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PubMed1997

A comparison of three methods of bag valve mask ventilation.

A method of bag valve mask ventilation in which the resuscitator compresses the self inflating bag between their open palm and the side of their body was compared with conventional single and two resuscitator bag valve mask ventilation. Fifteen nurses each ventilated three patients for 4 min following the induction of general anaesthesia, using one method per patient in random order. Tidal volume and peak mask pressures were higher with the two resuscitator technique than with either form of single resuscitator ventilation; There were no significant differences between the two methods of single resuscitator ventilation. Tidal volume: mean (S.D.); 'open palm': 270 ml (160); single resuscitator: 260 ml (220); two resuscitators: 480 ml (210). Peak mask pressure (mmHg): mean (SD); 'open palm': 19 (8); single resuscitator: 17(9); two resuscitator: 28 (11).

Adult↗

PubMed2001

Masking and purging mutations following EMS treatment in haploid, diploid and tetraploid yeast (Saccharomyces cerevisiae).

The yeast, Saccharomyces cerevisiae, was used as a model to investigate theories of ploidy evolution. Mutagenesis experiments using the alkylating agent EMS (ethane methyl sulphonate) were conducted to assess the relative importance that masking of deleterious mutations has on response to and recovery from DNA damage. In particular, we tested whether cells with higher ploidy levels have relatively higher fitnesses after mutagenesis, whether the advantages of masking are more pronounced in tetraploids than in diploids, and whether purging of mutations allows more rapid recovery of haploid cells than cells with higher ploidy levels. Separate experiments were performed on asexually propagating stationary phase cells using (1) prototrophic haploid (MAT alpha) and diploid (MATa/alpha) strains and (2) isogenic haploid, diploid and tetraploid strains lacking a functional mating type locus. In both sets of experiments, haploids showed a more pronounced decrease in apparent growth rate than diploids, but both haploids and diploids appeared to recover very rapidly. Tetraploids did not show increased benefits of masking compared with diploids but volume measurements and FACScan analyses on the auxotrophic strains indicated that all treated tetraploid strains decreased in ploidy level and that some of the treated haploid lines increased in ploidy level. Results from these experiments confirm that while masking deleterious mutations provides an immediate advantage to higher ploidy levels in the presence of mutagens, selection is extremely efficient at removing induced mutations, leading growth rates to increase rapidly over time at all ploidy levels. Furthermore, ploidy level is itself a mutable trait in the presence of EMS, with both haploids and tetraploids often evolving towards diploidy (the ancestral state of S. cerevisiae) during the course of the experiment.

Cell Division↗

PubMed2000

Masked fear words produce increased SCRs: an anomaly for Ohman's theory of pre-attentive processing in anxiety.

A. Ohman and J.J.F. Soares (1994) demonstrated that masked presentation of phobic pictures produces increased skin conductance responses (SCRs) in phobic subjects. A. Ohman (1993) explained this phenomenon in terms of a hypothetical "feature detector" that identifies physical characteristics of stimuli and activates the arousal system without involving significance evaluation or consciousness. By exposing spider phobics to spider words, general threat words, and neutral words instead of pictures, this explanation was tested. Words were presented both masked and unmasked while electrodermal activity was measured. Under unmasked conditions, SCRs were largest for spider words followed by general threat words, then neutral words. When masked, the difference between spider words and general threat words disappeared but SCRs remained significantly smaller for neutral words. It is concluded that activation of the arousal system by masked threat cues does not necessarily depend on their perceptual characteristics.

Adult↗

PubMed2002

Masked o-benzoquinones in organic synthesis.

An account of the synthetic utility of masked o-benzoquinones is provided. The inter- and intramolecular Diels-Alder reactions of in situ generated masked o-benzoquinones produced cycloadducts in excellent selectivities. New synthetic methodologies have been developed for the synthesis of highly substituted ring systems including bicyclo[2.2.2]octenones, oxatricycles, triquinanes, polysubstituted cyclohexanes, and bicyclo[4.2.2]decenones with complete stereocontrol from easily accessible 2-methoxyphenols via the Diels-Alder reaction of masked o-benzoquinones. Other reactions of adducts derived from masked o-benzoquinones are also described. The efficacy of our methodology is demonstrated by several examples of the total synthesis of natural products.

Journal Article↗

PubMed2006

New bitter-masking compounds: hydroxylated benzoic acid amides of aromatic amines as structural analogues of homoeriodictyol.

