Various studies suggest that the manner of an individualís cardiovascular reaction to stress may play an important role in the development of hypertension.
Definitions of "high" blood pressure (hypertension) do vary, but pressure above 150/90 mmHg are generally considered excessive.
Essential hypertension refers to high blood pressure for which there is no detectable medical or organic cause. The majority of hypertension patients have essential hypertension. It is a substantial problem, with 15% of adult Western population estimated as exhibiting it.
Sufferers of hypertension are 3X more likely to suffer from myocardial infarction, and 8X more likely to have a stroke.
A mechanism has been outlined whereby additional cardiac activity in response to stress could contribute to hypertension.
Some sorts of psychological stressor that demand active attention and vigilance provoke in some people increases in cardiac activity. This is termed additional cardiac activity as it is an increase over and above that which is required to meet the physical energy demands of the individual.
This leads to overperfusion of tissues, especially skeletal muscle, which precipitates autoregulation. Autoregulation involves adjustments to the circulation in order to compensate for this overperfusion, and take the form of increased arterial resistance, ie arterial constriction.
NB ( BP = Cardiac Output X Peripheral Resistance)
It is argued that a sustained rise in BP results. An initial rise of BP as a result of increased cardiac activity is then maintained by autoregulatory vasoconstriction and resistance.
Hence the repeated exposure of responsive individuals to acute psychological stress and the sustained rise in BP that results will, over time, lead to a resetting of an individualís BP to new, higher, levels.
This additional cardiac activity is thought to stem from psychological stresses eliciting the "fight or flight" mobilisation of the cardiovascular system.
What determines if an individual responds to stress with cardiac reactions that are excessive in terms of energy expenditure?
There appears to be a large genetic component to this. Some individuals are biologically primed to respond with exaggerated cardiac reactions.
This has been borne-out by studies carried out on individuals at risk for hypertension due to having parents with high BP. People with a positive family history of hypertension display the most marked heart rate and BP reactions to psychological stress.
Not surprisingly, the kidneys have also been implicated in the development of hypertension, due to their control of salt and water excretion.
The kidneys normally respond to an increase in BP by increasing salt and water excretion to lower BP. Evidence suggests that stress may compromise the functioning of this mechanism.
Individuals exhibiting additional cardiac activity to stress also show salt and water retention. This hints that abnormal cardiac and renal reactions to stress may be the products of a common mechanism.
© 1997 Hannah Cole
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