Calculation Of Oxygen Saturation Research Articles

Investigation of a Camera-Based Contactless Pulse Oximeter with Time-Division Multiplex Illumination Applied on Piglets for Neonatological Applications

(1) Objective: This study aims to lay a foundation for noncontact intensive care monitoring of premature babies. (2) Methods: Arterial oxygen saturation and heart rate were measured using a monochrome camera and time-division multiplex controlled lighting at three different wavelengths (660 nm, 810 nm and 940 nm) on a piglet model. (3) Results: Using this camera system and our newly designed algorithm for further analysis, the detection of a heartbeat and the calculation of oxygen saturation were evaluated. In motionless individuals, heartbeat and respiration were separated clearly during light breathing and with only minor intervention. In this case, the mean difference between noncontact and contact saturation measurements was 0.7% (RMSE = 3.8%, MAE = 2.93%). (4) Conclusions: The new sensor was proven effective under ideal animal experimental conditions. The results allow a systematic improvement for the further development of contactless vital sign monitoring systems. The results presented here are a major step towards the development of an incubator with noncontact sensor systems for use in the neonatal intensive care unit.

CARDIOVASCULAR AND HEMATOLOGICAL RESPONSES TO A DRY DYNAMIC APNEA IN BREATH HOLD DIVERS.

The mammalian dive reflex, characterized by bradycardia and peripheral vasoconstriction, occurs in all mammals, including humans, in response to apnea. However, the dive reflex to a single, maximal, dry, dynamic apnea (DYN), and how it compares to a time-matched exercise control trial (EX) or dry static apnea (SA), has not been studied. We examined the hypotheses that, compared to EX and SA, the magnitude of the (a) cardiovascular response and (b) hematological response to DYN would be greater. Cardiovascular parameters (heart rate [HR], systolic [SBP], diastolic [DBP], and mean arterial [MAP] blood pressure) were continuously collected in twenty-three (F=6) moderate and elite freedivers, first during a maximal DYN, then during a time-matched SA and EX on a swimming ergometer in randomized order. Venous blood draws were made prior to and following each trial. The change in calculated oxygen saturation (DYN:-17±13%, EX:-2±1%, ΔSA:-2±1%;P<0.05, all comparisons) was greater during DYN compared to EX and SA. During DYN, ΔSBP (DYN:104±31mmHg, EX:38±23mmHg, SA:20±11mmHg), ΔDBP (DYN:45±12mmHg, EX:14±10mmHg, SA:15±8mmHg) and ΔMAP (DYN:65±17mmHg EX:22±13mmHg, SA:16±9mmHg) were increased compared to EX and SA, while ΔHR was greater during EX (DYN:-24±23bpm, EX:33±13bpm, SA:-1±10bpm) than either DYN or SA (P<0.0001, all comparisons). Females had greater pressor response to EX (ΔSBP:59±30mmHg, ΔDBP:24±14mmHg, ΔMAP:35±8mmHg) than males (ΔSBP:31±15mmHg, ΔDBP:11±6mmHg, ΔMAP:18±8mmHg; P<0.01, all comparisons). Together, these data indicate that DYN elicits a distinct, exaggerated cardiovascular response compared to EX or SA alone.

A New Model of Air-Oxygen Blender for Mechanical Ventilators Using Dynamic Pressure Sensors.

Respiratory diseases are among the leading causes of death globally, with the COVID-19 pandemic serving as a prominent example. Issues such as infections affect a large population and, depending on the mode of transmission, can rapidly spread worldwide, impacting thousands of individuals. These diseases manifest in mild and severe forms, with severely affected patients requiring ventilatory support. The air-oxygen blender is a critical component of mechanical ventilators, responsible for mixing air and oxygen in precise proportions to ensure a constant supply. The most commonly used version of this equipment is the analog model, which faces several challenges. These include a lack of precision in adjustments and the inspiratory fraction of oxygen, as well as gas wastage from cylinders as pressure decreases. The research proposes a blender model utilizing only dynamic pressure sensors to calculate oxygen saturation, based on Bernoulli's equation. The model underwent validation through simulation, revealing a linear relationship between pressures and oxygen saturation up to a mixture outlet pressure of 500 cmH2O. Beyond this value, the relationship begins to exhibit non-linearities. However, these non-linearities can be mitigated through a calibration algorithm that adjusts the mathematical model. This research represents a relevant advancement in the field, addressing the scarcity of work focused on this essential equipment crucial for saving lives.

