9 research outputs found
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Development of an Optoelectronic Sensor for the Investigation of Photoplethysmographic Signals from the Anterior Fontanel of the Newborn
There is a need for more reliable, non-invasive and alternative measurement sites for the monitoring of arterial blood oxygen saturation in critically ill newborns at times of peripheral compromise. The anterior fontanelle, a unique anatomical feature of the newborn, has been presented as an alternative site for the estimation of oxygen saturation. A multi-wavelength non-invasive optoelectronic sensor has been designed and developed for the investigation of photoplethysmographic (PPG) signals and blood oxygen saturation values from the fontanelle. In vivo thermal tests of the optical sensor show that under normal operating conditions the heating at the skin surface was negligible (<0.1°C). Good quality PPGs with large amplitudes and high signal to noise ratio were recorded at all three (red, infrared and green) wavelengths prior to clinical measurements
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Photoplethysmographic and SpO2 readings from the neonatal anterior fontanelle: a case study
There is a need for a more reliable, noninvasive and alternative measurement site for the monitoring of arterial blood oxygen saturation in critically ill neonates when peripheral perfusion is poor. The anterior fontanelle, a unique anatomical feature of the neonate, has been presented as an alternative site for the estimation of arterial blood oxygen saturation (SpO2). A new fontanelle photoplethysmographic sensor and processing system has been developed to investigate fontanelle photoplethysmographic (PPG) signals and estimate SpO2 values at this anatomical location. Preliminary clinical trials have shown that good quality PPG signals with large amplitudes and high signal to noise ratio can be obtained from the neonatal fontanelle. The estimation of SpO2 values from the fontanelle were in broad agreement with a commercial foot pulse oximeter
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Pilot investigation of anterior fontanelle photoplethysmographic signals and their suitability in estimating arterial oxygen saturation
There is a need for more reliable, non-invasive and alternative measurement sites for the monitoring of arterial blood oxygen saturation in critically ill newborns at times of peripheral compromise. A pilot investigation on 14 Intensive Care Unit (ICU) newborns was conducted utilizing custom-made reflectance photoplethysmographic (PPG) sensors placed at the fontanelle and foot. The results suggest that the fontanelle is sensitive to changes in saturation, where saturation values obtained from the custom sensor were compared against commercial pulse oximeter values and results from a blood gas analyzer, however careful placement of the sensor at the fontanelle is an issue that needs further investigation
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Esophageal SpO2 measurements from a pediatric burns-patient: A case study
Pulse oximetry is being used in everyday clinical practice in anesthesia utilizing peripheral saturation sensors. However, it may be unreliable in certain clinical situations such as peripheral hypoperfusion. Similar situations occur in burns patients and more importantly burns to extremities which limit the sites available for measurement of peripheral oxygen saturation (SpO2). To overcome these limitations, the esophagus has been investigated as an alternative measurement site, as perfusion may be preferentially preserved centrally. A miniaturized reflectance esophageal saturation (SpO2 probe has been constructed utilizing infrared and red photodiodes and a photodetector. Our case study was aimed at evaluating the reliability of esophageal pulse oximetry in a major burns infant. Measurable photoplethysmographic (PPG) traces and SpO2 values were obtained in the neonatal esophagus. It was found that the esophageal pulse oximeter results were in good agreement with oxygen saturation measurements obtained by a commercial ear lobe pulse oximeter. This study suggests that the esophagus can be used as an alternative site for monitoring arterial blood oxygen saturation by pulse oximetry in burned infants
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A Novel Photoplethysmography Sensor for Vital Signs Monitoring from the Human Trachea
Current pulse oximeter sensors can be challenged in working accurately and continuously in situations of reduced periphery perfusion, especially among anaesthetised patients. A novel tracheal photoplethysmography (PPG) sensor has been developed in an effort to address the limitations of current pulse oximeters. The sensor has been designed to estimate oxygen saturation (SpO2) and pulse rate, and has been manufactured on a flexible printed circuit board (PCB) that can adhere to a standard endotracheal (ET) tube. A pilot clinical trial was carried out as a feasibility study on 10 anaesthetised patients. Good quality PPGs from the trachea were acquired at red and infrared wavelengths in all patients. The mean SpO2 reading for the ET tube was 97.1% (SD 1.0%) vs. the clinical monitor at 98.7% (SD 0.7%). The mean pulse rate for the ET sensor was 65.4 bpm (SD 10.0 bpm) vs. the clinical monitor at 64.7 bpm (SD 9.9 bpm). This study supports the hypothesis that the human trachea could be a suitable monitoring site of SpO2 and other physiological parameters, at times where the periphery circulation might be compromised
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Investigation of photoplethysmographs from the anterior fontanelle of neonates
