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PubMed2000

An effective protection factor study of respirators used by primary lead smelter workers.

An industrial hygiene study was conducted at a primary lead smelter to determine the effective protection factors for negative pressure and powered air purifying half-mask respirators. The study involved 99 paired personal samples taken in six different work areas, in which randomly chosen subjects from the workforce wore dual sampling pumps connected to closed-face 37-mm cassettes. The cassettes were attached either to the workers' lapels for exposure measurements outside the respirator or to a ported respirator for exposure measurements inside the respirator. Samples were collected throughout the work shift and analyzed for lead according to National Institute of Occupational Safety and Health (NIOSH) Method 7082. Using particle size distribution data obtained for the same workplaces, the within-mask samples were corrected for sampling bias. The negative pressure half-mask respirators showed a mean effective protection factor of 6.5 and a mean corrected effective protection factor of 4.56, with a 5th percentile less than 0.5. Approximately 80 percent and 90 percent of the effective protection factors and the corrected effective protection factors, respectively, were equal to or less than the assigned protection factor of 10. For the powered air purifying half-mask respirators, the means for effective protection factor and corrected effective protection factor were 18.20 and 11.92, respectively, with a 5th percentile of 1.0 or less. Approximately 90 percent and 95 percent of the effective protection factors and the corrected effective protection factors, respectively, were equal to or less than the assigned protection factor of 50. The uncorrected and corrected within-mask lead concentrations for both types of respirators exceeded the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for lead by 19 percent to 58 percent. These results indicate that the straight application of assigned protection factors to actual workplace situations may not always be appropriate.

Adult↗
PubMed1981

Clinical pulmonary function and industrial respirator wear.

This investigation was the initial step in determining a clinical pulmonary test which could be used to evaluate workers as to their suitability to industrial respirator wear. Sixty subjects, 12 superior, 37 normal, and 11 moderately impaired with respect to lung function tests were evaluated with a battery of clinical pulmonary tests while wearing an industrial respirator. The respirator was a full-face mask (MSA-Ultravue) "demand" breathing type equipped with an inspiratory resistance of 85 mm H2O at 85 L/min air flow and an expiratory resistance of 25 mmH2O at 85 L/min air flow. Comparisons of these tests were made between the three groups of subjects both with and without a respirator. It appears that those lung tests which measure the flow characteristics of the lung especially those that are effort dependent are more susceptible to change as a result of respirator wear. Hence, the respirator affects the person with superior lung function to a greater degree than the moderately impaired person. It was suggested that the clinical test of 15 second maximum voluntary ventilations (MVV.25) may be the test of choice for determining worker capability in wearing an industrial respirator.

Adolescent↗
PubMed1991

A feasibility study of quantitative respirator fit testing by controlled negative pressure.

The feasibility of using a direct measure of respirator leakage flow rate as a quantitative index of respirator face seal fit has been explored through the use of a new controlled negative pressure method. The method is based on exhausting air from a temporarily sealed respirator facepiece at a rate sufficient to generate and then sustain a constant negative pressure inside the facepiece while the wearer holds his breath. The magnitude of the negative pressure is preselected to replicate the mean inspiratory pressure inside the mask during normal wear. With the air-purifying paths into the respirator temporarily blocked, measurement of the exhaust flow rate yields a synonymous measure of the leakage flow rate into the mask during inspiration under normal use conditions. The feasibility of using the new method to quantify respirator fit was assessed in a preliminary study that compared its performance with a quantitative fit test method based on the use of dichlorodifluoromethane as a challenge agent. Study data exhibit a high degree of correlation (r greater than 0.99) and no significant difference between the two methods over a range of controlled mask leakage rates. A major advantage of the new method is that a worker can be fit tested with his assigned respirator because the method does not require a destructive sampling probe. Other significant benefits compared to current methods used to quantify respirator fit appear to include (1) ease of test administration, (2) simplicity of test components, (3) lack of a potentially toxic challenge agent, (4) a straightforward calibration procedure, (5) multiple test capability, (6) immediacy of test results, and (7) field portability of the test system.

Air Pollutants↗
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

Aerosol penetration through filtering facepieces and respirator cartridges.

