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At least 1,207 records · Page 67Linked to original sources
PubMed2005

A prospective observational study of the use of the Proseal laryngeal mask airway for postpartum tubal ligation.

BACKGROUND: Though controversial, the risk of pulmonary aspiration during general anaesthesia in the immediate postpartum period appears low. The efficacy of the Proseal laryngeal mask airway was studied prospectively in a group of patients undergoing postpartum tubal ligation. METHODS: The Proseal laryngeal mask airway was employed for airway management in 90 fasted patients undergoing tubal ligation via minilaparotomy at least 8 h after normal vaginal delivery (mean 36.5, range 8-96 h). Gastric volume and pH were measured, using aspiration through a gastric tube. RESULT: Proseal laryngeal mask airway insertion was successful in all patients, requiring one attempt in 75 patients (83%). The median (range) leak pressure was 35 (23-40) cmH2O. Twenty-two patients (25%) had a leak pressure of 40 cmH2O or greater. Gastric tube placement was successful in all patients, described as easy in 79 (87%), and difficult in 11 (13%). The mean initial volume of gastric aspirate was 10.7 (0-64) mL and the final volume 15.6 (0-71) mL. The mean pH of the gastric aspirate was 2.6 (1.2-6.6). There were no incidents of suspected fluid regurgitation or aspiration, but two patients required intubation during surgery. Ten patients (11.1%) complained of sore throat in the recovery room, nine of which were described as mild. All patients reported being satisfied with their anaesthesia. CONCLUSION: The Proseal laryngeal mask airway provides an effective airway for general anaesthesia in fasted patients undergoing tubal ligation from 8 h after normal vaginal delivery. While the safety of an unprotected airway in this population remains uncertain, this study suggested a low risk of regurgitation, especially in the first 24 h post partum.

Adult↗
PubMed2005

Randomized trial on two types of thermoplastic masks for patient immobilization during radiation therapy for head-and-neck cancer.

PURPOSE: Radiation therapy for head-and-neck cancer requires a reliable immobilization for an accurate and consistent treatment setup. This prospective, randomized study was done to compare two types of Posicast thermoplastic face masks, in terms of reproducibility, patient comfort, tolerability, and skin damage. METHODS AND MATERIALS: The patients were randomly assigned to use a head mask (HM) or a head-and-shoulder mask (HSM). Three-dimensional treatment planning was followed by fractionated external-beam radiation therapy. Reproducibility was assessed by comparing port films with simulator films twice during treatment and by comparing actual treatment table positions weekly. Patient tolerability and comfort were studied weekly. The radiation-induced skin damage was assessed every week according to the World Health Organization toxicity scale. RESULTS: A total of 260 patients were included, and 241 (93%) were evaluated. There were no statistically significant differences between the groups (HM or HSM) in terms of reproducibility. Patients using HSM experienced significantly more claustrophobia (p = 0.023). Patients allocated to HSM receiving > or = 60 Gy were found to have more skin reactions. CONCLUSIONS: The smaller HM reduced feelings of claustrophobia, as well as skin reactions, for patients receiving > or = 60 Gy. The smaller mask did not compromise the reproducibility of the setup.

Adult↗
PubMed2005

Time-course of masked response priming and inhibition in Parkinson's disease.

Parkinson's disease patients have enhanced interference effects arising from the conflict between competing responses, as probed in various 'conflict tasks'. The possibility that this is due to an inhibitory deficit received recent support from a masked response priming task [Seiss, E., & Praamstra, P. (2004). The basal ganglia and inhibitory mechanisms in response selection: Evidence from subliminal priming of motor responses in Parkinson's disease. Brain, 127, 330-339]. The added information from a masked priming task is that the introduction of a delay between presentation of prime and target stimuli reveals an inhibition of the covert response activation induced by the masked prime stimulus. This inhibition results in a reversal of normal priming effects, such that performance is better with incompatible than with compatible prime-target pairs. We previously found that this reversal is attenuated in Parkinson's disease, when tested at a prime-target delay of 100 ms, thus revealing deficient inhibition of covert response activation. The present study was undertaken to investigate the time course of the underlying inhibition process, using five prime-target ISIs between 0 and 200 ms. While we reproduced the attenuation at ISI 100 ms, the time course information revealed that the rate of change of the compatibility effect over ISIs from 0 to 200 ms was identical for patients and controls. This result indicates that the inhibition underlying the reversal of masked priming effects is normal in Parkinson's disease.

