Fig. 2. Pulse oximeter arterial hemoglobin oxygen saturation (Spo2) trend readings for a typical subject in supine (0°) and two Trendelenburg positions (TP; −10° and −15°). Forehead sensor and two digit sensor readings were simultaneously recorded. The headband was used at its lower tension setting in this subject, except during the periods in which it was removed as noted in the figure. The bold segments of the forehead sensor tracing indicate the sampled data used in the numerical analysis.