Air-purifying respirators must be certified following the National Institute for Occupational Safety and Health (NIOSH) filter test criteria (30 CFR 11). The criteria specify a range for the mean particle size and the measure of spread permissible for the test aerosol. The authors' experiments have shown that aerosol penetration as a function of particle size differs considerably among certified respirators of the same type. Filtering facepieces (disposable respirators) and cartridges of the dust-mist, dust-mist-fume, and high-efficiency particulate air type were tested. The respirators were sealed to mannequins in a test chamber. The aerosol concentrations inside and outside the respirator were measured by an aerodynamic particle sizer and a laser aerosol spectrometer over a particle size range of 0.1 to 15 microns. Five flow rates ranging from 5 to 100 L/min were used to study flow dependency. The aerosol penetration through the filters is presented as a function of particle size. Aerosol penetration and pressure drop are combined to express the performance of each filter in terms of "quality factor." Under the same test conditions, the quality factor of one respirator may be as much as 6.6 times more than that of another respirator of the same type. The filter quality factor has a greater aerosol size dependency as airflow and aerosol size increase. In general, cartridges have a larger surface area than filtering facepieces but not necessarily lower filter penetration or higher filter quality.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1994

Variation in quantitative respirator fit factors due to fluctuations in leak size during fit testing.

Variation in fit factors during quantitative respirator fit testing was studied for a high degree of fit (aerosol fit factors > 1000) and a low degree of fit (aerosol fit factors < 1000). In a controlled human study, fit factors were determined sequentially for three different exercises by (1) an aerosol fit test (using a portable condensation nuclei counter and room aerosol as the test agent) and (2) the newly developed dichotomous-flow fit test (Dichot). For the higher level of respirator fit, the aerosol fit factors were 30 to 60 times the corresponding flow fit factors, and for the lower level of respirator fit they were 2 to 4 times the flow fit factors. A coefficient of variation (CV) of 84% (GSD 1.6) for the higher respirator fit and 178% (GSD 2.2) for the lower respirator fit data was observed in the human study when aerosol fit factors for the three exercises were pooled. In a similar mannequin study, the center sampling probe gave aerosol fit factors with a CV of 5.4% (GSD 1.05). The flow fit factors for all three exercises pooled had a CV of 36% (GSD 1.3) for the higher respirator fit and 40% (GSD 1.5) for the lower respirator fit data, while the mannequin study gave flow fit factors with a CV of 2.2% (GSD 1.02). Thus, the variation in fit factors obtained in the human study was much higher than that obtained in a mannequin study. However, the variation in the aerosol method relative to the flow method, in the human study, os of the same order of magnitude as in the mannequin study.(ABSTRACT TRUNCATED AT 250 WORDS)

Air↗
PubMed1998

Method for measuring the spatial variability of aerosol penetration through respirator filters.

Fibrous filter media are widely used in respirators to remove airborne particulate matter from the inhaled airflow of workers. The N95 half-mask particulate respirator appears to be the most frequently used respirator under the new NIOSH regulation, 42 CFR 84. Considerable spatial variability in light penetration through the fibrous filter medium of an N95 respirator can be seen by visual observation when it is held to the light. This variability is due to the way in which the fibers are manufactured and laid down to form the filter medium. Similar spatial variability is expected in the aerosol penetration through the filters. Therefore, a test method has been developed for measuring the spatial variability in aerosol penetration. The main components of this method are an aerosol generator, a filter test stand with a movable sampling inlet, an aerosol size spectrometer, and an aerosol photometer. Measurements with the filter media of N95 respirators, tested at average filtration velocities corresponding to light, moderate, and heavy work loads, have shown spatial variations in aerosol penetration in excess of 100% relative to the average aerosol penetration for the entire respirator. N95 respirators are required to be at least 95% efficient (i.e., less than 5% penetrating) at the most penetrating particle size, when tested at 85 L/min. Tests with the new method have shown that the aerosol penetration of the most penetrating particles of about 0.1 micron diameter may locally be higher than 5%, while the average aerosol penetration of 0.1 micron particles is less than 5%.

Aerosols↗
PubMed1998

Respirator performance ratings for speech intelligibility.

