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Biomedical subjects

A R Ward

Publications and source records attributed to A R Ward.

15 recordsLinked to original sources
PubMed1998

Sensory, motor, and pain thresholds for stimulation with medium frequency alternating current.

OBJECTIVES: To investigate the effect of frequency of alternating current on the sensory, motor, and pain thresholds in normal subjects, and to establish the optimal frequency for motor stimulation with minimal subject discomfort. DESIGN: A repeated measures design using two groups of 11 subjects. SETTING: A laboratory setting was used. PARTICIPANTS: Participants were volunteers who met the inclusion criteria. INTERVENTIONS: Alternating current with 20 different carrier frequencies between 1 and 35 kHz, all modulated at 50 Hz, was applied to each subject on two separate occasions. For half the subjects, the frequency was increased or decreased sequentially (reversed on second occasion), and for the other half, it was applied in a different random order on each occasion. MAIN OUTCOME MEASURES: The voltage at the sensory threshold was recorded for each applied frequency. This was subsequently repeated for motor and pain thresholds. RESULTS: Sensory, motor, and pain thresholds decreased with increasing frequency between 1 kHz and approximately 10 kHz. Above 10 kHz, the thresholds increased. The ratio pain threshold/sensory threshold increased systematically with increasing frequency over the range examined. By contrast, the ratio pain threshold/motor threshold showed a distinct maximum at a frequency of 10 kHz. Marked accommodation to motor and pain fiber stimulation was observed. CONCLUSIONS: For comfortable sensory stimulation, a high frequency of alternating current is preferable. Discrimination between pain and motor stimulation is maximal at a frequency of approximately 10 kHz. This suggests that the optimal frequency for comfortable motor stimulation, one that is least likely to elicit pain fiber stimulation, is close to 10 kHz.

Adult↗
PubMed1998

Variation in torque production with frequency using medium frequency alternating current.

OBJECTIVES: To investigate the effect of frequency of alternating current on electrically induced torque in healthy subjects, and to establish an optimum frequency for motor stimulation. DESIGN: A repeated-measures design using 12 subjects (part 1) and 3 subjects (part 2). SETTING: A laboratory setting was used. PARTICIPANTS: Participants were volunteers who met the inclusion criteria. INTERVENTIONS: Alternating current with carrier frequencies between 1 and 15kHz, modulated at 50Hz, was applied to each subject on two separate occasions. The frequencies were applied in a different random order on each occasion and different random orders were used between subjects. For part 1 of this study, six frequencies were used: 1, 2, 4, 7, 10, and 15kHz. For part 2, three frequencies were used: 1, 4, and 10kHz. MAIN OUTCOME MEASURES: Part 1: The maximum electrically induced torque, defined as the torque induced at the pain threshold, was recorded for each applied frequency. Part 2: The variation of torque with increasing stimulus intensity was recorded for each applied frequency. RESULTS: Highest electrically induced torque was produced at the lowest frequency examined (1kHz). Torque decreased systematically with increasing frequency over the frequency range examined. The rate of increase in torque with applied stimulus intensity was also found to decrease systematically with increasing frequency in a way that depended strongly on the skinfold thickness of the subject. CONCLUSIONS: Electrical stimulators using an alternating current waveform typically use a carrier frequency in the range of 2kHz to 4kHz for motor stimulation. This study shows that carrier frequencies in this range, modulated at 50Hz, are a compromise between comfort and maximum torque production. For maximum comfort with a low torque, a frequency close to 10kHz is indicated. For maximum torque, a lower frequency of alternating current (1kHz or less) is preferable.

Adult↗
PubMed1997

Topical application of nerve growth factor improves fracture healing in rats.

The aim of the present study was to examine the effects of nerve growth factor on the healing of unsplinted fractured ribs. After fracture of a rib in male rats, nerve growth factor was delivered by a miniosmotic pump to the fracture site for 7 days at the rate of 1.4 micrograms/day. Callus catecholamine concentrations, bone callus size, histomorphometry, and biomechanical properties of the repairing rib were measured at 7, 21, and 42 days after fracture. After 21 days, concentrations of norepinephrine and epinephrine were significantly increased in the group treated with nerve growth factor compared with those in the control group (211% norepinephrine and 322% epinephrine). Also, the midline longitudinal area of non-osseous (fibrous tissue and cartilage) callus of the fracture was significantly smaller (54%) and had a higher proportion of cartilage in the treated group than in the controls. By 42 days, there was only bony callus between the fracture ends in both the control group and the treated group. The treated group, however, again showed significantly elevated concentrations of norepinephrine and epinephrine (286 and 382%, respectively) and significantly elevated breaking stress (50%) and Young's modulus (51%), together with a reduction in the transverse cross-sectional area of the repair site (57%). The resultant increases in effectiveness and rate of repair of bone with administration of nerve growth factor suggest that it may play an important role in the healing processes of fractured bone.

Administration, Topical↗
PubMed1996

Limited interchangeability of methods of applying 1MHz ultrasound.

