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PubMed1990

The use of a laryngeal mask airway in spontaneously breathing patients.

The Laryngeal Mask Airway (LMA) is a new type of oropharyngeal airway that provides an alternative to endotracheal intubation and standard mask anaesthesia in certain cases. Once the patient is adequately anaesthetised, it can be inserted blindly, without recourse to laryngoscopy or muscle relaxants. Anaesthetists of all grades, given minimum instruction, were able to provide a clinically satisfactory airway in 49 out of 50 spontaneously breathing, anaesthetised patients. The advantages over standard mask anaesthesia are: better airway control, minimal leakage of anaesthetic gases, secure airway during transport to the recovery ward, and it frees the anaesthetist's hands, as no mandibular support is needed. Postoperative problems were minimal and 97.6% of our patients said that they would prefer a similar anaesthetic in future. LMA does not guarantee against the risk of aspiration and it is not recommended for use in patients who may have a full stomach.

Adolescent↗
PubMed1993

Flexible fibreoptic bronchoscopy via the laryngeal mask.

The efficacy of flexible fibreoptic bronchoscopy through the laryngeal mask was investigated in 20 patients under total intravenous anaesthesia with propofol, fentanyl, atropine and suxamethonium. Mask size 4 was used for men and size 3 for women. Ventilation was performed with oxygen in air, FIO2 0.6. The ventilatory pressures were median 18 (9-40) cmH2O (1.8 (0.9-3.9) kPa) before the bronchoscope was inserted. When the tip of the bronchoscope was above the vocal cords the ventilatory pressures increased to 22 (10-43) mmHg (2.2 (1.0-4.2) kPa) (P < 0.001), and when the tip was situated at the mid-tracheal level there was a further increase to 24 (12-50) mmHg (2.4 (1.2-4.9) kPa) (P < 0.001). Maximal gas leakages were median 1 (0-2) l/min-1. PEEP at the mid-tracheal level was 3 (0-7) cmH2O (0.3(0-0.7) kPa). When 15 min of the procedure had elapsed, PaO2 was 232 (112-350) mmHg (30.9 (14.9-46.6) kPa) and PaCO2 39 (33-46) mmHg (5.2(4.4-6.1) kPa). The lowest oxygen saturation was median 98 (96-100)% and the highest end-tidal CO2 34 (24-41) mmHg (4.5(3.2-5.5) kPa). It was easy to examine the laryngeal opening and a good assessment of vocal cord function was allowed when muscle relaxation ceased. We conclude that flexible fibreoptic bronchoscopy through the laryngeal mask is a safe technique provided that total intravenous anaesthesia is used. It is a valuable alternative to flexible bronchoscopy performed with topical anaesthesia.

Adult↗
PubMed1997

Nasal mask continuous positive airway pressure in the treatment of chronic nocturnal cough in a young child.

The objective of this case report was to define the effects of nasal mask continuous positive airway pressure (CPAP) on the respiratory and sleep characteristics of a 3 year-old boy with a 2 year history of snoring and 1 year history of chronic nocturnal cough. The method employed was all-night polysomnography before and during treatment with CPAP after the identification of partial upper airway obstruction in association with cough. The results indicated that the child had evidence of mild upper airways obstruction on initial all-night sleep study. Nasal mask CPAP was instituted. On a subsequent sleep study 4 weeks later, this was documented to prevent the upper airway obstruction at a pressure of 5.2 cm of water. In addition, nasal mask CPAP markedly reduced the nocturnal coughing, the total number of coughs decreasing from 92 to one. The rate of cough per h of study (cough disturbance index) decreased from 9.8-0.1. Sleep efficiency (total sleep time as a percentage of study duration) improved on CPAP from 87 to 99%. This study suggests that chronic nocturnal cough can result from upper airway obstruction in sleep in children and is an important initial observation.

Child, Preschool↗
PubMed1980

A follow-up study of very low-birthweight infants receiving ventilatory support by face mask.

