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New Publications are available now online for this publication.
Please follow the links to view the publication.Automatic breath sound detection and removal for cognitive studies of speech and language
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1704
Speech has been previously investigated as means of gaining insight into certain psychiatric disorders. Correlation has been found between temporal characteristics of speech and negative symptoms associated with schizophrenia. However the presence of breath sounds in speech may lead to a decreased performance of classification between patient and control groups. This study presents an algorithmic approach for both breath sounds detection and removal, and also analyses its impact on the ability of a Linear Discriminant Analysis (LDA) classifier to discriminate between schizophrenic patients and control subject. Results demonstrate that more accurate feature extraction yielded to a 6.7% increase in discrimination ability from 67.5% to 74.2% to differentiate between schizophrenic patients and control subject based on speech alone. (6 pages)Optimizing the assessment of autoregulation from black-box models
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080464
Autoregulation mechanisms maintain blood flow approximately stable when blood pressure changes. Impairment in autoregulatory function can be identified by black-box modelling with blood pressure as input, and blood flow as output, using only spontaneous variability in both signals. The current paper addresses the issue of how to assess autoregulaton from the model parameters. We propose using a test input in the shape of a band-pass filtered impulse, that reflects the characteristics of blood pressure variations more accurately than the more commonly used step response. Features extracted from the relationship between the new impulse and the best-fit model response are shown to have better dynamic range and stability than a comparable index derived from the step response. (4 pages)Segmentation and analysis of the glomerular basement membrane using active contour models
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080442
Some renal diseases are associated with significant alterations in the structure of the glomerular basement membranes (GBM). Increased thickness is commonly seen in diabetic nephropathy, where it may be an early sign of renal involvement. Abnormally thin GBMs are associated with the passing of blood in the urine, or hematuria. Measurement of the GBM thickness is carried out on images obtained from transmission electron microscopy (TEM). We propose image processing methods for the detection and measurement of the GBM. The methods include edge detection, morphological image processing, active contour modeling, skeletonization, and statistical analysis of the width of the GBM. The proposed methods were applied to 34 TEM images of six patients. The mean and standard deviation of the GBM width for a patient with normal GBM were estimated to be 348 ± 135 nm; those for a patient with thin GBMs associated with familial hematuria were 227 ± 94 nm; and those for a patient with diabetic nephropathy were 1152 ± 411 nm. Comparative analysis of the results of image processing with manual measurements by an experienced renal pathologist indicated low error in the range of 36 ± 11 nm. (4 pages)Accelerometer and footswitch evaluation of movement in three elderly patient groups
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080647
We examined anterior-posterior (AP) and medio-lateral (ML) head and trunk movements during gait using accelerometers, and a footswitch evaluation of temporal parameters of gait during walking of two distinct elderly faller groups. Elderly fallers with a primary diagnosis of orthostatic hypotension, elderly fallers without a diagnosis of Orthostatic Hypotension and a control group of healthy elderly non-fallers were examined to determine if both sets of measures can be used to differentiate between the three groups. Using different parameters of AP and ML trunk movement and certain temporal parameters of gait we were able to significantly differentiate between the three groups to the same extent using both sets of measures. These results are exploratory and need to be confirmed in a definitive more high powered study.Obtaining DSC MRI cerebral blood flow estimates without tissue specific errors
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080456
The singular value decomposition (SVD) deconvolution implementation is in common use in magnetic resonance (MR) dynamic susceptibility contrast (DSC) studies. The zdSVD SVD variant involves computationally manipulating DSC concentration signals to have zero arterial-tissue delay (ATD) prior to using SVD. Our proposed zdSVD improvements show how considering other signal time shifts leads to cerebral blood flow estimates whose accuracy shows a minimal dependency on the tissue mean transit times (MTT) values. This characteristic leads to greater absolute CBF accuracy across all MTT values after scaling MR studies to match PET flow values. A comparison is made between the modified zdSVD algorithm and other DSC-specific deconvolution algorithms. (4 pages)Prediction of elevated pulse pressure in elderly using in-home monitoring sensors: a pilot study
http://dl-live.theiet.org/content/conferences/10.1049/cp_20081095
In this paper we describe the possibility of employing the data generated by a continuous, unobtrusive home monitoring system for predicting abnormal blood pressure (BP) in elderly. Blood pressure may be used for both early detection of clinical conditions (such as heart attacks or strokes) and long term assessment of functional or cognitive decline. We investigated several factors that influence abnormal BP prediction such as sensor type, number of days prior to the BP measurement and algorithm choice. In our algorithms we used the pulse pressure (the difference between systolic and diastolic BP) that is believed to be a better predictor for clinical events. We conducted a retrospective pilot study on two residents of the TigerPlace aging in place facility with age over 70, that had blood pressure measured between 100 and 300 times during a period of two years. The pilot study suggested that abnormal pulse pressure can be reasonably well estimated (an area under ROC curve of about 0.75) using apartment bed and motion sensors. (4 pages)A soft sensing method for monitoring ambulatory activities of patients with venous ulceration
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080459