Photoplethysmography (PPG) signals have been investigated at a new anatomical site, the anterior fontanelle (ANTF), on the hypothesis that blood supply at this location is preferentially preserved during cases of poor peripheral circulation which might cause the commercial pulse oximeters to fail to estimate accurately arterial blood oxygen saturation (SpO2). Two custom built reflectance PPG sensors have been developed, one for placement on the fontanelle and one on the periphery (foot). A PPG processing system and software were also developed to process the raw PPG signals and to estimate SpO2. A pilot study on sixteen babies, (9 male, 7 female) with a median age of 15.5 d (interquartile range = 46.8 d) and a median weight of 3.15 kg (SD = 0.93 kg), on a neonatal intensive care unit (NICU) has been carried out. PPG signals from the ANTF were of good quality and high signal-to-noise ratio. The amplitudes of the ANTF PPGs were found to be sensitive to changes in amplitude when amplitudes were observed at the reference PPG site. Bland-Altman analysis of the gold standard blood gas analysis reveals that all three sensors are inaccurate at SaO2 < 85–90 %, but the ANTF sensor shows better mean difference than the commercial device
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Investigation of fontanelle photoplethysmographs and oxygen saturations in intensive care neonates and infants utilising miniature photometric sensors
In children and newborn babies on intensive care, information regarding blood oxygen saturation (SpO2) is determined non-invasively by a device called a pulse oximeter. Sensors are usually placed on a hand or foot where their operation relies on the presence of pulsatile arterial blood. Light shines at two or more wavelengths (usually red and infrared) into the tissue where the pulsatile blood modulates, absorbs and scatters the different wavelengths of light in varying amounts and is detected by a photo-detector as a photoplethysmograph (PPG). The spectral information received is then processed electronically and digitally to determine the amount of haemoglobin present.
In the sickest of children blood supply can become compromised to these sensor locations and the pulsatile component of the blood may diminish and pulse oximeter readings may become unreliable, especially at times when accurate blood oxygen information would be vital. Currently the alternative is to take blood from an arterial line and run a relatively lengthy analysis (pulse oximeters are near-instantaneous in their operation) that may be unnecessary if the pulse oximeter could be relied upon at these critical moments. In the smallest of babies invasive sampling of blood becomes even more of an issue as any blood loss could lead to hypovolaemia and introduce extra sites of infection plus it causes a lot of stress to the neonate.
Since central blood flow may be preferentially preserved, the anterior fontanelle was investigated as an alternative monitoring site. Custom reflectance fontanelle and reference PPG sensors have been designed and built to investigate the fontanelle in those children at risk of peripheral supply compromise. Dedicated instrumentation and software has also been successfully developed for the control of the sensor electronics and the data-logging of PPG signals for retrospective analysis.
Sixteen neonates were recruited for fontanelle monitoring; all were ASA 1 – 3 (ASA ranges from 1 to 5 where 1 is the least sick and 5 is the most critically ill). As part of the approved protocol the delivered oxygen to the patients was artificially altered to look for corresponding changes in PPG signal amplitudes. Amplitude results reveal strong correlations (R > 0.5) between the reference sensor (placed on the foot) and the fontanelle sensor. This suggests that the fontanelle sensor is sensitive to changes in amplitude when oxygen in the blood alters. Correlation of the health of the child, using the ASA score, and the difference in amplitudes of PPGs between the sensors reveals that the fontanelle sensor does detect increasing fontanelle PPG amplitudes when compared to the PPGs from the reference sensor the sicker the child is, confirming that pulsatile flow is being preferentially preserved at the fontanelle in those children who are the most at risk from peripheral supply compromise. SpO2 estimation at the fontanelle reveals a mean difference of 2.2 % to the SpO2 as read by the commercial device and a 1.7 % difference to the blood gas results. These results confirm that the anterior fontanelle may be used as an alternative location for SpO2 measurement in those who are at most risk of peripheral supply compromise
Investigation of fontanelle photoplethysmographs and oxygen saturations in intensive care neonates and infants utilising miniature photometric sensors
In children and newborn babies on intensive care, information regarding blood oxygen saturation (SpO2) is determined non-invasively by a device called a pulse oximeter. Sensors are usually placed on a hand or foot where their operation relies on the presence of pulsatile arterial blood. Light shines at two or more wavelengths (usually red and infrared) into the tissue where the pulsatile blood modulates, absorbs and scatters the different wavelengths of light in varying amounts and is detected by a photo-detector as a photoplethysmograph (PPG). The spectral information received is then processed electronically and digitally to determine the amount of haemoglobin present. In the sickest of children blood supply can become compromised to these sensor locations and the pulsatile component of the blood may diminish and pulse oximeter readings may become