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Biomedical subjects

R D Phillips

Publications and source records attributed to R D Phillips.

At least 19 recordsLinked to original sources
PubMed1992

Rats are not aversive when exposed to 60-Hz magnetic fields at 3.03 mT.

Thirty-two male rats were tested in two replicates of an experiment to determine whether body currents induced by 60-Hz magnetic fields might lead to avoidance behavior comparable to that which results from exposure to strong 60-Hz electric fields. The test apparatus was a two-compartment Plexiglas shuttlebox enclosed in a sound-attenuating plywood chamber, which in turn was encompassed by two copper bus bars that, when energized, served as a source of 60-Hz magnetic fields. Location of the rat, and traverse activity in the shuttlebox were monitored by nine infra-red photo detectors equally spaced along the length of the apparatus. Rats were divided into 2 groups: 1 group of rats (n = 8 per group per replicate) was sham exposed while rats in the other group (n = 8 per group per replicate) were exposed to a 3.03 mT (30.3 G), 60-Hz magnetic field whenever they traversed to or were located on the side (L or R) predetermined as the exposed side. To control artifact incident to side preference, the side exposed (L or R) was alternated over the exposed rats. Each rat was tested individually in a 1-h session. A 2-factor ANOVA (exposed vs. control, replicate 1 vs. replicate 2) failed to reveal any significant effects due to either factor or to an interaction between factors. These data demonstrate that rats do not avoid exposure to 60-Hz magnetic fields at a flux density of 3.03 mT and further imply that the avoidance by rats of high level 60-Hz electric fields is mediated by something other than the internal body currents induced by the exposure.

Animals↗
PubMed1992

Clinical determination of the linear equation for the subtalar joint axis.

The authors present a methodology to measure the frontal plane angular and linear displacement and the transverse plane angular displacement of subtalar joint movement. This method is combined with a modification of the Kirby method for determining the transverse plane projection of the subtalar joint axis onto the plantar foot. A mathematical model is then used to construct the subtalar joint axis into a three-dimensional linear equation. Data are obtained from an in vivo series of 62 feet that indicates that within acceptable clinical errors of measurement the subtalar joint is a ginglymus type of joint that moves around a single fixed axis. Results also indicate that the subtalar joint axis is more superior and lateral to the neutral foot than any previous studies on cadaver feet have shown. Finally, the authors show that once the subtalar joint axis can be accurately located, the torque on the joint axis produced by ground reactive forces and muscular forces can be computed.

Adolescent↗
PubMed1992

Dosimetry Workshop: extremely-low-frequency electric and magnetic fields.

A workshop on the dosimetry of extremely-low-frequency fields was held to assess current knowledge in this field and to develop a set of recommendations for new research that meets the needs of health risk assessment, in particular, the assessment of cancer risk. The workshop was sponsored by the Electric Power Research Institute and was held on March 20-22, 1991, in Carmel, California. Major topics of the workshop were microdosimetry of induced electric fields, scaling of induced fields among biological systems from cells to humans, and the problem of defining a biologically effective "dose." A number of research recommendations were developed, the most important of which are to (1) characterize the natural background electric and magnetic fields in tissues and near cells, (2) improve experimental exposure geometries to allow accurate characterization of induced fields in samples, (3) design experiments to distinguish between electric and magnetic field mechanisms, (4) develop standard in vitro biological systems with reproducible and well-established responses to fields, and (5) develop definition of dose with respect to fields at the primary site of interaction.

Electromagnetic Fields↗
PubMed1991

Modification of high-heeled shoes to decrease pronation during gait.

One of the reasons that high heels may contribute to the formation of halux valgus is that the wearers pronate during propulsion. This pilot study was performed to determine whether relocation of the heel under the counter of a fashion high-heeled pump could change the degree of pronation of the foot during the gait cycle. The authors report that more foot stability was experienced by the subjects when the center of the heel was offset between 2 and 4 mm medial to the center of the heel counter. This study is designed to promote further research into whether the shoe industry should change the design parameters of high-heeled fashion shoes in order to improve foot function.

Adult↗
PubMed1990

Shock absorption.

Abnormal shock is a major cause of chronic and overuse injuries to all aspects of the lower extremity. The two major causes of abnormal shock are (1) decreased fat pad under the calcaneus and (2) dysfunction of the subtalar joint pronation mechanism during contact. Enough literature now exists to indicate that podiatrists should provide prophylactic therapy for patients that exhibit abnormal shock during contact before symptomatology in the lower extremity or spine exhibits itself.

Biomechanical Phenomena↗
PubMed1989

The dermal carcinogenic potential of unrefined and hydrotreated lubricating oils.

