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Biomedical subjects

R D Traub

Publications and source records attributed to R D Traub.

At least 37 records · Page 2Linked to original sources
PubMed2000

Neuronal fast oscillations as a target site for psychoactive drugs.

Neuronal oscillations within the electroencephalogram beta and gamma bands (15-80 Hz) are associated with intense mental activity and cognitive function in general. Specifically, recent advances have implicated gamma oscillations in the processing of sensory stimuli and demonstrated that synchronous gamma oscillations, appearing concurrently in spatially separate brain regions, can induce beta activity. beta activity generated in this manner represents established synchronous communication between brain regions and is thought to represent a neuronal network correlate of the "binding phenomenon" in cognitive theory. This review will outline the mechanisms of generation of these oscillations at the cellular and network level, and will highlight the effects of drugs that may modify these mechanisms. Possible modification of fast oscillations by disease processes and clinical intervention are discussed.

Animals↗
PubMed2000

A model of gamma-frequency network oscillations induced in the rat CA3 region by carbachol in vitro.

Carbachol (> 20 microM) and kainate (100 nM) induce, in the in vitro CA3 region, synchronized neuronal population oscillations at approximately 40 Hz having distinctive features: (i) the oscillations persist for hours; (ii) interneurons in kainate fire at 5-20 Hz and their firing is tightly locked to field potential maxima (recorded in s. radiatum); (iii) in contrast, pyramidal cells, in both carbachol and kainate, fire at frequencies as low as 2 Hz, and their firing is less tightly locked to field potentials; (iv) the oscillations require GABAA receptors, AMPA receptors and gap junctions. Using a network of 3072 pyramidal cells and 384 interneurons (each multicompartmental and containing a segment of unmyelinated axon), we employed computer simulations to examine conditions under which network oscillations might occur with the experimentally determined properties. We found that such network oscillations could be generated, robustly, when gap junctions were located between pyramidal cell axons, as suggested to occur based on studies of spontaneous high-frequency (> 100 Hz) network oscillations in the in vitro hippocampus. In the model, pyramidal cell somatic firing was not essential for the oscillations. Critical components of the model are (i) the plexus of pyramidal cell axons, randomly and sparsely interconnected by gap junctions; (ii) glutamate synapses onto interneurons; (iii) synaptic inhibition between interneurons and onto pyramidal cell axons and somata; (iv) a sufficiently high rate of spontaneous action potentials generated in pyramidal cell axons. This model explains the dependence of network oscillations on GABA(A) and AMPA receptors, as well as on gap junctions. Besides the existence of axon-axon gap junctions, the model predicts that many of the pyramidal cell action potentials, during sustained gamma oscillations, are initiated in axons.

Action Potentials↗
PubMed2000

Sequencing cases in the operating room: predicting whether one surgical case will last longer than another.

UNLABELLED: A microscope will be used for the first case of the day in operating room (OR) 1 and then may be used in the second case of the day by a different surgeon in a different OR, OR 2. Provided that the probability is reasonably high that the first case of the day in OR 2 will last longer than the first case in OR 1, the OR manager can be confident in scheduling the microscope to be used by both surgeons on the same day. The OR manager can use statistical decision theory to sequence cases to decrease the impact of limitations in equipment or personnel on case scheduling. This increases utilization of both the capital equipment and OR time. In this study, we derived equations that can be programmed into a surgical services information system to reliably estimate the probability that one case will have a longer duration than another. We confirmed the accuracy of our method by using actual case duration data. IMPLICATIONS: Our statistical method uses historical case duration data from an operating room information system to estimate the actual probability to within 1.5% that the second case of a pair will last longer than the first case of a pair.

Appointments and Schedules↗
PubMed2000

The lack of systematic month-to-month variation over one-year periods in ambulatory surgery caseload -application to anesthesia staffing.

