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At least 505 records · Page 28Linked to original sources
PubMed1994

CPAP therapy via oronasal mask for obstructive sleep apnea.

STUDY OBJECTIVE: To determine the effectiveness of oronasal masks for positive pressure therapy in alleviating obstructive sleep apnea (OSA). METHODS AND PROCEDURES: Polysomnographic records of all 245 patients with OSA who underwent therapeutic trials of either continuous positive airway pressure (CPAP) or bilevel positive airway pressure between January 1991 and December 1992 were reviewed. Thirty patients who had been prescribed positive pressure therapy employing an oronasal mask were identified. Two patients known to be successfully treated with CPAP via oronasal mask underwent repeat polysomnography. The initial portion of the study was a diagnostic evaluation during which the patients were untreated. During the second portion of the study, both patients used CPAP via an oronasal mask while wearing a mouthpiece designed to maintain oral patency. RESULTS: The 30 patients with OSA who were identified in this study had significant amelioration of OSA while receiving positive pressure therapy via oronasal mask compared with the baseline, diagnostic polysomnogram (apnea index: 55.3 +/- 36.9-->1.6 +/- 3.7, p < 0.001; hypopnea index: 21.2 +/- 20-->2.7 +/- 4.9, p < 0.001; nadir of SaO2: 72.5 +/- 13.9-->87.1 +/- 4.3, p < 0.001, mean +/- SD). Improvement of OSA did not depend on maintenance of a closed mouth, as evidenced by elimination of sleep-disordered breathing in the two patients receiving positive pressure via oronasal mask while wearing a mouthpiece to keep the mouth open. CONCLUSION: Oronasal masks are a viable alternative interface for alleviating OSA with positive pressure therapy in those patients who are unwilling or unable to tolerate conventional nasal interfaces. Although there were no adverse consequences associated with the use of oronasal masks in our patients, appropriate safety precautions should be taken to minimize the possibility of aspiration of gastric contents and avoid untoward sequelae due to positive pressure device failure.

Adult↗
PubMed1995

Management of pediatric acute hypoxemic respiratory insufficiency with bilevel positive pressure (BiPAP) nasal mask ventilation.

OBJECTIVES: To evaluate the efficacy and complications of noninvasive nasal mask bilevel continuous positive airway pressure ventilation in pediatric patients with hypoxemic respiratory insufficiency. DESIGN: Retrospective chart review. SETTING: Intensive care unit, university affiliated tertiary care children's hospital. PATIENTS AND METHODS: The study reviewed all patients admitted to the pediatric ICU with acute hypoxemic respiratory insufficiency who received bilevel noninvasive continuous nasal mask positive airway pressure delivered by a bilevel positive airway pressure system (BiPAP; Respironics Inc; Murrysville, Pa). RESULTS: Bilevel nasal mask positive pressure ventilation was utilized in 28 patients. Median patient age was 8 years (range, 4 to 204 months). The most common primary diagnosis was pneumonia. Nine patients demonstrated severe underlying neurologic disease or immunocompromise. Median duration of nasal mask ventilation was 72 h (range, 20 to 840 h). Clinical and laboratory variables immediately prior to bilevel nasal mask positive airway pressure and approximately 1 h after institution were evaluated. Respiratory rate decreased significantly with nasal mask ventilation (45 +/- 18 breaths per minute to 33 +/- 11, mean +/- SD, p < 0.001). Arterial blood gas PaO2 (71 +/- 13 mm Hg to 115 +/- 55), PaCO2, pulse oximetry saturation, and pH all improved significantly (p < 0.01). Using standard estimates for inspired oxygen, calculated alveolar-arterial gradients (271 +/- 157 to 117 +/- 65, p = 0.001), and PaO2/FIo2 ratios (141 +/- 54 to 280 +/- 146, p < 0.001), both improved significantly with nasal mask ventilation. Only 3 of 28 patients required intubation or reintubation. CONCLUSIONS: We conclude that noninvasive nasal positive pressure mask ventilation can be safely and effectively used in pediatric patients to improve oxygenation in mild to moderate hypoxemic respiratory insufficiency. It may be particularly useful in patients whose underlying condition warrants avoidance of intubation.

