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

Objective.Noninvasive measurement of oxygen saturation (SpO2) 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 ofSpO2using rPPGs.Approach.In this paper, a correction factor or 'pathlength ratio'ßis introduced in an existing calibration-free algorithm that compensates the patient-dependent pathlength variations, and improved accuracy is obtained in the measurement ofSpO2using rPPGs. The proposed pathlength ratioßis 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,ßis determined.Main results.The results of the analysis show that a specific combination of theßand 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 measuringSpO2values reduces to 1 %.Significance.The human hypoxia study data used for this work, obtained in a previous study, coversSpO2values in the range from 70 % to 100 %, and thus shows that the pathlength ratioßproposed 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 determineSpO2using reflective PPGs with the incorporation of the correction factorß. Our algorithm significantly reduces the number of parameters needed for the estimation, while keeping the RMSE below the clinically accepted 2 %.

Clinical outcomes in vaccinated individuals hospitalized with Delta variant of SARS-CoV-2

Emerging variants of SARS-CoV-2 with increased transmissibility or immune escape have been causing large outbreaks of COVID-19 infections across the world. As most of the vaccines currently in use have been derived from viral strains circulating in the early part of the pandemic, it becomes imperative to constantly assess the efficacy of these vaccines against emerging variants. In this hospital-based cohort study, we analysed clinical profiles and outcomes of 1161 COVID-19 hospitalized patients (vaccinated with COVISHIELD (ChAdOx1) or COVAXIN (BBV-152), n = 495 and unvaccinated n = 666) in Hyderabad, India between April 24th and May 31st 2021. Viral genome sequencing revealed that >90% of patients in both groups were harbouring the Delta variant (Pango lineage B.1.617.2) of SARS-CoV-2. Vaccinated individuals showed higher neutralizing antibodies (545{+/-}1256 AU/ml Vs 51.1{+/-}296 AU/ml; p<0.001) and significantly decreased Ferritin (392.26 {+/-} 448.4 ng/mL Vs 544.82 {+/-} 641.41 ng/mL; p<0.001) and LDH (559.45 {+/-} 324.05 U/L Vs 644.99 {+/-} 294.03 U/L; p<0.001), when compared to the unvaccinated group. Severity of the disease (3.2% Vs 7.2%; p=0.0039) and requirement of ventilatory support (2.8% Vs 5.9%; p=0.0154) were significantly low in the vaccinated group despite the fact that these individuals had significantly higher age and risk factors. The rate of mortality was about 50% lower (2/132=1.51%) in the completely vaccinated breakthrough infections although mortality in individuals who had received a single dose was similar to the unvaccinated group (9/269=3.35% vs 23/666= 3.45%). Our results demonstrate that both COVISHIELD and COVAXIN are effective in preventing disease severity and mortality against the Delta variant in completely vaccinated hospitalized patients.