Physiology · Year 1 · from Physiology

Case 3: Orthostatic Hypotension - Autonomic Failure

Clinical Image

Source: Clinical illustration of baroreceptor reflex and autonomic dysfunction

Patient Presentation

A 72-year-old male with a 15-year history of type 2 diabetes mellitus presents with recurrent near-syncope and falls over the past year. Episodes occur when he stands up from sitting or lying down, particularly in the morning or after meals. He reports feeling lightheaded and having "graying" of vision when standing. He also mentions longstanding erectile dysfunction, constipation alternating with diarrhea, urinary hesitancy with incomplete bladder emptying, and inability to sense when his bladder is full. His diabetes has been poorly controlled for years.

Demographics

  • Age: 72 years
  • Sex: Male
  • Past Medical History: Type 2 DM x 15 years, HbA1c 9.2%, peripheral neuropathy

Chief Complaint

Recurrent near-syncope and falls when standing

Physical Examination

Supine:

  • BP: 152/88 mmHg, HR: 76 bpm

Standing (after 3 minutes):

  • BP: 98/62 mmHg (drop >20 systolic, >10 diastolic), HR: 78 bpm (minimal increase - impaired reflex)

Additional findings:

  • Neurological: Stocking-glove sensory loss to light touch and vibration, absent ankle reflexes
  • Cardiovascular: No carotid bruits, regular rhythm
  • Extremities: Dry skin, decreased hair on lower legs, diminished pedal pulses

Workup

  • Orthostatic vital signs: Confirmed >20 mmHg systolic drop without appropriate heart rate increase
  • ECG: Normal sinus rhythm, no conduction abnormalities
  • Echocardiogram: Normal LV function (rules out cardiac cause)
  • Tilt-table testing: Neurogenic orthostatic hypotension confirmed (BP drops without compensatory tachycardia)
  • Autonomic function tests:
  • Heart rate variability with deep breathing: Reduced (parasympathetic dysfunction)
  • Valsalva maneuver: Absent overshoot and reduced heart rate response
  • Quantitative sudomotor axon reflex test (QSART): Reduced sweat output in feet
  • Post-void residual: 180 mL (indicates neurogenic bladder)
  • HbA1c: 9.2%

Diagnosis

Diabetic Autonomic Neuropathy with Neurogenic Orthostatic Hypotension

Treatment

  1. Non-pharmacological measures first:
  • Rise slowly from sitting/lying
  • Leg crossing and squatting when symptomatic
  • Compression stockings (waist-high, 30-40 mmHg)
  • Increase salt intake (if no contraindication) and fluid intake
  • Elevate head of bed 10-15 degrees at night
  • Avoid large meals, alcohol, and hot environments
  1. Medication review: Discontinue or reduce diuretics, alpha-blockers, and other offending medications
  2. If refractory, pharmacotherapy:
  • Midodrine (alpha-1 agonist) 5-10 mg TID (not at bedtime - causes supine hypertension)
  • Fludrocortisone 0.1-0.2 mg daily (volume expansion via mineralocorticoid effect)
  • Droxidopa (norepinephrine prodrug) for neurogenic orthostatic hypotension
  1. Aggressive glycemic control to prevent further neuropathy progression
  2. Manage other autonomic symptoms:
  • Gastroparesis: Small frequent meals, metoclopramide
  • Neurogenic bladder: Timed voiding, consider intermittent catheterization
  • Erectile dysfunction: PDE5 inhibitors

Physiological Principles Demonstrated

  • Baroreceptor reflex: Upon standing, blood pools in lower extremities due to gravity, reducing venous return and cardiac output. Baroreceptors in the carotid sinus and aortic arch detect the pressure drop and signal the medulla to increase sympathetic and decrease parasympathetic output, raising heart rate and vasoconstriction to maintain BP.
  • Neurogenic vs. non-neurogenic OH: In neurogenic OH (as in diabetic autonomic neuropathy), heart rate fails to increase appropriately because sympathetic efferent pathways are damaged. In non-neurogenic causes (e.g., volume depletion), heart rate increases appropriately.
  • Autonomic tone concept: At rest, both sympathetic and parasympathetic systems maintain tonic activity. Loss of sympathetic vascular tone (vasoconstriction) contributes to orthostatic hypotension. Loss of parasympathetic variability reduces heart rate responsiveness.
  • Diabetic autonomic neuropathy spectrum: Involves multiple systems - cardiovascular (orthostatic hypotension, resting tachycardia, reduced heart rate variability), gastrointestinal (gastroparesis, constipation, diarrhea), genitourinary (bladder dysfunction, erectile dysfunction), and sudomotor (anhidrosis in feet, compensatory hyperhidrosis elsewhere).
  • Midodrine mechanism: Direct alpha-1 adrenergic agonist causes vasoconstriction, raising peripheral resistance and blood pressure. Must be avoided at bedtime to prevent supine hypertension.
  • Fludrocortisone mechanism: Synthetic mineralocorticoid promotes renal sodium and water retention, expanding plasma volume to compensate for reduced vasoconstrictor response.

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