Search PubMed⌕ Search

Biomedical subjects

A Starr

Publications and source records attributed to A Starr.

At least 109 records · Page 6Linked to original sources
PubMed1993

Binaural interaction in auditory evoked potentials: brainstem, middle- and long-latency components.

Binaural interaction occurs in the auditory evoked potentials when the sum of the monaural auditory evoked potentials are not equivalent to the binaural evoked auditory potentials. Binaural interaction of the early- (0-10 ms), middle- (10-50 ms) and long-latency (50-200 ms) auditory evoked potentials was studied in 17 normal young adults. For the early components, binaural interaction was maximal at 7.35 ms accounting for a reduction of 21% of the amplitude of the binaural evoked potentials. For the middle latency auditory evoked potentials, binaural interaction was maximal at 39.6 ms accounting for a reduction of 48% of the binaural evoked potential. For the long-latency auditory evoked potentials, binaural interaction was maximal at 145 ms accounting for a reduction of 38% of the binaural evoked potential. In all of the auditory evoked potentials binaural interaction was long lasting around the maxima. The binaural interaction component extends for several milliseconds in the brainstem to tens of milliseconds in the middle- and long-latency components. Binaural interaction takes the form of a reduction of amplitude of the binaural evoked potential relative to the sum of the monaural responses, suggests that inhibitory processes are represented in binaural interaction using evoked potentials. Binaural processing in the auditory pathway is maximal in the time domain of the middle-latency components reflecting activity in the thalamo-cortical portions of the auditory pathways.

Acoustic Stimulation↗
PubMed1993

Survival 15 to 20 years after coronary bypass surgery for angina.

OBJECTIVES: The aim of this study was to determine the 15- to 20-year outcome of coronary bypass surgery in patients with angina. BACKGROUND: Coronary bypass surgery has been performed for > 20 years; we need to know the expected outcome of a very long-term follow-up. METHODS: Using actuarial techniques, we determined the outcome of coronary bypass surgery performed for chronic stable and unstable angina in 7,529 patients from 1969 to 1988. RESULTS: The 5-, 10-, 15- and 20-year survival rates (mean +/- SE) were 88 +/- 1, 73 +/- 1, 53 +/- 1 and 38 +/- 3%, respectively, for the whole group. Compared with patients operated on in 1974 to 1988 (n = 7,026), patients operated on in 1969 to 1973 (n = 503) were younger and had less coronary artery disease but had a higher operative mortality rate and a shorter long-term survival time; 15- and 20-year survival of the 1969 to 1973 cohort was 47 +/- 2% and 33 +/- 3%, respectively. The 1974 to 1988 cohort of patients had a 2.1% operative mortality rate and a 10- and 15-year survival probability of 74 +/- 1% and 55 +/- 2%, respectively. For 2,128 patients with "normal" left ventricular function, the 10- and 15-year survival probability was 82 +/- 1% and 64 +/- 3%, respectively, and for 2,413 patients with "abnormal" left ventricular function, it was 66 +/- 1% and 47 +/- 3%, respectively (p < 0.0001); for men it was 74 +/- 1% and 56 +/- 2%, respectively, and for women, 70 +/- 2% and 52 +/- 5%, respectively, p < 0.05. The actuarial percentages of reoperation and myocardial infarction at 15 years were 33 +/- 2% and 26 +/- 2%, respectively; these values did not differ significantly between men and women. There was a significant (p < 0.001) difference between men and women in angina status; 81% of the men versus 74% of the women had no angina or mild angina at the most recent follow-up study. CONCLUSIONS: Coronary bypass surgery is an effective form of therapy for angina (for 15 to 20 years) in both men and women.

Age Factors↗
PubMed1993

Blinking in patients with memory disorders during short term memory tasks.