OBJECTIVE: To investigate the interchangeability of two different methods used to apply 1 MHz ultrasound for deep tissue heating, namely, the direct contact and the subaqueous methods. DESIGN: An intervention study with a crossover design. SETTING: The setting was a laboratory. PARTICIPANTS: Four specimens, cross-sections of nonliving pig tissue, were used. INTERVENTIONS: Specimens were each exposed to 1 MHz ultrasound under five different conditions: in contact with gel, and subaqueous at 0, 1, 2, and 4 cm from the applicator to the skin. MAIN OUTCOME MEASURES: Tissue temperatures were measured at six thermocouple sites at different depths from the skin surface. RESULTS: Subaqueous ultrasound applied at a distance of 0 cm from the skin produced significantly less tissue heating than direct contact (with gel) ultrasound at the same intensity. Increasing the distance from the applicator to the skin from 0 to 1, 2 and 4 cm resulted in significantly lower mean maximum temperature increases of 69%, 56%, and 44%, respectively, of the 0 cm values. CONCLUSIONS: The methods used clinically to apply ultrasound have only limited interchangeability. Large corrections to the power output are required to compensate when using subaqueous rather than direct (in air) ultrasound, and for applicator to skin distances of beyond 0 cm in subaqueous ultrasound.

Animals↗
PubMed1996

Dosage factors for the subaqueous application of 1MHz ultrasound.

OBJECTIVE: To determine and validate correction factors necessary to ensure consistent dosage of 1MHz ultrasound when applied in water at different applicator-to-skin distances and different levels of intensity. DESIGN: An intervention study with a crossover design. SETTING: A laboratory. PARTICIPANTS: Cross-sections of nonliving pig tissue. INTERVENTIONS: Specimens were each exposed to 1MHz ultrasound under four subaqueous conditions: in contact with the skin and at 1, 2, and 4 centimeters from the applicator to the skin. These conditions were repeated for each of three intensity levels: 0.5W/cm2, 1.0 W/cm2, and 2.0 W/cm2. MAIN OUTCOME MEASURES: Tissue temperatures were measured at six thermocouple locations at different depths from the skin surface. RESULTS: Increasing the distance from the applicator to the skin from 0 to 1, 2, and 4 centimeters resulted in progressive and significantly lower mean maximum temperature increases. The same relation of distance to temperature increase was identified at all intensity levels and was used to calculate dosage factors for distance in water. By multiplying the required intensity by the calculated dosage factors, the temperature increases in tissue were found to equal those produced at 0 centimeters distance. CONCLUSIONS: Large corrections to the intensity output are required to compensate when using ultrasound in water at different applicator-to-skin distances. These dosage (correction) factors are reliable for the range of intensity levels tested under the conditions examined.

Analysis of Variance↗
PubMed1996

Comparison of heating of nonliving soft tissue produced by 45 kHz and 1 MHz frequency ultrasound machines.

Ultrasound of 1 MHz frequency is used routinely for patient treatment because it can penetrate to and heat deeply located tissue. Benefits are claimed for newly introduced 45 kHz ultrasound machines, yet little evidence is available to confirm these benefits. This paper compares claims supporting the therapeutic use of 45 kHz ultrasound with those supporting the traditional MHz frequencies. The results of an empirical study comparing the heating effects are also presented. Thermocouples placed at different tissue depths in nonliving pig tissue measured temperature variations over a 40-minute period. Direct heating produced by the 45 kHz ultrasound machine was very superficial. By contrast, the 1 MHz ultrasound machine produced direct heating at all tissue depths. The results confirmed that although 45 kHz ultrasound machines may be useful for heating superficial tissues, they have limited or no use in heating deeper tissues. For treatment of deeply located tissue, 1 MHz ultrasound should continue to be used.

Hot Temperature↗
PubMed1995

Oestradiol acutely stimulates exocytosis of oxytocin and vasopressin from dendrites and somata of hypothalamic magnocellular neurons.

