The Relationship Between Restrictive Regulation of Midwives, Practice Environment, and Professional Burnout: A 7-State Mixed-Methods Comparison of Autonomous and Restrictive State Regulation.

PURPOSE: The purpose of the study was to investigate the relationship between state regulation of the midwifery workforce, practice environment, and burnout. BACKGROUND: Burnout threatens the US midwifery workforce, with over 40% of certified nurse-midwives meeting criteria. Burnout can lead to poorer physical and mental health and withdrawal from the workforce. Burnout in midwives has been associated with lack of control and autonomy. In the United States, midwives' autonomy is restricted through state-level regulation that limits scope of practice and professional independence. METHODS: A mixed-methods study was conducted using an explanatory sequential approach. Quantitative and qualitative data were collected by online surveys and analyzed in a 2-stage process, followed by data integration. RESULTS: State regulation was not found to be independently associated with burnout (n = 248; P = .250); however, mediation analysis showed a significant association between state regulation, practice environment, and burnout. Qualitative analysis mirrored the importance of practice environment and expanded on its features. CONCLUSION: For midwives, unrestrictive practice regulation may not translate to burnout prevention without supportive practice environments. IMPLICATIONS FOR PRACTICE AND RESEARCH: Interventions should focus on promoting job flexibility, realistic demands, and professional values. While midwives' commitment to patients and the profession can help bolster the workforce, it can also amplify negative experiences of the practice environment.

Examining nurse/patient relationships in care coordination: A qualitative metasynthesis.

BACKGROUND: The combination of education, experience, skill mix, and frequency of nursing care provided has not been broadly studied from a systems theory perspective, in the care coordination process, or within transitions of care. PURPOSE: To examine nurse/patient relationships (as a proxy for nurse dose) in the care coordination experience through a qualitative metasynthesis using a systems theory approach. DESIGN: The study was a qualitative metasynthesis with four sequential processes; (1) a systematic literature search to answer the structured research question, (2) formal quality appraisal and data immersion, (3) interpretive synthesis of the data within and across studies, and (4) re-situating the derived themes through reciprocal translation to each of the primary studies. CINHAL, Cochrane Library, Embase and PubMed were searched, and 159 articles retrieved. Eight articles remained after inclusion/exclusion criteria and quality review criteria were applied. RESULTS: Key themes were organized using a systems theory perspective (Structure, Process and Outcomes). The need for a coordinated nurse-patient relationship and the ability of the nurse to calm the complexity that occurs forms the structure of the relationship. The process includes having an awareness of challenges of the coordinated nurse-patient relationship and the transitions that occur, nurses going above and beyond, providing meaningful communication, and navigating system complexity. The outcomes are the value of a coordinated nurse-patient relationship and managing the illness/wellness journey. CONCLUSIONS: The information from this metasynthesis provides an integrated view for nursing leaders and insight into factors that promote an effective and coordinated nurse-patient relationship.

Differences in statin associated neuroprotection corresponds with either decreased production of IL-1ß or TNF-α in an in vitro model of neuroinflammation-induced neurodegeneration.

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) have been associated with conflicting effects within the central nervous system (CNS), with underlying mechanisms remaining unclear. Although differences between individual statins' CNS effects have been reported clinically, few studies to date have compared multiple statins' neuroprotective effects. This study aimed to compare six statins (atorvastatin, fluvastatin, pitavastatin, pravastatin, rosuvastatin, simvastatin; 0-100 µM) using an in vitro model of lipopolysaccharide (LPS)-induced neuroinflammation and subsequent neurodegeneration. To achieve this, HAPI microglia were treated with LPS (0.1 µg/mL; 24 h), resulting in increased reactive oxygen species (ROS), nitric oxide, and IL-1ß, TNF-α and PGE2 release. Conditioned media ("HAPI-CM") was then transferred to SH-SY5Y neuroblastoma cells, and effects on cellular viability, mitochondrial membrane permeability, apoptosis, autophagy and ROS production assessed. Of the statins investigated, only atorvastatin, pravastatin and rosuvastatin protected SH-SY5Y cells from LPS-induced decreases in cellular viability; this appeared mediated through reduced caspase 3/7 activation and was associated with decreased IL-1ß (atorvastatin, pravastatin) and/or TNF-α (atorvastatin, pravastatin, rosuvastatin). Only pravastatin conferred protection at all tested concentrations. ROS production and autophagic vacuole formation was decreased by all statins, suggesting these two mechanisms are unlikely to be sole mediators of neuroprotection seen with selected statins. Ultimately, our model suggests that despite all statins reducing microglial inflammation, subsequent effects on neuronal viability and cell death signalling pathways varies between statins. Our findings highlight the need to consider individual statins as inducing discrete pharmacological effects within the CNS in future in vitro/in vivo studies and in clinical practice.

