Sunday, October 25, 2009

What changes occur in the circulatory system when a person stands up from a prone position?

How do these changes affect the heart rate and blood pressure of the individual?
Typically when we stand from prone, the blood in our venous system tends to pool in our lower extremities. This causes a reduction to the blood flow to our heart, in medical terms, decreased preload. Since there is a small decrease to the total volume of blood going to the heart, the heart compensates by increasing its heart rate. People may experience a very small drop in blood pressure only for a short time.
In healthy individuals, the little changes in heart rate and blood pressure are not enough for us to feel any different.
There are compensatory mechanisms that prevent too severe drop in blood pressure. The carotid sinus has pressure receptors that determine if there's a significant change in MAP (mean arterial pressure) and respond by increasing or decreasing the capacitance of the vessels thereby compensating. In the elderly, these mechanisms are sluggish and decreased.

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