Question

Orthohypotension why? Blood Pressure 120/80 mmHg, Heart Rate 110/min - Supine; BP 90/60 mmHg; HR Thready - Standing (Patient complains of dizziness upon standing).

Answer 1

When a person stands up from sitting or lying position, the body needs to pump sufficient amount of blood to reach to brain to provide adequate amount of oxygen. When the body fails to do this, there is fall in blood pressure and person experiences lightheadedness. The autonomic nervous system is responsible to regulate the blood pressure of the body. During the change of position, the autonomic nervous system makes changes in the blood pressure and heart rate so that the brain gets adequate supply of blood. This fall of blood pressure due to postural change is called orthostatic hypotension.  

When body moves to a standing position from supine, the baroreceptors in the carotid arteries and aorta sense this drop of blood pressure due to gravity that causes blood to flow towards gravity. This stimulates the sympathetic nervous system which causes the blood vessels to constrict and blood is pushed forcefully upwards resulting in increased heart rate. These combined action results to maintain the adequate blood flow to the brain and other organs. If these changes donot occur then the gravity will cause blood to flow downwards resulting in low blood pressure and person experiences symptoms of orthosatic hypotension.

The symptoms are lightheadedness, weakness, blurred vision and syncope. Orthostatic hypotension is seen in conditions like dehydration, anaemia, blood loss, beta blockers and other antihypertensive medications.