A test of the interaction between central and peripheral respiratory chemoreflexes in humans.

How central and peripheral chemoreceptor drives to breathe interact in humans remains contentious. We measured the peripheral chemoreflex sensitivity to hypoxia (PChS) at various isocapnic CO2 tensions ( ) to determine the form of the relationship between PChS and central . Twenty participants (10F) completed three repetitions of modified rebreathing tests with end-tidal ( ) clamped at 150, 70, 60 and 45mmHg. End-tidal ( ), , ventilation ( E ) and calculated oxygen saturation (SC O2 ) were measured breath-by-breath by gas-analyser and pneumotach. The E - relationship of repeat-trials were linear-interpolated, combined, averaged into 1mmHg bins, and fitted with a double-linear function ( E S, L min-1 mmHg-1 ). PChS was computed at intervals of 1mmHg of as follows: the difference in E between the three hypoxic profiles and the hyperoxic profile (∆ E ) was calculated; three ∆ E values were plotted against corresponding SC O2 ; and linear regression determined PChS (Lmin-1 mmHg-1 %SC O2 -1 ). These processing steps were repeated at each to produce the PChS vs. isocapnic relationship. These were fitted with linear and polynomial functions, and Akaike information criterion identified the best-fit model. One-way repeated measures analysis of variance assessed between-condition differences. E S increased (P<0.0001) with isoxic from 3.7±1.5 L min-1 mmHg-1 at 150mmHg to 4.4±1.8, 5.0±1.6 and 6.0±2.2 Lmin-1 mmHg-1 at 70, 60 and 45mmHg, respectively. Mean SC O2 fell progressively (99.3±0%, 93.7±0.1%, 90.4±0.1% and 80.5±0.1%; P<0.0001). In all individuals, PChS increased with , and this relationship was best described by a linear model in 75%. Despite increasing central chemoreflex activation, PChS increased linearly with indicative of an additive central-peripheral chemoreflex response. KEY POINTS: How central and peripheral chemoreceptor drives to breathe interact in humans remains contentious. We measured peripheral chemoreflex sensitivity to hypoxia (PChS) at various isocapnic carbon dioxide tensions ( ) to determine the form of the relationship between PChS and central . Participants performed three repetitions of modified rebreathing with end-tidal fixed at 150, 70, 60 and 45mmHg. PChS was computed at intervals of 1mmHg of end-tidal ( ) as follows: the difference in E between the three hypoxic profiles and the hyperoxic profile (∆ E ) was calculated; three ∆ E values were plotted against corresponding calculated oxygen saturation (SC O2 ); and linear regression determined PChS (Lmin-1 mmHg-1 %SC O2 -1 ). In all individuals, PChS increased with , and this relationship was best described by a linear (rather than polynomial) model in 15 of 20. Most participants did not exhibit a hypo- or hyper-additive effect of central chemoreceptors on the peripheral chemoreflex indicating that the interaction was additive.

Measurements of cerebral microvascular blood flow, oxygenation, and morphology in a mouse model of whole-brain irradiation-induced cognitive impairment by two-photon microscopy and optical coherence tomography: evidence for microvascular injury in the cerebral white matter.

Whole-brain irradiation (WBI, also known as whole-brain radiation therapy) is a mainstay treatment modality for patients with multiple brain metastases. It is also used as a prophylactic treatment for microscopic tumors that cannot be detected by magnetic resonance imaging. WBI induces a progressive cognitive decline in ~ 50% of the patients surviving over 6months, significantly compromising the quality of life. There is increasing preclinical evidence that radiation-induced injury to the cerebral microvasculature and accelerated neurovascular senescence plays a central role in this side effect of WBI. To better understand this side effect, male C57BL/6 mice were first subjected to a clinically relevant protocol of fractionated WBI (5Gy, two doses per week, for 4weeks). Nine months post the WBI treatment, we applied two-photon microscopy and Doppler optical coherence tomography to measure capillary red-blood-cell (RBC) flux, capillary morphology, and microvascular oxygen partial pressure (PO2) in the cerebral somatosensory cortex in the awake, head-restrained, WPI-treated mice and their age-matched controls, through a cover-glass-sealed chronic cranial window. Thanks to the extended penetration depth with the fluorophore - Alexa680, measurements of capillary blood flow properties (e.g., RBC flux, speed, and linear density) in the cerebral subcortical white matter were enabled. We found that the WBI-treated mice exhibited a significantly decreased capillary RBC flux in the white matter. WBI also caused a significant reduction in capillary diameter, as well as a large (although insignificant) reduction in segment density at the deeper cortical layers (e.g., 600-700μm), while the other morphological properties (e.g., segment length and tortuosity) were not obviously affected. In addition, we found that PO2 measured in the arterioles and venules, as well as the calculated oxygen saturation and oxygen extraction fraction, were not obviously affected by WBI. Lastly, WBI was associated with a significant increase in the erythrocyte-associated transients of PO2, while the changes of other cerebral capillary PO2 properties (e.g., capillary mean-PO2, RBC-PO2, and InterRBC-PO2) were not significant. Collectively, our findings support the notion that WBI results in persistent cerebral white matter microvascular impairment, which likely contributes to the WBI-induced brain injury and cognitive decline. Further studies are warranted to assess the WBI-induced changes in brain tissue oxygenation and malfunction of the white matter microvasculature as well.