Anesthesia groups forecast future workload so that staffing and future hiring can be adjusted. Statistical methods have been developed to estimate the number of anesthesia providers needed to minimize labor costs during regularly scheduled hours, second-shifts, and weekends. These methods are simple, in that they assume that, on this medium-range (11-mo) basis, workload varies irregularly around a mean workload. To test whether this assumption is likely to hold for many anesthesia groups nationwide, raw data from the 1994 to 1996 National Survey of Ambulatory Surgery were reanalyzed. To assure that month-to-month systematic variation in workload (e.g., seasonal variation) could be detected if it were present, the average number of myringotomy tubes inserted each day in ambulatory surgery centers of the United States was also examined. The average number of ambulatory surgery cases performed with an anesthesia provider each day in the United States per 10,000 population was found to have not varied systematically month to month on a medium-range (11-mo) basis. In contrast, the average number of tubes inserted each day varied systematically among months for all 26 of the overlapping 11-mo periods in the 36 mo of the survey. These findings suggest that the relatively simple statistical methods that are available to estimate future anesthesia workload will work for many anesthesia groups.

Ambulatory Surgical Procedures↗
PubMed2000

Statistical method for predicting when patients should be ready on the day of surgery.

BACKGROUND: Previously, mathematical theory was developed for determining when a patient should be ready for surgery on the day of surgery. To apply this theory, a method is needed to predict the earliest start time of the case. METHODS: The authors calculated a time estimate such that the probability is 0.05 that the preceding case in the patient's operating room (OR) will be finished before the patient is ready for surgery. This implies there will be a 5% risk of OR personnel being idle and waiting for the patient. This 0. 05 value was chosen by considering the relative cost valuation of an average patient's time to that of an average surgical team based on national salary data. Case duration data from a surgical services information system were used to test different statistical methods to estimate earliest start times. RESULTS: Simulations found that 0.05 prediction bounds, calculated assuming case durations followed log-normal distributions, achieved actual risks for the OR staff to wait for patients of 0.050 to 0.053 (SEM = 0.001). Nonparametric prediction bounds performed no better than the parametric method. Having patients ready a fixed number of hours before the scheduled starts of their operations is not reliable. If the preceding case in an OR had been underway for 0.5 to 1.5 h, the parametric 0.05 prediction bounds for the time remaining achieved actual risks for OR staff waiting of 0.055 to 0.058 (SEM = 0.001). CONCLUSION: The earliest start time of a case can be estimated using the 0.05 prediction bound for the duration of the preceding case. The authors show 0.05 prediction bounds can be estimated accurately assuming that case durations follow log-normal distributions.

Appointments and Schedules↗
PubMed2000

Ripple (approximately 200-Hz) oscillations in temporal structures.

Spontaneous network oscillations near 200 Hz have been described in the hippocampus and parahippocampal regions of rodents and humans. During the last decade the characteristics and the mechanisms behind these field "ripples" have been studied extensively, mainly in rodents. They occur during rest or slow-wave sleep and provide a very fast, short-lasting (approximately 50 msec) rhythmic and synchronous activation of specific projection cells and interneurons. Ripples are frequently triggered by a massive synaptic activation from the hippocampal CA3 subfield, which is called a sharp wave. Recent evidence suggests that ripples have a specific task in memory processing-namely, that they convey information stored in the hippocampus to the cortex where it can be preserved permanently. Network mechanisms involved in ripple oscillations may be relevant for understanding pathologic synchronization processes in temporal lobe epilepsy.

Electroencephalography↗
PubMed2000

Statistical method using operating room information system data to determine anesthetist weekend call requirements.

We present a statistical method that uses data from surgical services information systems to determine the minimum number of anesthetists to be scheduled for weekend call in an operating room suite. The staffing coverage is predicted that provides for sufficient anesthetists to cover each hour of a 24-hour weekend period, while satisfying a specified risk for being understaffed. The statistical method incorporates shifts of varying start times and durations, as well as historical weekend operating room caseload data. By using this method to schedule weekend staff, an anesthesia group can assure as few anesthetists are on call as possible, and for as few hours as possible, while maintaining the level of risk of understaffing that the anesthesia group is willing to accept. An anesthesia group also can use the method to calculate its risk of being understaffed in the surgical suite based on its existing weekend staffing plan.

Data Interpretation, Statistical↗
PubMed2000

Determining staffing requirements for a second shift of anesthetists by graphical analysis of data from operating room information systems.

Some operating room (OR) managers face the dilemma whereby all cases in a surgical suite are not completed during a regularly scheduled (e.g., 8-hour) day. If the anesthesia group at the surgical suite plans for its employed anesthetists to work a fixed number of hours each day, then more than 1 shift of anesthetists may be needed to care for the patients in the ORs. We developed a graphical statistical method that anesthetists and anesthesiologists can use to determine how many anesthesia providers are required on the second shift to minimize labor costs. The method uses data from surgical services information systems or hospital information systems to compensate for seasonality or seasonal variation in the number of ORs running at different times of the day. We also consider application of our method to scheduling surgical nurses with multiple overlapping shifts throughout the day.