Acute Disease↗
PubMed2002

Modulation of backward pattern masking by focal visual attention.

The effect of focal visual attention on backward pattern masking was investigated using an orientation discrimination task. The results show that attention reduces primarily the effect of interruption masking, the later component of pattern masking, which occurs when the delay between the target and mask onset is about 50-150 ms. The strongest spatial cueing effect, i.e. the strongest reduction of the orientation discrimination threshold due to focal attention, was observed at intermediate (approximately 100 ms) target-to-mask stimulus onset asynchrony (SOA). There was a weak effect of cueing at shorter SOAs, and no or a very weak attentional effect was present at longer target-to-mask SOAs, where the pattern masking effect is absent. The dynamics of attentional modulation of backward pattern masking correlates closely with the dynamics of the attentional modulation of neuronal responses in the early visual cortex.

Attention↗
PubMed1980

Pure-tone masking of tinnitus.

Experiments were initiated to determine the frequency most closely associated with a continuous atonal tinnitus reported by a listener with a sloping sensorineural hearing loss in his left ear. The procedure was modeled after that used to obtain a psychophysical tuning curve. Pure tones presented binaurally and monaurally between 521 and 3629 Hz were adjusted in level by the listener to just mask his tinnitus, which functioned as a signal. Masking curves for binaural and monaural masker presentation were found to be of similar shape but they varied in terms of absolute level, variability of estimates, and with regard to fine detail of the curves. The magnitude of the tinnitus as also estimated by a loudness match with a pure tone to the opposite ear. The masking levels required to mask the tinnitus were found to be consistent with those reported necessary to mask the equally loud pure tone. These findings are consistent with Langenbeck's [1953, 1965] hypothesis that tinnitus arising from the inner ear should be masked in a manner similar to an externally presented tone at the same effective level. Information derived from the masking of tinnitus by pure tones may be useful in fitting tinnitus-masking devices and also for diagnosing the site of lesion associated with tinnitus.

Adult↗
PubMed1986

Spread of masking in normal subjects and in subjects with high-frequency hearing loss.

Upward spread of masking and remote masking were investigated in 4 subjects with closely matched high-frequency hearing losses. Masked thresholds in the presence of a high-frequency or a low-frequency bandpass noise were obtained using an adaptive-threshold procedure. 'Abnormal' upward spread of masking existed for the impaired subjects at some test frequencies when compared to the masking predicted on the basis of normal masking results and hearing-impaired quiet thresholds. Remote masking thresholds were usually shifted to the same absolute levels for normal and hearing-impaired subjects. These results demonstrate that speech reception in noise for listeners with high-frequency hearing loss could be affected by spread of masking and levels of hearing loss.

Acoustic Stimulation↗
PubMed1990

Evoked-response tone-on-tone masking in the chinchilla: effect of masker frequency.

Tone-on-tone masking patterns were measured at 0.5, 1, and 4 kHz using the auditory-evoked response from the inferior colliculus of the chinchilla. Masking profiles obtained with a masking level of 30 dB SPL were relatively symmetrical; however, as masker level increased, masking spread toward the high frequencies, particularly with the 0.5-kHz masker. For masker frequencies of 1 and 4 kHz, a low-threshold notch was observed in the masking profile 2/3 of an octave above the frequency of the masker. The low-threshold notch may represent a response to the distortion tone 2F1-F2. The notch was absent in the 0.5-kHz masking profile. The masking profiles obtained with the evoked response are somewhat wider, but otherwise qualitatively similar to those measured psychophysically in humans. Thus, the evoked-response procedure may provide a convenient way of evaluating the spread of masking and the presence of distortion tones in difficult-to-test subjects.

