Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Masks”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,729 records · Page 96Linked to original sources
PubMed1997

[Use of the laryngeal mask in adenoidectomy in childhood--a comparison with endotracheal intubation].

PURPOSE: Anaesthesia for adenoidectomy is possible during infancy without succinylcholine. One possibility is intubation with vecuronium bromide, whereas another possibility is the use of the laryngeal mask (LMN). The conditions for intubation as well as further details during anaesthesia are listed and compared. METHODS: 200 children are divided into 4 groups. Group A: intubation with thiopental and vecuronium bromide. Group B: LMN with thiopental, Group C and D: as A and B but the thiopental replaced by propofol. The following aspects are compared: the conditions of intubation; circulation conditions; oxygen saturation; the behaviour when coming out of anaesthesia; complications; the assessment by the surgeons. A further control of 100 routine LMN covers the complications which arose. RESULTS: Adenoidectomy can be carried out successfully with both kinds of anaesthesia. Tracheal intubation attained a better assessment by most surgeons and is easier to administer. Brief declines in the saturation of oxygen occur more frequently when using LMN. LMN has its advantages in the low irritation of the respiratory mucous membranes and results in improved behaviour on coming out of the anaesthesia, especially if used with propofol. Problems arise mainly through the use of the mouth clamp which can result in obstructions of the respiratory tract and re-intubation. These problems arise less frequently when the use of this method has become routine. CONCLUSION: LMN takes time to get used to, and places greater demands on the anaesthetist. Success of LMN depends on the cooperation and collaboration to the surgeon to lower the risk of complications. Once specific improvements in the LMN have been made, it may become the standard method for adenoidectomy in future. It is already used by us and in some outpatient departments, as well as in England and America. Our suggestions are as follows: Aims at convincing the surgeons and improving their co-operation; No routine fixation of the laryngeal mask. The laryngeal mask should be kept slightly taut before opening--preferably slowly--the mouth clamp; possible technical modifications of the mouth clamp itself, which produce a wider gap, could be adapted to the new conditions of the wider LM; reaching the necessary depth of anaesthesia through higher doses of propofol or possibly by total intravenous anaesthesia; routine wearing of the LM in the recovery room until it is no longer tolerated by the child.

Adenoidectomy↗
PubMed1990

Reversal of acute exacerbations of chronic obstructive lung disease by inspiratory assistance with a face mask.

BACKGROUND: Patients with acute exacerbations of chronic obstructive pulmonary disease may require endotracheal intubation with mechanical ventilation. We designed, and here report on the efficacy of, a noninvasive ventilatory-assistance apparatus to provide inspiratory-pressure support by means of a face mask. METHODS: We assessed the short-term (45-minute) physiologic effects of the apparatus in 11 patients with acute exacerbations of chronic obstructive pulmonary disease and evaluated its therapeutic efficacy in 13 such patients (including 3 of the 11 in the physiologic study) who were treated for several days and compared with 13 matched historical-control patients. RESULTS: In the physiologic study, after 45 minutes of inspiratory positive airway pressure by face mask, the mean (+/- SD) arterial pH rose from 7.31 +/- 0.08 to 7.38 +/- 0.07 (P less than 0.01), the partial pressure of carbon dioxide fell from 68 +/- 17 mm Hg to 55 +/- 15 mm Hg (P less than 0.01), and the partial pressure of oxygen rose from 52 +/- 12 mm Hg to 69 +/- 16 mm Hg (P less than 0.05). These changes were accompanied by marked reductions in respiratory rate (from 31 +/- 7 to 21 +/- 9 breaths per minute, P less than 0.01). Only 1 of the 13 patients treated with inspiratory positive airway pressure needed tracheal intubation and mechanical ventilation, as compared with 11 of the 13 historical controls (P less than 0.001). Two patients in each group died. As compared with the controls, the treated patients had a more transient need for ventilatory assistance (3 +/- 1 vs. 12 +/- 11 days, P less than 0.01) and a shorter stay in the intensive care unit (7 +/- 3 vs. 19 +/- 13 days, P less than 0.01). CONCLUSIONS: Inspiratory positive airway pressure delivered by a face mask can obviate the need for conventional mechanical ventilation in patients with acute exacerbations of chronic obstructive pulmonary disease.

Acute Disease↗
PubMed1991

Treatment of severe cardiogenic pulmonary edema with continuous positive airway pressure delivered by face mask.