unreliable, especially at times when accurate blood oxygen information would be vital. Currently the alternative is to take blood from an arterial line and run a relatively lengthy analysis (pulse oximeters are near-instantaneous in their operation) that may be unnecessary if the pulse oximeter could be relied upon at these critical moments. In the smallest of babies invasive sampling of blood becomes even more of an issue as any blood loss could lead to hypovolaemia and introduce extra sites of infection plus it causes a lot of stress to the neonate. Since central blood flow may be preferentially preserved, the anterior fontanelle was investigated as an alternative monitoring site. Custom reflectance fontanelle and reference PPG sensors have been designed and built to investigate the fontanelle in those children at risk of peripheral supply compromise. Dedicated instrumentation and software has also been successfully developed for the control of the sensor electronics and the data-logging of PPG signals for retrospective analysis. Sixteen neonates were recruited for fontanelle monitoring; all were ASA 1 – 3 (ASA ranges from 1 to 5 where 1 is the least sick and 5 is the most critically ill). As part of the approved protocol the delivered oxygen to the patients was artificially altered to look for corresponding changes in PPG signal amplitudes. Amplitude results reveal strong correlations (R > 0.5) between the reference sensor (placed on the foot) and the fontanelle sensor. This suggests that the fontanelle sensor is sensitive to changes in amplitude when oxygen in the blood alters. Correlation of the health of the child, using the ASA score, and the difference in amplitudes of PPGs between the sensors reveals that the fontanelle sensor does detect increasing fontanelle PPG amplitudes when compared to the PPGs from the reference sensor the sicker the child is, confirming that pulsatile flow is being preferentially preserved at the fontanelle in those children who are the most at risk from peripheral supply compromise. SpO2 estimation at the fontanelle reveals a mean difference of 2.2 % to the SpO2 as read by the commercial device and a 1.7 % difference to the blood gas results. These results confirm that the anterior fontanelle may be used as an alternative location for SpO2 measurement in those who are at most risk of peripheral supply compromise.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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In vivo investigations of photoplethysmograms and arterial oxygen saturation from the auditory canal in conditions of compromised peripheral perfusion
Pulse oximeters rely on the technique of photoplethysmography (PPG) to estimate arterial oxygen saturation (SpO2). In conditions of poor peripheral perfusion such as hypotension, hypothermia, and vasoconstriction, the PPG signals detected are often small and noisy, or in some cases unobtainable. Hence, pulse oximeters produce erroneous SpO2 readings in these circumstances. The problem arises as most commercial pulse oximeter probes are designed to be attached to peripheral sites such as the finger or toes, which are easily affected by vasoconstriction. In order to overcome this problem, the ear canal was investigated as an alternative site for measuring reliable SpO2 on the hypothesis that blood flow to this central site is preferentially preserved. Novel miniature ear canal PPG sensors were developed along with a state of the art PPG processing unit and a data acquisition system to allow for PPG measurements from different depths and surfaces of the ear canal. A preliminary in vivo investigation on seven healthy volunteers has revealed that good quality PPG signals with high amplitude can be obtained from the posterior surface of the outer ear canal. Based on these observations, a second prototype probe suitable for acquisition of PPGs from the posterior surface of the outer ear canal was developed. A pilot study was then carried out on 15 healthy volunteers to validate the feasibility of measuring PPGs and SpO2 from the ear canal in conditions of induced local peripheral vasoconstriction (right hand immersion in ice water). The PPG signals acquired from the ear canal probe were compared with those obtained simultaneously from finger probes attached to the left and the right index fingers. Significant drop (p 45%) and right (> 50%) index fingers during the ice water immersion, while good quality PPG signals with relatively constant amplitude were obtained from the ear canal. Also, the SpO2 values showed that the ear canal pulse oximeter performed better than the two finger pulse oximeters (mean failure rate 30%). A second in vivo investigation was carried out in 15 healthy volunteers, where hypoperfusion was induced more naturally by exposing the volunteer to cold temperatures of 10C for 10min. Normalised Pulse Amplitude (NPA) and SpO2 was calculated from the PPG signals acquired from the ear canal, the finger and the earlobe. By the end of the cold exposure, a mean drop of > 80% was found in the NPA of finger PPGs. The % drop in the NPA of red and infrared earlobe PPG signals was 20% and 26% respectively. Contrarily to both these sites, the NPA of the ear canal PPGs had only dropped by 0.2% and 13% respectively. The SpO2 estimated from the finger sensor was below 90% in 5 volunteers (failure) by the end of the cold exposure. The earlobe pulse oximeter failed in 3 volunteers. The ear canal sensor on the other hand had only failed in 1 volunteer. These results strongly suggest that the ear canal may be used as a suitable alternative site for reliable monitoring of PPGs and SpO2 in cases of compromised peripheral perfusion