The occurrence of blinking during short term memory tasks was analyzed for 32 subjects divided into three groups: 12 memory impaired patients, 10 elderly normals (age-matched to the patients), and 10 young normals. The subjects were participating in a study of brain evoked potentials accompanying memory activities. They were instructed not to blink during the performance of the memory tasks for reasons related to the quality of the recorded potentials. In this context, the withholding of blinking can be considered a secondary task. Blinking during the short term memory tasks was inversely related to performance accuracy (r = -.57). Age, mini-mental score and reaction time were also significantly related to the frequency of blinking. Dividing the memory patients into two groups according to the incidence of blinking, ("high-blinking" and "low-blinking"), revealed a significant difference in overall task accuracy with the high-blinking group performing more poorly than the low-blinking group.

Adult↗
PubMed1993

Survival at 15 to 18 years after coronary bypass surgery for angina in women.

BACKGROUND: Coronary bypass surgery in women is associated with lower survival than in men. We need to know whether this is because of patient-related factors and whether the lower survival is present in all subgroups of patients and for all time periods during which the surgery was performed. METHODS AND RESULTS: Using actuarial techniques, we determined the outcome of coronary bypass surgery performed for chronic stable and unstable angina in 1979 women and 6927 men. The operative mortality was 2.7% for women and 1.9% for men (P = .02). The higher operative mortality in women was seen in those with three-vessel disease or greater and abnormal left ventricular function (5.4% versus 2.8%, P = .009) and those with stable angina (2.6% versus 1.5%, P = .006). The 5-, 10-, 15-, and 18-year survival for women was 86 +/- 0.9%, 70 +/- 1.5%, 50 +/- 2.5%, and 37 +/- 6.4%, respectively, and for men, 88 +/- 0.4%, 73 +/- 0.7%, 54 +/- 1.2%, and 42 +/- 1.9%, respectively (P = .03). The lower survival in women compared with men was seen in those with three-vessel disease or greater and abnormal left ventricular function (at 10 years, 69 +/- 1.8% versus 73 +/- 0.8%, P = .005). At 15 years, the incidence of reoperation was 26 +/- 2.4% versus 28 +/- 1.2% and of myocardial infarction, 30 +/- 2.8% versus 32 +/- 1.3%, P = NS for either. The incidence of no angina or mild angina was 70% in women and 78% in men, P < .0001. The operative mortality and late survival of those operated on in different time periods for either women or men was not significantly different. Women were older (64 +/- 9.4 versus 61 +/- 9.9 years, P < .0001) and smaller (body surface area, 2.0 +/- 0.2 versus 1.7 +/- 0.2 m2, P < .0001), had a higher incidence of diabetes, systemic hypertension, and unstable angina, and had a smaller lumen of the left anterior descending coronary artery (1.7 +/- 0.4 versus 1.9 +/- 0.4 mm, P < .0001), right coronary artery, and diagonal arteries. More men were smokers, and men had a higher incidence of prior myocardial infarction, previous coronary bypass surgery, and extent of coronary disease and of abnormal left ventricular function. The Cox regression model of survival showed that independent risk factors for lower survival were older age, previous coronary bypass surgery, previous myocardial infarction, and diabetes. Sex was not an independent risk factor for poorer survival. CONCLUSIONS: Women have a higher operative mortality and lower long-term survival than men after coronary bypass surgery for angina. However, the differences are small, even if statistically significant. Importantly, patient-related factors and not sex are independent predictors of poorer survival. Therefore, coronary bypass surgery should not be delayed or denied to women who have the usual indications for surgery.

Actuarial Analysis↗
PubMed1993

Utilization of manufacturers' implant card data to estimate heart valve failure.

