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PubMed1994

Nasal masks for domiciliary positive pressure ventilation: patient usage and complications.

BACKGROUND: Nasal mask discomfort is a major factor in compliance with treatment by nasal intermittent positive pressure ventilation (NIPPV) and nasal continuous positive airway pressure (CPAP). METHODS: A study of skin complications resulting from mask usage, with particular reference to predisposing factors, was carried out in 66 patients by means of a postal questionnaire. An effective means of managing ulceration at the nasal bridge while continuing therapy is described. RESULTS: Some disruption of treatment due solely to mask discomfort was experienced by 35 patients (53%), consisting of broken skin or open sores in 11 cases (17%). CONCLUSIONS-Although complications resulting from nasal mask usage are common, early identification of patients at risk of developing such complications and appropriate intervention will result in improved patient compliance.

Adult↗
PubMed1982

A respiratory mask for resting and exercising dogs.

A respiratory face mask has been developed for use with unsedated beagles trained to run on a treadmill. The latex rubber mask, shaped to fit the animal's muzzle, incorporates two modified, commercially available, pulmonary valves for separating inspiratory and expiratory flows. The mask has a dead space of 30 cm3 and a flow resistance below 1 cmH2O . 1(-1) . s. The flexible mask is used to measure breath-by-breath respiratory variables over extended periods of time during rest and exercise.

Animals↗
PubMed1993

Antimasking effects of the olivocochlear reflex. II. Enhancement of auditory-nerve response to masked tones.

1. The antimasking effects of olivocochlear (OC) efferent feedback were studied in anesthetized or decerebrate cats by comparing responses of single auditory-nerve fibers (ANFs) to tone bursts in continuous masking noise seen with and without addition of a moderate-level contralateral noise known to activate the OC reflex. Responses were measured as a function of tone-burst intensity, tone-burst frequency, and masker intensity and were analyzed so as to allow quantitative estimates of the detectability of the tone bursts against the noise background. 2. Addition of the contralateral OC elicitor both increased the maximum discharge rates to the masked tone bursts and decreased the rates to the ipsilateral masker. The rate increases to the tone bursts could be explained on the basis of a decrease in adaptation caused by decreasing the steady response to the masker. The result is a steepening of the rate-versus-level function for masked tone bursts and a concomitant increase in the estimated discriminability of small increments of tone-burst intensity. 3. For tone bursts at the fiber's characteristic frequency (CF), the OC effects on detection threshold for the masked tone bursts depended on masker level, with small increases in threshold for low masker levels and somewhat larger decreases in threshold for higher masker levels. For tone bursts below CF, OC effects, when present, always decreased the detection threshold. 4. The largest antimasking effects were seen for fibers with CFs between 6 and 12 kHz and for masker levels within 20 dB of the fiber's threshold to the masker. These trends appeared to hold for fibers of all spontaneous rates (SRs). 5. Enhancement of the response to unmasked tone bursts and concomitant decrease in the "spontaneous rate" was elicited by OC activation in fibers if threshold sensitivity approached -10 dB SPL. This "enhancement-in-quiet" appears to arise when an animal-generated noise produces a continuous response (in the absence of purposely applied sound) that is suppressed by OC activity. This finding raises questions as to the range of "true" spontaneous rates in the cat. 6. The results highlight two important distinctions between the effects of OC feedback in quiet versus those in noise. In quiet, the effects are predominately suppressive and are restricted to stimuli at frequencies near a fiber's CF and at intensities within its dynamic range. In continuous background noise, the OC reflex can enhance the responses to transient stimuli. Such effects are seen throughout the fiber's response area.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Cochlear implant place psychophysics. 2. Comparison of forward masking and pitch estimation data.

Results for forward masking and numerical estimation of pitch were compared in a group of 6 adult subjects implanted with cochlear prostheses manufactured by Cochlear Limited. Data were collected for bipolar + 1 stimulation in all subjects, and for stimulation in one other mode, either common ground or monopolar, for all subjects but one. The pitch data show various irregularities and in each case can be seen to be broadly consistent with the corresponding forward masking data. It is shown that a 'centre of gravity' of the forward masking distribution varies with masker electrode in a manner that is qualitatively very similar to the variation of pitch estimate. It is suggested that, while pitch estimation results are consistent with those from forward masking, the latter contain more detailed information that may be useful in understanding intersubject variations in speech comprehension.

