What Is Orthostatic Hypotension A Symptom Of?
Orthostatic hypotension is the fall in blood pressure when a person changes its posture from sitting or lying down to standing position. It is usually occurring when there is a decreased tone of blood vessels specially venular system which usually counters for the blood pooling occurring under the lower part of the body. When the person is in standing position, the gravity on the circulatory volume of blood acts in the downward direction and increases the tendency of blood to remain in the lower blood vessels especially in lower limbs.
In a normal person, the blood vessels in the lower limbs have an inherent tone that tries to maintain the circulation by reverse pumping the blood in an upward direction. But whenever there is the loss of that tone due to any reason, the blood pressure falls causing the orthostatic hypotension.
The causative factor for the generation of the condition of orthostatic hypotension is a defective parasympathetic and sympathetic system of the body which are both comprised in the autonomic nervous system. The most common reason is the idiopathic orthostatic hypotension which means there is not a known cause for the failure of the autonomic system. It is also known as a pure autonomic failure because there are only the autonomic functions affected in the circulatory system of the body. Rest all of the functions are good going and well to do. There can be other reasons for orthostatic hypotension also like an autoimmune autonomic failure ( AAF ) and multiple system atrophy ( MSA).(1) Apart from the above causes, there is a separate cause of orthostatic hypotension in which only the sympathetic system is involved and it is known as postural orthostatic tachycardia syndrome (POTS).
What Happens To Heart Rate When You Have Orthostatic Hypotension?
To find the reason behind the change in heart rate when there is a fall in blood pressure, it has to be followed from basic physiology. In orthostatic hypotension, as there is venous pooling of the blood in the venular system of the body, the body gets the shortage of blood in the circulatory system which has to be managed in some way to maintain the circulation. To counter the fall in the circulatory volume of the blood, the heart tries to compensate by increasing the pumping speed of itself. It results in a higher volume of pumping of blood from the heart at the same time interval and the fall in volume gets compensated. Hence, there is an increase in heart rate whenever there is venous pooling of the blood as in the case of orthostatic hypotension.
In such patients who are suffering from orthostatic hypotension, the reverse phenomenon can also be seen. If the patient is standing already, is made to lie down and instantly the blood pressure of the patient is checked it will show a rise and the pulse rate will fall as compared to the rate when he was standing. It can clarify the change in heart rate with the orthostatic hypotension.(1)
Orthostatic hypotension is a symptom of the failure of the autonomic nervous system of the body. It has both sympathetic and parasympathetic systems as its constituents. Orthostatic hypotension is more commonly associated with the defective sympathetic nervous system because it affects the cardiovascular system directly as well as indirectly. It can affect both the blood vessel dilation and constriction as well as control the heart rate also. Idiopathic orthostatic hypotension is the most common diagnosis for falls in blood pressure while standing from lying down position.
The effect of orthostatic hypotension on the heart rate can easily be measured by palpating the pulse of the patient and comparing the rate in a posture of lying down and standing. This maneuver should be done quickly because the body can compensate for the change in position rapidly.
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