Gender differences in autonomic functions associated with blood pressure regulation

By: Victor A. Convertino 

Journal of American Physiology 

 

Women have a decreased ability to regulate blood pressure. This could be due to many factors, including decreased baroreflex sensitivity, reduced blood volume, lower stroke volume (amount of blood pumped per beat) and cardiac output (amount of blood pumped per minute), and increased venous compliance in the lower extremities (causes blood flow to slow down so that any autonomic regulatory response would be slower). Because of this decreased regulatory ability, women are more prone to loss of consciousness and syncopal episodes than men. In this study, blood pressure regulation was compared specifically in orthostatic state (when standing).  

 

Seven women and ten men were age-matched and asked to complete a variety of orthostatic challenges. One test was performed to look at lower body negative pressure (LBNP). The pressure around the participant's lower body was gradually decreased until they began experiencing pre-syncopal symptoms, such as decreased systolic pressure, nausea, dizziness, and gray-outs. This procedure was carried out with the patient in supine position; as the pressure around the lower body decreases, the blood moves towards the head. The study found that women have LBNP threshold almost 35% lower than men. However, the HR at which pre-syncopal symptoms on-set was not significantly different between men and women (this would suggest that women have higher HR variability).  

 

Another test considered adrenoreceptor responsiveness. The study looked at two types of adrenoreceptors: α1- and β-.  Adrenoreceptor-agonists were administered intravenously to observe changes in blood pressure. The study found that adrenoreceptors were more responsive in women than men.  

 

In addition, MAP was compared using the Valsalva maneuver (forceful expiration against a closed nose and mouth – close mouth, pinch nose, exhale). This maneuver decreases blood pressure. At one stage of the maneuver, it was observed that the male HR increased at a higher rate than the females, in response to the decrease in blood pressure.  

 

There was one interesting hypothesis presented in the abstract that was not directly addressed elsewhere: when men stand up, they respond with greater sympathetic stimulation to periphery; when women stand up, they respond with greater vagal withdrawal.  

 

-- S. Kulkarni