Adolescent↗
PubMedDate not supplied

Remote masking in normal-hearing and noise-exposed chinchillas.

Remote masking (RM), the phenomenon whereby an intense high-frequency masking noise elevates thresholds for low-frequency signals, has been shown to be sensitive to various types of hearing loss in humans. We performed two experiments to evaluate the chinchilla as a model of RM and to examine changes in RM associated with temporary threshold shifts (TTSs) induced by low-frequency noise exposure. Thresholds for 0.5-, 1- and 2-kHz tones were measured in quiet, then in the presence of a narrow-band (300-Hz-wide) masking noise centered at 3 kHz. In Experiment I, effective masking was measured as a function of masker level, from 48 to 98 dB sound pressure level (SPL; referenced to 20 microPa), to determine threshold and rate of growth of RM in the chinchilla. In Experiment II, RM was measured before, during and after exposure to a low-frequency noise known to produce TTSs in chinchillas (i.e., a 0.5-kHz octave band noise at 90 dB SPL for 6 h/day for 10 days). The results show that normal-hearing chinchillas have the same pattern of RM as humans, and that a noise exposure that produces TTSs also produces rapid and significant changes in RM.

Animals↗
PubMed2003

Backward masking is not required to elicit the central performance drop.

In some circumstances, texture discrimination performance peaks in the parafovea rather than at the fovea. Kehrer (1987) referred to this phenomenon as the central performance drop (CPD). In most studies showing the CPD, task performance has been limited by a backward mask. Morikawa (2000) has argued that in these studies the backward mask was critical to the emergence of the CPD. In three studies we use textures comprising left and right oblique line segments and limit performance by manipulating the orientation variability within the foreground and background textures. Using this method we demonstrate that significant CPDs emerge whether or not there is a backward mask. We conclude that in past studies of the CPD the backward mask functioned primarily as a source of spatial noise and that its temporal relation to the texture display is not critical to the emergence of the CPD.

Humans↗
PubMed2004

Rapid iconic erasure without masking.

We report on the erasure of the iconic memory of an array of 12 black letters flashed on a continuously- present white field. Erasure is accomplished by replacing the 16 ms letter array (frame 1) with a blank white frame for 16 ms (frame 2). The letter array returns in frame 3, with from one to six letters missing. Report of the missing letters is accurate without the blank white frame but is impoverished with it, as if interposing the blank erases the icon. Erasure occurs without any obvious luminance masking, 'mud splashes', pattern masking (backward, forward, or metacontrast), lateral masking, or masking by object substitution. Erasure is greatly decreased if the blank is presented one frame earlier or later. We speculate that erasure is due to a rapid reset of the icon produced by an informational mis-match.

Humans↗
PubMed1994

Hemodynamic effects of nasal and face mask continuous positive airway pressure.

Studies of the hemodynamic effects of nasal continuous positive airway pressure (n-CPAP) in normal subjects have had conflicting results. The largest study (n = 19) found no effect of up to 15 cm H2O on heart rate (HR), cardiac stroke volume (SV), or cardiac index. We hypothesized that n-CPAP, by increasing intrathoracic pressure, should decrease SV and cardiac output (CO) in a dose-dependent fashion in normal subjects. We also hypothesized that mouth position, i.e., open or closed, could affect intrathoracic pressure and thus SV and CO. Six normal subjects were tested with four levels of CPAP (5, 10, 15, and 20 cm H2O) under three mask conditions-face mask and nasal mask with the mouth open (mo) or with the mouth closed (mc). Noninvasive pulsed Doppler measurements of SV and HR were made under each condition. N-CPAP (mc) and face mask CPAP (f-CPAP) resulted in significant dose-dependent decreases of SV-24 +/- 5 ml (21%) and 33 +/- 5 ml (28%), respectively--from baseline to 20 cm H2O (p < 0.05). HR were unchanged and CO significantly decreased with n-CPAP(mc) and with f-CPAP, 1.6 +/- 0.38 L/min (23%) and 2.29 +/- 0.54 L/min (31%), respectively, from baseline to 20 cm H2O (p < 0.05). Esophageal pressure measurements verified increasing intrathoracic pressure with increasing levels of f-CPAP and n-CPAP (mc) but not with n-CPAP (mo). In conclusion, n-CPAP (mc) and f-CPAP resulted in significant and similar dose-dependent decreases in SV and CO.

