Figure 2.

Mean ∫Phr amplitude and burst frequency immediately following doxapram injection. Data are presented from five experimental groups: intermittent doxapram (2 mg/kg), single doxapram (2 or 6 mg/kg), vehicle injection and time control. The plots are labeled “1, 2 or 3” to correspond to the intermittent doxapram injections. In the four groups that did not receive intermittent injections, measures of phrenic activity were taken at a comparable time point. All of the doxapram treated groups showed a similar increase in phrenic output during period 1. A progressive augmentation of ∫Phr amplitude occurred in rats receiving intermittent doxapram injections. *, significantly higher vs. single doxapram (2mg/kg and 6mg/kg), vehicle injections and time control; #, significantly different vs. doxapram injections; ‡, significantly different than injections 2 and 3, or comparable time points.