Recent evidence has suggested that face-mask ventilation of very low birthweight (VLBW) infants may have serious neurological consequences. The 30 surviving VLBW infants from the neonatal intensive care unit at Hammersmith Hospital who had received ventilatory support via face masks over a 25-month period have been reviewed and compared with a control group. Neuropathological findings in the VLBW infants who died during this time have also been reviewed in relation to their ventilatory management. The findings suggest that face-mask treament did not have a major deleterious effect on the surviving infants. The factors which may determine the neurological sequelae of this form of ventilatory support are discussed.

Brain Diseases↗
PubMed2005

A randomized trial comparing oxygen delivery on intermittent positive pressure with nasal cannulae versus facial mask in neonatal primary resuscitation.

AIM: To compare, in a prospective clinical trial, oxygen delivery on intermittent positive pressure with nasal cannulae versus facial mask in primary resuscitation of the newborn with moderate asphyxia. METHODS: 617 neonates with moderate asphyxia at birth were randomized: 303 were resuscitated by oxygen on intermittent positive pressure with nasal cannuale and 314 neonates by mask. Resuscitation followed the Neonatal Resuscitation Program guidelines of the American Academy of Pediatrics, 3rd edition. RESULTS: Resuscitation through the nasal route less frequently requires chest compressions and intubations (26 neonates needed chest compression and 20 needed intubation out of 314 resuscitated by mask; five neonates needed chest compression and two needed intubation out of 303 resuscitated by nasal cannulae). Apgar scores, admission rates to neonatal intensive care units, air-leak syndromes, birthweight, gestational age, use of prenatal steroids and deaths did not differ between groups. CONCLUSION: Oxygen delivery on intermittent positive pressure with nasal cannulae in primary resuscitation of the newborn with moderate asphyxia is a less aggressive and potentially advantageous alternative to the traditional oral route.

Analysis of Variance↗
PubMed2000

Masking in three pinnipeds: underwater, low-frequency critical ratios.

Behavioral techniques were used to determine underwater masked hearing thresholds for a northern elephant seal (Mirounga angustirostris), a harbor seal (Phoca vitulina), and a California sea lion (Zalophus californianus). Octave-band white noise maskers were centered at five test frequencies ranging from 200 to 2500 Hz; a slightly wider noise band was used for testing at 100 Hz. Critical ratios were calculated at one masking noise level for each test frequency. Above 200 Hz, critical ratios increased with frequency. This pattern is similar to that observed in most animals tested, and indicates that these pinnipeds lack specializations for detecting low-frequency tonal sounds in noise. However, the individual pinnipeds in this study, particularly the northern elephant seal, detected signals at relatively low signal-to-noise ratios. These results provide a means of estimating zones of auditory masking for pinnipeds exposed to anthropogenic noise sources.

Animals↗
PubMed2000

Effects of hearing impairment and presentation level on masking period patterns for Schroeder-phase harmonic complexes.

Masking period patterns (MPPs) for Schroeder-phase harmonic complexes containing equal-amplitude harmonics of a 100-Hz fundamental were determined for 5-ms tonal probes at 4,000 and 1,000 Hz. Maskers consisted of harmonics 2-50 (200-5,000 Hz bandwidth) for 4,000-Hz probes and harmonics 2-20 (200-2,000 Hz) for 1,000-Hz signals. Masked thresholds were determined for probe onsets 153, 155.5, 158, 160.5, and 163 ms following masker onset (masker duration=460 ms). Overall, results were similar for both probe frequencies. For listeners with normal hearing, MPPs for positive Schroeder-phase complexes masking 60 dB SPL probes were highly modulated and became flatter when probe level was increased to 80 dB SPL. MPPs were less modulated for listeners with sensorineural hearing loss than for normally hearing listeners at both 60 and 80 dB SPL probe levels. Thresholds in negative Schroeder-phase maskers were more similar across the two groups of listeners and across differences in probe position and probe level. The findings support an interpretation involving differences in the shape of the basilar-membrane waveform generated by each masker and possible influences of nonlinear cochlear processing on these internal responses. For normally hearing listeners, 60 dB SPL probes were most difficult to detect when temporally positioned so that probe frequency and masker instantaneous frequency were closely matched. For 80 dB SPL probes and for hearing-impaired listeners, probes presented at these same positions were often more easily detected than probes at other positions. The latter result appears to involve benefit associated with in-phase addition of the probe to a portion of the masker similar to the probe in both frequency and phase. This benefit was reduced or entirely eliminated when probe phase was altered so that this in-phase addition did not occur.

