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At least 739 records · Page 41Linked to original sources
PubMed2006

The effects of masking on the activation of auditory-associated cortex during speech listening in white noise.

CONCLUSIONS: Noise-induced masking has different effects on the two hemispheres during speech listening. Auditory-associated cortices in the left hemisphere were more affected by masking than the right side. However, activation of primary and secondary auditory cortices was not affected in both sides under the masking with high signal to noise ratio. OBJECTIVES: The purpose of this study was to investigate the effects of masking on the central auditory system during speech listening in white noise. MATERIALS AND METHODS: Twelve healthy young subjects with normal hearing participated in this study. Functional magnetic resonance imaging (fMRI) was performed while subjects were listening to speech sounds alone and speech plus white noise binaurally. RESULTS: In humans, the activation of several regions including the middle parts of the superior and middle temporal gyri, parahippocampal gyrus, cuneus and thalamus of the left hemisphere was significantly reduced under the masking paradigm with +5 dB signal to noise ratio. In addition, reduced activation was also found at the lingual gyrus, anterior and middle parts of the superior temporal gyrus (STG), uncus, fusiform gyrus, and inferior frontal gyrus of the right hemisphere during masking.

Acoustic Stimulation↗
PubMed1976

The energetics of mask wear.

Experimental data further defining the region of predominant respiratory stress is presented. Within this region, energy requirements of respiration increase disproportionately to the overall energy expenditure of the body as excercise intensity increases. Addition of a mask accentuates this tendency, especially since no physiological compensation is possible in mask parameters. Mask technology has improved masks to the point where they no longer dominate the man-mask system, but instead contribute resistances and dead volumes approximately equal to those naturally occurring in man. Modeling base on minimization of respiratory energy rate of expenditure in the human is applied to this man-mask system and predictions are made which to this point have been nearly impossible to obtain from experimental data.

Body Temperature↗
PubMed2005

A psychophysical forward masking comparison of longitudinal spread of neural excitation in the Contour and straight Nucleus electrode arrays.

The objective of the study was to compare the widths of forward masking profiles in subjects implanted with the Nucleus 24 Contour or straight electrode array. The Contour array is typically positioned closer to the modiolus than the straight array. Subjects were fourteen postlingually hearing-impaired adults with severe-profound hearing loss, seven used the Contour array and seven used the straight array. Forward masking profiles were measured at three positions along the array (apical, mid, and basal) using maskers at the 15% loudness level. It was hypothesized that masking profile widths would be more sensitive to differences in distance from the neural structures using low-level maskers. Masking width was calculated at the 50% point of the masking peak amplitude. There were no significant differences in masking widths between Contour and straight array subject groups. Current levels for hearing thresholds and maximum comfortable listening levels were significantly lower for the Contour array subjects.

Acoustic Stimulation↗
PubMed1993

Comparison of the reinforced laryngeal mask airway and tracheal intubation for adenotonsillectomy.

One-hundred and four patients were allocated randomly to receive anaesthesia for adenotonsillectomy via either a reinforced laryngeal mask airway or tracheal tube. Airway maintenance and protection were assessed during and after operation. The reinforced laryngeal mask did not interfere with surgical access; it resisted compression and protected the lower airway from contamination with blood. Four patients were withdrawn from the laryngeal mask airway group: two because difficulty with placement, and two because the laryngeal mask was obstructed distally when the Boyle Davis gag was opened fully. In children, recovery was less eventful in the laryngeal mask airway group, with less airway obstruction (P < 0.001) and better airway acceptance (P < 0.05). The reinforced laryngeal mask airway provided a clear, secure airway until recovery of protective reflexes.

Adenoidectomy↗
PubMed1993

Comparison of nasal cannulae with face mask for oxygen administration to postoperative patients.

Thirty postoperative patients were allocated randomly to receive oxygen by Hudson face mask at 4 litre min-1 (group I) or 2 litre min-1 (group II) via nasal cannulae. From 22:00 on the first night after operation, the position of the nasal cannula or face mask was observed for 8 h using video and oxyhaemoglobin saturation (SpO2) recorded simultaneously. In group I the mask remained on and positioned correctly in five patients. In the 10 other patients it was removed a total of 28 times, 17 for nursing tasks, for a median time of 2 min 39 s (range 30 s to 7 h 40 min 40 s). In group II the nasal cannula was removed once in one patient for 16 min 38 s and eight times in another for a total of 1 h 18 min 7 s. Average SpO2 with mask on was 98% (range 96.1-99.9%), with mask off 95% (range 89.8-98.8%) and with cannula 97% (range 90.8-99.3%). We conclude that nasal cannulae are more likely to remain in position than face masks and maintain an adequate saturation in most patients.

