Abraham Otero

Addressing the flaws of current critical alarms: a fuzzy constraint satisfaction approach

OBJECTIVES Threshold alarms, the support supplied by commercial monitoring devices to supervise the signs that pathologies produce over physiological variables, generate a large amount of false positives, owing to the high number of artifacts in monitoring signals, and they are not capable of satisfactorily representing and identifying all monitoring criteria used by healthcare staff. The lack of an adequate support for monitoring the evolution of physical variables prevents the suitable exploitation of the information obtained when monitoring critical patients. This work proposes a solution for designing intelligent alarms capable of addressing the flaws and limitations of threshold alarms. MATERIALS AND METHODS The solution proposed is based on the multivariable fuzzy temporal profile (MFTP) model, a formal model for describing certain monitoring criteria as a set of morphologies defined over the temporal evolution of the patients physiological variables, and a set of relations between them. The MFTP model represents these morphologies through a network of fuzzy constraints between a set of points in the evolution of the variables which the physician considers especially relevant. We also provide a knowledge acquisition tool, TRACE, with which clinical staff can design and edit alarms based on the MFTP model. RESULTS Sixteen alarms were designed using the MFTP model; these were capable of supervising monitoring criteria that could be satisfactorily supervised with commercial monitoring devices. The alarms were validated over a total of 196h of recordings of physiological variables from 78 different patients admitted to an intensive care unit. Of the 912 alarm triggerings, only 7% were false positives. A study of the usability of the tool TRACE was also carried out. After a brief training seminar, five physicians and four nurses designed a number of alarms with this tool. They were then asked to fill in the standard System Usability Scale test. The average score was 68.2. CONCLUSION The proposal presented herein for describing monitoring criteria, comprising the MFTP model and TRACE, permits the supervision of monitoring criteria that cannot be represented by means of thresholds, and makes it possible to construct alarms that give a rate of false positives far below that for threshold alarms.

Landmark detection in mobile robotics using fuzzy temporal rules

Detection of landmarks is essential in mobile robotics for navigation tasks like building topological maps or robot localization. Doors are one of the most common landmarks since they show the topological structure of indoor environments. In this paper, the novel paradigm of fuzzy temporal rules is used for detecting doors from the information of ultrasound sensors. This paradigm can be used both to model the necessary knowledge for detection and to consider the temporal variation of several sensor signals. Experimental results using a Nomad 200 mobile robot in a real environment produce 91% of doors were correctly detected, which show the reliability and robustness of the system.

Nocturnal evolution of heart rate variability indices in sleep apnea

Heart rate variability (HRV) is a valuable clinical tool in diagnosing multiple diseases. This paper presents the results of a spectral HRV analysis conducted with 46 patients. HRV indices for the whole night show differences among patients with severe and mild apnea, and healthy subjects. These differences also appear when performing the analysis over 5-min intervals, regarding apneas being present or not in the intervals. Differences were also observed when analyzing the HRV nocturnal evolution. Results are consistent with the hypothesis that cardiovascular risk remains constant for OSA patients while it increases towards the end of the night for healthy subjects.

A new algorithm for wavelet-based heart rate variability analysis

Abstract One of the most promising non-invasive markers of the activity of the autonomic nervous system is heart rate variability (HRV). HRV analysis toolkits often provide spectral analysis techniques using the Fourier transform, which assumes that the heart rate series is stationary. To overcome this issue, the Short Time Fourier Transform (STFT) is often used. However, the wavelet transform is thought to be a more suitable tool for analyzing non-stationary signals than the STFT. Given the lack of support for wavelet-based analysis in HRV toolkits, such analysis must be implemented by the researcher. This has made this technique underutilized. This paper presents a new algorithm to perform HRV power spectrum analysis based on the Maximal Overlap Discrete Wavelet Packet Transform (MODWPT). The algorithm calculates the power in any spectral band with a given tolerance for the bands boundaries. The MODWPT decomposition tree is pruned to avoid calculating unnecessary wavelet coefficients, thereby optimizing execution time. The center of energy shift correction is applied to achieve optimum alignment of the wavelet coefficients. This algorithm has been implemented in RHRV, an open-source package for HRV analysis. To the best of our knowledge, RHRV is the first HRV toolkit with support for wavelet-based spectral analysis.

Algorithms for the analysis of polysomnographic recordings with customizable criteria

The diagnosis of Sleep Apnoea-Hypopnoea Syndrome requires the visual inspection of a recording containing a large number of physiological parameters of the patient - the polysomnogram. The purpose of this visual inspection is the identification and characterization of different types of pathological events that occur over these parameters. These events are defined by a set of morphological criteria. Based on these criteria, commercial tools have been developed to support clinicians in the task of visually inspecting polysomnograms. This article argues that the standard morphological criteria are just guiding recommendations that experienced physicians often adapt to each specific diagnostic context. Thus, tools that support the analysis of polysomnograms ideally should use flexible criteria that could be easily customizable by clinicians. In this paper, we propose algorithms capable of identifying pathological events relevant in the diagnosis of SAHS using custom criteria that are acquired directly from the clinician. These algorithms take advantage of the Fuzzy Set Theory to capture and handle the vagueness and uncertainty that are characteristics of medical knowledge. Knowledge acquisition using the traditional linguistic approach of the Fuzzy Sets Theory is supported by a desktop tool. However, the authors feel that some of the criteria that need to be acquired are more visual in nature than linguistic. An alternative mechanism for the visual acquisition of these criteria is proposed. Finally, when presenting the pathological events that have been identified, the tool uses several visual metaphors designed to simplify visual inspection of the polysomnogram. We have validated our proposal over 69h of polysomnographic recordings arising from 12 patients that were subjected to a sleep study. 95.7% of the events identified were correct detections. The rate of false negatives was 1.6%.