Non-contact photoplethysmographic sensors for monitoring students' cardiovascular system functional state in an IoT system

This article explores the technical feasibility of a hardware complex that employs photoplethysmographic sensors to measure the parameters of students' cardiovascular system functional state. The method of photoplethysmography utilizes non-contact sensors, which eliminate circulatory disorders caused by artery compression and enable the calculation of oxygen saturation via the pulse wave. The proposed hardware consists of several optocouplers arranged in series, parallel, or parallel-series configurations, with the mode of operation controlled by the intensity of the received pulse wave signal, depending on the individual's body constitution. The edge device hardware is a component of an Internet of Things (IoT) system that includes another edge device, which instantaneously transmits data to a database on the edge server for further processing and storage.

Assessing central and peripheral respiratory chemoreceptor interaction in humans.

What is the central question of this study? We investigated the interaction between central and peripheral respiratory chemoreceptors in healthy, awake human participants by using a background of step increases in steady-state normoxic fraction of inspired carbon dioxide to alter central chemoreceptor activation and by using the transient hypoxia test to target the peripheral chemoreceptors. What is the main finding and its importance? Our data suggest that the interaction between central and peripheral respiratory chemoreceptors is additive in minute ventilation and respiratory rate, but hypo-additive in tidal volume. Our study adds important new data in reconciling chemoreceptor interaction in awake healthy humans and is consistent with previous reports of simple addition in intact rodents and humans. Arterial blood gas levels are maintained through respiratory chemoreflexes, mediated by central chemoreceptors in the CNS and peripheral chemoreceptors located in the carotid bodies. The interaction between central and peripheral chemoreceptors is controversial, and few studies have investigated this interaction in awake, healthy humans, owing, in part, to methodological challenges. We investigated the interaction between the central and peripheral chemoreceptors in healthy humans using a transient hypoxia test (three consecutive breaths of 100% N2 ; TT-HVR), which targets the temporal domain and stimulus specificity of the peripheral chemoreceptors. The TT-HVRs were superimposed upon three randomized background levels of steady-state inspired fraction of normoxic CO2 ( ; 0, 0.02 and 0.04). Chemostimuli [calculated oxygen saturation ( )] and respiratory variable responses [respiratory rate (RR ), inspired tidal volume (VTI ) and ventilation ( )] were averaged from all three TT-HVR trials at each level. Responses were assessed as: (1) a change (∆) from baseline; and (2) indexed against . Aside from a significantly lower ∆VTI response in 0.04 (P=0.01), the hypoxic rate responses (∆RR or ∆RR / ; P=0.46 and P=0.81), hypoxic tidal volume response ( ; P=0.08) and the hypoxic ventilatory responses ( and ; P=0.09 and P=0.31) were not significantly different across trials. Our data suggest simple addition between central and peripheral chemoreceptors in , which is mediated through simple addition in RR responses, but hypo-addition in VTI responses. Our study adds important new data in reconciling chemoreceptor interaction in awake, healthy humans and is consistent with previous reports of simple addition in intact rodents and humans.

Multi-Detector Heart Rate Extraction Method for Transabdominal Fetal Pulse Oximetry.

