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At least 883 records · Page 49Linked to original sources
PubMed1987

Respiratory syncytial virus (RSV) infection rate in personnel caring for children with RSV infections. Routine isolation procedure vs routine procedure supplemented by use of masks and goggles.

Respiratory syncytial virus (RSV) infections in hospitalized children were identified by indirect fluorescent antibody technique. Patients with RSV infections were assigned to one of two isolation categories. In one category, the health care workers entering the child's room did not wear masks and goggles; in the other category, the workers did wear masks and goggles. The RSV illness rate in health care workers using masks and goggles was 5%, but the rate for those not using masks and goggles was 61%. In the no mask/goggles group, the RSV illness rates in the health care workers correlated directly with the number of exposures. In this modest study, the use of masks and goggles was associated with a significant reduction of RSV illnesses in pediatric health care workers.

Adult↗
PubMed1989

Wearing of caps and masks not necessary during cardiac catheterization.

Although cardiac catheterization-related infections are rare, caps and masks are often worn to minimize this complication. However, documentation of the value of caps and masks for this purpose is lacking. We, therefore, prospectively evaluated the experience of 504 patients undergoing percutaneous left heart catheterization, seeking evidence of a relationship between whether caps and/or masks were worn by the operators and the incidence of infection. No infections were found in any patient, regardless of whether a cap or mask was used. Thus, we found no evidence that caps or masks need to be worn during percutaneous cardiac catheterization.

Cardiac Catheterization↗
PubMed1993

Developmental changes in chickens' masked thresholds.

Masked thresholds were estimated at four frequencies (.25, .5, 1, and 2 kHz) in three levels of broadband noise (approximately 0, 10, and 20 dB/Hz) in over 100 chickens at 0 and 4 days of age. An adaptive procedure was based on delays in ongoing peeps that occurred when chicks heard the tones over the background noise. Masked thresholds decreased an average of 1 dB per day immediately after birth. This increasing sensitivity is more likely due to nonsensory factors, similar to distraction masking reported in human neonates, than to improving frequency resolution. Masked thresholds in these neonates are otherwise affected by spectrum level and frequency in the same way as the responses of mature subjects: thresholds increase by nearly 1 dB for each dB of increase in the spectrum level of the masker, and by approximately 3 dB for each octave of frequency. Thus, although elevated by some nonsensory effect, masked thresholds in newborn chicks are similar to those in humans.

Animals↗
PubMed1993

Three different mask physiotherapy regimens for prevention of post-operative pulmonary complications after heart and pulmonary surgery.

OBJECTIVE: An investigation into the incidence of post-operative complications after thoracic surgery with 3 different physiotherapy masks. DESIGN: A prospective, consecutive, randomized comparison. SETTING: Department of Thoracic and Heart Surgery at a University Hospital. The treatments were performed by experienced and specially trained physiotherapists. PATIENTS: 160 patients were evaluated. 60 patients undergoing heart surgery, 59 patients having pulmonary resection, and 41 patients with exploratory thoracotomy. INTERVENTIONS: In each operative category the patients were treated with one of three face mask systems used in addition to routine chest physiotherapy. These were either continuous positive airway pressure (CPAP), positive expiratory pressure (PEP), or inspiratory resistance - positive expiratory pressure (IR-PEP). MEASUREMENTS AND RESULTS: Post-operative pulmonary complications were assessed by forced vital capacity (FVC), arterial oxygen tension (PaO2), and chest X-ray examination, all measured pre-operatively and on the fourth and ninth post-operative day. The patients filled in a questionnaire expressing their opinion about their mask treatment. There was an equal decrease in FVC, FVC%, and PaO2, and equal frequency of atelectasis in the 3 mask treatments. More patients with the PEP mask favoured their system than did those with the other 2 systems. CONCLUSION: There was no statistically significant difference between the treatments: continuous positive airway pressure (CPAP), positive expiratory pressure (PEP), and inspiratory resistance - positive expiratory pressure (IR-PEP) on post-operative complications. Any of the three treatments may be used as supplement to standard chest physiotherapy.

Blood Gas Analysis↗
PubMedDate not supplied

Properties of derived cochlear action potentials in forward tonal masking in guinea pigs.

