Noninvasive Measurement Of Oxygen Saturation Research Articles

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 %.

The use of protective masks and the level of arterial oxygen saturation at rest and after exercise.

Studies of influenza, and human coronaviruses provide evidence that the use of a medical mask can prevent the spread of infectious droplets from an infected person to someone else. After global public health emergency of coronavirus SARS-CoV-2 causing illness of COVID-19 was changing frequency of wearing a mask. Therefore, study was undertaken to assess whether the use of protective masks affects the level of oxygen saturation during rest and during exercise. The test consisted of a non-invasive measurement of oxygen saturation by percutaneous determination of arterial oxygen saturation with the use of the pulse oximeter. Oxygen saturation was measured during rest and after physical exertion performed without a protective mask (2 types of masks were used: surgical and FFP2), as well as during rest and after physical exertion performed with the use of a protective mask. The analysis of the oxygen saturation, heart rate, blood pressure and respiratory rate included data on 48 subjects. Comparing the post-exercise and pre-exercise values showed a significant difference between all of them. There were no differences found in any variables according to the mask/no-mask status. A short-term physical exercise performed in a group of healthy young people using protective masks did not affect oxygen saturation, heart rate, blood pressure and respiratory rate. Med Pr. 2022;73(5):363-68.

Noninvasive Measurement of Oxygen Saturation in Human Retinal Blood Vessels and Tissues With Multispectral Confocal Imaging.

Proof of concept for the first system of noninvasive human retinal vessel and tissue oxygenation measurement in axial and radial directions. A confocal imaging system capable of calculating and mapping relative retinal blood oxygenation in radial and axial directions from three eyes of two healthy subjects was built. The relationship between oxygenation and retinal depth in vivo was analyzed to illustrate application of this novel system. The system shows capacity for measuring oxygenation along retinal depth for the first time. (1) Arteriovenous oxygenation difference decreases with blood vessel diameter. (2) Artery-tissue oxygenation difference is greater than vein-tissue oxygenation difference in the same region. (3) Intravascular-extravascular oxygenation difference decreases with blood vessel diameter. (4) Oxygenation data reported with a 95% CI are as follows: A1 91.5% ± 18.2%, V1 32.8% ± 18.6%, A2 97.3% ± 17.8%, V2 64.4% ± 11.2%, A3 73.2% ± 19.1%, V3 52.9% ± 15.3%, and Tissue 56.6% ± 00.4%. This article demonstrates proof of concept for retinal oxygenation calculation in radial and axial dimensions for the first time. Initial results provide biological validity to this method. Future aims include further characterization of this system's results in healthy subjects and subsequent comparison of oxygenation between diseased and healthy retinae. [Ophthalmic Surg Lasers Imaging Retina. 2022;53:275-283.].

Randomised controlled trial to assess the effectiveness of apnoeic oxygenation in adults using low-flow or high-flow nasal cannula with head side elevation versus usual care to prevent desaturation during endotracheal intubation in the emergency department (ApOxED): study protocol

IntroductionApnoeic oxygenation is a process of delivering continuous oxygen through nasal cannula during direct laryngoscopy. The oxygen that is delivered through these nasal cannulas is either low flow or high...

Photoacoustic imaging of real-time oxygen changes in chronic leg ulcers after topical application of a haemoglobin spray: a pilot study

To use a non-invasive measurement of oxygen saturation in chronic leg ulcers after the application of a topical haemoglobin spray to investigate if photoacoustic tomography is able to measure the oxygen saturation and if the stimulated oxygen increase can be demonstrated. We measured the oxygen saturation of the ulcer tissue in five patients with chronic leg ulcers before application and 5 and 20 minutes after application of the haemoglobin spray, using photoacoustic tomography as a new method to assess oxygenation in real-time. The average oxygen saturation showed a significant increase from 56.4% before to 69% (p=0.042) after 5 minutes and 78.8% (p=0.043) 20 minutes after the topical haemoglobin application. The oxygenation status of chronic, hard-to-heal wounds is gaining increasing interest in modern wound therapy. Topical haemoglobin spray is a new and effective method to increase the oxygenation in the ulcer tissue, but until now the link between clinical results and the mode of action was unclear. We were able to show for the first time that the use of a topical haemoglobin spray leads to an increase in oxygen saturation in vivo using photoacoustic tomography. Joachim Dissemond received financial support from the company SastoMed for several scientific projects as well as for lectures and as an advisor. The haemoglobin spray was provided by SastoMed GmbH (Georgsmarienhütte, Germany).

