30. Orthostatic hypotension in the young and the elderly
Physiological response to assuming a standing posture
Going from supine to a standing posture results in 0,5 – 1L of blood pooling in the lower extremities due to gravity. This causes a decrease in venous return to the heart, resulting in a decreased cardiac output and blood pressure.
In normal cases, this fall in blood pressure triggers a compensatory reflex which increases sympathetic tone. This reflex is fast and mostly mediated by baroreceptors. The increased sympathetic tone increases peripheral vascular resistance and venous return and returns the pooling blood in the extremities to the functional circulation, thereby increasing cardiac output and blood pressure and preventing them from being significantly decreased compared to the supine values.
Orthostatic hypotension
When you stand up suddenly from a sitting or supine position, you may experience the feeling of seeing stars, feeling dizzy and losing consciousness. This happens when your body don’t get enough time to adapt, and so the blood pressure drops.
Orthostatic hypotension refers to a significant decrease in blood pressure due to failure of the compensatory mechanisms. This may cause dizziness, seeing stars, or even syncope due to the decreased perfusion to the brain. It can be diagnosed by measuring the blood pressure when lying down and after standing up, and comparing them.
This phenomenon occurs mostly in elderly, as the most common causes occur mostly in elderly. Causes of orthostatic hypotension include:
- Hot environments (fluid loss, skin vasodilation)
- Dehydration
- Disorders which disrupt the baroreflex
- Diabetic neuropathy
- Uremic neuropathy
- Neurodegenerative disorders (Parkinson, etc.)
- Age-related reduced baroreceptor sensitivity
- Antihypertensive or diuretic drugs
With aging, the sensitivity of the baroreceptors decreases, which contributes to the development of orthostatic hypotension.
Orthostatic hypotension in young is much less common but can occur due to baroreflex failure, due to diabetes or other autonomic neuropathies.
Orthostatic hypotension can be dangerous as it can cause syncope and falls, but in and of itself it’s mosty benign.