Statins Reduce Lipopolysaccharide-Induced Cytokine and Inflammatory Mediator Release in an In Vitro Model of Microglial-Like Cells.

The anti-inflammatory effects of statins (HMG-CoA reductase inhibitors) within the cardiovascular system are well-established; however, their neuroinflammatory potential is unclear. It is currently unknown whether statins' neurological effects are lipid-dependent or due to pleiotropic mechanisms. Therefore, the assumption that all statin compounds will have the same effect within the central nervous system is potentially inappropriate, with no studies to date having compared all statins in a single model. Thus, the aim of this study was to compare the effects of the six statins (atorvastatin, fluvastatin, pitavastatin, pravastatin, rosuvastatin, and simvastatin) within a single in vitro model of neuroinflammation. To achieve this, PMA-differentiated THP-1 cells were used as surrogate microglial cells, and LPS was used to induce inflammatory conditions. Here, we show that pretreatment with all statins was able to significantly reduce LPS-induced interleukin (IL)-1ß and tumour necrosis factor (TNF)-α release, as well as decrease LPS-induced prostaglandin E2 (PGE2). Similarly, global reactive oxygen species (ROS) and nitric oxide (NO) production were decreased following pretreatment with all statins. Based on these findings, it is suggested that more complex cellular models should be considered to further compare individual statin compounds, including translation into in vivo models of acute and/or chronic neuroinflammation.

The economic benefits of surgical site infection prevention in adults: a systematic review.

BACKGROUND: Surgical site infections (SSIs) present a significant burden to healthcare and patients in terms of excess length of stay, distress, disability and death. SSI risk and the associated economic burden may be reduced through adherence to prevention guidelines although the irreducible minimum is unclear. AIM: To evaluate the methods used to estimate the cost-effectiveness of prevention strategies for all SSIs. METHODS: PubMed, Medline, CINAHL, and UK National Health Service Economic Evaluation Database were searched from inception to January 2020 to identify English language economic evaluation studies, embedded economic evaluations, and studies with some analysis in relation to cost and benefit in adult patients receiving surgical care in any setting. Risk of bias was assessed using two published checklists. FINDINGS: Thirty-two studies involving 24,043 participants were included. Most studies evaluated SSI prevention in orthopaedic surgeries. Antibiotic prophylaxis, screening, treating, or decolonization of meticillin-resistant Staphylococcus aureus and surgical wound closure were the main methods evaluated. Methods ranged from cost-analyses to cost-effectiveness and cost-utility analyses. Synthesis of results was not possible due to heterogeneity. All studies reported some economic benefit associated with preventing SSI; however, measures of benefit were not reported consistently and the quality of studies was low to moderate. Limited evidence in relation to SSI impact on quality of life was identified. CONCLUSION: Current evidence in relation to the economic benefits of SSI prevention is limited. Further robust studies that utilize sound economic and epidemiological methods are required to inform future investment decisions in SSI prevention.

A qualitative meta-synthesis of women's experiences of labor dystocia.