Acoustic Stimulation↗
PubMedDate not supplied

Comparison of growth of masking functions and speech discrimination abilities in younger and older adults.

This study examined the possibility that age-related differences in speech discrimination abilities may reflect individual differences in the amount of masking and in the rate of growth of on- and off-frequency masking. Young (mean age = 26 years) and older (mean age = 60 years) adult listeners were selected, all of whom had hearing thresholds equal to or better than 30 dB HL at audiometric frequencies < or = 2000 Hz and equal or better than 40 dB HL at audiometric frequencies from 3000 to 6000 Hz. Listeners were tested on a consonant identification task in which nonsense words were presented in quiet, high-pass-filtered, low-pass-filtered and in wide-band noise. Despite their good hearing thresholds, the older listeners made significantly more errors in all four test conditions. Masked thresholds and growth of masking functions were obtained for all listeners at signal frequencies of 750, 1000, and 1500 Hz, in the presence of a one-third-octave band of noise centred at 1000 Hz, with four noise levels from 50 to 80 dB SPL. The older listeners had higher masked thresholds overall, when compared to younger listeners, even though their audiometric thresholds at these frequencies were within normal limits. However, the slope of the growth of masking functions at and above the masker frequency did not differ with age. These results show that older listeners show reduced speech discrimination abilities both in difficult listening conditions and in quiet, even when their pure-tone thresholds are within normal limits. Moreover, these effects cannot be attributed to differences in masked thresholds or in the rate of growth of masking.

Adult↗
PubMed1984

Derived acoustically evoked brainstem responses by means of narrow-band and notched-noise masking in normal-hearing subjects.

Derived acoustically evoked brainstem responses determined by narrow-band and notched-noise masking at 2000 Hz frequencies and below were investigated and compared with those obtained in the use of the common high-pass masking technique. With all three masking methods a dominant late wave Wa could be detected at less than or equal to 1 600 Hz centre frequencies of the derived band and this wave is typical of the excitation of the apical section of the cochlea. The latency of this wave increases when the centre frequency is decreased at a constant stimulation level. For a constant centre frequency of the derived band the latency of wave Wa increases when the stimulation level of the click and in parallel to that the masking level is decreased. Wave Wa could be found near the hearing threshold in all three masking methods. The notched-noise masking method offers major advantages provided that full masking of the frequency regions above and below the notch frequency range is carried out. A direct frequency-specific stimulation takes place and there is no need for subtracting one response from a second one. This reduces the investigation time and the memory capacity of the measuring device. The advantages and applicability of the notched-noise masking method have to be re-checked in patients with different frequency-dependent loss of hearing.

Adolescent↗
PubMed2002

Gestalt grouping and common onset masking.

A four-dot mask that surrounds and is presented simultaneously with a briefly presented target will reduce a person's ability to identity that target if the mask persists beyond target offset and attention is divided (Enns & Di Lollo, 1997, 2000). This masking effect, referred to as common onset masking, reflects reentrant processing in the visual system and can best be explained with a theory of object substitution (Di Lollo, Enns, & Rensink, 2000). In the present experiments, we investigated whether Gestalt grouping variables would influence the strength of common onset masking. The results indicated that (1) masking was impervious to grouping by form, similarity of color, position, luminance polarity, and common region and (2) masking increased with the number of elements in the masking display.

Humans↗
PubMed2002

The effect of smoking on sensory and attentional masking.

This study examined the influence of smoking on low-level sensory and higher level visual cognitive abilities. Three groups (nonsmokers, deprived smokers, and nondeprived smokers) of 22 observers were tested using a visual target discrimination task. To assess sensory and visual cognitive differences, a masking task developed by Enns and Di Lollo (1997) was used. In the task, the target was masked by either a contour mask (contour masking) or an object mask (attentional masking by object substitution). The strongest masking effects were found in the group of nondeprived smokers, for both sensory and attentional masking. This pattern of results as well as results in the deprived smokers indicated changes in transient visual processing channels due to the acute actions of nicotine, not mediated by withdrawal relief.

