Reflectance Pulse Oximetry Research Articles

Design and validation of dual-point time-differentiated photoplethysmogram (2PPG) wearable for cuffless blood pressure estimation

Background & objectivesMeasurement of blood pressure (BP) in ambulatory patients is crucial for at high-risk cardiovascular patients. A non-obtrusive, non-occluding device that continuously measures BP via photoplethysmography will enable long-term ambulatory assessment of BP. The aim of this study is to validate the metasense 2PPG cuffless wearable design for continuous BP estimation without ECG. MethodsA customized high-speed electronic optical sensor architecture with laterally spaced reflectance pulse oximetry was designed into a simple unobtrusive low-power wearable in the form of a watch. 78 volunteers with a mean age of 32.72 ± 7.4 years (21 to 64), 51% male, 49% female were recruited with ECG-2PPG signals acquired. The fiducial features of the 2PPG morphologies were then attributed to the estimator. A 9–1 K-fold cross-validation was applied in the ML. ResultsThe correlation for PTT-SBP was 0.971 and for PTT-DBP was 0.954. The mean absolute error was 3.167±1.636 mmHg for SBP and 6.4 ± 3.9 mm Hg for DBP. The ambulatory estimate for SBP and DBP for an individual over 3 days with 8-hour recordings was 0.70–0.81 for SBP and 0.42–0.51 for DBP with a ± 2.65 mmHg for SBP and ±2.02 mmHg for DBP. For SBP, 98% of metasense measurements were within 15 mm Hg and for DBP, 91% of metasense measurements were within 10 mmHg ConclusionsThe metasense device provides continuous, non-invasive BP estimations that are comparable to ambulatory BP meters. The portability and unobtrusiveness of this device, as well as the ability to continuously measure BP could one day enable long-term ambulatory BP measurement for precision cardiovascular therapeutic regimens.

Pulse oximetry methods: opportunities and limitations

The aim of this review was to evaluate the current literature on various methods of pulse oximetry, their advantages and disadvantages. Modern pulse oximetry methods generally correlate well with invasive saturation monitoring, which makes it possible to be widely used in clinical practice. At the same time, in order to improve the accuracy of saturation measurements, existing limitations of various pulse oximetry methods should be taken into account. The emergence and introduction into clinical practice of reflectance pulse oximetry can largely compensate for the limitations of traditional transmission pulse oximetry regarding peripheral hypoperfusion, low response time, and features of patient's nails. In the event of special situations when pulse oximetry may not be accurate enough (carbon monoxide poisoning, methemoglobinemia, severe anemia, severe tricuspid insufficiency, etc.), a thorough clinical assessment of the patient is recommen ded, as well as invasive saturation monitoring.

Pulse oximetry methods: opportunities and limitations

The aim of this review was to evaluate the current literature on various methods of pulse oximetry, their advantages and disadvantages. Modern pulse oximetry methods generally correlate well with invasive saturation monitoring, which makes it possible to be widely used in clinical practice. At the same time, in order to improve the accuracy of saturation measurements, existing limitations of various pulse oximetry methods should be taken into account. The emergence and introduction into clinical practice of reflectance pulse oximetry can largely compensate for the limitations of traditional transmission pulse oximetry regarding peripheral hypoperfusion, low response time, and features of patient's nails. In the event of special situations when pulse oximetry may not be accurate enough (carbon monoxide poisoning, methemoglobinemia, severe anemia, severe tricuspid insufficiency, etc.), a thorough clinical assessment of the patient is recommen ded, as well as invasive saturation monitoring.

Accuracy enhancement in reflective pulse oximetry by considering wavelength-dependent pathlengths