Intrapartum fetal well-being assessment relies on fetal heart rate (FHR) monitoring. Studies have shown that FHR monitoring has a high false-positive rate for detecting fetal hypoxia during labor and delivery. A transabdominal fetal pulse oximeter device that measures fetal oxygen saturation non-invasively through NIR light source and photodetectors could increase the accuracy of hypoxia detection. As light travels through both maternal and fetal tissue, photodetectors on the surface of mother's abdomen capture mixed signals comprising fetal and maternal information. The fetal information should be extracted first to enable fetal oxygen saturation calculation. A multi-detector fetal signal extraction method is presented in this paper where adaptive noise cancellation is applied to four mixed signals captured by four separate photodetectors placed at varying distances from the light source. As a result of adaptive noise cancellation, we obtain four separate FHR by peak detection. Weighting, outlier rejection and averaging are applied to these four fetal heart rates and a mean FHR is reported. The method is evaluated in utero on data collected from hypoxic lamb model. Ground truth for FHR is measured through hemodynamics. The results showed that using multi-detector fetal signal extraction gave up to 18.56% lower root-mean-square FHR error, and up to 57.87% lower maximum absolute FHR error compared to single-detector fetal signal extraction.

Frequency of Undiagnosed Hypoxia in Patients

Aim: To determine frequency of undiagnosed hypoxia in pts which was medically sick admitted in chest wards. Study design: Cross-sectional. Place and duration of study: Department of Medicine, Social Security Hospital, Multan Road Lahore from 1st January 2020 to 30th June 2020. Methodology: Two hundred and ninety patients were included in this study. Patients detailed demographics age, sex, and body mass index were recorded after taking written consent and admitted in chest wards. Presented patients were aged between 20-70 years. Pulse oximeter was used to measure the oxygen saturation levels. Mean time of hospitalization was also measured. Results: There were 170(60%) males and 120(40%) females with mean age of the patients were 40.78±18.64 years. Mean BMI was 27.78±12.64 kg/m2. Majority of the patients 160(55.17%) were from the age group 35-70 years. Calculated oxygen saturation rate was 91.98±9.42% in which minimum rate was 80% and the maximum rate was 105%. Mean heart rate was 92.96±19.20 per minute. Patients were admitted due to tuberculosis were 102(35.17%), patients with chronic pulmonary disease were 70 (24.17%), patients with pleural effusion were 30(10.34%) and the patients of asthma were 20(6.9%). In this study hypoxia was observed in 44 (15.17%) patients and was absent in 246 (84.83%) patients. Conclusion: The frequency of hypoxia was most prevalent in male patients with increasing age as compared to females and in chronic obstructive pulmonary disease patients, it was observed more commonly. Keywords: Pulse oximeter, Oxygen saturation, Undiagnosed hypoxia

A Textile Sleeve for Monitoring Oxygen Saturation Using Multichannel Optical Fibre Photoplethysmography.

Textile-based systems are an attractive prospect for wearable technology as they can provide monitoring of key physiological parameters in a comfortable and unobtrusive form. A novel system based on multichannel optical fibre sensor probes integrated into a textile sleeve is described. The system measures the photoplethysmogram (PPG) at two wavelengths (660 and 830 nm), which is then used to calculate oxygen saturation (SpO2). In order to achieve reliable measurement without adjusting the position of the garment, four plastic optical fibre (POF) probes are utilised to increase the likelihood that a high-quality PPG is obtained due to at least one of the probes being positioned over a blood vessel. Each probe transmits and receives light into the skin to measure the PPG and SpO2. All POFs are integrated in a stretchable textile sleeve with a circumference of 15 cm to keep the sensor in contact with the subject’s wrist and to minimise motion artefacts. Tests on healthy volunteers show that the multichannel PPG sensor faithfully provides an SpO2 reading in at least one of the four sensor channels in all cases with no need for adjusting the position of the sleeve. This could not be achieved using a single sensor alone. The multichannel sensor is used to monitor the SpO2 of 10 participants with an average wrist circumference of 16.0 ± 0.6 cm. Comparing the developed sensor’s SpO2 readings to a reference commercial oximeter (reflectance Masimo Radical-7) illustrates that the mean difference between the two sensors’ readings is −0.03%, the upper limit of agreement (LOA) is 0.52% and the lower LOA is −0.58%. This multichannel sensor has the potential to achieve reliable, unobtrusive and comfortable textile-based monitoring of both heart rate and SpO2 during everyday life.