Adolescent↗
PubMed2001

Normalization models applied to orientation masking in the human infant.

Human infants can discriminate the orientation of lines within the first week after birth (Atkinson et al., 1988; Slater et al., 1988) but have immature orientation-selective pattern masking until after 6 months of age (Morrone and Burr, 1986). Here the development of orientation processing is further examined using a visual-evoked potential paradigm and normalization models of pattern masking. Contrast response functions were measured for 1 cycle per degree (cpd) gratings, counterphase-reversed in contrast at either 3.3 or 5.5 Hz. A second 1 cpd, 20% contrast, 8.3 Hz grating of either the same or orthogonal orientation was added as a mask. Evoked responses associated with the test grating, the mask, and intermodulation between the two were individually extracted using spectral analysis of the scalp-recorded EEG. Adults exhibited orientation selectivity in the masking of their test component responses and in nonlinear intermodulation between the test and mask stimuli. Infants <5 months old, however, demonstrated nonselective masking or a reversed selectivity in their responses to the test component, with adult-like orientation selectivity in their intermodulation responses. Within the context of a normalization model of pattern masking, the results are consistent with the existence of oriented filters early in life the responses of which are normalized immaturely until approximately 5 months of age.

Adult↗
PubMed2006

Risk of blood splashes to masks and goggles during cesarean section.

INTRODUCTION: The study arose out of concern about the transmission of infectious diseases through mucocutaneous contact with blood and body fluids. The purpose was to identify the risk of blood splashes to masks and goggles during cesarean section. MATERIAL/METHODS: The prospective study spanned 6 months between January and June 1998 to determine the incidence of blood splashes to the masks and goggles of surgeons, assistants, and scrub nurses. All the doctors and scrub nurses who participated in surgery were requested to wear masks and goggles for all the cesarean section cases during the study period. At the end of surgery, the surgeon examined all the masks and goggles for obvious blood splashes and documented these in a data sheet. RESULTS: There were 144 cases of cesarean section performed during the period, of which 13.2% (19) were elective and 86.8% (125) were emergencies. 74.3% (107) of the patients registered for antenatal care and delivered in the institution, while 25.7% (37) cases were not booked but admitted for delivery. The mean age of the parturient and parity were 27.4+/-2.8 years and 5.8+/-2.4, respectively. The rate of blood splashes was 62.5% on the surgeons' masks, 63.2% on surgeons' goggles, 35.4% on assistants' masks, 38.9% on assistants' goggles, 11.1% on scrub nurses' masks, and 16.0% on scrub nurses' goggles. CONCLUSIONS: We therefore recommend the use of masks and protective eye wear as part of routine surgical attire to avoid body fluid contamination that can result in acquiring infectious diseases.

Adult↗
PubMed2006

Different forward masking patterns of sustained noise burst and segmental noise burst in the inferior collicular neurons of the mouse.

Although there has been a growing body of literature showing the neural correlation of forward masking caused by a pure tone masker in the auditory neurons, relative few studies have addressed the description of how the forward masking caused by a noise burst, especially a sequence of noise burst, is transformed into neuronal representation in the central auditory system. Using a noise forward masking paradigm under free field stimuli conditions, this in vivo study was devoted to exploring it in the inferior collicular (IC) neurons of the mouse (Mus musculus KM). A total of 96 IC neurons were recorded. Rate-intensity functions (RIFs) with and without the presentation of masker, sustained noise burst (SNB) or segmental noise burst (SGNB), were measured in 51 neurons. We found that the relative masker intensities were distributed over a wide range between 21 dB below the minimum threshold (MT) and 19 dB above the MT of the corresponding probe tone. The masking effect of the SGNB on firing rate in nearly half of neurons (type I, 45.10%) was stronger than that of the SNB (P<0.001), whereas in a smaller fraction of neurons (type III, 17.65%), it was weaker than that of the SNB (P<0.001). There was no significant difference in masking effect between the SNB and SGNB in type II neurons (37.25%, P>0.05). Irrespective of type I or type III neurons, the inhibitory effects of both kinds of maskers were all greater at lower probe intensities but decreased significantly with the increase of probe intensity (P<0.001). Interestingly, as the probe intensity increased, the difference of masking effect between the SNB and SGNB disappeared (P>0.05). In addition, we observed that temporal masking pattern could be transformed when the masker was changed from the SNB to SGNB. The main type of this transformation was from early-inhibition to proportional-inhibition pattern (53.85%, 7/13). Our data provide the evidence that the inhibitory effects of these two maskers have differential weights over time and intensity domains of the IC neurons responding to a pure tone. This suggests that the forward masking of noise is by no means the source of simply suppression in neuronal firing rate. There might be a few of active neural modulating ways in which the coding of temporal acoustical information can be operated.

