A clinical study of short-term sternal photoplethysmography: Recordings from patients with obstructive airways diseases

Traditionally, measurements of the oxygen saturation (SpO2) has been confound to the extremities. In this study, we therefore investigated the possibility for reliable estimation of clinically relevant SpO2 levels from photoplethysmography (PPG) obtained on the sternum of patients with obstructive airway diseases. We initiated the study with a calibration of a prototype sternal PPG sensor. In accordance with the ISO 80601-2-61:2011 guidelines, the calibration was conducted as a controlled desaturation study. We obtained a calibration accuracy of 1.75% which is well within the clinically and commercially accepted range. We then compared the SpO2 levels simultaneously obtained from the sternal PPGs and a commercially available finger pulse oximeter on 28 admitted patients with either asthma or Chronic Obstructive Pulmonary Disease (COPD). The Pearson correlation between the SpO2 levels estimated from the two body locations was found to be 0.89 (p<;0.05) and the mean system bias was only 0.052% with upper and lower limits of agreement of 2.5% and -2.4%, respectively. This finding is very promising for the future design of new sternum based patch technologies that might be able to provide continuous estimates of the SpO2 levels on critically or chronically ill patients.