Chronic experiments on guinea pigs were used to study the characteristics of cochlear nerve action potentials and the derived potential in conditions of forward masking. The auditory nerve action potential was recorded from the round window of the cochlea. The derived potential was obtained by subtracting the action potential recorded with masking from the response obtained in silence. These studies showed that the derived potential showed higher sensitivity to masking than the traditional measure of masking, i.e., the decrement in the amplitude of the auditory nerve action potential. The derived potential reflects not only changes in the action potential during masking, but also changes in its shape. Differences between the derived potential and the action potential decrement provide evidence that the amplitude and time changes in the derived potential provide more complete information on the nature of activity in the auditory fibers.

Action Potentials↗
PubMed1990

The laryngeal mask airway: clinical appraisal in 250 patients.

The laryngeal mask airway consists of a tubular oropharyngeal airway to the distal end of which is sealed a silicone laryngeal mask with an inflatable rim which provides an airtight seal around the larynx. It provided a clear airway in 238 of 250 elective and emergency non-obstetrical patients for a wide variety of surgical procedures, ranging from minor gynaecological and urological procedures to major abdominal and orthopaedic surgery with either spontaneous respiration or intermittent positive pressure ventilation. Anaesthetic techniques and drugs were similar to those which would have been used for the same procedures if face-mask or tracheal intubation had been employed. Blind insertion of the laryngeal mask airway was successful at the first attempt in 187 patients, some manipulation was required in 61 patients, and insertion was impossible in two patients, each of whom had a small mouth. In ten patients tracheal intubation was required because of airway obstruction or a large gas leak. The LM airway does not require laryngoscopy for its insertion, it relieves the anaesthetist's hands from holding a face-mask, it cannot be misplaced in the oesophagus, and it is well tolerated during emergence from anaesthesia.

Adolescent↗
PubMed1999

Awake tracheal intubation through the intubating laryngeal mask.

PURPOSE: To report successful awake insertion of the intubating laryngeal mask (Fastrach) and subsequent tracheal intubation through it, in a patient with predicted difficult tracheal intubation, due to limited mouth opening, and difficult ventilation through a facemask, due to a large mass at the corner of the mouth. CLINICAL FEATURES: A 53-yr-old woman with a large post-gangrenous mass on the right cheek to the angle of the mouth was scheduled for its resection. The right side of her face was damaged by a bomb attack followed by cancrum oris 50 yr ago. The distance between the incisors during maximum mouth opening was 2 cm and that between the gums on the right side < 1 cm. After preoxygenation and 50 micrograms fentanyl and 30 mg propofol i.v., propofol was infused at 2 mg.kg-1.hr-1. Lidocaine, 8%, was sprayed on the oropharynx. A #4 intubating laryngeal mask was inserted with a little difficulty. A fibrescope was passed through a 7.5-mm ID RAE tracheal tube, and the combination was easily passed through the laryngeal mask into the trachea. General ansthesia was then induced. Finally, the intubating laryngeal mask was removed, while the RAE tube was being stabilized using an uncuffed 6.0-mm ID tracheal tube. CONCLUSION: Awake tracheal intubation through the intubating laryngeal mask is a useful technique in patients with limited mouth opening in whom ventilation via a facemask is expected to be difficult.

Anesthetics, Intravenous↗
PubMed1999

Comparison of the flexible and standard laryngeal mask airways.

PURPOSE: To determine mucosal pressures, ease of insertion, mask position and oropharyngeal leak pressures for the flexible (FLMA) and standard laryngeal mask airway (LMA). METHODS: Forty anesthetized, paralysed adult patients were randomly allocated to receive either the FLMA or LMA. Microchip sensors were attached to the LMA or FLMA at identical locations corresponding to the base of tongue, hypopharynx, lateral pharynx, oropharynx, posterior pharynx and pyriform fossa. Mucosal pressure, oropharyngeal leak pressure (OLP) and mask position (assessed fibreoptically) were recorded during inflation of the cuff from 0-40 ml in 10 ml increments. RESULTS: Ease of insertion and mask position were similar between devices. Mean OLP was higher for the LMA (22 vs 19 cm H2O), but the maximum OLP was similar (25 vs 24 cm H2O). Mean mucosal pressures were generally low (< 12 cm H2O) for both devices, but were higher for the LMA in the lateral pharynx (4 vs 1 cm H2O) and oropharynx (13 vs 3 cm H2O) and higher in the posterior pharynx for the FLMA (4 vs 2 cm H2O). The OLP for both devices increased with increasing intracuff volume from 0-10 ml and 10-20 ml, and from 20-30 ml for the FLMA. CONCLUSIONS: We conclude that the LMA and FLMA perform similarly in terms of ease of insertion and mask position, but OLP and mucosal pressures are slightly higher for the LMA. Pharyngeal mucosal pressures for both devices are lower than those considered safe for the tracheal mucosa. The overall clinical performance between the two devices is similar.