Adult↗
PubMed1997

Nasal mask pressure waveform and inspiratory muscle rest during nasal assisted ventilation.

In mechanically ventilated patients, pressure and flow tracings can be used to assess respiratory pump muscle activity or rest. When the ventilation is delivered through an endotracheal tube, the respiratory system can be considered a one-compartment model, and activation of the respiratory muscles results in deformations and variability of the pressure tracings. This is also true when mechanical ventilation is delivered nasally. With intermittent positive-pressure ventilation delivered through a nasal mask (nIPPV), we have recently shown that the glottis can interfere with ventilation even in the absence of diaphragmatic surface electromyographic (EMG) activity. On the basis of our observations, we suggested that when mechanical ventilation is delivered through a nasal means of access, the respiratory system cannot be considered a one-compartment model. To confirm this hypothesis, we submitted one healthy subject to nIPPV while his glottis was continuously monitored through a fiberoptic bronchoscope and his diaphragmatic activity was monitored with a bipolar esophageal electrode. During wakefulness or sleep, we observed irregularities in the nasal mask pressure waveform, in nasal mask peak pressure, and in actual VT despite the absence of respiratory pump muscle activity. These irregularities were related to significant variations in the glottic width, rather than to the reappearance of transient phasic inspiratory muscle activity. We conclude that during nIPPV, deformations in the mask pressure waveform can be induced by variations in the glottic aperture without activation of the diaphragm. Thus, when mechanical ventilation does not bypass the glottis, the respiratory system does not behave like a one-compartment model, and EMG remains the only reliable technique for assessing diaphragmatic muscle activity.

Adult↗
PubMed2003

The use of modified VBM laryngeal tube compared to Laryngeal Mask Airway during spontaneous ventilation.

We have compared the use of the laryngeal mask airway with the new modified laryngeal tube in a prospective randomized controlled study. Sixty ASA 1 or 2 patients, aged 18 to 65 years, scheduled for elective surgery and breathing spontaneously under general anaesthesia, were studied. After preoxygenation, anaesthesia was induced with fentanyl and propofol. The patients were randomized to receive either a laryngeal mask airway or a laryngeal tube. Anaesthesia was maintained with nitrous oxide, oxygen and isoflurane. We recorded the speed and the ease of insertion, the number of attempts needed to successfully secure the airway and intraoperative complications, such as partial airway obstruction needing airway manipulation. The airway devices were removed with the patients fully awake at the end of surgery. Systolic arterial blood pressure, heart rate and end-tidal CO2 were recorded at various time intervals. Postoperative complications were recorded. We found that the incidence of partial airway obstruction needing intraoperative airway manipulation was higher with the laryngeal tube than with the laryngeal mask airway. We conclude that during spontaneous ventilation the modified laryngeal tube is not as reliable in providing a satisfactory airway and we consider it is not a suitable alternative to the laryngeal mask airway.

Adult↗
PubMedDate not supplied

The use of the laryngeal mask airway in children with subglottic stenosis.

Patients with tracheal stenosis have a high incidence of difficult or failed tracheal intubation. Airway management with the laryngeal mask airway during fibreoptic laryngoscopy was used in two children with acquired subglottic stenosis during spontaneous breathing. The laryngeal mask airway may be superior to tracheal intubation or use of a face mask during anaesthesia management in severe subglottic stenosis. Ventilation may be improved and the use of a laryngeal mask airway can reduce or eliminate some of the problems associated with the other methods of airway management, such as further damage to stenotic tissue and gastric distention.