Adult↗
PubMed1999

Brief foveal masking during scene perception.

In the present experiment, participants were exploring line drawings of scenes in the context of an object-decision task, while eye-contingent display changes manipulated the appearance of the foveal part of the image. Foveal information was replaced by an ovoid noise mask for 83 ms, after a preset delay of 15, 35, 60, or 85 ms following the onset of fixations. In control conditions, a red ellipse appeared for 83 ms, centered around the fixation position, after the same delays as in the noise-mask conditions. It was found that scene exploration was hampered especially when foveal masking occurred early during fixations, replicating earlier findings. Furthermore, fixation durations were shown to increase linearly as the mask delay decreased, which validates the fixation duration as a measure of perceptual processing speed.

Fovea Centralis↗
PubMed2002

Selective orienting of attention to masked threat faces in social anxiety.

The aims of the study were two-fold: to examine whether previous evidence of a pre-attentive bias for masked threat faces in anxious individuals could be replicated, and to assess the relationship between the predicted bias and measures of trait and social anxiety. Pairs of face stimuli were briefly displayed and masked in a modified version of the visual probe task. Results indicated that high anxious individuals were faster to respond to probes occurring in the spatial location of masked threat rather than neutral faces; consistent with their attention being automatically captured by sub-threshold threat cues. Furthermore, this vigilance effect for masked threat faces appeared to be primarily a function of social anxiety and social avoidance, rather than trait anxiety. It was also more apparent when threat faces were presented in the left visual field, suggestive of right hemisphere involvement.

Adult↗
PubMed2001

Increased amygdala response to masked emotional faces in depressed subjects resolves with antidepressant treatment: an fMRI study.

BACKGROUND: The amygdala has a central role in processing emotions, particularly fear. During functional magnetic resonance imaging (fMRI) amygdala activation has been demonstrated outside of conscious awareness using masked emotional faces. METHODS: We applied the masked faces paradigm to patients with major depression (n = 11) and matched control subjects (n = 11) during fMRI to compare amygdala activation in response to masked emotional faces before and after antidepressant treatment. Data were analyzed using left and right amygdala a priori regions of interest, in an analysis of variance block analysis and random effects model. RESULTS: Depressed patients had exaggerated left amygdala activation to all faces, greater for fearful faces. Right amygdala did not differ from control subjects. Following treatment, patients had bilateral reduced amygdala activation to masked fearful faces and bilateral reduced amygdala activation to all faces. Control subjects had no differences between the two scanning sessions. CONCLUSIONS: Depressed patients have left amygdala hyperarousal, even when processing stimuli outside conscious awareness. Increased amygdala activation normalizes with antidepressant treatment.

Adolescent↗
PubMed2003

Developing a new quantitative account of backward masking.

A new general explanation for u-shaped backward masking is analyzed and found to predict shifts in the interstimulus interval (ISI) that produces strongest masking. This predicted shift is then compared to six sets of masking data. The resulting comparisons force the general explanation to make certain assumptions to account for the data. In this way, the experimental data promote the development of a new theory of backward masking. The new theory suggests interpretations of the data that are sometimes novel, often more precise, and sometimes contrary to interpretations that are prevalent in the literature.

Attention↗
PubMed2001

Peripheral and parafoveal cueing and masking effects on saccadic selectivity in a gaze-contingent window paradigm.