Unrefined lubricating oils contain relatively high levels of polycyclic aromatic hydrocarbons (PAH) and have been shown to induce tumors in mouse skin. Exxon has developed a new method of refining these materials, a severe hydrotreatment process that is optimized for PAH removal. The specific objectives of the current study were to assess PAH reduction and then to evaluate directly the dermal carcinogenic potential of the materials that spanned the range of products produced by this method. The test samples included unrefined light and heavy vacuum distillates from a naphthenic crude oil, as well as the corresponding severely hydrotreated products. Two sets of samples were prepared to assess the effects of various operating parameters in the reactor. Additionally, positive (benzo[a]pyrene), negative (white mineral oil) and vehicle (toluene) control groups were included to assess the sensitivity and specificity of the bioassay. Each sample was applied in twice-weekly aliquots to the backs of 40 male C3H mice. In the analytical studies, significant reductions in the levels of several specific PAH were demonstrated. In the dermal carcinogenesis studies, the unrefined oils and the positive control induced tumors and also significantly reduced survival. None of the mice treated with severely hydrotreated oils or with the negative or vehicle controls developed skin tumors, and survival of these mice was not significantly different from the control. Thus, the data demonstrated that this new, severe hydrotreatment process was an effective means of converting carcinogenic feedstocks to non-carcinogenic products.

Animals↗
PubMed1989

Amino acid composition protein quality and water-soluble vitamin content of germinated cowpeas (Vigna unguiculata).

Amino acid composition, protein digestibility, calculated protein efficiency ratio (C-PER and DC-PER), chemical scores and water-soluble vitamin content of cowpea seeds germinated at 25 degrees C or 30 degrees C for 24 h were determined. Also, the effect of processing steps (heated-air drying, decortication and cooking) on these parameters were examined. Germination had little effect on amino acid profile of cowpeas. In vitro protein digestibility was not improved significantly by germination nor by decortication but was improved by cooking. C-PER and DC-PER ranged from 1.95 to 2.21 and from 1.63 to 1.82, respectively. DC-PER compared well with reported rat PER of cowpea products and seemed more sensitive than C-PER. Based on whole egg values, chemical scores ranged from 37.7 to 45.8% (mean +/- SD; 42.2 +/- 2.4%). Germination increased the contents of niacin, thiamin and riboflavin significantly. Decortication resulted in up to 30% loss in niacin while thiamin content was reduced 41% by cooking.

Amino Acids↗
PubMed1988

Mutagenicity studies on ketone solvents: methyl ethyl ketone, methyl isobutyl ketone, and isophorone.

3 ketone solvents (methyl ethyl ketone (MEK), methyl isobutyl ketone (MiBK), and isophorone) were tested for potential genotoxicity. The assays of MEK and MiBK included the Salmonella/microsome (Ames) assay, L5178Y/TK+/- mouse lymphoma (ML) assay, BALB/3T3 cell transformation (CT) assay, unscheduled DNA synthesis (UDS) assay, and micronucleus (MN) assay. Only the ML, UDS, and MN assays were conducted on samples of isophorone. No genotoxicity was found for MEK or isophorone. The presence of a marginal response only at the highest, cytotoxic concentration tested in the ML assay, the lack of reproducibility in the CT assay, and clearly negative results in the Ames assay, UDS and MN assays, suggest that MiBK is unlikely to be genotoxic in mammalian systems.

Animals↗
PubMed1976

Automated rodent respiratory monitor and histogram computer--a preliminary report.

The system described in this paper was designed to monitor total inhaled volume (V), tidal volume (VT), and respiratory frequency (f) of Fisher rats before, during, and after exposure to cigarette smoke. The systems consists of three major subsystems: plethysmograph, analog signal conditioner, and histogram computer. The volume type whole body plethysmograph incorporates a rubber nose seal. Tidal flow rate (V) from the tube, measured by a pneumotachometer, is integrated by the signal conditioning system to obtain VT and V. Both V and V are displayed on a strip chart recorder. A rat will often exhibit considerable sniffing, especially in the presence of cigarette smoke. Consequently, average tidal volume (VT) and average respiratory frequency (f) are not accurate measurements of typical VT and f. Sensitivity of the system to changes in typical VT and f is important snce the system will be used to evaluate the effects of subtle differences in types of experimental cigarettes. A microprocessor was used in conjunction with a cathode ray tube to compute and display both the VT and respiratory period (T = 1/f) as histograms. From the histograms the most common (typical) VT (mode of the histogram) and the most common T can be easily observed and recorded. The histogram computer also calculates and digitally displays VT and f.

Analog-Digital Conversion↗
PubMed1975

Thermoregulatory, metabolic, and cardiovascular response of rats to microwaves.