Acoustic Stimulation↗
PubMed1991

[The use of the laryngeal mask--a practical method?].

In 1985 Brain et al. published their first experience with the laryngeal mask, developed by themselves. With this mask it is possible to seal the larynx and ventilate a patient during anesthesia without endotracheal intubation. Meanwhile, further reports of successful use have been published, especially in Great Britain. We decided to investigate this new anesthetic device. In 15 patients (ASA groups I and II) undergoing elective operations in the supine position the laryngeal mask was inserted after induction of anesthesia with propofol and alfentanil (Fig. 1). Positioning of the laryngeal mask was carried out as described by Brain. In all patients the laryngeal masks could be inserted without any problems, manual ventilation of the patient was performed immediately, and ventilating pressures never exceeded 15 cm H2O. We observed neither complications related to airway control nor technical problems. Cardiovascular parameters and arterial oxygen saturations were always in the normal range (Fig. 2). In 3 patients quick movements of the head were carried out during repositioning of a fractured zygomatic arch, but no complications due to a possible changed position of the laryngeal mask occurred. Postoperatively two patients reported airway complaints such as sore throat. Our investigation confirmed the previously described advantages of the laryngeal mask. We consider its use to be especially indicated in general anesthesia for short surgical or diagnostic procedures or if specific complications of endotracheal intubation should be avoided. A critical aspect in the use of the laryngeal mask is the fact that there is no complete isolation of the trachea and, therefore, an insufflation of the stomach or aspiration could occur, especially during critical situations (e.g. bronchospasms).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesiology↗
PubMed1990

[The double mask].

While the consequences of occupational exposure to anesthetic gases and volatile agents on morbidity in operating room staff are controversial (survey in Swiss investigations show a distinct correlation with subjective complaints, e.g. tiredness and headache on the day of exposure (Table 1). In Sweden, rigorous control of occupational exposure to anesthetic gases has prompted development of various scavenging systems, among which the double mask (Fig. 1) is the latest and most advanced. During mask anesthesia, escaping anesthetic gases are evacuated at the point of leakage via a thin slot between a flexible silicone inner mask and a rigid plastic outer mask. A small plate in the mask produces turbulence in the otherwise laminar flow of anesthetic gases, thus reducing the speed of gas leakage. A silicone chamber is mounted on the mask and connected to a fan, requiring a flow of 35 m3/h for optimal function. This chamber does, however, also associate the system with two practical problems: the system with its evacuation tube is heavier to hold than conventional masks, and it is associated with increased dead-space that is only partly minimized by a modification of the Y-connector. While the handling is largely a matter of routine and the weight of the system is minimized when the evacuation tube is arranged to draw slightly upward, the increased dead space may reduce the practicality of the double mask in infants.

Gas Scavengers↗
PubMed1980

Developmental differences in visual backward masking.

