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PubMed2004

Minimal olfactory perception during sleep: why odor alarms will not work for humans.

STUDY OBJECTIVES: To examine olfactory arousal threshold during sleep in comparison to an auditory tone. DESIGN: On night 1, participants rated odor intensity when awake and experienced olfactory stimuli during stage 1 sleep. Night 2 involved stage 2, stage 4, and rapid-eye-movement (REM) sleep trials using the "staircase" threshold-detection method. Electroencephalogram, electrooculogram, electromyogram, electrocardiogram, and respiration were recorded along with behavioral response. An 800-Hz tone was given on trials when odors failed to arouse. SETTING: Participants slept in individual rooms. Stimulus-delivery systems were operated from a separate room, where an experimenter observed physiologic recordings and behavioral responses. PARTICIPANTS: Three healthy men and 3 women aged 20 to 25 years (mean, 22 years). INTERVENTIONS: Two odorants, peppermint and pyridine, at 4 concentrations were presented through nasal cannulas using an air-dilution olfactometer. Tones were played over a speaker. MEASUREMENTS: Behavioral (button press and oral) responses, electroencephalographic activation, and changes in breathing and heart rate were assessed. RESULTS: Participants responded to odors on 92% of stage 1 sleep trials. Peppermint was ineffective in stages 2, 4, and REM sleep. Pyridine produced behavioral threshold on 45% of stage 2 trials, none in stage 4, and one third of REM sleep trials. Tones were effective on at least 75% of trials. Heart rate increased significantly only following behavioral responses to odors or tones across sleep stages. CONCLUSIONS: The data indicate that human olfaction is not reliably capable of alerting a sleeper.

Adult↗
PubMed1989

Alarms and their limits in monitoring.

The need to incorporate alarms in monitoring systems is related to the growing complexity of monitoring and the large number of variables. For sophisticated alarms, information about the inputs to the patient is of importance; for example, clinical interventions such as drug administration and ventilation readjustment need to be known to the monitoring system. Alarms are triggered by signals or signal features that exceed thresholds. Each threshold must be seen as a level that needs to be set, either manually or automatically. The large number of levels to be set creates an extra workload for the clinician. Approaches to determine such levels automatically are discussed in this article. Most promising seems the multiple signal approach using an expert system. It seems reasonable to expect that information concerning alarm limits, needed for the operation of knowledge-based alarm systems, may come from integrated departmental data bases.

Anesthesia, General↗
PubMed1994

Primary nocturnal enuresis in children. Background and treatment.

UNLABELLED: The aim of the present studies was to investigate background factors and treatment in children with monosymptomatic primary nocturnal enuresis. The study material comprised enuretics, former enuretics and controls from the municipal community of Falkenberg on the west coast of Sweden. Whenever possible all investigations were made with the children staying in their own home environment. Different background factors have been suspected as being causative: sleep disturbances, behavioural or psychological disturbances, small bladder capacity, increased night diuresis and an insufficient production of the antidiuretic hormone during sleep. These factors have been investigated in these studies. The treatment of enuresis has been dominated by the alarm and antidiuretic treatment with DDAVP. Primary nocturnal monosymptomatic enuresis is a common problem in childhood. In this study the prevalence among 392 seven year old children was 7.3%. A prior history of enuresis was found in 65% of families of the enuretics compared to 25% in controls. The enuretic children showed no statistically significant differences in behavioural or psychological problems compared to non-enuretic children. Enuretic children were described as heavy sleepers by their parents and a wake-up test performed at home showed that they were statistically significantly harder to arouse than the controls. Children with nocturnal enuresis, former enuretics and controls did not differ in social or behavioural traits in an interview study. No signs of symptom substitution was found when enuresis was resolved. Enuretic children had a normal bladder capacity and no statistically significant difference was found compared to controls and former enuretics. The enuretic children showed a normal calcium-creatinine quota in the urine. Former enuretic children showed a significantly enhanced calcium/creatinine quota compared to enuretics and controls. Enuretic children had a statistically significant lower morning plasma level of the anti diuretic hormone vasopressin than non-enuretic children. Enuretic children were treated for 12 weeks with DDAVP or the alarm. DDAVP treated patients had a more rapid effect compared with alarm treated patients. Alarm treated children had a lower relapse frequency. Enuretic children were treated in a randomised, double blind, double dummy, cross over, placebo-controlled study with DDAVP 20 micrograms intranasally by a single dose pipette or 200 micrograms orally as a tablet. Both methods were equally effective in controlling enuresis, but significantly superior to placebo. CONCLUSION: Enuretic children are normal, well adjusted children with a normal bladder capacity, a high level of arousal threshold, and a low morning level of plasma vasopressin. The alarm and DDAVP are equally effective in treating enuresis.(ABSTRACT TRUNCATED AT 400 WORDS)

Academic Dissertations as Topic↗
PubMed2005

Hypoglycemia prediction and detection using optimal estimation.