Health Monitoring of Human Multiple Physiological Parameters Based on Wireless Remote Medical System

Telemedicine, as a new technical means and medical model, can truly realize the sharing and monitoring of telemedicine information, and ultimately ensure that everyone has equal access to medical and health resources. Based on the research on the status of telemedicine application and wireless communication technology, this paper proposes a multi-physical parameter wireless telemedicine health monitoring system solution, and analyzes the overall structure and functional requirements of the system. Human physiological parameters of the wireless remote medical system for health monitoring include body temperature, respiration, blood oxygen saturation, pulse, blood pressure, and electrocardiogram. In this paper, fabric electrodes are used to extract human bioimpedance signals, discrete Fourier transform algorithm is used to detect human respiratory signals, and respiratory rate is detected based on dynamic differential threshold peak detection technology. The reflection type photoelectric sensor is used to realize the reflection of the human pulse signal, and the continuous measurement of the cuff-free blood pressure based on the pulse wave conduction time is combined with the ECG (Electrocardiogram) data. A self-learning threshold algorithm based on near-infrared photo plethysmo graphy signal trough detection is designed on the reflective blood oxygen saturation calculation algorithm. The difference threshold method is used to extract the QRS band feature points. We tested the overall operation of the system. The results show that the collected human physiological signal data is accurate. After a series of tests, the validity and reliability of the collected physiological signals have been proven.

Single-shot photoacoustic microscopy of hemoglobin concentration, oxygen saturation, and blood flow in sub-microseconds

We present fast functional optical-resolution photoacoustic microscopy (OR-PAM) that can simultaneously image hemoglobin concentration, blood flow speed, and oxygen saturation with three-pulse excitation. To instantaneously determine the blood flow speed, dual-pulse photoacoustic flowmetry is developed to determine the blood flow speed from photoacoustic signal decay in sub-microseconds. Grueneisen relaxation effect is compensated for in the oxygen saturation calculation. The blood flow imaging is validated in phantom and in vivo experiments. The results show that the flow speed can be measured accurately in sub-microseconds by comparing the dual-pulse flowmetric method with photoacoustic Doppler flowmetry. Wide-field OR-PAM of hemoglobin concentration, blood flow speed, and oxygen saturation are demonstrated in the mouse ear. This technical advance enables more biomedical applications for fast functional OR-PAM.

Low pO2 Contributes to Potential Error in Oxygen Saturation Calculations Using a Point-of-Care Assay.

The present study addressed the accuracy of calculated oxygen saturation (sO2) using point-of-care (POC) testing compared with measured values on a blood gas analyzer. In total, 3,323 sO2 values were measured in 1,180 patients using a CO-oximeter (ABL 800 Flex; Radiometer, Copenhagen, Denmark). Measured parameters were then used to calculate an expected sO2 for the POC method (Abbott i-STAT; Abbott POC, Princeton, NJ). Cases in which calculated sO2 differed from measured sO2 by 10% or more were analyzed. Of the 3,323 comparisons performed, 260 (8%) showed discrepancies (± ≥10%) between measured and calculated sO2 values. Ninety-four of discrepant measurements (245 of 260) occurred when pO2 was less than 50 mm Hg. pH and bicarbonate distributions shifted to lower values in discrepant vs nondiscrepant cases. Our results suggest that the likelihood of discrepant sO2 is 27% among patients with pO2 less than 50 mm Hg. Direct measurement of sO2 by CO-oximetry is strongly suggested in this clinical scenario.

An efficient optimization method to improve the measuring accuracy of oxygen saturation by using triangular wave optical signal

The oxygen saturation is one of the important parameters to evaluate human health. This paper presents an efficient optimization method that can improve the accuracy of oxygen saturation measurement, which employs an optical frequency division triangular wave signal as the excitation signal to obtain dynamic spectrum and calculate oxygen saturation. In comparison to the traditional method measured RMSE (root mean square error) of SpO2 which is 0.1705, this proposed method significantly reduced the measured RMSE which is 0.0965. It is notable that the accuracy of oxygen saturation measurement has been improved significantly. The method can simplify the circuit and bring down the demand of elements. Furthermore, it has a great reference value on improving the signal to noise ratio of other physiological signals.

Dual-wavelength retinal images denoising algorithm for improving the accuracy of oxygen saturation calculation.