Administration, Intranasal↗
PubMed1998

Appropriate size and inflation of the laryngeal mask airway.

We have compared size 3 and size 4 laryngeal masks in 30 females and size 4 and size 5 in 30 males for success rate of insertion, incidence of airleak and pressure exerted on the pharynx. First, the ex vivo volume-pressure relationship of the mask was obtained. Second, after insertion of a mask, the cuff was inflated with the recommended maximum volume of air and intracuff pressure measured. Third, the incidence of airleak during a steady airway pressure of 18 cm H2O was noted. Fourth, the cuff was deflated until it just prevented airleak, and cuff pressure was measured. The mask was removed, the other size was inserted and the same procedure repeated. At the end of operation, final in vivo and ex vivo pressures were measured. The pressure exerted on the pharynx was calculated as the difference between ex vivo and in vivo intracuff pressures. It was always possible to insert both sizes in both sexes. In females, airleak occurred in 15 patients with the size 3 and in five patients with the size 4 (difference: P = 0.005) and in males, 21 patients with the size 4 and in four patients with the size 5 (P < 0.001). Removal of air to the minimum effective volume significantly decreased intracuff pressure and pressure on the pharynx; on removal of the mask, pressures were similar to, or lower than, initial pressures. Therefore, a larger mask (size 4 in females and size 5 in males) provided a better seal than a smaller size without producing higher pressures on the pharynx.

Adolescent↗
PubMed1998

Ease of placement of the laryngeal mask during manual in-line neck stabilization.

We studied 20 patients, in a randomized, cross-over study, to determine if manual in-line stabilization of the head and neck altered the ease of insertion of the laryngeal mask and its correct positioning. After induction of anaesthesia and neuromuscular block, the laryngeal mask was inserted and adequacy of ventilation assessed while the patient's head and neck were placed in the Magill and manual in-line positions, in turn. Ease of insertion of the mask was assessed using a 10-cm visual analogue scale (VAS) and position using a fibreoptic bronchoscope. Time for insertion of the mask was measured. The laryngeal mask was inserted and adequate ventilation obtained at the first attempt in all 20 patients in the Magill position and in 19 of 20 patients in the manual in-line position. Insertion was always more difficult (P << 0.001; 95% CI for difference in VAS 20-55 mm) and time for insertion longer (P << 0.001; 95% CI for difference 4.9-11.9 s) in the manual in-line position compared with the Magill position. The incidence of a suboptimal position was significantly higher for the manual in-line position (seven patients) than for the Magill position (15 patients) (P < 0.005). We conclude that in paralysed patients, manual in-line stabilization of the head and neck made insertion of the laryngeal mask and its correct positioning more difficult.

Anesthesia, General↗
PubMed1991

Visual masking: a reliable measure for the assessment of cognitive dysfunction in the elderly?

Reliable assessment of cognitive dysfunction in the elderly is a prerequisite for the evaluation of treatment of age-related cognitive decline. Psychophysical thresholds are known to be more reliable than psychometric tests, as assessed by stability of performance in visual masking. A backward (Till & Franklin, 1981) and a forward masking study (Coyne, 1981) were replicated. Thereafter, the same volunteers carried out a backward and forward masking task adapted to minimize noncognitive age-related influences: target and mask duration were individually adjusted to control for reduced eye transmissiveness. Attention was assessed with the electrooculogram; a dependent variable insensitive to sporadic decreases of attention was selected. Test-retest stability in the elderly after 2-4 weeks was r = .97 in backward and r = .86 in forward masking. As Alzheimer's disease mainly affects the cortex, backward masking, which is primarily cortical, may be useful to assess aspects of cognitive dysfunction.

Adult↗
PubMed1990

The laryngeal mask airway in pediatric radiotherapy.

