Showing papers by "Panayiotis A. Kyriacou published in 2009"

Empirical mode decomposition (EMD) analysis of HRV data from locally anesthetized patients

Abstract: Spectral analysis of Heart Rate Variability (HRV) is used for the assessment of cardiovascular autonomic control. In this study data driven adaptive technique Empirical Mode Decomposition (EMD) and the associated Hilbert spectrum has been used to evaluate the effect of local anesthesia on HRV parameters in a group of fourteen patients undergoing brachial plexus block (local anesthesia) using transarterial technique. The confidence limit for the stopping criteria was establish and the S value that gave the smallest squared deviation from the mean was considered optimal. The normalized amplitude Hilbert spectrum was used to calculate the error index associated with the instantaneous frequency. The amplitude and the frequency values were corrected in the region where the error was higher than twice the standard deviation. The Intrinsic Mode Function (IMF) components were assigned to the Low Frequency (LF) and the High Frequency (HF) part of the signal by making use of the center frequency and the standard deviation spectral extension estimated from the marginal spectrum of the IMF components. The analysis procedure was validated with the help of a simulated signal which consisted of two components in the LF and the HF region of the HRV signal with varying amplitude and frequency. The optimal range of the stopping criterion was found to be between 4 and 9 for the HRV data. The statistical analysis showed that the LF/HF amplitude ratio decreased within an hour of the application of the brachial plexus block compared to the values at the start of the procedure. These changes were observed in thirteen of the fourteen patients included in this study.

Time-frequency analysis of HRV data from locally anesthetized patients

Abstract: Spectral analysis of Heart Rate Variability (HRV) can be used for the assessment of cardiovascular autonomic control. In this study Smoothed-Pseudo Wigner-Ville Distribution (SPWVD) has been used to evaluate the effect of local anesthesia on HRV parameters in a group of fourteen patients undergoing brachial plexus block (local anesthesia) using the transarterial technique. Instead of using the fixed boundaries of the LF (0.04–0.15 Hz) and the HF (0.15–0.4 Hz) components, the center frequency and the standard deviation spectral extension was used to estimate the boundaries related to the two components of the HRV signal. The boundaries related to the HF component of the signal were estimated using the cross-spectrum between the HRV signal and the respiration signal. The LF component boundaries were estimated directly from the time-frequency representation of the HRV signal. The statistical analysis showed that the LF/HF amplitude ratio decreased within an hour of the application of the brachial plexus block compared to the values at the start of the procedure. These changes were observed in eleven of the fourteen patients included in this study.

Investigation of photoplethysmographic changes using a static compression model of spinal cord injury

Abstract: Little is known about cell death in spinal cord tissue following compression injury, despite compression being a key component of spinal injuries. Currently models are used to mimic compression injury in animals and the effects of the compression evaluated by observing the extent and duration of recovery of normal motor function in the days and weeks following the injury. A fiber-optic photoplethysmography system was used to investigate whether pulsation of the small arteries in the spinal cord occurred before, during and after compressive loads were applied to the tissue. It was found that the signal amplitudes were reduced and this reduction persisted for at least five minutes after the compression ceased. It is hoped that results from this preliminary study may improve knowledge of the mechanism of spinal cord injury.

A novel non-invasive trans-reflectance photoplethysmographic probe for use in cases of low peripheral blood perfusion

Abstract: The acquisition of reliable and meaningful photo-plethysmographic (PPG) signals using conventional pulse oxime-try technology may be compromised by conditions of low tissue perfusion. We have developed a novel ‘trans-reflectance’ PPG measurement system which combines reflectance and transmit-tance together into a single mode. For comparison purposes the system also enables the independent display of reflectance and transmittance PPG signals simultaneously. Preliminary experiments were performed on volunteers to assess the performance of the probe, where, artificial hypoperfusion was created in individuals and data was recorded with the newly developed trans-reflectance photoplethysmographic mode, and the conventional transmittance and reflectance PPG modes. The PPG signals recorded during hypoperfusion using the trans-reflectance mode were of good quality with higher signal-to-noise ratio than those obtained from the transmittance and reflectance modes.