The present study employed the gaze-contingent window paradigm to investigate parafoveal and peripheral cueing and masking effects on saccadic selectivity in a triple-conjunction visual search task. In the cueing conditions, the information shown outside the gaze-contingent window was restricted to the feature or feature pair shared between the target and a particular distractor type. In the masking conditions, no stimulus features were shown outside the window. Significant cueing and masking effects on saccadic selectivity were observed for saccades directed at items within the window, where all features were visible across experimental conditions. Cueing a particular feature or feature pair biased saccadic selectivity towards this feature or feature pair, while masking generally reduced saccadic selectivity. These findings support the concept of visual guidance being a preattentive process that operates in parallel across the display.

Analysis of Variance↗
PubMed2003

Temporal asymmetry in motion masking: a shortening of the temporal impulse response function.

Morgan and Chubb observed a striking temporal asymmetry in motion masking (Vis. Res. 39 (1999) 4217). Motion was produced with a two-frame sequence of gratings presented in spatial quadrature phase; the second grating (100 ms) was presented immediately after the first grating (100 ms), with no temporal overlap. The contrast threshold for detecting the direction of motion of the stimulus pair was facilitated when the first grating was of low-contrast and the second grating was of high-contrast, but strong masking occurred when the order was reversed, so the high-contrast grating came first. We replicated this result, but showed that the masking mostly disappeared when the two gratings temporally overlapped only slightly. The high sensitivity to the precise temporal pattern of the stimulus can be explained by a small temporal 'shortening' of the temporal impulse response function (IRF) as stimulus contrast is increased. The IRF is biphasic with a negative inhibitory lobe. When the first grating has high-contrast, its flash response (owing to the shortening of the IRF) may be in a fairly strong negative phase by the time that the positive response to the second, lower-contrast grating has reached appreciable strength--this reduces the magnitude of the motion signal generated by the two flashes and can account for the masking. A shortening of the IRF with increased contrast (a nonlinearity) is supported by psychophysical studies in humans and by recordings of magnocellular retinal ganglion cells in macaque, and the present results bolster this concept.

Contrast Sensitivity↗
PubMed2003

The what and where in visual masking.

A metacontrast mask suppresses the visibility of, without influencing the reaction time (RT) to, the target. We investigated whether this dissociation results from a sensori-motor pathway immune to masking effects or from the characteristics of stimulus timing in mutually inhibitory sustained and transient channels. For target visibility, para- and metacontrast yielded the usual U-shaped functions. Peak paracontrast occurred at stimulus onset asynchronies (SOAs) of -150 to -100 ms. RTs were relatively low for metacontrast and did not show a systematic change as a function of SOA. The RT contribution from contour-masking was greatest at an SOA of -150 ms (paracontrast) and declined to near zero in the metacontrast regime. The dissociation between visibility and RT seen in metacontrast did not occur in paracontrast, rejecting the theory that RTs are elicited by a single sensori-motor pathway immune to masking. The dependence of the dissociation on stimulus timing can be explained by RECOD, a dual-pathway model wherein fast and slow activities interact.

Contrast Sensitivity↗
PubMed1999

Texture filling-in and texture segregation revealed by transient masking.

When a texture pattern was briefly presented followed by a small annular mask, it was found that the central area of the texture was strongly suppressed within the mask. Analogous to filling-in of brightness in a uniform luminance area (Paradiso, M. A. & Nakayama, K. (1991) Vision Research, 31, 1221-1236), this phenomenon demonstrates filling-in of texture; the texture area was unperceived because filling-in of the texture area was interrupted by the contour in the mask. However, odd local features within the texture, which were assumed to pop out, were selectively perceived while other features were suppressed within the mask. These results suggest that: (1) rapid pattern segregation occurs before and/or separately from texture filling-in, and that (2) filling-in is initiated at boundaries between surfaces rather than at luminance gradients.

Form Perception↗
PubMed1999

Spatial masking does not reveal mechanisms selective to combined luminance and red-green color.