A respirator degrades speech intelligibility and thus interferes with the ability of the wearer to communicate. The magnitude of this degradation is not well-studied and can vary as a function of numerous parameters. This study investigated the performance degradation of speech intelligibility in low-level noise for different speaker-listener distances and message sets (single words or predictable sentences) that occurred while wearing a respirator compared with not wearing a respirator. Thirteen speaker-listener pairs with normal hearing and speech were used. Speaker-listener separation distances were 0.61, 1.22, 1.83, 2.44, 3.05, and 3.66 m (2, 4, 6, 8, 10, and 12 ft) for the respirator condition and 1.22, 2.44, 3.05, 6.1, 9.15, and 12.2 m (4, 8, 10, 20, 30, and 40 ft) for the no-respirator condition. The means of the scores were used to determine the speech performance rating for both the single-word and sentence comprehension tests. The performance rating expresses the percentage of performance that can be expected while wearing a respirator compared with not wearing a respirator. Scores were interpolated linearly at distances at which no data were obtained. As expected, the speech performance rating was higher for the sentence comprehension test than for the single-word comprehension test at each distance. At a distance of 12.2 m, the speech performance rating for the sentence comprehension was 70%. For the single-word comprehension test, the speech performance rating was zero for distances greater than 9.1 m.

Adolescent↗
PubMed2006

Investigation of respiration of individual bovine embryos produced in vivo and in vitro and correlation with viability following transfer.

BACKGROUND: Quantification of oxygen consumption by individual preimplantation embryos has the potential to improve embryo selection. This study investigated whether respiration rates of individual embryos are useful indicators of embryo viability. The effect of the Nanorespirometer on embryo viability was also evaluated. METHODS: The respiration rates of individual day 7 bovine in vivo- (n=44) and in vitro-produced (n=156) embryos were measured using the Nanorespirometer. In vivo-produced embryos were individually transferred to recipients. RESULTS: The respiration rates of in vivo-produced embryos increased with increasing morphological quality and stage of development (P < 0.05). Pregnancy rates on days 35 and 60 were 65 and 60%, respectively. The mean respiration rate did not differ significantly between embryos producing and not producing a pregnancy, but the transfer of embryos with respiration rates <0.78 nl/h, between 0.78 and 1.10 nl/h, and >1.10 nl/h resulted in 48, 100 and 25% pregnancy rate, respectively. The mean respiration rate of in vitro-produced embryos was higher than that of in vivo-produced embryos because of differences in the morphological quality and stage of development. CONCLUSION: The Nanorespirometer does not adversely influence embryo viability, but the sample size was too small to confirm the significance of the correlation observed between respiration rates and viability.

Animals↗
PubMed1975

Effect of cyclic nucleotides on the cyanide-insensitive respiration of polymorphonuclear leucocytes.

The effects of N6,O2'-dibutyryladenosine 3',5'-monophosphate (Bu2-cyclic AMP) and N2,O2'-dibutyrylguanosine 3',5'-monophosphate (Bu2-cyclic GMP) on the cyanide-insensitive respiration of guinea pig peritoneal exudate polymorphonuclear leucocytes were studied. Bu2-cyclic AMP inhibited the respiration induced both by phagocytosis of E. coli and by the interaction with trypsin-digested rat liver microsomes. The addition of theophylline gave rise to an inhibitory pattern similar to that with Bu2-cyclic AMP against both the respirations induced. On the other hand, Bu2-cyclic GMP did not affect the respiration induced by phagocytosis whereas it inhibited the respiration induced by the addition of myristic acid was inhibited by Bu2-cyclic AMP, which was similar to that with E. coli. The respiration induced by methylene blue was inhibited neither by Bu2-cyclic AMP nor by Bu2-cyclic GMP. These observations suggest that the cyanide-insensitive respiration of polymorphonuclear leucocytes may be classified into at least three types from the inhibitory pattern of cyclic AMP and cyclic GMP.

Animals↗
PubMed2003

Effects of butyltin compounds on mitochondrial respiration and its relation to hepatotoxicity in mice and Guinea pigs.