Adult↗
PubMed2001

Monaural masking release in random-phase and low-noise noise.

Two masking-release paradigms thought to involve across-channel processing are comodulation masking release (CMR) and profile analysis. Similarities between these two paradigms were explored by comparing signal detection in maskers that varied only in degree of envelope fluctuation. The narrow-band-noise maskers were 10 Hz wide and their envelope fluctuations were manipulated using the low-noise noise algorithm of Pumplin [J. Acoust. Soc. Am. 78, 100-104 (1985)]. Masking conditions included the classic CMR conditions of an on-frequency band, multiple (five) incoherent bands, or multiple coherent bands. Detection was compared using both random-phase noise (RPN) and low-noise noise (LNN) maskers. In one set of conditions, the signal was identical to the on-frequency masker, yielding an intensity discrimination task. Conditions that included RPN maskers and tonal signals resembled the classic CMR paradigm, whereas conditions including LNN and noise signals more closely resembled the classic profile analysis paradigm. Other conditions may be considered hybrids. This combination of conditions provided a wide variety of within- and across-channel cues for detection. The results suggest that CMR and profile analysis could be based upon the same set of stimulus cues and perhaps the same perceptual processes.

Adult↗
PubMed2001

The effect of basilar-membrane nonlinearity on the shapes of masking period patterns in normal and impaired hearing.

Masking period patterns (MPPs) were measured in listeners with normal and impaired hearing using amplitude-modulated tonal maskers and short tonal probes. The frequency of the masker was either the same as the frequency of the probe (on-frequency masking) or was one octave below the frequency of the probe (off-frequency masking). In experiment 1, MPPs were measured for listeners with normal hearing using different masker levels. Carrier frequencies of 3 and 6 kHz were used for the masker. The probe had a frequency of 6 kHz. For all masker levels, the off-frequency MPPs exhibited deeper and longer valleys compared with the on-frequency MPPs. Hearing-impaired listeners were tested in experiment 2. For some hearing-impaired subjects, masker frequencies of 1.5 kHz and 3 kHz were paired with a probe frequency of 3 kHz. MPPs measured for listeners with hearing loss had similar shapes for on- and off-frequency maskers. It was hypothesized that the shapes of MPPs reflect nonlinear processing at the level of the basilar membrane in normal hearing and more linear processing in impaired hearing. A model assuming different cochlear gains for normal versus impaired hearing and similar parameters of the temporal integrator for both groups of listeners successfully predicted the MPPs.

Auditory Perception↗
PubMed2001

Psychophysical recovery from single-pulse forward masking in electric hearing.

Psychophysical single-pulse forward-masking (SPFM) recovery functions were measured for three electrodes in each of eight subjects with the nucleus mini-22 cochlear implant. Masker and probe stimuli were single 200-micros/phase biphasic current pulses. Recovery functions were measured at several masker levels spanning the electric dynamic range of electrodes chosen from the apical, middle, and basal regions of each subject's electrode array. Recovery functions were described by an exponential process in which threshold shift (in microA) decreased exponentially with increasing time delay between the masker and probe pulses. Two recovery processes were observed: An initial, rapid-recovery process with an average time constant of 5.5 ms was complete by about 10 ms. A second, slow-recovery process involved less masking than the rapid-recovery process but encompassed much longer time delays, sometimes as long as several hundred milliseconds. Growth-of-masking slopes for the rapid process depended upon time delay, as expected in an exponential recovery process. Unity slopes were observed at a time delay of 0 ms, whereas progressively shallower slopes were observed at time delays of 2 ms and 5 ms. Many recovery functions demonstrated nonmonotonicities or "facilitation" at very short masker-probe delays (1-2 ms). Such nonmonotonicities were usually most pronounced at low masker levels. Time constants for the rapid-recovery process did not vary systematically with masker level or with electrode location along the implanted array. Most subjects demonstrated rapid-recovery time constants less than 7 ms; however, the subject with the longest duration of deafness prior to implantation exhibited clearly prolonged time constants (9-24 ms). Time constants obtained on basal electrodes were inversely related to word recognition scores.