A Device for Automatically Measuring and Supervising the Critical Care Patient’S Urine Output

Critical care units are equipped with commercial monitoring devices capable of sensing patients’ physiological parameters and supervising the achievement of the established therapeutic goals. This avoids human errors in this task and considerably decreases the workload of the healthcare staff. However, at present there still is a very relevant physiological parameter that is measured and supervised manually by the critical care units’ healthcare staff: urine output. This paper presents a patent-pending device capable of automatically recording and supervising the urine output of a critical care patient. A high precision scale is used to measure the weight of a commercial urine meter. On the scale’s pan there is a support frame made up of Bosch profiles that isolates the scale from force transmission from the patient’s bed, and guarantees that the urine flows properly through the urine meter input tube. The scale’s readings are sent to a PC via Bluetooth where an application supervises the achievement of the therapeutic goals. The device is currently undergoing tests at a research unit associated with the University Hospital of Getafe in Spain.

An Evaluation of Indexes as Support Tools in the Diagnosis of Sleep Apnea

This article evaluates several indexes as support tools to diagnose patients with Sleep Apnea-Hypopnea Syndrome (SAHS). Some of these indexes, such as the Apnea-Hypopnea Index, have been standardized and studied in depth in the literature. Other indexes are used extensively in the reports that commercial polysomnographs generate. However, they have not been studied in detail and clinicians have no standardized guidelines for interpreting them. Examples are the mean and maximum duration of apneas and hypopneas. Finally, several novel indexes proposed by the authors are also evaluated. To evaluate the indexes, we have used a database of 274 patients who have undergone a polysomnographic test. Several feature selection techniques were used to assess the capability of each index to discriminate between healthy and SAHS patients. The capability of the indexes for diagnosing the patients was analyzed by using decision trees which were trained using each index individually, and all the indexes together. Our results suggest that some indexes which are often present in the reports of commercial polysomnographs provide little or no information. On the other hand, other indexes that are usually not considered have a great capability to discern between SAHS and control patients.

A low cost screening test for Obstructive Sleep Apnea that can be performed at the patient's home

This paper presents a new screening test for Obstructive Sleep Apnea-Hypopnea (OSAH) Syndrome based on a PDA platform capable of recording the patients electrocardiogram during his/her nightly rest. OSAH patients present alterations in certain bands of the heart rate variability power spectrum. The more serious the disorder afflicting the patient it is, the greater these alterations are. An algorithm running on the PDA identifies the heart beats, and it calculates the RR intervals time series. Then the algorithm calculates an index that quantifies the magnitude of the heart rate variability power spectrum alterations, and therefore the severity of the patients condition. The reliability of this index has been validated using the Apnea-ECG Database. After the first night of use of the device at the patients home, the PDA communicates the test results to the hospital via the Internet using a WiFi connection, or through GPRS/UMTS. In the hospital, the physicians can decide whether the results are conclusive, or whether it is preferable to repeat the test. Sometimes it may be necessary to repeat the test just because one of the sensors of the electrocardiograph was disconnected during the night. This decision is communicated through the PDA to the patient, who then knows whether he/she should return the device, or if he/she should use it again the following night. The end result is a cheap and reliable OSAH screening test that neither involves a long waiting list nor requires an overnight stay in the hospital for a polysomnographic test.

Fuzzy structural algorithms to identify and characterize apnea and hypopnea episodes

We present a new automated method to identify apneas and hypopneas and to relate them to the drops in blood oxyhemoglobin saturation that they produce. The algorithm takes advantage of the fuzzy set theory for the representation and manipulation of the vagueness of the medical knowledge on which it is based. Its structural nature allows us to easily modify the morphological detection criteria, and to perform a detailed characterization of the identified events. Based on this proposal, a tool for screening polysomnographic records has been developed. The tool allows the physician to modify the morphological criteria that define apneas, hypopneas, and desaturations as well as to inspect the descriptors that make up their characterization. Using this tool we have analyzed five polysomnographic recordings obtaining an overall correct detection rate of 95%. The false negative rate was 6.6% and the false positive rate was 4.3%.

OntologyTest: A Tool to Evaluate Ontologies through Tests Defined by the User

The ontology evaluation utilities that are currently available allow the user to check the internal consistency of an ontology, its syntactical correctness and, at most, the fulfillment of some philosophical constraints related to rigidity or identity. However, there is no contribution in the ontology evaluation field that proposes a method to dynamically test ontologies with regard to their functional specification. Thus, no software for this task has been built until now. This paper presents a tool, OntologyTest, designed to overcome this drawback. The tool allows the user to define a set of tests to check the ontologys functional requirements, to execute them, and to inspect the results of the execution. The whole set of tests (or a particular test) can be executed at any time; thus it simplifies the testing of ontology both during its development and during its evolution.