Search PubMed⌕ Search

Biomedical subjects

J R Boston

Publications and source records attributed to J R Boston.

13 recordsLinked to original sources
PubMed1992

Correlations of neuroanatomical measures to auditory brain stem response latencies.

Magnetic resonance imaging (MRI) was used to obtain measures presumed to scale the dimensions of the lower auditory pathway in humans for the purpose of further defining the relationship between length of the auditory pathway and auditory brain stem response (ABR) latencies. Specifically, measurements of soft tissue structures, that is, the eighth nerve and brain stem, were made for comparison with skull dimensions and ABR latencies. It was hypothesized that the brain stem dimensions covary significantly with skull dimensions and that the ABR parameters covary with both skull and brain stem dimensions. In general, only weak correlations were obtained with coefficients failing to reach statistical significance for most comparisons. These findings suggest that variance in ABR latencies cannot be attributed completely to variance in brain stem dimensions and raise suspicion that skull dimensions do not directly reflect brain stem dimensions.

Acoustic Impedance Tests↗
PubMed1992

Effect of 33% xenon inhalation on whole-brain blood flow and metabolism in awake and fentanyl-anesthetized monkeys.

BACKGROUND AND PURPOSE: Despite the documented diagnostic value of local cerebral blood flow maps by xenon-enhanced computed tomography, reports of cerebral blood flow activation by inhaled 33% Xe raised concerns about the method's safety and accuracy. We evaluated the effect of 33% Xe inhalation on cerebral blood flow and cerebral metabolic rates for oxygen and glucose in four awake and six fentanyl-anesthetized rhesus monkeys. METHODS: Platinum microelectrodes and catheters in the torcular Herophili were used to measure cerebral blood flow by hydrogen clearance, and oxygen and glucose concentrations. Cerebral variables were measured after 5 and 35 minutes of exposure to room air followed randomly by 67% O2 in 33% N2 or Xe. Five- and 35-minute measurements were combined because the duration of exposure had no effect. RESULTS: In awake monkeys, 33% Xe compared with 33% N2 reduced (p less than 0.05) cerebral blood flow from 75 +/- 12 to 66 +/- 9 (mean +/- SD) ml.100 g-1.min-1 and oxygen consumption from 6.1 +/- 0.7 to 5.1 +/- 0.6 ml.100 g-1.min-1. In fentanyl-anesthetized monkeys, cerebral variables during 33% N2 versus 33% Xe were cerebral blood flow, 84 +/- 26 versus 79 +/- 23 ml.100 g-1.min-1; oxygen consumption, 5.0 +/- 0.7 versus 4.9 +/- 0.5 ml.100 g-1.min-1; and glucose consumption, 8.4 +/- 1.9 versus 7.9 +/- 2.0 mg.100 g-1.min-1. CONCLUSIONS: In awake monkeys, 33% Xe reduced rather than activated cerebral blood flow and oxygen consumption by 12% and 16%, respectively; it had no effect in fentanyl-anesthetized monkeys.

Administration, Inhalation↗
PubMed1991

Safety and efficacy of alfentanil and halothane in paediatric surgical patients.