This paper sets out to investigate the characteristics of two relatively new sensors, the Flexpoint bend sensor <sup xmlns="http://pub2web.metastore.ingenta.com/ns/">®</sup> and the ionic polymeric metal composite (IPMC), for use outside of the clinical setting to monitor the activity of patients who have venous ulceration. Results from testing these sensors show that they achieve consistent results in tests over a range of frequencies, and therefore that it is possible to use them as motion detectors in human movement. (4 pages)Application of quartz tuning forks in multiple-breath-helium washout measurement
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080463
Multiple-breath-washout (MBW) measurements are regarded as a sensitive technique for lung function studies which can reflect the ventilation inhomogeneity of our respiratory airways [7,8,9]. Typically nitrogen is used as the tracer gas and is washed out by pure oxygen in multi-breath-nitrogen (MBNW) washout tests. In this work, instead of using nitrogen, 4He is used as the tracer gas. A commercial quartz tuning fork with a resonance frequency of f-32 kHz has been used for detecting the concentration of 4He gas at room temperature. This low-cost sensor has been used previously for detecting the gas density [11]. The resonance frequency of the tuning fork decreases linearly with increasing density of the surrounding gas and we use this effect to determine the helium concentration. The resulting washout curve from an asthmatic volunteer has smaller curve linearity compared to a normal healthy person which reflects the higher ventilation inhomogeneity of the respiratory airways. (4 pages)Design of medical wireless location network based on Zigbee protocol
http://dl-live.theiet.org/content/conferences/10.1049/cp_20070247
A medical wireless location network based on Zigbee/IEEE802.15.4 is issued. The blood pressure values and location information of inpatients could be obtained and handled in time via the wireless network. The kernel chip of the system hardware is CC2430/2431. To calculate the position of mobile sensor nodes, the Location Engine of CC2431 implements a distributed computation algorithm that uses received signal strength indicator (RSSI) values from known reference nodes. This network is a typical location application of Zigbee network.Ultra-wideband respiratory monitoring system
http://dl-live.theiet.org/content/conferences/10.1049/ic_20060507
In this paper, we present a method for respiratory monitoring which uses UWB signaling to detect the displacement of a human chest. Compared to other techniques that use more narrowband sources, UWB signaling offers several unique advantages, including improved resolution ability, no need for direct skin contact, lower cost and lower power consumption, among others. We present a system setup, discuss a model of the human thorax, and focus on signal processing steps used at the receiver. In particular, we present a high-resolution frequency domain approach to detecting respiratory movements. Some of the techniques we use have been already encountered in the spectral estimation framework, allowing for a relatively simple hardware implementation and sub-Nyquist sampling rates. We also present numerical studies based on the frequency-dependent finite-difference time-domain method, illustrating the efficiency of the proposed method in respiratory monitoring. Our scheme can be used in a variety of medical applications, such as preventive medicine in home health care and intensive care units.Continuous blood pressure estimation using pulse arrival time and photoplethysmogram
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060391
Pulse arrival time and the amplitude of the finger photoplethysmogram were used to track continuous systolic blood pressure over 10-minute intervals. The measures were recorded with a holter-oximeter from a sample of 8 young, healthy human subjects in the supine and standing positions. Results show that, with individual calibration, systolic blood pressure can be estimated with an average error of ±5 mmHg. Using pulse arrival time in combination with the amplitude of the finger photoplethysmogram gave better results than using any one alone. (5 pages)Wavelet filter evaluation for HRV signal processing
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060360
All of wavelet functions are designed for a particular form of dynamics, therefore, a choice of one particular function may not be appropriate to capture heart rate variability (HRV) dynamics. The aim of this paper is to examine a set of wavelet functions (wavelets) for implementation in HRV analysis and to highlight the benefit of this transform relating to today's methods. The basis functions of the wavelet transforms should be able to represent HRV signal feature locally and adapt to slow and fast variations of the signal. This paper discusses the important features of wavelet transform in heart rate variability analysis, including the extent to which the limitations of nonparametric methods like data stationarity and detection of transient episodes can be do away with. The effects of different wavelet functions and their order are assessed and the Daubechies (DW-3) has been proposed as most suitable basis on the basis of performance of various basis and their orders under supine resting and deep-breathing test. (4 pages)The value of data fusion for predicting alarms in critical care
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060393
Studies show that patients who have in-hospital cardiac arrests or unexpectedly require admission to an Intensive Care Unit frequently show physiological signs of deterioration prior to the event. This deterioration frequently goes unnoticed and hence is not acted on. To combat this there has been increased use of mandated vital sign measurement and medical emergency teams (MET) - groups of clinical experts who are called according to criteria relating to changes in physiological parameters. An automated system for detecting patient deterioration through data fusion of heart rate, breathing rate, oxygen saturation, temperature, and blood pressure has been developed. Its performance is tested against current techniques for generating MET calls and early warning of such events is demonstrated. (4 pages)Gray box modelling of arterial vasoaction
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060456