Adult↗
PubMed2002

Rhythmic masking release: contribution of cues for perceptual organization to the cross-spectral fusion of concurrent narrow-band noises.

The contribution of temporal asynchrony, spatial separation, and frequency separation to the cross-spectral fusion of temporally contiguous brief narrow-band noise bursts was studied using the Rhythmic Masking Release paradigm (RMR). RMR involves the discrimination of one of two possible rhythms, despite perceptual masking of the rhythm by an irregular sequence of sounds identical to the rhythmic bursts, interleaved among them. The release of the rhythm from masking can be induced by causing the fusion of the irregular interfering sounds with concurrent "flanking" sounds situated in different frequency regions. The accuracy and the rated clarity of the identified rhythm in a 2-AFC procedure were employed to estimate the degree of fusion of the interferring sounds with flanking sounds. The results suggest that while synchrony fully fuses short-duration noise bursts across frequency and across space (i.e., across ears and loudspeakers), an asynchrony of 20-40 ms produces no fusion. Intermediate asynchronies of 10-20 ms produce partial fusion, where the presence of other cues is critical for unambiguous grouping. Though frequency and spatial separation reduced fusion, neither of these manipulations was sufficient to abolish it. For the parameters varied in this study, stimulus onset asynchrony was the dominant cue determining fusion, but there were additive effects of the other cues. Temporal synchrony appears to be critical in determining whether brief sounds with abrupt onsets and offsets are heard as one event or more than one.

Acoustic Stimulation↗
PubMed2002

Effects of signal delay on auditory filter shapes derived from psychophysical tuning curves and notched-noise data obtained in simultaneous masking.

Psychophysical tuning curves (PTCs) measured in simultaneous masking usually sharpen as a short duration signal is moved from the onset to the temporal center of a longer duration masker. Filter shapes derived from notched-noise maskers have not consistently shown this effect. One possible explanation for this difference is that the signal level is fixed in the PTC paradigm, whereas the masker level is usually fixed in the notched-noise paradigm. In the present study, the signal level was fixed at 10 dB SL in both paradigms. The signal was 20 ms in duration, and presented at the onset or temporal center of the 400-ms masker. The masker was a pure tone presented in quiet (PTC) or in the presence of a pure-tone "restrictor" intended to limit off-frequency listening (PTCr), or it was a noise with a spectral notch placed symmetrically or asymmetrically about the 2-kHz signal frequency. Filter shapes were derived from the PTC, PTCr, and notched-noise data using the roex (p, w, t) model. The effects of signal delay and masking paradigm on filter bandwidth were analyzed with a two-factor repeated-measures ANOVA. There was a significant effect of signal delay (the filters sharpened with time) and masking paradigm (the filters derived from the notched-noise data were significantly wider than those derived from either of the PTC measurements, which did not differ from one another). Although the interaction between delay and paradigm was not significant, the filter derived from the notched-noise data sharpened more with time than did the other filters, and thus the bandwidth of the filters from the three paradigms were more similar at the longer delay than at the shorter delay. It is likely that the tuning-curve and notched-noise paradigms measure the same underlying filtering, but that various other factors contribute differentially to the derived filter shapes.

Adult↗
PubMed2002

Comodulation masking release in consonant recognition.

