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Biomedical subjects

A Starr

Publications and source records attributed to A Starr.

At least 127 records · Page 7Linked to original sources
PubMed1991

Magnetic stimulation of muscle evokes cerebral potentials.

Somatosensory evoked potentials (SEPs) were recorded from the scalp in man to magnetic stimulation of various skeletal muscles. The potentials consisted of several components, the earliest of which decreased in latency as the stimulated site moved rostrally, ranging from 46 msec for stimulation of the gastrocnemius, to 14 msec for stimulation of the deltoid. Experiments were performed to distinguish the mechanisms by which magnetic stimulation of the muscle was effective in evoking these cerebral potentials. For the gastrocnemius, the intensity of the magnetic stimulus needed for evoking cerebral potentials was less than that required for activating mixed or sensory nerves in proximity to the muscle belly (eg, posterior tibial nerve in the popliteal fossa, sural nerve at the ankle). Vibration of the muscle or passive lengthening of the muscle, procedures which activate muscle spindles, were accompanied by a significant attenuation of the potentials evoked by magnetic stimulation of the muscle. Anesthesia of the skin underlying the stimulating coil had no effect on the latency or amplitude of the early components of the magnetically evoked potentials, whereas electrically evoked potentials from skin electrodes were abolished. Thus, the cerebral potentials accompanying magnetic stimulation of the muscle appear to be due to activation of muscle afferents. We suggest that magnetic stimulation of muscle can provide a relatively simple method for quantifying the function of muscle afferents originating from a wide variety of skeletal musculature.

Adult↗
PubMed1991

Physiology of short-term verbal memory.

These studies document a series of brain events accompanying short-term memory functions. For auditory verbal material the sequence involves at least two different sites within auditory cortex subserving sensory and cognitive processes of memorization. During the scanning of the short-term store structures within the medial temporal lobes, presumably the hippocampus, are active. There is an inconsistency between these results and the clinical observations of the need for an intact dominant parietal lobe for auditory short-term memory to function normally. Magnetic recordings showed no focal dipolar source of activity in the parietal lobe during any aspect of auditory short-term memory. The discrepancy could be accounted for by considering the parietal lobe lesion as "disconnecting" the lateral temporal cortex from the deep medial hippocampal structures thereby impeding auditory short-term functions (Geschwind, 1965). These studies show that the physiological analysis of brain events in the msec range can provide information about relatively complex cognitive processes underlying short-term memory. The magnetic and electrical recording methods provide a noninvasive way to study human brain functions involved in cognition that can then be correlated with behavioral measures of specific cognitive activities.

Brain↗
PubMed1991

Event-related potential correlates of the serial position effect in short-term memory.

Event-related potential (ERP) correlates of the serial position effect in short-term memory were investigated using a memory scanning task. Nine normal young adults (18-39 years) indicated whether a probe item was a member of a previously presented 5-item memory set by pressing 1 of 2 reaction-time buttons. Three types of stimuli were used: verbal digits presented both auditorily and visually, and musical notes presented auditorily. The ERPs to the probes were separately averaged according to the serial position of the probe (1, 2, 3, 4 or 5) in the memory set. The ERPs to the memory set items in positions 1, 3 and 5 also were separately averaged. Both baseline-to-peak and average amplitudes of a late positive parietal potential to the probes were larger to probe items presented in the last position in the memory set than to probes presented in the middle positions (2, 3 and 4), showing a significant recency effect, but only for auditory digits. Reaction time reflected significant recency effects for both auditory digits and notes, but not for visual digits. Response accuracy (percent correct) showed a significant recency effect only for notes. For each stimulus type, both the baseline-to-peak and average amplitudes of a late frontal component to the memory set items became more negative (in the case of the visual digits, less positive) in the third and last serial position of the memory set compared to the first. These findings provide electrophysiological evidence of serial position effects in short-term memory, which, during memory scanning, are dependent on stimulus modality (auditory, visual) and type (verbal, non-verbal).

Adolescent↗
PubMed1991

Effects of myelin or cell body brainstem lesions on 3-channel Lissajous' trajectories of feline auditory brainstem evoked potentials.