Detection thresholds plotted in the L and M cone-contrast plane have shown that there are two primary detection mechanisms, a red-green hue mechanism and a light-dark luminance mechanism. However, previous masking results suggest there may be additional mechanisms, responsive to combined features like bright and red or dark and green. We measured detection thresholds for a 1.2 c deg-1 sine-wave grating in the presence of a spatially matched mask grating which was either stationary, dynamically jittered or flickered. The stimuli could be set to any direction in the L,M plane. The appearance of selectivity for combined hue and luminance arose only in conditions where adding the test to the mask modified the spatial phase offset between the luminance and red-green stimulus components. Sensitivity was very high for detecting this spatial phase offset. When this extra cue was eliminated, masking contours in the L,M plane could be largely described by the classical red-green and luminance mechanisms.

Color Perception↗
PubMed1984

Performance of the large-reservoir oxygen mask (Ventimask).

The performance of large-reservoir Venturi masks ('Ventimask') giving nominal inspired oxygen (O2) concentrations ranging from 24% to 60% was assessed in a face model, in six normal subjects, and in ten patients with severe chronic airflow obstruction at the O2 flow rates recommended. Instantaneous oxygen concentrations were measured with a mass spectrometer ('Centronics MGA200') and volume-weighted to give mean inspired concentrations (FiO2). In human studies volume-weighting was achieved by simultaneous measurement of tidal volume from chest and abdominal motion by the use of a respiratory inductance plethysmograph ('Respitrace'). Reinspiration of dead space from the mask was assessed by measuring FiCO2, which varied from 0.2 to 0.4% (normals) and was 0.6 +/- 0.4% in patients. In normal subjects and patients breathing at rest the FiO2% in 24, 28, 35, and 40% ventimasks was within 1.9% absolute of nominal (range-1.2 to +1.9%) but the 60% mask read low (50.3%). Various factors can make FiO2 less than nominal but the human and model studies indicated that reinspiration of dead space from the mask was more important than hyperventilation. In tachypnoeic patients (frequency greater than 30/min), the O2 flow should be increased to 50% above recommended.

Aged↗
PubMed2002

Frontal and striatal brain lesions increase susceptibility to masking in perceptual decisions.

Recent data suggest that perceptual decisions on masked stimuli involve neural activity in frontal cortex. We examined the effect of damage to frontal and striatal brain regions in man on the susceptibility to backward masking in rapid stimulus streams. Patients with unilateral frontal excisions and patients with early Huntington's disease were compared to controls in the identification of a brief white letter embedded in short streams of black letters at two presentation rates: (a) 9 letters/s; (b) 12.5 letters/s and also in a control condition in which the first post-target masking letter was absent. Patients could identify the target when the post-target mask was absent, but reducing the delay between stimuli significantly increased the error rates in patients. Intrusion errors often involved reporting post-target or pre-target distractors instead of the target. These results suggest that fronto-striatal lesions increase the period during which perceptual decisions are susceptible to perturbation. This deficit is compatible with a functional role of frontal systems in the cognitive control of brief perceptual decisions.

Adult↗
PubMed2001

An improved pocket rescue mask incorporating a novel visual breathing indicator.

The difficulties inherent in the 'Look, Listen and Feel' method of identifying respiratory arrest prompted the authors to develop a simple mechanical breathing indicator that can show clearly, at a glance, whether or not a patient is breathing. The novel indicator was designed to be highly visible so that its interpretation should be obvious to medical personnel and the lay public, and yet sufficiently simple so that it could be easily and inexpensively incorporated into the type of pocket rescue masks currently in use. The indicator needs no power source, works indoors and outdoors and does not interfere with the delivery of rescue breaths during resuscitation. A prototype of the improved pocket mask incorporating the new indicator was made and was tested for its ability to detect breaths over a range of inspiratory flow rates and inspiratory pressures. The authors found that the indicator responded to peak inspiratory flow rates of between 15 and 120 l/min, inspiratory pressures as low as 0.18 cm H(2)O with no supplemental oxygen flowing to the mask and 0.22 cm H(2)O with supplemental oxygen flowing at 9 l/min, minute ventilation volumes between 7.1 and 21.8 l/min, tidal volumes between 0.36 and 2.92 l and a respiratory rate range of 7-24 breaths per min. The authors conclude that the new indicator, when attached to a pocket rescue mask, is sensitive enough to identify clearly and reliably those patients at the scene of collapse who have stopped breathing. Additionally it may assist rescuers in timing the delivery of assisted rescue breaths in those patients with poor respiratory effort.

