Search PubMed⌕ Search

Biomedical subjects

D L Swift

Publications and source records attributed to D L Swift.

At least 37 records · Page 2Linked to original sources
PubMed1985

A critique of MSHA procedures for determination of permissible respirable coal mine dust containing free silica.

The literature in selected technical subject areas related to the Mine Safety and Health Administration's (MSHA) respirable mine dust control policy was critically reviewed. Specific topics included: (1) the technical aspects of respirable dust sampling, (2) the development of a sampling strategy and (3) currently used analytical techniques for free silica content of respirable coal mine dust. The 2.0 Lpm MSHA respirable dust sampling flow rate does not conform with published results which indicate that to simulate existing pulmonary particle deposition models, the sampling flow rate should range from 1.4 to 1.7 Lpm. MSHA's sampling strategy focuses on controlling respirable coal mine dust with both area and personal samples of workers in selected occupations or activities. Many uncertainties are encountered as area samples are used to estimate personal exposures. Although all of the analytical methods for crystalline free silica are sufficiently sensitive to be able to detect and quantitate free silica at environmentally significant concentrations, they are all plagued with similar difficulties. Analytical standards representing the various forms of silica are not available. Available analytical methods do not differentiate among polymorphs of silica. Recommendations are presented to resolve identified problem areas.

Air Pollutants, Occupational↗
PubMed1984

A simplified method for detecting the heat-labile enterotoxin of Escherichia coli.

A tissue-culture method is described that is suitable for screening large numbers of Escherichia coli isolates for heat-labile enterotoxin production. The method uses readily available laboratory media for culture of the E. coli and does not require cell-free extracts. Antibiotics are used to increase toxin production to levels that allow cultures from several different colonies to be pooled for testing, thus minimising the number of tissue-culture monolayers required. Y1 mouse adrenal cells are used in microplate cultures. The method is simple, sensitive and economical and is suitable for use in a routine diagnostic microbiology laboratory.

Animals↗
PubMed1983

Production of pharmacologic monodisperse aerosols.

Monodisperse aerosols containing a range of chemical material, including pharmacologically active substances, were produced by using a modified Sinclair-LaMer condensation generator. Instead of the usual hot-wire technique, an ultrasonic nebulizer was used to suspend nuclei in the gas phase as an aqueous polydisperse aerosol. This technique allowed the generation of monodisperse oil (sebacate) aerosols containing nuclei of sodium chloride, histamine, methacholine, antigen, iron oxide, methylene blue, uranine, radioactive technetium pertechnetate, and technetium-labeled human serum albumin. Quantitative agonist activity was demonstrated for each active nucleus. Particle sizes ranged from 0.65 to 3 microns, with a geometric standard deviation of 1.1-1.2. This system can produce a stable, monodisperse, biologically active radiolabeled aerosol for a period of several hours.

Aerosols↗
PubMed1982

A new apparatus for generating hygroscopic radioactive aerosols for inhalation studies.

Radioaerosols are being used increasingly to assess pulmonary ventilation in patients, and to study patterns distribution and rates of clearance in experimental studies. No completely satisfactory means have been developed to permit the safe and effective administration of suitable aerosols. In this report, a new system is described for producing and delivering monodisperse radioactive aerosol particles. The major advantages of the system are: (1) the monodispersion (sigma g=1.23) of the particles from modifier A; (2) 95% of the particles are less than 2 micrometer in diameter from modifier B, and (3) the method is simple and compact.

Aerosols↗
PubMed1981

Response of collateral channels to histamine: lack of vagal effect.

A new technique using a monodispersed aerosol of histamine delivered to sublobar bronchi through a flexible fiber-optic bronchoscope was used to study the role of the vagus nerve and the effect of anesthesia in the response of collateral channels to exogenous histamine. Studies were performed in paralyzed dogs anesthetized with pentobarbital sodium or alpha-chloralose. Challenges with histamine aerosol were delivered to separate bronchi in each animal before and after bilateral cervical vagotomy. Resistance through collateral channels increased in a reproducible manner following histamine challenge. Vagotomy resulted in no significant change in base-line resistance through collateral channels. The response of collateral channels to exogenous histamine aerosol was not significantly affected by vagotomy or the type of anesthesia used. We conclude that vagal reflexes do not play a significant role in the response of collateral channels to exogenous histamine.

Airway Resistance↗
PubMed1980

Spontaneous retroperitoneal hemorrhage: a diagnostic challenge.

Spontaneous retroperitoneal hemorrhage can present a difficult diagnostic dilemma. We present 4 illustrative cases within the last 2 years at our institutions. Excluding traumatic injury to the retroperitoneum and abdominal aortic aneurysms, about 75 per cent of the cases are related to neoplasms or vascular anomalies. An awareness of predisposing disease states is important. A high index of suspicion and an aggressive diagnostic approach are necessary. If evaluation does not disclose an etiology for retroperitoneal hemorrhage then non-operative management may be considered. This is especially true if an underlying systemic condition is present.

Adrenal Gland Diseases↗
PubMed1979

Human response to controlled levels of inert dust.