Gray box modelling of physiological systems involves constructing a model structure based on physical knowledge of the system and model parameterisation using numerical techniques. This paper presents a gray box model of arterial vasoaction (the process of constricting and dilating blood vessels in order to maintain an appropriate level of blood pressure and blood flow). The model structure is built in accordance with the physical system. The initial parameterisation was manual, with the model consequently optimised using gradient techniques and genetic algorithms. The model was validated by demonstrating good correlation between experimental results and model output.Improved assessment of pulsatile blood flow during resuscitation using Doppler ultrasound
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060357
Early defibrillation is critical for successful resuscitation of a sudden cardiac arrest patient. Defibrillators currently do not assess the patient's heartbeat or blood circulation and the responder has to manually check for the pulse, a procedure known to be very inaccurate. Previously we had developed an ultrasound Doppler based approach to determine the presence of blood flow in the context of resuscitation. Here we extend our earlier work to develop a generalized pulsation index based on a spectral analysis of the Doppler signal. This new method has the advantage to better distinguish between states of pulse and pulselessness, since it aims at capturing the essentially non-sinusoidal behaviour of cardiac activity. In turn, this leads to better sensitivity and specificity for pulsatile flow assessment. The method was demonstrated on data from pigs undergoing cardiac arrest and defibrillation. (4 pages)Prediction of tumour motion using interacting multiple model filter
http://dl-live.theiet.org/content/conferences/10.1049/cp_20060350
Accurate prediction of tumour motion - over a prescribed time - is essential for enabling adaptive radiotherapy. The prediction time horizon is determined by measurement processing time, predictor algorithm processing time and the time-to-adapt radiation delivery. A trade off between the predictor algorithm complexity and the required prediction time horizon, therefore, has to be made. This paper proposes an interacting multiple model (IMM) filter and two Kalman filters to predict 0.2 s ahead respiratory tumour motions. The performance of the filters is evaluated using 333 traces of 4 minutes respiratory motions for 24 adult patients. The average RMSE of the IMM filter and the best Kalman filter with 5 Hz measurements rate are 0.98 mm and 1.1 mm, which are improvements of 38% and 30% compared to use of measurements only. (4 pages)BIOSIGN™ : multi-parameter monitoring for early warning of patient deterioration
http://dl-live.theiet.org/content/conferences/10.1049/ic_20050334
Early recognition of abnormalities in the physiological parameters of hospital patients followed by rapid intervention should result in an improvement in functional outcome or mortality rate. We have developed a real-time system, BioSign™, capable of analysing physiological parameters in order to identify adverse trends in multi-parameter space (departure from "normality") and prompt clinical staff to intervene. The model of normality is based on five vital signs, which can all be recorded non-invasively: the heart rate, blood pressure, arterial oxygen saturation, respiration rate and temperature. We have evaluated the trained model of normality in a two-year randomised controlled trial of 405 patients monitored on general medical and surgical wards. Preliminary results show that BioSign™ can provide early warning of changes in clinical status and deterioration in patient condition.A bootstrap approach to testing for an association between bursts in the neonatal EEG and changes in cerebral blood flow
http://dl-live.theiet.org/content/conferences/10.1049/ic_20050324
In normal premature neonates, a pattern of EEG, known as trace discontinu, is common, which contains bursts of relatively high voltage, in an otherwise lower voltage background. The current work investigates whether these bursts are associated with changes in the velocity of blood, measured by transcranial Doppler ultrasound in the middle cerebral artery. A measure of consistency in the response from repeated bursts is proposed, and in order to test its significance, a bootstrap method was devised. With this method signals that are interrupted by `missing samples', where segments of the signal are lost due to excessive noise or artifact (as was the case in our recordings), can also be analysed. Monte Carlo simulation studies demonstrate the potential of this approach. In tests on 12 recordings from premature babies it was found that 3 had significantly consistent responses, with a peak in cerebral blood flow velocity some 5-12 seconds after the onset of the bursts. Overall, the results suggest that there is an association between bursts and blood-flow, at least in some subjects, but the causal mechanisms require further studies.Improved detection of embolic signals using multi scale wavelet filtering, AR and ANN, for TCD ultrasound
http://dl-live.theiet.org/content/conferences/10.1049/ic_20050332
Transcranial Doppler ultrasound can be used to detect emboli in blood flow in the brain. The presence of emboli is an indication of high risk of stroke. Embolic signals have characteristic transient chirps suitable for wavelet analysis. We have implemented an on-line intelligent wavelet pre-filter combined with a new frequency based neural network classification system (NFS) to produce a new online detection system. Initial results show an improvement in accuracy compared with the widely used FS-1 system. Our system makes, use of multi-scale wavelet denoising using an adaptive coefficient threshold. The pre-filtering system is combined with a detection system which uses a two layer neural classifier and a new auto-regressive event detector. For conditions such as carotid stenosis an improvement of 20% in detection accuracy was obtained. Our online (real time) intelligent wavelet amplifier and its matrix optimised form uses the matched filter properties of multiple coefficients from multiple wavelets to significantly enhance embolic signals and improve classification performance.Applications of signal recognition algorithms to diagnosis and monitoring in chest medicine
http://dl-live.theiet.org/content/conferences/10.1049/ic_20050343