Objective. Noninvasive measurement of oxygen saturation (SpO 2) using transmissive photoplethysmography (tPPG) is clinically accepted and widely employed. However, reflective photoplethysmography (rPPG)—currently present in smartwatches—has not become equally accepted, partially because the pathlengths of the red and infrared PPGs are patient-dependent. Thus, even the most popular ‘Ratio of Modulation’ (R) method requires patient-dependent calibration to reduce the errors in the measurement of SpO 2 using rPPGs. Approach. In this paper, a correction factor or ‘pathlength ratio’ β is introduced in an existing calibration-free algorithm that compensates the patient-dependent pathlength variations, and improved accuracy is obtained in the measurement of SpO 2 using rPPGs. The proposed pathlength ratio β is derived through the analytical model of a rPPG signal. Using the new expression and data obtained from a human hypoxia study wherein arterial oxygen saturation values acquired through Blood Gas Analysis were employed as a reference, β is determined. Main results. The results of the analysis show that a specific combination of the β and the measurements on the pulsating part of the natural logarithm of the red and infrared PPG signals yields a reduced root-mean-square error (RMSE). It is shown that the average RMSE in measuring SpO 2 values reduces to 1 %. Significance. The human hypoxia study data used for this work, obtained in a previous study, covers SpO 2 values in the range from 70 % to 100 %, and thus shows that the pathlength ratio β proposed here works well in the range of clinical interest. This work demonstrates that the calibration-free method applicable for transmission type PPGs can be extended to determine SpO 2 using reflective PPGs with the incorporation of the correction factor β. Our algorithm significantly reduces the number of parameters needed for the estimation, while keeping the RMSE below the clinically accepted 2 %.

Enabling Continuous Wearable Reflectance Pulse Oximetry at the Sternum.

In light of the recent Coronavirus disease (COVID-19) pandemic, peripheral oxygen saturation (SpO2) has shown to be amongst the vital signs most indicative of deterioration in persons with COVID-19. To allow for the continuous monitoring of SpO2, we attempted to demonstrate accurate SpO2 estimation using our custom chest-based wearable patch biosensor, capable of measuring electrocardiogram (ECG) and photoplethysmogram (PPG) signals with high fidelity. Through a breath-hold protocol, we collected physiological data with a wide dynamic range of SpO2 from 20 subjects. The ratio of ratios (R) used in pulse oximetry to estimate SpO2 was robustly extracted from the red and infrared PPG signals during the breath-hold segments using novel feature extraction and PPGgreen-based outlier rejection algorithms. Through subject independent training, we achieved a low root-mean-square error (RMSE) of 2.64 ± 1.14% and a Pearson correlation coefficient (PCC) of 0.89. With subject-specific calibration, we further reduced the RMSE to 2.27 ± 0.76% and increased the PCC to 0.91. In addition, we showed that calibration is more efficiently accomplished by standardizing and focusing on the duration of breath-hold rather than the resulting range in SpO2. The accurate SpO2 estimation provided by our custom biosensor and the algorithms provide research opportunities for a wide range of disease and wellness monitoring applications.

Influence of Measurement Location on Reflectance Pulse Oximetry in Sleep Apnea Patients: Wrist vs. Upper Arm.

Peripheral oxygen saturation (SpO2) plays a key role in diagnosing sleep apnea. It is mainly measured via transmission pulse oximetry at the fingertip, an approach less suited for long-term monitoring over several nights.In this study we tested a more patient-friendly solution via a reflectance pulse oximetry device. Having previously observed issues with pulse oximetry at the wrist, we investigated in this study the influence of the location of our device (upper arm vs. wrist) to measure SpO2. Accuracy was compared against state-of-the-art fingertip SpO2 measurements during a full overnight polysomnography in nine patients with suspected sleep apnea.The upper arm location clearly showed a lower root mean square error ARMS = 1.8% than the wrist ARMS = 2.5% and a lower rate of automatic data rejection (19% vs 25%). Irrespective of the measurement location the accuracies obtained comply with the ISO standard and the FDA guidance for pulse oximeters. In contrast to the wrist, the upper arm location seemed to be more resilient to deteriorating influences such as venous blood.Reflectance pulse oximetry at the wrist remains challenging but the upper arm could provide remedy for more robust SpO2 estimates to reliably screen for sleep apnea and other diseases.Clinical Relevance- The performance of reflectance pulse oximetry measured at the upper arm during sleep is superior to measurements at the wrist which are perturbed by undesired large fluctuations suspected to be caused by venous blood. If confirmed, this could also apply to the optical measurement of other vital signs such as blood pressure.

Comparison of Transmittance and Reflectance Pulse Oximetry in Anesthetized Dogs.