PROBLEM: Researchers have prioritized understanding and differentiating the pathophysiologic mechanisms to improve precision in diagnosis and individualization of care, however the experiences of women with labor dystocia have been underexamined. BACKGROUND: Management of labor dystocia has been identified as an opportunity for reducing the rate of unnecessary cesarean births and the associated risks to women and their infants. This meta-synthesis explores women's experiences of labor dystocia to enrich the discussion of care practices and contextualize discussions of shared decision making in what is most meaningful to women. QUESTIONS: How does prolonged labor influence women's experience of birth and motherhood? What are women's experiences with decision-making about labor augmentation during prolonged labor? METHODS: Sandelowski and Barroso's meta-synthesis approach was used to analyze primary qualitative studies of women's experiences of labor dystocia. Through inductive thematic synthesis and reciprocal translation, themes identified in qualitative research, quotations, and coded meaning units were aggregated and interpreted into derived categories and themes. FINDINGS: Fourteen qualitative studies were analyzed. Women experienced labor dystocia as a transition from healthy labor to abnormal labor requiring medical support consistent with Transition Theory by Meleis. Six new categories and thirty themes were identified. Each category and theme reflects a distinct component of the experience of labor dystocia. DISCUSSION/CONCLUSION: There is wide variation in the way women experience labor dystocia. Facilitation of the transition from healthy labor to labor dystocia can be supported by a fluid, adaptable method of caring for women in the face of uncertainty and loss of choice.

The experiences of midwives in integrated maternity care: A qualitative metasynthesis.

OBJECTIVES: To conduct a metasynthesis of eight qualitative studies of the experiences of midwives in integrated maternity practice; to identify common motifs among the eight studies through a thematic interpretive integration known as reciprocal translation; and to explore the effects on midwifery processes of care in the setting of integrated maternity practice. DESIGN: A qualitative metasynthesis to analyze, synthesize, and interpret eight qualitative studies on the experiences of midwives and the effect on the midwifery processes of care in the setting of integrated maternity practice. SAMPLE AND SETTING: Participants from the primary studies included a total of 160 midwives providing hospital-based intrapartum care. All primary studies were conducted in settings with midwives and obstetricians working together in an integrated or collaborative manner. FINDINGS: Three overarching themes emerged from the data: professional dissonance, functioning from a position of risk, and practicing down. KEY CONCLUSIONS: The findings indicated that integrated maternity practice affects the professional experience of midwives. Through a qualitative exploration, a clear process of deprofessionalization and deviation from the midwifery model of care is detailed. Midwives experienced decreasing opportunity to provide the quality woman-centered physiologic care that evidence shows benefits childbearing women. IMPLICATIONS FOR PRACTICE: Integrated maternity practice, where low-risk and high-risk pregnancies are managed by midwife/physician teams, have proliferated as a solution to the need for quality, safe, and efficient health care. Insufficient evidence exists detailing the success or failure of this model of care. Qualitative studies suggest that the increasing medicalization occurring in integrated maternity practices minimizes the profession of midwifery and the ability to provide evidence-based quality midwifery care.

Bioaerosol concentrator performance: comparative tests with viable and with solid and liquid nonviable particles.

AIMS: Generally it is more economical to first characterize a concentrator system with nonbiological particles followed by more rigorous bioaerosol testing. This study compares sampling system performance for various particle types and sizes. METHODS AND RESULTS: Performances of five concentrators were characterized with five nonviable and viable laboratory aerosols, although not every concentrator was tested with all aerosol types. For particle sizes less than c. 6 microm aerodynamic diameter, similar efficiencies are obtained for all test particles; however, for larger sizes there is a significant difference between liquid and dry particles. CONCLUSIONS: Aluminium oxide particles provide results over a broad range of sizes with a single test, but the method is less reproducible than other methods. A combination of monodisperse polystyrene spheres and oleic acid droplets provides an accurate representation of the system performance, but ultimately biological particle tests are needed. SIGNIFICANCE AND IMPACT OF THE STUDY: Devices are being developed for concentrating bioaerosol particles in the size range of 1-10 microm aerodynamic diameter and this study provides insight into data quality for different test methodologies. Also, the results show some current concentrators perform quite poorly.

Vocalizations produced by humpback whale (Megaptera novaeangliae) calves recorded in Hawaii.

