Methods: Fourteen healthy volunteers (9 men, 5 women; 25 ± 3.7 years) received single oral doses of 5 mg nebivolol, 50 mg atenolol, and 100 mg atenolol, each taken for a 2-week period. Heart rate variability (HRV) measurements in time- (SDNN; rMSSD; pNN50) and frequency-domain (low frequency-LF; high frequency-HF; LF/HF ratio) were used to study the autonomic effects of the three regimens on the same patients from serial 24-hour ECGs.

Results: Both nebivolol and atenolol, the 50 mg dose as well as the 100 mg dose, produced similar decreases in heart rate compared with baseline throughout the 24-h period (from 82 ± 9 beats/min to 72 ± 7 beats/min, 69 ± 9, and 68 ± 8 beats/min, respectively, p < 0.001).="" overall,="" the="" administration="" of="" each=""> -blocker led to directionally similar increases in the HRV variables, which were most significant following 100 mg atenolol. Nebivolol and the 50 mg dose of atenolol produced similar increases in rMSSD and pNN50 during the entire 24-h period, and in HF power, particularly during the nighttime (p < 0.05).="" however,="" the="" coefficient="" of="" hf="" variance="" resulted="" in="" similar="" values="" after="" either=""> -blocker regimen. The LF/HF ratio was most reduced throughout the 24-h period following 100 mg atenolol (p < 0.001),="" and="" to="" a="" similar="" extent="" decreased="" in="" the="" nighttime="" following="" nebivolol="" and="" atenolol="" 50="" mg="">p <>

Conclusions: Nebivolol 5 mg exerts similar effects on time and frequency domain indexes of HRV as 50 mg atenolol. Nebivolol attenuates sympathetic tone, but does not appear to promote vagal activity more than atenolol.