Objectives: The tongue is the standard site for placement of a pulse oximeter probe but is difficult to access during certain procedures such as dental and ophthalmic procedures and computerized tomography of the head. The aim of this study was to evaluate the performance of a new-generation reflectance pulse oximeter using the tail and tibia as sites for probe attachment.Materials and Methods: A total of 100 client-owned dogs that underwent anesthesia for various reasons were premedicated with butorphanol (n = 50; 0.2 mg/kg; group BUT) or butorphanol and dexmedetomidine (n = 50; 5 μg/kg; group DEX), administered intravenously. Anesthesia was induced with propofol and maintained with sevoflurane. A transmittance pulse oximeter probe was placed on the tongue and served as the reference standard. A reflectance probe was randomly placed on the tail base or the proximal tibia, and the position changed after testing. Signals from three consecutive measurements were obtained at each position. Failure was defined as “no signal,” “low signal,” or a pulse difference >10/min compared with the ECG heart rate. Data were analyzed using chi-square test, Wilcoxon matched-pair signed-rank test, and Bland-Altman analysis. P < 0.05 was considered significant.Results: In both groups (BUT and DEX), failure rate was higher when the tibia and tail were used as probe sites compared with the tongue. In both groups, the failure rate was higher for the tibia than for the tail. Dexmedetomidine-induced vasoconstriction increased failure rate at all probe positions.Clinical Significance: The tail base, but not the tibia, is an acceptable position for reflectance pulse oximeter probes in dogs. The tongue remains the probe site of choice, if accessible.

Pulse Oximetry at the Wrist During Sleep: Performance, Challenges and Perspectives.

The state-of-the-art non-invasive measurement of peripheral oxygen saturation (SpO2) during sleep is mainly based on pulse oximetry at the fingertip. Although this approach is noninvasive, it can still be obtrusive and cumbersome to apply, in particular for ambulatory monitoring over several nights.We developed a wrist-worn reflectance pulse oximetry device which can be embedded in a watch, making it less obtrusive and easy to apply. This device was tested in an ongoing clinical study on 57 subjects (33 patients and 24 healthy volunteers) undergoing a full overnight polysomnography recording. The accuracy was evaluated against state-of-the-art fingertip SpO2 measurements.In the 54 subjects available for analysis we obtained an SpO2 accuracy (ARMS) of 3.4 % when automatically rejecting 17.7 % of signals due to low quality. When further excluding measurements suffering from insufficient contact of the watch with the skin an ARMS of 2.7 % was obtained while rejecting a total of 23.2 % measurements. These accuracies comply with the ISO standard and the FDA guidance for pulse oximeters.The present results are promising and pave the way for unobtrusive and continuous monitoring of SpO2 to screen for sleep disordered breathing. Nonetheless, contact pressure and venous blood have shown to adversely affect the SpO2 estimation and remain a challenge for wrist-based reflectance pulse oximetry.

TRANSCUTANEOUS OXYGEN MONITORING IN LOUISIANA PINE SNAKES (PITUOPHIS RUTHVENI)

Hypoxic physiological states may occur during anesthetic events of snakes but accurate monitoring of oxygenation is challenging. Oxygenation levels of nine Louisiana pine snakes (Pituophis ruthveni) were assessed using transcutaneous regional oxygen saturation (rSO2) at the level of the liver (rSO2Liver) and at the halfway point of the body (rSO2Half ). Reflectance pulse oximetry measured SpO2, with a sensor overlying the heart. Values were compared with the venous partial pressure of oxygen (PvO2). Measurements were taken during four phases, simulating an anesthetic event: phase 1, breathing room air; phase 2, while supplied with supplemental oxygen via face mask; phase 3, during ketamine and dexmedetomidine sedation; and phase 4, after receiving atipamezole. There were no significant changes in any oxygenation parameters between concurrent phases, but respiratory rate significantly decreased (P = 0.02) between phases 1 and 2. Strong positive associations were found between both rSO2Liver and rSO2Half when compared with PvO2 irrespective of phase (r = 0.72, r = 0.63 respectively), but not with SpO2 (r = 0.3). Strength of correlation varied with each phase but was uniformly strongest for rSO2Liver. The measurement of rSO2 appears superior compared with traditional pulse oximetry for assessing oxygenation levels of snakes.

