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Optical Techniques for Blood and Tissue Oxygenation

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Abstract

Throughout human history, light has played an important role in medicine. New optical techniques, many involving light emitting diodes, lasers, and fiber optics, are revolutionizing the field of diagnostic monitoring and therapy. Although at an adolescent stage, the power and potential of optical techniques, especially in monitoring blood and tissue oxygenation, has been well recognized, but is still rapidly developing. This review will cover various optical techniques currently used in the in vivo measurement of blood and tissue oxygenation, both in clinical and research settings. These include some well-established techniques such as pulse oximetry, fiber optic venous oximetry, and near-infrared spectroscopy, as well as other techniques that are not yet widely used such as white light spectrophotometry and fluorescence quenching. The review will describe the principles and applications of these techniques, in an attempt to illustrate their capabilities and limitations in measuring oxygenation in blood and tissues.

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... Oxygen must be constantly transported from the lungs to all organs for the body to function properly. For healthy people, oxygen saturation remains at the level of 95-100% [21]. This value can drop during exhaustive training, when the circulatory system does not keep pace with the oxygen supply, or when the oxygen is cut off. ...
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... However, a wavelength of 970 nm above is water absorption area in body tissues, so that a wavelength of 970 nm cannot be used to characterize the absorption of Deoxyhemoglobin. At a wavelength of 940 nm, light absorption by water in body tissues is very low, and Deoxyhemoglobin absorption is relatively high [7,8]. ...
... However, a wavelength of 970 nm above is water absorption area in body tissues, so that a wavelength of 970 nm cannot be used to characterize the absorption of Deoxyhemoglobin. At a wavelength of 940 nm, light absorption by water in body tissues is very low, and Deoxyhemoglobin absorption is relatively high [7,8]. ...
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... The prediction of tissue oxygen status is based on the interpretation of changes in light reflectance with medium's absorptivity [3]. The latter is a function of wavelength and it varies with oxygen binding capacity of hemoglobin; therefore no dye is required in its visualization [4][5]. Single point spectroscopy, multispectral and hyperspectral imaging systems are among the technologies that have been designed to adopt this approach [5][6][7]. ...
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Chapter
Since its discovery, photoplethysmography (PPG) has been almost exclusively associated with pulse oximetry, a noninvasive and continuous technique measuring oxygen saturation levels in blood. This chapter will describe how PPG signals are utilized in pulse oximetry to measure blood oxygen saturation (SpO2). The chapter will also provide a snapshot on the capabilities and potentials of PPG in the clinical monitoring of oxygenation and perfusion. The first part of the chapter covers the principles, latest advancements, and applications of pulse oximetry, whereas the second part covers the application of PPG in measuring blood volume changes and perfusion among other parameters.
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Monitoring changes in blood volume, blood flow, and oxygenation in tissues is of vital importance in fields such as reconstructive surgery and trauma medicine. Near infrared spectroscopy (NIRS), laser Doppler (LDF) flowmetry, photoplethysmography (PPG), and pulse oximetry (PO) contribute to such fields due to their safe and noninvasive nature. However, the techniques have been rarely investigated simultaneously or altogether. The aim of this study was to investigate all the techniques simultaneously on healthy subjects during vascular occlusion challenges. Sensors were attached on the forearm (NIRS and LDF) and fingers (PPG and PO) of 19 healthy volunteers. Different degrees of vascular occlusion were induced by inflating a pressure cuff on the upper arm. The responses of tissue oxygenation index (NIRS), tissue haemoglobin index (NIRS), flux (LDF), perfusion index (PPG), and arterial oxygen saturation (PO) have been recorded and analyzed. Moreover, the optical densities were calculated from slow varying dc PPG, in order to distinguish changes in venous blood volumes. The indexes showed significant changes (p < 0.05) in almost all occlusions, either venous or over-systolic occlusions. However, differentiation between venous and arterial occlusion by LDF may be challenging and the perfusion index (PI) may not be adequate to indicate venous occlusions. Optical densities may be an additional tool to detect venous occlusions by PPG.