2 experiments were conducted to examine developmental differences in visual recognition masking when verbal encoding and response demands are minimized. Precautions were taken in the experiments to ensure the implication of the central visual system in the backward-masking component of each experiment. Sampling was conducted across the kindergarten, third-grade, sixth-grade, and college levels. In the first experiment, no-mask target recognition was set at 100% correct. The results indicated systematic grade differences in backward masking such that older children and adults showed more rapid recognition improvement across stimulus onset asynchronies (SOAs) than did young subjects (i.e., a grade x SOA interaction). Although this finding could be interpreted to suggest developmental differences in the rate of visual information processing, such an interpretation would be inappropriate. The problem is that the masking functions for all grade levels reach asymptote at 100% correct (i.e., a ceiling effect). Thus, the grade X SOA interaction could have been produced for reasons other than rate-of-processing differences (e.g., developmental differences in the quality of stimulus reception). Thus, experiment 2 was designed to assess this possibility by evaluating developmental differences in visual backward masking when no-mask target recognition was set at the 75% level for the grades sampled. The grade x SOA interaction observed in experiment 1 was not observed in experiment 2. The results from the studies indicate that, when the ceiling effects in no-mask target recognition are removed, the visual information processing rates for children and adults can be considered equivalent.

Adolescent↗
PubMed1994

[Behavioral effect of a subliminal (masked) signal].

Three experiments investigated the influence of a non-consciously perceived visual signal on motor reaction time when subjects were exposed to a stimulus contingency according to the general rules of the Pavlovian conditioning procedure. Conscious perception was prevented by meta-contrast backward masking. A total of 128 adult subjects had to discriminate between two imperative stimuli by means of a choice reaction. Each imperative stimulus was signalled by a different brief figural stimulus (signal). In Experiment 1, the signal was not masked during the training period but was masked during the subsequent test period. The subjects were unable to report the stimulus-contingency to which they were exposed during the training period. Inspite of masking, the signal remained efficient, i.e., reaction time increased when the stimulus-contingency was inverted. In Experiment 2, the signal was masked during the training period but not during the test period. There was no evidence that the masked signal influenced reaction time. In Experiment 3, during the training period, the signal was followed by a distractor instead of the mask. As a result, the distractor prevented the signal from becoming an efficient stimulus similar to the mask in Experiment 2. The data suggest that preattentive (non-conscious) processing is sufficient for a previously learned signal to influence reaction time. On the other hand, focussed attention seems to be a precondition for a stimulus becoming an efficient signal.

Adolescent↗
PubMed1995

[Application of the laryngeal mask in pediatric anesthesiology].

To analyze problems with inserting, maintaining and removing a laryngeal mask in children, as well as to assess the possible involvement of certain factors (experience with the laryngeal mask, type of anesthesia, duration of surgery, type of surgery, obesity, etc.) in favoring the development of complications. One hundred eighty-nine children undergoing a variety of surgical procedures under general anesthesia were studied; patients with full stomachs and/or a history of hiatus hernia were excluded. The agent used for anesthetic induction and the method of ventilation were chosen by the anesthesiologist responsible for each case. Variables monitored in all patients were continuous ECG, heart rate, systolic and diastolic arterial pressure, capnography, pulse oximetry, airways pressure and respiratory rate. Values were recorded at five times: before induction (T1), immediately after induction (T2), after placement of the laryngeal mask (T3), before removing the laryngeal mask (T4) and after removing the laryngeal mask (T5). Correct insertion was achieved on the first try in 85%. The remaining 15% required 2 or more tries. There were no cases in which a tracheal tube or face mask were required. We found no correlation between type or duration of surgery and the occurrence of complications. Complications were more frequent when the laryngeal mask was placed by inexperienced personnel, when inhalational anesthetics were used for induction and maintenance, and when a No. 1 laryngeal mask was used. Adequate ventilation was provided for the patients who required it with an airways pressure between 8 and 18 cmH2O, arterial oxygen saturation over 98% and end-expiratory CO2 pressure under 35 mmHg. Cardiovascular repercussions were slight and hemodynamic stability was good.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