Electronic stethoscopes capable of recording and digitally storing lung sounds have been available for several years. The clinical advantage of these devices is that recordings can be stored and replayed for comparison, either at a later time or to another physician. The next logical step is to offer the user an automatic, objective 'diagnosis' of the clinical condition. This paper presents wavelet-based algorithms that have been developed to detect and quantify crackles and wheezes, associated with asthma, chronic obstructive pulmonary disease and lung fibrosis. However, signal processing is not the only challenge. Practical application for real clinical uses requires a robust and appropriate user platform and the definition of suitable uses, which will complement expert judgement. The potential for applications in chronic disease monitoring, medication regime development, emergency triage and routine screening is discussed. Issues regarding user acceptability, ergonomics and clinical validation are outlined, based on clinical feedback from users of existing commercial devices.Noninvasive detection and classification of coronary artery occlusions using wavelet analysis of heart sounds with neural networks
http://dl-live.theiet.org/content/conferences/10.1049/ic_20050342
Coronary artery disease (CAD) is a main cause of death around the world. Most of olds somehow suffer a kind of cardiovascular disorder. So the on-time diagnosis and treatment of coronary occlusions is very crucial to them. It has been widely reported that coronary stenoses produce sounds due to the turbulent blood flow in partially occluded arteries. In this paper, we make use of wavelet analysis and artificial neural networks to analyze heart sounds for detection and classification of CAD's. Our heart sound signals are recorded synchronously with ECG and are sampled at 4 k-sample per second with 12 bit resolution. Results show that successive classification of normal and coronary occluded patients is fulfilled with a resolution of 90% for normal group and with a resolution of 85% for abnormal group increasing performance over previous systems.Virtual nasal surgery
http://dl-live.theiet.org/content/conferences/10.1049/cp_20040584
A method of objective surgical assessment for ear, nose and throat (ENT) care is proposed. Virtual surgery has been carried out on an anatomically accurate model of a diseased human nasal cavity. The model is generated from a series of 2D computed tomography (CT) scans from a patient awaiting surgical intervention to improve nasal breathing. A 3D model is used to carry out airflow analysis before and after virtual correction of a nasal obstructive disorder. This case illustrates how advances in computational methods may be employed, as a tool, to enhance pre-operative ENT surgical planning.Design and development of interactive modules for language therapy rehabilitation
http://dl-live.theiet.org/content/conferences/10.1049/ic.2004.0691
Language therapy utilizes assisted rehabilitation techniques that function based on high-cost devices, hard to obtain by the Venezuelan health centers, personnel and patients that require them. This paper presents the design and development of three modules used in the area of language therapy and augmented communication. These microprocessor-based modules employ low-cost, low-power solid state technologies. They are: a reaction-time meter, a random light sequence generator, and a digital karaoke machine. The reaction time meter allows for the measurement of the patient's concentration ability, his ability to discriminate colors and his hand-eye coordination. The random sequence generator is used to work on the Feldman categories, based on Piaget, while also addressing the belated semantic reactions, such as association, conceptualization, opposite analogies, hypothetical problems, additive and/or visual absurdities, riddles. The digital karaoke machine has a digital audio recorder/player and an intensity display. Its function is to make the language rehabilitation therapy more interactive, allowing for the recording of the patient's voice and its later reproduction for evaluation by the therapist. Some of the pathologies that can be treated in this manner are: aphasias, stuttering, phoneme pronunciation problems and respiratory coordination. It is also possible to use them in the rehabilitation of patients with alterations in the vocal cords, treatment of disartries, improvement of the speech rhythm, children with attention and comprehension deficits, as well as patients with limited vision. These devices, used and evaluated in the "Centro Nacional de Rehabilitacion" have proved to be a low-cost solution, accessible for the treatment of patients with language disabilities, besides bringing a novel approach to the treatment itself, allowing (in the case of the digital karaoke machine) the feedback to the patient in-treatment, while the therapist can visually verify the normality of the voice-intensity parameters. (3 pages)PhiSAS: a low-cost medical system for the observation of respiratory dysfunction
http://dl-live.theiet.org/content/conferences/10.1049/ic_20020042
Respiratory illness is recognised internationally as one of the commonest medical disorders affecting the world's populous, and is especially a major problem that affects the third world. The World Health Organisation (WHO) pursues an extensive health program that is aimed at reducing the plight of respiratory disorders by treatment and education. As with the majority of third-world health care programs, the effectiveness is limited by the availability of resources and finance. PhiSAS (Physiological Signal Analysis System) is a novel system developed for the observation of lung sounds. The system consists of a Personal Computer (PC) supported with dedicated software and hardware. Lung sounds can be recorded via chest microphones into the computer system for storage in digital form. This data can then be retrieved for post-processing using an array of software-based Digital Signal Processing (DSP) techniques that can mathematically manipulate lung sounds to extract important features. Data and results can be presented audibly by sound playback, or graphically by using spectrographs. The spectrograph is a representation of lung sound spectral energy with respect to time and frequency. PhiSAS has the ability to present three types of analysis based on conventional and novel mathematical techniques: Fourier, Wavelet and Time-Frequency Analysis. The purpose of the PhiSAS system is to provide objective analysis of lung sounds. The practice of auscultation (the art of listening to body sounds) has been practiced by physicians since the days of Hippocratic medicine. However, many physicians believe that respiratory auscultation performed with a stethoscope offers little scientific value due to the way it is practiced. For example, observations can be subjective depending on the physicians hearing ability and experience. Moreover, descriptions of lung sounds are described using onomatopoeic references that are ambiguous. By exploiting advances in low-cost PC technology and techniques in signal analysis, the physician can express sound observations in a more precise scientific manner. (5 pages)Visualisation and categorisation of respiratory mechanism using self-organising maps