Noninvasive measurement of hemoglobin oxygen saturation ( SO 2 ) in retinal vessels is based on spectrophotometry and spectral absorption characteristics of tissue. Retinal images at 570 and 600 nm are simultaneously captured by dual-wavelength retinal oximetry based on fundus camera. SO 2 is finally measured after vessel segmentation, image registration, and calculation of optical density ratio of two images. However, image noise can dramatically affect subsequent image processing and SO 2 calculation accuracy. The aforementioned problem remains to be addressed. The purpose of this study was to improve image quality and SO 2 calculation accuracy by noise analysis and denoising algorithm for dual-wavelength images. First, noise parameters were estimated by mixed Poisson–Gaussian (MPG) noise model. Second, an MPG denoising algorithm which we called variance stabilizing transform (VST) + dual-domain image denoising (DDID) was proposed based on VST and improved dual-domain filter. The results show that VST + DDID is able to effectively remove MPG noise and preserve image edge details. VST + DDID is better than VST + block-matching and three-dimensional filtering, especially in preserving low-contrast details. The following simulation and analysis indicate that MPG noise in the retinal images can lead to erroneously low measurement for SO 2 , and the denoised images can provide more accurate grayscale values for retinal oximetry.

Automatisation and improved repeatability of retinal oximetry

PurposeTo develop and test an automatic method for analysing retinal oximetry images.MethodsThe dual‐wavelength Oxymap T1 oximeter captures images for calculation of oxygen saturation in retinal vessels. Images were taken of healthy subjects for testing of repeatability and sensitivity, the latter during 100% O2 breathing (n = 21). Images were also taken of patients with diabetes and no DR (n = 16) and patients with non‐proliferative DR (n = 24). The diabetic groups were compared with 54 healthy subjects.Semi‐automatic and fully automatic computer programs were used for analysis. The main differences are: The automatic program automatically categorises vessel points into arterioles and venules and then gives averages for each retinal image. The automatic program uses all pixels on vessel cross‐sections for calculations.ResultsFor arterioles in healthy, the standard deviation between repeated measurements was 0.98 percentage points (pp) with the semi‐automatic method but 0.66 pp with the automatic method. The corresponding values for venules were 1.99 pp (semi‐auto) and 1.50 pp (auto). The automatic program detected an increase of 5.1 pp in arteriolar saturation and 17.4 pp in venules when healthy subjects inhaled pure oxygen (p &lt; 0.0001 in both cases). Similar values were found with the semi‐automatic software.Higher venous saturation was detected in patients with non‐proliferative DR (p &lt; 0.05 with both programs). Values (mean ± SD) from the automatic software were 68.5 ± 5.6% (NPDR), 63.3 ± 6.0% (DM but no DR) and 64.9 ± 4.7% (healthy).ConclusionsAutomatic analysis of retinal oximetry images yields good repeatability. The automatic method is sensitive to changes in saturation during 100% O2 breathing and detects higher venous saturation in diabetic retinopathy. Automatic analysis is much faster than the semi‐automatic approach and is less subjective.

Two methods to adapt the human haemoglobin–oxygen dissociation algorithm to the blood of white rhinoceros (Ceratotherium simum) and to determine the accuracy of pulse oximetry

ObjectivesTo adapt the algorithm for the calculation of oxygen saturation to the blood characteristics of the white rhinoceros by two different methods and to determine the accuracy of conventional pulse oximetry measurements. Study designAdaptation of two mathematical models of the oxygen dissociation curve (ODC). AnimalsTwenty-five captive white rhinoceros (Ceratotherium simum), including 12 males and 13 females, aged 6–32 years. MethodsDuring 33 anaesthetic events, 94 arterial blood gas samples with 72 simultaneous pulse oximetry measurements were analysed. The calculation of oxygen saturation was adapted to the characteristics of rhinoceros blood using two different methods. Firstly, a mathematical model developed in 1984 and, secondly, an oxygen status algorithm (OSA) produced by the same developer in 2005 were tested for their applicability for clinical use. ResultsWhen arterial partial pressure of oxygen is >7.98 kPa (60 mmHg), oxygen saturation exceeds 95%. At partial pressures of 6.12–6.52 kPa (46–49 mmHg) Method 1 determined oxygen saturations of 92.5–95.3% and Method 2 oxygen saturations of 90.2–91.6%. Both methods resulted in similar ODCs and accounted for the low p50 value of rhinoceros blood. Method 1 provided better adaptation in respect to the physiological parameters of the rhinoceros, especially with regard to the Bohr effect, than Method 2. Pulse oximetry was an unreliable method of monitoring arterial oxygen saturation during general anaesthesia in this species. ConclusionAdapting the oxygen saturation algorithm to consider the left shift of the ODC provides a useful tool for monitoring oxygen status, especially as pulse oximetry is insufficiently accurate. Experimental determination of the complete Hill curve is required to further validate and optimize the algorithm for use in the white rhinoceros. Clinical relevanceThe method will facilitate the accurate interpretation of oxygen saturation calculated by blood gas analysis in white rhinoceros.