Auditory brainstem evoked potentials (ABEP) were recorded from 16 awake cats to obtain 3-Channel Lissajous' Trajectories (3CLTs) using three orthogonal differential electrode configurations (nasion-midline nuchal ridge, left-right mastoids, vertex-midline under the mandible). Potentials, evoked by monaural 80 dBnHL (re, human threshold) clicks, were studied before, and up to 7 weeks after inducing neuronal lesions localized to the cochlear nucleus (CN) or the superior olivary complex (SOC), or myelin lesions localized to the fibers of the trapezoid body connecting these two structures. Neuronal lesions were induced by injection of kainic acid (KA), while myelin lesions were induced by injection of L-alpha-lysophosphatidylcholine (LPC). With CN neuronal lesions the major changes in 3CLT were in the time domain of 'b', 'c' and 'd' (components P2, P3 and P4 of single-channel ABEP). With SOC neuronal lesions the major changes were in 'c' and 'd' of 3CLT (P3 and P4 of ABEP). With trapezoid body lesions the major change was in 'c' (P3 of ABEP). The results are compatible with the peripheral generation of the first ABEP components (P1a and P1b). The second component (P2) is generated by ipsilateral CN neurones and their outputs. The third component (P3) is generated primarily by ipsilateral SOC neurones and their outputs, with the ipsilateral CN providing input. The The fourth component (P4) is generated bilaterally by the SOC neurones and their outputs, receiving their inputs from ipsilateral CN. The fifth ABEP component (P5) is generated by structures central to the SOCs and their immediate outputs. Neither focal neuronal nor myelin lesions were sufficient to produce obliteration of any component, consistent with a set of generators for each of the ABEP components, consisting of both cell bodies and their output fibers, that is distributed spatially in the brainstem.

Animals↗
PubMed1991

Aortic valve replacement in patients over 80 years of age: a comparative standard for balloon valvuloplasty.

Elderly patients who develop symptomatic aortic valvular malfunction have a grave prognosis. Until recently they have not been seriously considered for active treatment, such as valvular surgery or balloon valvuloplasty. Between January 1972 and July 1989, 88 patients over the age of 80 years underwent aortic valve replacement and have been prospectively followed for a total of 185 patient-years. The majority were in New York Heart Association functional class III (48%) or IV (48%) preoperatively. Valvular pathology was pure aortic stenosis in 81%, regurgitation alone in 6%, and mixed lesions in 13% of the cases. Before 1982 the majority of patients received mechanical valves, whereas tissue valves have predominated since then (76% of total). Forty-three percent of the patients had concomitant coronary artery bypass grafting. The overall operative mortality was 16%. Emergency surgery, isolated aortic valve replacement, advanced preoperative functional class, and female gender carried a statistically higher operative mortality. The overall actuarial survival (standard error) at 5 years was 64(7)%. Survival was significantly higher at 5 years for concomitant coronary bypass grafting than for isolated aortic valve replacement, 70 (11)% versus 59(8%), and for males compared to females, 73(9)% versus 55(9)%. The 5-year event-free rates for valve-related death and valve re-replacement were 97(2)% and 93(5)%, respectively. These data provide a firm basis for aortic valve replacement as the standard form of treatment in patients over 80.

Actuarial Analysis↗
PubMed1991

Absence of both auditory evoked potentials and auditory percepts dependent on timing cues.

An 11-yr-old girl had an absence of sensory components of auditory evoked potentials (brainstem, middle and long-latency) to click and tone burst stimuli that she could clearly hear. Psychoacoustic tests revealed a marked impairment of those auditory perceptions dependent on temporal cues, that is, lateralization of binaural clicks, change of binaural masked threshold with changes in signal phase, binaural beats, detection of paired monaural clicks, monaural detection of a silent gap in a sound, and monaural threshold elevation for short duration tones. In contrast, auditory functions reflecting intensity or frequency discriminations (difference limens) were only minimally impaired. Pure tone audiometry showed a moderate (50 dB) bilateral hearing loss with a disproportionate severe loss of word intelligibility. Those auditory evoked potentials that were preserved included (1) cochlear microphonics reflecting hair cell activity; (2) cortical sustained potentials reflecting processing of slowly changing signals; and (3) long-latency cognitive components (P300, processing negativity) reflecting endogenous auditory cognitive processes. Both the evoked potential and perceptual deficits are attributed to changes in temporal encoding of acoustic signals perhaps occurring at the synapse between hair cell and eighth nerve dendrites. The results from this patient are discussed in relation to previously published cases with absent auditory evoked potentials and preserved hearing.