Patients with diabetes play with a double-edged sword when it comes to deciding glucose and A1c target levels. On the one side, tight control has been shown to be crucial in avoiding long-term complications; on the other, tighter control leads to an increased risk of iatrogenic hypoglycemia, which is compounded when hypoglycemia unawareness sets in. Development of continuous glucose monitoring systems has led to the possibility of being able not only to detect hypoglycemic episodes, but to make predictions based on trends that would allow the patient to take preemptive action to entirely avoid the condition. Using an optimal estimation theory approach to hypoglycemia prediction, we demonstrate the effect of measurement sampling frequency, threshold level, and prediction horizon on the sensitivity and specificity of the predictions. We discuss how optimal estimators can be tuned to trade-off the false alarm rate with the rate of missed predicted hypoglycemic episodes. We also suggest the use of different alarm levels as a function of current and future estimates of glucose and the hypoglycemic threshold and prediction horizon.

Algorithms↗
PubMed1997

A method for detecting microcalcifications in digital mammograms.

Microcalcification clusters are often an important indicator for the detection of malignancy in mammograms. In many cases, microcalcifications are the only indication of a malignancy. However, the detection of microcalcifications can be a difficult process. They are small and can be embedded in dense tissue. This paper presents a method for automatically detecting microcalcifications. We utilize a high-boost filter to suppress background clutter enabling segmentation even in very dense breast tissue. We then use a threshholding and region growing technique to extract candidate microcalcifications. Likely microcalcifications are then identified by a linear classifier. We apply this method to images selected from the LLNL/UCSF Digital Mammogram Library, and produce a receiver operating characteristic (ROC) curves to detail the trade-off between probability of detection and false alarms. Finally, we exam the ability to properly select a threshold to achieve a desired probability of detection based upon a training set. This is a US government work. There are no restrictions on its use.

Breast Neoplasms↗
PubMed1997

How should Helicobacter pylori infection be diagnosed?

The ideal approach for the initial diagnosis of Helicobacter pylori infection is to perform an endoscopy to obtain biopsy specimens for histology and culture. Histology allows classification of any gastritis lesions present and may have prognostic value, and culture enables susceptibility testing of antimicrobial agents to direct proper treatment. Biopsy specimens must also be taken from the corpus if the patient was pretreated with proton pump inhibitors. The cost of these tests and the delay in receiving results limits their use in clinical practice. Therefore, the urease test, a quick and inexpensive test, is used to detect the presence of H. pylori and constitutes the basic invasive test for H. pylori. A new urease test based on a strip instead of an agar disk may be the test of choice in the future, because of its increased sensitivity and 2-hour delay (instead of 24 hours) in obtaining the result. In some countries, because of the cost, endoscopy will be used in selected patients only, either because of alarm symptoms or age > 45 years, which is considered a threshold for gastric cancer risk. In other patients, the noninvasive tests will be used. The cost of serology makes it more attractive compared with the urea breath test. Currently, there are accurate enzyme-linked immunosorbent assay tests that can be performed in any laboratory and that provide precise and quick diagnoses. In the event of a doubtful result, an immunoblot can be performed, as is the case for other infections. Patient follow-up after treatment provides a different situation because bacterial load is usually lower. A noninvasive test should be performed, and only the urea breath test can be used within the timing originally proposed to test eradication efficacy (i.e., 4-6 weeks after treatment). If the result is positive, susceptibility testing is required before administering a second course of treatment. The increasing use of antimicrobial agents to treat H. pylori is likely to result in antimicrobial resistance, requiring that bacteriologic surveillance programs be implemented. There are numerous research projects ongoing in this area, and one can expect that improved methods, such as colorimetric polymerase chain reaction (PCR) and improved antibody tests, will also be used in the future.

