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At least 1,333 records · Page 74Linked to original sources
PubMed1994

Intra-ocular pressure changes in patients with glaucoma. Comparison between the laryngeal mask airway and tracheal tube.

We performed a randomised prospective study in 20 patients with glaucoma to examine the effects of tracheal intubation and laryngeal mask insertion on intra-ocular pressure, mean arterial blood pressure and heart rate. After induction of anaesthesia with propofol, intra-ocular pressure decreased significantly below baseline values in both the laryngeal mask and tracheal tube groups. After insertion of the laryngeal mask, intra-ocular pressure remained significantly below baseline values in all patients. In contrast, tracheal intubation was associated with a significant increase in intra-ocular pressure to above baseline values in three out of eight patients. Insertion of the laryngeal mask had minimal effects on mean arterial blood pressure and heart rate, whereas tracheal intubation significantly increased both factors relative to pre-intubation values.

Adolescent↗
PubMed1995

The effects of 2% lignocaine gel on incidence of retching with the use of the laryngeal mask airway.

This randomised, single-blind study investigated the incidence of retching during emergence from general anaesthesia with a laryngeal mask airway in place. Eighty four patients, ASA grade 1 and 2, aged 15 to 60 years, were randomly divided into two groups. Each patient received fentanyl 1 microgram.kg-1 and propofol 2 mg.kg-1 for induction. A laryngeal mask airway was then inserted and the patient breathed spontaneously on a nitrous oxide-oxygen mixture with isoflurane. Lubafax gel was the lubricant in the control group and 2% lignocaine gel was used in the test group. The patients were allowed to wake up at the end of surgery with the laryngeal mask airway in place while a blinded observer observed for retching. The age, sex, weight and duration of surgery were similar in both groups. The test group had a significantly lower incidence of retching on emergence from general anaesthesia with the laryngeal mask airway in place (p < 0.005, Chi-squared test).

Adolescent↗
PubMed1995

Facilitation of laryngeal mask insertion. Effects of lignocaine given intravenously before induction with propofol.

The effects of pretreatment with lignocaine administered intravenously on the insertion of the laryngeal mask airway were investigated in 80 unpremedicated, ASA 1 or 2, adult day-case patients in a randomised, double-blind, placebo-controlled trial. Patients received either intravenous lignocaine 1.5 mg.kg-1 or an equivalent volume of sodium chloride 0.9%. Induction of anaesthesia was achieved with propofol given via a syringe driver at a fixed rate of 600 ml.h-1 until the patient dropped a weighted syringe. No opioid or sedative drugs were given prior to induction. Pain on injection of propofol was recorded. Jaw opening, ease of insertion of the laryngeal mask, coughing, gagging and airway patency were all scored on three-point scales immediately after mask insertion re-attempted. This cycle was continued until success was achieved and the number of such cycles recorded. There were no differences between the lignocaine and control groups with respect to induction dose of propofol, degree of jaw opening, or amount of gagging. Laryngeal mask insertion was facilitated by pretreatment with lignocaine administered intravenously, without an alteration in induction dose of propofol (p < 0.05). Coughing and airway obstruction were both significantly reduced by pretreatment with lignocaine, as was the incidence of failure of insertion requiring deepening of anaesthesia (p < 0.05).

Adult↗
PubMed1996

Analysis of 1500 laryngeal mask uses by one anaesthetist in adults undergoing routine anaesthesia.

An analysis of 1500 laryngeal mask airway uses by one anaesthetist using the standard insertion technique was conducted to determine successful insertion rates, position by fibreoptic larynoscopy, complication rates and whether there is a long-term learning curve. The correlation between laryngeal mask airway placement and modified Mallampati grade was also determined. The first time insertion rate was 95.5% with an overall failure rate after three attempts of 0.4%. One hundred and fifteen patients were Mallampati III or IV. All failed placements were Mallampati I or II. Problems occurred in 94 patients (6.27%), but oxygen saturation decreased below 90% on only ten occasions and below 80% on one occasion. There were no episodes of regurgitation. The vocal cords were visible from the mask aperture bars in 97.1%. Comparison of insertion rates, fibreoptic position and complications for the first and second 750 insertions provides evidence for a 'long' term learning curve. These data could be used as a guide for 'optimal' or expected successful laryngeal mask airway insertion rates in adults undergoing routine anaesthesia.

