Supplemental Figure S1

Supplemental Figure 1. An example of the contamination of the plethysmographic flow signal by cardiovascular pulsation. These data are taken from a rat equipped with a telemetric blood pressure sensor and placed in the same plethysmography setup used in this study. The data are not included in this study but are presented to demonstrate the presence of cardiac pulsation that exists in the flow signal, particularly during the period of apnea and recovery after fentanyl. The top panel shows 10 minutes of flow and blood pressure (BP) signal before and after a bolus of 150 ug/kg fentanyl IV. The bottom panel is 10 seconds of recording during the recovery. Lines have been drawn to demonstrate the heartbeat and the corresponding alteration of the flow signal.