Acoustic Stimulation↗
PubMed1990

Five-year results of coronary bypass grafting for patients older than 70 years: role of internal mammary artery.

Despite numerous references to the superiority of the internal mammary artery (IMA) over the saphenous vein for myocardial revascularization, its role in the elderly is still in question. From January 1984 through December 1988, 1,081 patients older than 70 years (mean age, 74.9 years) underwent bypass grafting, 354 (33%) receiving left IMA grafts based on the surgeon's preference and 727 (67%) receiving vein grafts only. Selection bias resulted in a higher incidence of known risk factors (such as cardiomegaly, arrhythmias, left ventricular failure, wall motion abnormalities, and preoperative combined New York Heart Association/Canadian Cardiovascular Association functional class IV) in patients in whom the IMA was not used. However, unstable angina, acute myocardial infarction, left ventricular dysfunction, and left main disease were not contraindications for using IMA grafts. The operative mortality rate was significantly lower in IMA patients (2.8% versus 7.6%). The actuarial 5-year survival rate (standard error) was higher in patients with IMA grafts, 89% (3%) versus 78% (2%), and postoperative functional class improved to a greater extent in IMA patients (87% of patients were in classes I and II). Arrhythmias and myocardial infarction were significant causes of late death only in patients with vein grafts. When patients are older than 70 years, patient selection factors clearly play an important role in the differential results between patients in whom the IMA is used and patients in whom vein grafts are used. As in younger patients, excellent results can be achieved in the elderly.

Actuarial Analysis↗
PubMed1990

Eighth nerve contributions to cat auditory brainstem responses (ABR).

There is a temporal correspondence between some of the early components of the auditory brainstem potentials in cat and the negative peak of the triphasic nerve action potential recorded from selected points along the VIII cranial nerve. The intracranial portion of the VIII nerve in cat has a conduction velocity of 10 meters/s. The initial peak of the ABR, P1a, is coincident with the negative portion of the triphasic VIII nerve action potential within the cochlea as recorded from the round window. The next peak (P1b) of the ABR occurs 400 microseconds later and is coincident with the negative portion of the triphasic VIII nerve action potential recorded from just within the lateral border of the cochlear nucleus. These results are similar to studies of the human ABR that show waves I and II are correlated with activity of the VIII nerve. It is likely that waves P1a and P1b in cat are homologous to waves I and II in human. In cat, these first two peaks of the ABR can be distinguished in vertex to neck recordings but not in vertex to ipsilateral mastoid derivations.

Animals↗
PubMed1990

Long-term neurophysiologic outcome after neonatal extracorporeal membrane oxygenation.

We examined clinical and neurophysiologic measures in 10 children 4 to 9 years after neonatal extracorporeal membrane oxygenation. Electroencephalograms did not correlate with clinical or other neurophysiologic measures of interhemispheric asymmetry. By ultrasound imaging, the right internal carotid artery velocity was approximately 62% of that on the left, and right internal carotid flow was reduced by 74% (p less than or equal to 0.01), whereas an age-matched control group showed no differences. A decrease in the amplitude of the long-latency auditory and somatosensory evoked potentials was noted over the right hemisphere after left-sided stimulation compared with the left hemispheric potentials after right-sided stimulation (p less than or equal to 0.005). No significant differences in hemispheric symmetry were noted in the amplitudes for wave V of the auditory brain-stem response or in the P30 component of the middle-latency auditory evoked potentials. Likewise, latency measures of the evoked potentials were symmetric. We conclude that (1) neonatal extracorporeal membrane oxygenation is associated with long-lasting decreased right internal carotid blood flow with compensatory increased flow through the left carotid system and (2) there is a consistent reduction in the amplitude of right hemispheric long-latency evoked potentials. These latter findings may reflect redirected cerebral blood flow patterns after extracorporeal membrane oxygenation.

