Supplemental Figure S2

Supplemental Figure 2. Examples of the effect of band-pass filtering on the flow signal acquired from a rat in our plethysmography system. The signal in panel 1. was taken during a period of normal breathing, and the calculation of frequency (f) and the sum of the positive integral is straightforward. However, during the first minute of recovery from fentanyl-induced apnea, as seen in panel 2., discrimination between breath and artifact is critical. The data in panel 2. shows an unfiltered flow signal (V̇) collected during the recovery period after 150 mg/kg fentanyl IV. Arrows indicate individual breaths. In 3., a filter of 0.1 Hz is applied only to remove the DC component. Sum VT is calculated by integrating the positive flow signal over 5 seconds. In 3., an additional filter above 5 Hz applied to the signal is shown. This eliminates signal contamination and provides a more accurate calculation of f. The sum VT is also slightly reduced but only integrates breaths, so it is a more precise measure of breathing.