Heart valve manufacturers possess the most complete inventory of world-wide mechanical valve failures, but to convert failures to time-related risks requires estimates of patient follow up. Since manufacturers did not actively track patients, they needed a model that incorporates an assumed death rate to decrease the numbers of patients at risk. We present a method for using a manufacturer's implant card database to estimate time-related complication rates for patient subsets, and illustrate its use by examining the risk of outlet strut fracture (OSF) with the Björk-Shiley 60 degrees Convexo-Concave valve (CC60). We developed a parametric model for valve patient survival based on actively followed valve patients from three centers using only variables typically available from implant cards. Using this survival model, a simulated lifetime was produced for each valve in the CC60 implant database for which the required covariates were known. These lifetimes were then used to analyze OSF as if they were true follow up times. This allowed the use of conventional methods of univariate and multivariate analysis for OSF, including parametric statistical models. According to the approximate linearity of the cumulative hazard functions, OSF risk over time appeared to be fairly constant. Several risk factors were identified, including valve size, patient age at implant and valve position. Using parametric models for both patient survival and OSF permits the estimation of the probability of OSF before death for an individual patient (as opposed to the usual actuarial probability of OSF given that the patient does not die). Because the patient may die before his valve would have failed, this cumulative incidence of OSF is always less than the actuarial risk. For all but the very highest risk patients, the cumulative incidence over their relatively short remaining lifetimes is very small.

Actuarial Analysis↗
PubMed1992

The H-reflex to magnetic stimulation of lower-limb nerves.

We elicited H-reflexes by magnetic and electrical stimulation of several different nerves in 10 healthy subjects and two patients with S-1 radiculopathy. The posterior tibial nerve at the popliteal fossa and the femoral nerve at the inguinal ligament were tested with both electrical and magnetic stimulation; the proximal sciatic nerve was tested only with magnetic stimulation. Muscle activity was recorded from the soleus muscle for posterior tibial and sciatic nerve stimulation and from the vastus medialis muscle for femoral nerve stimulation. No significant difference was found between the latency of H-reflexes evoked by magnetic or electrical stimulation. With magnetic stimulation, the mean (+/- SD) Ia sensory fiber conduction velocity in the proximal segment of the sciatic nerve was 72.4 +/- 3.3 m/s, while the motor nerve fiber conduction velocity in the same portion of the nerve was significantly slower, at 60.6 +/- 2.0 m/s. In two patients with unilateral S-1 radiculopathy, the latency of the H-reflex from the soleus muscle to both magnetic and electrical stimulation of the posterior tibial nerve was absent or prolonged on the affected side. Magnetic stimulation can be used to study the H-reflex and Ia fiber conduction velocity and is particularly advantageous when testing deeply located nerve trunks.

Adult↗
PubMed1992

'Fatigue' in patients with multiple sclerosis. Motor pathway conduction and event-related potentials.

Ten patients with a definite diagnosis of multiple sclerosis and complaints of "fatigue" were studied using (1) reaction times and event-related potentials accompanying the performance of auditory memory tasks (target detection, verbal short-term memory) and (2) motor conduction velocities of the pyramidal tract elicited by cerebral and cervical magnetic stimulation. Patients were studied when "rested" and when fatigued. Reaction times of the patients when rested were significantly delayed in the short-term memory but not the target-detection tasks when compared with normal controls. When patients were fatigued, their reaction times became significantly longer in all tasks compared with when they were rested. Event-related potentials in these tasks consist of N1/P2 sensory components and P3a and P3b cognitive components. The N1 component latency was longer and P3a and P3b amplitudes were reduced in patients compared with controls. Fatigue in patients with multiple sclerosis was accompanied by a shortening of P3a latency and an increase in P3a and P3b amplitudes compared with these measures when patients were rested. Pyramidal tract conduction velocities did not differ between rested and fatigued conditions. Thus, fatigue in patients with multiple sclerosis was associated with a slowing of performance (reaction time) on memory tasks, whereas brain potentials reflecting neural events of stimulus encoding and classification were either unchanged or paradoxically speeded up in latency in the fatigued compared with the rested conditions. We postulate that, in patients with multiple sclerosis, fatigue affects neural processes acting after stimulus evaluation but before activation of the primary motor pathways.

Adult↗
PubMed1992

Cortical DC potential shifts accompanying auditory and visual short-term memory.