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Normal oxygen transport (S A Clark). Motivation of pulse oximetry (D J Sebald). Blood oxygen measurement (J Farmer). Light absorbance in pulse oximetry (O Wieben). Light-emitting diodes and their control (B W J Bourgeois). Photodetectors and amplifiers (J S Schowalter). Probes (M V S Reddy). Electronic instrument control (K S Paranjape). Signal processing algorithms (S Palreddy). Calibration (J S Schowalter). Accuracy and errors (S Tungjitkusolmun). User interface for a pulse oximeter (A Lozano-Nieto). Applications of pulse oximetry (J B Ruchala). Glossary. Index.
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The relatively good transparency of biological materials in the near infrared region of the spectrum permits sufficient photon transmission through organs in situ for the monitoring of cellular events. Observations by infrared transillumination in the exposed heart and in the brain in cephalo without surgical intervention show that oxygen sufficiency for cytochrome a,a3, function, changes in tissue blood volume, and the average hemoglobin-oxyhemoglobin equilibrium can be recorded effectively and in continuous fashion for research and clinical purposes. The copper atom associated with heme a3 did not respond to anoxia and may be reduced under normoxic conditions, whereas the heme-a copper was at least partially reducible.
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Background: Pulse oximetry is a noninvasive photometric technique that provides information about arterial blood oxygen saturation (SpO2) and heart rate and has widespread clinical applications. This is accomplished via peripheral pulse oximetry probes mainly attached to the finger, toe, or earlobe. The direct application of pulse oximetry to an organ, such as the esophagus, liver, bowel, stomach or free flap, might provide an indication of how well perfused an organ or a free flap is. Also, the placement of a pulse oximetry probe at a more central site, such as the esophagus, might be more reliable at a time when conventional peripheral pulse oximetry fails. Methods: The focus of this article is the development and in vivo applications of new custom-made photoplethysmographic (PPG) and pulse oximetry optical and fiberoptic probes and instrumentation in an effort to investigate their suitability for the estimation of arterial blood oxygen saturation at different organs and tissues. The article will cover examples of application areas including real-time PPG and SpO2 monitoring for the esophagus and solid organs, including free flaps, using custom-made probes. Results: Clinical studies have successfully demonstrated the feasibility of acquiring PPGs and estimating arterial blood oxygen saturation values from a variety of organs and tissues. Conclusions: The technological developments and the measurements presented in this work pave the way to a new era of pulse oximetry where direct and continuous monitoring of blood oxygen saturation of internal organs and tissues (esophagus, bowel, liver, stomach, free flaps) could be possible.
Article
A new clinical tissue oxygenation monitor, the NIRO-300, has been developed. In addition to monitoring changes in hemoglobin concentration and redox state of cytochrome oxidase, the instrument can measure a Tissue Oxygenation Index (TOI), which is the ratio of oxygenated to total tissue hemoglobin, by utilizing NIR spatially resolved spectroscopy (SRS). In SRS, the slope of light attenuation versus distance is measured at a distant point from the light input, from which the TOI is calculated using photon diffusion theory. Four laser diodes are used as the light source and Class 1 laser light (IEC 825) is irradiated onto the skin. A high gain and low noise amplifier is used in the detector, which enables a large emitter-detector separations of around 5cm. To evaluate the TOI measured by the NIRO-300, it was compared to the data from a blood gas analyzer (SO, value) in measurements made on phantoms containing intralipid and blood. We also made simultaneous measurements by the NIRO-300 and an NIRS machine based on time resolved spectroscopy (TRS) on human arms. In the both measurements, TOI showed an excellent correlation with the data from brood gas analyzer and the TRS machine, which suggests the efficacy of the TOI data also in clinical use.
Article
The microcirculation plays an essential role in health and disease. Microvascular perfusion can be assessed directly using laser Doppler flowmetry and various imaging techniques or indirectly using regional capnometry and measurement of indicators of mismatch between oxygen delivery and oxygen consumption or indices of disturbed cellular oxygen utilization. Assessment of microvascular oxygen availability implies measurement of oxygen pressure or measurement of hemoglobin oxygen saturation. Microvascular function is assessed using other methods, including venous plethysmography. In this paper, I review current knowledge concerning assessment of the microcirculation with special emphasis on methods that could be used at the bedside.