Adolescent↗
PubMed1996

Topical lignocaine and thiopentone for the insertion of a laryngeal mask airway; a comparison with propofol.

We assessed conditions for insertion of a laryngeal mask airway in 90 unpremedicated adult patients who received either thiopentone 5 mg.kg-1 preceded by 40 mg of topical lignocaine spray to the posterior pharyngeal wall or propofol 2.5 mg.kg-1 alone in a randomised, single-blinded trial. All patients received fentanyl 1 microgram.kg-1. Gagging, coughing and laryngospasm following laryngeal mask insertion were graded and haemodynamic data and apnoea times were recorded. There were no significant differences between the two groups with regard to the incidence of gagging, coughing and laryngospasm, but the apnoea time was significantly less in the thiopentone group (p < 0.005). The decrease in systolic and diastolic blood pressure, following induction and the insertion of a laryngeal mask with propofol was significantly greater than following thiopentone (p < 0.05--systolic, p < 0.01--diastolic). We conclude that thiopentone preceded by topical lignocaine spray provides conditions for insertion of a laryngeal mask equal to those of propofol, with more haemodynamic stability and a shorter period of apnoea.

Adolescent↗
PubMed1997

The effect of laryngeal mask airway insertion on the position of the internal jugular vein.

A high-quality ultrasound system (Dyasonics Prisma) was used to study the effect of laryngeal mask airway insertion and cuff inflation on the position and relations of the internal jugular vein in eight healthy young patients undergoing elective surgery. On insertion of the laryngeal mask, with the cuff pre-inflated with 10 ml of air, some minor movement was discernible in the larynx. Neither the larynx nor surrounding structures changed significantly in position. However, on full inflation of the laryngeal mask cuff there was a more noticeable movement of the larynx, which visibly distended in an anterior direction. The mean anterior displacement was 0.8 cm (range 0.6-1.1 cm). There was no significant lateral displacement of the carotid artery or internal jugular vein and there was no significant compression of these structures. We conclude that in the presence of a laryngeal mask airway fixed landmarks such as the sternal notch and angle of the jaw should be used to identify the likely position of the internal jugular vein. Difficulty in cannulation may be experienced if the mobile laryngeal structures are used as landmarks.

Adolescent↗
PubMed1997

A comparison of the nasal mask and the nasopharyngeal airway in paediatric chair dental anaesthesia.

This study compared the quality of anaesthesia and surgical access afforded by two techniques for the administration of anaesthesia during paediatric chair dental procedures. A total of 50 ASA 1 paediatric day case patients were randomly assigned to receive anaesthesia through either the traditional Goldman nasal mask or through a nasopharyngeal airway. Patients in the nasal mask group were judged to have significantly worse airway patency (p = 0.0001) and significantly more episodes of airway obstruction (14 vs. 4; p = 0.0032) than those in the nasopharyngeal airway group. Anaesthetic, surgical and oxygen saturation data did not differ significantly between the two groups. Operating conditions were universally graded as excellent in the nasopharyngeal airway group, while those in the nasal mask group were graded as excellent/good in only 79% of cases (p < 0.0001). These results suggest that better quality anaesthesia and operating conditions can be achieved by using a nasopharyngeal airway rather than the traditional nasal mask for the administration of anaesthesia to paediatric chair dental patients.

Adolescent↗
PubMed1997

Intra-ocular pressure changes following laryngeal mask airway insertion: a comparative study.

We compared the effects of the Brain laryngeal mask airway with a tracheal tube on intra-ocular pressure. Propofol was used as induction agent and atracurium as relaxant. Twenty-six patients with normal intra-ocular pressure undergoing cataract surgery were randomly allocated to two groups. Group A (n = 13) had a laryngeal mask airway inserted and Group B (n = 13) had a tracheal tube inserted. Intra-ocular pressure was measured just before insertion of the airway, 20 s after insertion and at 2 min. In the laryngeal mask airway group there were no significant changes in mean intra-ocular pressure. In the tracheal tube group there was a significant rise in mean intra-ocular pressure at 20 s (p = 0.0056) which returned to pre-insertion levels at 2 min. We conclude that the laryngeal mask airway continues to have advantages over the tracheal tube for ophthalmic surgery despite the use of propofol and atracurium as anaesthetic agents.