Comodulation masking release (CMR) refers to an improvement in the detection threshold of a signal masked by noise with coherent amplitude fluctuation across frequency, as compared to noise without the envelope coherence. The present study tested whether such an advantage for signal detection would facilitate the identification of speech phonemes. Consonant identification of bandpass speech was measured under the following three masker conditions: (1) a single band of noise in the speech band ("on-frequency" masker); (2) two bands of noise, one in the on-frequency band and the other in the "flanking band," with coherence of temporal envelope fluctuation between the two bands (comodulation); and (3) two bands of noise (on-frequency band and flanking band), without the coherence of the envelopes (noncomodulation). A pilot experiment with a small number of consonant tokens was followed by the main experiment with 12 consonants and the following masking conditions: three frequency locations of the flanking band and two masker levels. Results showed that in all conditions, the comodulation condition provided higher identification scores than the noncomodulation condition, and the difference in score was 3.5% on average. No significant difference was observed between the on-frequency only condition and the comodulation condition, i.e., an "unmasking" effect by the addition of a comodulated flaking band was not observed. The positive effect of CMR on consonant recognition found in the present study endorses a "cued-listening" theory, rather than an envelope correlation theory, as a basis of CMR in a suprathreshold task.

Adult↗
PubMed2002

Psychophysical recovery from pulse-train forward masking in electric hearing.

Psychophysical pulse-train forward-masking (PTFM) recovery functions were measured in fifteen subjects with the Nucleus mini-22 cochlear implant and six subjects with the Clarion cochlear implant. Masker and probe stimuli were 500-Hz trains of 200- or 77-micros/phase biphasic current pulses. Electrode configurations were bipolar for Nucleus subjects and monopolar for Clarion subjects. Masker duration was 320 ms. Probe duration was either 10 ms or 30 ms. Recovery functions were measured for a high-level masker on a middle electrode in all 21 subjects, on apical and basal electrodes in 7 of the Nucleus and 3 of the Clarion subjects, and for multiple masker levels on the middle electrode in 8 Nucleus subjects and 6 Clarion subjects. Recovery functions were described by an exponential process in which threshold shift (in microA) decreased exponentially with increasing time delay between the offset of the masker pulse train and the offset of the probe pulse train. All but 3 of the 21 subjects demonstrated recovery time constants on a middle electrode that were less than 95 ms. The mean time constant for these 18 subjects was 54 ms (s.d. 17 ms). Three other subjects tested on three electrodes exhibited time constants larger than 95 ms from an apical electrode only. Growth-of-masking slopes depended upon time delay, as expected from an exponential recovery process, i.e., progressively shallower slopes were observed at time delays of 10 ms and 50 ms. Recovery of threshold shift (in microA) for PTFM in electrical hearing behaves inthe same way as recovery of threshold shift (in dB) for pure-tone forward masking in acoustic hearing. This supports the concept that linear microamps are the electrical equivalent of acoustic decibels. Recovery from PTFM was not related to speech recognition in a simple manner. Three subjects with prolonged PTFM recovery demonstrated poor speech scores. The remaining subjects with apparently normal PTFM recovery demonstrated speech scores ranging from poor to excellent. Findings suggest that normal PTFM recovery is only one of several factors associated with good speech recognition in cochlear-implant listeners. Comparisons of recovery curves for 10- and 30-ms probe durations in two subjects showed little or no temporal integration at time delays less than 95 ms where recovery functions have steep slopes. The same subjects exhibited large amounts of temporal integration at longer time delays where recovery slopes are more gradual. This suggests that probe detection depends primarily on detection of the final pulses in the probe stimulus and supports the use of offset-to-offset time delays for characterizing PTFM recovery in electric hearing.

Adult↗
PubMed2004

Masker-first advantage for cues in informational masking.