BACKGROUND: Severe cardiogenic pulmonary edema is a frequent cause of respiratory failure, and many patients with this condition require endotracheal intubation and mechanical ventilation. We investigated whether continuous positive airway pressure delivered by means of a face mask had physiologic benefit and would reduce the need for intubation and mechanical ventilation. METHODS: We randomly assigned 39 consecutive patients with respiratory failure due to severe cardiogenic pulmonary edema to receive either oxygen alone or oxygen plus continuous positive airway pressure delivered through a face mask. It was not possible to blind the investigators to the assigned treatment. Physiologic measurements were made over the subsequent 24 hours, and the patients were followed to hospital discharge. RESULTS: After 30 minutes, both respiratory rate and arterial carbon dioxide tension had decreased more in the patients who received oxygen plus continuous positive airway pressure. The mean (+/- SD) respiratory rate at 30 minutes decreased from 32 +/- 6 to 33 +/- 9 breaths per minute in the patients receiving oxygen alone and from 35 +/- 8 to 27 +/- 6 breaths per minute in those receiving oxygen plus continuous positive airway pressure (P = 0.008); the arterial carbon dioxide tension decreased from 64 +/- 17 to 62 +/- 14 mm Hg in those receiving oxygen alone and from 58 +/- 8 to 46 +/- 4 mm Hg in those receiving oxygen plus continuous positive airway pressure (P less than 0.001). The patients receiving continuous positive airway pressure also had a greater increase in the arterial pH (oxygen alone, from 7.15 +/- 0.11 to 7.18 +/- 0.18; oxygen plus continuous positive airway pressure, from 7.18 +/- 0.08 to 7.28 +/- 0.06; P less than 0.001) and in the ratio of arterial oxygen tension to the fraction of inspired oxygen (oxygen alone, from 136 +/- 44 to 126 +/- 47; oxygen plus continuous positive airway pressure, from 138 +/- 32 to 206 +/- 126; P = 0.01). After 24 hours, however, there were no significant differences between the two treatment groups in any of these respiratory indexes. Seven (35 percent) of the patients who received oxygen alone but none who received oxygen plus continuous positive airway pressure required intubation and mechanical ventilation (P = 0.005). However, no significant difference was found in in-hospital mortality (oxygen alone, 4 of 20 patients; oxygen plus continuous positive airway pressure, 2 of 19; P = 0.36) or the length of the hospital stay. CONCLUSIONS: Continuous positive airway pressure delivered by face mask in patients with severe cardiogenic pulmonary edema can result in early physiologic improvement and reduce the need for intubation and mechanical ventilation. This short-term study could not establish whether continuous positive airway pressure has any long-term benefit or whether a larger study would have shown a difference in mortality between the treatment groups.

Aged↗
PubMed1983

Interruption of dot processing by a backward mask.

A white target field with 0-10 randomly positioned black dots was presented for 20 ms, and followed by a patterned mask with a duration of 200 ms. Subjects reported target numerosity, with strict or lax criteria. Numerosity functions, and control forced-choice discrimination results, supported an interruption model for backward masking by pattern, even for stimulus onset asynchronies as short as 50 ms. When the same targets were degraded by reducing their contrast, but not otherwise masked, results supported an integration model.

Discrimination Learning↗
PubMed1995

The 'uniqueness constraint' and binocular masking.

In stereo-matching algorithms, the 'uniqueness constraint' requires that a feature in one stereo half-image be matched to, at most, one similar feature in the other half-image. Experiments are reported in which binocular contrast thresholds and depth-discrimination judgments have been used to determine whether the human stereo system makes unique matches. A single high-spatial-frequency target in the left eye was paired stereoscopically with two identical targets, presented near retinal correspondence (+/- 3.5 min of disparity), in the right eye. Contrast-increment thresholds were measured for each of the targets in the right eye, and it was found that the target in the left eye masked both. Indeed, the amount of binocular masking for each member of the double target nearly equaled the masking observed when only a single target was presented to the right eye. Depth judgments confirmed that the target in the left eye had been matched to both targets in the right eye. It is concluded that uniqueness is not an absolute constraint on human stereo matching.

Algorithms↗
PubMed2000

Informational masking in normal-hearing and hearing-impaired listeners.

