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At least 865 records · Page 48Linked to original sources
PubMed1989

Investigation on the protective value of breathing masks in farmer's lung using an inhalation provocation test.

Six subjects with farmer's lung underwent double inhalation challenge tests, each lasting 60 min, using natural antigen exposure. Subjects underwent the tests first without and then with protection by a particle-filtering half mask. Our purpose was to determine whether and to what extent the use of such masks reduced or prevented symptoms in affected patients. Clinical assessment included general and pulmonary symptoms, HR, temperature, WBC count, R, ITGV, VC, TLC, PO2, DCO, and chest x-ray film. The unprotected challenge provoked late responses characteristic of extrinsic allergic alveolitis. In the challenge using the mask, all six patients reported to be completely free of symptoms. Compared with the test without a mask, a statistically significant reduction in the rise of temperature, WBCs, HR, R, TLC, and PO2 was observed. Compared with the initial values, a statistically significant reduced increase of temperature and leukocytes was demonstrated in the test using the mask. Pulmonary and systemic alterations were significantly reduced but not completely prevented by the application of the particle-filtering half mask.

Airway Resistance↗
PubMed1998

Detection of small low-contrast objects in mammography: effect of viewbox masking and luminance.

OBJECTIVE: Viewing conditions can affect an observer's performance in object detection. Our objective was to determine the effect of viewbox masking and luminance on the detection of small low-contrast objects revealed by mammography. MATERIALS AND METHODS: Mammographic contrast-detail images having various film densities were viewed on masked and unmasked viewboxes. Similar images with fixed film contrast and density were viewed when luminance ranged from 250 to 8000 nits (1 nit = 1 cd/m2). RESULTS: Detection of small low-contrast objects was significantly easier using a masked viewbox with high luminance that using a regular unmasked viewbox. When a regular viewbox (approximately 3000 nits) was used masking had a more significant effect on films with high optical densities than on films with low optical densities. Brighter, masked viewboxes improved detection on films with higher optical densities. CONCLUSION: Better detection of small low-contrast objects results when mammographic images are masked and viewed on high-luminance viewboxes than when a regular unmasked viewbox is used.

Female↗
PubMed2000

Automatic detection and quantification of ground-glass opacities on high-resolution CT using multiple neural networks: comparison with a density mask.

OBJECTIVE: We compared multiple neural networks with a density mask for the automatic detection and quantification of ground-glass opacities on high-resolution CT under clinical conditions. SUBJECTS AND METHODS: Eighty-four patients (54 men and 30 women; age range, 18-82 years; mean age, 49 years) with a total of 99 consecutive high-resolution CT scans were enrolled in the study. The neural network was designed to detect ground-glass opacities with high sensitivity and to omit air-tissue interfaces to increase specificity. The results of the neural network were compared with those of a density mask (thresholds, -750/-300 H), with a radiologist serving as the gold standard. RESULTS: The neural network classified 6% of the total lung area as ground-glass opacities. The density mask failed to detect 1.3%, and this percentage represented the increase in sensitivity that was achieved by the neural network. The density mask identified another 17.3% of the total lung area to be ground-glass opacities that were not detected by the neural network. This area represented the increase in specificity achieved by the neural network. Related to the extent of the ground-glass opacities as classified by the radiologist, the neural network (density mask) reached a sensitivity of 99% (89%), specificity of 83% (55%), positive predictive value of 78% (18%), negative predictive value of 99% (98%), and accuracy of 89% (58%). CONCLUSION: Automatic segmentation and quantification of ground-glass opacities on high-resolution CT by a neural network are sufficiently accurate to be implemented for the preinterpretation of images in a clinical environment; it is superior to a double-threshold density mask.

Absorptiometry, Photon↗
PubMed1999

Masking: history, definitions, and measurement.

Masking and entrainment are two different processes that result in rhythms in physiology and behavior. Considering its functional importance, lamentably little study has been devoted to masking compared to that lavished on entrainment. This paper discusses the origin and definition of terminology (positive and negative masking, paradoxical masking) and methods of quantifying masking. How masking is scored can greatly influence the interpretation of results.

