30 research outputs found
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Filtering techniques for the removal of ventilator artefact in oesophageal pulse oximetry
The oesophagus has been shown to be a reliable site for monitoring blood oxygen saturation (SpO2). However, the photoplethysmographic (PPG) signals from the lower oesophagus are frequently contaminated by a ventilator artefact making the estimation of SpO2 impossible. A 776th order finite impulse response (FIR) filter and a 695th order interpolated finite impulse response (IFIR) filter were implemented to suppress the artefact. Both filters attenuated the ventilator artefact satisfactorily without distorting the morphology of the PPG when processing recorded data from ten cardiopulmonary bypass patients. The IFIR filter was the better since it conformed more closely to the desired filter specifications and allowed real-time processing. The average improvements in signal-to-noise ratio (SNR) achieved by the FIR and IFIR filters for the fundamental component of the red PPG signals with respect to the fundamental component of the artefact were 57.96 and 60.60 dB, respectively. The corresponding average improvements achieved by the FIR and IFIR filters for the infrared PPG signals were 54.83 and 60.96 dB, respectively. Both filters were also compared with their equivalent tenth order Butterworth filters. The average SNR improvements for the FIR and IFIR filters were significantly higher than those for the Butterworth filters
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Venous pooling and drainage affects photoplethysmographic signals at different vertical hand positions
The aim of the current work is to investigate the possibility of augmenting pulse oximetry algorithms to enable the estimation of venous parameters in peripheral tissues. In order to further understand the contribution of venous blood to the photoplethysmographic (PPG) signal, recordings were made from six healthy volunteer subjects during an exercise in which the right hand was placed in various positions above and below heart level. The left hand was kept at heart level as a control while the right hand was moved. A custom-made two-channel dual wavelength PPG instrumentation system was used to obtain the red and infrared plethysmographic signals from both the right and left index fingers simultaneously using identical sensors. Laser Doppler flowmetry signals were also recorded from an adjacent fingertip on the right hand. Analysis of all acquired PPG signals indicated changes in both ac and dc amplitude of the right hand when the position was changed, while those obtained from the left (control) hand remained relatively constant. Most clearly, in the change from heart level to 50cm below heart level there is a substantial decrease in both dc and ac amplitudes. This decrease in dc amplitude most likely corresponds to increased venous pooling, and hence increased absorption of light. It is speculated that the decrease in ac PPG amplitude is due to reduced arterial emptying during diastole due to increased downstream resistance due to venous pooling
Clinical evaluation of a new optical fibre method of measuring oxygen saturation using photoplethysmograph signals reflected from internal tissues
MD (Res)Traditional methods of measuring oxygen saturation, e.g. pulse oximetry, depend on
an adequate peripheral circulation and have a 20–30 second lag time before readings
are obtained. This was a series of evaluations of novel optical probes, designed to
measure oxygen saturation using fibreoptic technology directly from internal organs
including the brain, oesophagus and organs with splanchnic circulations. A series of
pilot studies were proposed and research ethics approval obtained to carry out
studies in humans, under general anaesthesia, using these probes. Innovative
reflectance probes were designed specifically for each of the four applications, so as
to obtain potentially useful signals needed for signal processing, analysis and
evaluation.
Signals were successfully obtained from the brain, oesophagus and splanchnic region
in almost all of the patients recruited. Good quality photoplethysmograph signals
were recorded and these were translated into clinically meaningful values of oxygen
saturation comparable to traditional methods of pulse oximetry. Overall, the signals
were prone to movement artefacts as well as occasional interference from surgical
diathermy and other sources. Nonetheless, the probes could prove to be a useful
alternative to conventional external transmittance pulse oximetry methods as well as
providing useful information regarding regional perfusion and oxygenation. The
success of these pilot studies will form the basis of more research in the area and
further development of such probes on the medical engineering front
FotopletismografÃa laparoscópica: Nueva técnica mÃnimamente invasiva y estudios experimentales iniciales
In the endoscopic procedures there is not possible to use the sense of touch for the detection of weak palpitations as in open surgery, neither to directly evaluate the oxygenation and perfusion of intra-corporeal organs and tissues. Here, we present the initial results after the application of laparoscopic photoplethysmography, a novel technique developed by our group, which allows obtaining specific clinical parameters and overcome the cited drawbacks. From the photoplethysmograpic signals of different wavelengths recorded in intra-abdominal organs and territories of animal models, their pulse values and oxygenation related quotients have been derived. © Sociedad Española de Óptica.Este trabajo ha sido financiado por el proyecto PI 04/0715 del Fondo de Investigaciones Sanitarias. Agradecemos la colaboración prestada durante el estudio experimental por Dr. José Carlos Manuel Palazuelos, Dr. Juan Carlos González Cueli y las diplomadas en EnfermerÃa del CENDOS. Parte de los resultados aquà expuestos han sido presentados oralmente en el Congreso de la Sociedad Española de Laparoscopia (SECLA 2009) celebrado en Santander en mayo de 2009. SMLS está contratada por el Programa I3P con financiación del Fondo Social Europeo.Peer Reviewe
On the development of intelligent medical systems for pre-operative anaesthesia assessment