http://dl-live.theiet.org/content/conferences/10.1049/cp_20000355
In post-operative patients, it is sometimes necessary to push morphine-like analgesics to their limits for pain relief. Unfortunately, this can sometimes bring a significant risk of disrupting the control of breathing, and precipitating life-threatening conditions. A possible way of monitoring patients is by studying the correlation between analgesia, airway obstruction and hypoxia. The first step towards achieving this objective is by visualising the relationship between different pairs of signals involved in respiratory mechanics. Based on previous work where self-organising maps were used for representing these relationships on a breath-by-breath basis, this paper demonstrates how it is now possible to automatically label nodes in the self-organising maps based on the classification of the signals by a clinician. In addition, the ability to visualise the transitions between categories should enable further research into the significance of transitions between the categories and the presence of possible new sub-categories.A method for respiration monitoring by the use of a bioacoustic signal
http://dl-live.theiet.org/content/conferences/10.1049/cp_20000312
The sound that generates during the act of respiration can be picked up by a bioacoustic sensor, a specially designed microphone. The aim of the work was to describe a method for monitoring of respiration and where the start and stop of the respiration phases can be timed accurately. A method is presented where the time position of the different respiration phases can be determined by a time resolution of 51 ms. A microphone applied over the trachea and the features of the respiration sounds frequency content was used for the development of the method.The future of low flow breathing systems in anaesthesia
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990342
The traditional circle system was devised as a means of purifying and recycling used anaesthetic gases and vapours without the requirement of having the absorber positioned close to the patient's head. The theory of circle system agent delivery was founded on the concept of a known fresh gas mixture being used to replace agents taken up by the patient. This focuses our techniques of anaesthetic administration on the fresh gas constitution entering the circle as this is the factor that is able to be adjusted by the anaesthetist. However, what truly matters to the conduct of the anaesthetic is the specific balance of the inhalational components that is presented to the patient through the patient connection. Until the advent of system gas and volatile analysers within the theatre, the manual adjustment of the gaseous and volatile input into the circle was the only mechanism of controlling the mixture presented to the patient albeit through the buffering mechanism of the circle system itself. The technology is now available to close the servo-feedback loop with the mixture sensed at the patient connection. Accurate and reliable agent delivery systems and computer coordinated modulation are vital links in this process. It is therefore now a logical step for anaesthetists to think in terms of target patient end-tidal volatile and gas values. The anaesthetist is accustomed to monitoring such values during routine anaesthesia. A servo system would be able to achieve a targeted value and equally importantly maintain a steady value throughout the constantly changing patient uptake. (2 pages)An electronic manometer for blood-pressure measurement
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990491
This article reports the development of an electronic pressure gauge that can be incorporated into existing sphygmomanometers, acting only as a replacement for the traditional aneroid or mercury gauge, but leaving the clinical auscultatory procedure for determining blood pressure undisturbed. (5 pages)Amsorb - a new carbon dioxide absorbent for use in anesthetic breathing systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990337
We have developed a new carbon dioxide absorbent for use during low flow or circle system anesthesia. The material does not contain the strong base sodium and/or potassium hydroxide. This paper discusses the efficiency and chemical inertness of the new material. (2 pages)Low flow breathing systems in diving
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990340
An alternative method of providing the diver with breathing gas is to use a re-breathing system. These have been extensively used for military purposes from the 1940s and are currently a growth area for recreational use. These systems are akin to “low flow breathing systems in anaesthesia”. The operating principle of a diving re-breather is that the diver may conserve gas by continuously exhaling and inhaling the same gas. Prior to re-inhaling the gas, any previously exhaled carbon dioxide is removed and oxygen added to maintain the inspired partial pressure of oxygen (PO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub>) at a physiologically acceptable level. Although diving re-breathers have many different configurations, all have the same basic components. The fundamental building block of a re-breather is the breathing circuit or breathing loop comprising: facepiece and breathing hoses (typically gas is forced to flow in one direction round the breathing circuit by non-return valves positioned either side of the facepiece), counterlung and absorbent canister. To complete a simple system attached to the breathing circuit are: relief valve, gas supply system and harness. The gas supply and associated inspired PO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> control systems are discussed. (4 pages)Breathing systems in aerospace
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990341
Closed circuit breathing systems are employed in aerospace activities where great economy in the use of oxygen is required as on the surface of the moon away from the spacecraft. The high efficiency, reliability and compactness of modern molecular sieve oxygen concentrators operating on bleed air from the aircraft engines have made this technology the method of choice for the supply of breathing gas to the pilot especially in high performance combat aircraft. This technology is slowly being applied to larger passenger carrying aircraft. (4 pages)Vaporisers and anaesthetic agent delivery