Adolescent↗
PubMed2002

Aspiration prevented by the ProSeal laryngeal mask airway: a case report.

PURPOSE: To describe a case of intraoperative passive regurgitation where the ProSeal laryngeal mask airway (PLMA) successfully protected the airway from the respiratory tract. CLINICAL FEATURES: A 32-yr-old man was electively scheduled for change of dressings and application of plaster of Paris to both legs. A size 5 PLMA was inserted on the first attempt and the patient allowed to breathe spontaneously. Twenty-five minutes into the procedure brown fluid was noticed in the drainage tube of the mask. There was no change in respiratory pattern nor any evidence of coughing retching or vomiting. Twenty-five millilitres of fluid were suctioned out of the tube which tested positive for acid. The PLMA was left in place and the procedure continued uneventfully. After removal of the mask pH testing showed the dorsum of the mask to have a pH of 7 and the ventrum/bowl of the mask to be dry with a pH of 7. The patient had no respiratory symptoms in the recovery room and the postoperative course was uneventful. CONCLUSIONS: This case illustrates that passive regurgitation can occur unexpectedly intraoperatively and shows that the PLMA can protect the airway during such an event by allowing the regurgitated fluid to pass up the drainage tube without leaking into the glottis.

Adult↗
PubMed2000

Biting the laryngeal mask: an unusual cause of negative pressure pulmonary edema.

PURPOSE: To describe negative pressure pulmonary edema due to biting of the laryngeal mask tube at emergence from general anesthesia. CLINICAL FEATURES: A healthy patient underwent general anesthesia using a laryngeal mask airway and mechanical ventilation. During recovery, the patient strongly bit the laryngeal mask and made very forceful inspiratory efforts until the mask was removed. Five minutes later, the patient developed dyspnea and had an hemoptysis of 50 ml fresh blood. Chest radiograph showed bilateral alveolar infiltrates. Pharyngo-laryngeal examination was normal. Bronchoscopy revealed no injury but diffuse pink frothy edema fluid. Clinical examination and chest radiograph became normal after 12 hr of nasal oxygen therapy confirming airway obstruction as the most available cause of this pulmonary edema. CONCLUSION: Airway obstruction due to biting of a laryngeal mask tube may result in negative pressure pulmonary edema.

Adult↗
PubMed2003

Perceptual latency priming by masked and unmasked stimuli: evidence for an attentional interpretation.

Four experiments investigated the influence of a metacontrast-masked prime on temporal order judgments. The main results were (1) that a masked prime reduced the latency of the mask's conscious perception (perceptual latency priming), (2) that this effect was independent of whether the prime suffered strong or weak masking, (3) that it was unaffected by the degree of visual similarity between the prime and the mask, and that (4) there was no difference between congruent and incongruent primes. Finding (1) suggests that location cueing affects not only response times but also the latency of conscious perception. (2) The finding that priming was unaffected by the prime's detectability argues against a response bias interpretation of this effect. (3) Since visual similarity had no effect on the prime's efficiency, it is unlikely that sensory priming was involved. (4) The lack of a divergence between the effects of congruent and incongruent primes implies a functional difference between the judgments in the temporal order judgment task and speeded responses that have demonstrated differential effects of congruent and incongruent primes (e.g., Klotz & Neumann, 1999). These results can best be interpreted by assuming that the prime affects perceptual latency by initiating a shift of attention, as suggested by the Asynchronous Updating Model (AUM; Neumann 1978, 1982).

Adult↗
PubMed2003

Forward masking additivity and auditory compression at low and high frequencies.