This thesis describes the research and development of a decision support tool for determining a medical patient's suitability for surgical anaesthesia. At present, there is a change in the way that patients are clinically assessedp rior to surgery. The pre-operative assessment, usually conducted by a qualified anaesthetist, is being more frequently performed by nursing grade staff. The pre-operative assessmenet xists to minimise the risk of surgical complications for the patient. Nursing grade staff are often not as experienced as qualified anaesthetists, and thus are not as well suited to the role of performing the pre-operative assessment. This research project used data collected during pre-operative assessments to develop a decision support tool that would assist the nurse (or anaesthetist) in determining whether a patient is suitable for surgical anaesthesia. The three main objectives are: firstly, to research and develop an automated intelligent systems technique for classifying heart and lung sounds and hence identifying cardio-respiratory pathology. Secondly, to research and develop an automated intelligent systems technique for assessing the patient's blood oxygen level and pulse waveform. Finally, to develop a decision support tool that would combine the assessmentsa bove in forming a decision as to whether the patient is suitable for surgical anaesthesia. Clinical data were collected from hospital outpatient departments and recorded alongside the diagnoses made by a qualified anaesthetist. Heart and lung sounds were collected using an electronic stethoscope. Using this data two ensembles of artificial neural networks were trained to classify the different heart and lung sounds into different pathology groups. Classification accuracies up to 99.77% for the heart sounds, and 100% for the lung sounds has been obtained. Oxygen saturation and pulse waveform measurements were recorded using a pulse oximeter. Using this data an artificial neural network was trained to discriminate between normal and abnormal pulse waveforms. A discrimination accuracy of 98% has been obtained from the system. A fuzzy inference system was generated to classify the patient's blood oxygen level as being either an inhibiting or non-inhibiting factor in their suitability for surgical anaesthesia. When tested the system successfully classified 100% of the test dataset. A decision support tool, applying the genetic programming evolutionary technique to a fuzzy classification system was created. The decision support tool combined the results from the heart sound, lung sound and pulse oximetry classifiers in determining whether a patient was suitable for surgical anaesthesia. The evolved fuzzy system attained a classification accuracy of 91.79%. The principal conclusion from this thesis is that intelligent systems, such as artificial neural networks, genetic programming, and fuzzy inference systems, can be successfully applied to the creation of medical decision support tools.EThOS - Electronic Theses Online ServiceMedicdirect.co.uk Ltd.GBUnited Kingdo
A proof of concept study of respiratory physiology in preterm neonates during high flow nasal cannula therapy
PhD ThesisIntroduction and rationale: High flow nasal cannula therapy is being increasingly used as a
form of respiratory support across the world. Its adoption and popularity have been rapid but
little is known regarding its key mechanism of action even after more than a decade of its use.
I conducted a proof of concept study of respiratory physiology during high flow therapy in
preterm neonates.
Methods: The study protocol involved measurement of nasopharyngeal airway pressures and
gas concentrations as well as measurement of tidal breathing indices. A detailed descriptive
review of clinical efficacy of high flow nasal cannula in preterm infants was performed. In
order to identify the optimum measuring techniques, in this proof of concept study, three
types of pressure measuring techniques, a gas analyser device and a non-invasive tidal
breathing indices device were studied and the results are presented in this thesis. In addition, a
detailed protocol for a larger randomised crossover study of respiratory physiology during
continuous positive airway pressure of 6 cm H2O and high flow nasal cannula therapy ranging
from 2-8 litres per minute flow was designed..
Results: In this thesis, the results of a proof of concept physiological study have been
presented. The results of the measurements performed in six babies of varying gestational age
(less than 37 weeks of gestation) and birth weight are presented. Valid tidal volumes were
measured in all babies, nasopharyngeal gas concentrations and pressure measurements in five
and two babies respectively. There were no adverse events.
Conclusions: It is feasible to measure nasopharyngeal air way pressures and gas
concentrations as well as non-invasive tidal breathing indices in babies on high flow nasal
cannula therapy safely. This study was successfully followed up by a larger randomised cross
over study involving 45 infants with the same protocol.Special Trustees at Newcastle Hospital
Multimodal Signal Processing for Diagnosis of Cardiorespiratory Disorders
This thesis addresses the use of multimodal signal processing to develop algorithms for the automated processing of two cardiorespiratory disorders. The aim of the first application of this thesis was to reduce false alarm rate in an intensive care unit. The goal was to detect five critical arrhythmias using processing of multimodal signals including photoplethysmography, arterial blood pressure, Lead II and augmented right arm electrocardiogram (ECG). A hierarchical approach was used to process the signals as well as a custom signal processing technique for each arrhythmia type. Sleep disorders are a prevalent health issue, currently costly and inconvenient to diagnose, as they normally require an overnight hospital stay by the patient. In the second application of this project, we designed automated signal processing algorithms for the diagnosis of sleep apnoea with a main focus on the ECG signal processing. We estimated the ECG-derived respiratory (EDR) signal using different methods: QRS-complex area, principal component analysis (PCA) and kernel PCA. We proposed two algorithms (segmented PCA and approximated PCA) for EDR estimation to enable applying the PCA method to overnight recordings and rectify the computational issues and memory requirement. We compared the EDR information against the chest respiratory effort signals. The performance was evaluated using three automated machine learning algorithms of linear discriminant analysis (LDA), extreme learning machine (ELM) and support vector machine (SVM) on two databases: the MIT PhysioNet database and the St. Vincent’s database. The results showed that the QRS area method for EDR estimation combined with the LDA classifier was the highest performing method and the EDR signals contain respiratory information useful for discriminating sleep apnoea. As a final step, heart rate variability (HRV) and cardiopulmonary coupling (CPC) features were extracted and combined with the EDR features and temporal optimisation techniques were applied. The cross-validation results of the minute-by-minute apnoea classification achieved an accuracy of 89%, a sensitivity of 90%, a specificity of 88%, and an AUC of 0.95 which is comparable to the best results reported in the literature
Respiratory physiotherapy in intensive care.