This study was undertaken to determine the effects of 2,450-MHz microwave irradiation on thermoregulation, metabolism, and cardiovascular function of rats. Young adult male animals (430 g) were exposed for 30 min to 2,450-MHz microwaves in a cavity at absorbed dose rates of 0, 4.5, 6.5, or 11.1 mW/G. For animals of the size used in this study, these dose rates represent absorption of energy at the rate of 27.7, 40.1, and 68.2 cal/min, respectively. For a period of 5 h following exposure, measurements were made of colonic temperature, skin temperature, oxygen consumption, carbon dioxide production, respiratory quotient, and heart rate. Rats that received 27.7 cal/min for 30 min exhibited an initial transient increase in colonic and skin temperatures but no alterations in other functions. The group irradiated at 40.1 cal/min had greater elevations in colonic and skin temperatures immediately after exposure, followed by overcompensation and lower than normal colonic temperatures for about 3 h. The metabolic rate was depressed in this group for 3 h. Bradycardia developed within 20 min after exposure and persisted for about 3 h. The group of rats that received 68.2 cal/min for 30 min had responses similar to those of the 40.1 cal/min group, but the changes were more severe and lasted longer. In addition, a number of transient abnormalities were noted in the ECG tracings of rats that had received the highest dose, including irregular rhythms and incomplete heart block. The physiological changes observed in this study can be attributed to the heating induced by irradiation.

Animals↗
PubMedDate not supplied

Distribution and excretion of [14C]citrinin in rats.

The distribution and excretion of radioactivity from [14C]citrinin (3 mg/kg, i.v) was determined in male rats. At 0.5 h after administration maximum values of 14.7% and 5.6% of total radioactivity were observed in the liver and kidneys, respectively, and by 6 h decreased to 7.5% in the liver and 4.7% in the kidney. Plasma concentration of 14C decreased from 9.2% at 0.5 h to 4.7% at 6.0 h. 2 plasma elimination rates were observed, with half-lives of 2.6 and 14.9 h, respectively. Approximately 80% of the administered 14C activity was excreted in feces and urine by 24 h after administration. A second group of rats was pretreated with 50 mg/kg of citrinin, i.p., 4 days prior to administration of 3 mg/kg [14C]citrinin, i.v. 30% of the pretreated animals died and the remaining animals were divided into 2 groups on day 4 after pretreatment; rats which were "nephrotoxic" and rats which had "recovered" from the initial insult of citrinin. Proteinuria and glucosuria as well as enhanced urine output were observed in "nephrotoxic" rats 4 days after pretreatment. 24 h after [14C]citrinin, only 13% of 14C activity was detected in the urine of "nephrotoxic" rats. The plasma disappearance curve had 2 elimination rates, with half-lives of 0.6 and 14.1 h. "Nephrotoxic" rats retained 7.5% of the administered radioactivity in the liver compared to 1.3% in the "recovered" rats 24 h after the tracer dose and 47% of the radioactivity was either excreted in feces or in the colon contents after 72 h compared to 17.5% in "recovered" rats. Extraction of urine samples from "nephrotoxic" and "recovered" rats with chloroform suggested increased water soluble metabolites of citrinin in the urine from "nephrotoxic" rats. These data also suggested that in normal rats the kidneys are the major route of elimination of citrinin and its metabolite(s) while in rats rendered nephrotoxic by citrinin pretreatment, elimination is more dependent on hepatic excretion.

Animals↗
PubMedDate not supplied

A 90-day toxicity study of the effects of petroleum middle distillates on the skin of C3H mice.

Petroleum middle distillates (PMDs) elicit skin tumors in mouse epidermal carcinogenesis studies. The response is characterized by a long latency with only a small percentage of animals developing tumors. Although the carcinogenic activity of certain other petroleum hydrocarbons largely depends upon the presence of polycyclic aromatic hydrocarbons (PAHs), many PMDs contain relatively low concentrations of PAHs. PMDs are also irritating to mouse skin, and chronic irritation may be involved in the development of skin tumors. This study was conducted to investigate the patterns of cutaneous irritation elicited by topical application of PMDs having compositional differences. The three PMDs selected for study were a steam cracked gas oil (SCGO), a lightly refined paraffinic oil (LRPO), and a jet fuel (JF). Male C3H/HeNCr1BR mice (25/group) were treated topically (37.5 microliters 2x/week for 13 weeks) with 10%, 50% or 100% (undiluted) concentrations of each PMD. Catalytically cracked clarified oil (CCCO, 10%), a potent carcinogen to mouse skin, was also tested. The vehicle was a noncarcinogenic mineral oil with a viscosity of 90 SUS. Cutaneous changes were evaluated by gross observations and light microscopy. Cutaneous irritation was the only significant toxic response in this study. Neither the vehicle nor any of the 10% PMD concentrations produced significant cutaneous irritation. The 10% CCCO and 50% PMD treatments all elicited slight to moderate proliferative and inflammatory changes in mouse skin. Ulcers were also observed microscopically in mice treated with 10% CCCO and 50% SCGO. The 100% SCGO treatment produced evidence of necrosis on Days 1-7 but not later in the study despite continued treatment. In contrast, the irritating effects of 100% LRPO were not evident until 2-3 weeks of study, and at study completion were characterized by moderately severe inflammatory and proliferative changes. The effects of 100% JF were qualitatively similar to 100% LRPO but less marked. Thus, the SCGO caused a different pattern of cutaneous responses than either LRPO or JF. The possible relationships of these cutaneous changes to epidermal carcinogenesis are being studied further.

Animals↗