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

Traditionally, measurements of the oxygen saturation (S_pO₂) has been confound to the extremities. In this study, we therefore investigated the possibility for reliable estimation of clinically relevant S_pO₂ 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 S_pO₂ 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 S_pO₂ 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 S_pO₂ levels on critically or chronically ill patients.