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990338
An important point when considering the behaviour of circle systems with low fresh gas flows is that the measured fresh gas composition no longer represents the gas mixture being delivered to the patient. As the total flow is reduced to the point where no gas is vented from the system, so called Closed System Anaesthesia, the fresh gas flow represents the replacement of the gases taken up by the patient. Typically as the gas flow is reduced there is a need for a more oxygen-rich supply since oxygen uptake exceeds nitrous oxide uptake after around 30 to 40 minutes of anaesthesia. Thus the monitoring of oxygen concentrations within the system is vital as is the anaesthetic vapour concentration since the uptake of this will vary with time according to its own characteristics and these vary from agent to agent. The four means by which a volatile agent may be introduced into the breathing system are discussed: vaporiser outside the circle; vaporiser in the circle; volumetric addition to the fresh gas flow; volumetric addition into the circle. (4 pages)The history and development of low flow breathing systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990335
A breathing system is the assemblage of tubes, reservoirs and valves from and into which a subject breaths. The function of the breathing system is to supply oxygen and to eliminate expired carbon dioxide. A “low flow” system is one in which the carbon dioxide is chemically removed so that the fresh gas supplied to the system needs only to be sufficient to supply the subject's oxygen requirements. By contrast, in a “high flow” system there is no chemical removal of carbon dioxide, instead it is diluted and dispersed by a fresh gas flow rate which must at least equal the alveolar ventilation. This high efficiency is only achieved in systems in which the dead space gas (one third of the tidal volume and free of carbon dioxide) is rebreathed. These considerations indicate that the minimum fresh gas flow rate into a completely closed system is 200 mls/min and in a high flow system of the highest efficiency the minimum flow rate is 3.2 L/min. These figures relate to the traditional 70 Kg anaesthetised subject. In practice high flow systems usually require at least 5 L/min and fresh gas flow rates below 4 L/min are loosely termed “low flow”. In all modes of operation, except the completely closed, excess gas in the system is vented via an adjustable pressure limiting valve. The evolution of the theory and practice of such closed breathing systems is discussed. (4 pages)Theory of gas delivery from low flow systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990336
The prime requirements of any breathing system are that it should remove carbon dioxide from the subject, and supply him or her with the required inhalation mixture. The simplest way to achieve this is with a non-rebreathing system in which all expired gas, carrying CO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub>, is discharged through a spill valve and all inspired gas comes directly from the anaesthetic machine via a reservoir bag or demand valve. In a low-flow system, efficient absorption can remove CO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub>, but the inspired gas will be a mixture of expired and fresh gas-assuming that any anaesthetic vaporizer is in the fresh-gas supply line. Gas exchange in the subject makes the expired mixture different from that inspired; therefore the inspired mixture is different from the fresh-gas mixture. Throughout anaesthesia, anaesthetic is being taken up by the patient so the expired concentration is less then the inspired; and therefore, assuming that the vaporizer is in the fresh-gas supply line, the fresh-gas concentration must be greater than the inspired concentration to make up the difference. However, if the vaporizer is inside the breathing system then, soon after turning on the vaporizer, the gas entering it will already contain vapour expired by the patient so that the inspired concentration will be greater than the vaporizer concentration-where that is defined as the concentration delivered when vapour-free gas enters it. In order to control the inspired mixture, it would be possible to monitor that mixture and adjust the fresh-gas mixture-either manually or by a servo mechanism-to attain, and then maintain, the desired inspired mixture. The author discusses the relationship between inspired and fresh-gas concentrations as a guide to manual control, or to enable the servo engineer to devise something more sophisticated than a simple PID controller. (3 pages)Monitoring the breathing system
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990339
All breathing systems need to be monitored in clinical use, but little is amenable to the unaided observation of the anaesthetist. Reliance is therefore placed on the components of the breathing system itself and on the monitoring equipment. The purpose of monitoring is mainly to confirm our expectations of its results. When an unexpected finding appears the anaesthetist's response may range from immediate action to ignoring the result. Several factors influence this decision: the anaesthetist's confidence in his ability to predict the correct result, the clinical importance of the finding, support from different monitoring equipment, etc. It is, of course, possible to overwhelm an observer with information, and monitoring must be selective. It is also impossible to monitor everything, and although we may yearn for a central nervous system PO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub>-meter, we can't have one. Even when it is possible to monitor something (e.g. intrapulmonary shunt) we may not consider it worth the expense and effort. It is with these points in mind that I have approached the subject of monitoring the breathing system. Some monitoring applies equally to open and to low flow breathing systems, but some is of much greater importance as the flow is reduced because the anaesthetist's confidence in his own predictions is weakened. I will consider airway pressure, gas flow, gas temperature briefly, and concentrate on the analysis of gas composition. (4 pages)On the use of a novel air flow transducer in a clinical environment
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990495