Computer Graphics↗
PubMed1999

On the mechanism of the gamma --> beta frequency shift in neuronal oscillations induced in rat hippocampal slices by tetanic stimulation.

Tetanic stimulation of the CA1 region of rat hippocampal slices can induce gamma frequency population oscillations (30-100 Hz) after a latency of 50-150 msec that are synchronized to within 1-2 msec when simultaneous stimuli are delivered to two sites 2 mm or more apart. When tetanic stimuli, twice-threshold for eliciting gamma oscillations, are used, new phenomena occur. (1) After a period of gamma, there is a switch to beta frequencies (10-25 Hz); (2) during the switch, pyramidal cell spike afterhyperpolarizations (AHPs) increase and rhythmic EPSPs occur in pyramidal cells; and (3) after an episode of single-site, twice-threshold-induced gamma/beta oscillations, simultaneous two-site threshold stimuli induce gamma oscillations that are locally synchronized, but no longer are capable of long-range synchrony. We studied the cellular mechanisms of the gamma/beta switch with electrophysiological techniques and computer simulations. Our model predicts that the observed increases in both pyramidal cell AHPs and in pyramidal/pyramidal cell EPSPs are necessary and sufficient for the beta switch to occur. Firing patterns generated by the model, both for pyramidal cells and for interneurons, resemble experimental records. A one-site twice-threshold stimulus might lead to an inability of the two sites to synchronize at gamma frequencies, after subsequent two-site stimulation, via this mechanism. If depression is induced at synapses coupling pyramidal cells at one site to interneurons at the other site, then two-site stimulation cannot produce interneuron doublets; hence, as shown previously, the two sites will be unable to synchronize. This mechanism works in simulations, and we provide experimental evidence that synaptic depression and loss of doublets occur after a sufficiently strong local tetanus to one site. We suggest that long-range excitatory connections onto interneurons determine whether different pyramidal cell "assemblies" can synchronize at gamma frequencies, whereas excitatory connections onto pyramidal cells determine whether such assemblies can synchronize at beta frequencies.

Animals↗
PubMed1999

High-frequency population oscillations are predicted to occur in hippocampal pyramidal neuronal networks interconnected by axoaxonal gap junctions.

In hippocampal slices, high-frequency (125-333 Hz) synchronized oscillations have been shown to occur amongst populations of pyramidal neurons, in a manner that is independent of chemical synaptic transmission, but which is dependent upon gap junctions. At the intracellular level, high-frequency oscillations are associated with full-sized action potentials and with fast prepotentials. Using simulations of two pyramidal neurons, we previously argued that the submillisecond synchrony, and the rapid time-course of fast prepotentials, could be explained, in principle, if the requisite gap junctions were located between pyramidal cell axons. Here, we use network simulations (3072 pyramidal cells) to explore further the hypothesis that gap junctions occur between axons and could explain high-frequency oscillations. We show that, in randomly connected networks with an average of two gap junctions per cell, or less, synchronized network bursts can arise without chemical synapses, with frequencies in the experimentally observed range (spectral peaks 125-182 Hz). These bursts are associated with fast prepotentials (or partial spikes and spikelets) as observed in physiological recordings. The critical assumptions we must make for the oscillations to occur are: (i) there is a background of ectopic axonal spikes, which can occur at low frequency (one event per 25 s per axon); (ii) the gap junction resistance is small enough that a spike in one axon can induce a spike in the coupled axon at short latency (in the model, a resistance of 273 M omega works, with an associated latency of 0.25 ms). We predict that axoaxonal gap junctions, in combination with recurrent excitatory synapses, can induce the occurrence of high-frequency population spikes superimposed on epileptiform field potentials.

Action Potentials↗
PubMed1999

Optimal sequencing of urgent surgical cases. Scheduling cases using operating room information systems.