Although humpback whale (Megaptera novaeangliae) calves are reported to vocalize, this has not been measurably verified. During March 2006, an underwater video camera and two-element hydrophone array were used to record nonsong vocalizations from a mother-calf escort off Hawaii. Acoustic data were analyzed; measured time delays between hydrophones provided bearings to 21 distinct vocalizations produced by the male calf. Signals were pulsed (71%), frequency modulated (19%), or amplitude modulated (10%). They were of simple structure, low frequency (mean=220 Hz), brief duration (mean=170 ms), and relatively narrow bandwidth (mean=2 kHz). The calf produced three series of "grunts" when approaching the diver. During winters of the years 2001-2005 in Hawaii, nonsong vocalizations were recorded in 109 (65%) of 169 groups with a calf using an underwater video and single (omnidirectional) hydrophone. Nonsong vocalizations were most common (34 of 39) in lone mother-calf pairs. A subsample from this dataset of 60 signals assessed to be vocalizations provided strong evidence that 10 male and 18 female calves vocalized based on statistical similarity to the 21 verified calf signals, proximity to an isolated calf (27 of 28 calves), strong signal-to-noise ratio, and/or bubble emissions coincident to sound.

Estimating excess length of stay due to healthcare-associated infections: a systematic review and meta-analysis of statistical methodology.

BACKGROUND: Healthcare-associated infection (HCAI) affects millions of patients worldwide. HCAI is associated with increased healthcare costs, owing primarily to increased hospital length of stay (LOS) but calculating these costs is complicated due to time-dependent bias. Accurate estimation of excess LOS due to HCAI is essential to ensure that we invest in cost-effective infection prevention and control (IPC) measures. AIM: To identify and review the main statistical methods that have been employed to estimate differential LOS between patients with, and without, HCAI; to highlight and discuss potential biases of all statistical approaches. METHODS: A systematic review from 1997 to April 2017 was conducted in PubMed, CINAHL, ProQuest and EconLit databases. Studies were quality-assessed using an adapted Newcastle-Ottawa Scale (NOS). Methods were categorized as time-fixed or time-varying, with the former exhibiting time-dependent bias. Two examples of meta-analysis were used to illustrate how estimates of excess LOS differ between different studies. FINDINGS: Ninety-two studies with estimates on excess LOS were identified. The majority of articles employed time-fixed methods (75%). Studies using time-varying methods are of higher quality according to NOS. Studies using time-fixed methods overestimate additional LOS attributable to HCAI. Undertaking meta-analysis is challenging due to a variety of study designs and reporting styles. Study differences are further magnified by heterogeneous populations, case definitions, causative organisms, and susceptibilities. CONCLUSION: Methodologies have evolved over the last 20 years but there is still a significant body of evidence reliant upon time-fixed methods. Robust estimates are required to inform investment in cost-effective IPC interventions.

Physical and biological studies of coal and oil fly ash.

Studies were performed to compare the physical and chemical characteristics and the in vitro macrophage cytotoxicity of oil and coal fly ash. Sampling methodology was developed to collect size-fractionated particulate matter from the smokestack of either a coal-fired or an oil-fired power plant. Morphological studies demonstrated particle heterogeneity, although most coal fly ash particles appeared to be spherical. Oil fly ash contained two major morphologies; nonopaque amorphous particles and opaque amorphous particles. Elemental analysis indicates that the coal ash is predominantly composed of aluminosilicate particles, while the oil ash is predominantly inorganic sulfates and carbonaceous particles. In vitro macrophage assays demonstrate that the finest coal fly ash particles are the most cytotoxic; the cytotoxicity is significantly less than that of alpha-quartz, the positive control particle. In contrast, the oil fly ash particles are more cytotoxic than quartz. The cytotoxicity of oil fly ash is due to soluble components, possibly vanadium salts.

Emotional mood states and retrieval in episodic memory.

The effect of an experimentally induced depressed mood state on recall of target words embedded in sentences was examined. The objective was to determine if the induction of a depressed mood can affect output or retrieval from episodic memory. The experimental sequence was as follows: All subjects studied a list of either elaborated or base sentences, rating them for complexity, in an incidental retention paradigm; this was followed by the induction of a depressed or neutral (control) mood, using a standard and a short form of the Velten mood induction procedure; finally, subjects were given an unanticipated cued recall test of the target adjectives. In all tests, subjects showed a reduction in recall owing to the depressed mood, which provided evidence for retrieval effects of the mood state. Elaboration led to superior recall of target items, and there was no effect of delayed recall. The results are briefly discussed within the framework of a resource allocation theory.

