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At least 685 records · Page 38Linked to original sources
PubMed2004

Redesigned face mask improves "real life" aerosol delivery for Nebuchamber.

The currently available facemask interface for the Nebuchamber (N) valved-holding chamber (VHC) provides a very poor seal to the face, which, on average, decreases the aerosol dose and was previously shown to increase the variability of aerosol delivery. The efficiency of a redesigned mask (RD) for the Nebuchamber with a potentially better seal was compared to the standard mask (SM) supplied with the N in a randomized real-life crossover clinical trial. Twenty children (mean age, 26 +/- 10 months) were randomized to use the Nebuchamber for 1 week with the old mask and then for another week with the newer mask, and vice versa. Filters, changed daily, inserted between the mask and the VHC, trapped the delivered drug (budesonide). The dose of budesonide was quantified by high-performance liquid chromatography (HPLC). Use of the redesigned mask improved aerosol delivery to the filter by 30%, compared to the SM (mean 28.1 +/- 7.7% of nominal dose with RD vs. 21.6 +/- 9.6% with SM, P = 0.017). The relatively high within-subject variability in aerosol delivery (36-38%) did not change, however. Facemasks are arguably the most important determinants of aerosol delivery. The newly developed RD for the Nebuchamber proved to be considerably more efficient than the SM for aerosol delivery to young children. Patient-related factors may be more important with respect to the variability observed.

Asthma↗
PubMed1996

Cricoid pressure impedes positioning and ventilation through the laryngeal mask airway.

PURPOSE: To assess the effect of cricoid pressure on the positioning of and ventilation through the laryngeal mask airway (LMA). METHODS: In a double-blind, randomized design, the LMA was inserted with (CP[+] group, n = 20) or without double-handed cricoid pressure (CP[-] group, n = 20). Ventilation through the LMA was assessed by measuring expiratory tidal volume and judged as adequate when a mean expiratory tidal volume of > or = 10 ml.kg-1 could be obtained. The LMA position was examined by fibreoscopy. The position of the mask relative to the cricoid cartilage and the cervical spine was radiologically examined (n = 10 in each group). RESULTS: Ventilation was adequate in all patients in the CP[-] group but in only five patients (25%) of the CP[+] group (P < 0.001). The glottis was visible fibreoptically below the mask aperture in all patients in the CP[-] group, but in only three patients in the CP[+] group (P < 0.001). Fibreoscopy showed that the mask was not inserted far enough in the remaining 17 patients of the CP[+] group. The reason for unsuccessful ventilation in the CP[+] group was excessive gas leakage (n = 2) and/or partial or complete airway obstruction (n = 13), which was noted fibreoptically. The radiographs showed that the tip of the mask in the CP[-] group was located below the level of the cricoid cartilage (C6 or C7 vertebra). The mask tip in the CP[+] group was above this level (C4 or C5 vertebra) (P < 0.01). CONCLUSION: Cricoid pressure impedes positioning of and ventilation through the LMA.

Adult↗
PubMed2002

[Preoxygenation with the NasOral((R)) system or the standard face mask?].

INTRODUCTION: Adequate preoxygenation of patients before onset of apnea for orotracheal intubation is of major importance in general anaesthesia. Various preoxygenation techniques are available but a face mask providing an oxygen supply via the circle absorber system of a mechanical respirator is most frequently used. Recently, a new device for preoxygenation - the NasOral((R)) system - has become available. The aim of the present study was to compare the efficacy of intrapulmonary oxygen storage with either the NasOral((R)) device or the standard face mask. METHODS: After informed and written consent and ethics committee approval was obtained, 40 elective patients (ASA I and II) undergoing surgical procedures of the neck and mouth area, were enrolled in this randomized, prospective study. In group A ( n=20), preoxygenation was performed using the NasOral((R)) system. Patients inhaled 100% oxygen through the nose and exhaled orally through unidirectional valves. In group B ( n=20), a conventional face mask with an O(2) flow of 15 l/min and an open airway pressure release valve was used for preoxygenation. In both groups preoxygenation lasted for 2.5 min. Induction of general anaesthesia was performed in a standardized manner. After intubation patients were not ventilated until the O(2) saturation in pulse oximetry (psaO(2)) dropped to 95%. This time of apnea was recorded in both groups and we determined the hemoglobin concentration (cHb) after beginning of ventilation. RESULTS: There were no significant differences with regard to demographic data and cHb. Time of apnea leading to a O(2) saturation of 95% was 6.0+/-2.1 min in group A and 6.3+/-2.1 min in group B (mean+/-SD, p>0.05). CONCLUSIONS: Both the NasOral((R)) system and the face mask are effective for intrapulmonary oxygen storage. In both systems the O(2) flow has to be adequately high and the masks have to be held tightly in order to avoid any contamination of the inhaled oxygen with nitrogen. Due to its unidirectional flow, the NasOral((R)) system additionally requires the patient to be cooperative. As the NasOral((R)) system is more expensive and has no clinical advantages without apneic oxygenation, we prefer the standard face mask for patient preoxygenation.