Child↗
PubMed1992

Comparative effects of laryngeal mask airway and endotracheal tube insertion on intraocular pressure in children.

Intraocular pressure (IOP) measurements in children are frequently performed under halothane-nitrous oxide anesthesia; however, anesthesia face masks may limit access to the eyes, and tracheal intubation is associated with transient increases in IOP. Use of the laryngeal mask airway (LMA) permits the maintenance of a patent airway without the need for laryngoscopy and tracheal intubation. In a randomized study of 41 children, we compared the IOP, hemoglobin oxygen saturation, and hemodynamic responses to the insertion of an LMA or tracheal tube during a standardized steady-state anesthetic technique consisting of 1 MAC halothane and 66% nitrous oxide. Baseline measurements of IOP, hemoglobin oxygen saturation, heart rate, and arterial blood pressure were recorded and repeated within 15-30 s after insertion of the airway device and at 1-min intervals for 5 min. Insertion of the LMA required significantly less time (26 +/- 16 vs 39 +/- 17 s [mean +/- SD]) and was associated with higher hemoglobin oxygen saturation values compared with the tracheal intubation. The LMA did not increase IOP, heart rate, or arterial blood pressure above baseline values. In contrast, tracheal intubation was associated with significant increases of IOP, heart rate, and arterial blood pressure. We concluded that the laryngeal mask offers advantages over tracheal intubation and the face mask for airway management in patients undergoing IOP measurements.

Anesthesia↗
PubMed2004

Mechanical versus manual ventilation via a face mask during the induction of anesthesia: a prospective, randomized, crossover study.

UNLABELLED: One approach to make ventilation safer in an unprotected airway has been to limit tidal volumes; another one might be to limit peak airway pressure, although it is unknown whether adequate tidal volumes can be delivered. Accordingly, the purpose of this study was to evaluate the quality of automatic pressure-controlled ventilation versus manual circle system face-mask ventilation regarding ventilatory variables in an unprotected airway. We studied 41 adults (ASA status I-II) in a prospective, randomized, crossover design with both devices during the induction of anesthesia. Respiratory variables were measured with a pulmonary monitor (CP-100). Pressure-controlled mask ventilation versus circle system ventilation resulted in lower (mean +/- SD) peak airway pressures (10.6 +/- 1.5 cm H(2)O versus 14.4 +/- 2.4 cm H(2)O; P < 0.001), delta airway pressures (8.5 +/- 1.5 cm H(2)O versus 11.9 +/- 2.3 cm H(2)O; P < 0.001), expiratory tidal volume (650 +/- 100 mL versus 680 +/- 100 mL; P = 0.001), minute ventilation (10.4 +/- 1.8 L/min versus 11.6 +/- 1.8 L/min; P < 0.001), and peak inspiratory flow rates (0.81 +/- 0.06 L/s versus 1.06 +/- 0.26 L/s; P < 0.001) but higher inspiratory time fraction (48% +/- 0.8% versus 33% +/- 7.7%; P < 0.001) and end-tidal carbon dioxide (34 +/- 3 mm Hg versus 33 +/- 4 mm Hg; not significant). We conclude that in this model of apneic patients with an unprotected airway, pressure-controlled ventilation resulted in reduced inspiratory peak flow rates and peak airway pressures when compared with circle system ventilation, thus providing an additional patient safety effect during mask ventilation. IMPLICATIONS: In this model of apneic patients with an unprotected airway, pressure-controlled ventilation resulted in reduced inspiratory peak flow rates and lower peak airway pressures when compared with circle system ventilation, thus providing an additional patient safety effect during face-mask ventilation.

Adolescent↗
PubMed2004

Failed obstetric tracheal intubation and postoperative respiratory support with the ProSeal laryngeal mask airway.

