia in critically ill patients. Intensive Care Unit Group of Infection Control
No full textIn 724 critically ill patients who had received prolonged (greater than 24 h) ventilatory assistance since admission to the ward, we analyzed the relationship between artificial ventilatory support and pulmonary infection. Two different approaches were used. The first, plotting the incidence of pneumonia versus the duration of ventilatory support, confirms previous data: the incidence rises from 5% in patients receiving one day of respiratory assistance to 68.8% in patients receiving more than 30 days. In the second approach, the same data were computed as an actuarial life table with the day of pneumonia onset as terminal event. This different approach, focusing on the onset of infection rather than on incidence, allows a new insight into the problem of nosocomial infection: pneumonia in patients with respiratory support is an early occurrence with a high and constant rate of acquisition and, therefore, a high risk of infection in the first eight to ten days. Later pneumonia acquisitions were rare, and the risk after ten days of ventilatory support is low
Retrobulbar structure visualization with enhanced depth imaging optical coherence tomography
No full textPURPOSE:
To assess enhanced depth imaging optical coherence tomography (EDI-OCT) visualization of deep posterior pole structures and retrobulbar tissues in myopic eyes and evaluate ocular structural elements that influence this capability.
METHODS:
Thirty consecutive myopic eyes (>-6 diopters) from 21 patients were enrolled. Exclusion criteria included any pathological condition affecting the posterior pole. Patients underwent biometry to assess axial length, and irises were classified as darkly or lightly pigmented. EDI-OCT scans were obtained by spectral-domain OCT to image posterior pole and retrobulbar structures. Choroidal thickness was measured manually, and for eyes in which the sclera was fully visible, scleral thickness was also measured manually. The influence of central retinal thickness, axial length, refractive error, mean choroidal thickness, mean scleral thickness, and iris pigmentation on EDI-OCT visualization of structures beyond the choroid was tested.
RESULTS:
Choroidal thickness was measurable in all eyes. In 11 of 30 eyes, the sclera was not completely visible (group 1). In 19 eyes, the full scleral thickness was measurable (group 2). In seven of the group 2 eyes, the full sclera was the deepest structure detected. In the remaining 11 eyes, deeper structures were visible. Choroidal thickness was the only parameter that correlated with the ability to visualize the full sclera (P < 0.001) and deeper structures (P = 0.044).
CONCLUSIONS:
The full thickness of the choroid was visualized by EDI-OCT in all eyes. Full thicknesses of the sclera and retrobulbar structures were not always visible. Choroidal thickness was the only parameter that significantly correlated with EDI-OCT visualization of deeper structures
Epidemiology and risk factors of pneumonia in critically ill patients. Intensive Care Unit Group for Infection Control
No full textRisk factors for pneumonia were analysed in a large population of critically ill patients, collected in two prospective multicentre "pneumonia studies" in Italy. Twenty-three intensive care units were involved and the study time was 150 unit months. Only patients without previous pulmonary infection, with intensive care unit stay greater than or equal to 48 hours and no rapidly irreversible illness at admission were included. The incidence of pneumonia in the 1475 selected patients was 15% (220 cases). 239 patients died in ICU; the mortality rate was significantly higher in patients developing pneumonia (p less than 0.0001); pneumonia was found to be an independent highly significant risk factor for death in critically ill patients (OR = 3.88; p less than 0.0001). Multivariate analysis of seven risk factors for pneumonia showed a significantly higher risk in patients with neuromuscular disease (OR = 3.8, p less than 0.002), impairment of airway reflexes at admission (OR = 2.93, p less than 0.0001), and greater than or equal to 24h respiratory assistance (OR = 3.05, p less than 0.0001). Impairment of airway reflexes at admission to the emergency room or intensive care unit identifies the population who will experience 3/4 of the overall lower respiratory tract infections. Rapid recognition of at-risk patients seems clinically important and may improve awareness programs and preventive approaches
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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