Animals↗
PubMed1999

Masked priming of words and nonwords in a naming task: further evidence for a nonlexical basis for priming.

Masked priming effects in word identification tasks such as lexical decision and word naming have been attributed to a lexical mechanism whereby the masked prime opens a lexical entry corresponding to the target word. Two experiments are reported in which masked repetition priming effects of similar magnitude were obtained with word and nonword targets in a naming task. Masked orthographic priming was more stable for word than for nonword targets, although morphological primes produced no advantage beyond that achieved by matched orthographic primes. These results, taken together with the recent finding that repetition priming of nonwords can be obtained in the lexical decision task, support the view that masked priming of words and nonwords has a nonlexical component. We suggest that masked primes can enhance target identification by contributing to the construction of an orthographic or a phonological representation of the target, regardless of the target's lexical status.

Adult↗
PubMed2005

On the role of mask structure in subliminal priming.

Choice reaction times to visual stimuli may be influenced by preceding subliminal stimuli (primes). Some authors reported a straight priming effect i.e., responses were faster when primes and targets called for the same response than when they called for different responses. Other authors found a reversed pattern of results. Our results suggest that the sign of the priming effect depends on mask structure. Inverse priming was obtained only for masks containing the searched-for feature even though informational content of the masks was neutral. With masks of irrelevant structure, straight priming effects were found. Thus, masks are not passive stimuli whose roles are limited to rendering the prime invisible. Processing of the mask may interact with prime and target processing. Implications of the results are discussed for two hypotheses trying to account for straight and inverse priming (the self-inhibition hypothesis and object-updating hypothesis).

Adult↗
PubMed1999

Near-field speech intelligibility in chemical-biological warfare masks.

It is common knowledge among field personnel that poor speech intelligibility can occur when chemical-biological warfare (CBW) masks are worn: indeed, many users resort to hand signals for person-to-person communicative purposes. This study was conducted in an effort to generate basic information about the problem; its focus was on the assessment of, and comparisons among, the communicative efficiency of seven different CBW units. Near-field word intelligibility was assessed by use of rhyming minimal contrast tests; user and acoustic restrictions were studied by means of diadochokinetic tests and system frequency response. The near-field word intelligibility of six American-designed masks varied somewhat, but overall it was reasonably good; however, a Russian unit did not perform well. Second, three of the U.S. masks were found to produce less physiological restraint than the others, and the Soviet mask produced the greatest physiological restraint. Finally, a few of the CBW masks also exhibited very low levels of acoustic distortion. Accordingly, it was concluded that two of the several configurations studied exhibited superior features. Other factors being equal, they can be recommended for field use and as a basis for the development of future generations of CBW masks. However, it also should be noted that although these devices provided reasonably good speech intelligibility when the listener was close to the talker, they do not appear to do so even at minimal distances.

Adult↗
PubMed2002

Dental treatment of children using propofol and a laryngeal mask.

AIM: Sedation regimens for toddlers and preschoolers are still open for further studies. Propofol is rapidly finding its way into medical routine. The aim of this pilot study was to re-evaluate the need for sedation in young children and to further investigate the use of propofol as an intravenous agent combined with the use of a flexible laryngeal mask for treatment of the youngest group of dental patients. METHODS: A randomised clinical trial with 54 children involved was conducted comparing one group receiving propofol sedation only with a study group receiving propofol with the use of a reinforced laryngeal mask. Assessments were made as to depth of sedation, quantity of propofol used, desaturations and recovery times. RESULTS: The use of a laryngeal mask improved the treatment conditions by decreasing the number of desaturations during treatment (p</=0.001, t=5.74). When using a laryngeal mask, the average amount (in ml) of propofol used was significantly higher (p</=0.016, t=-2.22) and the average waking up time in minutes significantly longer (p</=0.016, t=-2.23). CONCLUSION: It was also found that deepening the sedation to be able to insert the laryngeal mask effectively reached such a level that it should be renamed as anaesthesia, thereby possibly limiting its use to hospital settings. The study supported, however, the safety aspects of the laryngeal mask.