Helicobacter Infections↗
PubMed1993

Errors in automated reticulocyte counts due to Heinz bodies.

Serial reticulocyte counts on a patient with an unstable haemoglobin haemolytic anaemia whose red cells contained Heinz bodies were obtained by two automated methods. One false low and several false high counts were obtained with standard threshold settings; each was accompanied by activation of the appropriate alarm. With the FACScan a bimodal red cell distribution was found, corresponding to the proportions of Heinz body positive and negative cells. This case illustrates the fact that Heinz bodies can interfere with automated reticulocyte counting methods, and to a degree that could be clinically important.

Anemia, Hemolytic↗
PubMed2003

Detection, identification, and estimation of biological aerosols and vapors with a Fourier-transform infrared spectrometer.

Two experiments were conducted with a Fourier-transform infrared (FTIR) spectrometer. The purpose of the first experiment was to detect and identify Bacillus subtilis subsp. niger (BG) bioaerosol spores and kaolin dust in an open-air release for which the thermal contrast between the aerosol temperature and background brightness temperature is small. The second experiment estimated the concentration of a small amount of triethyl phosphate (TEP) vapor in a closed chamber in which an external blackbody radiation source was used and where the thermal contrast was large. The deduced BG (TEP) extinction spectrum (identification) showed an excellent match to the library BG (TEP) extinction spectrum. Analysis of the time sequence of the measurements coincided well with the presence (detection) of the BG during the measurements, and the estimated concentration of time-dependent TEP vapor was excellent. The data were analyzed with hyperspectral detection, identification, and estimation algorithms. The algorithms were based on radiative transfer theory and statistical signal-processing methods. A subspace orthogonal projection operator was used to statistically subtract the large thermal background contribution to the measurements, and a robust maximum-likelihood solution was used to deduce the target (aerosol or vapor cloud) spectrum and estimate its mass-column concentration. A Gaussian-mixture probability model for the deduced mass-column concentration was computed with an expectation-maximization algorithm to produce the detection threshold, the probability of detection, and the probability of false alarm. The results of this study are encouraging, as they suggest for the first time to the authors' knowledge the feasibility of detecting biological aerosols with passive FTIR sensors.

Journal Article↗
PubMed1994

Event detection on patient monitoring data using Causal Probabilistic Networks.

Applications are described of the knowledge-representation technique Causal Probabilistic Networks for the detection of events related to the patient and the monitoring equipment, in the context of intensive care patient monitoring. The purpose of the event detection is to reduce the number of false alarms generated by the patient monitor, and to generate alarms related to patient or equipment events rather than to threshold violation. A PC-based system has been developed and tested on patient data. A system for real-time use in patient monitoring is under development.

Diagnosis, Computer-Assisted↗
PubMed1986

The detection of phantom targets in noise by serotine bats; negative evidence for the coherent receiver.

Using a target simulator three serotine bats, Eptesicus serotinus, were trained to judge whether a phantom target was present or absent. The echolocation sounds emitted by the bats during the detection were intercepted by a microphone, amplified and returned by a loudspeaker as an artificial echo, with a delay of 3.2 ms and a sound level determined by the overall gain and cry amplitude. The cry level of each pulse was measured and the echo level received by the bat was calculated. The target was presented in 50% of the trials and the gain adjusted using conventional up/down procedures. Under these conditions between 40 and 48 dB peSPL were required for 50% detection (Figs. 2, 3). In a subsequent experiment the phantom target was masked with white noise (No) with a spectrum level of -113 dB re. 1 Pa X Hz-1/2. The thresholds were increased by 7-14 dB. Energy density (S) of a single pulse was measured and used to estimate S/No, which ranged from 36-49 dB at threshold. Theoretically the coherent receiver model predicts the ratio between hits and false alarms observed for the bats at a S/No of ca. 1-2 dB. Since the bats require 40-50 dB higher S/No (Fig. 3), this is taken as negative evidence for coherent reception (cross correlation). Furthermore, a strong sensitivity to clutter was found since there seemed to exist a fixed relationship between thresholds and clutter level.

Animals↗
PubMed2006

Correcting for false alarms in a simple reaction time task.