Optimal sequencing of urgent cases (i.e., selecting which urgent case should be performed first and which second) may enhance patient safety, increase patient satisfaction with timeliness of surgery, and minimize surgeons' complaints. Before determining the optimal sequence of urgent cases, an operating room (OR) suite must identify the primary scheduling objective to be satisfied when prioritizing pending urgent cases. These scheduling objectives may include: 1) perform the cases in the sequence that minimizes the average length of time each surgeon and patient waits; 2) perform the cases in the order that they were submitted; or 3) perform the cases based on medical priority, as prioritized by an OR director, or surgeons discussing the cases among themselves. We provide mathematical structure which can be used to program a computerized surgical services information system to assist in optimizing the sequence of urgent cases. We use an example to illustrate that the optimal sequence varies depending on the scheduling objective chosen.

Algorithms↗
PubMed1999

Comparison of statistical methods to predict the time to complete a series of surgical cases.

We present a statistical model for predicting the time to complete a series of successive, elective surgical cases. The use of sample means of case times and turnover times when scheduling cases does not minimize the operating room labor costs associated with errors in predicting times to complete series of cases. The problem of minimizing associated labor costs (both under and over utilization) can be converted to the problem of least absolute deviation regression. The dependent variables are the times to complete series of cases. The independent variables are the numbers of cases in each series that are in various categories (i.e., combinations of scheduled procedures and surgeons). Although the computational method is preferred on theoretical grounds to that involving sample means, application of both methods shows that the more practical method is to use the sample means of previous case times and turnovers.

Elective Surgical Procedures↗
PubMed1999

Anaesthetic/amnesic agents disrupt beta frequency oscillations associated with potentiation of excitatory synaptic potentials in the rat hippocampal slice.

1. Anaesthetic agents produce disruption in cognitive function typified by reductions in sensory perception and memory formation. Oscillations within the EEG gamma and beta bands have been linked to sensory perception and memory and have been shown to be modified by anaesthetic agents. 2. Synchronous gamma oscillations generated by brief tetanic stimulation in two regions of hippocampal area CA1 in slices in vitro were seen to potentiate excitatory synaptic communication between the areas. This synaptic potentiation, was seen to contribute to a transition from gamma frequency (30 - 70 Hz) to beta frequency (12 - 30 Hz) oscillations. 3. Four drugs having anaesthetic/hypnotic and amnesic properties were tested on this synchronous gamma-induced beta oscillation. Thiopental 10 - 200 microM, Diazepam 0.05 - 1.0 microM, Morphine 10 - 200 microM, and Ketamine 10 - 200 microM were all added to the bathing medium. Each drug markedly disrupted the formation of beta oscillations in a manner consistent with their primary modes of action. Thiopental and morphine disrupted synchrony of gamma oscillations and prevented potentiation of recurrent excitatory potentials measured in stratum oriens (fEPSPs). Neither diazepam, nor ketamine produced such marked changes in synchrony at gamma frequencies or reduction in potentiation of fEPSPs. However, each disrupted expression of subsequent beta oscillation via changes in the magnitude of inhibitory network gamma oscillations and the duration and magnitude of tetanus-induced depolarization respectively. 4. The degree of disruption of fEPSP potentiation correlated quantitatively with the degree of disruption in synchrony between sites during gamma oscillations. The data indicate that synchronous gamma-induced beta oscillations represent a mode of expression of excitatory synaptic potentiation in the hippocampus, and that anaesthetic/amnesic agents can disrupt this process markedly.

Anesthetics↗
PubMed1999

An operating room scheduling strategy to maximize the use of operating room block time: computer simulation of patient scheduling and survey of patients' preferences for surgical waiting time.

UNLABELLED: Determining the appropriate amount of block time to allocate to surgeons and selecting the days on which to schedule elective cases can maximize operating room (OR) use. We used computer simulation to model OR scheduling. Inputs in the computer model included different methods to determine when a patient will have surgery (on-line bin-packing algorithms), case durations, lengths of time patients wait for surgery (2 wk is the median longest length of time that the outpatients [n = 367] surveyed considered acceptable), hours of block time each day, and number of blocks each week. For block time to be allocated to maximize OR utilization, two parameters must be specified: the method used to decide on what day a patient will have surgery and the average length of time patients wait to have surgery. OR utilization depends greatly on, and increases as, the average length of time patients wait for surgery increases. IMPLICATIONS: Operating room utilization can be maximized by allocating block time for the elective cases based on expected total hours of elective cases, scheduling patients into the first available date provided open block time is available within 4 wk, and otherwise scheduling patients in "overflow" time outside of the block time.