Oestrogen has many direct or indirect actions upon the magnocellular system of the hypothalamus. We have examined the possibility of acute actions of oestrogen upon the magnocellular system by stimulating slices of supraoptic nucleus in vitro with various concentrations of oestrogen, for varying lengths of time, and assessing the intrahypothalamic release of oxytocin and vasopressin under these conditions. Slices were stimulated in the presence of tannic acid, which precipitates extracellular protein and thereby stabilizes exocytosed neurosecretory granule cores. Stimulation for 5 or 20 min of slices of hypothalamus containing the supraoptic nuclei with 2.66 nM-26.6 microM 17 beta-oestradiol benzoate caused the exocytosis of granules from both dendrites and cell bodies of the magnocellular neurons; exocytosis from the dendrites predominated. Granules of both oxytocin- and vasopressin-producing cells were exocytosed to a similar extent. The incidence of exocytosis of both hormones after stimulation by oestrogen was significantly higher than after exposure either to physiological saline or to 17 alpha-oestradiol, but significantly lower than after stimulation by 56 mM potassium. The various doses of steroid and durations of stimulation all resulted in similar amounts of captured exocytosis. Furthermore, the oestradiol-induced release was not inhibited by removal of extracellular calcium, whereas the potassium-stimulated release was abolished. Exposure for 20 min to either testosterone or progesterone did not induce intranuclear release of significant numbers of neurosecretory granules from the magnocellular neurons. In contrast to its effect on the hypothalamus, 26.6 microM oestradiol for either 20 min or 5 min did not induce exocytosis of neurosecretory granules from the posterior pituitary. We conclude that oestrogen can exert acute non-genomic actions on the magnocellular neurons to promote intrahypothalamic release of oxytocin and vasopressin. This effect is probably direct on the magnocellular neurons as it is not dependent on external calcium. Such actions may be important in the development of the functional and morphological plasticity of the magnocellular system that occurs in parturition and lactation.

Animals↗
PubMed1995

Subaqueous ultrasound: 45kHz and 1MHz machines compared.

This study compared the tissue heating produced by 45kHz and 1MHz ultrasound machines used subaqueously in metal and in plastic basins. An intervention study with cross-over design was used. The setting was a laboratory. Two cross-sections of nonliving pig tissue were used with thermocouples positioned, in the tissues, at different distances along the ultrasound beam axis. Specimens were each exposed subaqueously to ultrasound produced by a 45kHz machine and a 1MHz machine. Both metal and plastic treatment basins were used (2 machines x 2 basin types). Thermocouples measured temperature variations for 30 minutes with each machine on and 10 minutes with it off. Temperature increases at different tissue depths varied with both the ultrasound machine and the type of basin used. The 45kHz frequency ultrasound machine produced a maximum temperature increase of 0.4 degrees C and an initial rate of heating of 0.05 degrees C per minute. The 1MHz machine consistently produced greater temperature increases. These were further increased by 2.65 degrees C (average) if a metal rather than plastic basin was used. The 45kHz machine, operated at maximum output, produced little heating of the irradiated tissue. By contrast, the 1MHz ultrasound unit produced appreciable heating to almost the full depth of the tissue irradiated. Use of a metal basin, rather than plastic, resulted in a markedly higher maximum temperature increase and a significantly greater initial rate of heating.

Animals↗
PubMed1992

Immuno-electron microscopic evidence for two different types of partial somatic repair of the mutant Brattleboro vasopressin gene.

In homozygous Brattleboro rats a frame-shift mutation in the vasopressin gene prevents secretion of vasopressin by magnocellular neurosecretory neurons and thus causes diabetes insipidus. Whereas most "vasopressin" neurons in Brattleboro homozygotes apparently lack vasopressin and its associated neurophysin and glycopeptide, some isolated cells overcome the mutation and "revert" to producing readily detectable amounts of vasopressin. We describe here two morphologically and immunocytochemically distinct subsets of such "revertant" cells. One subset contain, in their rough endoplasmic reticulum cisterns, electron-dense aggregates immunoreactive for vasopressin, for parts of oxytocin-neurophysin, and for CP14 (a peptide with a sequence deduced from the mutated precursor), but not for vasopressin-associated glycopeptide ("glycopeptide") or vasopressin-neurophysin. In Brattleboro heterozygotes, which have one mutant and one normal copy of the vasopressin gene, morphologically similar revertant cells exist; the aggregates in the rough endoplasmic reticulum of these cells do not immuno-label for CP14, but the cells do produce 160-nm neurosecretory granules immunoreactive for vasopressin, vasopressin-neurophysin and glycopeptide. In Brattleboro homozygotes, the second, more abundant subset of neurons which recover vasopressin immunoreactivity also express vasopressin-associated glycopeptide and CP14 but not oxytocin-neurophysin; both glycopeptide and CP14 are restricted to the rough endoplasmic reticulum but do not form aggregates. We conclude that two different somatic repairs of the Brattleboro mutation can occur. We propose that, in aggregate-containing neurons, exons B and C have been exchanged between the vasopressin and oxytocin genes; glycopeptide-immunoreactive neurons have either undergone mismatch repair or exchanged exon B.

Animals↗
PubMed1990

Complications of tissue plasminogen activator therapy after vitrectomy for diabetes.

Human recombinant tissue plasminogen activator (25 micrograms) was injected into seven eyes of six patients who had developed massive fibrin deposition after vitrectomy surgery for diabetes. Six eyes had developed pupillary membranes and recurrence of tractional retinal detachment from fibrin membranes, and one eye had developed only a pupillary membrane. All pupillary membranes resolved within one hour of administration of tissue plasminogen activator, and five tractional retinal detachments resolved within 24 hours. All eyes developed evidence of intraocular bleeding after tissue plasminogen activator injection. Subsequently, six of seven eyes developed recurrence of fibrin accumulation and tractional retinal detachment.

Adult↗