Because the mechanisms responsible for the difference in toxicity between different experimental animal species remain unclear, the effects of tributyltin chloride (TBTC) and dibutyltin dichloride (DBTC) on mitochondrial respiration were compared among the livers of mice and guinea pigs in vitro and in vivo. Further, the levels of these butyltin compounds and their derivatives in the mitochondrial fractions of the hepatocytes were investigated in these animal species. Administration of TBTC and DBTC to mice resulted in the obvious elevation of serum enzymatic activities, as well as the inhibition of succinate-linked State 3 respiration in hepatic mitochondria at 24 h after administration. On the other hand, these metal compounds failed to induce such hepatotoxicity or to inhibit mitochondrial respiration in guinea pigs. There was no significant difference between mice and guinea pigs in the IC50 (metal concentration observed in 50% inhibition of mitochondrial respiration) of TBTC and DBTC against the succinate-linked State 3 respiration of hepatic mitochondria in vitro, although the mitochondrial respiration of succinate-linked State 3 was inhibited in the liver of mice treated with the metals in vivo. The levels of total butyltin compounds in the mitochondrial fractions of hepatocytes were higher in the mice than in the guinea pigs, and the main butyltin compound in the mitochondrial fractions was DBTC in both species at 24 h after TBTC or DBTC administration. The amount of sulfhydryl groups, which were capable of binding with DBTC, in mice hepatic mitochondria was twice as large as that in guinea pigs, and the affinity of DBTC for the isolated hepatic mitochondria was higher in mice than in guinea pigs in vitro. These results suggested that the induction of hepatotoxicity by TBTC and DBTC in vivo was closely associated with the depression of mitochondrial respiration and that the difference in susceptibility to the metal-induced mitochondrial damages between mice and guinea pigs might result from the high affinity of butyltin compounds, in particular DBTC, for hepatic mitochondria in mice containing higher levels of sulfhydryl groups, compared with guinea pigs.

Administration, Oral↗
PubMed1996

Estimating stem maintenance respiration rates of dissimilar balsam fir stands.

Stem maintenance respiration rates were measured in five contrasting balsam fir (Abies balsamea (L.) Mill.) stands. At 15 degrees C, average respiration rates for individual stands ranged from 120 to 235 micro mol m(-3) s(-1) when expressed per unit of sapwood volume, from 0.80 to 1.80 micro mol m(-2) s(-1) when expressed per unit of stem surface area, and from 0.50 to 1.00 micro mol g(-1) s(-1) when expressed per unit of nitrogen in the living stem biomass, but differences among stands were not statistically significant. Coefficients of variation ranged from 50 to 100% within stands and were similar for all bases used to express respiration rates. Coefficients of determination for regressions between chamber flux and chamber values of sapwood volume, stem surface area and nitrogen content varied between stands and no one base was consistently higher than the other bases. We conclude that the bases for expressing stem respiration are equally useful. Respiration rates were more closely correlated to stem temperature observed approximately 2 h earlier than to current stem temperature. Among stands, annual stem maintenance respiration per hectare varied from 0.1 to 0.4 Mmol ha(-1) year(-1), primarily because of large differences in sapwood volumes per hectare. Annual stem maintenance respiration per unit of leaf area ranged from 3 to 6 mol m(-2) year(-1), increasing as sapwood volume per hectare increased.

Journal Article↗
PubMed1999

Interspecific and environmentally induced variation in foliar dark respiration among eighteen southeastern deciduous tree species.

We measured variations in leaf dark respiration rate (Rd) and leaf nitrogen (N) across species, canopy light environment, and elevation for 18 co-occurring deciduous hardwood species in the southern Appalachian mountains of western North Carolina. Our overall objective was to estimate leaf respiration rates under typical conditions and to determine how they varied within and among species. Mean dark respiration rate at 20 degrees C (Rd,mass, micromol CO2 per kg leaf dry mass per s) for all 18 species was 7.31 micromol per kg per s. Mean Rd,mass of individual species varied from 5.17 micromol per kg per s for Quercus coccinea Muenchh. to 8.25 micromol per kg per s for Liriodendron tulipifera L. Dark respiration rate varied by leaf canopy position and was higher in leaves collected from high-light environments. When expressed on an area basis, dark respiration rate (Rd,area, micromol CO2 per kg leaf dry area per s) showed a strong linear relationship with the predictor variables leaf nitrogen (Narea, g N per square m leaf area) and leaf structure (LMA, g leaf dry mass per square m leaf area) (r squared = 0.62). This covariance was largely a result of changes in leaf structure with canopy position; smaller thicker leaves occur at upper canopy positions in high-light environments. Mass-based expression of leaf nitrogen and dark respiration rate showed that nitrogen concentration (Nmass, mg N per g leaf dry mass) was only moderately predictive of variation in Rd,mass for all leaves pooled (r squared = 0.11), within species, or among species. We found distinct elevational trends, with both Rd,mass and Nmass higher in trees originating from high-elevation, cooler growth environments. Consideration of interspecies differences, vertical gradients in canopy light environment, and elevation, may improve our ability to scale leaf respiration to the canopy in forest process models.

Journal Article↗
PubMed2001

Seasonal dynamics of soil carbon dioxide efflux and simulated rhizosphere respiration in a beech forest.