Simple reaction times (RTs) constitute an important source of information and tool in human and animal psychophysics, in cognitive neuroscience, and in the clinic. We measure simple RTs to auditory stimuli, in a high signal rate vigilance design, to examine the possibility that simple RT may be used as a tool to study mechanisms of temporal summation at absolute threshold. By means of catch trials, we monitor the subjects' tendencies to produce false alarms, that is reactions not controlled by the reaction stimulus. Here we examine the possibility that a model of a race between a stimulus-controlled reaction process and a false alarm process can account for the numbers as well as for the timing of early and late RTs on stimulus trials in our experiments. We show that the responses in both tails of our empirical RT distributions on stimulus trials are indeed correctly predicted by the race model and can be considered false alarms. This suggests that the race model might also provide a reasonable description of the way in which false alarms and stimulus-controlled reactions combine when they overlap in time. We examine the magnitudes of the estimated effects of false alarms on several parameters of the RT distributions by application of the race model. The analyses reveal that the effects not only vary with false alarm rate but also with stimulus parameters. Our data suggest that the race model may provide a theoretically reasonable and easy means of correcting for false alarms in simple RT paradigms and thus may constitute a useful alternative to the common practice of truncation.

Adult↗
PubMed2000

The design of a practical and reliable fall detector for community and institutional telecare.

Falls are one of the greatest obstacles to independent living for frail and elderly people. Their early detection is an important step in providing people with the reassurance and confidence necessary to maintain an active lifestyle. We have investigated a worn fall detector linked to a community alarm system. A worn device is the only one which is satisfactory, provided that it generates few false alarms. The fall detector we have developed is the size of a small radio pager. It uses a two-stage detection process which senses shock and the orientation of the wearer. A fall is detected within 20 s and triggers a radio signal to a community alarm system. Tests were devised using a jointed mannequin to simulate five modes of falling to understand the effects of impact at different parts of the body. This allowed us to select the appropriate trigger threshold and wearing positions for the sensor. Prototypes were evaluated with 20 people to observe false alarms. The final design allowed reliable detection in 180 different falling scenarios.

Accidental Falls↗
PubMed2005

Identification of gastroenteric viruses by electron microscopy using higher order spectral features.

BACKGROUND: Many paediatric illnesses are caused by viral agents, for example, acute gastroenteritis. Electron microscopy can provide images of viral particles and can be used to identify the agents. OBJECTIVES: The use of electron microscopy as a diagnostic tool is limited by the need for high level of expertise in interpreting these images and the time required. A semi-automated method is proposed in this paper. STUDY DESIGN: The method is based on bispectal features that capture contour and texture information while providing robustness to shift, rotation, changes in size and noise. The magnification or true size of the viral particles need not be known precisely, but if available can be used additionally for improved classification. Viral particles from one or more images are segmented and analyzed to verify whether they belong to a particular class (such as Adenovirus, Rotavirus, etc.) or not. Two experiments were conducted-depending on the populations from which virus particle images were collected for training and testing, respectively. In the first, disjoint subsets from a pooled population of virus particles obtained from several images were used. In the second, separate populations from separate images were used. The performance of the method on viruses of similar size was separately evaluated using Astrovirus, HAV and Poliovirus. A Gaussian Mixture Model was used for the probability density of the features. A threshold on the log-likelihood is varied to study false alarm and false rejection trade-off. Features from many particles and/or likelihoods from independent tests are averaged to yield better performance. RESULTS: An equal error rate (EER) of 2% is obtained for verification of Rotavirus (tested against three other viruses) when features from 15 viral particle images are averaged. It drops further to less than 0.2% when scores from two tests are averaged to make a decision. For verification of Astrovirus (tested against two others of the same size) the EER was less than 2% when 20 particles and two tests were used. CONCLUSION: Bispectral features and Gaussian mixture modelling of their probability density are shown to be effective in identifying viruses from electron microscope images. With the use of digital imaging in electron microscopes, this method can be fully automated.

Adenoviruses, Human↗
PubMed2006

Robust filters for intensive care monitoring: beyond the running median.

Current alarm systems in intensive care units create a very high rate of false positive alarms because most of them simply compare physiological measurements to fixed thresholds. An improvement can be expected when the actual measurements are replaced by smoothed estimates of the underlying signal. However, classical filtering procedures are not appropriate for signal extraction, as standard assumptions, such as stationarity, do no hold here: the time series measured often show long periods without change, but also upward or downward trends, sudden shifts and numerous large measurement artefacts. Alternative approaches are needed to extract the relevant information from the data, i.e., the underlying signal of the monitored variables and the relevant patterns of change, such as abrupt shifts and trends. This article reviews recent research on filter-based online signal extraction methods designed for application in intensive care.

