RESPIRATION PHYSIOLOGY: VENTILATION -- Ventilation Pathophysiology

PATHOPHYSIOLOGY OF RESPIRATORY VENTILATION

A. Physiological Classification

CAUSE	EXAMPLE	PATHOPHYSIOLOGY
Muscle Excitation		Inadequate muscle excitation
	Polio	Destruction of motor nerves
	CNS depression
Elastic Force		Increased stiffness (or Compliance decrease)
chest wall	Skeletal deformity (e.g. kyphoscoliosis)
lung tissue	Fibrosis (e.g. silicosis, asbestosis, black lung)
surface tension	Hyaline membrane disease (e.g. respiratory distress syndrome of the newborn)
space occupying lesion	Thoracic cancer
Airway Resistance		Increased airway resistance
upper airway	Aspirate solid object Laryngospasm Croup
lower airway: acute	Asthma
lower airway: chronic	COLD or COPD (Chronic Obstructive Lung Disease or Chronic Obstructive Pulmonary Disease)	chronic bronchitis emphysema

(Note: SIDS -- Sudden Infant Death Syndrome)

B. Clinical Classification

1. Restrictive

a. associated with reduced total lung capacity
b. due to increased stiffness
c. diagnosed from TLC↓ or C↓

2. Obstructive

a. associated with reduced air velocity
b. due to increased airway resistance
c. diagnosed from R_aw↑ or FEV1/VC↓ (< 80%) or Peak Exp. Flow Rate (PEF) ↓
d. "pink puffer " = emphysema & "blue bloater " = chronic bronchitis
e. acute (e.g. asthma) and chronic pulmonary disease can be distinguished as acute disease is relieved by broncodialator but chronic disease is not releaved

3. CNS Disease

a.    reduced muscle stimulation by the nervous system
b.    reduced muscle strength
c.    reduced muscle strength can be diagnosed from maximum inspiratory and expiratory pressure measurement

SUMMARY (==>)

C. Pathophysiology of Emphysema

1. characteristics (==>)

a. degeneration of lung tissue (irreversible) -- pathological diagnosis
b. high RV and FRC and TLC (large, barrel chest)
c. low VC (frequently)
d. high R_aw on expiration, while inspiration may be normal (check-valve effect)

2. physiological basis

a. loss of lung tissue causes RV↑ & FRC↑ & P_pl↑ in the relaxed position
b. forced expiration leads to further P_pl↑, which increases airway compression on expiration
c. hence, on expiration, increased airway resistance and gas trapping