Respiration of the rhizosphere in a beech (Fagus sylvatica L.) forest was calculated by subtracting microbial respiration associated with organic matter decomposition from daily mean soil CO2 efflux. We used a semi-mechanistic soil organic matter model to simulate microbial respiration, which was validated against "no roots" data from trenched subplots. Rhizosphere respiration exhibited pronounced seasonal variation from 0.2 g C m(-2) day(-1) in January to 2.3 g C m(-2) day(-1) in July. Rhizosphere respiration accounted for 30 to 60% of total soil CO2 efflux, with an annual mean of 52%. The high Q10 (3.9) for in situ rhizosphere respiration was ascribed to the confounding effects of temperature and changes in root biomass and root and shoot activities. When data were normalized to the same soil temperature based on a physiologically relevant Q10 value of 2.2, the lowest values of temperature-normalized rhizosphere respiration were observed from January to March, whereas the highest value was observed in early July when fine root growth is thought to be maximal.

Carbon Dioxide↗
PubMed1991

Root respiration in Chamaecyparis obtusa trees.

We examined the respiration rate of root segments, which had a constant length in relation to their diameter, from three small and two large 26-year-old Chamaecyparis obtusa (Siebold & Zucc.) Endl. trees. The dependence of respiration rate on segment diameter was described by a power function with an exponent of about 1.5, except for the smallest sample tree, for which the exponent was 1.74. Unlike stem segments, root segments of similar diameter showed similar rates of respiration regardless of the tree from which the root segments had been taken. On the basis of the power function, we propose a new equation to estimate the total root respiration rate of a tree. The relationship between root respiration rate per tree and root weight can be expressed by a power function with an exponent of 1.11. The ratio of the specific respiration rate of stems to that of roots was 0.7 for the three smaller trees, and 1.1 to 1.3 for the two larger trees. In November, the stand respiration rate of roots was estimated to be 0.36 kg CO(2) ha(-1) h(-1) for a root biomass (dry weight) of 28 Mg ha(-1).

Journal Article↗
PubMed1991

Foliage dark respiration in Abies amabilis (Dougl.) Forbes: variation within the canopy.

Dark respiration of foliage was measured in a 30-year-old stand of Abies amabilis in western Washington from June to November. Both laboratory and field measurements were used to study the effect of environmental and tree variables on respiration. Foliage respiration rates were most strongly influenced by needle temperature. After accounting for leaf temperature differences, foliage respiration decreased with depth in the canopy for all age classes of foliage. Respiration differences attributed to location within the canopy were greatest early in the growing season, but were still significant in November. Younger foliage respired more than older foliage in the upper canopy, but not in the lower canopy. Respiration differences due to foliage age were highly significant in the early growing season, but were not detectable by mid-October.

Journal Article↗
PubMed1986

Screening prospective workers for the ability to use respirators.

A physician should determine the ability to use a respirator, taking into account the employee's health, the respirator, and the work conditions. This report reviews the effects of respirator wear and provides referenced, reasonable guidelines for determining a worker's fitness to wear a respirator. The effects discussed include pulmonary, cardiac, body temperature, diminished senses, psychological reactions, and local irritation. Examining physicians should realize that heavy exercise with a respirator usually causes stress primarily on the cardiovascular system and that heavy (eg, self-contained, atmosphere-supplying) respirators can substantially increase this stress. Accordingly, exercise stress tests, with ECG monitoring, should be considered in these circumstances when cardiovascular risk factors are present. Available literature is noted that should help physicians screen prospective workers for the ability to use respirators.

Health Status↗
PubMed1999

Medical surveillance for respirator users.

The Occupational Safety and Health Administration has changed the content and frequency of medical assessments required by the Respiratory Protection Standard. The revised Standard contains a mandatory questionnaire to be used for preplacement evaluation of all users. The requirement for periodic reevaluations has been replaced by a requirement to reevaluate users when they experience difficulty with respirator use, or when their workplace changes in such a way as to significantly impact the physiologic stresses of the job. The experience of medical surveillance programs for respirator users suggests that routine surveillance is not necessary. The frequency of disease sufficiently debilitating to preclude respirator use found through medical surveillance is low; adverse outcomes experienced by respirator users, although potentially tragic, are not outcomes for which medical surveillance plays a preventive role. In an effort to better use resources once spent on repetitive examination of asymptomatic respirator users without compromising their health, this article proposes an approach for addressing symptomatic respirator users in which the respirator components are evaluated before the user is subjected to medical investigations.

Female↗