Assessment of Acute Mild Hypoxia on Retinal Oxygen Saturation Using Snapshot Retinal Oximetry

To study the effect of acute mild hypoxia on retinal oxygen saturation. Spectral retinal images were acquired under normoxic and hypoxic conditions for 10 healthy human volunteers (six male, four female, aged 25 ± 5 years [mean ± SD]) using a modified fundus camera fitted with an image-replicating imaging spectrometer (IRIS). Acute, mild hypoxia was induced by changing the oxygen saturation of inhaled air from 21% to 15% using a hypoxia generator with subjects breathing the hypoxic gas mixture for 10 minutes. Peripheral arterial oxygen saturation of the subjects was monitored using fingertip-pulse oximetry. Images were processed to calculate oxygen saturation, arteriovenous difference in oxygen saturation, and vessel diameter. Data are presented as mean ± SD and were analyzed using paired sample t-test with significance accepted at P < 0.05. The retinal arterial and venous oxygen saturation was 98.5% ± 1.6% and 70.7% ± 2.7% during normoxia. A reduction in the fraction of inspired oxygen resulted in a decline (P < 0.001) in both retinal-arterial and venous oxygen saturation to 90.3% ± 2.0% and 62.4% ± 2.2%, respectively. The arteriovenous oxygen saturation difference in normoxia (27.8% ± 2.9%) and hypoxia (27.9% ± 2.1%) did not change. Retinal arteriolar and venular diameters increased (P < 0.001) by 4% and 3%, respectively, under hypoxia. The acute inhalation of a hypoxic gas mixture resulted in a decline in both retinal-arterial and venous saturation, while arteriovenous oxygen difference was maintained with an accompanying significant increase in retinal vessel diameter. This may suggest an autoregulatory response to acute mild hypoxia.

Continuous noninvasive hemoglobin monitoring: The standard of care and future impact*

While the authors present analysis of trends, observations reflect more static, than dynamic hematological conditions, and they suggest that CNHM “…may be a feasible alternative to invasive hemoglobin monitoring”. However, they do not present decision-making or outcomes results, per se, and wisely, stop short of implying CNHM should replace discrete in vitro diagnostic hemoglobin testing when the article ends with the somewhat circuitous caveat, “A laboratory hemoglobin determination could be limited to situations where a blood transfusion is considered”. Oxygen saturation measured noninvasively by traditional pulse oximetry using red (~660 nm) and infrared (~905 nm) light emitting diodes (LEDs) differentiates oxy- versus deoxyhemoglobin, respectively (2). The ratio of red versus infrared light is correlated with a calibration curve empirically derived from clinical studies to calculate oxygen saturation over a limited range (2, 3), while pulse rate is determined from the plethysmogram. Newer devices incorporate robust treatment of the red/infrared ratio, multiple wavelengths, advanced algorithms, and proprietary sensor calibrations integrated (3). These principles extend to pulse co-oximetry, where up to twelve wavelengths and sophisticated signal reduction enable measurement of carboxyhemoglobin, methemoglobin, total hemoglobin,

Quantitative impact of small angle forward scatter on whole blood oximetry using a Beer–Lambert absorbance model

It is well known that red blood cell scattering has an impact on whole blood oximetry as well as in vivo retinal oxygen saturation measurements. The goal of this study was to quantify the impact of small angle forward scatter on whole blood oximetry for scattering angles found in retinal oximetry light paths. Transmittance spectra of whole blood were measured in two different experimental setups: one that included small angle scatter in the transmitted signal and one that measured the transmitted signal only, at absorbance path lengths of 25, 50, 100, 250 and 500 µm. Oxygen saturation was determined by multiple linear regression in the 520-600 nm wavelength range and compared between path lengths and experimental setups. Mean calculated oxygen saturation differences between setups were greater than 10% at every absorbance path length. The deviations to the Beer-Lambert absorbance model had different spectral dependences between experimental setups, with the highest deviations found in the 520-540 nm range when scatter was added to the transmitted signal. These results are consistent with other models of forward scatter that predict different spectral dependences of the red blood cell scattering cross-section and haemoglobin extinction coefficients in this wavelength range.