Starting from the known bitter-masking flavanones eriodictyol and homoeriodictyol from herba santa some structurally related hydroxybenzoic acid amides of benzylamines were synthesized and evaluated as masking agents toward bitterness of caffeine by sensory methods. The closest structural relatives of homoeriodictyol, the hydroxybenzoic acid vanillylamides 5-9, were the most active and were able to reduce the bitterness of a 500 mg L(-1) caffeine solution by about 30% at a concentration of 100 mg L(-1). 2,4-Dihydroxybenzoic acid vanillylamide 7 showed a clear dose-dependent activity as inhibitor of the bitter taste of caffein between 5 and 500 mg L(-1). Additionally, it was possible to reduce the bitterness of quinine and salicine but not of the bitter peptide N-l-leucyl-l-tryptophan. Combinations of homoeriodictyol and amide 7 showed no synergistic or antagonistic changes in activity. The results for model compound 7 suggested that the hitherto unknown masking mechanism is probably the same for flavanones and the new amides. In the future, the new amides may be alternatives for the expensive flavanones to create flavor solutions to mask bitterness of pharmaceuticals or foodstuffs.

Amides↗

PubMed1998

Mammographic breast density and risk of breast cancer: masking bias or causality?

Masking bias is hypothesized to explain associations between breast density and breast cancer risk. Tumours in dense breasts may be concealed at the initial examination, but manifest themselves in later years, suggesting an increase in breast cancer incidence. We studied the association between breast density and breast cancer risk in 0, 1-2, 3-4 and 5-6 year periods between initial examination and diagnosis. We studied 359 cases and 922 referents, identified in a breast cancer screening programme in Nijmegen, The Netherlands. Breast density was assessed at the initial examination and classified as 'dense' (if > 25% of the breast was composed of density) or 'lucent' (< or = 25% density). In women examined with mid-1970s film screen mammography, we found that at time 0 the odds ratio (OR) for women with dense breasts compared to those with lucent breasts was 1.4 (95% confidence interval (CI): 0.7-6.2). After a 3-4 year period the risk was increased to 3.3 (95% CI: 1.5-7.1). Then, the risk decreased again (OR: 1.2, 95% CI: 0.6-2.7). This rise and decline in risk are in accordance with the masking hypothesis. The observation, however, that the risk at time 0 does not appear to be lower for women with dense breasts than for those with lucent breasts, seems to be inconsistent with the masking hypothesis and may be indicative of causality. The same analysis were performed in women whose initial screening examination was done with current high-quality mammography. Due to the small size of this study group no firm conclusions could be drawn, but it seems as if masking bias could still play a role with high-quality mammography.

Adult↗

PubMed2002

Parametric modeling for survival with competing risks and masked failure causes.

We consider a life testing situation in which systems are subject to failure from independent competing risks. Following a failure, immediate (stage-1) procedures are used in an attempt to reach a definitive diagnosis. If these procedures fail to result in a diagnosis, this phenomenon is called masking. Stage-2 procedures, such as failure analysis or autopsy, provide definitive diagnosis for a sample of the masked cases. We show how stage-1 and stage-2 information can be combined to provide statistical inference about (a) survival functions of the individual risks, (b) the proportions of failures associated with individual risks and (c) probability, for a specified masked case, that each of the masked competing risks is responsible for the failure. Our development is based on parametric distributional assumptions and the special case for which the failure times for the competing risks have a Weibull distribution is discussed in detail.

Carcinoma, Non-Small-Cell Lung↗

PubMed1997

Event-related brain potential examination of implicit memory processes: masked and unmasked repetition priming.

The proposition that cortically based perceptual representation systems (PRSs) are responsible for some implicit priming phenomena was examined by using event-related potentials (ERPs) in repetition and masked word priming. Experiment 1 used an explicit recognition task, in which repeated words replicated previous ERP repetition priming effects, whereas masked repetition priming revealed a new ERP effect with a posterior topography. Experiment 2 demonstrated ERP and behavioral priming in a lexical decision task for repetition and masked repetition priming. Topographical mapping of ERP repetition priming effects involved both early and late effects over the right and left anterior regions, whereas masked priming produced only an early ERP effect posteriorly. These results suggest differences between early and late ERP priming effects in terms of explicit recollection. Moreover, a posterior PRS may not be involved in some longer term implicit repetition priming effects.

Adolescent↗

PubMed2006

Impaired light masking in dopamine D2 receptor-null mice.

Disruption of overt circadian rhythms can occur without influencing the endogenous pacemaker, the so-called 'masking' effect classically elicited by light. As the physiological pathways involved in light masking remain elusive, we analyzed mice lacking the dopamine D2 receptor. Although circadian rhythmicity was normal, D2R-null mice showed a markedly deficient light masking response, indicating that D2R-mediated signaling is an essential component of the neuronal pathways leading to light masking of circadian rhythms.