MyCare Card development: the patient held electronic health record device

Abstract: In the UK, in emergency situations, health professionals rely on patients to provide information about their medical history. However, in some cases patients may not remember their medication, long term illnesses or allergies, or be able to communicate this information. As a national on-line integrated patient record system has not yet been established, this paper introduces an on-going project ‘MyCare Card’ abbreviated as MyC2 which aims to design and implement a patient held electronic health record device and corresponding user interface software.

Evaluation of a fiber-optic esophageal pulse oximeter

Abstract: A dual-wavelength fiber-optic pulse oximetry system was developed for the purposes of estimating oxygen saturation from the esophagus. A probe containing miniature right-angled glass prisms was used to record photoplethysmographic (PPG) signals from the esophageal wall. Signals were recorded successfully in 19 of 20 patients, demonstrating that PPG signals could be reliably obtained from an internal vascularized tissue site such as the esophageal epithelium. The value of the mean oxygen saturation recorded from the esophagus was 94.0 ± 4.0%. These results demonstrate that SpO 2 may be estimated in the esophagus using a fiber-optic probe and this may be the first report of such measurements.

Establishing user requirements for a patient held electronic record system in the United Kingdom

Abstract: In the UK, in emergency situations, health professionals rely on patients to provide information about their medical history. However, in some cases patients may not remember their medication, long term illnesses or allergies, or be able to communicate this information. As a national on-line integrated patient record system has not yet been etablished, a patient held electronic health record has been proposed. This paper summarizes the results of a survey to establish the public’s and health care professionals` requirements for such a system.

An oesophageal pulse oximetry system utilising a fibre-optic probe

Abstract: A dual-wavelength fibre-optic pulse oximetry system is described for the purposes of estimating oxygen saturation (SpO2) from the oesophagus. A probe containing miniature right-angled glass prisms was used to record photoplethysmographic (PPG) signals from the oesophageal wall. Signals were recorded successfully in 19 of 20 patients, demonstrating that PPG signals could be reliably obtained from an internal vascularised tissue site such as the oesophageal epithelium. The value of the mean oxygen saturation recorded from the oesophagus was 94.0 ± 4.0%. These results demonstrate that SpO2 may be estimated in the oesophagus using a fibre-optic probe.

Measurements of cerebral arterial oxygen saturation using a fiber-optic pulse oximeter

Abstract: This pilot investigation was undertaken to assess the performance of a novel fiber-optic cerebral pulse oximetry system. A fiber-optic probe designed to pass through the lumen of a cranial bolt of the type used to make intracranial pressure measurements was used to obtain optical reflectance signals directly from the brain tissue. Preliminary results from seven patients measured in the operating theatre and ITU are presented. Estimations of cerebral arterial oxygen saturation derived from a frequency domain-based algorithm are compared with pulse oximetry (SpO 2 ) and hemoximeter (SaO 2 ) blood samples. The mean (±SD) difference between cerebral oxygen saturation (ScaO 2 ) and finger SpO 2 (in saturation units) was -7.47(±3.4)%. The mean (±SD) difference between ScaO 2 and blood SaO 2 was -7.37(±2.8)%.

Photoplethysmographic signals recorded from human abdominal organs using a fibreoptic probe

Abstract: Copyright & reuse City University London has developed City Research Online so that its users may access the research outputs of City University London's staff. Copyright © and Moral Rights for this paper are retained by the individual author(s) and/ or other copyright holders. All material in City Research Online is checked for eligibility for copyright before being made available in the live archive. URLs from City Research Online may be freely distributed and linked to from other web pages.