Extensive calibration of a novel air flow transducer, which mimics a Wells turbine, has led to a mathematical model expressing its linear pressure-flow characteristics over a wide range of flow-rates. The transducer has subsequently been tested as the core component of a pneumotachograph for lung function monitoring on patients at the respiratory clinic of a partnering hospital. The results collected and their comparison to those obtained from existing devices have demonstrated excellent suitability of the transducer to the measurement of flows in the range encountered in human respiration, and possibly to other application areas. (3 pages)Automatic tracking of vortical flow patterns with MR velocity mapping
http://dl-live.theiet.org/content/conferences/10.1049/cp_19990353
This paper describes an automatic method based on the phase portrait theory for studying vortical flow features. The potential of this technique for studying blood flow features using multi-directional magnetic resonance velocity imaging is demonstrated both in normal subjects and in patients. The method relies on detecting critical flow features prior to analysing dynamical indices of the fluid, and therefore is well suited to the topological study of complex flow patterns.The use of LabView and Matlab in the development of a novel pneumotachograph
http://dl-live.theiet.org/content/conferences/10.1049/ic_19980592
A novel pneumotachograph is currently under development which exploits the properties of the Wells turbine used in many wave energy projects during the eighties and the nineties. In order to employ a small scale model of the Wells turbine as a highly sensitive flow transducer a suitable constant speed motor controller is required. This controller has best designed and thoroughly analysed using Matlab with Simulink. Typically airflow data, collected from a pneumatachograph, needs further processing before physicians can extract relevant patient diagnostic data. The now data processing software has been developed using LabView because of its built-in capabilities specifically aimed at data acquisition and data processing. (5 pages)Computer simulation of heart rate and blood pressure changes, and comparison with clinical data
http://dl-live.theiet.org/content/conferences/10.1049/ic_19981098
The human body has highly complex physiological mechanisms to ensure that its physiological functions remain stable and are able to respond to peak demands. Physiologists and other clinical scientists have discovered much about the detailed functioning of the body, but its overall control is often difficult to predict. This is where simulation techniques are helpful. Simulation allows physiological responses to be predicted, and then compared with actual clinical data. This enables different models to be assessed, and hence improves one's understanding of the body's control mechanisms. One example which researchers have considered, is that of blood pressure control. In the authors' research, they have taken a published model for the control of blood pressure, discovered its limitations, and then improved the model so that it would more accurately predict actual clinical changes. (3 pages)Development of a knowledge-based simulator for haemodynamic support of septic shock
http://dl-live.theiet.org/content/conferences/10.1049/ic_19981093
The authors' previous work has demonstrated self-learning fuzzy control as a powerful, flexible and versatile control technique which adapts itself easily to changing patient conditions. It has never previously been applied to multiple input/output parameter controllers in medicine. The authors are investigating this technique for providing automated control of drug infusions supporting the cardiovascular and renal systems of patients in `septic shock'. To construct the control system the authors are using this stratagem: modelling the shocked patient; verification of the model; validation of the model; controller strategy development in simulation using the validated model; physical control system development; clinical trials. Here, the authors highlight their validation techniques. (4 pages)Autoregressive models in the estimation of respiratory impedance
http://dl-live.theiet.org/content/conferences/10.1049/ic_19970065
The work has focused on attempting to develop an alternative, more robust impedance estimate based on the use of parametric models. Autoregressive models of various order have been computed using Matlab<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">TM</sup> and initial results are presented and discussed. Typical model based estimates are shown. (4 pages)Model based investigation of cardiovascular variability
http://dl-live.theiet.org/content/conferences/10.1049/ic_19970064
It is shown that the effect of using different model based spectral estimation techniques is small compared to the overall variability in baroreflex sensitivity. (3 pages)Obstetrics and technology
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961024
Most of the technological developments in obstetrics have been focussed on improving access to and assessment of the fetus. The great majority of these developments have included ultrasound in one form or another. The five technologies in obstetrics upon which the author concentrates are: (1) real-time ultrasound imaging of the fetus; (2) antenatal fetal heart rate monitoring using Doppler ultrasound; (3) umbilical artery blood flow recording with Doppler ultrasound; (4) intrapartum fetal heart rate recording with either Doppler ultrasound or a scalp electrode; (5) intrapartum fetal electrocardiogram recording. (6 pages)Microfluidic instrumentation for microvascular research
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961012
We present an application of micromachined silicon microfluidic flow cells for the in-vitro measurement of blood flow at dimensions comparable to those of the physiological capillary system. In order to address these problems we have developed an instrument allying microengineering with real-time image processing and `mesofluidic' control systems. The work described is centered at the University of Hertfordshire but we wish to highlight the very important contributions being made by our colleagues at Imperial College, London and Technical University Chemnitz-Zwickau in Germany. (3 pages)Fluid flow in a neonatal respiratory support system: a preliminary investigation
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961038