Adolescent↗
PubMed1996

[Intraoperative airway obstruction during use of a laryngeal mask. A case report and fiber optic findings].

Laryngeal obstruction is a challenging complication during anaesthesia with a face mask or laryngeal mask and is due to insufficient analgesia in most cases. However, with a laryngeal mask in place it must be differentiated whether the airway obstruction is caused by the laryngeal mask itself or by other factors. Knowledge of the pathophysiology of the laryngeal closure and experience with the use of the laryngeal mask are essential for adequate treatment. Not the removal of a correctly inserted laryngeal mask which initially provided a satisfying airway, but the relaxation of laryngeal muscle activity by adequate anaesthesia is the first mandatory treatment if intraoperative airway obstruction occurs.

Adult↗
PubMed1997

[Effectiveness of partial and complete instrumental masking in chronic tinnitus. Studies with reference to retraining therapy].

Jastreboff und Hazell [9] developed a neurophysiological approach to tinnitus perception, including the important role of the central nervous system in the maintenance and intrusiveness of tinnitus. They introduced tinnitus-retraining therapy, consisting of four different strategies: (1) directive and person-centered counseling; (2) hearing aids and/or noise generators and/or environmental sounds; (3) psychological therapy; (4) adjacent therapies. Tinnitus should not be masked as with a tinnitus-masker, but must be able to be heard in addition to the noise! A noise generator or hearing aid should be worn at least 6-8 h per day over a period of up to 18 months. In additions several clinical visits are required in order to reinforce the counseling. The actual results show complete tinnitus remission for about 20-30% and partial remission for 50-60% of the patients [6]. We report on a retrospective study in patients wearing hearing aids or tinnitus-maskers over a period of 3 years. We compared the results of patients using partial tinnitus masking to those using complete masking. The tinnitus-related and general psychological complaints were acquired by the 52-item tinnitus questionnaire developed by Hallam et al. [4] and modified by Goebel and Hiller [3]. To describe the dimensions of tinnitus-related distress the scales are labelled emotional distress, cognitive distress, emotional and cognitive distress, intrusiveness, auditory perceptual difficulties, sleep disturbance and somatic complaints. Positive changes for the global tinnitus questionnaire score of more than 10 points are significant in the dimensions of tinnitus-related distress and are described as partial tinnitus-reduction. The group with partial masking effects can be compared to those performing retraining therapy to day because directive and personal centered counseling were integrated for all patients. Patients reporting partial masking effects through their aids (hearing aid or noise generator) showed more effective treatment results (reduced or disappeared tinnitus) than those using complete masking effects (P < 0.05). The reported results are improved by current investigations in Germany showing about 20-30% tinnitus remission and 50-60% significant reduction after 1 year of treatment [1]. Further scientific investigations must be carried out to evaluate the appropriateness and effectiveness of the retraining therapy and with regard to unique quality standards.

Cognitive Behavioral Therapy↗
PubMed2004

Spatio-temporal luminance contrast sensitivity and visual backward masking in schizophrenia.

The aim of two experiments was to investigate the relationship between spatio-temporal contrast sensitivity and visual backward masking in normal observers and in subgroups with positive or negative symptoms in schizophrenia. Experiment 1 measured contrast sensitivity for stationary and counterphase-modulated sinusoidal gratings at four spatial (0.5, 2.0, 4.0, 8.0 cycles/degree) and four temporal frequencies (0, 4.0, 8.0, 16.0 Hz). The results showed that there were no differences in spatio-temporal contrast sensitivity between the control and positive-symptom group, and in comparison with these groups, contrast sensitivity was significantly lower at all spatial and temporal frequencies in the negative-symptom group. Experiment 2 measured the visibility of a Landolt C target with a constant target stimulus duration of 4.0 ms followed by a 150-ms backward mask, which was presented at 12 stimulus onset asynchronies from 0 to 110 ms in the same groups of observers. Consistent with the findings of the previous experiment, there were no significant differences in backward masking between the control and positive-symptom group, and in comparison with these groups, visual backward masking was significantly higher at all stimulus onset asynchronies from 40 to 110 ms in the negative-symptom group. The present findings show that there were no significant differences in contrast sensitivity and in backward masking between normal observers and a group with positive symptoms in schizophrenia. It was concluded that the reduction in contrast sensitivity for low spatial frequency counterphase flicker in the negative-symptom group is consistent with a reduction in the 'contrast gain control' mechanism of magnocellular channels, and that the reduction in contrast sensitivity for medium and high stationary gratings is consistent with a disorder in parvocellular channels. It was proposed that a disorder in magnocellular channels in the negative-symptom group may enforce a reliance on parvocellular channels that results in longer temporal summation and visible persistence, slower visual processing of single target stimuli at threshold and higher levels of sensory integration, and backward masking when multiple stimuli are presented rapidly in time.

