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Biomedical subjects

A Talalla

Publications and source records attributed to A Talalla.

At least 19 recordsLinked to original sources
PubMed1992

Neurocardiac responses to vagoafferent electrostimulation in humans.

UNLABELLED: To determine if cardiac vagal tone is enhanced by vagal electrostimulation (VES), we examined the heart rate autospectrum (HRA) in eight patients with implanted stimulators for complex partial seizures. In four patients the VES was activated at 30 Hz and 500-msec pulse (HiStim group) compared to 2 Hz and 130-msec pulse for the LoStim group (n = 4). Continuous ECG and respiratory waveforms were recorded for 45 minutes every 8 hours (7-8 AM; 3-4 PM 11-12 PM) during resting supine wakeful epochs both before and 15 days after surgical implantation. From the HRA cardiac sympathovagal balance was expressed as the ratio of the low frequency (LF) power to the high frequency (HF) power. RESULTS: There were no presurgical differences between the groups in heart rate, its variance, or the energies contained in any autospectral band. The LoStim group showed no significant change in heart rate (HR), HF peak power, or LF:HF ratios during 2 weeks of VES. Conversely, in the HiStim group, the LF:HF peak power ratio (an expression of sympathetic dominance) decreased from 2.5 +/- 1.5 preimplant to 1.5 +/- 0.49 (P < 0.02) with VES. During VES there was a significantly higher HF power in the HiStim compared to LoStim group. No diurnal variations in HRA values were seen for either group. CONCLUSIONS: (1) A relationship exists between selective vagal nerve electrostimulation and the HRA; and (2) high stimulation frequency of the vagus nerve in man is associated with sustained augmentation of cardiac vagal tone throughout a 24-hour cycle.

Adult↗
PubMed1992

Effects of chronic left vagal stimulation on visceral vagal function in man.

We examined the effects of chronic left vagal electrostimulation on afferent and efferent gastrointestinal vagal function in eight patients. Afferent function was assessed using cortical evoked responses to electrical stimulation of the esophagus and to direct vagal stimulation using the implanted left vagal electrode. Efferent gastrointestinal vagal function was measured by examining the basal, maximal, and sham fed stimulated gastric acid output prior to and with chronic left vagal electrostimulation. Esophageal electrostimulation produced a cortical evoked response consisting of three negative and three positive peaks within 400 msec after stimulation. Prior to vagal electrostimulation the mean conduction velocity of the afferent signal was measured at 8.72 +/- 3.39 m/sec, compatible with A-delta fibers involvement. Basal, maximal, and sham fed acid output were 1.11, 21.87, and 9.37 mmol/hour, respectively. The evoked response to esophageal electrical stimulation was not changed with chronic left vagal electrostimulation. Direct vagal stimulation also produced evoked potentials that were comparable to those obtained with esophageal stimulation. The mean conduction velocity was 6.26 +/- 2.72 m/sec (NS) so that there was no evidence of loss of myelinated fibers with chronic stimulation. No differences were detected in basal (1.29 mmol/h), maximal (21.64 mmol/h), or sham fed stimulated (8.03 mmol/h) acid output, showing that vagal electrostimulation has no effect on either total or vagally mediated acid output, an efferent vagal function. In conclusion, chronic left vagal electrostimulation has no significant adverse effect on gastrointestinal vagal function.

Adult↗
PubMed1992

Effect of vagal nerve electrostimulation on the power spectrum of heart rate variability in man.