The use of the laryngeal mask airway, a new form of airway, is described in infants and young children receiving radiotherapy under general anesthesia. The laryngeal mask airway consists of a tube, at the distal end of which is attached an elliptically shaped cuff resembling a miniature face mask. The laryngeal mask is inserted blindly into the pharynx, and its cuff forms a low pressure seal around the larynx through which the patient can breathe spontaneously. No complications occurred during use of the laryngeal mask in 25 children who received 312 anesthetics. This experience suggests that the laryngeal mask airway has a valuable role in this situation and may contribute to the safety of anesthesia.

Anesthesia, General↗
PubMed2005

Involvement of V5/MT+ in object substitution masking: evidence from repetitive transcranial magnetic stimulation.

The visibility of a briefly presented target can be reduced by a subsequent weak mask that does not touch it, when the target is encoded in low spatiotemporal resolution. This phenomenon, called object substitution masking, has recently been proposed to reflect information updating in object-level representation, with perception of the target and the mask belonging to a single object through apparent motion. We investigated this issue by applying repetitive transcranial magnetic stimulation over V5/MT+, specialized in visual motion processing. The transient functional disruption of V5/MT+ produced by repetitive transcranial magnetic stimulation attenuated object substitution masking, while sham stimulation did not. Our results suggest that object substitution masking is mediated by normal functioning of V5/MT+. We conclude that repetitive transcranial magnetic stimulation of V5/MT+ impaired perceived object continuity and reduced object substitution masking accordingly.

Adult↗
PubMed1992

Noise reduction hearing aids: release from masking and release from distortion.

Automatic frequency response (AFR) hearing aids usually reduce their low-frequency gain in the presence of noise; several investigators have reported improved recognition of high-frequency speech information in low-frequency band-limited noise with AFR versus non-AFR hearing aids. In this work, masking patterns (masked threshold for frequency-modulated probe tones as a function of probe frequency) were obtained for a narrowband low-frequency noise. Speech recognition threshold for a set of high-frequency loaded monosyllables also was obtained in the presence of the same noise. Aided speech and masking pattern data for one normal and two hearing-impaired subjects wearing a master hearing aid incorporating a commercially available AFR circuit showed modest AFR effects. Moreover, masking noise spectra measured in ear canals of subjects wearing the master hearing aid showed evidence of substantial hearing aid-generated distortion products in the AFR-off condition. Results obtained from the normal subject listening with a low-distortion laboratory simulation of an AFR hearing aid showed greater release from masking for the same low-frequency attenuation as provided by the hearing aid. Improvements of speech recognition in noise observed with AFR hearing aids may result from some combination of release from upward spread of masking and reduction of distortion products generated by the hearing aid in the non-AFR setting.

Adult↗
PubMed1998

Binaural masking level difference in human binaural interaction components.

OBJECTIVE: The purpose of this study was to compare the effects of monaural and binaural broadband masking noise on binaural interaction components (BICs) of the human auditory brain stem evoked potentials (ABEPs). DESIGN: The BICs of the human ABEPs were studied by subtracting the potentials to binaural clicks from the algebraic sum of monaurally evoked potentials to clicks alone or to clicks with ipsilateral monaural or binaural broadband masking noise. Alternating polarity, 11/sec clicks were presented at 65 dB nHL, and noise was presented at 45 dB nHL. Analysis included peak-to-prestimulus baseline amplitudes and latencies of BICs' peaks and troughs from the vertex-mastoid (A) and vertex-neck (Z) channels. In addition, 3-channel Lissajous' trajectory (3-CLT) analysis, estimating the single, centrally located dipole equivalent of surface activity, was performed on data recorded from three orthogonally positioned electrode pairs. 3-CLT measures included apex latency, amplitude, and orientation, as well as planar segment duration, size, shape, and orientation. RESULTS: All BICs 3-CLTs included five main components (labeled BdI, BdII, BdIII, BeI, and BeII). In general, apex latencies were longer with masking noise. However, BdII and BeI apex latencies were shorter with binaural than with ipsilateral monaural masking noise. Apex amplitude and planar segment size of component BeI, as well as P1 peak amplitude in BICs of the Z-channel records, were larger with binaural than with monaural noise. No significant difference between the monaural and binaural noise conditions was found in durations, shapes, and orientations of planar segments of BICs 3-CLT, nor in peak latency of BICs in the A- and Z-channel records. CONCLUSIONS: We suggest that these effects on the latency and amplitude of BICs reflect binaural processing in the human brain stem. In particular, the larger amplitudes and shorter latencies of P1 and BeI with binaural than with ipsilateral monaural masking may be associated with the psychophysical effect of binaural masking level difference.

