Simultaneous estimation of arterial and venous oxygen saturation using a camera

摘要

Optical monitoring of arterial blood oxygonation, SpO_2, using cameras has recently been shown feasible by measuring the relative amplitudes of the remotely sensed PPG waveforms captured at different wavelengths. SvO_2 measures the venous blood oxygenation which together with SpO_2 provides an indication of tissue oxygen consumption. In contrast to SpO_2 it usually still requires a blood sample from a pulmonary artery catheter. In this work we present a method which suggests simultaneous estimation of SpO_2 and SvO_2 with a camera. Contrary to earlier work, our method does not require external cuffs leading to better usability and improved comfort. Since the arterial blood varies synchronously with the heart rate, all frequencies outside the heart rate band are typically filtered out for SpO_2 measurements. For SvO_2 estimation, we include intensity variations in the respiratory frequency range since respiration modulates venous blood due to intrathoracic pressure variations in the chest and abdomen. Consequently, under static conditions, the two dominant components in the PPG signals are respiration and pulse. By measuring the amplitude ratios of these components, it seems possible to monitor both SpO_2 and SvO_2 continuously. We asked healthy subjects to follow an auditory breathing pattern while recording the face and hand. Results show a difference in estimated SpO_2 and SvO_2 values in the range 5-30 percent for both anatomical locations, which is normal for healthy people. This continuous, non-contact, method shows promise to alert the clinician to a change in patient condition sooner than SpO_2 alone.