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Biomedical subjects

D W Riffle

Publications and source records attributed to D W Riffle.

9 recordsLinked to original sources
PubMed2000

Multi-night exposure to 60 Hz magnetic fields: effects on melatonin and its enzymatic metabolite.

Magnetic field-induced suppression of nocturnal melatonin in humans has been reported in occupational and residential studies, but not in laboratory-based exposure studies. The present study examined whether this contrasting pattern of results might be related to associated differences in exposure duration or to field-induced measurement instability over time. Thirty healthy young men were evaluated using a randomized, double-blind test protocol. Statistical analysis indicated that 4 consecutive nights of exposure to power-frequency magnetic fields at occupational intensity (resultant flux density = 28.3 microtesla, muT, [283 milligauss, mG]) had no differential effect on concentrations of melatonin or its major enzymatic metabolite (6-hydroxymelatonin sulfate, 6-OHMS) in daily morning urine samples, compared to equivalent no-exposure sham control conditions. The consistency of intra-individual urinary measurements over the 4 test nights also was quite high (P < 0.01) in the sham control condition. In contrast, repeated nightly exposure to the magnetic field was associated with reduced consistency. Morning urinary measures obtained after exposure on night 4 differed (P < 0.01) from similar measures obtained after the second and third exposure night. Thus, while the overall results of this study do not support the melatonin hypothesis, there is some suggestion of a possible cumulative effect of magnetic field exposure on the stability of individual melatonin measurements over time. Additional research with longer periods of controlled exposure may be warranted.

Adolescent↗
PubMed2000

Exposure to strong ELF magnetic fields does not alter cardiac autonomic control mechanisms.

Clinical and epidemiological studies attest that alterations in heart rate variability (HRV) are predictive of specific types of cardiovascular morbidity and mortality in otherwise healthy persons. Recent reports also suggest that changes in HRV may be associated with exposure to intermittent magnetic fields (60 Hz, 28.3 microT) in the laboratory and that mortality is increased in cardiac disease categories related to altered HRV for utility workers whose jobs involve longer exposure to elevated magnetic fields. This study combined three approaches to learn more about the specific exposure circumstances under which changes in HRV occur. First, cardiac autonomic control, as indexed by HRV spectral analysis measures, was measured in 24 men during exposure to a much higher intensity field than any previously examined (resultant flux density = 127.3 microT [1273 milliGauss, mG]). Second, HRV measures from the same individual were compared across three relevant test conditions: intermittent and continuous field exposure and during a no-exposure, control condition. Third, electrocardiographic data were analyzed to determine if the precise timing of when the magnetic field switched on or off in relation to the cardiac cycle results in phase-resetting of the human cardiac rhythm. HRV measures were not altered by either field exposure condition compared to the control condition, and no evidence for a phase-resetting mechanism was found. Further research is needed to resolve the differences between the present and the earlier laboratory-based studies of HRV and to determine if cardiac rhythm disturbances are associated with exposure to the more complex magnetic fields found in the man-made environment.

Adult↗
PubMed1999

Human exposure to 60-Hz magnetic fields: neurophysiological effects.

The neurophysiological effects of exposure to power-frequency magnetic fields at two occupationally-relevant intensities were evaluated in a single-blind study with 18 male and 18 female volunteers. Auditory brainstem (BAEP) and somatosensory (SEP) evoked potentials were recorded before, during and after field exposure (duration = 45 min, frequency = 60 Hz, field intensities = 14.1 or 28.3 microtesla, microT), or an equivalent sham-exposure control period. Visual event-related potentials (VEP) to pattern reversal stimuli were also recorded before and after the exposure period. Field exposure had no differential effects on the BAEP, the VEP, or on SEP measures of central conduction time. Men and women showed a similar lack of sensitivity to exposure. The present results do not support the mechanistic hypothesis that the transmission of sensory information to appropriate cortical centers is delayed or distorted by exposure to power-frequency magnetic fields at occupational intensities.

Adolescent↗
PubMed1997

Human melatonin during continuous magnetic field exposure.

This report describes the third in a series of double-blind, laboratory-based studies that were aimed at determining the effects of nocturnal exposure to power frequency magnetic fields on blood levels of melatonin in human volunteers. Our two earlier studies evaluated effects on melatonin of intermittent exposure to 60 Hz circularly polarized magnetic fields at 10 and 200 mG. No overall effects on melatonin levels were found. In the present study, men were exposed continuously rather than intermittently through the night to the same 200 mG magnetic field condition that was used previously; again, no overall effects on melatonin levels were found. We conclude that the intermittent and continuous exposure conditions used in our laboratory to date are not effective in altering nocturnal blood levels of melatonin in human volunteers.

