Measurements of cerebral arterial oxygen saturation using a fiber-optic pulse oximeter (original) (raw)
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Cerebral Arterial Oxygen Saturation Measurements Using a Fiber-Optic Pulse Oximeter
Background A 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 brain tissue. Methods Short-duration measurements were made in six patients undergoing neurosurgery. These were followed by a longer duration measurement in a patient recovering from an intracerebral hematoma. Estimations of cerebral arterial oxygen saturation derived from a frequency domain-based algorithm are compared with simultaneous pulse oximetry (SpO 2) and hemoximeter (SaO 2) blood samples. Results The short-duration measurements showed that reliable photoplethysmographic signals could be obtained from the brain tissue. In the long-duration study, 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)%. Conclusions This pilot study demonstrated that arterial oxygen saturation may be estimated from brain tissue via a fiber-optic pulse oximeter used in conjunction with a cranial bolt. Further studies are needed to confirm the clinical utility of the technique.
Preliminary evaluation of a new fibre-optic cerebral oximetry system
A new system for measuring the oxygen saturation of blood within tissue has been developed, for a variety of patient monitoring applications. A particular unmet need is in the central nervous system, and this project aims to devise a means for measuring blood oxygen saturation in the brain tissue of patients recovering from neurosurgery or head injury. Coupling light sources and a photodetector to optical fibres results in a probe small enough to pass through a cranial bolt of the type already in use for intra-cranial pressure monitoring. The development and evaluation of a two-wavelength fibre-optic reflectance photoplethysmography (PPG) system are described. It was found that good quality red and near-infrared PPG signals could be obtained from the finger using a fibre-optic probe. Experiments were conducted to find the inter-fibre spacings that yield signals most suitable for calculating oxygen saturation. Reliable signals could be obtained for inter-fibre spacings between 2 mm and 5 mm, the latter being the size of the maximum aperture in the cranial bolt. A preliminary measurement from human brain tissue is also presented.
A new, continuous method of monitoring splanchnic organ oxygen saturation (SpO 2) would make the early detection of inadequate tissue oxygenation feasible, reducing the risk of hypoperfusion, severe ischaemia, and, ultimately, death. In an attempt to provide such a device, a new fibre optic based reflectance pulse oximeter probe and processing system were developed followed by an in vivo evaluation of the technology on seventeen patients undergoing elective laparotomy. Photoplethysmographic (PPG) signals of good quality and high signal-to-noise ratio were obtained from the small bowel, large bowel, liver and stomach. Simultaneous peripheral PPG signals from the finger were also obtained for comparison purposes. Analysis of the amplitudes of all acquired PPG signals indicated much larger amplitudes for those signals obtained from splanchnic organs than those obtained from the finger. Estimated SpO 2 values for splanchnic organs showed good agreement with those obtained from the finger fibre optic probe and those obtained from a commercial device. These preliminary results suggest that a miniaturized 'indwelling' fibre optic sensor may be a suitable method for pre-operative and post-operative evaluation of splanchnic organ SpO 2 and their health.
Sensors
On average, arterial oxygen saturation measured by pulse oximetry (SpO2) is higher in hypoxemia than the true oxygen saturation measured invasively (SaO2), thereby increasing the risk of occult hypoxemia. In the current article, measurements of SpO2 on 17 cyanotic newborns were performed by means of a Nellcor pulse oximeter (POx), based on light with two wavelengths in the red and infrared regions (660 and 900 nm), and by means of a novel POx, based on two wavelengths in the infrared region (761 and 820 nm). The SpO2 readings from the two POxs showed higher values than the invasive SaO2 readings, and the disparity increased with decreasing SaO2. SpO2 measured using the two infrared wavelengths showed better correlation with SaO2 than SpO2 measured using the red and infrared wavelengths. After appropriate calibration, the standard deviation of the individual SpO2−SaO2 differences for the two-infrared POx was smaller (3.6%) than that for the red and infrared POx (6.5%, p < 0.05). T...
Pulse oximetry of body cavities and organs
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2013
The focus of this paper will be in the development and in vivo applications of new custom made photoplethysmographic (PPG) and pulse oximetry optical and fiber optic sensors and instrumentation in an effort to investigate their suitability in the estimation of blood oxygen saturation and their contribution in the assessment of organ/tissue perfusion and viability. The paper describes the development of optical and fiber optic PPG and blood oxygen saturation (SpO2) sensors and covers examples of application areas including real-time PPG monitoring from body cavities (esophagus) and solid or hollow organs (bowel, liver, stomach, brain, etc). The clinical studies presented successfully demonstrated the feasibility in acquiring PPGs and estimating blood oxygen saturation values from a variety of organs and tissues. The technological developments and the measurements presented in this work pave the way in a new era of pulse oximetry where direct and continuous monitoring of blood oxygen ...
Noninvasive Optical Quantification of Cerebral Venous Oxygen Saturation in Humans
Academic Radiology, 2014
Rationale and Objectives: Cerebral oxygen extraction, defined as the difference between arterial and venous oxygen saturations (SaO 2 and SvO 2 ), is a critical parameter for managing intensive care patients at risk for neurological collapse. Although quantification of SaO 2 is easily performed with pulse oximetry or moderately invasive arterial blood draws in peripheral vessels, cerebral SvO 2 is frequently not monitored because of the invasiveness and risk associated with obtaining jugular bulb or super vena cava (SVC) blood samples.
