Influence of vagal nervous activity on blood pressure variability.

In our previous studies, it was shown that blood pressure variability was largely independent from the adrenergic nervous system. In the present work, vagal nervous influence on blood pressure variability was analysed both in dogs and in men. In eight chronically instrumented conscious dogs, striking fluctuations of blood pressure were observed when quietly resting; these fluctuations correlate well with fluctuation of heart rate. Atropine abolished all variations both of heart rate and of pressure. Reflex stimulation of vagal tone by neosynephrine increased variability of both parameters. Thus, in dogs, blood pressure variability is related to variability of heart rate which is largely influenced by vagal tone. The same question was approached in seven male volunteers; blood pressure and heart rate were measured automatically every 2 min, during 1 h, before and after atropine. In control conditions, no correlation between variability of heart rate and of blood pressure was observed. Atropine clearly decreased variability of heart rate and of diastolic blood pressure. These data confirm the animal results; however, the influence of vagal nerves on variability is less pronounced in man than in dogs.