Aged↗
PubMed2006

Chronic partial sleep loss increases the facilitatory role of a masked prime in a word recognition task.

Neurobehavioural performance deficits associated with sleep loss have been extensively studied, in particular, the effects on psychomotor performance. However, there is no consensus as to which, if any, cognitive functions are impaired by sleep loss. To examine how sleep loss might affect cognition, the automatic processes supporting word recognition were examined using the masked priming paradigm in participants who had been exposed to two consecutive days of sleep restriction. Twelve healthy volunteers (mean age 24.5 years) were recruited. Nocturnal sleep duration was restricted to 60% of each participant's habitual sleep duration for two consecutive nights by delaying scheduled time of sleep onset and advancing time of awakening. In controlled laboratory conditions, participants completed the Psychomotor Vigilance Task and Karolinska Sleepiness Scale and a masked priming word recognition task. As expected, significant increases in subjective sleepiness and impaired psychomotor performance were observed after sleep loss. In contrast, response times and error rate on the masked priming task were not significantly affected. However, the magnitude of the masked priming effect, which can be taken as an index of automaticity of lexical processing, increased following sleep loss. These findings suggest that while no evidence of impairment to lexical access was observed after sleep loss, an increase in automatic processing may occur as a consequence of compensatory mechanisms.

Adolescent↗
PubMed2004

Ocular refractive changes in patients receiving hyperbaric oxygen administered by oronasal mask or hood.

PURPOSE: The aim of this study was to quantify ocular refractive changes after a standard hyperbaric oxygen (HBO) treatment protocol and to characterize the time period of recovery. PATIENTS AND METHODS: Hyperbaric oxygen therapy was given for 90 min daily at a pressure of 240 kPa for 21 days. Oxygen was administered to 20 patients using an oronasal mask and to 12 patients using a hood. Follow-up examinations were carried out 2-4 days after treatment, and thereafter regularly for up to 10 weeks in both groups. Refraction was assessed automatically and by the monocular subjective refraction method. A subgroup of nine of the 20 patients to whom oxygen was administered by an oronasal mask underwent a separate eye examination, which included crystalline lens opacity measurements and LOCS III gradings. RESULTS: In the patients given oxygen by mask, there was a significant myopic shift in the mean spherical equivalent, which was largest 2-4 days after treatment. The shift was - 0.55 +/- 0.40 D in the right eye and - 0.53 +/- 0.42 D in the left eye. In the patients given oxygen by hood, the largest shift was observed after 12-16 days, and was - 1.06 +/- 0.52 D in the right eye and - 1.10 +/- 0.57 D in the left eye. The refractive changes returned to baseline 6 weeks and 10 weeks after HBO treatment, respectively. No significant changes in crystalline lens transparency were revealed. CONCLUSIONS: The myopic shift after HBO therapy recovers within 10 weeks and may be more pronounced when patients are given oxygen using a hood compared with using an oronasal mask.

Cystitis↗
PubMed2006

Object substitution masking interferes with semantic processing: evidence from event-related potentials.

Object substitution masking (OSM) refers to impaired target identification caused by common onset, but delayed offset, of a surrounding dot mask. This effect has been hypothesized to reflect reentrant processes that result in the mask replacing the target representation. However, little is known about the depth of processing associated with masked targets in this paradigm. We investigated this issue by examining the effect of OSM on the N400 component of the event-related potential, which reflects the degree of semantic mismatch between a target and its context. Participants read a context word followed by a semantically related or unrelated target word surrounded by dots. As expected, delayed dot offset significantly reduced accuracy in identifying the target. The N400 amplitude was also diminished by OSM. These findings offer the first evidence that substitution interferes with target processing prior to semantic analysis, demonstrating an important difference between OSM and other visual phenomena, such as the attentional blink, in which semantic processing is independent of awareness.

Adolescent↗
PubMedDate not supplied

General anesthesia for developmentally disabled dental care patients: a comparison of reinforced laryngeal mask airway and endotracheal intubation anesthesia.

