Ch 13.2B -- Respiratory Mechanics -- VTPP 435

Ch 13.2B -- Respiratory Mechanics -- VTPP 435

Premature Airway Collapse during COPD during expiration at higher lung volumes, 2 reasons

1) Pressure drop along airways magnified due to increased airway resistance
2) Intrapleural pressure higher due to loss of lung tissue that removes lung's ability to recoil and lower intrapleural pressure

Two Things Involved in Pulmonary Elasticity

-Compliance
-Elastic Recoil

Compliance

-how easily lungs can be stretched
-less compliance = more transmural pressure needed

Pulmonary Fibrosis

-normal lung tissue replaced with scar-forming fibrous connective tissue
-occurs from breathing in asbestos or irritants
-decreased respiratory compliance

Elastic Recoil

-rebound of lungs after having been stretched
-helps lungs return to pre-inspiratory volume
-needs elastin fibers in lung tissue
-needs Alveolar Surface tension

Alveolar Surface Tension

-surface tension of fluid lining the alveoli in lungs
-resists any force that increases its surface area to oppose expansion of alveolus

Pulmonary Surfactant

-a phospholipoprotein complex
-secreted by Type II alveolar cells
-causes lowering of surface tension within lungs
-increases pulmonary compliance
-reduces lungs tendency to recoil

Law of LaPlace

magnitude of inward directing collapsing pressure is directly proportional to surface tension and inversely proportional to radius of bubble

Work of Breathing Increased in 4 Situations

1) Pulmonary compliance decreased
2) Airway resistance increased
3) Elastic recoil decreased in Emphysema
4) When a need for increased ventilation

Spirometer

-measures changes in lung volume
-records on a spirogram

Tidal Volume (TV)

-volume of air entering or leaving lungs during a single breath
-avg 500 mL

Inspiratory Reserve Volume (IRV)

-extra volume of air that can be maximally inspired over and above typical resting TV
-avg 3000 mL

Inspiratory Capacity (IC)

-max volume of air that can be inspired at end of normal quiet expiration
-IC = IRV + TV
-avg 3500 mL

Expiratory Reserve Volume (ERV)

-extra volume of air that can be actively expired by max contracting expiratory muscles beyond normal passive expiration
-below TV
-avg 1000 mL

Residual Volume (RV)

-min volume of air left in lungs even after max expiration
-avg 1200 mL

Functional Residual Capacity (FRC)

-volume of air in lungs at end of normal passive expiration
-FRC = ERV + RV
-avg 2200 mL

Vital Capacity (VC)

-max volume of air that can be moved during a single breath after max inspiration
-VC = IRV + TV + ERV
-avg 4500 mL

Total Lung Capacity (TLC)

-max volume of air lungs can hold
-TLC = VC + RV
-avg 5700 mL

Forced Expiratory Volume in 1 Second (FEV1)

-volume of air that can be expired during first second of expiration in VC determination
-Avg = 0.8 * VC