We studied nasal mucous flow, airway resistance, and subjective response in 16 young healthy subjects during 5-hour exposures to 2, 10, and 25 mg of inert dust per m3 in an environmental chamber. The dust was a fully polymerized plastic dust containing carbon black. The number of these particles in room air, expressed as a per cent of the total number of particles was 36, 41, 14, 7, and 2, respectively, for the aerodynamic size ranges less than or equal to 1.8, 1.9 to 5.3, 5.4 to 8.9, 9.0 to 12.4, and greater than or equal to 12.5 micron. No significant changes in nasal mucociliary clearance rate or nasal resistance were observed. At all dust concentrations there was a decrease in 1-sec forced expiratory volume, but not in the forced vital capacity or the forced expiratory flow during the middle half of the forced vital capacity. The nasal penetration fraction of particles was approximately 55 per cent for the smallest particles and 20 per cent for the largest particles. Discomfort was proportional to the concentration of dust, but lagged almost 2 hours behind the changes in dust concentration. The discomfort was never excessive; the main complaints were dryness in the nose and pharynx.

Adult↗
PubMed1978

An animal model simulating acute infective upper airway obstruction of childhood and its use in the investigation of croup therapy.

Twelve heartworm-free mongrel dogs (10 males, 2 females) mean weight 22.2 kg (range 17.7--28.2 kg) were sedated and placed in a supine position with the neck extended. A double tracheotomy was performed under sterile conditions. The first tracheotomy tube was inserted 2 cm above the sternum in the direction of the carina using a shortened Silastic American tracheotomy tube (id 10 mm); the second was inserted two cartilage rings proximal to the first and approximately 5 cm distal to the larynx. All animals were kept deeply anesthesized by repeated iv injections of 3--6 mg/kg pentobarbitone sodium so that all reflexes (in particular laryngeal and palatal) were abolished. After control translaryngeal pressure measurements were obtained, the vocal cords were visualized, and steam was introduced onto the through the cords for a mean of 10 sec from above. For 2 hr after this, repeat pressure measurements, as described above, were made. After an overnight stabilizing period, two to three of five randomly chosen air environments were passed over the larynx at 10 liters/min via the proximal tracheotomy, and four half-hourly pressure measurements taken with control periods of at least 2 hr, as described above, separating each experiment. Environments utilized were as follows: i) "cold dry" air, i.e., air at a mean temperature of 9 degrees, obtained by passing compressed air through a coil placed in a solution of alcohol/Dry Ice; ii) "cold moist" air, i.e., air as above, subsequently passed over cold water at a mean temperature of 11 degrees; iii) "warm dry" air, i.e., air at a mean temperature of 36.5 degrees, obtained by passing compressed air through a copper coil, immersed in hot water; iv) "warm moist" air at a mean temperature of 36 degrees, obtained by passing compressed air through a heated Puritan humidifier; v) "ultrasonically produced mist" at room temperature (24 degrees), produced by a De Vilbiss ultrasonic nebulizer 900, set at maximum output. Six 2-hr experimental periods were utilized for each regimen of treatment (i--v). The mean of the combined experimental resistance calculations for each environment were compared statistically with those of its similarly acquired control data, expressed as a positive or negative percentage change, and displayed as a histogram. In addition, the data from each experimental environment were compared with the others, and mean percentage changes from control against time were calculated. Results indicate no statistically significant change in resistance from control for ultrasonic mist or warm moist treatment regimens. Warm dry, cold dry, and cold moist treatments, however, all produced significant reductions in translaryngeal resistance (74%, 60%, and 54%, respectively), there being no difference between cold dry and cold moist and warm dry and cold dry. Significant differences between warm dry and cold moist treatments were obtained, the former decreasing translaryngeal resistance the greatest amount...

Acute Disease↗
PubMed1976

Airway visualization by tantalum inhalation bronchography.

A novel technique for the generation of tantalum aerosols (aerodynamic mass median diameter, 5.8 mum; sigma g, +/-2.14) for inhalation bronchography via the mouth was applied in 26 anesthetized dogs. Ventilatory patterns during periods of aerosol inhalation were controlled by either bilateral electrophrenic stimulation of the diaphragm (EPS), or by intermittent, negative pressure at the body surface (INPV). We studied patterns of tracheobronchial deposition with regard to both the sites of particle deposition longitudinally along airways within lobes, and the topographic distribution of aerosol among the lung lobes. Bronchographic patterns were accordingly studied after inhalations by either (1) EPS and INPV in the supine posture with constant tidal volumes, but varied inspiratory flow (30 to 90 liter per min); or (2) EPS with constant tidal volume and peak inspiratory flow in the prine, right, and left lateral decubitus body positions. Under all airflow conditions, the aerosol was deposited on the surfaces of ciliated airways. Deposition was nearly entirely confined to subsegmental bronchi and above with vigorous inspirations, but extended distally to subsegmental bronchi in greater proportion with decreases in the inspiratory flow. Airways among the basal lung lobes were particularly subject to distal subsegmental and bronchiolar deposition with low rates of inspiratory airflow. Regionally, the aerosol was deposited preferentially in dependent lung lobes after inhalations with EPS in the right and left lateral decubitus positions, and in the basal lung lobes with EPS in the supine posture. A greater caudocranial uniformity in lobar aerosol distribution occurred with inhalations by INPV in the supine posture, and by EPS in the prone posture. The canine model strongly suggests that for clinical inhalation bronchography, nonhomogeneities in lobar deposition may be averted by inhalations in multiple body positions, and that deposition of the aerosol may be confined to ciliated airway surfaces by inertial impaction accompanying high rates of inspiratory airflow.

Aerosols↗