[A new procedure for the estimation of physical fitness of patients during clinical rehabilitation using the 6-minutes walk test]

Equity-Driven Sensing System for Measuring Skin Tone-Calibrated Peripheral Blood Oxygen Saturation (OptoBeat): Development, Design, and Evaluation Study

BACKGROUND

Many commodity pulse oximeters are insufficiently calibrated for patients with darker skin. We demonstrate a quantitative measurement of this disparity in peripheral blood oxygen saturation (SpO2) with a controlled experiment. To mitigate this, we present OptoBeat, an ultra-low-cost smartphone-based optical sensing system that captures SpO2 and heart rate while calibrating for differences in skin tone. Our sensing system can be constructed from commodity components and 3D-printed clips for approximately US $1. In our experiments, we demonstrate the efficacy of the OptoBeat system, which can measure SpO2 within 1% of the ground truth in levels as low as 75%.

OBJECTIVE

The objective of this work is to test the following hypotheses and implement an ultra-low-cost smartphone adapter to measure SpO2: skin tone has a significant effect on pulse oximeter measurements (hypothesis 1), images of skin tone can be used to calibrate pulse oximeter error (hypothesis 2), and SpO2 can be measured with a smartphone camera using the screen as a light source (hypothesis 3).

METHODS

Synthetic skin with the same optical properties as human skin was used in ex vivo experiments. A skin tone scale was placed in images for calibration and ground truth. To achieve a wide range of SpO2 for measurement, we reoxygenated sheep blood and pumped it through synthetic arteries. A custom optical system was connected from the smartphone screen (flashing red and blue) to the analyte and into the phone's camera for measurement.

RESULTS

The 3 skin tones were accurately classified according to the Fitzpatrick scale as types 2, 3, and 5. Classification was performed using the Euclidean distance between the measured red, green, and blue values. Traditional pulse oximeter measurements (n=2000) showed significant differences between skin tones in both alternating current and direct current measurements using ANOVA (direct current: F2,5997=3.1170 × 105, P<.01; alternating current: F2,5997=8.07 × 106, P<.01). Continuous SpO2 measurements (n=400; 10-second samples, 67 minutes total) from 95% to 75% were captured using OptoBeat in an ex vivo experiment. The accuracy was measured to be within 1% of the ground truth via quadratic support vector machine regression and 10-fold cross-validation (R2=0.97, root mean square error=0.7, mean square error=0.49, and mean absolute error=0.5). In the human-participant proof-of-concept experiment (N=3; samples=3 × N, duration=20-30 seconds per sample), SpO2 measurements were accurate to within 0.5% of the ground truth, and pulse rate measurements were accurate to within 1.7% of the ground truth.

CONCLUSIONS

In this work, we demonstrate that skin tone has a significant effect on SpO2 measurements and the design and evaluation of OptoBeat. The ultra-low-cost OptoBeat system enables smartphones to classify skin tone for calibration, reliably measure SpO2 as low as 75%, and normalize to avoid skin tone-based bias.

Evaluation of functional capacity and muscle metabolism in individuals with peripheral arterial disease with and without diabetes

OBJECTIVE

Peripheral arterial disease (PAD) is characterized by intermittent claudication, which interferes with walking and leads to worsening of functional capacity. This mechanism has not been clearly defined in PAD. Thus, the aim of our study was to identify the muscular metabolism and vascular function variables using near-infrared spectroscopy (NIRS) and their possible associations with functional capacity in individuals with PAD and secondly to verify the differences in these variables between persons with PAD and diabetes mellitus (DM) and those with PAD without DM.

METHODS

A total of 39 participants with intermittent claudication were enrolled, 14 of whom had DM. They were assessed for functional capacity by the total distance covered in the treadmill test with the speed and grade constant and for muscle function and metabolism using near-infrared spectroscopy at rest and during the treadmill test. The Spearman correlation coefficient was computed to assess the presence of an association between the variables, and multiple linear regression analysis was performed, considering the total test distance as the dependent variable. The assessment between groups was performed using the independent t test or Mann-Whitney U test.

RESULTS

The near-infrared spectroscopy variables related to tissue oxygen saturation in the test recovery phase were correlated with the functional performance during the treadmill test. Thus, those with a longer or slower recovery time and those with greater tissue deoxygenation had walked a shorter distance. A significant difference (P = .049) was noted between those with PAD stratified by DM in the reoxygenation time required for an occlusion.

CONCLUSIONS

These findings reinforce the hypothesis that peripheral factors related to vascular function and muscular metabolism can affect the walking capacity of persons with PAD and that microvascular dysfunction is more prevalent among those with PAD and DM.