Isoelectric focusing and capillary zone electrophoretic studies using luteinizing hormone releasing hormone and its analog.

Iontophoresis is the movement of charged compounds into and through the skin under an external electromotive force. A molecule's charge and size, as well as other factors, will determine its ability to be iontophoresed. One can gain insight into certain electrical aspects of a molecule by determining its isoelectric point as well as its electrophoretic mobility. In the present study, isoelectric focusing and capillary zone electrophoretic studies of luteinizing hormone releasing hormone, (LHRH) and one of its analogs are performed in order to predict their ability to be iontophoresed. The pI of LHRH is determined to be 9.6 while that of its free acid is 6.9. In addition, it is concluded that although the two compounds are chemically similar, the native compound is more mobile at pH > 2.5. These results suggest that the native compound might be better suited for iontophoretic delivery than is the free-acid analog.

Proteoglycan synthesis by scleral chondrocytes is modulated by a vision dependent mechanism.

Proteoglycan synthesis was measured in chick sclera at the onset of form-deprivation myopia, as well as in the period immediately following removal of the occluder. Two day-old chicks were monocularly form vision deprived for periods from one to ten days and proteoglycan synthesis was determined after placing posterior scleral buttons in organ culture and measuring 35SO4 incorporation into glycosaminoglycans. Following 24 hrs of form-deprivation, proteoglycan synthesis was 33% higher in myopic eyes as compared with paired control eyes. The rate of proteoglycan synthesis further increased to levels 83% higher than controls after four days of form-deprivation and remained elevated throughout the ten day period of deprivation. Removal of the occluder after 10 days of form-deprivation resulted in a rapid drop in the rate of proteoglycan synthesis to control levels within 24 hrs. Proteoglycan synthesis was also measured in scleral chondrocytes isolated from control and myopic eyes after 10 days of form-deprivation. Proteoglycan synthesis by chondrocytes from myopic eyes did not return to control levels until 48 hrs after plating. Since the rate of proteoglycan synthesis returns to control levels more quickly during the recovery period ex vivo than when scleral chondrocytes from myopic eyes are placed in cell culture, we suggest that a mechanism is present within the eye which rapidly lowers the rate of proteoglycan synthesis in response to form vision.

Suitability of air sampling locations downstream of bends and static mixing elements.

The revised standard for sampling effluent air from stacks and ducts of the nuclear industry places limits on the non-uniformity of velocity and contaminant profiles at the sampling location; namely, the coefficients of variation must not exceed 20% over an area that encompasses at least the center 2/3 of the cross sectional area. Tests were conducted to characterize the degree of mixing at downstream locations as affected by several types of flow disturbances, including 90 degree elbows and commercial static mixing devices. Flow straighteners were incorporated into the ducting upstream of the mixer to be tested to simulate the dampening of flow turbulence that might occur because of upstream HEPA filters. The coefficients of variation of velocity and tracer gas concentration measured in a straight tube at a distance of 3 diameters downstream from a 90 degree elbow were 17% and 69%, respectively. The mixing is impacted by the upstream flow turbulence. Without a flow straightener, the tracer gas concentration coefficient of variation was reduced to 33% at the 3-diameter location. The use of static mixing elements can greatly enhance the mixing process. A ring placed just downstream of a 90 degree elbow, which blocks the outer 56% of the cross sectional area, results in a coefficient of variation of 19% for tracer gas concentration at the 3-diameter location. Pressure loss across the elbow with the ring is about nine times that of the basic elbow. One of the commercially available static mixers provides coefficients of variation that are less than 10% for both velocity and tracer gas concentration at 4 diameters downstream from the mixer with a pressure loss that is only about 3.5 times as large as that of a 90 degree elbow.

Gas mixing for achieving suitable conditions for single point aerosol sampling in a straight tube: experimental and numerical results.