Providing dental care for developmentally disabled patients who require general anesthesia is challenging for both and dentists and anesthesiologists. This study aimed to compare the efficacy of two anesthetic methods for dental care. The researchers retrospectively analyzed morbidity data following anesthesia using either a reinforced laryngeal mask airway (LMA) or endotracheal intubation anesthesia for a two-year time period. The subjects were developmentally disabled patients receiving dental care. Statistical analyses were by unpaired student t-tests and chi-square tests. Patients were who anesthetized with a reinforced laryngeal mask airway had a significantly shorter recovery period and lower postanesthetic complication rates when compared to patients undergoing endotracheal intubation anesthesia. Although hypoxemia (SPO2 < 90%) during dental care occurred more frequently when using the reinforced laryngeal mask airway, the difference was not significant. Nausea and vomiting were the major complications in the postanesthetic care unit and after discharge. When complication rates were compared in the two patient groups, nausea and vomiting were significantly higher during postanesthetic care and after discharge in the intubated group. In conclusion, reinforced laryngeal mask airway provides general anesthesia with less risk of side effects for developmentally disabled patients undergoing dental care.

Adolescent↗
PubMed2001

Forward masking: adaptation or integration?

The aim of this study was to attempt to distinguish between neural adaptation and persistence (or temporal integration) as possible explanations of forward masking. Thresholds were measured for a sinusoidal signal as a function of signal duration for conditions where the delay between the masker offset and the signal offset (the offset-offset interval) was fixed. The masker was a 200-ms broadband noise, presented at a spectrum level of 40 dB (re: 20 microPa), and the signal was a 4-kHz sinusoid, gated with 2-ms ramps. The offset-offset interval was fixed at various durations between 4 and 102 ms and signal thresholds were measured for a range of signal durations at each interval. A substantial decrease in thresholds was observed with increasing duration for signal durations up to about 20 ms. At short offset-offset intervals, the amount of temporal integration exceeded that normally found in quiet. The results were simulated using models of temporal integration (the temporal-window model) and adaptation. For both models, the inclusion of a peripheral nonlinearity, similar to that observed physiologically in studies of the basilar membrane, was essential in producing a good fit to the data. Both models were about equally successful in accounting for the present data. However, the temporal-window model provided a somewhat better account of similar data from a simultaneous-masking experiment, using the same parameters. This suggests that the linear, time-invariant properties of the temporal-window approach are appropriate for modeling forward masking. Overall the results confirm that forward masking can be described in terms of peripheral nonlinearity followed by linear temporal integration at higher levels in the auditory system. However, the difference in predictions between the adaptation and integration models is relatively small, meaning that influence of adaptation cannot be ruled out.

Adaptation, Physiological↗
PubMed2001

Measurement of auditory temporal processing using modified masking period patterns.

A common metric of auditory temporal processing is the difference in the threshold for a pure-tone signal masked by either unmodulated or amplitude-modulated noise. This technique may be viewed as a modification of the masking period pattern technique. Such measurements have been proposed as an efficient means of estimating auditory temporal resolution in a clinical setting, although in many cases threshold differences may reflect additional spectro-temporal processes. The primary purpose of the present experiment was to examine interactions among signal frequency and masker bandwidth and the effects of modulation frequency on modified masking period patterns. The results revealed unmodulated-modulated threshold differences that increased with increasing masker bandwidth and decreased with increasing modulation frequency. There was little effect of signal frequency for narrow-band noise maskers that were equal in absolute bandwidth across frequency. However, unmodulated-modulated threshold differences increased substantially with increasing signal frequency for bandwidths proportional to the signal frequency and for wideband maskers. Although the results are interpreted in terms of a combination of both within-channel and across-channel cues, the specific contributions of these cues in particular conditions are difficult to ascertain. Because modified masking period patterns depend strongly upon a number of specific stimulus parameters, and because it is difficult to determine with any precision the underlying perceptual processes, this technique is not recommended for use as a clinical measure of auditory temporal processing.

Acoustic Stimulation↗
PubMed2002

Modeling the influence of inherent envelope fluctuations in simultaneous masking experiments.

Masked thresholds are measured and simulated for bandpass-noise signals ranging in bandwidth from 4 to 256 Hz in the presence of a masking bandpass noise also ranging in bandwidth from 4 to 256 Hz. Signal and masker are centered at 2 kHz. To investigate the role of temporal processing in simultaneous masking, simulations were performed with the modulation-filterbank model by Dau et al. [J. Acoust. Soc Am. 102, 2906-2919 (1997)]. For a fixed masker bandwidth, thresholds are independent of the signal bandwidth as long as the signal bandwidth does not exceed the masker bandwidth and thresholds decrease with increasing masker bandwidth in those conditions. A simple modulation-low-pass filter (energy integrator) would be sufficient to describe the experimental results in those conditions. In contrast, the processing by a modulation filterbank is necessary to account for the conditions of "asymmetry of masking," where thresholds for signals with bandwidths larger than the masker bandwidth are much lower than those for the reversed condition. In those conditions, the modulation-filterbank model is able to use the inherent higher modulation frequencies of the signal as an additional cue.