Blood Flow Velocity↗
PubMed1990

Abnormal EEG slow activity in left temporal areas in senile dementia of the Alzheimer type.

Resting 32-channel topographical measures of EEG slow activity were compared in 12 elderly controls and 12 patients with senile dementia of the Alzheimer type. The patients had higher amplitude delta and theta than controls, especially in the left temporal regions. This greater amount of low frequency EEG activity in the left temporal area is consistent with recent EEG, neuropsychological assessment, and positron emission tomography findings in SDAT patients. Five patients with mild-to-moderate dementia (as determined by the Folstein Mini-Mental State scale) primarily exhibited focal, abnormal slow activity in the left temporal regions. Seven patients with severe dementia exhibited increased slow activity across the head, which was still most abnormal in the left temporal regions.

Aged↗
PubMed1990

A critical analysis of morbidity and mortality as it relates to recipient age following cardiac transplantation.

Older patients (age greater than 55) are now being accepted as candidates for cardiac transplantation. The outcome following cardiac transplantation in this older age group has been largely limited to an analysis of mortality and rejection and infection incidence. In addition to these factors, this report investigates whether morbidity related to other organ system disease is greater in older patients. Seventy-eight cardiac transplant operations in patients aged 15 through 64 have been performed using the identical immunosuppression protocol from December 1985 to May 1989. Of these, 58 patients were under the age of 55 (younger), and 20 were 55 years of age or older (older). One- and 2-yr survival tended to be lower in the older group compared to the younger group, but was not statistically significant (1 yr--87% vs. 77%, respectively; 2 yr--84% vs. 77%, respectively, p=0.143). There were no statistical differences between groups in length of initial transplant hospitalization, number of readmissions or total duration of time in hospital (including readmissions) either absolutely or normalized to total months of follow-up for each patient. Neurologic and vascular problems represented a greater proportion of readmissions and rejection a lower proportion of readmissions in the older group compared to the younger group (p less than 0.05). Using hospitalization as a marker for important morbidity, there appears to be little impact of older age on post-cardiac transplant outcome.

Adolescent↗
PubMed1990

Stress, coping, and quality of life in family members of kidney transplant recipients.

This study explored specific stressors and identified coping strategies used by family members of kidney transplant recipients in the first 6 months following transplantation. Quality of life was also briefly examined as the outcome measure. Health-related items were identified as most stressful, and work-related items as least stressful. Self-controlling and problem-solving coping strategies were most frequently used, and escape/avoidance strategies were least used. Findings from this study have implications for development of specific teaching plans for transplant recipient families, as well as for collaborative team exploration of family stress and coping.

Adaptation, Psychological↗
PubMed1989

Somatosensory evoked potentials in cerebral palsy after partial dorsal root rhizotomy.

Somatosensory evoked potentials (SEPs) were studied in 20 children with cerebral palsy and severe lower extremity spasticity before and after selective partial dorsal root rhizotomy of the lumbosacral cord. The potentials from stimulating nerves in the lower extremity were abnormal in two thirds of the children before the operation, whereas the potentials were generally normal from upper extremity nerves. Dorsal root rhizotomies caused an attenuation of nerve root entry volleys recorded over the lumbar cord but did not change SEPs recorded over the cortex. The exception to this was that the incidence of abnormal sural nerve SEPs decreased postoperatively. Lumbar cord functions measured by H-reflexes or by tendon jerks were depressed following the operation. These results indicate a significant degree of abnormality of somatosensory transmission from the lower extremity in a group of cerebral palsied children with severe spasticity. Moreover, selective sectioning of approximately 50% of the dorsal root fibers in the lumbosacral cord had little influence on cortical evoked potentials.

Cerebral Palsy↗
PubMed1989

Electrophysiological measures during acupuncture-induced surgical analgesia.

Electrophysiological recordings (electroencephalograms, somatosensory-evoked potentials, cognitive-evoked potentials) were made in five patients during acupuncture-induced analgesia for removal of a thyroid tumor. The electrophysiological measures were unchanged during the operation. Acupuncture's modes of action in producing analgesia are not revealed in this study.

Acupuncture Therapy↗