Experimental measurements of velocity and tracer gas concentration are taken in a straight tube to evaluate the effectiveness of mixing in achieving conditions as required by ANSI N13.1-1999 for single point extractive sampling from stacks and ducts of nuclear facilities. Mixing is evaluated for inlet turbulent intensities of 1.5%, 10%, and 20%, achieved by introducing various bi-plane grids, and for conditions generated by a commercial static gas mixer. The data obtained (at Reynolds number = 15,000) highlight the importance of inlet turbulence intensity in the process of turbulent dispersion of a dilute gas. The gas mixer does not introduce significant pressure losses and unlike bi-plane grids, the turbulence downstream of the mixer is not homogenous. A judicious choice of the release location that uses the large scale eddies and inhomogeneity of the turbulence ensures that the specified ANSI N13.1-1999 criteria are attained within 7 diameters downstream of the duct inlet. This is significantly more effective than a bi-plane grid where even with 20% inlet intensity the criteria are met only at 21 diameters downstream. The predictions of a proposed semi-empirical correlation match favorably with data. For example, at 18 diameters downstream with inlet intensities of 1.5% and 10%, the predicted coefficients of variation (COVs) of 150% and 65% are close to the actual values of 154% and 50%; where the COV of a set of measurements is the ratio of the standard deviation of the set to its mean value. The corresponding results obtained using commercially available software are 141% and 12%. Results from a particle-tracking model show good qualitative trends, but they should not be used to determine compliance with the requirements of the ANSI standard.

A constant flow filter air sampler for workplace environments.

A filter air sampler has been developed for sampling radionuclide aerosol particles from the workplace environment. It provides easy filter changing, constant flow sampling, and a visual display to indicate proper operation. An experimental study was conducted to characterize the collection efficiency of the sampler as affected by variations in room air velocity, particle size, sampling flow rate, inlet geometry, and inlet orientation to the free stream. Tests were carried out in a wind tunnel at velocities between 0.3 m s(-1) and 2.0 m s(-1), which is a range that covers anticipated velocities in the typical highly ventilated workplace environment of a nuclear facility. Nearly monodisperse aerosols with sizes between 5 and 20 microm aerodynamic diameter were sampled at flow rates between 28.3 and 84.9 L min(-1). Inlet orientations of 0 degrees, 90 degrees, and 180 degrees from the horizontal were selected for evaluation. When the sampler was oriented at 0 degrees over various ranges of free stream velocities, sampling flow rates and particle sizes, the transmission efficiency of aerosol was typically greater than 95%. The transmission efficiencies varied from 80% to 106% for 10-microm aerodynamic diameter particles over the previously noted range of free stream velocities and inlet orientations. Uniformity of deposits of 10 microm aerodynamic diameter particles on collection filters was examined for a sampling rate of 57 L min(-1), a sampler orientation of 90 degrees into the wind and wind speeds of 0.3-2 m s(-1). The coefficients of variation for the areal density of the deposits ranged from 6.1% to 37.2%. A miniature critical flow venturi with a constant sampling flow rate of 57 L min(-1) was developed for application to the new filter air sampler. It was demonstrated that the performance of the new filter air sampler is quite acceptable over a wide range of conditions. Overall the new filter air sampler design has been shown to provide enhanced performance with regard to sample handling, constant calibrated volumetric sample flow rate, and relatively unbiased sample aspiration performance compared with a traditional filter air sampler design.

Factors that affect alpha particle detection in continuous air monitor applications.

An experimental study was conducted to characterize the full-width half-maximum values, peak shapes, and peak shifts of the energy spectra from alpha emitters in the forms of particulate matter on sampling filters and electro-deposited plated sources. Monodisperse 1.0-microns anhydrous uranium acetate aerosol particles were collected on seven types of sampling filters. Full-width half-maximum values at atmospheric pressure varied from 373 keV for a 3-microns pore size Fluoropore filter to 584 keV for a glass fiber filter. Monodisperse uranium acetate aerosols from 1.2-8.1 microns were collected on Millipore 1.2-microns pore size membrane filters to examine the self-absorption effect. Under vacuum, the corresponding full-width half-maximum values ranged from 241-1,011 keV. Successively heavier mass loadings of monodisperse 1.8-microns uranium acetate particles from 13.7-127 micrograms cm-2 caused the values to increase from 420 to 580 keV. With an electroplated 23.9-mm-diameter 239Pu source and a 25.4-mm detector, the distance between source and detector was incrementally increased from 3.2 to 6.4 mm--a range of distances that is typical of those found in alpha continuous air monitors. At atmospheric pressure, the values increased from 280 to 330 keV and the detector efficiency decreased from 30.5% to 20.9%. Tests with various sizes of sources and detectors suggest that a continuous air monitor should be designed so that the two are of approximately equal size.

