Work of ventilation 2 Flashcards
non elastic work in breathing
frictional/resistive work
force to overcome air-flow resistance - force to move air through airways
airway resistance definition
the impedance of air flow through the tracheobronchial tree as a result of friction of gas molecules
Very important contribution to the work of breathing
when is airway resistance present
during both inspiration and expiration
what does increased airway resistance require
greater pressure gradient to drive airflow and result in the same tidal volume of approximately 500 ml
2 main components to determine the airway resistance
Diameter of the airway (cross sectional area) and distance air has to travel Lung volume Bronchial smooth muscle tone Thickness of mucous lining and submucosa Mucus layer flow type/pattern - laminar or turbulent
driving pressure
pressure difference between mouth and alveoli
hagen-poiseuille law relates to
Relates flow rate (volume transported per time unit) to airway radius and to distance the air is transported
flow rate
(V/t) = ΔP π r4/ 8 η l ΔP = Driving Pressure; r = Radius; η = viscosity; l = Length
what law is used to express airway resistance
hagen-poiseuille law
resistance definition
the ratio between the driving pressure and the associated flow rate.
resistance formula
Resistance (R) = ΔP/V/t = 8ηl /πr4
if airway radius is reduced to 50% by how much is the resistance increased
increased 16 fold
1/(0.5)4*
is the resistance in trachea or bronchioles higher and why
bronchioles have smaller radius than trachea but a more of them than trachea - overall the airway widens
resistance in trachea is higher than bronchioles
as the airway resistance decreases ..
lung volume increases
increases airway diameter
what contributes to the diameter airways of trachea and bronchi
cartilage prevent collapse
what contributes to the airway diameter in the small bronchi and bronchioles
no supporting cartilages pull of surrounding tissue innervated smooth muscle small diameter easily obstructed offer little resistance
what features of the lungs in the walls of the airways contribute to the airway diameter
Smooth muscle tone
Thickness of mucosa/submucosa
what features in the lumen of the airway contribute to the airway diameter
mucus
what intrinsically controls the smooth muscle tone
chemical mediators - mast cell degranulation (via release of histamine) and inflammatory mediators lead to bronchoconstriction
when CO2 is raised it leads to
bronchodilation
when CO2 is lowered it leads to
bronchoconstriction
factors influencing secretions
Secretions of seromucous glands and goblet cells that line respiratory system
where are the seromucous glands and goblets cells
5-10 μm thick, inner layer more watery to allow ciliary action and upper layer more viscid to trap particles
seromucous glands and goblet cells are controlled by what category of the CNS
by parasympathetic nervous system reflexes and local chemical stimulation
activities of seromucous glands and goblet are increased in
bronchitis
activities of seromucous glands and goblet are decreased in
atropine
how does turbulence affect air flow resistance
increase airflow resistance
how is reynolds number expressed in straight tubes
R = 2rvd/η r = Radius; v = velocity; d = Fluid density; η = Fluid viscosity
what promotes turbulences
high velocities and large diameters
turbulence in airway can lead to
Empty Nose Syndrome/paradoxical obstruction
why don’t turbulences occur in bronchioles
velocities are low and diameters are small
sites of airway resistance
greatest resistance in large airways
1/2 in nose, pharynx and larynx
where does 80% of airway resistance occur
Below larynx –in trachea and main bronchi
where does less than 20% of airway resistance occur
in bronchioles
how is asthma caused
lung inflammation
how is asthma treated and explain the treatments mechanism
Treat with bronchodilators and corticosteroids
Bronchodilators relax bronchial smooth muscle and widen airways
Corticosteroids reduce inflammation and reduce secretions
chronic obstructive pulmonary disease examples
chronic bronchitis
emphysema
how is chronic bronchitis affect work of ventilation
excess production of mucus
increased flow work
leads to cough, production of sputum
how is chronic bronchitis treated
cessation of smoking, antibiotics (if bacterial), bronchodilators
how does emphysema impact work of ventilation
Loss of elastic tissue due to uncontrolled action of proteolytic enzymes
loss of elastic work
how is emphysema treated
Treat by cessation of smoking, avoiding irritants, lung transplant
pulmonary fibrosis
Formation of excess fibrous connective tissue in the lung.
Restrictive lung disease, reduces compliance
causes of pulmonary fibrosis
Idiopathic
Inhalation of pollutants (coal dust, asbestos)
Certain medications (bleomycin)
Disease (Sarcoidosis)
treatment of pulmonary fibrosis
Immune supressive agents (corticosteroids)
Oxygen supplementation (improves QOL)
Lung transplantation
what is the difference between obstructive and restrictive respiratory disease
Obstructive - interfere with MOVEMENT of air, increase FLOW- RESISTIVE work, no effect on ELASTIC work, decrease FEV1, NOT FVC
Restrictive - Interfere w/ ABILITY to EXPAND LUNGS, increases ELASTIC work, NO EFFECT on FLOW- RESISTIVE work, decrease FEV1 AND FVC
determinants of airway diameters
lung volume
bronchial smooth muscle tone
thickness of mucous lining and submucosa
mucus layer
what features outside the airway contribute to the airway diameter
radial traction of elastic tissue
pressure from lymph nodes
smoking can cause goblet cell hyperplasia which subsequently causes increased mucus production. What effect would this have on the work of breathing.
increases flow resistive work
how do we know if turbulence occurs in reynolds number
if reynolds number is greater than approx. 2000
how does the hagen poiseuille equation relate to another law
resistance = driving pressure/ flow rate
ohm’s law resistance = voltage / current