Negative DC potential shifts appeared over the scalp during the performance of verbal and non-verbal short-term memory tasks. Three items were successively presented (presentation of memory items) and then had to be retained in memory for 3 sec (memory retention) before being compared to a probe which was either a member (in set) or not a member (out of set) of the memory set. Verbal items (the digits "1" through "9") were tested in the auditory and visual modality and non-verbal items (musical notes) were tested in the auditory modality. Stimulus modality had a significant effect on DC potential shifts during both presentation of memory items and memory retention. There was a sustained negative shift during these periods which was larger over frontal regions with auditory than with visual material whereas the negative shift was larger over posterior temporal regions with visual than with auditory material. Out of 21 subjects who participated in the study, 9 reported the use of visual images in the auditory task, 5 used subvocal auditory rehearsal in the visual task and 7 used imagery concordant with the stimulus modality being memorized. These different strategies had a significant effect on the amplitudes and distribution of the DC potential shifts. The speed of response affected the amplitude of the DC potential shifts in the frontal regions, being larger with fast RTs than with slow RTs but only when verbal items were being processed. These results indicate that stimulus modality, modality of mental imagery, and speed of scanning of the memory store affect DC potential shifts during a 3 sec period of memory retention.

Acoustic Stimulation↗
PubMed1992

Inadequate internal mammary artery graft as a cause of postoperative ischemia: incidence, diagnosis and management.

Inadequate left internal mammary artery (LIMA) graft to the left anterior descending artery (LAD) was encountered in 10 of 3,076 patients between 1984 and July 1990. The mean number of bypass grafts was 2.9 per patient. All patients with inadequate LIMA grafts were stable preoperatively with normal to moderately reduced left ventricular function. No technical difficulties were encountered during surgery. All patients were weaned off cardiopulmonary bypass with minimal or no inotropic support. Each patient developed myocardial ischemia of the LAD territory and/or circulatory collapse or recurrent ventricular dysrhythmia during the first 24 h postoperatively. Six patients, who were immediately re-operated on and had an additional saphenous graft to the LAD, recovered with no infarction and good functional results. Four patients, who were medically treated, developed myocardial infarction. In cases of refractory circulatory collapse and/or ventricular dysrhythmia, inadequate LIMA flow should be suspected. We recommend urgent re-operation with additional saphenous vein graft to the LAD.

Aged↗
PubMed1992

Biocompatible circuits: an adjunct to non-cardiac extracorporeal cardiopulmonary support.

The utilization of cardiopulmonary bypass systems, for circulatory and/or pulmonary support of patients undergoing non-cardiac procedures, has been previously reported. There is, however, a sub-group of patients for whom total systemic anticoagulation for cardiopulmonary support is extremely undesirable or contraindicated altogether, due to the presenting pathology or procedure to be performed. Clinical and experimental reports have suggested that with the use of heparin-bonded bypass circuits, the amount of heparin required for anticoagulation of the patient may be substantially reduced, or eliminated, safely. This allows the resuscitation and/or support of patients in whom bypass would otherwise be contraindicated. We present our clinical experience with heparin-bonded, biocompatible circuits, for support of patients undergoing non-cardiac procedures. In each case, low-dose or no heparin was administered. The group includes patients with trauma related pulmonary insufficiency, pulmonary embolism, hypothermia, neurosurgery, aortic aneurysm, aortic transection, respiratory distress syndrome, pericardiectomy, and cardiogenic shock.

Adolescent↗
PubMed1992

Alternatives to randomization in surgical studies.

The purpose of randomization is to provide unbiased estimates of treatment effects and valid probability statements for hypothesis tests in comparative studies. Difficulties with randomized allocation of patients in surgical studies include: patient selection--due to protocol limitations, possible changes in referral patterns, the need for patient consent, and physician co-operation; disruption of the patient-physician relationship; static protocol not responsive to changes as surgical skill evolves and experience regarding patient selection is acquired; the larger number of patients required causes a longer study and more patients receiving what may be a worse therapy. Moreover, for evaluating a new heart valve, the primary purpose should be estimation rather than comparison with a current device. This can be accomplished faster, in a more generalizable way and with more concern for patient care by using non-randomized comparison groups.