by Alice Yee-men Jones (Nee Ho).Thesis (M.Phil.)--Chinese University of Hong Kong, 1992.Includes bibliographical references (leaves [196]-221).Abstract --- p.iPublications --- p.iiiAcknowledgement --- p.vChapter SECTION I --- INTRODUCTIONChapter Chapter 1 --- General Introduction --- p.1Chapter 1.1 --- ObjectivesChapter 1.2 --- History & Advances in Chest PhysiotherapyChapter 1.3 --- Problems of Chest Physiotherapy ResearchChapter 1.4 --- Plan of workChapter Chapter 2 --- Previous Studies in Chest Physiotherapy --- p.15Chapter 2.1 --- Chest Physiotherapy and oxygenationChapter 2.2 --- Chest Physiotherapy and sputum clearanceChapter 2.3 --- Chest Physiotherapy and lung functionChapter Chapter 3 --- "Chest Physiotherapy Practice in ICUs in Australia, the UK and Hong Kong" --- p.34Chapter SECTION II --- METHODSChapter Chapter 4 --- Measurement of Oxygenation --- p.55Chapter 4.1 --- Measurement of arterial oxygenationChapter 4.2 --- Indirect measurement of arterial oxygenationChapter Chapter 5 --- Respiratory Function Analysis --- p.66Chapter 5.1 --- Spirometry measurementChapter 5.2 --- Measurement of lung mechanicsChapter Chapter 6 --- Transcutaneous Electrical Nerve Stimulation --- p.74Chapter SECTION III --- RESPIRATORY PHYSIOTHERAPY TECHNIQUESChapter Chapter 7 --- Effects of Percussion and Bagging on Static Lung Compliance --- p.80Chapter Chapter 8 --- Peak Expiratory Flow from two Breathing Circuits --- p.106Chapter Chapter 9 --- Peak Expiratory Flow in Tracheal Intubated Patients --- p.127Chapter SECTION IV --- PHYSIOTHERAPY AND PAIN MANA GEMENT IN ICU PATIENTSChapter Chapter 10 --- Transcutaneous Electrical Nerve Stimulation (TENS) following Thoracotomy --- p.142Chapter Chapter 11 --- TENS following Cholecystectomy --- p.154Chapter Chapter 12 --- TENS and Entonox --- p.167Chapter SECTION V --- SUMMARY AND CONCLUSIONSChapter Chapter 13 --- Summary --- p.185Chapter Chapter 14 --- Conclusion --- p.194Chapter SECTION VI --- REFERENCES --- p.197Chapter SECTION VII --- APPENDICES --- p.22
Non-invasive measurement of respiratory mechanics and work of breathing
The mechanical properties of the respiratory system such as resistance, elastance and mechanical work of breathing are rarely measured directly but are inferred from the effect of respiratory disease on maximal lung volumes and flows. Although such tests have proved very useful, they have shortcomings, e.g. changes in lung volumes are poor at detecting progression in interstitial lung disease and correlate only weakly with changes in functional capacity achieved post-bronchodilator in patients with airways obstruction.
The direct measurement of mechanical properties is of interest as they have an obvious physical interpretation but their usefulness has as yet not been systematically tested. Resistance aside, their measurement is rarely performed as it is invasive, requiring either a sedated patient on controlled ventilation to abolish spontaneous respiratory muscle activity or measurement of oesophageal and gastric pressures.
The aim of this thesis was to explore the feasibility and potential clinical value of non-invasive measurements of respiratory mechanics and work of breathing. The work is presented in three sections. Firstly, conventional methods for measuring resistance, elastance and mechanical work of breathing were reviewed and the methods for the non-invasive approaches to be used were described in detail. The results from the non-invasive methods were then validated by comparison with conventional techniques in both ventilated patients and in subjects in the pulmonary function laboratory where oesophagal and gastric manometry were performed. Finally, the non-invasive methods were evaluated in three clinical scenarios: bronchodilator reversibility testing, assessment of progression in interstitial lung disease, and monitoring recovery from exacerbation of chronic obstructive pulmonary disease