The additivity of nonsimultaneous masking can be used as a measure of nonlinearity in the auditory system. For example, two equally effective forward maskers should produce 3 dB of additional masking when they are combined, assuming linearity with respect to intensity. A combined effect greater than this (excess masking) indicates compression. In the present experiments, the signal was a 10-ms pure tone presented 20 ms after a 200-ms narrowband noise masker and/or immediately after a 20-ms narrow-band noise masker. The signal frequency was 250, 500, or 4000 Hz. The signal threshold produced by combining two equally effective maskers was measured. At all three frequencies, little excess masking was observed for a signal 10 dB above absolute threshold, indicating linear additivity (no compression). At signal levels 30 dB above absolute threshold, excess masking was observed at all three frequencies. The estimated compression exponents were 0.29 at 250 Hz, 0.34 at 500 Hz, and 0.17 at 4000 Hz. In contrast with physiological studies on other mammals, the present results provide evidence for substantial compression at low frequencies in humans.

Acoustic Stimulation↗
PubMed2001

Psychophysical estimates of cochlear phase response: masking by harmonic complexes.

Harmonic complexes with identical component frequencies and amplitudes but different phase spectra may be differentially effective as maskers. Such harmonic waveforms, constructed with positive or negative Schroeder phases, have similar envelopes and identical long-term power spectra, but the positive Schroeder-phase waveform is typically a less effective masker than the negative Schroeder-phase waveform. These masking differences have been attributed to an interaction between the masker phase spectrum and the phase characteristic of the basilar membrane. To explore this relationship, the gradient of stimulus phase change across masker bandwidth was varied by systematically altering the Schroeder-phase algorithm. Observers detected a signal tone added in-phase to a single component of a masker whose frequencies ranged from 200 to 5000 Hz, with a fundamental frequency of 100 Hz. For signal frequencies of 1000-4000 Hz, differences in masking across the harmonic complexes could be as large as 5-10 dB for phase gradients changing by only 10%. The phase gradient that resulted in a minimum amount of masking varied with signal frequency, with low frequencies masked least effectively by stimuli with rapidly changing component phases and high frequencies masked by stimuli with more shallow phase gradients. A gammachirp filter was implemented to model these results, predicting the qualitative changes in curvature of the phase-byfrequency function estimated from the empirical data: In some cases, small modifications to the gammachirp filter produced better quantitative predictions of curvature changes across frequency, but this filter, as implemented here, was unable to accurately represent all the data.

Acoustic Stimulation↗
PubMed1988

Spatial phase dependence and the role of motion detection in monocular and dichoptic forward masking.

Contrast thresholds for briefly flashed gratings were measured by the QUEST procedure, under conditions of forward masking by gratings of the same spatial frequency (usually 1 c/deg). Low-contrast masks reduced threshold at short onset asynchronies (0 to 50 msec), while higher contrasts raised threshold over a broader temporal range (0 to 100-140 msec). Both effects depended on the spatial phase relation, but in different ways. Threshold reduction at 0- +/- 90 deg phases probably arises from spatio-temporal filtering by direction-selective mechanisms. This conclusion was supported by computer simulation of a motion detector model. The direction-selective stage of motion analysis may be entirely monocular, since facilitation at 90 deg was abolished by dichoptic presentation. Threshold elevation was phase-dependent at short SOA's (20-50 msec), with a minimum at +/- 90 deg, but was not phase-dependent at longer SOA's (70-140 msec). In-phase masking (0 deg) was about equally strong monocularly and dichoptically, but dichoptic threshold elevation showed no phase-dependence at any SOA. Threshold elevation at longer SOA's, and with dichoptic presentation, may reflect a purely suppressive binocular masking effect, unselective for spatial phase, and its basis may be the same as contrast adaptation. At short SOA's, monocular and binocular masking data apparently reflect a mixture of this phase-independent suppression and phase-selective facilitation.

Contrast Sensitivity↗
PubMed1994

Spatial-frequency specific contrast gain and flicker masking of human transient VEP.