Adolescent↗
PubMed2005

Effects of low-pass noise masking on auditory event-related potentials to speech.

OBJECTIVE: This study investigated the effects of decreased audibility in low-frequency spectral regions, produced by low-pass noise masking, on cortical event-related potentials (ERPs) to the speech sounds /ba/ and /da/. DESIGN: The speech sounds were presented to normal-hearing adults (N = 10) at 65- and 80-dB peak-to-peak equivalent SPL while they were engaged in an active condition (pressing a button to deviant sounds) and a passive condition (ignoring the stimuli and reading a book). Broadband masking noise was simultaneously presented at an intensity sufficient to mask the response to the 65-dB speech sounds and subsequently low-pass filtered. The conditions were quiet (no masking), low-pass noise cutoff frequencies of 250, 500, 1000, 2000, and 4000 Hz, and broadband noise. RESULTS: As the cutoff frequency of the low-pass noise masker was raised, ERP latencies increased and amplitudes decreased. The low-pass noise affected N1 differently than the other ERP or behavioral measures, particularly for responses to 80-dB speech stimuli. N1 showed a smaller decrease in amplitude and a smaller increase in latency compared with the other measures. Further, the cutoff frequency where changes first occurred was different for N1. For 80-dB stimuli, N1 amplitudes showed significant changes when the low-pass noise masker cutoff was raised to 4000 Hz. In contrast, d', MMN, N2, and P3 amplitudes did not change significantly until the low-pass noise masker was raised to 2000 Hz. N1 latencies showed significant changes when the low-pass noise masker was raised to 1000 Hz, whereas RT, MMN, N2, and P3 latencies did not change significantly until the low-pass noise masker was raised to 2000 Hz. No significant differences in response amplitudes were seen across the hemispheres (electrode sites C3M versus C4M) in quiet, or in masking noise. CONCLUSIONS: These results indicate that decreased audibility, resulting from the masking, affects N1 in a differential manner compared with MMN, N2, P3, and behavioral measures. N1 indexes the presence of audible stimulus energy, being present when speech sounds are audible, whether or not they are discriminable. MMN indexes stimulus discrimination at a pre-attentive level. It was present only when behavioral measures indicated the ability to differentiate the speech sounds. N2 and P3 also were present only when the speech sounds were behaviorally discriminated. N2 and P3 index stimulus discrimination at a conscious level. These cortical ERP in low-pass noise studies provide insight into the changes in brain processes and behavioral performance that occur when audibility is reduced, such as with low frequency hearing loss.

Adult↗
PubMedDate not supplied

Fabrication of total-contact burn masks by use of human body topography and computer-aided design and manufacturing.

Total-contact burn masks are used to treat scar tissue hypertrophy of the face. The mask should conform very closely to the contours of the face and provide evenly distributed pressure. The mask is worn continually throughout wound maturation. Lack of fit because of an inability to obtain exact facial contours by use of an alginate material diminishes the effectiveness of the mask. A multidisciplinary team representing physical therapy, CAD/CAM (computer-aided design and computer-aided manufacturing), biomedical engineering, and prosthetics has advanced the method of developing total-contact burn masks by use of human body electronic imaging, computer graphics, and numerically controlled milling processes. High-resolution surface scanning and CAD/CAM have been used successfully to accurately fabricate three such masks. The methodology and preliminary results from use of these state-of-the-art techniques are described in this article.

Burns↗
PubMed1994

The use of the laryngeal mask airway by nurses during cardiopulmonary resuscitation. Results of a multicentre trial.