Article
Near infrared spectroscopy (NIRS) is a light-based technology used to monitor tissue oxygen status. Refinements to the method since it was first described have extended its applicability to different research and clinical settings due to its non-invasiveness, instrument portability and ease of use. Classic NIRS recordings, based in the Beer-Lambert law, can be used for the trend monitoring of changes in tissue perfusion-oxygenation parting from an arbitrary zero point. However, in order to derive intermittently quantitative values in absolute terms, certain manoeuvres must be performed. More recently, the evolution of the technique has led to the development of instruments that provide an absolute value of regional hemoglobin saturation in a continuous manner. This review will focus on the physical principles of tissue spectroscopy including a brief description of the different operating principles that are currently in use or under development. The theoretical details, experimental procedures and data analysis involved in the measurements of physiological variables using NIRS will be described. The future beyond the scope of NIRS and potential lines of research will also be discussed.
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Reflectance spectroscopy is an emerging technology which provides rapid and safe evaluation of tissue for dysplasia and ischemia. The probe-based devices can be passed through most endoscopes. Current applications include detection of dysplasia in Barrett's esophagus, colitis, and colon polyps.
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The pulse oximeter, a widely used noninvasive monitor of arterial oxygen saturation, has numerous applications in anesthesiology and critical care. Although pulse oximetry is considered sufficiently accurate for many clinical purposes, there are significant limitations on the accuracy and availability of pulse oximetry data. This article reviews both the clinical uses of the pulse oximeter and the limitations on its performance. The pulse oximeter is generally acknowledged to be one of the most important advances in the history of clinical monitoring.
Article
Pulse oximetry has emerged as a clinical tool in anesthesia and newborn monitoring within the last 7 years as a result of recent technological and theoretical advances. Oximeters measure the different absorption spectra of oxygenated and deoxygenated hemoglobin. Electronic measures of oxygenation at the peak of the pulse allow computation and display of oxygen saturation of the arterial blood almost instantly. Correlation coefficients between pulse oximetry and direct blood oxygen saturation measurement range from 0.77-0.99 when oxygen saturation is greater than 60%. The method is noninvasive (a clip or tape on a finger), simple to operate, and adaptable to various patient populations. Pulse oximetry monitors continuously and instantaneously, is responsive to change, and is accurate. Factors adversely affecting the accuracy of pulse oximeter output include transducer movement, peripheral vasoconstriction, a nonpulsating vascular bed, hypotension, anemia, changes in systemic vascular resistance, hypothermia, presence of intravascular dyes, and nail polish. Pulse oximetry has been used to monitor oxygen saturation intraoperatively in the adult and neonatal intensive care units and to monitor pregnant patients and their infants at delivery. Once the advantages and limitations of pulse oximetry are recognized, this monitoring technique can play an important role in the care of patients with cardiovascular and respiratory compromise.
Article
The pulse oximeter has become an essential tool in the modern practice of emergency medicine. However, despite the reliance placed on the information this monitor offers, the underlying principles and associated limitations of pulse oximetry are poorly understood by medical practitioners. This article reviews the principles of pulse oximetry, with an eye toward recognizing the limitations of this tool. Among these are performance limitations in the settings of carboxyhemoglobinemia, methemoglobinemia, motion artifact, hypotension, vasoconstriction, and anemia. The accuracy of pulse oximetry is discussed in light of these factors, with further discussion of applications for pulse oximetry in emergency medicine, including both oximetric and plethysmographic operation. The pulse oximeter is an invaluable instrument for emergency medicine practice, but as with any test the data it offers must be critically appraised for proper interpretation and utilization.
Article
Interrogation of tissue with light offers the potential for noninvasive chemical measurement, and penetration with near-infrared wavelengths (750-1000 nm) is greater than with visible light. Specific absorption by clinically relevant compounds such as oxy- and deoxyhemoglobin and the intracellular respiratory enzyme cytochrome oxidase enable in vivo measurement of these to be performed safely and conveniently. This is the basis of in vivo near-infrared spectroscopy (ivNIRS). Multiple scattering of the interrogating beam by tissues leads to an optical path that is considerably longer than the simple physical pathlength and this complicates the analysis. Modeling of photon propagation through tissues with, for example, finite element and Monte Carlo methods, is assisting in improving the ivNIRS methodology. Instrumentation has advanced from simple continuous wave approaches, through time-resolved methods based on either time-domain or frequency-domain approaches, to spatially resolved measurement based on diffuse reflectance. Initial clinical applications were for monitoring the brain in the neonate and fetus and muscle in adults. Currently, use in adults and children for neurological assessments are of growing interest.