The present study aimed to test whether central, across-channel, informational auditory processing abilities are altered by hearing loss. The informational masking effect exerted on a 1 kHz tone-pip by a simultaneous four-tone masker, whose spectral content changed within as well as across trials, was measured in the left and right ears of normal-hearing subjects and hearing-impaired subjects with either symmetrical or asymmetrical hearing loss between the two ears. In the subjects with normal-hearing or symmetrical hearing loss, the level of the masker was set to 40 dB SL in each ear, in the subjects with asymmetrical hearing loss, the masker was set to 40 dB SL in the best ear and loudness-balanced in the other ear. The results failed to reveal significant differences in informational masking between normal-hearing and hearing-impaired subjects. However, in subjects with asymmetric hearing loss, less informational masking was observed in the ear with the more elevated absolute thresholds than in the opposite ear. Since the latter finding can be explained in terms of across-ear differences in loudness recruitment, it is suggested that central, across-channel, informational processing abilities are not substantially different in hearing-impaired than in normal-hearing ears.

Adult↗
PubMed1975

Age differences in backward dichoptic masking.

An investigation of age differences in backward dichoptic visual noise masking was carried out with young, middle-aged and old subjects. Older subjects were found to be significantly more susceptible to the backward masking effect over longer delays between the target and masking stimuli. These results indicate a decrease with age in the rate at which stimuli can be cleared through the central mechanisms concerned with perceptual processing. These data appear to support the "stimulus persistence" and "arousal" models of aging.

Adult↗
PubMed1982

Dichoptic backward masking of letters, words, and trigrams in old and young subjects.

Age differences in central visual processing were studied in 30 older adults (mean age 67.9 years) and in 30 young adults (mean age 19.8 years) using a dichoptic backward masking paradigm. Single letters, three-letter words, and consonant trigrams were used as target stimuli with a patterned masking stimulus. A significant age difference (p less than .001) was found in the interstimulus intervals necessary to escape the masking effect (ISIc) with older subjects requiring approximately 75 msec longer than the younger ones at each of three target durations. The effect of letters, words, and trigrams on ISIc for both young and old also yielded a significant difference (p = .01) with words most readily identified, letters intermediate, and trigrams requiring the longest processing time. Implications of these data with respect to previous studies and theoretical models are considered.

Adolescent↗
PubMed2004

Effect of masker frequency on N1m amplitude in forward masking.

The effect of frequency on N1m has been investigated by various methods. However, it has not yet been measured using forward masking. In this study, the frequency specificity of N1m was investigated using forward masking. Although the masker frequency had some influence on N1m amplitudes, the results suggested that the frequency specificity of N1m was worse than that of a single-neuron or psychological tuning curve. This is probably because N1m includes various components, both frequency-specific and non-specific, some of which may be less affected by masking. Thus, our results agree with those of previous studies using intervening tones that suggested widespread neural representation in the auditory cortex.

Acoustic Stimulation↗
PubMed2006

Difficult intubation of a child through laryngeal mask airway with two tracheal tubes.

UNLABELLED: Difficult tracheal intubation occurs infrequently. It is estimated that difficult laryngoscopy occurs in 1-2% of patients. Tracheal intubation of especially small infants can be challenging. When faced with a difficult airway, intubation through a laryngeal mask airway is one method of obtaining a secure airway. Here, we report a 23-mo-old girl with chronic lung disease and severe pneumonia, who was admitted to our paediatric intensive care unit. Since the patient could not be intubated by the standard method, because her larynx was up and forward, she was intubated successfully with a laryngeal mask airway through which two consecutive tracheal tubes were inserted. CONCLUSION: Laryngeal mask airway has an important role as a back-up device in case direct visualization of the larynx is not possible.

Female↗
PubMed1991

Across-channel masking of changes in modulation depth for amplitude- and frequency-modulated signals.