Animals↗

PubMed2001

Dense inflammation does not mask residual primary basal cell carcinoma during Mohs micrographic surgery.

BACKGROUND: Areas of dense inflammation are commonly removed during Mohs micrographic surgery for basal cell carcinoma because of the concern that they may mask areas of tumor. OBJECTIVE: Our purpose was to determine whether inflammation masks tumor during Mohs surgery for primary basal cell carcinoma. METHODS: Twenty-five consecutive cases of primary basal cell carcinoma with areas of dense inflammation encountered during Mohs surgery were sectioned and stained with hematoxylin and eosin and Ber-EP4. RESULTS: In no cases did the dense inflammation mask residual tumor. CONCLUSION: Dense inflammation does not mask primary basal cell carcinoma during Mohs surgery and should be carefully evaluated before additional surgery is performed.

Antibodies, Monoclonal↗

PubMed1996

Human T-cell leukemia virus type I tax masks c-Myc function through a cAMP-dependent pathway.

Human T-cell leukemia virus type I Tax is a pleiotropic gene regulator that functions through CREB/ATF- and NF-kappaB-mediated pathways. In most contexts, Tax is a potent gene activator. Here, we describe an unexpected finding of Myc repression by Tax. In cells that overexpress human T-cell leukemia virus type I Tax, the detection of c-Myc protein in the nucleus by a monoclonal antibody was masked. Tax prevented immunological visualization of a Myc epitope contained within amino acids 45-104, resulting in interference with Myc function in transcription and in anchorage-independent cell growth. Tax did not affect steady-state protein levels since detection of c-Myc with other antibodies was unperturbed. Four observations suggest that this Tax-Myc interaction is mediated through CREB/ATF signal transduction. 1) Tax point mutants, selectively defective for activation of CREB/ATF but not NF-kappaB, failed to mask c-Myc; 2) masking of Myc was abolished when Tax-expressing cells were treated with protein kinase inhibitor H-9; 3) Tax-specific shielding of Myc is absent in cells (B1R) that are genetically defective for cAMP signaling; and 4) forskolin treatment of cells mimicked Tax in masking the Myc epitope. Considered collectively, these findings suggest a regulation of Myc function at the level of localized protein conformation.

Animals↗

PubMed1976

Measurement of protection factors of chemical cartridge, half-mask respirators under working conditions in a copper smelter.

The performance of three commonly used chemical cartridge respirators for SO2 was measured under working conditions in a copper smelter. An effective SO2 protection factor for each man-respirator trial was calculated as the ratio between average SO2 concentrations sampled outside the respirator mask and that simultaneously sampled from inside the mask. The in-use SO2 protection afforded by the three respirators proved to be highly variable with mean protection factors of 22, 18, and 13. The distributions of the protection factors and the effects of mask type, facial size, and mask comfort are discussed.

Air Pollutants, Occupational↗

PubMed1993

Circadian rhythms and masking: an overview.

Masking, as is well known, enables an organism to act immediately and in an appropriate way to changes of the environment, integrating with internally produced rhythmicity. It now appears that masking can be used to cover a far wider range of problems than was originally intended. To separate masking effects from the effects due to an internal oscillator, several techniques have been used. Such protocols, however, like the constant routine protocol, often replace one form of masking by another. The situation becomes even more complex when one realizes that the output of an internal oscillator modifies the input. The question might be asked whether it is possible to study the properties of the internal oscillator in vivo at all. This article attempts to produce a framework for future discussions.

Adaptation, Physiological↗

PubMed1991

Physiologic and subjective effects of respirator mask type.

The effect of alternate airflow path designs on full-face mask air-purifying respirators was assessed in 14 healthy volunteers during submaximal exercise. Respirator designs included no respirator (N), full-face mask, dual-cartridge with no nasal deflector (FN), full-face mask respirator with nasal deflector (FD), and a powered air-purifying respirator (PA). Physiologic effects were measured by using respiratory inductive plethysmography and subjective responses by two visual analog scales. There were significant effects of airflow path design upon the physiologic parameters of ventilation, tidal volume, and mean flow rate. There were no significant physiologic or subjective differences between the full-face mask respirators with and without the nasal deflector in place. The PA had less physiologic impact than the nonpowered models but did not show significant subjective benefit. The study suggests that both subjective and objective physiologic responses must be utilized in assessing respirator design.