UNLABELLED: The ProSeal laryngeal mask airway (ProSeal LMA) provides a better seal and probably better airway protection than the classic laryngeal mask airway (classic LMA). We report the use of the ProSeal LMA in a 26-yr-old female with HELLP syndrome for failed obstetric intubation and postoperative respiratory support. Both laryngoscope-guided tracheal intubation and face mask ventilation failed, but a size 4 ProSeal LMA was easily inserted and high tidal volumes obtained. A gastric tube was inserted through the ProSeal LMA drain tube and 300 mL of clear fluid was removed from the stomach. There were no hemodynamic changes during ProSeal LMA insertion. Postoperatively, the patient was transferred to the intensive care unit, where she was ventilated via the ProSeal LMA for 8 h until the platelet count had increased and she was hemodynamically stable. Weaning and ProSeal LMA removal were uneventful. There is anecdotal evidence supporting the use of the LMA devices for failed obstetric intubation (19 cases) and for postoperative respiratory support (8 cases). In principle, the ProSeal LMA may offer some advantages over the classic LMA in both these situations. IMPLICATIONS: We report the successful use of the ProSeal laryngeal mask airway for failed obstetric intubation and postoperative respiratory support in a patient with HELLP syndrome.

Adult↗
PubMed1985

Spatial-frequency masking and Birdsall's theorem.

We measured the masking of a spatial 4-cycle/deg sinusoid in the presence of both random and sinusoidal masks. Subjects used a variety of detection strategies, depending on psychophysical technique and familiarity with the mask. Some strategies produce Weber's-law behavior and appear formally equivalent to identification tasks; we hypothesize that these exemplify the operation of Birdsall's theorem. Other strategies produce power-law behavior and are more like the simpler detection task. Our results suggest that criterion change (commonly uncontrolled in masking studies) can produce an unacceptably large bias in the results.

Attention↗
PubMed1989

Temporal properties of information extraction in reading studied by a text-mask replacement technique.

A text was replaced with a visual mask for a fixed duration every time the reader made a saccade. The threshold duration was measured when the mask was presented at the beginning of a saccade or a fixation, or at a certain delay after the onset of a fixation. The effect of the mask on reading time, as well as on the subjective legibility of the text, was also investigated. It was shown that saccadic suppression exists in reading; subjects are not affected by a mask as long as it is inserted during the saccade. The visual sensitivity is recovered only partially at the initial part of fixation and is recovered fully approximately 70 msec after the beginning of the fixation. The visual information can be extracted during a later part of the fixation period as efficiently as or even more efficiently than during the early part of the fixation.

Adult↗
PubMed2004

Dispersal of respiratory droplets with open vs closed oxygen delivery masks: implications for the transmission of severe acute respiratory syndrome.

Nosocomial transmission of droplet-borne respiratory infections such as severe acute respiratory syndrome (SARS) may be influenced by the choice of oxygen face mask. A subject inhaled saline mist and exhaled through three oxygen masks to illustrate the pattern of dispersal of pulmonary gas. In two commonly used masks, exhaled gas formed a plume emanating from the side vents, while a third mask with a valved manifold, which was modified by adding a respiratory filter, retained the droplets. Maintaining respiratory isolation during the administration of oxygen may reduce the risk of the nosocomial transmission of respiratory infections such as SARS.

Aerosols↗
PubMed1991

Intermittent volume cycled mechanical ventilation via nasal mask in patients with respiratory failure due to COPD.

Intermittent mechanical ventilation via nasal CPAP mask was provided to 13 patients admitted to this institution for exacerbation of chronic respiratory failure. Ten suffered from COPD, two suffered from obesity hypoventilation syndrome (OHS), and one from severe hypothyroidism. All except one presented with dyspnea and hypercapnia due solely to progression of their underlying disease processes. Six of the patients with COPD and the patient with hypothyroidism responded to positive pressure ventilation by mask with improvements in blood gas values and clinical status. The remaining two patients with COPD and the two patients with OHS were unable to use the system. Four of the patients with COPD and chronic respiratory failure have been subsequently maintained on daily volume ventilation via nasal mask for about 20 months with persistent clinical and physiologic improvements. Application of volume ventilation through the nasal CPAP mask is a feasible strategy for providing long-term mechanical ventilation to selected patients with COPD and respiratory failure.

Adult↗