5,200 research outputs found
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Evaluation of oesophageal pulse oximetry in patients undergoing cardiothoracic surgery
Pulse oximetry probes placed peripherally may fail to give accurate values of blood oxygen saturation when the peripheral circulation is poor. Because central blood flow may be preferentially preserved, we investigated the oesophagus as an alternative monitoring site. A reflectance blood oxygen saturation probe was developed and evaluated in 49 patients undergoing cardiothoracic surgery. The oesophageal pulse oximeter results were in good agreement with oxygen saturation measurements obtained by a blood gas analyser, a CO-oximeter and a commercial finger pulse oximeter. The median (IQR [range]) difference between the oesophageal oxygen saturation results and those from blood gas analysis were 0.00 (-0.30 to 0.30 [-4.47 to 2.60]), and between the oesophageal oxygen saturation results and those from CO-oximetry were 0.75 (0.30 to 1.20 [-1.80 to 1.80]). Bland-Altman analysis showed that the bias and the limits of agreement between the oesophageal and finger pulse oximeters were -0.3% and -3.3 to 2.7%, respectively. In five (10.2%) patients, the finger pulse oximeter failed for at least 10 min, whereas the oesophageal readings remained reliable. The results suggest that the oesophagus may be used as an alternative monitoring site for pulse oximetry even in patients with compromised peripheral perfusion
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An oesophageal pulse oximetry system utilising a fibre-optic probe
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
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Assessment of photoplethysmographic signals for the determination of splanchnic oxygen saturation in humans
The need for a clinically applicable method of detecting splanchnic hypoxia has led to experimental animal studies which indicated the usefulness of intestinal pulse oximetry. Pulse oximetry relies on detection of photoplethysmographic signals. Before developing a pulse oximeter for the measurement of organ oxygen saturation peri-operatively, we designed a system based on a reflectance photoplethysmographic probe to investigate photoplethysmographic signals from human viscera (bowel, liver, and kidney). Recordings were obtained simultaneously from the abdominal viscera and the finger using identical probes. The probe was held sequentially for up to 2 min on the surface of viscera of 12 patients during routine laparotomy. Measurable splanchnic photoplethysmographic signals were recorded for the first time in humans. There were no statistically significant differences between photoplethysmographic amplitudes from viscera and those from the finger. Our results indicate the feasibility of pulse oximetry for the measurement of visceral oxygenation in humans
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Optimization of Tetrapolar Impedance Electrodes in Microfluidic Devices for Point of Care Diagnostics using Finite Element Modeling
Electrophoresis is widely applied in the field of biochemistry and molecular biology. Tetrapolar electrical impedance sensing (TEIS) has been shown capable of replacing the conventional detection technology in order to develop a point of care electrophoretic analyzer. Besides the advantages of reduced influence of electrode polarization, TEIS is affected by sensitivity distribution depending on the electrode design. A well reported practice outside of electrophoresis, systematic investigation of the effects of sensitivity distribution on the TEIS in microfluidic devices has not been conducted. Here we utilize finite element modeling, backed by experimental results, to optimize the sensor design within an electrophoretic separation device. Numerous sensor designs were validated regarding detectability, sensitivity and spatial resolution. The results show, that minimizing the distance between the central/pick-up electrodes increases sensitivity and spatial resolution whereas the distance between the central electrodes and the outer electrode do not influence sensitivity and spatial resolution
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Measuring venous oxygenation using the photoplethysmograph waveform
OBJECTIVE: We investigate the hypothesis that the photoplethysmograph (PPG) waveform can be analyzed to infer regional venous oxygen saturation.
METHODS: Fundamental to the successful isolation of the venous saturation is the identification of PPG characteristics that are unique to the peripheral venous system. Two such characteristics have been identified. First, the peripheral venous waveform tends to reflect atrial contraction. Second, ventilation tends to move venous blood preferentially due to the low pressure and high compliance of the venous system. Red (660 nm) and IR (940 nm) PPG waveforms were collected from 10 cardiac surgery patients using an esophageal PPG probe. These waveforms were analyzed using algorithms written in Mathematica. Four time-domain saturation algorithms (ArtSat, VenSat, ArtInstSat, VenInstSat) and four frequency-domain saturation algorithms (RespDC, RespAC, Cardiac, and Harmonic) were applied to the data set.
RESULTS: Three of the algorithms for calculating venous saturation (VenSat, VenInstSat, and RespDC) demonstrate significant difference from ArtSat (the conventional time-domain algorithm for measuring arterial saturation) using the Wilcoxon signed-rank test with Bonferroni correction (p < 0.0071).
