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Biomedical subjects

J R Boston

Publications and source records attributed to J R Boston.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1984

Sensory evoked potentials: a system for clinical testing and patient monitoring.

There is increasing interest in the use of averaged sensory evoked potentials for diagnostic testing and patient monitoring. This testing technique offers an opportunity to obtain information on function in the central nervous system and can be used in uncooperative and comatose patients. However, in the clinical situation background noise is often high, due for example to posturing by the patient, and even with extensive signal averaging it can be difficult to determine whether a response is present. This paper describes a data acquisition technique we have implemented for patient testing in the intensive care unit and the operating room to facilitate analysis of the responses. The averaging system delivers the stimulus in the middle of the data window, providing a pre-stimulus control interval from which to estimate residual background noise in the average. In addition, two averages are formed simultaneously to determine reproducibility of the response. This technique has been modified to provide a method of continuous monitoring that allows rapid detection of large changes in the response plus automatic tracking of selected response peak parameters.

Data Collection↗
PubMed1982

Intraoperative monitoring of brain-stem auditory evoked potentials.

Brain-stem auditory evoked potentials (BAEP) were monitored during 545 neurosurgical operations in the cerebellopontine angle. The BAEP were irreversibly obliterated in five patients who required deliberate section of the auditory nerve. Technical difficulties interfered with monitoring in three cases, and three patients had deafness and absent BAEP preoperatively. Reversible alterations in BAEP were seen during 32 operations, with recovery after as long as 177 minutes of virtually complete obliteration. Changes in BAEP were associated with surgical retraction, operative manipulation, positioning of the head and neck for retromastoid craniectomy, and the combination of hypocarbia and moderate hypotension. In 19 cases, waveforms improved after specific interventions made by the surgeon or anesthesiologist because of deteriorating BAEP. In 13 other cases, BAEP recovered after maneuvers not specifically related to the electrophysiological monitoring, most often completion of operative manipulation. Whenever BAEP returned toward normal by the end of anesthesia, even after transient obliteration, hearing was preserved. Irreversible loss of BAEP occurred only when the auditory nerve was deliberately sacrificed. The authors conclude that monitoring of BAEP may help prevent injury to the auditory nerve and brain stem during operations in the cerebellopontine angle.

Adult↗
PubMed1980

Comparison of brain stem auditory evoked potentials for monaural and binaural stimuli.

This study examined the relation of brain stem auditory evoked potentials (BAEPs) for monaural and binaural click stimuli. Responses were recorded from normal subjects for 4 stimulus levels of 50, 70, 90 and 110 dB peSPL peak-to-peak, corresponding to monaural sensation levels of 7, 27, 47 and 67 dB SL. Wave amplitude and latency values were analyzed for the effects of the binaural stimulus condition. Responses to binaural stimuli were compared to the summed responses to monaural stimuli to estimate binaural interactions. The results show that responses to a binaural stimulus have significantly greater wave amplitudes than responses to a monaural stimulus. If a response to a binaural stimulus is compared to the sum of the responses to the corresponding monaural stimuli, however, there are no significant differences in wave V amplitudes. Latency values are equal for the two stimulus conditions. Calculations of a continuous wave form representing the difference (point-by-point) between the response to a binaural stimulus and the summed response to the two monaural stimuli shows that significant binaural interactions occur with a latency of 7-10 msec. Additional interactions occur with a latency of 12-16 msec. Although neural and sonomotor sources may contribute to these short latency binaural interactions, acoustic cross-talk appears to account for a significant portion of the observed interaction.

Auditory Perception↗
PubMed1980

Effects of analog and digital filtering on brain stem auditory evoked potentials.

Most investigators of the brains stem auditory evoked potentials utilize analog filters to reduce the noise content of the averaged signals, but different investigators use different filter bandwidths. Data presented in this note compare the effects of different upper and lower cutoff frequencies for both analog and zero-phase shift digital filters. Effects on response wave form and on measured values of amplitude and latency of wave V are considered. It is concluded that, for given cutoff frequencies, analog filtering causes more distortion of the response than digital filtering, due primarily to phase distortion introduced by the analog filter. It is likely that differences in filter cutoff frequencies, especially lower cutoff frequencies, are a significant source of variability in results reported by different investigators.

Auditory Perception↗
PubMed1980

A model of lateral line microphonic response to high-level stimuli.

The electrical potential recorded from the lateral line canal organs of fish in response to a sinusoidal vibratory stimulus consists of a microphonic component with frequency twice that of the stimulus plus a dc shift. This paper describes the behavior of both components as functions of stimulus frequency (from 100 to 400 Hz) and amplitude. The microphonic decreases with frequency, while the dc shift increases, and the two components have different input-output functions. An analytical model of hair cell electrical properties with an asymmetric saturating nonlinear conductance is presented that describes the behavior of both the microphonic and the dc shift.

Acoustic Stimulation↗
PubMedDate not supplied

Dynamic systemic vascular resistance in a sheep supported with a Nimbus AxiPump.

Changes in systemic vascular resistance (SVR) in response to diminished pulse perfusion were analyzed over a dynamic range of flow conditions. An axial flow LVAD (Nimbus AxiPump, Rancho Cordova, CA) was implanted in a sheep for 28 days, during which time SVR was determined over several conditions of posture and excitability. Total arterial resistance (TR) was calculated dynamically as an index of SVR by analysis of pump flow in diastole, and systemic pressure estimated from the characteristic pressure-flow-speed relation of the AxiPump. TR was evaluated over a range of flow rates, including maximum flow--for which the pressures and flows were essentially nonpulsatile. Throughout the course of support, and independent of pulsatility, TR dropped when the sheep stood and was significantly lower than that in the sitting position (P < 0.01). Response to excitement followed the same trend: TR was significantly higher during agitation than during normal temper (P < 0.01). In spite of changes in pulse pressure and flow rate, SVR changes occurred according to expected physiologic responses for pulsatile perfusion. Because pump flow and pressure are sensitive to afterload, the results of these studies suggest that pump speed control must compensate for changes in SVR to maintain acceptable perfusion.

Animals↗
PubMedDate not supplied

Pressure-volume relationship of a pulsatile blood pump for ventricular assist device development.

A mathematical model describing the pressure-volume relationship of the Novacor left ventricular assist system (LVAS) was developed. The model consists of lumped resistance, capacitance, and inductance elements with one time varying capacitor to estimate the cyclic pressure generation of the pump using pump volume measurement. The ejection and filling portions of the pump cycle were modeled with two separate functions. The corresponding model parameters were estimated by least squares fit to experimental data obtained in the laboratory. Pressure and volume waveforms obtained from the model were compared with data obtained from laboratory tests and from patients. It performed well in simulating pump operation throughout the entire cycle. This model can be used for the evaluation of LVAS performance, for on-line estimation of an LVAS patient's cardiovascular parameters, for pump controller development, and as a tool for engineer training.

Heart-Assist Devices↗