Adult↗

PubMed1992

Determination of program protection factors for half-mask respirators used at a mineral sands separation plant.

A study was conducted at a mineral sands separation plant to evaluate the workplace performance of half-mask filter cartridge respirators. Inhalation exposure was estimated by measuring the dust and radioactivity concentration inside the respirator while it was worn or hanging around the worker's neck. The program protection factor was determined by simultaneously measuring inside-mask and ambient (outside-mask) concentrations. A total of 27 tests were conducted, covering three brands of half-mask respirators; facial hair on test subjects ranged from clean-shaven to bearded. Program protection factors varied from 1.8 to 13 for dust exposure and 2.5 to 21 for radioactivity exposure. The geometric mean program protection factor over all tests was 5.1 (geometric standard deviation [GSD] = 1.7) for dust exposure and 7.5 (GSD = 1.7) for radioactivity exposure. A minimum program protection factor of 3.5 could be applied to ambient airborne concentration data to obtain a conservative, but more realistic, estimate of inhalation exposure on a worker category basis.

Air Pollutants, Radioactive↗

PubMed1993

Respirator mask design modules and their interactions.

The respirator performance rating table (PRT) scheme has been offered as a way to organize physiological information to be useful for mask design. Designers do not usually deal exclusively with one kind or another of mask physiological effect. This paper presents normal mask design modules and how they relate to mask physiological effects as given in the PRT.

Equipment Design↗

PubMed1994

Surface-epitope masking: a strategy for the development of monoclonal antibodies specific for molecules expressed on the cell surface.

BACKGROUND: Producing monoclonal antibodies against specific targets, including tumor-specific antigens, is a tedious and extremely inefficient process. PURPOSE: Our purpose was to determine whether DNA transfection combined with an immunologic masking tactic could be used to efficiently generate hybridomas that secrete monoclonal antibodies. The quest was for monoclonal antibodies that would react with molecules existing on the surface of genetically altered cells. METHODS: We developed a masking technique called surface-epitope masking (SEM). The SEM procedure involves the selective blocking of surface antigens present in a genetically engineered cell (referred to as a "tester") with high-titer polyclonal antibodies that have been produced against the untransfected parental cell (referred to as a "driver"). Surface-epitope-masked tester cells were injected into BALB/c mice; immune spleen cells then taken from these mice were fused with myeloma cells. RESULTS: This process resulted in the efficient generation of hybridomas that secreted monoclonal antibodies that reacted with cell-surface antigens on transfected tester cells and with additional cell types that expressed the same surface molecules. In one case, CREF-Trans 6 cells were engineered to express a typical multidrug-resistant (MDR) phenotype. Using CREF-Trans 6:MDR cells as a tester cell line, we utilized the SEM procedure to produce monoclonal antibodies that displayed surface reactivity to both CREF-Trans 6:MDR cells and MDR human breast carcinoma (MCF7) cells. In a second case, human prostatic carcinoma CREF-Trans 6 cells, which were DNA transfected and derived from nude mouse tumors, were used as the tester cell line. The SEM procedure was again used to produce monoclonal antibodies. These antibodies were designed to and did react with: (a) tumor-associated antigens on the surface of the original LNCaP cell line used to obtain human prostatic carcinoma DNA, (b) primary and secondary nude mouse transfectants derived from tumors, and (c) two additional human prostatic carcinoma cell lines, DU-145 and PC-3. CONCLUSIONS: The SEM approach was used for the efficient and selective development of monoclonal antibodies that react with cell-surface molecules with both known and unknown functions. IMPLICATIONS: The SEM procedure should be useful in producing monoclonal antibodies and identifying genes associated with important cellular processes, including immunologic recognition, tumorigenesis, metastasis, atypical multidrug resistance, and autoimmune diseases.

Animals↗

PubMedDate not supplied

The masked rat. An X-ray induced mutant with chronic blepharitis, alopecia, and pasteurellosis.

An autosomal recessive mutation had been previously X-ray-induced in the rat and named the masked rat (genotype mk/mk). This study describes the mutant's appearance, histology, and microflora. The rat's eyelids were swollen, often to the point of closure, and its face was partially covered by a brownish crust, giving the mutant a mask-like appearance. The chronic blepharitis was also accompanied by alopecia that appeared as bare patches across the mutant's back. Pasteurella pneumotropica was found in eyelids and on skin from all masked rats. The normal rat demonstrated a resistance to Pasteurella pneumotropica infection, or, conversely, the masked rat appeared to be genetically predisposed to pasteurellosis.

Alopecia↗