Orthostatic Hypotension (OH)
The syndrome characterized by syncope upon moving from supine to upright position is called orthostatic hypotension (OH), which is defined as a drop in systolic blood pressure of ≥20 mmHg or diastolic blood pressure of ≥10 mmHg with assumption of an upright posture 1.
Key Terminology and Distinctions
The 2017 ACC/AHA/HRS guidelines provide precise definitions for several related but distinct conditions that occur with postural changes 1:
Types of Orthostatic Hypotension
Initial (Immediate) OH: A transient BP decrease within 15 seconds after standing, with presyncope or syncope 1
Classic OH: A sustained reduction of systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg within 3 minutes of assuming upright posture 1
Delayed OH: A sustained reduction of systolic BP ≥20 mmHg (or 30 mmHg in patients with supine hypertension) or diastolic BP ≥10 mmHg that takes >3 minutes of upright posture to develop 1
Neurogenic OH: A subtype due to autonomic nervous system dysfunction rather than environmental triggers like dehydration or drugs, involving lesions of central or peripheral autonomic nerves 1
Related but Different Conditions
Orthostatic intolerance is a broader syndrome consisting of frequent, recurrent, or persistent lightheadedness, palpitations, tremulousness, generalized weakness, blurred vision, exercise intolerance, and fatigue upon standing—which can occur with or without orthostatic tachycardia, OH, or syncope 1.
Postural Orthostatic Tachycardia Syndrome (POTS) is characterized by: 1) frequent symptoms with standing, 2) heart rate increase ≥30 bpm (or ≥40 bpm in ages 12-19) during positional change from supine to standing, and 3) absence of OH (standing heart rate often >120 bpm) 1.
Clinical Context
Vasovagal syncope (VVS) is the most common form of reflex syncope that may occur with upright posture, typically characterized by diaphoresis, warmth, nausea, and pallor, associated with vasodepressor hypotension and/or inappropriate bradycardia 1, 2. While VVS can occur with postural changes, it differs mechanistically from OH as it involves a reflex causing vasodilation and/or bradycardia rather than a fixed blood pressure drop with position change.
Important Clinical Pitfalls
The relationship between blood pressure fall and symptoms is not straightforward 3. Some patients with significant OH may be asymptomatic, while others with smaller BP drops experience severe symptoms. Recent evidence suggests that complaint recognition correlates with larger BP falls, but the pathophysiology involves multiple factors including cerebral perfusion variability 3.
Testing should be performed in patients with orthostatic symptoms (vision changes, dizziness occurring only when upright and improving when seated/lying down), as well as asymptomatic high-risk groups including adults with frailty older than 70 years, individuals with neurodegenerative or autonomic disorders, and patients with unexplained falls 4.