Fiber-optic pulseoximeter for local oxygen saturation determination using a Monte Carlo multi-layer model for calibration

Background and objectiveLocal tissue oxygenation determines the relationship between the supply and the demand for oxygen by the tissue and it is an important indicator of the physiological or pathological condition of the tissue. Moreover, some therapeutic methods strongly depend on the oxygen content of the tissue. In photodynamic therapy, when molecular oxygen is present, the irradiation of the photosensitizer with light triggers the generation of reactive oxygen species that kill the target diseased cells within the treated tissue. To ensure the best possible therapy response, the tissue must be well oxygenated; hence, oxygen concentration measurement becomes a decisive factor. In this work, the design, construction and calibration of a module to locally measure the blood oxygen saturation in tissue is presented. MethodsThe system is built using a red (660-nm) and an infrared (940-nm) light emitting diodes as light sources, a photodiode as a detector, and a homemade handheld fiber optic-based reflectance pulse oximetry sensor. In addition, the developed sensor was modeled by means of multilayered Monte Carlo simulations, to study its behavior when used in different thickness and melanin content skin. ResultsFrom the simulation reflectance values, the oxygen saturation calibration curves considering different melanin concentrations and skin thicknesses were obtained for two different skin models, one comprising three skin layers and the second, assuming seven different layers for the skin. A comparison of the performances of the developed pulse oximeter sensor with a commercial one is also presented. ConclusionsA new pulseoximeter for the measurement of local oxygenation in tissue was developed. Its calibration strongly depends on the site of measurement due to the influence of tissue thickness, vascularization, and melanin content. A three-layer skin model is proved to be suitable for the calibration of the pulseoximeter in thin and medium thickness skin.

Novel transcutaneous sensor combining optical tcPO2 and electrochemical tcPCO2 monitoring with reflectance pulse oximetry.

This study investigated the accuracy, drift, and clinical usefulness of a new optical transcutaneous oxygen tension (tcPO2) measuring technique, combined with a conventional electrochemical transcutaneous carbon dioxide (tcPCO2) measurement and reflectance pulse oximetry in the novel transcutaneous OxiVenT™ Sensor. In vitro gas studies were performed to measure accuracy and drift of tcPO2 and tcPCO2. Clinical usefulness for tcPO2 and tcPCO2 monitoring was assessed in neonates. In healthy adult volunteers, measured oxygen saturation values (SpO2) were compared with arterially sampled oxygen saturation values (SaO2) during controlled hypoxemia. In vitro correlation and agreement with gas mixtures of tcPO2 (r = 0.999, bias 3.0 mm Hg, limits of agreement − 6.6 to 4.9 mm Hg) and tcPCO2 (r = 0.999, bias 0.8 mm Hg, limits of agreement − 0.7 to 2.2 mm Hg) were excellent. In vitro drift was negligible for tcPO2 (0.30 (0.63 SD) mm Hg/24 h) and highly acceptable for tcPCO2 (− 2.53 (1.04 SD) mm Hg/12 h). Clinical use in neonates showed good usability and feasibility. SpO2-SaO2 correlation (r = 0.979) and agreement (bias 0.13%, limits of agreement − 3.95 to 4.21%) in healthy adult volunteers were excellent. The investigated combined tcPO2, tcPCO2, and SpO2 sensor with a new oxygen fluorescence quenching technique is clinically usable and provides good overall accuracy and negligible tcPO2 drift. Accurate and low-drift tcPO2 monitoring offers improved measurement validity for long-term monitoring of blood and tissue oxygenation.Graphical abstract

Toward all-day wearable health monitoring: An ultralow-power, reflective organic pulse oximetry sensing patch.

Pulse oximetry sensors have been playing a key role as devices to monitor elemental yet critical human health states. Conventional pulse oximetry sensors, however, have relatively large power consumption, impeding their use as stand-alone, continuous monitoring systems that can easily be integrated with everyday life. Here, we exploit the design freedom offered by organic technologies to realize a reflective patch-type pulse oximetry sensor with ultralow power consumption. On the basis of flexible organic light-emitting diodes and organic photodiodes designed via an optical simulation of color-sensitive light propagation within human skin, the proposed monolithically integrated organic pulse oximetry sensor heads exhibit successful operation at electrical power as low as 24 μW on average. We thereby demonstrate that organic devices not only have form factor advantages for such applications but also hold great promise as enablers for all-day wearable health monitoring systems.