The power spectrum of heart rate variability contains low frequency (LF = 0.08-0.12 Hz) and high frequency (HF = 0.18-0.30 Hz) components said to represent neurocardiac rhythms. To verify whether such a relationship exists we report a unique study where the heart rate autospectrum was determined in a 28-year-old epileptic male patient with an implanted vagal electrical stimulator. The stimulator was activated at 20 Hz, 300 microseconds pulse, and 1.25 V. Continuous ECG and respiratory waveform records were obtained over 45 minutes every 8 hours (7-8 AM; 3-4 PM; 11-12 PM) with the stimulator ON, then 24 hours OFF and then 24 hours ON again. The overall LF:HF peak ratio increased from 0.64 to 1.99 (P less than 0.001) after the stimulator was turned OFF. There was a dramatic increase in the LF peak power (greater than 60%) and a corresponding decrease in the HF peak power (greater than 65%) when the stimulator was turned OFF. These values were reversed when the stimulator was turned ON again. In the early morning and late evening hours, there was a significant rightward shift in the LF peak power frequency (average 0.057 to 0.075 Hz) whenever the stimulator was ON. Otherwise, there were no significant circadian variations in any of the autospectral components. The results demonstrate an unequivocal relationship between selective vagal nerve electrostimulation and alterations in the heart rate autospectrum.

Adult↗
PubMed1991

Secondary erythrocytosis due to a cerebellar hemangioblastoma: demonstration of erythropoietin mRNA in the tumor.

Cerebellar hemangioblastoma is a rare cause of secondary erythrocytosis. Although the erythrocytosis is a result of erythropoietin (Ep) stimulation, direct evidence of Ep synthesis by the tumor has been lacking. In an erythrocytotic patient with a cerebellar hemangioblastoma we found elevated levels of Ep in the tumor cyst fluid and for the first time demonstrated Ep mRNA in the tumor by Northern blotting. This finding confirms cerebellar hemangioblastoma as a site of ectopic Ep production.

Adult↗
PubMed1990

The effect of intrathecal baclofen on the lower urinary tract in paraplegia.

The effect of intrathecal baclofen on urethral pressure was investigated in 6 spinal cord injured patients. Although the response was inconsistent, and further studies are necessary to define its role more clearly in the bladder management of these patients, its possible application as an alternative to sensory rhizotomy to improve bladder emptying in patients having sacral nerve stimulation procedures is discussed.

Baclofen↗
PubMed1989

Intrathecal baclofen and the H-reflex.

Baclofen was given intrathecally to six patients with severe lower limb spasticity due to traumatic spinal cord injury. The effects of the drug on spasticity and the ratio between the maximum amplitude of the H reflex and the M response from the soleus (Hmax/Mmax ratio) were assessed. In each patient, spasticity was reduced following intrathecal baclofen and in four patients there was a reduction in the amplitude of the H reflex and Hmax/Mmax ratio. These results suggest that the Hmax/Mmax ratio may be helpful in establishing optimum drug dosage, particularly when the drug is used on a chronic basis.

Adult↗
PubMed1987

FES for bladder: direct or indirect means?

Efforts to restore function to the neurologically disabled lower urinary tract by direct electrical stimulation of the bladder wall have met with only very limited success. This has been due to pain and cocontraction of bladder outlet mechanisms caused by presumed spread of the large currents required to effectively directly stimulate the detrusor muscle. Stimulation at the four anatomical sites of the sacral neural outflow on the other hand has been more successful. Conus medullaris stimulation has resulted in "good results" in just over half of the 28 patients so treated. Acceptance of this technique has been limited by the poor selectivity of the intramedullary electrodes in stimulating only the target motor neurons and the resultant clinical problems with the consequent stimulus current spread. Sacral anterior root stimulation has been used in at least 88 patients with generally good results. Cocontraction of the detrusor and external urethral sphincter are circumvented by the use of an intermittent pattern of stimulation. The primary disadvantage of this technique is the obligatory placement of the electrodes within the cerebrospinal fluid compartment. Clinical experience with stimulation of the extradural sacral mixed nerves is limited. Experimental studies indicate that success with this technique requires dorsal rhizotomy and pudendal neurotomy. Preliminary clinical experience suggests that these surgical manipulations may not be necessary for a successful outcome. The literature on clinical application of pelvic nerve stimulation is too limited for detailed comment on this technique. A definitive technique for restoration of bladder function by electrical stimulation remains to be developed.

Electric Stimulation Therapy↗
PubMed1986

Successful intraspinal extradural sacral nerve stimulation for bladder emptying in a victim of traumatic spinal cord transection.