The detectability of a pure-tone signal may be reduced by adding a small number of randomly drawn masker tones remote from the signal frequency, an effect attributed to informational masking. A pretrial cue consisting of either the upcoming signal or masker releases informational masking, but a pretrial cue of the signal-plus-masker stimulus does not. In these experiments the relative potency of pre- and posttrial cues in releasing informational masking was examined. In separate conditions the masker-alone and signal-plus-masker stimuli were cues. The results indicated a masker-first advantage, i.e., sensitivity was superior when a masker cue preceded a yes/no trial interval compared to (a) when a signal-plus-masker preceded the trial, and (b) when either cue type followed the yes/no trial interval. A masker-first advantage was also obtained when the results from a two-interval forced-choice same/different task were examined. In contrast, a masker-first advantage was not obtained when the frequency of the signal to be detected was random. For detection tasks using random multi-tone maskers there may be differences in processing efficiency depending on the order in which stimuli are presented. The "masker-first advantage" may depend, in part, on observers maintaining their attention at the signal frequency.

Acoustic Stimulation↗
PubMed2005

A computer model of the auditory-nerve response to forward-masking stimuli.

A computer model of the auditory periphery is used to study the involvement of auditory-nerve (AN) adaptation in forward-masking effects. An existing model is shown to simulate published AN recovery functions both qualitatively and quantitatively after appropriate parameter adjustments. It also simulates published data showing only small threshold shifts when a psychophysical forward-masking paradigm is applied to AN responses. The model is extended to simulate a simple but physiologically plausible mechanism for making threshold decisions based on coincidental firing of a number of AN fibers. When this is used, much larger threshold shifts are observed of a size consistent with published psychophysical observations. The problem of how stimulus-driven firing can be distinguished from spontaneous activity near threshold is also addressed by the same decision mechanism. Overall, the modeling results suggest that poststimulatory reductions in AN activity can make a substantial contribution to the raised thresholds observed in many psychophysical studies of forward masking.

Acoustic Stimulation↗
PubMed2005

Recognition of filtered words in noise at higher-than-normal levels: decreases in scores with and without increases in masking.

To examine spectral effects on declines in speech recognition in noise at high levels, word recognition for 18 young adults with normal hearing was assessed for low-pass-filtered speech and speech-shaped maskers or high-pass-filtered speech and speech-shaped maskers at three speech levels (70, 77, and 84 dB SPL) for each of three signal-to-noise ratios (+8, +3, and -2 dB). An additional low-level noise produced equivalent masked thresholds for all subjects. Pure-tone thresholds were measured in quiet and in all maskers. If word recognition was determined entirely by signal-to-noise ratio, and was independent of signal levels and the spectral content of speech and maskers, scores should remain constant with increasing level for both low- and high-frequency speech and maskers. Recognition of low-frequency speech in low-frequency maskers and high-frequency speech in high-frequency maskers decreased significantly with increasing speech level when signal-to-noise ratio was held constant. For low-frequency speech and speech-shaped maskers, the decline was attributed to nonlinear growth of masking which reduced the "effective" signal-to-noise ratio at high levels, similar to previous results for broadband speech and speech-shaped maskers. Masking growth and reduced "effective" signal-to-noise ratio accounted for some but not all the decline in recognition of high-frequency speech in high-frequency maskers.

Acoustic Stimulation↗
PubMed2006

Effect of masker type and age on speech intelligibility and spatial release from masking in children and adults.

Speech recognition in noisy environments improves when the speech signal is spatially separated from the interfering sound. This effect, known as spatial release from masking (SRM), was recently shown in young children. The present study compared SRM in children of ages 5-7 with adults for interferers introducing energetic, informational, and/or linguistic components. Three types of interferers were used: speech, reversed speech, and modulated white noise. Two female voices with different long-term spectra were also used. Speech reception thresholds (SRTs) were compared for: Quiet (target 0 degrees front, no interferer), Front (target and interferer both 0 degrees front), and Right (interferer 90 degrees right, target 0 degrees front). Children had higher SRTs and greater masking than adults. When spatial cues were not available, adults, but not children, were able to use differences in interferer type to separate the target from the interferer. Both children and adults showed SRM. Children, unlike adults, demonstrated large amounts of SRM for a time-reversed speech interferer. In conclusion, masking and SRM vary with the type of interfering sound, and this variation interacts with age; SRM may not depend on the spectral peculiarities of a particular type of voice when the target speech and interfering speech are different sex talkers.

Acoustic Stimulation↗

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