Journal Article↗
PubMed2002

Removal Tools are Faster and Produce Less Force and Torque on the Helmet Than Cutting Tools During Face-Mask Retraction.

OBJECTIVE: To investigate the retraction time, forces, and torques applied to the football helmet during removal of the face mask with different face-mask removal tools. DESIGN AND SETTING: Subjects retracted the face mask of a football helmet mounted to a force platform in a laboratory setting. They removed a standard face mask by cutting or removing (or both) the lateral plastic loop straps using 4 different tools: the Trainer's Angel (TA), FM Extractor (FM), power screwdriver (SD), and Quick Release System (QR) in a counterbalanced fashion. SUBJECTS: Eighteen certified athletic trainers participated in this study. MEASUREMENTS: We started measuring time when the subject picked up the tool and ended when the face mask was in a fully retracted position. Maximum forces and torques were measured from the force platform during the retraction process. RESULTS: The SD and QR retracted the face mask significantly faster than the TA and FM. Forces producing superior-inferior translation were least with the SD. The SD and QR produced less lateral translation and rotation and lateral flexion moment than the TA and FM. The FM produced less torque in the lateral flexion moment than the TA. CONCLUSIONS: Tools that removed the loop straps (SD, QR) were faster and produced less force and torque on the helmet than the tools that cut through the loop straps (TA, FM).

Journal Article↗
PubMedDate not supplied

Auditory brainstem response in the cat. Effect of masking level on derived-band contributions.

The auditory brainstem responses evoked by 1 and 4 kHz tone-bursts and clicks at stimulus levels 40 dB above response threshold have been recorded in the anaesthetized cat, and octave-wide derived bands were obtained by the differential high-pass masking procedure. Masking level was varied systematically. Raising masking level to maximally 10 dB of over-masking results in a basalward shift of derived-band contributions, the amplitude of both waves I and IV increasing in the highest frequency band and falling in the most apical. Higher masking levels produce an increase in wave latency in the individual bands, which is greatest at the lowest frequencies. Comparable levels of under-masking have opposite but lesser effects.

Acoustic Stimulation↗
PubMed1987

Digital mammography. ROC studies of the effects of pixel size and unsharp-mask filtering on the detection of subtle microcalcifications.

We investigated the spatial resolution requirement and the effect of unsharp-mask filtering on the detectability of subtle microcalcifications in digital mammography. Digital images were obtained by digitizing conventional screen-film mammograms with a 0.1 X 0.1 mm2 pixel size, processed with unsharp masking, and then reconstituted on film with a Fuji image processing/simulation system (Fuji Photo Film Co., Tokyo, Japan). Twenty normal cases and 12 cases with subtle microcalcifications were included. Observer performance experiments were conducted to assess the detectability of subtle microcalcifications in the conventional, the unprocessed digital, and the unsharp-masked mammograms. The observer response data were evaluated using receiver operating characteristic (ROC) and LROC (ROC with localization) analyses. Our results indicate that digital mammograms obtained with 0.1 X 0.1 mm2 pixels provide lower detectability than the conventional screen-film mammograms. The detectability of microcalcifications in the digital mammograms is improved by unsharp-mask filtering; the processed mammograms still provide lower accuracy than the conventional mammograms, however, chiefly because of increased false-positive detection rates for the processed images at each subjective confidence level. Viewing unprocessed digital and unsharp-masked images in pairs resulted in approximately the same detectability as that obtained with the unsharp-masked images alone. However, this result may be influenced by the fact that the same limited viewing time was necessarily divided between the two images.

Breast Neoplasms↗
PubMed1979

[The concept of masked depression (author's transl)].

Masked depression is an endogenous or psychogenic depressive state in which the somatic symptoms predominate while the psychical symptoms are only present in the background. Therefore it is a matter of phenomenological diagnosis. An enquiry conducted among general practitioners in Germany, France, Austria and Switzerland has shown that up to 10% of the patients consulting a physician are suffering from depression and half of the cases are masked depressions. An enquiry disclosed in 1978 among 74 practising physicians proved that 18% of the patients seeking medical advice suffer from depressive states and that about half of the cases are masked depressions. Diagnosis and therapy of masked depression are of great practical importance in everyday practice because of its frequency. The diagnosis has to be established on the basis of the depressive background symptoms. The masked depressions often show anxious-hypochondrical character and therefore have to be treated with antidepressant drugs with anxiolytic effect. The choice of the antidepressant drug with the right activity profile is decisive for the success of the therapy. Finally, there is a short review about diagnosis and therapy of masked depression.