We studied the effects of grating contrast and luminance-flicker masking on the early waves of human visually evoked potentials (VEPs) recorded at the onset-offset of sinusoidal gratings of varying spatial frequencies (SFs). At high SFs, the response waveform was simple and VEP was dominated by a negative wave (N110). At low SFs, several positive-negative deflections were recorded, the earliest dominating wave being positive (P90). The amplitude of P90 was saturated at a contrast of about 0.1 and it was attenuated by flicker masking. Masking involved to a lesser extent the waves following P90. It was weaker at the flicker frequency of 5 Hz than at 10 and 20 Hz. No flicker masking was found at SFs higher than 2-4 c/deg. At medium and high SFs, VEPs were obtained at higher contrast levels. No saturation (max contrast tested 0.5) and no flicker masking of N110 were observed. These results suggest that the early VEP components recorded at low and high SFs are related to different types of neuronal activity. Correlation between VEP properties and properties of magnocellular and parvocellular pathways is considered with an emphasis on recent morphological data about the human retina.

Adolescent↗
PubMed1995

Spatial frequency channels in experimentally strabismic monkeys revealed by oblique masking.

Although the spatial vision deficits of human strabismic amblyopes have been well documented, surprisingly little is known about the mechanisms underlying their visual performance. In an effort to reveal the structure underlying the spatial vision deficits associated with strabismic amblyopia, we measured the performance of monkeys (Macaca nemestrina) with experimental strabismus in a contrast detection task with oblique masks. The masks were two adjacent identical oblique sine-wave gratings modulated in space by a Gaussian envelope. The target stimulus was a vertically oriented Gabor patch that appeared superimposed on the center of either the left or the right mask. The animals were trained by operant methods to indicate the location of the target. We measured detection thresholds in each eye independently for a large number of test and mask spatial frequencies. For each test spatial frequency, detection thresholds were elevated in the presence of the mask. The threshold evaluations showed a peak for a particular spatial frequency that was typically similar to the test spatial frequency. This pattern of results is consistent with the idea that the tests are detected by a discrete number of channels tuned to a narrow range of spatial frequencies. The data from the deviated eyes did not appear qualitatively different from those of the fellow eyes, and could be accounted by the same number of channels in both eyes. Quantitative estimates of the channels' characteristics revealed that the channels derived from the deviated eyes' data were similar to those yielded by the fellow eyes, but showed a reduction in their sensitivity to contrast.

Amblyopia↗
PubMed1996

Spatial properties of filters underlying vernier acuity revealed by masking: evidence for collator mechanisms.

Models of vernier acuity based on the differential response of oriented filters receive support from the finding that vernier threshold elevation peaks for grating mask orientations which are slightly different from the orientation of the vernier bars. We replicate this effect using long, abutting vernier bars, and masks which possess gaps up to 22.5' wide (Experiments 1 and 3); a surprising result considering that vernier acuity improves little for bars longer than 10'. To account for this we suggest the involvement of elongated mechanisms (referred to as collators or collectors) that "integrate" responses of numerous smaller filters along the axis of their common orientation. The collator model explains patterns of threshold elevation obtained with a variety of mask-vernier configurations. In particular, the model predicts that masks located midway between separated vernier bars will interfere with integrative processes occurring over the entire region encompassing both bars (Experiment 2). In confirmation of this prediction we find that centrally placed masks produce significant orientation-specific threshold elevation. In suggesting a contribution to vernier acuity from integrative mechanisms, our results, along with others, emphasize the importance of global processes in vernier acuity.

Filtration↗
PubMed1990

Neural representation of sound amplitude in the auditory cortex: effects of noise masking.

Single auditory cortical neurons express their sensitivity to the amplitude of a preferred-frequency tone pulse as either a monotonic, saturating intensity profile or as a non-monotonic, bell-shaped intensity function. In the presence of continuous, wideband noise masking, the tone intensity profile is displaced toward higher tone levels. The magnitude of the tone threshold adjustments brought about by increments in noise level very closely match the elevations in noise amplitude. The mechanisms underlying the threshold adjustments likely include neural adaptation. This is because the tone threshold shifts seen in the spike count data are paralleled by spike latency data, and because recovery of tonal sensitivity following noise offset proceeds in a negatively-accelerating fashion. In some instances, the slope of the masked tone intensity profile is greater than that for unmasked tones. For masked tone levels evoking submaximal responses, this has the consequence that cortical responses to masked tones are somewhat more salient than those for unmasked tones of comparable suprathreshold level. These observations bolster our understanding of the psychophysics of noise-masking in normal listeners, and they provide a partial explanation of the difficulty shown by patients with temporal lobe lesions in discriminating signals in noise.

Animals↗