What are the diagnostic criteria for orthostatic hypotension?

Diagnostic Criteria for Orthostatic Hypotension

Classical orthostatic hypotension is definitively diagnosed when there is a sustained decrease in systolic blood pressure ≥20 mmHg, diastolic blood pressure ≥10 mmHg, or a sustained decrease in systolic blood pressure to an absolute value <90 mmHg within 3 minutes of active standing or head-up tilt of at least 60 degrees. 1

Types of Orthostatic Hypotension

Orthostatic hypotension can be classified into several distinct types based on timing and presentation:

1. Classical Orthostatic Hypotension

• Definition: Sustained BP decrease (systolic ≥20 mmHg, diastolic ≥10 mmHg, or systolic decrease to <90 mmHg) within 3 minutes of standing 1
• Special consideration: In patients with supine hypertension, a systolic BP drop ≥30 mmHg should be considered diagnostic 1
• Pathophysiology: Impaired increase in total peripheral resistance and heart rate in autonomic failure resulting in blood pooling 1
• Heart rate response: Blunted in neurogenic OH (usually <10 beats per minute); preserved or enhanced in hypovolemic OH 1

2. Initial Orthostatic Hypotension

• Definition: BP decrease >40 mmHg systolic and/or >20 mmHg diastolic within 15 seconds of standing 1
• Key feature: BP spontaneously returns to normal within 40 seconds 1
• Clinical significance: Rate of BP recovery after initial fall has prognostic implications in elderly patients 1

3. Delayed Orthostatic Hypotension

• Definition: OH occurring beyond 3 minutes of head-up tilt or active standing 1
• Characteristics: Slow progressive decrease in BP without bradycardia 1
• Distinction: Absence of bradycardia helps differentiate from reflex syncope 1

Diagnostic Testing Protocol

Active Standing Test (Preferred Initial Test)

1. Preparation:

   • Patient should be fasted for at least 4 hours prior to testing 1
   • Avoid vasoactive medications before testing when possible

2. Measurement technique:

   • Measure BP supine after at least 5 minutes of rest 1
   • Have patient stand actively (not assisted)
   • Measure BP at 1 minute and 3 minutes of standing 1
   • If BP continues to fall at 3 minutes, continue measurements 1
   • If patient cannot tolerate standing, record lowest systolic BP during upright posture 1

3. Equipment:

   • Standard sphygmomanometer is adequate for routine clinical testing 1
   • Continuous beat-to-beat non-invasive BP measurement may be helpful in cases of doubt 1
   • Note: Automatic arm-cuff devices may be disadvantageous due to programmed repeat measurements when discrepant values are recorded 1

Clinical Implications

Orthostatic hypotension has significant clinical implications:

• Mortality risk: Classical OH is associated with increased mortality and cardiovascular disease prevalence 1
• Symptom variability: Symptoms depend more on absolute BP level than magnitude of fall 1
• Cerebral autoregulation: Plays key role in symptom manifestation 1
• Common symptoms: Dizziness, light-headedness, weakness, fatigue, visual and hearing disturbances 1
• Special populations: More common in frail elderly, patients on vasoactive drugs or diuretics, and those with autonomic failure or hypovolemia 1

Common Pitfalls and Caveats

1. Measurement errors:

   • Inadequate rest period before baseline measurement
   • Insufficient measurement frequency during standing
   • Using automatic devices that delay repeat measurements

2. Clinical interpretation:

   • Failure to consider higher threshold (≥30 mmHg systolic drop) in patients with supine hypertension 1
   • Not distinguishing between different types of OH (classical, initial, delayed)
   • Overlooking asymptomatic OH, which still carries prognostic significance 1

3. Testing conditions:

   • Food ingestion, time of day, medications, ambient temperature, hydration status, and deconditioning can all affect orthostatic BP responses 1
   • Recent vigorous exercise may exacerbate orthostatic changes 1

By following these diagnostic criteria and testing protocols, clinicians can accurately diagnose orthostatic hypotension and its specific subtypes, leading to appropriate management strategies that can reduce morbidity and mortality in affected patients.