This study examines a form of masking that can take place when the signal and masker are widely separated in frequency and cannot be explained in terms of the traditional concept of the auditory filter or critical band. We refer to this as across-channel masking. The task of the subject was to detect an increment in modulation depth of a 1000-Hz sinusoidal carrier. The carrier could either be sinusoidally amplitude modulated or sinusoidally frequency modulated at a 10-Hz rate. Modulation increment thresholds of this "target" signal were measured for the target alone, and in the presence of two interfering sounds with carrier frequencies of 230 and 3300 Hz. When the interfering sounds were unmodulated, they had no effect on modulation increment thresholds. When the interfering sounds were either amplitude or frequency modulated, thresholds increased. Amplitude modulation (AM) increment thresholds were affected by both amplitude-modulated and frequency-modulated interference. Similarly, frequency modulation (FM) increment thresholds were affected by both amplitude-modulated and frequency-modulated interference. For both types of signal, the interference was tuned for modulation rate; across-channel masking was greatest when the interfering sounds were modulated at rates close to 10 Hz, and declined for higher or lower rates. However, the tuning was rather broad. When the target and interfering sounds were modulated at the same rate, there was no effect of the relative phase of the modulators. Two possible explanations for the results are discussed. One is based on the idea that carriers that are modulated in a similar way tend to be perceptually "grouped". The other is based on the idea that there are "channels" in the auditory system tuned for AM and FM rate. Neither explanation appears completely satisfactory.

Adult↗
PubMed1991

Relative contributions of envelope maxima and minima to comodulation masking release.

Comodulation masking release (CMR) is a phenomenon that demonstrates the sensitivity of the auditory system to across-frequency differences in the temporal modulation pattern of a complex waveform. In this paper, we review briefly some of the data on the physical parameters that affect CMR and describe models that have been proposed to account for CMR--namely, models based upon envelope equalization/cancellation, across-frequency envelope correlation, and "dip listening". The present literature is ambiguous with regard to the relative importance of energy in the peak and dip regions of the waveform envelope. We therefore performed a series of experiments to investigate this issue. In the first experiment, we examined CMR for signals that resulted either in a uniform increment or in uniform decrement in the masking noise centred on the signal frequency. This was accomplished by using a 20-Hz-wide noise band centred on 700 Hz as both the masker and as the signal, adjusting the phase angle between the signal and masker to either 0 degree (increment) or 180 degrees (decrement). Conditions were examined where either zero, one, two, four, or six comodulated flanking bands were present. Results indicated positive CMRs for all conditions in which a comodulated flanking band was present. CMR increased as the number of flanking bands increased for intensity increments, but not for intensity decrements. The remaining experiments examined conditions where signals were present only in masker peaks, or only in masker dips. The results of these experiments indicated relatively large CMRs when the signal occurred in dip regions, but no CMR when the signal occurred in peak regions. Whereas some of the results of the above experiments would be difficult to account for in terms of the dip listening hypothesis of CMR, the present findings did indicate that the stimulus cues that give rise to CMR appear to be derived primarily from the dip regions of the masking noise.

Adult↗
PubMed1991

Frequency selectivity for hearing-impaired and broadband-noise-masked normal listeners.

When evaluating frequency selectivity, it is difficult to determine if the deviation from normal performance observed for hearing-impaired listeners reflects abnormal cochlear function or normal, level-dependent changes in frequency selectivity. This experiment was designed to investigate the dependence of frequency-selectivity measures on threshold and signal level. Auditory-filter characteristics, critical ratios, forward-masked psychophysical tuning curves, and narrowband-noise masking patterns were obtained from normal-hearing listeners in quite and in the presence of broadband noise at five levels. These findings were then compared to previously obtained frequency-selectivity measurements for subjects with mild-to-moderate sensorineural hearing loss whose absolute thresholds are comparable to the normal-hearing listeners' masked thresholds. The results suggest that frequency selectivity deterioriates as threshold increases for all subjects. However, the poor frequency selectivity exhibited by hearing-impaired listeners may not be explained entirely by the effects of threshold and signal level. Nevertheless, because frequency selectivity is poorer in the normal auditory system at higher stimulus levels, the deviation from normal performance observed for hearing-impaired listeners may not be as large as previously suggested.

Adolescent↗
PubMed1992

Cricoid pressure may prevent insertion of the laryngeal mask airway.

We have studied 42 female patients undergoing elective day-case surgery allocated randomly to two groups. After induction of anaesthesia an attempt was made to insert a laryngeal mask airway after application of cricoid pressure in one group or with no cricoid pressure in the other. The anaesthetist was unaware of the application, or not, of cricoid pressure. Successful insertion was achieved at the first or second attempt in 19 of the 22 patients in the non-cricoid pressure group, but in only three of the 20 patients in the cricoid pressure group (chi 2 18.62, P < 0.001). The laryngeal mask airway was then inserted successfully in all 17 patients after removal of cricoid pressure. The implications of having to remove cricoid pressure if a laryngeal mask airway is to be inserted are discussed.

