FIG. 4.

Baroreceptor sensitivity assay. (A) Sigmoidal relationship between changes in mean blood pressure (BP) and beat-to-beat interval (RR) in two representative littermates. Changes in mean blood pressure were plotted against changes in the RR interval occurring spontaneously or with drug infusion. (B) Comparison of regression coefficients calculated for each animal from the sigmoidal curve (P < 0.02 by Fisher's R to z test). Open and closed circles in panels A and B represent wild-type and KH animals, respectively. (C) Ratio of changes in heart rate to the maximum change in blood pressure in response to 20 μg of either phenylephrine (PHE) or nitroprusside (SNP)/kg in KH (black bars) and wild-type (white bars) mice. Significance, as determined by unpaired Student's t test, was as follows: P = 0.05 during infusion of phenylephrine and P = 0.06 during infusion of nitroprusside.