Pulse Oximetry for the Measurement of Oxygen Saturation in Arterial Blood
2021
The method of photoplethysmography (PPG) detailed in Chapters 1 and 2 gained enormous prominence due to the development of pulse oximetry. In pulse oximetry, the fact that hemoglobin bound with oxygen (called oxyhemoglobin) and hemoglobin without oxygen (deoxy-hemoglobin or reduced hemoglobin) absorb/reflect light differently is exploited in ascertaining, noninvasively, oxygen saturation in arterial blood. Most pulse oximeters that are in existence today use a couple of PPGs obtained using red and infrared wavelength light sources and calculate oxygen saturation in arterial blood using the red and IR PPGs and an empirical equation. This chapter details the development of pulse oximetry. It describes in detail a couple of novel methods of oxygen saturation calculation using the red and IR PPGs. The methods presented here do not need any calibration to be performed. 3.1 Physiological Signals for Diagnostics Dynamic and static measurements on the physical, electrical, chemical and acoustic signals of a human body will help ascertain its health [1-3]. Whenever a person is affected by a disease or gets injured, one or more of these physical, electrical, chemical and acoustic signals change. However, these physical, electrical, chemical and acoustic signals also change day to day due to natural variations in the life cycle. Moreover, the changes in these signals are a complex combination of different parameters. Hence it is very difficult to delineate the functioning or malfunctioning of the underlying biological parts or processes directly from these signals. The four traditional vital signs, namely, the pulse rate, the respiratory rhythm (and sound), the body temperature and the blood pressure are normally used by medical practitioners all over the globe to assess a patient's state of health. In the modern times, a fifth vital signal, namely, the oxygen saturation in blood has also gained importance. Today any patient with coronary or pulmonary problems must be evaluated for the oxygen
The principal advantage of optical sensors for medical applications is their intrinsic safety since there is no electrical contact between the patient and the equipment. (An added bonus is that they are also less suspect to electromagnetic interference). This has given rise to a variety of optical techniques to monitor physiological parameters: for example, the technique of Laser Doppler velocimetry to measure red blood cell velocity. However, in this lecture course we will concentrate on the technique of pulse oximetry for the non−invasive measurement of arterial oxygen saturation in the blood (although a second use of the technology will be discussed right at the end of the course). For patients at risk of respiratory failure, it is important to monitor the efficiency of gas exchange in the lungs, ie how well the arterial blood is oxygenated (as opposed to whether or not air is going in and out of the lungs). Preferably, such information should be available to clinicians of a continuous basis (rather than every few hours). Both of these requirements can be met non−invasively 2 with the technology of pulse oximetry. The technique is now well established and is in regular clinical use during anaesthesia and intensive care (especially neonatal intensive care since many premature infants undergo some form of ventilator therapy). Pulse oximetry is also being used in the monitoring of pulmonary disease in adults and in the investigation of sleep disorders.
Pulse oximetry: fundamentals and technology update
Medical Devices: Evidence and Research, 2014
Oxygen saturation in the arterial blood (SaO 2) provides information on the adequacy of respiratory function. SaO 2 can be assessed noninvasively by pulse oximetry, which is based on photoplethysmographic pulses in two wavelengths, generally in the red and infrared regions. The calibration of the measured photoplethysmographic signals is performed empirically for each type of commercial pulse-oximeter sensor, utilizing in vitro measurement of SaO 2 in extracted arterial blood by means of co-oximetry. Due to the discrepancy between the measurement of SaO 2 by pulse oximetry and the invasive technique, the former is denoted as SpO 2. Manufacturers of pulse oximeters generally claim an accuracy of 2%, evaluated by the standard deviation (SD) of the differences between SpO 2 and SaO 2 , measured simultaneously in healthy subjects. However, an SD of 2% reflects an expected error of 4% (two SDs) or more in 5% of the examinations, which is in accordance with an error of 3%-4%, reported in clinical studies. This level of accuracy is sufficient for the detection of a significant decline in respiratory function in patients, and pulse oximetry has been accepted as a reliable technique for that purpose. The accuracy of SpO 2 measurement is insufficient in several situations, such as critically ill patients receiving supplemental oxygen, and can be hazardous if it leads to elevated values of oxygen partial pressure in blood. In particular, preterm newborns are vulnerable to retinopathy of prematurity induced by high oxygen concentration in the blood. The low accuracy of SpO 2 measurement in critically ill patients and newborns can be attributed to the empirical calibration process, which is performed on healthy volunteers. Other limitations of pulse oximetry include the presence of dyshemoglobins, which has been addressed by multiwavelength pulse oximetry, as well as low perfusion and motion artifacts that are partially rectified by sophisticated algorithms and also by reflection pulse oximetry.
An Optical Fiber Photoplethysmographic System for Central Nervous System Tissue
2006 International Conference of the IEEE Engineering in Medicine and Biology Society, 2006
A new system for measuring the oxygen saturation of blood within tissue has been developed, for a number of potential patient monitoring applications. This proof of concept project aims to address the unmet need of real-time measurement of oxygen saturation in the central nervous system (CNS) for patients recovering from neurosurgery or trauma, by developing a fiber optic signal acquisition system for internal placement through small apertures. The development and testing of a two-wavelength optical fiber reflectance photoplethysmography (PPG) system is described. It was found that good quality red and near-infrared PPG signals could be consistently obtained from the human fingertip (n=6) and rat spinal cord (n=6) using the fiber optic probe. These findings justify further development and clinical evaluation of this fiber optic system.