Adolescent↗
PubMed1996

Nocturnal melatonin levels in human volunteers exposed to intermittent 60 Hz magnetic fields.

Two double-blind laboratory-based studies were performed to determine whether a suppression of nocturnal melatonin similar to that observed in rodents occurs when humans are exposed to magnetic fields at night. In study 1, 33 men were exposed to sham, 10 mG, or 200 mG intermittent, circularly polarized magnetic fields from 2300 to 0700 h under controlled environmental and exposure test conditions. Overall, exposure had no effect on melatonin levels. Men with preexisting low levels of melatonin, however, showed significantly greater suppression of melatonin when they were exposed to light and also when they were exposed to the 200 mG magnetic-field condition. Study 2 directly tested the hypothesis that low-melatonin subjects show enhanced sensitivity when exposed to light and to 200 mG magnetic fields. After preexposure screening, each of 40 men slept in the exposure facility on two nights. On one night, the men were sham exposed. On the other night, they were exposed to the 200 mG field condition used previously. Again, exposure had no overall effect on melatonin levels. The original finding of enhanced sensitivity in low-melatonin subjects was not replicated in this study. We conclude that the intermittent exposure conditions used in these two studies were not effective in altering nocturnal melatonin release patterns in human volunteers. Further research is underway with regard to exposure parameters, hormonal and immune system measures, and individual differences.

Adolescent↗
PubMed1993

The effect of intensive case management on hospitalization of patients with schizophrenia.

OBJECTIVE: The study aim was to determine if a community-based psychiatric rehabilitation program with intensive case management was more effective than traditional outpatient services in reducing hospitalization of chronic schizophrenic patients. METHODS: One hundred twelve schizophrenic patients enrolled in the intensive case management program were matched by age, number of previous hospitalizations, and days spent in the hospital with 112 schizophrenic patients who received medication services and minimal case management. The two groups were compared on the amount of services used and the number of hospitalizations and hospital days over a 24-month study period. RESULTS: Patients in the intensive case management program had been enrolled for a mean of 10.96 months, with a range from one to 24 months. They used significantly more mental health services during the study period compared with the patients in the control group. However, no significant differences were found between the two groups in number of hospitalizations and hospital days. Both groups showed an increase in the number of hospitalizations over the study period. CONCLUSIONS: A community-based psychiatric rehabilitation program with intensive case management was no more effective than medication services and minimal case management in reducing hospitalization among chronic schizophrenic patients.

Adult↗
PubMed1989

Computer-aided pattern analysis of temperature differentials.

Chiropractic analysis often incorporates the evaluation of heat distribution patterns observed in skin temperature profiles. Historically, temperature recordings of the spine have been made with a heat detection instrument using a thermocouple design. The advent of refinements in infrared technology, however, have greatly enhanced temperature detection in terms of accuracy and reliability. The present research reflects the development of computer software designed to express the data obtained with a dual channel heat sensing instrument. Two phases are involved: a) digital information, received from the sensing instrument, is standardized, stored for future analysis, and retrieved for comparisons with other graphs; b) stored data is graphically displayed, statistically analyzed, and otherwise compared. The data is displayed for visual observation as a) temperature data received from either channel of the sensing instrument or b) relative temperature differences between data from both channels of the sending instrument. For statistical evaluation, corresponding readings (comparisons between graphs) are plotted against one another and analyzed by a moving Pearson Product Moment correlation and moving t-test. This evaluation is graphically represented with a numeric display of pertinent statistical values. Current work indicates that a 10 point moving correlation and t-test will yield accurate comparisons between graphs.

Algorithms↗
PubMed1976

Monocular acquisition and interocular transfer in albino guinea pigs as mediated by ipsi- or contralateral fiber systems.

Monocular acquisition and interocular transfer of a horizontal-vertical discrimination were measured in 12 male albino guinea pigs with unilateral lesions of the striate cortex, and in 6 sham-operated controls. In accordance with electrophysiological and anatomical findings, the animals learned readily using the contralateral fibers, while the ipsilateral fibers were found to be incapable of mediating either acquisition, or retention, of the discrimination. The control animals learned readily, but showed incomplete transfer.

Animals↗