Performance evaluation of continuous air monitor (CAM) sampling heads.

Continuous air monitor (CAM) samplers are used to detect radioactive aerosol particles in nuclear facilities and to provide alarm signals should the concentrations exceed a multiple of the derived air concentration (DAC) of the radionuclide of concern in a set amount of time. Aerosol particles are drawn into a CAM sampler where collection is to take place upon a filter. Radioactivity of the particles is determined with a detector that is placed in close proximity to the filter face. An important determinant of CAM performance is the ability of the inlet and body of the CAM to transport particulate matter in the inhalable-size range (less than or equal to 10 microns aerodynamic diameter) to the filter without substantial loss or bias with respect to particulate size. Three types of CAM samplers were tested in a low-velocity aerosol wind tunnel to determine the degree to which particles penetrate through the flow systems to the collection filter under conditions typical of normal room air exchange rates. Two air velocities were used: 0.3 and 1.0 m s-1. The CAM samplers were primarily operated at a flow rate of 56.6 L min-1, although some tests were conducted at a flow rate of 28.3 L min-1. The CAM units were prototypes manufactured by Kurz Instruments, Eberline Instrument Corporation, and Victoreen Inc. These three units represent three different approaches to CAM head design. At an air speed of 1 m s-1, aerosol penetration to the filters of the Kurz unit was essentially 100% for particle sizes of 3 and 7-microns aerodynamic diameter and was 86% for a size of 15 microns. For the Eberline sampler, the penetration was over 80% for 3-microns particles but was reduced to less than 2% for 7-microns particles. The victoreen sampler showed penetration values of 98% for 3-microns aerodynamic diameter particles, 88% for 7-microns particles and 4% for a size of 15 microns. Air speed had little effect on the penetration results for the two speeds which were tested. Tests were conducted to determine the uniformity of deposits on the filters of the CAM samplers. For a particle size of 10 microns, the deposits were nonuniform for all three of the instruments.

An experimental study of aerosol penetration through horizontal tubes and Strom-type loops.

Because some designers of aerosol transport systems use the assumption that aerosol penetration through a system is maximized if the flow Reynolds number is 2,800, we have conducted tests to determine if such an assumption is appropriate. Although we do not believe that optimal performance of an aerosol sample transport system can be presented solely in terms of the Reynolds number, we have presented our results in terms of that parameter to compare our work with the results of an earlier study. Two types of experiments were performed. First, the penetration of liquid aerosol particles through horizontal tubes was experimentally investigated for a range of design and operational conditions. For a particle size of 10 microm aerodynamic diameter, the maximum penetration through a 6.7 mm diameter tube was associated with a Reynolds number of approximately 2,000; the maximum penetration through a tube of 15.9 mm occurred at a Reynolds number of about 3,000; and the maximum penetration through a 26.7 mm diameter tube occurred at about 4,000. It was also experimentally demonstrated that for a fixed flow rate through a horizontal tube, there is an optimum tube diameter for which the aerosol penetration is a maximum. An early study dealing with aerosol particle penetration through a 16.8 mm inside diameter loop of tubing (two vertical tubes, two horizontal tubes and three 90 degrees bends) suggested there was a fixed Reynolds number for optimal aerosol penetration independent of particle size. Those experiments were repeated here and the agreement with those tests is excellent; namely, the maximum penetration through a loop of 15.9 mm diameter tube occurs at a Reynolds number of approximately 2,800, independent of particle size. However, when the tube diameter of the transport system layout was changed to 26.7 mm, the Reynolds number associated with maximum penetration varied for different particle sizes, occurring at Reynolds numbers of approximately 5,600 for 8 microm AD particles, 3,800 for 10 microm particles and 3,000 for 15 microm particles.