Monitoring in the Intensive Care Unit: Its Past, Present, and Future

Monitoring in the critical care setting has dramatically improved during the past 50 years and has contributed significantly toimprove patients' safety and outcome [1–3]. New technologies have allowed the transfer ofadvances in biology, physiology, and bioengineering to the bedside to support data drivendecision making and continuous monitoring of the vulnerable critically ill patients.The most striking advances include the continuous and noninvasive measurement of oxygen saturation by pulseoximeters and of end tidal CO2 and the real-time displays of flow, volume, pressure time curves, and derived measures by modern ventilators as well as the development invasive and more recently noninvasive devices that provide beat-to-beat arterial pressure, stroke volume, and cardiac output monitoring. Despite these advances and the apparent impact made on patients' outcome, there are still a lot of progress to be made to bring monitoring to the level of safety and reliability achieved by industries such as aviation [3, 4]. The future of monitoring in the critical care setting probably relies less on global appraisal of descriptive variables and more on functional monitoring of organs. Ultimately monitoring complex organ function is more informative and will likely be more important than global and/or regional physiological parameterssuch as organs perfusion and oxygenation. Metabolic monitoring, reflecting the biologic functions of the organs, starts to emerge [5]. Noninvasive monitors and trend analysis will obviously continue to grow. In addition, more advanced monitoring of pain, sleep, wakefulness, and delirium are very much needed.Atthe end of the day, decision support systems and automated system will become instrumental and central in daily monitoring when such system can provide the high level of accuracy needed to allow health care providers to rely on them [6, 7]. In addition, decision support systems willonly make sense if they improveclinicians' decision making, not if they just synthesized clinical algorithms. We expect that decision support software that integrates monitoring signals to raise the safety, reliability, and efficiency bar and not to fully replace human being. Finally, there is still a lot to be learned regarding identifying which variables should be monitored to impact outcome and what constitute an appropriate as oppose to pathological harmful one to critical illnesses. Without such understanding, enhanced monitoring has the potential to lead to costly and counterproductive interventions. Finally, one has to ask whether new monitoring technologies must be evaluated and clearly demonstrate a positive impact on outcome before being used. There is no easy and universal answer to this question, we believe. Most hospital administrators may require outcome data before purchasing any new and potentially expensive technologies. This approach could, however, delay the implementation of useful technologies. It is indeed possible and likely that initial studies, even when well conducted, could only show no impact on outcome [8]. As an example, the pulse oximeter has been shown to have no impact on patients outcome [9, 10] despite the fact that this is considered standard of care. While some in the medical community are still wondering whether pulse oximeters do improve outcome since the data is lacking, in other industries such as aviation evidence-based data before implementing new technologies (monitors, autopilot, simulation) is not required and this industry has now reached an unmatched level of safety. On the other end, a more thoughtful assessment of clinical indication and physician education of physicians regarding Swan-Ganz catheter and hemodynamic management would have prevented many unhelpful right heart catheter placement over decades and possible harm. Clearly, there is not a single simple answer for every technology and/or problem at hand. In conclusion, monitoring in our specialty has come a long way. We are, however, still facing difficult challenges and the future holds great promisesfor our patient [3], particularly if, as an scientific community, we can learn from our past mistakes.This special issue on monitoring of critical patients illustrates some of the current and future challenges we are facing. Maxime Cannesson Alain Broccard Benoit Vallet Karim Bendjelid

Measurement of oxygen saturation in small retinal vessels with adaptive optics confocal scanning laser ophthalmoscope

We have used an adaptive optics confocal scanning laser ophthalmoscope to assess oxygen saturation in small retinal vessels. Images of the vessels with a diameter smaller than 50 μm are recorded at oxygen sensitive and isosbestic wavelengths (680 and 796 nm, respectively). The vessel optical densities (ODs) are determined by a computer algorithm. Then, OD ratios (ODRs), which are inversely proportional to oxygen saturation, are calculated. The results show that arterial ODRs are significantly smaller than venous ODRs, indicating that oxygen saturation in the artery is higher than that in the vein. To the best of our knowledge, this is the first noninvasive measurement of oxygen saturation in small retinal vessels.

Non-invasive measurement of oxygen saturation in the spinal vein using SWI: Quantitative evaluation under conditions of physiological and caffeine load