Alfentanil, a congener of the opioid fentanyl, possesses properties that make it an attractive choice for use during short operative procedures. Since the pharmacodynamic aspects of alfentanil have not been well documented in children, this study was undertaken to evaluate the safety, efficacy, and dose requirements of alfentanil when used with nitrous oxide or halothane in paediatric patients. Eighty unpremedicated patients, ASA physical status I or II and aged 2-12 yr were studied. Patients were randomly assigned to one of four groups. After induction of anaesthesia with nitrous oxide, oxygen, and halothane, the groups were treated as follows. In Group 1 (n = 19), after halothane was discontinued, alfentanil 50 micrograms.kg-1 was infused over 30 sec. In Group 2 (n = 20), the end-tidal halothan was maintained at 0.5% and alfentanil 25 micrograms.kg-1 was infused. In Group 3 (n = 20), the end-tidal halothane concentration was maintained at 1% and alfentanil 12.5 micrograms.kg-1 was infused. In Group 4 (n = 21), the end-tidal halothane concentration was maintained at 1.5% and no alfentanil was administered. Patients in Groups 1, 2, and 3 received bolus doses of alfentanil 12.5 micrograms.kg-1 as needed to maintain haemodynamic stability. After alfentanil administration, there were transient decreases in systolic blood pressure in Groups 1 and 2, and in heart rate in Group 2. With surgical stimulation, haemodynamic stability was well maintained except in patients in Group 1, who had an increase in systolic blood pressure. Children Group 1 were alert sooner and their tracheas were extubated earlier than those in Groups 2, 3, and 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Alfentanil↗
PubMed1991

Renal O2 consumption during progressive hemorrhage.

Most mammalian tissues regulate O2 utilization such that O2 consumption (VO2) is relatively constant at O2 delivery (DO2) higher than a critical value (DO2c). We studied the relationship between VO2 and DO2 of kidney and whole body during graded progressive exsanguination. The relationship between whole body VO2 and DO2 was biphasic, and whole body VO2 decreased by 5.6 +/- 14.4% (P = NS) from the initial value to the value nearest whole body DO2c. Kidney DO2 decreased in direct proportion to whole body DO2 such that the average R2 value describing the linear regression of kidney DO2 vs. whole body DO2 was 0.94 +/- 0.02. The relationship between kidney, like whole body, VO2 and DO2 appeared biphasic; however, kidney VO2 decreased by 63.3 +/- 10.4% (P less than 0.0001) from the initial value to the value nearest kidney DO2c. Renal O2 extraction ratio was relatively constant over a wide range of kidney DO2, whereas whole body O2 extraction ratio increased progressively at all whole body DO2 values as whole body DO2 decreased. However, final values of O2 extraction ratio were indistinguishable for whole body (0.86 +/- 0.1) and kidney (0.86 +/- 0.06) (P = NS). We conclude that the pattern of kidney and whole body VO2 response to decreasing DO2 differs during hemorrhage, particularly in the range of DO2 normally associated with tissue wellness.

Animals↗
PubMed1990

Correlation study of two-channel recordings of the brain stem auditory evoked potential.

Two-channel recordings of the brain stem auditory evoked potential (BAEP), for example, forehead to ipsilateral mastoid and forehead to contralateral mastoid, presumably provide "views" of the generators from different, nearly orthogonal, directions. The two channels thus are expected to register somewhat different waveforms, as revealed by past research. Still, the absolute latencies of the peaks are expected to be strongly correlated between channels. To test this notion, correlation analyses were made of the latencies of positive and negative peaks of normal-appearing BAEPs. The results demonstrated the expected high correlations for brain stem components but less tight coupling between peaks of waves of more peripheral origins. The possible influence of residual noise also was considered. Implications of the findings for clinical and multichannel recording applications are discussed.

Adult↗
PubMed1990

Rate of change of somatosensory evoked potentials during isoflurane anesthesia in newborn piglets.

Most studies of the effects of inhalation anesthetics on somatosensory evoked potentials (SSEPs) have examined SSEP at single times after initiation of an anesthetic. This study describes SSEP changes as functions of time of exposure to isoflurane. Both transient and sustained SSEP changes were observed. Nonlinear regression was used to fit exponential terms to the trend curves for end-tidal anesthetic concentration and SSEP peak latency. End-tidal concentrations could be well described by two exponential terms, one with a long and one with a short time constant. Isoflurane at 1% inspired concentration produced a sustained SSEP latency change that could be fit by a single exponential term; the time constant was essentially identical to the long time constant of end-tidal concentration. The long time constants ranged from 7 to 33 min. At 0.5% isoflurane, SSEP changes were often small or not sustained, and the changes could not always be well described by an exponential curve. These data suggest that the time-course of anesthetic effects on SSEPs may be prolonged and complex, and the possibility of changes over time should be considered both in experimental studies and during intra-operative monitoring.