Anesthesia↗
PubMed1999

Which algorithm for scheduling add-on elective cases maximizes operating room utilization? Use of bin packing algorithms and fuzzy constraints in operating room management.

BACKGROUND: The algorithm to schedule add-on elective cases that maximizes operating room (OR) suite utilization is unknown. The goal of this study was to use computer simulation to evaluate 10 scheduling algorithms described in the management sciences literature to determine their relative performance at scheduling as many hours of add-on elective cases as possible into open OR time. METHODS: From a surgical services information system for two separate surgical suites, the authors collected these data: (1) hours of open OR time available for add-on cases in each OR each day and (2) duration of each add-on case. These empirical data were used in computer simulations of case scheduling to compare algorithms appropriate for "variable-sized bin packing with bounded space." "Variable size" refers to differing amounts of open time in each "bin," or OR. The end point of the simulations was OR utilization (time an OR was used divided by the time the OR was available). RESULTS: Each day there were 0.24 +/- 0.11 and 0.28 +/- 0.23 simulated cases (mean +/- SD) scheduled to each OR in each of the two surgical suites. The algorithm that maximized OR utilization, Best Fit Descending with fuzzy constraints, achieved OR utilizations 4% larger than the algorithm with poorest performance. CONCLUSIONS: We identified the algorithm for scheduling add-on elective cases that maximizes OR utilization for surgical suites that usually have zero or one add-on elective case in each OR. The ease of implementation of the algorithm, either manually or in an OR information system, needs to be studied.

Algorithms↗
PubMed1999

Forecasting surgical groups' total hours of elective cases for allocation of block time: application of time series analysis to operating room management.

BACKGROUND: Allocation of the correct amount of operating room (OR) "block time" can provide surgeons with access to sufficient OR time to complete their elective cases while optimally matching staffing with the elective case workload (to maximize labor productivity). To evaluate how to predict accurately total hours of elective cases performed by a surgical group using data from surgical services information systems, the authors addressed the following questions: (1) How many previous 4-week periods of data should be used to minimize error in forecasting a surgical group's total hours of elective cases? (2) Using the number of 4-week periods from question #1, can we detect trends or correlations between successive periods that could be used to improve forecasting accuracy? (3) How can results from questions #1 and #2 be used to calculate an upper prediction bound (upper limit) for the total hours of elective cases that will be completed in a future period? Prediction bounds can be used to budget staffing accurately. METHODS: Time series analysis was performed on total hours of elective cases over 39 consecutive 4-week periods from 17 surgical groups. RESULTS: The average of 12 consecutive periods' total hours of elective cases had an appropriate error profile. The observations within each series of 12 consecutive 4-week periods followed a normal distribution, with each observation of total hours of elective cases not correlated with the subsequent observation. CONCLUSIONS: The average of the most recent 12 4-week periods can be used to predict surgical groups' future use of block time.

Algorithms↗
PubMed1999

Functionally relevant and functionally disruptive (epileptic) synchronized oscillations in brain slices.

Focal seizurelike events can be induced in experimental preparations by means of a number of distinct manipulations that differ in synaptic mechanisms. Nevertheless, the form of the seizurelike events can be explained with common principles, including long-lasting excitation of pyramidal cell dendrites and recurrent excitation between pyramidal cells that provides synchronization. One means of induction of seizurelike events, tetanic stimulation, induces a more physiologic type of activity before seizures are elicited, that is, gamma-frequency (> 20 Hz) oscillations. Such oscillations, called 40-Hz oscillations, are believed to be important for cognition in vivo. Experimental gamma oscillations depend critically on synaptic inhibition between interneurons, from interneurons to pyramidal cells, and on a tonic drive to pyramidal cells and interneurons by metabotropic glutamate receptors. The function of gamma oscillations appears to be imposition of a precise temporal structure on the firing patterns of pyramidal cells while still allowing the pyramidal cells to influence each other and be influenced by afferents selectively. We suggest that a relative loss of synaptic inhibition, occurring by any of a number of mechanisms, prevents the occurrence of gamma activity, allows recurrent pyramidal cell-pyramidal cell excitation to predominate, and thereby allows neuronal networks to generate functionally disruptive seizures.

Animals↗