RF91 USE OF NIRS AND REFLECTANCE PULSE OXIMETRY AS A MONITORING IN DISTAL PERFUSION OF THE LIMB DURING PERIPHERAL ECMO.

Background and aim: One of the biggest complications in patients treated with venoarterial ECMO is lower extremity ischemia, site of the peripheral cannulation. The ELSO database reports a 5% incidence of ischemic leg complications in patients with peripheral va-ECMO, leading to leg amputation in 1% of cases. The objective of the study is to optimize the perfusion of the cannulated limb for the reduction of the incidence of ischemia, pacing a distal perfusion catheter (8 Fr) in the superficial femoral artery, before the insertion of the deep femoral artery and monitoring of tissue oxygen saturation by NIRS and reflectance pulse oxymetry. Methods: Our study includes the analysis of the experience on a group of 9 patients in which tissue saturation was monitored by NIRS (group A) and another group that includes patients on whom the distal flow of the limb has been periodically detected by Eco Doppler SD2, without monitoring of tissue saturation (group B). Results: In the experience of group B a late diagnosis of ischemia of the cannulated limb was found despite the distal perfusion. In group A NIRS monitoring allowed to readily diagnose a hypoperfusion, detected with a variation of saturation &gt; 10% with respect to the tissue saturation of the contralateral limb and the basal value, resolving it with the immediate repositioning distal perfusion cannula. Conclusions: We conclude that transcutaneous NIRS and reflectance pulse oximetry may be an effective non-invasive method for continuous monitoring of leg perfusion in patients treated with peripheral ECMO and distal limb reperfusion.

Signal Separation for Transabdominal Non-invasive Fetal Pulse Oximetry using Comb Filters.

Non-invasive fetal pulse oximetry is the application of reflection pulse oximetry to the abdomen of a pregnant woman. Light sources and detectors areplaced on the belly. Emitted photons travel through maternal and fetal tissue and back to the detectors. The captured photoplethysmogram (PPG) is a complex mixture of the maternal and fetal pulse curve. A purely fetal PPG in time domain is needed to estimate the oxygen level of the unborn child. In this work we describe the application of comb filters to separate the fetalfrom the maternal signal. Finite element simulations and phantom measurements are utilized to generate and measure synthetic signals at different heart rates and noise levels. Comb filters with peak frequencies matched to the fetal heart rate are applied to the mixed PPGs. The filtered signals prove that the extraction of the fetal signal is sufficient even at a distance between the maternal and the fetal signal magnitudes of around 80 dB. The resulting signal quality is sufficient for beat to beat analysis and feature extraction in the time domain. We conclude that comb filtering is a suitable signal separation method for non-invasive fetal pulse oximetry.

Design of a new reflectance pulse oximeter by obtaining the optimal source-detector space

Pulse oximetry is an important medical monitoring technique. Interest in the use of reflectance mode of pulse oximeters has been grown for monitoring the arterial oxygen saturation (SaO2). The design sensor has an effective role in improvement of reflective pulse oximeters performance. In this study, the light propagation in tissue has been analyzed for development of reflection pulse oximetry. After analyzing theory, the optimal source-detector space was determined and a revision on SaO2 formulation calculated with Lambert–Beer law performed to reduce the errors. The new type of reflectance pulse oximeter was designed based on the theory calculation and then calibrated by in vivo experiments. The detecting signal have least dependence on changes in scattering properties of the tissue for obtained optimal space. One of the advantages of this design is reduction of influence of unconscious movement. In this novel design, calibration and validation experimental results show the repeatability potential and accuracy of the system.

