What are the causes of orthostatic hypotension (postural lightheadedness)?

From the Guidelines

Postural lightheadedness, also known as orthostatic hypotension, should be managed by making simple lifestyle changes, such as rising slowly from sitting or lying positions, staying well-hydrated, and avoiding alcohol and large meals, as these measures can help alleviate symptoms like dizziness, blurred vision, and weakness. To manage postural lightheadedness, the following steps can be taken:

• Rise slowly from sitting or lying positions to prevent sudden drops in blood pressure
• Stay well-hydrated by drinking 2-3 liters of water daily to maintain blood volume
• Increase salt intake, unless contraindicated by other health conditions, to help retain fluid
• Avoid alcohol and large meals, which can worsen symptoms
• Use compression stockings that extend to the waist to prevent blood pooling in the legs
• For persistent symptoms, medications like fludrocortisone (0.1-0.2 mg daily) or midodrine (2.5-10 mg three times daily) may be prescribed by a doctor, as noted in studies 1
• Physical countermaneuvers like crossing legs while standing, tensing calf muscles, or squeezing a rubber ball can temporarily increase blood pressure during episodes, as discussed in 1 These measures can help manage postural lightheadedness, which occurs when the nervous system's reflex to constrict blood vessels and increase heart rate is delayed or inadequate, causing blood to pool in the lower body and reducing circulation to the brain, as explained in 1.

From the FDA Drug Label

Midodrine has been studied in 3 principal controlled trials, one of 3-weeks duration and 2 of 1 to 2 days duration. All studies were randomized, double-blind and parallel-design trials in patients with orthostatic hypotension of any etiology and supine-to-standing fall of systolic blood pressure of at least 15 mmHg accompanied by at least moderate dizziness/lightheadedness After week 1, midodrine-treated patients had small improvements in dizziness/lightheadedness/unsteadiness scores and global evaluations, but these effects were made difficult to interpret by a high early drop-out rate (about 25% vs 5% on placebo). One-minute standing systolic blood pressures were increased 1 hour after each dose by about 15 mmHg and 3 hours after each dose by about 12 mmHg; 3-minute standing pressures were increased also at 1, but not 3, hours after dosing The 10 and 20 mg doses produced increases in standing 1-minute systolic pressure of about 30 mmHg at 1 hour; the increase was sustained in part for 2 hours after 10 mg and 4 hours after 20 mg.

Postural Lightheadedness is likely to be reduced with midodrine treatment, as the drug has been shown to improve dizziness/lightheadedness/unsteadiness scores in patients with orthostatic hypotension. The increase in standing systolic blood pressure of about 15-30 mmHg after midodrine administration suggests that the drug can help alleviate postural lightheadedness by improving blood flow to the brain when standing. However, the effects of midodrine on postural lightheadedness should be interpreted with caution due to the high early drop-out rate in some studies 2.

From the Research

Postural Lightheadedness

• Postural lightheadedness is a symptom of orthostatic hypotension, which is characterized by a decrease in blood pressure upon standing, associated with symptoms such as dizziness, visual "white-out", weakness, and near syncope or syncope 3.
• Orthostatic hypotension can be caused by various conditions, including neurogenic orthostatic hypotension, which is due to deficient peripheral vasoconstrictor tone in response to the upright position 3.
• Midodrine, a specific alpha-1-agonist, has been shown to be effective in treating neurogenic orthostatic hypotension by producing arteriolar constriction and decreasing venous pooling 3, 4.
• Midodrine has been compared to other medications, such as fludrocortisone, and has been found to have similar efficacy and a better safety profile 4, 5.
• Non-pharmacological strategies, such as maintaining adequate hydration, adding salt to the diet, and avoiding large carbohydrate-rich meals, are also important in managing postural lightheadedness 6, 7.
• However, a study found that higher sodium intake was associated with more frequent and severe lightheadedness in patients consuming the DASH diet, challenging traditional recommendations to increase sodium intake to prevent lightheadedness 6.
• The treatment of primary orthostatic hypotension should be guided by patient-specific factors, such as tolerability, adverse effects, and drug-drug and drug-disease interactions, and may involve the use of midodrine, droxidopa, fludrocortisone, pyridostigmine, atomoxetine, and other medications 7.