Depression↗
PubMed1995

Visual performance effects and user acceptance of the M43A1 aviation protective mask frontserts.

BACKGROUND: The initial M43 aviation protective mask was fielded without provisions for optical corrective devices. Contact lenses, an interim solution, were not entirely acceptable since a small segment of the population could not be fitted adequately with contacts. This study evaluated visual performance affects and user acceptance of the M43A1 mask with frontsert correction modifications. METHODS: The investigation was divided into three phases: 1) a helicopter simulator evaluation designed to experimentally test the suitability of the M43A1 frontserts, both in single vision and bifocal forms, for use in the aviation environment; 2) a static cockpit evaluation, designed to identify aircraft-specific problems with the frontsert system; and 3) an inflight evaluation to examine the stability and usability of the frontserts under actual flight conditions. The subjects were 30 U.S. Army aviators (28 men and 2 women). RESULTS: Objective data from flight simulation evaluations suggested there were no significant differences between flight performance with and without the mask, despite refractive status. Subjective data from static and flight evaluations reflected positive user acceptance of the new mask and frontserts. Problems may exist in smaller cockpits (OH-58 A/C, D), but evidence suggested that this may have been an artifact resulting from testing the mask while wearing protective body armor. CONCLUSIONS: Within the range of flight conditions and profiles examined, the M43A1 frontsert system meets U.S. Army aviation needs for optical correction when mission requirements dictate flying with chemical-biological protective masks.

Adult↗
PubMed1997

[Quantitative assessment of pulmonary emphysema with computerized tomography. Comparison of the visual score and high resolution computerized tomography, expiratory density mask with spiral computerized tomography and respiratory function tests].

CT is the most accurate method to detect pulmonary emphysema in vivo. We compared prospectively two different methods for emphysema quantitation in 5 normal volunteers and 20 consecutive patients with chronic obstructive pulmonary disease (COPD). All subjects were submitted to function tests and HRCT; three scans were acquired at preselected levels during inspiration. The type and extent of pulmonary emphysema were defined, using the time-honored visual score system, by two independent observers under blind conditions. Disagreements were subsequently settled by consent. All subjects were also examined with expiratory spiral CT, using a density mask program, at two different cut-off levels (-850, -900 HU). Visual score and expiratory spiral density mask values (-850 HU) were significantly correlated (r = 0.86), but the visual extent of emphysema was always higher than shown by expiratory spiral CT. The emphysema extent assessed with both CT methods correlated with the function result of expiratory airflow obstruction and gas diffusion impairment (visual score versus forced expiratory volume in one second: r = -0.81, versus single breath carbon monoxide diffusion: r = -0.78. Spiral expiratory density mask -850 HU versus forced expiratory volume in one second: r = -0.85, versus single breath carbon monoxide diffusion: r = -0.77). When -900 HU was used as the cut-off value for the expiratory density mask, the correlation with single breath carbon monoxide diffusion worsened (r = -0.56). Visual score and expiratory density mask -850 HU gave similar results and permitted COPD patients to be clearly distinguished from normal controls (p < 0.01). Residual lung volume, measured with expiratory spiral CT correlated significantly with residual volume measured with the helium dilution technique (r = 0.66), but CT values were always higher than function results. We believe the true residual volume should lie somewhere in between the CT value and the function results with the helium dilution technique and conclude that the extent of pulmonary emphysema can be confidently assessed with CT methods. Finally, the simple visual score may be as reliable as such highly sophisticated new methods as the spiral expiratory density mask. Expiratory studies offer new insights into different normal and abnormal features of COPD and respiratory impairment.

Aged↗
PubMed1994

A comparative study of the incidence of sore throat with the laryngeal mask airway.