Non-contact measurement using reflective pulse oximetry

Non-contact measurement using reflective pulse oximetry

Detection of angiospastic disorders in the microcirculatory bed using laser diagnostics technologies

The evaluation of the microcirculatory bed functional state and the identification of angiospastic disorders with related complications, when the pathological changes are reversible, have an important role in medical practice. The aim of this study was to evaluate the possibility of using optical noninvasive methods and the cold pressor test to solve this problem.A total of 33 patients with rheumatological diseases and 32 healthy volunteers were included in the study. Laser Doppler flowmetry, tissue reflectance oximetry and pulse oximetry were used as optical noninvasive methods. The parameters were recorded before, immediately after and 20[Formula: see text]min after the cold pressor test. Based on the measured parameters, the complex parameters of the microcirculatory bed were calculated.A detailed statistical analysis of the parameter changes for each individual in the two groups displayed diverse microcirculatory bed parameter responses upon cold exposure, with differing recovery of parameters after CPT. New diagnostic criteria were proposed for the identification of angiospastic disorders. According to the proposed criteria, 27 people of the volunteers group were confirmed to not display any disorders. In the patient group, however, 18 people were observed to have a relatively normal functional state of the microcirculatory bed, while 15 people were observed to have a possible tendency to angiospasm. To highlight the differences between a relatively normal state and presence of angiospastic disorders, statistical analysis of experimental data was carried out, which revealed significant differences. Further analysis of data with angiospastic disorders identified a relationship between their diagnoses and the results of laboratory studies.Thus, the evaluation of combined noninvasive optical diagnostic method use, the cold pressor test and proposed diagnostic criteria showed a positive result. This approach can be used to detect the presence of possible angiospastic disorders and related complications, as well as microcirculatory bed disorders against the background of other diseases.

Development and clinical evaluation of a new sensor design for buccal pulse oximetry in horses.

The use of pulse oximetry in horses is limited due to inadequate readings with conventional transmission sensor probes. The objectives of this study were to 1) develop an improved sensor design for horses to be used at an appropriate anatomical site, and 2) evaluate this design in an experimental study. In vivo experiment. A new sensor design for reflectance pulse oximetry at the buccal mucosa was developed. A conventional Nonin 2000SL sensor for transmission pulse oximetry was included into this design. Three different prototypes (N1, N2a, N2b) were constructed and used with the Nonin 2500A Vet pulse oximetry monitor. Thirteen anaesthetised warmblood horses were included into a desaturation protocol (100-70% SaO2 ). SpO2 and pulse frequency values were recorded, using SaO2 calculated from blood gas analysis and invasive pulse frequency measurements as reference methods. Bias and precision were evaluated by calculations of the root mean square deviation (Arms ). The agreement of the methods was tested with Bland-Altman analysis. The quality of the pulse frequency readings determined the quality of the SpO2 -readings. Good pulse signal strength resulted in a SpO2 -accuracy comparable to that of the original sensor (Nonin 2000SL: Arms = 3%; N1: Arms = 3.60%; N2b: Arms = 3.46%). Especially at heart rates ≤30 bpm, pulse rate readings that were about twice as high as the reference value occurred. Their exclusion from the dataset resulted in a pulse rate accuracy similar to that of the original sensor. Bland-Altman plots showed limits of agreement typical of pulse oximeters. The pulse frequency accuracy requires further improvement. The usability in clinical cases needs to be tested. The new sensor design has been shown to be suitable for buccal pulse oximetry in horses.

Pulse oximetry in the neck - a proof of concept.

Oxygen saturation levels are routinely monitored in clinical settings. Pulse oximetry, in transmittance operation mode, is the most common method of estimating oxygen saturation (SpO2). This is inexpensive and non-invasive and thus allows for long-term monitoring. However, it suffers from issues such as signal integrity, reliability and patient comfortability. As a result, there is an interest in exploring other locations on the body where oxygen saturation can be measured reliably. In this paper, a wearable device has been designed to study the feasibility of extracting photoplethysmogram (PPG) signals at the neck in reflectance pulse oximetry mode. It explores the signal integrity and strength compared to other locations as well as the presence of motion artefacts in that location. The results demonstrate that the PPG signals acquired at the neck show a very strong correlation (r=0.82) with the SpO2 values obtained using a commercial device. Further, the SpO2 values are calculated with an accuracy of 98.6%.

A systematic review of novel technology for monitoring infant and newborn heart rate.

This systematic review identified seven new technologies, including camera-based photoplethysmography, reflectance pulse oximetry, laser Doppler methods, capacitive sensors, piezoelectric sensors, electromyography and a digital stethoscope. Clinicians should be aware of several of these, which may become available for clinical use in the near future.