Adult↗
PubMed2004

Disruption of masking by hypothalamic lesions in Syrian hamsters.

Negative masking of locomotor activity by light in nocturnal rodents is mediated by a non-image-forming irradiance-detection system in the retina. Structures receiving input from this system potentially contribute to the masking response. The suprachiasmatic nucleus (SCN) regulates locomotor activity and receives dense innervation from the irradiance-detection system via the retinohypothalamic tract, but its role in masking is unclear. We studied masking in adult Syrian hamsters (Mesocricetus auratus) with electrolytic lesions directed at the SCN. Hamsters were exposed to a 3.5:3.5 ultradian light/dark cycle and their wheel-running activity was monitored. Intact hamsters showed robust masking, expressing less than 20% of their activity in the light even though light and dark occurred equally during their active times. In contrast, hamsters with lesions showed, on average, as much activity in the light as in the dark. Tracing of retinal projections using cholera toxin beta subunit showed that the lesions damaged retinal projections to the SCN and to the adjacent subparaventricular zone. Retinal innervation outside the hypothalamus was not obviously affected by the lesions. Our results indicate that retinohypothalamic projections, and the targets of these projections, to the SCN and/or adjacent hypothalamic areas play an important role in masking.

Activity Cycles↗
PubMed2003

Estimates of human cochlear tuning at low levels using forward and simultaneous masking.

Auditory filter shapes were derived from psychophysical measurements in eight normal-hearing listeners using a variant of the notched-noise method for brief signals in forward and simultaneous masking. Signal frequencies of 1, 2, 4, 6, and 8 kHz were tested. The signal level was fixed at 10 dB above absolute threshold in the forward-masking conditions and fixed at either 10 or 35 dB above absolute threshold in the simultaneous-masking conditions. The results show that filter equivalent rectangular bandwidths (ERBs) are substantially narrower in forward masking than has been found in previous studies using simultaneous masking. Furthermore, in contrast to earlier studies, the sharpness of tuning doubles over the range of frequencies tested, giving Q(ERB) values of about 10 and 20 at signal frequencies of 1 and 8 kHz, respectively. It is argued that the new estimates of auditory filter bandwidth provide a more accurate estimate of human cochlear tuning at low levels than earlier estimates using simultaneous masking at higher levels, and that they are therefore more suitable for comparison to cochlear tuning data from other species. The data may also prove helpful in defining the parameters for nonlinear models of human cochlear processing.

Acoustic Stimulation↗
PubMed1994

The spatial tuning of chromatic mechanisms identified by simultaneous masking.

We have investigated the spatial transfer characteristics of the mechanisms sensitive to color in the human visual system using a method of simultaneous spatial masking with isoluminant chromatic stimuli. The test stimuli were Gaussian enveloped red-green gratings of three spatial frequencies in the lowpass region of the color domain (0.25, 0.5 and 1 c/deg). The masking stimuli were red-green gratings at the orientation and phase of the test, presented at the same spatial frequency, and at +/- 1, and +/- 2 octaves from its spatial frequency. We obtained test contrast threshold as a function of mask contrast for a wide range of mask contrasts (TvC functions). Tuning functions were derived from linear fits of the masking data, by taking the mask contrast that doubled the minimum test threshold at each spatial frequency. Chromatic tuning functions show bandpass characteristics for all test spatial frequencies examined with an average full bandwidth at half-height of 2.6 octaves, which is similar to the luminance bandwidths obtained under comparable conditions. Thus, our results suggest that the color contrast sensitivity function is the upper envelope of a range of bandpass mechanisms whose peaks extend to very low spatial frequencies.

Color Perception↗
PubMed1993

Aerosol penetration and leakage characteristics of masks used in the health care industry.