This report concerns a patient with a functionally complete spinal cord transection due to trauma at T-6. Her clinical syndrome of a motor and sensory paraplegia was accompanied by hyperreflexic detrusor dysfunction. Radiofrequency-coupled bilateral stimulation of the 3rd sacral nerves in their intraspinal but extradural course achieved reliable, effective emptying of the bladder. This single case suggest that successful stimulation of the sacral neural outflow may not require intrathecal placement of stimulating electrodes, sensory rhizotomy, or pudendal neurotomy.

Adult↗
PubMed1985

Effect of pinealectomy on serum melatonin, luteinizing hormone and prolactin: a case report.

A patient, aged 47 is described in whom changes in hormonal profiles were observed following surgical excision of the pineal. She presented with a clinical syndrome of increased intracranial pressure and postmenopausal symptoms. Computerized tomographic scans showed obstructive hydrocephalus from a cystic lesion in the pineal region. Surgical removal of the cystic mass revealed a benign ependymal cyst and normal pineal tissue. After the operation, she had no nocturnal increase in serum melatonin. The morning basal LH was further elevated and night-time PRL showed little fluctuation from the basal levels.

Female↗
PubMed1976

A mathematical model of cerebrospinal fluid dynamics.

The ability to solve systems of simultaneous non-linear differential equations by a combination of analytical and computational techniques has encouraged the development of valid mathematical models of biological phenomena. The dynamics of the cerebrospinal fluid (CSF) system has been the subject of closer scrutiny in recent years since the recognition of symptomatic low-pressure hydrocephalic states in man. A mathematical model has been derived from 7 assumptions: (1) That the brain is a spherical shell. (2) That CSF is secreted at a constant rate. (3) That CSF absorption is linearly dependent on pressure. (4) That flow between the CSF compartments is proportional to the pressure difference. (5) That Laplace's Law holds for the visco-elastic properties of the brain. (6) That there is compliance in the spinal compartment of the CSF system. (7) That vascular pulsations in the cranial and spinal compartments are capacitatively coupled. Using known data (and estimates of as yet unknown values) for the several parameters, the validity of the model has been successfully tested against 3 clinical conditions. This model extends our understanding of derangements of CSF dynamics and suggest where further research may yield data at present lacking.

Cerebrospinal Fluid↗
PubMed1975

Electrical stimulation of the brain. II. Effects on the blood-brain barrier.

Acute and chronic studies of the effects of electrical stimulation on the blood-brain barrier (BBB) of the cat cerebral cortex are reported. The findings emphasize the importance of avoiding direct-coupled, monophasic waveforms in stimulating nervous tissue. Biphasic waveforms with balanced charges in each half-wave of the stimulating pulse can be used for up to 36 hours of continuous stimulation if the charge per phase (Q/ph) does not exceed 0.45 microcoulombs. Charge density (QD) is also an important parameter. When stimulating in the bipolar mode, BBB breakdown will occur first beneath the smaller electrode of the pair. Following electrical injury, the BBB will be partially restored within one week, and, with rare exceptions, be completely intact after one month.

Animals↗
PubMed1975

Electrical stimulation of the brain. I. Electrodes and electrode arrays.

Investigators engaged in studying the effects of electrical stimulation on the blood-brain barrier (BBB) and brain usually find it necessary to fabricate the electrodes and electrode arrays required in their acute and chronic experiments. Techniques for fabricating spring-mounted, concentric and salt-bridge electrodes and electrode arrays are described in this report.

Blood-Brain Barrier↗
PubMed1974

Electrical stimulation of the human visual cortex; preliminary report.

A feasibility study for the development of a human visual prosthesis has led several workers to observe the effects of electrical stimulation of the human visual cortex. Experience with such stimulations of three normal-sighted patients is reported. The results confirm some of the findings of other workers, but do not show that multiple phosphenes were experienced by our patients, using strictly limited parameters of stimulation.

Electric Stimulation↗