Pathophysiology
I-35. Immobilization syndrome — effects on autonomic functions
不動化症候群の自律機能への影響
Immobilization Syndrome — Autonomic Functions
Manifestations in cardiovascular, respiratory, GI, urogenital systems + hormonal/metabolic regulation.
Cardiovascular System
- ↑Resting HR (+5–15 bpm in first month, then steady).
- ↓Circulating blood volume: 5% in 1 day, 10% in 1 week, 20% in 2 weeks (body compensates up to 10% without BP/HR change — beyond, ↓CO then ↓BP).
- ↓Cardiac reserve, orthostatic intolerance, ↑thromboembolic risk.
Mechanism
- Lying posture → ↑venous return → ↑volume in large veins/atria.
- Wall stretch → low-pressure baroreceptors → ↓ADH + ↓aldosterone, ↑ANP → ↑diuresis → ↓blood volume.
- ↓Stroke volume → high-pressure baroreceptors → ↑HR. ↓SV + ↑HR → moderately ↓CO (cardiac reserve used at rest).
Orthostatic Intolerance
- Standing → ↑leg venous hydrostatic pressure → blood pools → ↓venous return → ↓CO → collapse.
- Normally compensated by SYM venoconstriction + myogenic response. Compromised in immobilization due to ↓blood volume (weak vis a tergo), impaired SYM/myogenic tone (vis a fronte), absent muscle-vein pump, and impaired thoraco-abdominal pump + heart pump.
Respiratory System
- ↓Vital capacity, tidal + residual volume, ↑infection risk (thicker mucus, ↓ciliary action), ↑atelectasis risk.
- Mechanism: respiratory muscle weakness, diaphragm pushed up (lying), ↑intrathoracic blood volume → ↓lung volume. ↓mucociliary clearance + ↑mucus viscosity → small-airway blockage → pathogen accumulation → pneumonia.
Urinary System
- Incontinence (especially elderly), recurrent UTI, urinary stones → cystitis (also from catheterization), bladder shrinkage (100–150 ml).
GI Tract
- ↓Secretion/absorption → weight loss (especially protein → negative nitrogen balance → ↓muscle strength), constipation, ↓appetite (protein foods), mucosal atrophy, malnutrition (hypoalbuminemia).
Metabolic Disorders
- Glucose intolerance: muscle activity sets insulin sensitivity → disuse → insulin resistance (from day 3). Isotonic exercise helps.
- ↑Body fat, ↓body mass, negative nitrogen balance, electrolyte loss (feces/urine), thermoregulation disturbance.
Prevention
- Minimize bed time.
- Regular in-bed exercises (respiratory, vascular, joint).
- Early mobilization (essential).
- Proper nourishment (eat sitting).
- Remove urethral catheter, use toilet.
- Skin hygiene, repositioning, daily hygiene routine.
- Intellectual challenges, active environment, social interaction.
一問一答
▶Which autonomic systems are affected in immobilization syndrome?
The cardiovascular, respiratory, GI, and urogenital systems, plus hormonal/metabolic regulation.
▶How does resting heart rate change with immobilization?
It increases by 5–15 bpm during the first month, then stabilizes.
▶How does circulating blood volume decrease over time during bed rest?
5% in 1 day, 10% in 1 week, 20% in 2 weeks; the body compensates up to ~10% loss without BP/HR change, beyond which CO and then BP fall.
▶Why does lying down lead to reduced blood volume during immobilization?
Lying → ↑venous return → atrial/vein wall stretch → low-pressure baroreceptors → ↓ADH, ↓aldosterone, ↑ANP → ↑diuresis → ↓blood volume.
▶What is the mechanism of orthostatic intolerance after immobilization?
Standing pools blood in the legs (↑venous hydrostatic pressure) → ↓venous return → ↓CO → collapse, because compensation is impaired (↓blood volume, impaired sympathetic/myogenic tone, absent muscle-vein pump).
▶What respiratory changes occur during immobilization?
↓Vital capacity, tidal and residual volume; increased risk of infection (thicker mucus, ↓ciliary action) and atelectasis.
▶Why does immobilization predispose to pneumonia?
Respiratory muscle weakness, upward diaphragm displacement, and ↑intrathoracic blood volume reduce lung volume; ↓mucociliary clearance + ↑mucus viscosity block small airways → pathogen accumulation.
▶What urinary complications arise from immobilization?
Incontinence (especially in the elderly), recurrent UTIs, urinary stones → cystitis (also from catheterization), and bladder shrinkage (100–150 ml).
▶What GI effects result from immobilization?
↓Secretion/absorption → weight loss (especially protein → negative nitrogen balance → ↓muscle strength), constipation, ↓appetite, mucosal atrophy, and malnutrition (hypoalbuminemia).
▶How does immobilization cause glucose intolerance?
Muscle activity sets insulin sensitivity, so disuse causes insulin resistance from about day 3; isotonic exercise helps prevent it.
▶What metabolic disorders develop during immobilization?
Glucose intolerance/insulin resistance, ↑body fat, ↓body mass, negative nitrogen balance, electrolyte loss, and thermoregulation disturbance.
▶Why does stroke volume fall and heart rate rise during immobilization?
Reduced blood volume lowers stroke volume → high-pressure baroreceptors raise HR; the combination moderately reduces CO (cardiac reserve is used even at rest).
▶What cardiovascular consequences result from immobilization besides tachycardia?
Reduced cardiac reserve, orthostatic intolerance, and increased thromboembolic risk.
▶Which pumps normally maintain venous return on standing, and how does immobilization impair them?
The muscle-vein pump, thoraco-abdominal pump, and heart pump, plus sympathetic venoconstriction and myogenic response; immobilization weakens or abolishes these, causing orthostatic intolerance.
▶Why is negative nitrogen balance significant in immobilization?
Net protein loss reduces muscle mass and strength, compounding weakness and malnutrition.
▶What are the key measures to prevent immobilization syndrome?
Minimize bed time, regular in-bed exercises (respiratory, vascular, joint), early mobilization, proper nourishment, removing the urethral catheter, skin hygiene/repositioning, and intellectual/social stimulation.
▶How does immobilization increase thromboembolic risk?
Venous stasis from absent muscle pumping, combined with increased blood viscosity, predisposes to thrombus formation and embolism.
▶Why does atelectasis develop during prolonged bed rest?
Reduced lung volumes, weak respiratory muscles, and impaired clearance lead to collapse of small airways/alveoli.
▶What hormonal changes mediate the diuresis of bed rest?
Atrial stretch lowers ADH and aldosterone and raises ANP, promoting diuresis and reduced blood volume.
▶Why does bladder shrinkage and stone formation occur in immobilization?
Reduced use and incomplete emptying shrink the bladder (100–150 ml), while hypercalciuria and urinary stasis (plus catheterization) promote stones and cystitis.