A multicentre study was undertaken to assess the potential value of the laryngeal mask airway when inserted by ward nurses during resuscitation as a method of airway management, prior to the arrival of the Advanced Life Support Team with tracheal intubation capability. The nurses underwent a training programme agreed by all the participating hospitals and followed an identical protocol and data recording system. One hundred and thirty nurses were trained and 164 cases of cardiac arrest were studied. The laryngeal mask airway was inserted at the first attempt in 71% and at the second attempt in 26% of cases. Satisfactory chest expansion occurred in 86% of cases. The mean interval between cardiac arrest and laryngeal mask airway insertion was 2.4 min. Regurgitation of gastric contents occurred before airway insertion in 20 cases (12%), during the insertion in three cases (2%), but there was clinical evidence of pulmonary aspiration in only one patient, who survived to leave hospital. We conclude that the laryngeal mask airway offers advantages over other methods of airway and ventilation management, such as the bag-valve-mask or mouth-to-mouth methods that are currently used by ward nurses in resuscitating patients with cardiac arrest. In this study, the laryngeal mask airway was not being compared with the tracheal tube.

Adult↗
PubMed1995

Laryngeal mask airway insertion using cricoid pressure and manual in-line neck stabilisation.

Forty patients were studied to assess the ease of insertion of the laryngeal mask in the simultaneous presence of cricoid pressure and manual in-line stabilisation of the neck. This was compared with the normal technique of laryngeal mask insertion in the same patients. Fibreoptic views obtained through the laryngeal mask were documented on each occasion. The device was inserted successfully in all 40 patients when the head was kept in the normal position. This was achieved on the first attempt in 33 patients. When cricoid pressure and manual in-line neck stabilisation were applied, successful laryngeal mask insertion was only possible in 29 patients, with correct placement at the first attempt in 14 patients. The differences were statistically significant (p < 0.001). When cricoid pressure and neck stabilisation were applied, vocal cord visualisation through the laryngeal mask with a fibreoptic bronchoscope was only possible in 15 patients. With the head in the normal position the vocal cords were seen in 33 patients. The implications of these results are discussed with respect to the role of the laryngeal mask in the multiply injured patient.

Adolescent↗
PubMed1996

Insertion methods of the laryngeal mask airway. A survey of current practice in Wales.

The efficacy of the laryngeal mask is widely accepted, but there is a lack of consensus on the best insertion method and on the use of the mask for certain surgical procedures. We sent a questionnaire to all anaesthetists in Wales to discover the frequency of use of the laryngeal mask and the preferred insertion method. The questionnaire also enquired about the use of the laryngeal mask during anaesthesia for laparoscopic clip sterilisation. Replies were received from 125 consultants (89% of those circulated) and 122 non-consultants (69%). The insertion method described in the manufacturer's instruction manual was preferred by 30% of consultants and 34% of the others. The next most popular option was insertion of the mask with the cuff partially inflated. Twenty-three per cent of consultants and 34% of non-consultants were prepared to use the laryngeal mask during anaesthesia for laparoscopic clip sterilisation. Although the insertion technique described in the instruction manual is the most widely employed, a large number of alternative methods are frequently used.

Anesthesia↗
PubMed1993

Endotracheal tube versus face mask with and without continuous positive airway pressure (CPAP).

Various ways of delivering continuous positive airway pressure (CPAP) have been extensively studied, with little attention, however, being paid to the effects of an intubation tube compared with breathing through a face mask, with or without CPAP. Pulmonary and cardiovascular variables were measured while 12 patients recovering from coronary artery bypass grafting were spontaneously breathing at ambient airway pressure, then at 7.4 mmHg (1 kPa) CPAP, and again at ambient pressure just before extubation. The same stages were repeated immediately after extubation, with patients breathing through a tight-fitting face mask. Arterial oxygen tension (Pao2, mean +/- s.d.) was better when the patients were breathing at ambient pressure through a face mask (11.7 +/- 2.8 kPa) than when they were intubated (10.6 +/- 2.4 kPa, P < 0.05). Compared with ambient pressure, CPAP (7.4 mmHg) (1 kPa) increased Pao2 in both modes (13.4 +/- 3.5 kPa with mask, and 12.6 +/- 3.5 kPa when intubated, n.s.). The best arterial oxygen saturation was measured during CPAP with a face mask (96 +/- 1%). Cardiac output remained unchanged in all the breathing modes. After coronary artery bypass grafting, spontaneous breathing with a face mask resulted in better Pao2 than breathing through an endotracheal tube, both with and without 7.4 mmHg (1 kPa) CPAP. This study indicates that unnecessary delay in extubation should be avoided.

Adult↗