Objective:To measure the cardiac vagus nerve activity and its circadian rhythm in patients with essential hypertension(EH group) and normontensive controls (NC group)

and to study the relationship between the cardiac vagus nerve activity and blood pressure.Methods:By dynamic electrocardiogram and ambulatory blood pressure monitoring

HF

PNN 50 and their circadian rhythm were compared between the EH group and NC group

and the relationship between HF

PNN 50 and blood pressure was analyzed.Results:During 24 hours

waking and sleeping hours

HF

PNN 50 were significantly lower(P<0.001)in EH group compared with NC group.HF

PNN 50 in EH group still remained a circadian rhythm:HF

PNN 50 were higher during the sleeping hours(P<0.001)

but their night-day differences were significantly smaller in EH group than that in NC group(P<0.001).HF and PNN 50 were inversely correlated with SBP

DBP during 24 hours(r=-0.74;-0.83

P=0.0001).Conclusion:In patients with essential hypertension

the cardiac vagal activity decreases;the circadian rhythm of its activity is markedly blunted.The changes in the cardiac vagus activity are correlated with blood pressure oscillations.