Brandon Pollock PhD, ACSM-EP-C
Proper redistribution of blood flow is of paramount importance both at rest and during exercise. Orthostatic hypotension, also known as postural hypotension, is a form of low blood pressure that occurs upon standing. In a healthy individual, in order to properly redistribute blood flow to the head, heart rate and blood pressure increase in response to standing. Orthostatic hypotension occurs when this response fails and blood remains pooled in the legs, resulting in decreased blood flow to the head. Many individuals describe experiencing orthostatic hypotension as a ‘head rush’, and symptoms include dizziness, blurred vision, nausea, headaches, lightheadedness, and in some cases even fainting.
Orthostatic hypotension is diagnosed as a drop in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg when a person assumes a standing position. Clinically, this is usually diagnosed through use of a tilt-table or lower body negative pressure.
Orthostatic hypotension is more common in the elderly and certain special populations, such as Parkinson’s disease. Interestingly, research now also suggests that females may experience more frequent symptoms of orthostatic hypotension compared to males. Reports suggest there are gender-specific differences in either nerve activity or blood flow responses, which may be responsible for females’ reduced orthostatic tolerance. In addition, women have been shown to respond primarily with vagal withdrawal while men show greater sympathetic activity. This is still somewhat controversial and the complicating roles played by comorbid factors and hormonal mechanisms are not well understood.
Recently as part of my doctoral dissertation our lab investigated the influence gender has on functional sympatholysis, a specific physiological response involved in the prevention of orthostatic hypotension. Although we found no significant differences between our males and females, we observed differences in heart rate responses suggesting the possibility that gender could in fact influence orthostatic intolerance.
So what could this all mean? Greater prevalence of orthostatic intolerance in females would predispose them to experience greater orthostatic hypotension and risk of syncope (fainting), especially during exercise. As of now, our research and that of previous investigators suggests that this may be the case. However, this is still controversial and future investigations are warranted to further determine whether gender differences are present in orthostatic hypotension and any of the associated physiological responses.
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