In a prospective study of 150 patients randomly assigned to three groups, we have compared the incidence and duration of sore throat after a standard anaesthetic regimen using three different methods of airway management: facemask; laryngeal mask, and laryngeal mask with insertion aid. The insertion aid is currently being developed by Portex Ltd and is intended both to facilitate accurate placement of the laryngeal mask and to reduce trauma during insertion. All the patients were women undergoing short operative procedures requiring minimal postoperative analgesia. The incidence of sore throat was significantly less with a facemask (8%) than with the laryngeal mask when used without the insertion aid (28.5%) (p < 0.02). When using the insertion aid the incidence was 18% and this was not statistically different from the facemask. The presence of blood on the laryngeal mask (22%) was less likely when the insertion aid was used (4%) (p < 0.02).

Adult↗
PubMed1995

The quality of breathing and capnography during laryngeal mask and facemask ventilation.

Clinical measures of ventilation and the relationship between arterial and end-tidal carbon dioxide tensions were studied during inhalational anaesthesia in 18 patients using a laryngeal mask airway or a facemask. Tidal volumes were similar in both groups but expired minute volume, respiratory rate and physiological deadspace ventilation were significantly increased in the facemask group. Both end-tidal and arterial carbon dioxide tensions were higher in the laryngeal mask group. Mean arterial to end-tidal carbon dioxide tension differences ranged from 0.13 to 4.13 kPa in the facemask group and from 0-1.73 kPa with the laryngeal mask airway. Pooled data analysis revealed a better correlation between arterial and end-tidal carbon dioxide tensions during laryngeal mask ventilation as compared to facemask breathing. With both techniques the arterial to end-tidal carbon dioxide tension difference was related to respiratory rate and physiological deadspace ventilation. Estimation of arterial carbon dioxide partial pressure by monitoring end-tidal carbon dioxide tension is more reliable with the laryngeal mask airway than during facemask breathing, in particular at small tidal volumes.

Adult↗
PubMed1996

Gas leakage and the laryngeal mask airway. A comparison with the tracheal tube and facemask during spontaneous ventilation using a circle breathing system.

The ability of the laryngeal mask airway, tracheal tube and facemask to provide a leak free seal in a clinical setting was assessed by measuring the minimal fresh gas flows needed in a closed circle system during spontaneous ventilation on 60 subjects. The fresh gas flow was reduced until no spillage occurred from the pop-off valve. This fresh gas flow was taken to represent the sum of gas uptake by the subject and gas leakage from the circuit. The median fresh gas flow after 20 minutes was 350 ml.min-1 in the laryngeal mask airway group, 350 ml.min-1 in the tracheal tube group and 450 ml.min-1 in the facemask group. The fresh gas flow required for the facemask group was significantly higher than that for the laryngeal mask airway or tracheal tube groups (p < 0.01). There was no significant difference between the fresh gas flows required for the tracheal tube and laryngeal mask airway group. We conclude that the laryngeal mask airway provides as good a gas tight seal as a tracheal tube in this context and would be of benefit in reducing anaesthetic gas pollution.

Adult↗
PubMedDate not supplied

The laryngeal mask airway. Safety, efficacy, and current use.

In 1983, the laryngeal mask airway (LMA) was introduced as a new airway device. It can be inserted without the aid of a laryngoscope or neuromuscular blockade. Compared with the face mask, the LMA allows for a more "hands-free approach" to airway management providing the anesthesiologist the freedom of not holding a mask. In addition, the LMA is more effective than the face mask, with or without a Guedel airway, during emergency resuscitation in situations where endotracheal intubation is difficult or not possible. The LMA seems to provide better oxygenation than the face mask; but unlike the endotracheal tube, it does not protect the airway from aspiration of gastric contents if regurgitation occurs. For this reason, it is believed that the LMA should not be used in place of an endotracheal tube during emergency rescue, but rather as an adjunct to airway management prior to intubation. It is possible that the risk of regurgitation with or without aspiration may be minimized if proper screening of patients is employed prior to use of the LMA. The current literature concerning its safety and efficacy is reviewed.

Adult↗