Anesthesia, Inhalation↗
PubMed1989

Automated interpretation of brainstem auditory evoked potentials: a prototype system.

This paper describes a preliminary version of an expert decision support system for interpretation of brainstem auditory evoked potentials. The design combines an analytical signal processing module with a rule-based module that incorporates the kinds of heuristic criteria used by human interpreters. The prototype system determines whether a sensory response is present in the waveform; if so, it identifies peak V, the most prominent peak. A level of confidence is associated with the identification. Results of applying the system to a test set of 20 waveforms, including some waveforms from comatose patients that showed no sensory response, are described. The system performed well when a response was present, but it was not as effective in interpreting waveforms with no response present.

Decision Support Techniques↗
PubMed1985

Automated monitoring of brainstem auditory evoked potentials in the operating room.

We monitored brainstem auditory evoked potentials in 112 patients undergoing retromastoid craniectomies for microvascular decompression. To provide information on latency changes as quickly as possible, we implemented a block averaging technique of data acquisition with automatic tracking of wave V latency, which is the most clinically useful information. A change in peak latency probably due to surgical manipulation was observed in 63% of the patients, and the change could be at least partially corrected by modification of surgical technique. Twenty percent of the 89 patients who underwent preoperative and postoperative audiometric testing showed a postoperative hearing decrement. Some patients had large intraoperative increases in latency without suffering postoperative hearing deficits, and some incurred hearing deficits even though the intraoperative latency increases were relatively small. However, patients whose brainstem auditory evoked potentials were lost during surgery, even temporarily, were likely to have postoperative hearing decrements. Patients who had deficits tended to have slightly greater increases in latency than patients without deficits, but the difference in the mean increases of the two groups was not statistically significant. Most of the deficits were small, and all resolved over time.

Computers↗
PubMed1985

An algorithm for monitoring sensory evoked potentials.

Brainstem auditory evoked potentials (BAEP) testing is used extensively to monitor auditory function during retromastoid craniectomies for microvascular decompression. The latency between BAEP peaks can change notably over a period of several seconds or minutes, a much shorter time than is necessary to acquire and analyze a conventionally averaged BAEP. This article describes a continuous monitoring algorithm that detects both large, rapid changes in waveform and slow changes in latency. A prestimulus control interval in the response data window provides a mechanism for evaluating the reliability of the response. The algorithm tracks the latency and amplitude of a selected peak, using several checks to avoid detecting the wrong peak. The tracking mechanism is simple yet effective and eliminates the need to suspend averaging for manual measurement of peak parameters. The peak latency and amplitude are displayed immediately. The algorithm indicates gross changes in the BAEP within 30 seconds and provides reliable data on latency trends. By increasing the frequency of acquiring new waveforms, the algorithm provides more immediate information for the surgeon.

Brain Stem↗
PubMed1985

Brainstem auditory-evoked potentials.

Brainstem auditory-evoked potentials (BAEPs) are generated in the ear and brainstem nuclei of the ascending auditory pathways following a transient acoustic stimulus. Because they can be recorded noninvasively in humans, BAEPs have a number of clinical and research applications. This paper reviews the properties of BAEPs, with particular emphasis on those characteristics that are relevant to the acquisition and analysis of the responses. Theories of the neural origins of the responses are reviewed. The dependence of the responses on the stimulus waveform and the problem of stimulus artifact are considered. Then, origins of the background noise are discussed, and the use of linear filtering and methods of artifact detection to improve the signal-to-noise ratio are reviewed. Finally, the problem of identifying parameters to quantify the responses is considered. The definition of response components in terms of response peaks and data on intra- and intersubject variability are reviewed, and the use of algorithms to measure parameters is discussed.

Acoustic Stimulation↗