Continuous respiratory rate monitoring during an acute hypoxic challenge using a depth sensing camera

Respiratory rate is a well-known to be a clinically important parameter with numerous clinical uses including the assessment of disease state and the prediction of deterioration. It is frequently monitored using simple spot checks where reporting is intermittent and often prone to error. We report here on an algorithm to determine respiratory rate continuously and robustly using a non-contact method based on depth sensing camera technology. The respiratory rate of 14 healthy volunteers was studied during an acute hypoxic challenge where blood oxygen saturation was reduced in steps to a target 70% oxygen saturation and which elicited a wide range of respiratory rates. Depth sensing data streams were acquired and processed to generate a respiratory rate (RR(depth)). This was compared to a reference respiratory rate determined from a capnograph (RR(cap)). The bias and root mean squared difference (RMSD) accuracy between RR(depth) and the reference RR(cap) was found to be 0.04 bpm and 0.66 bpm respectively. The least squares fit regression equation was determined to be: RR(depth) = 0.99 × RR(cap) + 0.13 and the resulting Pearson correlation coefficient, R, was 0.99 (p < 0.001). These results were achieved with a 100% reporting uptime. In conclusion, excellent agreement was found between RR(depth) and RR(cap). Further work should include a larger cohort combined with a protocol to further test algorithmic performance in the face of motion and interference typical of that experienced in the clinical setting.