Cardiovascular · Year 1 · from Cardiovascular

Case 3: Orthostatic Hypotension - Autonomic Dysfunction

Patient Presentation

Demographics: 75-year-old male

Chief Complaint: Dizziness and falls when standing

History of Present Illness: A 75-year-old male with Parkinson's disease (diagnosed 8 years ago) presents with 6 months of progressive dizziness and near-syncope upon standing. He has had 4 falls in the past month, all occurring shortly after standing up. Symptoms are worse in the morning and after meals. He also reports constipation, urinary hesitancy, and decreased sweating. Current medications include carbidopa-levodopa and pramipexole.

Physical Examination:

  • Vital Signs:
  • Supine: BP 145/85 mmHg, HR 70 bpm (after 5 min supine)
  • Standing (1 min): BP 98/60 mmHg, HR 74 bpm
  • Standing (3 min): BP 85/55 mmHg, HR 76 bpm
  • General: Masked facies, resting tremor, shuffling gait
  • Cardiovascular: Regular rhythm, no murmurs
  • Neurologic: Bradykinesia, rigidity, postural instability

Workup

  • Orthostatic BP testing: Systolic BP drop >40 mmHg with minimal HR increase
  • Head-up tilt table test: Reproduced orthostatic hypotension without vasovagal features
  • Labs: Basic metabolic panel normal, hemoglobin 13.5 g/dL, cortisol normal
  • Autonomic function testing:
  • Heart rate variability: Reduced
  • Valsalva ratio: Blunted (indicates parasympathetic dysfunction)
  • Sweat testing: Anhidrosis in lower extremities
  • Cardiac autonomic testing: Blunted HR response to deep breathing

Diagnosis

Neurogenic orthostatic hypotension secondary to Parkinson's disease with autonomic dysfunction

Blood Pressure Regulation Correlation:

Normal standing response:

  1. Standing → blood pools in lower extremities (500-800 mL)
  2. ↓ Venous return → ↓ CO → ↓ BP
  3. Baroreceptors detect ↓ BP → activate sympathetic response:
  • ↑ HR (normally increases 10-25 bpm)
  • Vasoconstriction (↑ SVR)
  • Venoconstriction (↑ venous return)
  1. Result: BP maintained within 10-20 mmHg of baseline

In autonomic failure:

  • Efferent sympathetic pathways damaged → cannot increase HR or vasoconstrict
  • α-synuclein deposits in autonomic ganglia (Parkinson's, MSA, Lewy body dementia)
  • Baroreceptor reflex arc disrupted
  • Result: Uncompensated BP drop, minimal HR response

Criteria for orthostatic hypotension:

  • Systolic BP drop ≥20 mmHg OR
  • Diastolic BP drop ≥10 mmHg
  • Within 3 minutes of standing

Neurogenic vs. non-neurogenic: Minimal HR increase (<15 bpm) suggests neurogenic cause

Treatment

  1. Non-pharmacologic measures:
  • Rise slowly from sitting/lying
  • Compression stockings (waist-high)
  • Abdominal binder
  • Increase salt and fluid intake (2-3 L/day, 6-10 g sodium)
  • Elevate head of bed 10-20°
  • Avoid large meals, alcohol, hot environments
  1. Medication review:
  • Reduce/eliminate offending agents (may need to adjust Parkinson's meds)
  1. Pharmacologic treatment:
  • Midodrine (α1 agonist): 5-10 mg TID before meals
  • Fludrocortisone (mineralocorticoid): 0.1-0.2 mg daily (volume expansion)
  • Droxidopa (norepinephrine prodrug): For neurogenic OH

Clinical Image

Image Description: Diagram illustrating the pathophysiology of orthostatic hypotension, showing blood pooling in lower extremities upon standing and the normal baroreceptor-mediated compensatory response that fails in autonomic dysfunction.

Source: Wikimedia Commons - Orthostatic hypotension License: CC BY-SA 4.0 URL: https://commons.wikimedia.org/wiki/File:Orthostatic_hypotension.svg

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