Effect of respiratory-induced intensity variations on finger SpO2 measurements in volunteers

Photoplethysmographic (PPG) signals were recorded from the fingers of 16 healthy volunteers with periods of timed and forced respiration. The aim of this pilot study was to compare estimations of arterial oxygen saturation (SpO₂) recorded using a dedicated pulse oximetry system while subjects were breathing regularly with and without a mouthpiece containing a flow resistor. The experiments were designed to mimic the effects of mechanical ventilation in anesthetized patients. The effect of estimated airway pressures of ±15 cmH₂O caused observable modulation in the recorded red and PPG signals. SpO₂ values were calculated from the pre-recorded PPG signals. Mean SpO₂ values were 95.4% with the flow resistor compared with 97.3% with no artificial resistance, with statistical significance demonstrated using a Student´s t-test (P = 0.006).