CONCLUSIONS: This work introduces new algorithms for PPG analysis. Three algorithms (VenSat, VenInstSat, and RespDC) succeed in detecting lower saturation blood. The next step is to confirm the accuracy of the measurement by comparing them to a gold standard (i.e., venous blood gas)
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Measuring Venous Oxygen Saturation Using the Photoplethysmograph Waveform
The pulse oximeter is now a standard-of-care monitor. In its most basic form it measures the arterial oxygenation saturation. It accomplishes this through the use of the photoplethysmograph waveform (PPG) at two or more wavelengths. Advances in digital signal processing are allowing for a re-examination of these waveforms. It has been recognized for some time that the movement of venous blood can be detected (1, 2) using the PPG. For the most part, this phenomenon has been seen as a source of artifact which interferes with calculation of arterial saturation. On the other hand, if venous saturation can be reliably measured, interesting new possibilities are opened. We hypothesize that the PPG waveform, obtained non-invasively by modern pulse oximeters, can be analyzed via digital signal processing to infer the venous oxygen saturation
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Calculation of Photon Path Changes due to Scatter in Monte Carlo Simulations
Computation using Monte Carlo simulations is widely used for modelling the light-tissue interaction. Despite this, many of the methods used for building such simulations are poorly described in the literature. In particular, a scheme for translating the scatter angles produced from a phase function into updated photon direction vectors is not explicitly reported. To address this, a method for calculating the change in photon direction following a scattering event is described, thus illuminating one of the fundamental `building blocks' for researchers developing their own Monte Carlo models. The equations derived in this paper may be readily incorporated into applicable Monte Carlo program code
Use of Transient Time Response as a Measure to Characterize Phononic Crystal Sensors
Phononic crystals are periodic composite structures with specific resonant features that are gaining popularity in the field as liquid sensors. The introduction of a structural defect in an otherwise periodic regular arrangement can generate a resonant mode, also called defect mode, inside the characteristic band gaps of phononic crystals. The morphology, as well as the frequency in which these defect modes appear, can give useful information on the composition and properties of an analyte. Currently, only gain and frequency measurements are performed using phononic crystal sensors. Other measurements like the transient response have been implemented in resonant sensors such as quartz microbalances showing great results and proving to be a great complimentary measure to the gain and frequency measurements. In the present paper, a study of the feasibility of using the transient response as a measure to acquire additional information about the analyte is presented. Theoretical studies using the transmission line model were realized to show the impact of variations in the concentration of an analyte, in this case, lithium carbonate solutions, in the transient time of the system. Experimental realizations were also performed showing that the proposed measurement scheme presents significant changes in the resulting data, indicating the potential use of this measure in phononic crystal sensors. This proposed measure could be implemented as a stand-alone measure or as a compliment to current sensing modalities
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Esophageal pulse oximetry utilizing reflectance photoplethysmography
Peripheral perfusion is often poor and barely pulsatile in patients undergoing prolonged major surgery. Hence, the arterial blood oxygen saturation (SpO2) readings from commercial finger pulse oximeters can become unreliable or cease when they are most needed. To overcome this limitation, the esophagus has been investigated as an alternative measurement site, as perfusion may be preferentially preserved centrally. A reflectance esophageal pulse oximeter probe, and a processing system implemented in LabVIEW were developed. The system was evaluated in clinical measurements on 49 cardiothoracic surgery patients. The SpO2 values from the esophagus were in good agreement with arterial blood oxygen saturation (SaO2) values obtained from blood gas analysis and CO-oximetry. The means (+/-SD) of the differences between the esophageal SpO2 and SaO2 results from blood gas analysis and CO-oximetry were 0.02 +/- 0.88% and -0.73 +/- 0.72%, respectively. In five (10.2%) of the patients, the finger pulse oximeter failed for at least 10 min while the esophageal SpO2 readings remained reliable. The results confirm that the esophagus may be used as an alternative monitoring site for pulse oximetry even in patients with compromised peripheral perfusion
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Investigation of photoplethysmographic signals in the human oesophagus
The continuous monitoring of blood oxygen saturation in patients with compromised peripheral perfusion is often difficult or impossible, since conventional non-invasive techniques such as pulse oximetry fail. Measurements of oxygen saturation are unreliable when patients are peripherally cool with low cardiac output and poor peripheral circulation. These clinical situations commonly occur after major surgery including cardiopulmonary bypass. We suggest that the above difficulties might be overcome if the sensor were to monitor a more central part of the body. It is proposed to use the oesophagus as measurement site and reflection techniques on the hypothesis that this site should be better perfused. A new probe was constructed utilising miniaturised opto-electronic devices designed to fit into a transparent oesophageal stomach tube. One infrared wavelength was used in this study at 880 nm and a circuit to analyse the photoplethysmograph (PPG) signal was developed. The output PPG signals were sampled and recorded by a data acquisition system and a laptop personal computer. Initial measurements were carried out to investigate the amplitude of the pulsatile signal in the oesophagus and preliminary results are presented
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