Equipment Design↗
PubMed2000

Smaller tidal volumes with room-air are not sufficient to ensure adequate oxygenation during bag-valve-mask ventilation.

The European Resuscitation Council has recommended decreasing tidal volume during basic life support ventilation from 800 to 1200 ml, as recommended by the American Heart Association, to 500 ml in order to minimise stomach inflation. However, if oxygen is not available at the scene of an emergency, and small tidal volumes are given during basic life support ventilation with a paediatric self-inflatable bag and room-air (21% oxygen), insufficient oxygenation and/or inadequate ventilation may result. When apnoea occurred after induction of anaesthesia, 40 patients were randomly allocated to room-air ventilation with either an adult (maximum volume, 1500 ml) or paediatric (maximum volume, 700 ml) self-inflatable bag for 5 min before intubation. When using an adult (n=20) versus paediatric (n=20) self-inflatable bag, mean +/-SEM tidal volumes and tidal volumes per kilogram were significantly (P<0.0001) larger (719+/-22 vs. 455+/-23 ml and 10.5+/-0.4 vs. 6.2+/-0.4 ml kg(-1), respectively). Compared with an adult self-inflatable bag, bag-valve-mask ventilation with room-air using a paediatric self-inflatable bag resulted in significantly (P<0.01) lower paO(2) values (73+/-4 vs. 87+/-4 mmHg), but comparable carbon dioxide elimination (40+/-2 vs. 37+/-1 mmHg; NS). In conclusion, our results indicate that smaller tidal volumes of approximately 6 ml kg(-1) ( approximately 500 ml) given with a paediatric self-inflatable bag and room-air maintain adequate carbon dioxide elimination, but do not result in sufficient oxygenation during bag-valve-mask ventilation. Thus, if small (6 ml kg(-1)) tidal volumes are being used during bag-valve-mask ventilation, additional oxygen is necessary. Accordingly, when additional oxygen during bag-valve-mask ventilation is not available, only large tidal volumes of approximately 11 ml kg(-1) were able to maintain both sufficient oxygenation and carbon dioxide elimination.

Adult↗
PubMed2001

Masking by harmonic complexes in birds: behavioral thresholds and cochlear responses.

Thresholds for pure tones embedded in harmonic complexes were measured behaviorally and physiologically for three species of birds, and physiologically in gerbils. The harmonic maskers were generated using the Schroeder-phase algorithm, characterized by monotonically increasing or decreasing phase across frequency. Previous work has shown that these stimuli produce large differences in masking in humans but not budgerigars. In this study, we show that for two additional species of birds, the patterns of masking were similar to those shown for budgerigars, with masking differing only slightly for the two Schroeder-phase waveforms, and in the opposite direction from that demonstrated in humans. Amounts of masking among species corresponded qualitatively to differences in their critical ratios. Evoked potential measurements in birds and gerbils indicated responses that were consistent with the behaviorally measured thresholds in birds and humans. Results are interpreted in light of differences in frequency selectivity and cochlear temporal processing across species.

Acoustic Stimulation↗
PubMed2003

Brain activity during auditory backward and simultaneous masking tasks.

Normal-hearing adult subjects performed a simultaneous and a backward auditory masking task, while their brain activity was recorded using functional magnetic resonance imaging. No differences between these tasks were observed in the auditory brain regions on the superior temporal lobes. Brain activity was larger for simultaneous than backward masking in the left inferior parietal lobe, the left inferior frontal cortex, the posterior cingulate cortex, and the cerebellum. In contrast, backward masking gave more activation in the left and right anterior temporal poles, and the anterior cingulate cortex. Apparently, backward and simultaneous masking tasks activate different auditory processing streams and require different cognitive brain resources.

Acoustic Stimulation↗