Figure 5.

Change in HRV as a function of HR induced by SNA blockade followed by PNA blockade. Plots of the TP, LF, and HF HRV, corrected for HR, as a function of HR at baseline (no drug), after propranolol, and after propranolol plus atropine. Propranolol administration reduced HR without affecting TP, LF, or HF HRV in exercised as well as sedentary mice. The subsequent administration of atropine, in the presence of propranolol, reduced TP (P < 0.005) and HF (P < 0.007) HRV while increasing (P < 0.001) HR in both exercise groups, similar to the responses to atropine in the absence of SNA blockade. Atropine had no measurable (P = 0.961) effect on HRV in sedentary mice despite also increasing HR. After complete cardiac autonomic blockade (propranolol + atropine), HR differences between groups were eliminated (P > 0.301). Data are presented as mean ± SD.