Algorithms↗
PubMed1983

Galvanic element produced by defective electrode insulation--a possible cause of abnormal pulse generator inhibition.

In patients with pacemaker, abnormal inhibition with prolongation of pacing intervals may cause alarming clinical symptoms. A case is described in which high current threshold in relation to voltage threshold indicated probability of an insulation defect with current leakage. Electrograms from the electrode disclosed false signals, which had appeared after replacement of a pulse generator six months earlier. A sharp bend of the wire in the tricuspid area was shown by X-ray and was accentuated by movements of the valve. Experimentally it was demonstrated that similar potentials, sufficient to inhibit a pulse generator, can be obtained from an electrode with defective insulation. A galvanic element forms between the metals of the electrode tip and the non-insulated cable, and potential variations are elicited by movement of the wire.

Arrhythmias, Cardiac↗
PubMed1986

Naturalistic psychophysics: thresholds of ducklings (Anas platyrynchos) and chicks (Gallus gallus) to tones that resemble mallard calls.

Neonatal ducklings and chickens were tested for responsiveness to a pulsing pure tone that was as similar as possible to the mallard maternal alarm call. It is known that ducklings momentarily cease vocalizing when they hear the alarm call and that chicks do the same when they hear pure tones. The duration of peep suppression can thus be used as a measure of whether subjects of either species heard the stimulus. Chicks might not be as sensitive as ducklings to a mallard alarm call because the signal is less significant to them. An adaptive or staircase procedure was used to estimate absolute thresholds, and group psychometric functions were reconstructed for each species from the trial-by-trial data. Ducklings had lower thresholds than chickens as well as steeper psychometric functions to this stimulus. The results suggest that more sensitive and consistent behavioral responses can be elicited by naturalistic sounds than by more arbitrary acoustic stimuli.

Animals↗
PubMed2006

Detection of cough signals in continuous audio recordings using hidden Markov models.

Cough is a common symptom of many respiratory diseases. The evaluation of its intensity and frequency of occurrence could provide valuable clinical information in the assessment of patients with chronic cough. In this paper we propose the use of hidden Markov models (HMMs) to automatically detect cough sounds from continuous ambulatory recordings. The recording system consists of a digital sound recorder and a microphone attached to the patient's chest. The recognition algorithm follows a keyword-spotting approach, with cough sounds representing the keywords. It was trained on 821 min selected from 10 ambulatory recordings, including 2473 manually labeled cough events, and tested on a database of nine recordings from separate patients with a total recording time of 3060 min and comprising 2155 cough events. The average detection rate was 82% at a false alarm rate of seven events/h, when considering only events above an energy threshold relative to each recording's average energy. These results suggest that HMMs can be applied to the detection of cough sounds from ambulatory patients. A postprocessing stage to perform a more detailed analysis on the detected events is under development, and could allow the rejection of some of the incorrectly detected events.

Algorithms↗
PubMed2006

The evaluation and treatment of therapy-resistant enuresis: a review.

Children with enuresis that neither responds to the alarm or to desmopressin medication usually have nocturnal detrusor over-activity combined with high arousal thresholds as a cause for their bedwetting. The evaluation of these children is focused on 1) excluding underlying pathology such as kidney disease, urinary tract infection or neurogenic bladder, 2) looking for concomitant day-time bladder problems or constipation, and 3) detecting possible reasons for failure of alarm treatment. A bladder diary is essential, but blood tests, radiological examinations or invasive procedures are seldom informative. The non-pharmacologic treatment of these children consists of eradication of constipation, if present, and the provision of advice regarding sound drinking and toilet habits. Such treatment is essential but not uniformly sufficient by itself. The first-line pharmacologic treatment of therapy-resistant enuresis is anticholinergic medication, although this is, as yet, not evidence-based. Anticholinergics can be combined with desmopressin for better efficiency. For children failing all these measures there is still a place for tricyclic antidepressant therapy, provided that adequate safety precautions are strictly observed.

Adrenergic Uptake Inhibitors↗