Adult↗
PubMed2002

Asymmetry of masking between complex tones and noise: the role of temporal structure and peripheral compression.

Thresholds for the detection of harmonic complex tones in noise were measured as a function of masker level. The rms level of the masker ranged from 40 to 70 dB SPL in 10-dB steps. The tones had a fundamental frequency (F0) of 62.5 or 250 Hz, and components were added in either cosine or random phase. The complex tones and the noise were bandpass filtered into the same frequency region, from the tenth harmonic up to 5 kHz. In a different condition, the roles of masker and signal were reversed, keeping all other parameters the same; subjects had to detect the noise in the presence of a harmonic tone masker. In both conditions, the masker was either gated synchronously with the 700-ms signal, or it started 400 ms before and stopped 200 ms after the signal. The results showed a large asymmetry in the effectiveness of masking between the tones and noise. Even though signal and masker had the same bandwidth, the noise was a more effective masker than the complex tone. The degree of asymmetry depended on F0, component phase, and the level of the masker. The maximum difference between masked thresholds for tone and noise was about 28 dB; this occurred when the F0 was 62.5 Hz, the components were in cosine phase, and the masker level was 70 dB SPL. In most conditions, the growth-of-masking functions had slopes close to 1 (on a dB versus dB scale). However, for the cosine-phase tone masker with an F0 of 62.5 Hz, a 10-dB increase in masker level led to an increase in masked threshold of the noise of only 3.7 dB, on average. We suggest that the results for this condition are strongly affected by the active mechanism in the cochlea.

Adult↗
PubMed2002

The effects of spatial separation in distance on the informational and energetic masking of a nearby speech signal.

Although many studies have shown that intelligibility improves when a speech signal and an interfering sound source are spatially separated in azimuth, little is known about the effect that spatial separation in distance has on the perception of competing sound sources near the head. In this experiment, head-related transfer functions (HRTFs) were used to process stimuli in order to simulate a target talker and a masking sound located at different distances along the listener's interaural axis. One of the signals was always presented at a distance of 1 m, and the other signal was presented 1 m, 25 cm, or 12 cm from the center of the listener's head. The results show that distance separation has very different effects on speech segregation for different types of maskers. When speech-shaped noise was used as the masker, most of the intelligibility advantages of spatial separation could be accounted for by spectral differences in the target and masking signals at the ear with the higher signal-to-noise ratio (SNR). When a same-sex talker was used as the masker, the intelligibility advantages of spatial separation in distance were dominated by binaural effects that produced the same performance improvements as a 4-5-dB increase in the SNR of a diotic stimulus. These results suggest that distance-dependent changes in the interaural difference cues of nearby sources play a much larger role in the reduction of the informational masking produced by an interfering speech signal than in the reduction of the energetic masking produced by an interfering noise source.

Adult↗
PubMed2003

Informational masking: counteracting the effects of stimulus uncertainty by decreasing target-masker similarity.

Previous work has indicated that target-masker similarity, as well as stimulus uncertainty, influences the amount of informational masking that occurs in detection, discrimination, and recognition tasks. In each of five experiments reported in this paper, the detection threshold for a tonal target in random multitone maskers presented simultaneously with the target tone was measured for two conditions using the same set of five listeners. In one condition, the target was constructed to be "similar" (S) to the masker; in the other condition, it was constructed to be "dissimilar" (D) to the masker. The specific masker varied across experiments, but was constant for the two conditions. Target-masker similarity varied in dimensions such as duration, perceived location, direction of frequency glide, and spectro-temporal coherence. Group-mean results show large decreases in the amount of masking for the D condition relative to the S condition. In addition, individual differences (a hallmark of informational masking) are found to be much greater in the S condition than in the D condition. Furthermore, listener vulnerability to informational masking is found to be consistent to at least a moderate degree across experiments.

Acoustic Stimulation↗