The subject of this study is a neonatal ventilatory support system marketed as The Infant Flow System<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">TM</sup> by E.M.E. (Electro Medical Equipment) Ltd. in Brighton, England. The work described was carried out as a final year project during a three year mechanical engineering degree course at The University of Sussex. The Infant Flow System consists of two major components: the Infant Flow Driver and the Infant Flow Generator. For the purposes of this study, focus was on the latter. The NCPAP Generator applies a continuous positive airway pressure (CPAP) to the patient airway via the nose. This type of ventilatory support assists the inspiratory process and prevents alveolar collapse during expiration. Preterm infants suffering from a variety of respiratory disorders including respiratory distress syndrome, pulmonary oedema, airway closure diseases, paralysis of the diaphragm and tracheomalacia, have been successfully treated with the device. (2 pages)Point-of-care sensor technology for critical care applications
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961040
There is still a need for improvements in the way one measures blood flow. Cardiac output is a fundamental physiological parameter and one that changes rapidly in the patient i.e. it is suitable for attention as a point-of-care (POC) measurement. Its accurate measurement with thermodilution comes at a high cost both clinically and financially. An ideal system would be less invasive, quicker, more cost effective and ultimately continuous. It is the authors' feeling that an improved indicator dilution method provides the first step towards the development of a continuous cardiac output (CCO) system. This has been described. The second step is to critically evaluate the synergy of the lithium indicator dilution cardiac output (LiDCO) system with a number of potentially continuous technologies. Early research on such combination technology suggests that a CCO system may be developed from combining the LiDCO system with a continuous technology based on arterial pressure waveform analysis. (3 pages)Intelligent CPAP
http://dl-live.theiet.org/content/conferences/10.1049/ic_19951590
CPAP, or more properly Nasal Continuous Positive Airway Pressure (nCPAP) was first used to treat obstructive sleep apnoea (OSA) patients by Professor Colin Sullivan of Sydney, Australia in the late 70's. Here, the author looks at the development and utility of `automatic' or `intelligent' self pressure setting CPAP systems rather than to describe the design of the pump system and the feedback required to produce an acceptable pressure during inhalation without an accompanying expiratory pressure rise. These machines have the aim of adjusting the CPAP pressure to the needs of the patient at any particular time, to have a minimal wake pressure and a lower mean pressure, and also to be able to document the night-time respiratory events. This latter mode lends itself to use in `titration' in the sleep laboratory where what is required is a self adjusting device which adapts the pressure to that needed for the patient without necessarily having an overnight technician present. (2 pages)Ambulatory blood pressure recording; principles and practice
http://dl-live.theiet.org/content/conferences/10.1049/ic_19951383
Continuous intra-arterial blood pressure recording in ambulant subjects was initially developed in 1969. This involves the use of arterial cannulation and a perfusion unit with either data recording on magnetic tape or the use of biotelemetry. This technique produces a very large amount of accurate data (approximately 100,000 data points during a twenty-four hour period) but is invasive and is therefore not suitable for routine clinical use or the study of normal subjects. The major clinical use of ambulatory blood pressure recording is the investigation of patients with mild hypertension when it is not clear whether the degree of blood pressure elevation warrants treatment. In primary health care mild hypertension is common, whereas severe hypertension, where the decision to treat is easy, is relatively uncommon. Some patients exhibit “white coat hypertension” with persistently elevation blood pressure when measured in the clinic or doctors surgery, but a normal ambulatory blood pressure outside the hospital or clinical environment. These individuals have a good prognosis and may not require drug therapy. Ambulatory blood pressure monitoring may also be useful in the investigation of episodic or resistant hypertension and is also useful in the assessment of blood pressure treatment and drug trial evaluation. (2 pages)An intravascular ultrasound imaging system
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950774
The authors discusses the design of an intravascular ultrasound imaging system. In particular they consider the bus data rate requirement, the bus interface, the choice of processor-the ADSP 21060 is considered appropriate-and its multiprocessing features. (5 pages)A multiresolution approach to flow feature extraction from phase contrast magnetic resonance angiography
http://dl-live.theiet.org/content/conferences/10.1049/ic_19950507
The authors considered a multi-resolution, model based segmentation method for magnetic resonance angiography (MRA). It is a spatial domain based technique and an extension to 3D of a 2D curve segmentation method reported elsewhere. The method has been demonstrated to produce a concise symbolic description of the MRA data (in the form of vessel centre lines) and is efficient in its computational complexity being equivalent in processing to filtering by a 3×3×3 kernel, and based on a generalised and flexible image model which has great potential as a basis for both qualitative and quantitative assessment of MRA data. The work and results presented thus far are preliminary and currently there are several areas where consolidation and enhancement is necessary. There is a need to assess the levels of noise in the data in situ, to better control the confidence levels used for the hypothesis testing. Curve tracing is currently done probabilistically based purely on the local curvature. By considering the physical measurements of the data being imaged, e.g. speed of blood and the vessel diameters, local connectivity could be established using a conservation of mass constraint. Also, there is need to explicitly define bifurcations as part of the signal model. With regards to visualisation, some experimentation has already been carried out to represent flow direction and using the multiresolution vectors for generating filtered maximum intensity projections and predicting probable flow. The segmentation is also being applied to the estimation of blood pressure gradients in vivo. (6 pages)