BACKGROUND: Historically, surgical masks have been worn to protect patients from being infected by large, pathogen-containing aerosol droplets emitted by health care personnel. Today, emphasis has shifted from solely protecting the patient to protecting the health care worker as well. As a result of new procedures used in operating rooms and clinical areas, aerosolized hazardous agents in the submicrometer size range are being produced, posing a potential threat to health care workers. METHODS: Eight surgical masks were tested for aerosol particle penetration through their filter media and through induced face-seal leaks. RESULTS: The percentage of filter penetration ranged from 20% to nearly 100% for submicrometer-sized particles. In comparison, a dust-mist-fume respirator used in industrial settings had significantly less penetration through its filter medium. When the surgical masks had artificially induced face-seal leaks, the concentration of submicrometer-sized particles inside the mask increased slightly; in contrast, the more protective dust-mist-fume respirator showed a fourfold increase in aerosol penetration into the mask with an artificial leak 4 mm in diameter. CONCLUSION: We conclude that the protection provided by surgical masks may be insufficient in environments containing potentially hazardous submicrometer-sized aerosols.

Aerosols↗
PubMed1987

Efficacy of face masks in preventing inhalation of airborne contaminants.

Use of surgical face masks has been advocated to protect clinicians from inhalation of aerosols containing organic and inorganic particulates. This study examined the ability of a 22 micron tracer particle to bypass the filtering capability of face mask material by peripheral marginal leakage of inspired air. For two popularly used face masks taped to a facial moulage, recovery of the tracer particle by an in vitro system was very low. When the masks were placed in the manner in which the product is commonly worn, however, significantly higher numbers of particles were recovered. Passage of inspired air around the periphery of two types of face masks appears to circumvent the masks' ability to screen airborne contaminants.

Aerosols↗
PubMed1981

Patterns of residual masking.

"Residual masking' was measured in a tonal forward masking paradigm. In one experiment, psychophysical tuning curves and masking patterns were obtained at several frequencies and levels for a fixed masker-probe time delay. In a second experiment, tuning curves and masking patterns were measured as masker-probe time delay was varied. Our results indicate that tuning curves and masking patterns are sharpest at low levels, high frequencies and brief masker-probe time delays. In addition, we observed that masked probe threshold returned to the level of unmasked probe threshold at approximately the same post-masker time regardless of masker level or the probe-to-masker frequency relationship. These findings suggest that frequency, level and time delay all affect the degree of frequency selectivity observed with these measures.

Adult↗
PubMed1984

Frequency threshold curves and simultaneous masking functions in high-threshold, broadly-tuned, fibres of the guinea pig auditory nerve.

Tuning curves for simultaneous masking were measured electrophysiologically, in single fibres of the auditory nerve. The recordings were made in guinea pigs with cochlear hearing losses. The masking paradigm was an analogy of that used in the determination of psychophysical tuning curves in man. Below the probe frequency, the slope of the masking function was similar to that of the frequency-threshold curve. Here, changes in the slope of the frequency-threshold curve with hearing loss were closely mirrored by changes in the slope of the masking function. Above the probe frequency, however, the masking function for low-threshold fibres had a shallower slope than the frequency-threshold curve. When the high-frequency slope of the frequency-threshold curve became shallower with hearing loss, the changes were not mirrored in the masking function, until the threshold was raised to 70-80 dB SPL. The results are discussed in terms of the influence of cochlear nonlinearity on frequency resolution, and the vulnerability of the nonlinearity.

Animals↗
PubMed1984

The microstructure of quiet and masked thresholds.

Factors leading to the microstructure of the audiogram (a constant pattern of threshold maxima and minima as a function of frequency) are shown to influence masked thresholds, changing the shape of masking functions when both constant and variable tonal maskers are used. Simultaneous masking with broadband noise gradually reduces the difference between threshold maxima and minima until no further differences can be seen when masked thresholds are above 40-50 dB SPL. Nonsimultaneous masking with broadband noise reveals a changed microstructure when thresholds are elevated above 30-40 dB SPL. Thus in both simultaneous and nonsimultaneous masking the rate of threshold growth with increasing masker level is different for tones from threshold minima than for tones from threshold maxima. These psychophysical measures are related to measures of evoked cochlear emissions and the results are discussed in terms of the implications for understanding the cochlear mechanisms responsible for the microstructure and for the interpretation of psychophysical measures with low level stimuli.

Audiometry, Pure-Tone↗
PubMed1986

Temporal effects in simultaneous pure-tone masking: effects of signal frequency, masker/signal frequency ratio, and masker level.