Article
The purpose of this study was to determine the prognostic value of sublingual PCO2 (P(SL)CO2), lactate concentration, and mixed venous oxygen saturation (S(MV)O2) in hemodynamically unstable intensive care patients and, additionally, to compare the temporal changes of these variables in response to treatment. Medical/surgical intensive care unit. Fifty-four patients, mean age 58 +/- 8 yrs. Oxyhemodynamic variables, arterial lactate concentration, and P(SL)CO2 were recorded in unselected sequential intensive care patients undergoing pulmonary artery catheterization. A data set was obtained immediately after insertion of the pulmonary artery catheter and repeated 4 and 8 hrs later. Twenty-one patients had severe sepsis or septic shock. Twenty-seven (50%) patients died. The initial P(SL)CO2_PaCO2 gradient (P(SL)CO2-diff) and the initial P(SL)CO2 were highly predictive of outcome (p =.0004 and p =.004, respectively); however, there was no difference in the arterial lactate concentration and S(MV)O2 between the survivors and nonsurvivors. The P(SL)CO2-diff had the best receiver operator characteristic characteristics (area under the curve, 0.75), with a P(SL)CO2-diff >25 mm Hg being the best discriminator of outcome. With treatment, the P(SL)CO2-diff decreased in both survivors and nonsurvivors; however, the lactate and S(MV)O2 remained relatively unchanged during the study period. The baseline P(SL)CO2-diff and P(SL)CO2 were better predictors of outcome than traditional markers of tissue hypoxia and were more responsive to therapeutic interventions. The P(SL)CO2-diff and/or P(SL)CO2 may prove to be a useful marker for goal-directed therapy and for assessing the response to clinical interventions aimed at improving tissue oxygenation.
Article
Pulse oximetry has been one of the most significant technological advances in clinical monitoring in the last two decades. Pulse oximetry is a non-invasive photometric technique that provides information about the arterial blood oxygen saturation (SpO(2)) and heart rate, and has widespread clinical applications. When peripheral perfusion is poor, as in states of hypovolaemia, hypothermia and vasoconstriction, oxygenation readings become unreliable or cease. The problem arises because conventional pulse oximetry sensors must be attached to the most peripheral parts of the body, such as finger, ear or toe, where pulsatile flow is most easily compromised. Since central blood flow may be preferentially preserved, this review explores a new alternative site, the oesophagus, for monitoring blood oxygen saturation by pulse oximetry. This review article presents the basic physics, technology and applications of pulse oximetry including photoplethysmography. The limitations of this technique are also discussed leading to the proposed development of the oesophageal pulse oximeter. In the majority, the report will be focused on the description of a new oesophageal photoplethysmographic/SpO(2) probe, which was developed to investigate the suitability of the oesophagus as an alternative monitoring site for the continuous measurement of SpO(2) in cases of poor peripheral circulation. The article concludes with a review of reported clinical investigations of the oesophageal pulse oximeter.
Article
This review celebrates the 30th anniversary of the first in vivo near-infrared (NIR) spectroscopy (NIRS) publication, which was authored by Professor Frans Jobsis. At first, NIRS was utilized to experimentally and clinically investigate cerebral oxygenation. Later it was applied to study muscle oxidative metabolism. Since 1993, the discovery that the functional activation of the human cerebral cortex can be explored by NIRS has added a new dimension to the research. To obtain simultaneous multiple and localized information, a further major step forward was achieved by introducing NIR imaging (NIRI) and tomography. This review reports on the progress of the NIRS and NIRI instrumentation for brain and muscle clinical applications 30 years after the discovery of in vivo NIRS. The review summarizes the measurable parameters in relation to the different techniques, the main characteristics of the prototypes under development, and the present commercially available NIRS and NIRI instrumentation. Moreover, it discusses strengths and limitations and gives an outlook into the "bright" future.
Theory and Clinical Application of Continuous Fiberoptic Central Venous Oximetry (ScvO2) Monitoring
  • J Frazier
Frazier J "Theory and Clinical Application of Continuous Fiberoptic Central Venous Oximetry (ScvO2) Monitoring," Edwards Lifesciences, no. 2nd. [Online]. Available: http://ht.edwards. com/scin/edwards/sitecollectionimages/edwards/products/presep/ar04012presepwhitepaper.pdf.