Figure 1. Derivation of cardiac baroslopes. (Top) Individual data points from a 165-s file in which bolus sodium nitroprusside (SNP) is given, followed 60 s later by a bolus of phenylephrine (Phe). Note that the decreasing and increasing paths are not identical, and thus, these slopes are analyzed separately. Data are averaged over 2 mm Hg blood pressure increments, and then the best fit line is drawn to the linear portion of the response: left side for decreasing pressure and right side for increasing pressure. The X on each graft represents the mean heart rate and blood pressure before drug administration.