The effect of the temporal relationship between a pure-tone masker and a pure-tone signal in simultaneous masking was investigated in three experiments. The experiments extend previous work by: studying the temporal effect over a wide range of signal frequencies, studying the change in masking over time for several masker/signal frequency ratios, and studying the growth of masking for a brief signal at different temporal positions within a longer duration masker. In the first experiment, threshold was measured for a 20-ms signal temporally centered in a masker whose duration ranged from 20 ms to continuous. Signal frequency (fs) was 0.5, 1.0, 2.0, 4.0, or 8.0 kHz; masker frequency (fm) was 1.2 fs. For all signal frequencies, the amount of masking decreased as masker duration increased. In the second experiment, threshold was measured for a 20-ms, 1.0-kHz signal as a function of the signal's temporal position within a 400-ms masker whose frequency ranged from 1.0 to 1.25 kHz. For all but the 1.0-kHz masker, for which threshold was almost independent of the signal's temporal position, threshold decreased as signal onset was delayed relative to masker onset, but then increased slightly as the signal approached masker offset. In the final experiment, growth-of-masking functions were measured for a 20-ms, 1.0-kHz signal positioned at the beginning, at the temporal center, or at the end of a 400-ms masker whose frequency was 1.20 or 1.25 kHz. The masking functions generally were steepest for a signal at the onset of the masker and, for a given temporal position, steepest for the 1.20-kHz masker.

Adaptation, Physiological↗
PubMed1993

Simultaneous masking in newborn chickens.

Simultaneous masking was used to investigate the development of frequency analysis in newborn animals. The ability of young chickens to detect a tone in the presence of a second tone was measured. In the first experiment data were collected with a 500-Hz masker presented at 15 or 25 dB above absolute threshold. Signals to be detected varied up to an octave from the masker (+/- 1/9, +/- 2/9, +/- 1/3, +/- 2/3, and -1 octave). Receiver operating characteristics (ROCs) were constructed from delays in ongoing peeps that occur when chicks detect the presence of the signal over the masker. Psychometric functions were fit by probit analysis using areas under these ROCs. Amounts of masking were estimated by the degree to which psychometric functions were shifted toward the right by the presence of the masker. There is no developmental change in these masking patterns, corroborating recent data from human infants. Masking was shown in a second experiment to be similar at a higher frequency (given intensities corrected for improving absolute thresholds). In conclusion, masking patterns derived from chicks' peeps are like those from adult humans. Frequency analysis, as measured by simultaneous masking, appears to be mature in chickens at hatching.

Acoustic Stimulation↗
PubMedDate not supplied

Use of the laryngeal mask prior to definitive intubation in a difficult airway: a case report.

The laryngeal mask, a relatively new airway adjunct, consists of a large tube with an inflatable shallow mask at its distal end which forms a seal around the glottic opening. We describe a case of a difficult intubation in the emergency department of an obese patient with microagnathia, a short bull neck, and a nasopharyngeal hemorrhage in which a laryngeal mask was used to temporarily manage the airway prior to definitive intubation. In difficult airway cases where it is impossible to ventilate the patient by face mask or intubate the trachea, ventilation with the laryngeal mask may be an alternative to transtracheal jet ventilation or cricothyrotomy. The laryngeal mask may be useful in managing the difficult airway provided that the risks of an inadequate seal, obstruction, coughing and laryngospasm, and lack of protection from aspiration are recognized.

Airway Obstruction↗
PubMed2006

Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks?

BACKGROUND: Respiratory protection devices are used to protect the wearers from inhaling particles suspended in the air. Filtering face piece respirators are usually tested utilizing nonbiologic particles, whereas their use often aims at reducing exposure to biologic aerosols, including infectious agents such as viruses and bacteria. METHODS: The performance of 2 types of N95 half-mask, filtering face piece respirators and 2 types of surgical masks were determined. The collection efficiency of these respiratory protection devices was investigated using MS2 virus (a nonharmful simulant of several pathogens). The virions were detected in the particle size range of 10 to 80 nm. RESULTS: The results indicate that the penetration of virions through the National Institute for Occupational Safety and Health (NIOSH)-certified N95 respirators can exceed an expected level of 5%. As anticipated, the tested surgical masks showed a much higher particle penetration because they are known to be less efficient than the N95 respirators. The 2 surgical masks, which originated from the same manufacturer, showed tremendously different penetration levels of the MS2 virions: 20.5% and 84.5%, respectively, at an inhalation flow rate of 85 L/min. CONCLUSION: The N95 filtering face piece respirators may not provide the expected protection level against small virions. Some surgical masks may let a significant fraction of airborne viruses penetrate through their filters, providing very low protection against aerosolized infectious agents in the size range of 10 to 80 nm. It should be noted that the surgical masks are primarily designed to protect the environment from the wearer, whereas the respirators are supposed to protect the wearer from the environment.

Air Microbiology↗