Ethics, Medical↗
PubMed1991

Localization of brain activity during auditory verbal short-term memory derived from magnetic recordings.

We have studied magnetic and electrical fields of the brain in normal subjects during the performance of an auditory verbal short-term memory task. On each trial 3 digits, selected from the numbers 'one' through 'nine', were presented for memorization followed by a probe number which could or could not be a member of the preceding memory set. The subject pressed an appropriate response button and accuracy and reaction time were measured. Magnetic fields recorded from up to 63 sites over both hemispheres revealed a transient field at 110 ms to both the memory item and the probe consistent with a dipole source in Heschl's gyrus; a sustained magnetic field between 300 and 800 ms to just the memory items localized to the temporal lobe slightly deeper and posterior to Heschl's gyri; and a sustained magnetic field between 300 and 800 ms to just the probes localized bilaterally to the medio-basal temporal lobes. These results are related to clinical disorders of short-term memory in man.

Adult↗
PubMed1991

Identification of mitochondrial and non-mitochondrial glutaminase within select neurons and glia of rat forebrain by electron microscopic immunocytochemistry.

Antibodies against the mitochondrial enzyme glutaminase (EC 3.5.1.2), have been used in previous immunocytochemical studies to help identify glutamate-releasing neurons among all glutamate-containing neurons. The studies were based on the idea that glutaminase is enriched within the releasable "transmitter" pools of glutamate. However, evidence is also available to suggest that the enzyme does not occur exclusively within glutamate-releasing neurons. Thus we sought to determine whether glutaminase was immunocytochemically detectable within presynaptic terminals forming asymmetric (putatively excitatory) synapses or, alternatively, occurs in association with mitochondria throughout the cell. For this purpose, we examined the cellular and subcellular distribution of glutaminase- immunoreactivity in neocortical (visual and somatosensory) areas known to contain glutamatergic perikarya. This localization was compared with the distribution in striatal (caudate-putamen and nucleus accumbens) regions recognized to contain high densities of glutamatergic terminals but fewer, if any, glutamatergic perikarya. Glutaminase-immunoreactive perikarya were numerous within the infragranular laminae of neocortex (approximately 1 per 1,000 microns 2 tissue area) but sparse within the caudate-putamen nuclei and accumbens nuclei (less than 1 per 20,000 microns 2.). In addition, heterogeneous distribution of small (less than 1 microns) punctate immunoreactive structures was notable. Relatively high densities of these punctate structures occurred within the supragranular laminae of neocortex, dorsolateral quadrant of the caudate-putamen nuclei, and surrounding certain groups of myelinated fiber bundles throughout the striatum. Electron microscopy revealed diffusely distributed peroxidase immunoreactivity in a select population of dendritic spines, glial processes, and axons. Eight percent of all synapses within the supra-granular laminae were formed by terminals labeled for glutaminase. These principally formed asymmetric junctions on spiny processes. When tissue was incubated with the antibody in the presence of a permeabilizing agent, Photo-flo, high levels of glutaminase immunoreactivity was detectable by electron microscopy within select mitochondria of neocortical (4%) and striatal (8%) perikarya and dendrites, while the diffuse distribution of immunoreactivity within axons and glia was greatly diminished. The differential ultrastructural conditions provide direct demonstration that glutaminase in brain occurs in at least two forms discriminable by their diffuse distribution within non-mitochondrial cytoplasm versus discrete localization within mitochondria. The morphological characteristics of synapses formed by axons exhibiting diffuse distributions of glutaminase immunoreactivity are consistent with the idea that glutaminase-enriched terminals mediate excitatory chemical transmission via the release of glutamate. Because glia containing glutaminase occur juxtaposed to the asymmetric junctions, the glia may utilize neuronally released glutamate for energy metabolism.

Animals↗