In-Vivo evaluation of a fiber-optic splanchnic photoplethysmographic sensor during open laparotomy

Abstract: There is a need for a reliable and continuous monitoring of abdominal organ oxygen saturation (SpO 2 ). Splanchnic ischemia may ultimately lead to cellular hypoxia and necrosis and may well contribute to the development of multiple organ failures and increased mortality. A new prototype reflectance fiber optic photoplethysmographic sensor and signal processing system was evaluated on six anaesthetized patients undergoing elective laparotomy. PPG signals were obtained from various organs, including large and small bowel, liver, and stomach. The normalized amplitudes of the splanchnic PPG signals were in good agreement with those obtained from the periphery using an identical fiber optic sensor. Furthermore, average SpO 2 values were in good agreement and showed correlation with those obtained from a commercial system. These preliminary results suggest that a miniaturized ‘indwelling’ fiber optic sensor may be a suitable method for pre-operative and post-operative evaluation of splanchnic organ SpO 2 and their health.

Public requirements for patient-held records

Abstract: Electronic patient-held record devices enable people to carry around information about their health. They need to be easily accessed in emergency situations and should provide enough information to enable front line staff to deliver effective care. Although it has been suggested that patients taking responsibility for their records could improve patient safety, little is known about attitudes towards this. In taking a user centred approach to the development of such a system, surveys were conducted with the public and health professionals. The survey of 258 members of the public showed that 85 thought patient-held records would be useful. The types of information that most people wanted to carry were name, allergies, long term conditions, current medication and blood group. A smart card design was preferred by 62 of the participants and 68 thought it should be provided free of charge.

Investigation of the in-vitro loading on an artificial spinal disk prosthesis

Abstract: Spinal diseases imposes considerable burden to both patients and society. In recent years, much surgical efforts have been made in advancing the treatment of neck and back pain. Of particular prominence is the increasing clinical acceptance and use of intervertebral artificial disk prosthesis for the treatment of discogenic back pain. Despite this increased use of such disks, their in-vivo monitoring remains rudimentary. In an effort to develop an intelligent artificial spinal disk where the in-vivo loading of the spine can by studied for the first time an experimental set up has been created in order to initially study the in-vitro loading on an artificial disc prosthesis. Eight strain gauges and two piezoresistive sensors were used and placed suitably in the artificial disk prosthesis. The results from the in-vitro loading showed linear relationship between loading and the outputs from the sensors with good repeatability and less hysteresis.

Penetration of high intensity focused ultrasound ex vivo and in vivo rabbit brain using MR imaging

Abstract: In this paper magnetic resonance imaging (MRI) is investigated for monitoring the penetration of high intensity focused ultrasound (HIFU) ex vivo and in vivo rabbit brain. A single element spherically focused transducer of 5 cm diameter, focusing at 10 cm and operating at 2 MHz was used. A prototype MRI- compatible positioning device is described. MRI images were taken using fast spin echo (FSE). The length of the lesions in vivo rabbit brain was much higher than the length ex vivo, proving that the penetration in the ex vivo brain is limited by reflection due to trapped bubbles in the blood vessels.

Photoplethysmographic signals from human splanchnic organs using a new fibre-optic sensor

Abstract: Copyright & reuse City University London has developed City Research Online so that its users may access the research outputs of City University London's staff. Copyright © and Moral Rights for this paper are retained by the individual author(s) and/ or other copyright holders. All material in City Research Online is checked for eligibility for copyright before being made available in the live archive. URLs from City Research Online may be freely distributed and linked to from other web pages.

Development and evaluation of a photometric fibre-optic sensor for monitoring abdominal organ photoplethysmographs and blood oxygen saturation

Abstract: A two wavelength photometric fibre-optic reflectance sensor was developed for assessing abdominal organ perfusion. In vitro tests showed that reliable photoplethysmographic (PPG) signals and blood oxygen saturation (SpO2) values were recorded when the separation between emitting and receiving fibres was at 3mm and the emitting current was between 20mA-40mA. In a clinical study, good quality PPG signals were obtained from the small and large bowel of a patient undergoing laparotomy. Abdominal organ SpO2 were in good agreement with those obtained from a commercial device. These observations suggest that the fibre-optic sensor may be suitable for monitoring abdominal organ perfusion.