Susceptibility-weighted imaging (SWI) has been used for quantitative and non-invasive measurement of blood oxygen saturation in the brain. In this study, we used SWI for quantitative measurement of oxygen saturation in the spinal vein to look for physiological- or caffeine-induced changes in venous oxygenation. SWI measurements were obtained for 5 healthy volunteers using 1.5-T MR units, under 1) 3 kinds of physiological load (breath holding, Bh; hyperventilation, Hv; and inspiration of highly concentrated oxygen, Ox) and 2) caffeine load. Oxygen saturation in the anterior spinal vein (ASV) was calculated. We evaluated changes in oxygen saturation induced by physiological load. We also evaluated the time-course of oxygen saturation after caffeine intake. For the physiological load measurements, the average oxygen saturation for the 5 subjects was significantly lower in Hv (0.75) and significantly higher in Bh (0.84) when compared with control (0.80). There was no significant difference between Ox (0.81) and control. Oxygen saturation gradually decreased after caffeine intake. The average values of oxygen saturation were 0.79 (0min), 0.76 (20min), 0.74 (40min), and 0.73 (60min), respectively. We demonstrated a significant difference in oxygen saturation at 40 and 60min after caffeine intake when compared with 0min.In conclusion, we demonstrated the feasibility of using SWI for non-invasive measurement of oxygen saturation in the spinal vein. We showed changes in oxygen saturation under physiological as well as caffeine load and suggest that this method is a useful tool for the clinical evaluation of spinal cord oxygenation.

Noninvasive measurement of oxygen saturation of the microvascular blood in Barrett's dysplasia by use of optical spectroscopy

Current investigations into endoscopic screening for the early detection of Barrett's esophageal adenocarcinoma have focused on visualization of the microvascular morphology by using narrow-band imaging (NBI). Adjustment of the center wavelength, particularly of the NBI blue imaging filter, may lead to improved image contrast, depending on the oxygen saturation of the microvascular blood of dysplastic and early cancerous Barrett's mucosa. To perform in vivo, noninvasive measurements of the oxygen saturation of the microvascular blood for different pathologic grades of Barrett's mucosa by using differential path-length spectroscopy (DPS). DPS measurements were made on normal (n = 7), low-grade dysplastic (n = 10), high-grade dysplastic (n = 7), and cancerous (n = 4) Barrett's mucosa by using a fiber-optic probe, and were correlated to the histologic outcome of biopsy specimens taken from the same location. Academic medical center. Fifteen patients with Barrett's esophagus who were undergoing gastroscopy. Biopsy specimens were taken from suspicious areas in the esophagus. The oxygen saturation of the microvascular blood of different pathologic grades of Barrett's mucosa was assessed. The oxygen saturation of the microvascular blood remains high (approximately 90%) throughout the metaplasia-dysplasia-adenocarcinoma sequence. The small number of patients. The current NBI blue imaging filter, centered on the peak absorption of oxyhemoglobin (415 nm), is well chosen, and little improvement in image contrast is to be expected from changes in this center wavelength.

An optical sensor for the non-invasive measurement of the blood oxygen saturation of an artificial heart according to the variation of hematocrit

Abstract This study describes a non-invasive optical sensor and sensor system used to measure the blood oxygen saturation of an artificial heart, in vitro . The reflection type optical sensor consists of an LED for the light source and a PIN photodiode for the light detector in a flat pack. The emission wavelengths of the LED are 665 and 805 nm. The blood oxygen saturation was measured using the reflectance ratio of 665 to 805 nm. The sensor system for measurement of the oxygen saturation has been breadboarded. Changes in the blood oxygen saturation were detected by the developed sensor system in real time. The experimental set-up was designed to be identical in effects and circumstances to a living body. The non-invasive measurement of oxygen saturation in vitro was carried out. Using a constant volume (30 cc) of blood and various volumes (0, 10, 20, 30 cc) of a physical saline solution, the hematocrit level of the blood was determined. When the change in oxygen saturation is compared at each wavelength, the variation at 665 nm is four times more than at 805 nm. At the 805 nm wavelength there was only a small change over the 100-60% range of oxygen saturation. The reflectance ratio decreased with reduction of the hematocrit level. As the oxygen saturation was varied from 100 to 60%, the reflectance ratio R 805/ R 665 over the whole hematocrit range changed linearly.

Comparative accuracy of pulse oximetry and transcutaneous oxygen in assessing arterial saturation in pediatric intensive care

Recent improvements in the noninvasive measurement of oxygen saturation by pulse oximetry (SapO2) have resulted in the development of easily used bedside monitors. We compared the performance of the Biox 3700 and Nellcor N100E models against arterial saturation (SaO2) measured on a Radiometer OSM2 hemoximeter and against transcutaneous SO2 (StcO2) derived from transcutaneous oxygen tensions (PtcO2) (632, Roche Kontron). Twenty-four hemodynamically stable patients were studied, all with indwelling arterial lines, aged between 1 month and 13 yr. Mean differences +/- SD between SapO2 and SaO2 were -0.77 +/- 3.23 for the Nellcor and -2.90 +/- 2.19 for the Biox. The Biox machine generally read lower than the Nellcor with a mean difference of -1.63 +/- 2.65. SaO2 derived from PtcO2 (StcO2) did not differ significantly (-0.27 +/- 2.12) from SaO2. In hemodynamically stable infants and children, StcO2 and SapO2 have similar accuracy limits when compared with each other and with SaO2.