28. Work of Ventilation 2 Flashcards
What is airway resistance?
Impedance of air flow through the tracheobronchial tree as a result of friction of gas molecules
What determines airway resistance?
Diameter of airway
Distance air has to travel
Flow type (laminar or turbulent)
What is the equation for flow rate?
Hagen-Poiseuille Law
ΔP π r4/ 8 η l
What is resistance defined as?
Ratio between the driving pressure and associated flow rate
Why is resistance in the trachea higher than in the bronchioles?
Larger number of bronchioles means overall airway widens
What determines airway diameter in bronchioles?
Elastic tissue Pressure from lymph nodes Smooth muscle tone Thickness of mucosa/submucosa Mucus
What effect do circulating catecholamines have on smooth muscle tone?
Bronchodilation via B2-receptors
What effect does the PNS have on smooth muscle tone?
Bronchoconstriction
ACh release and muscarinic receptors
What is Reynold’s number?
Dimensionless number to determine whether airflow is turbulent or laminar
Turbulence occurs if R>2000
Reynold’s number equation
2rvd/ η
v=average velocity
d=fluid density
n=viscosity
What conditions promote turbulence?
High velocity
Large diameters
Why might airways collapse in obstructive lung disease?
Intrapleural pressure is higher than normal because of loss of lung tissue
What is chronic bronchitis?
Obstructive
Excess production of mucus
How can chronic bronchitis be treated?
Stop smoking
Antibiotics
Bronchodilators
What is emphysema?
Obstructive
Loss of elastic tissue due to uncontrolled action of proteolytic enzymes
How can emphysema be treated?
Stop smoking
Avoid irritants
Lung transplant
What is pulmonary fibrosis?
Restrictive
Formation of excess fibrous connective tissue in the lung
How can pulmonary fibrosis be treated?
Immune suppressive agents
Oxygen supplementation
Lung transplant
What is the effect of COPD and asthma on the work of breathing?
Increases flow-resistive work
No effect on elastic work
What is the effect of pulmonary fibrosis on work of breathing?
Increases elastic work
No effect on flow resistive work