Adolescent↗
PubMed1993

Pressure exerted by the laryngeal mask airway cuff upon the pharyngeal mucosa.

Ten patients were studied for each of the sizes 2, 3 and 4 laryngeal mask airways (LMA) in order to calculate the pressure exerted by the cuff upon the pharyngeal mucosa. Using a non-invasive method of comparing intracuff pressures recorded both in vitro and in vivo, the transmitted pharyngeal mucosal pressures were calculated over the clinical range of injection volumes. Cuff inflation with the "normal" injection volumes recommended resulted in the residual volumes of the cuffs being exceeded. The intracuff pressures recorded with the mask in situ at these normal injection volumes were in the range 103-251 mm Hg. The calculated transmitted mucosal pressures were substantial for all three sizes of cuff and potentially exceeded the capillary perfusion pressure of the adjacent pharyngeal mucosa, despite apparent pharyngeal accommodation to the mask.

Adolescent↗
PubMed1995

Preoxygenation--the importance of a good face mask seal.

We have studied 16 healthy volunteers whose lungs were preoxygenated six times each in order to assess the amount of room air entrained during tidal volume preoxygenation if a good seal is not maintained between the face mask and the face. With a fresh gas flow of 10 litre min-1, we found that using gravity alone to hold the face mask in position, more than 20% room air was entrained; if the face mask was held adjacent to the face, more than 40% room air was entrained.

Adult↗
PubMed1996

Removal of the laryngeal mask airway in children: anaesthetized compared with awake.

We studied 60 children, aged 12 months to 8 yr, undergoing plastic surgery under general anaesthesia supplemented by regional anaesthesia. Patients were allocated randomly to have the laryngeal mask airway removed either on awakening or while anaesthetized. Subsequent observation of respiratory factors and oxygen saturation showed a significant difference between the groups for coughing (P < 0.001), with a greater incidence (17 of 33) in the awake group compared with those from whom the laryngeal mask airway was removed while anaesthetized (two of 27). There were no differences in the incidences of laryngospasm, desaturation (< 95%) and excess salivation between the groups. Removed of the laryngeal mask airway during deep anaesthesia reduced coughing in the immediate postoperative period.

Anesthesia, General↗
PubMed1997

The intubating laryngeal mask. II: A preliminary clinical report of a new means of intubating the trachea.

We have assessed the efficacy of a new laryngeal mask prototype, the intubating laryngeal mask airway (ILMA), as a ventilatory device and blind intubation guide. The ILMA consists of an anatomically curved, short, wide bore, stainless steel tube sheathed in silicone which is bonded to a laryngeal mask and a guiding handle. It has a single moveable aperture bar, a guiding ramp and can accommodate an 8 mm tracheal tube (TT). After induction of anaesthesia with propofol 2.5 mg kg-1 and fentanyl 2.5 micrograms kg-1, the device was inserted successfully at the first attempt in all 150 (100%) patients and adequate ventilation achieved in all, with minor adjustments required in four patients. Placement did not require movement of the head and neck or insertion of the fingers in the patient's mouth. Blind tracheal intubation using a straight silicone cuffed TT was attempted after administration of atracurium 0.5 mg kg-1. If resistance was felt during intubation, a sequence of adjusting manoeuvres was used based on the depth at which resistance occurred. Tracheal intubation was possible in 149 of 150 (99.3%) patients. In 75 (50%) patients no resistance was encountered and the trachea was intubated at the first attempt, 28 (19%) patients required one adjusting manoeuvre and 46 (31%) patients required 2-4 adjusting manoeuvres before intubation was successful. There were 13 patients with potential or known airway problems. The lungs of all of these patients were ventilated easily and the trachea intubated using the ILMA. In 10 of 13 (77%) of these patients, no resistance was encountered and the trachea was intubated at the first attempt; three of 13 (23%) patients required one adjusting manoeuvre. Tracheal intubation required significantly fewer adjusting manoeuvres in patients with a predicted or known difficult airway (P < 0.05). We conclude that the ILMA appeared on initial assessment to be an effective ventilatory device and intubation guide for routine and difficult airway patients not at risk of gastric aspiration.

Adult↗