Mechanisms of breathing Flashcards
what is lung compliance
lungs stretch on inhalation static measure (active respiration not occurring)
what happens during breathing
Lungs stretch on inhalation and recoil on expiration
Balanced by chest wall tendency to recoil in opposite direction
At end of quiet expiration, pressures balance
what muscles are involved in inspiration
Active process driven by inspiratory muscles Diaphragm (75% change in vol) External intercostals (contract up and forwards like a bucket handle) Accessory muscles (scalene and sternomastoids)
how does inspiration occur
Contract inspiratory muscles to increase intrathoracic volume
Causes decrease in intrapleural pressure (-2.5-6 mmhg)
Lungs pulled into more expanded position and airway pressure negative (air moves in)
At end pressures are equal, recoil of chest wall and lungs occurs
what is transpulmonary pressure
Chest wall exerts distending pressure on the pleural space which is transmitted to alveoli to increase its volume, lower pressure and generate airflow inwards.
Distending pressure is called transpulmonary pressure
Chest wall expansion done by muscles
how is compliance measured
Vol change per unit pressure change
how is compliance different to resistance
function of elastic resistance, dynamic accounts for airflow resistance
what is the balance point
when lung and chest are in equilibrium after exhaling (functional residual capacity)
what is the endpoint of compliance
total lung capacity (TLC) and residual volume (RV)
what does a pressure volume curve show about compliance
depends on inflation
lung volume increases, become less compliant
do compliance curves differ for inspiration and expiration
Compliance curves are different for inspiration and expiration (hysteresis, frictional resistance changes)
how compliant is the normal lung
compliance is right, good compliance for low work of inhalation and good retention of elasticity of alveolar units for effective inhalation
how does interstitial fibrosis effect compliance
compliance decreased, alveolar walls are stiff and scarred
how does emphysema effect lung compliance
compliance increased due to loss of alveolar interdependence
how does a compliance curve change for diseased lungs
Stepper lung compliance curve for emphysema and shallower for fibrosis
what happens during exhalation
Distending pressure is released
Built up potential in form of elastic recoil (passive relation of alveoli, decrease in alveolar volume, increase in Palv leading to outward air flow)
when does active exhalation occur
expiratory respiratory muscles are engaged but short of exercise and disease (usually don’t need these)
Loss of elastic recoil impairs this
what is surface tension
Cohesive forces between molecules
Molecules on surface have no molecules above them
Results in stronger attractive forces to nearest neighbours
how does surface tension affect liquids
In liquids, SA small as possible due to ST pressures. Can lead to alveolar collapse especially with emphysema and age
what is surfactant
Surfactant (type 2 alveolar cells) reduces surface tension (major component is phosphatidylcholine)
Hydrophilic and hydrophobic ends repel each other and interfere with liquid molecule attraction to lower surface tension
is a smaller or larger radius more likely to collapse
Higher pressure from smaller radius so more likely to collapse
why is surfactant important
Increases lung compliance (lung forces are reduced)
Promotes alveolar stability
Prevents alveolar collapse
Surface tension tends to suck fluid from capillaries into alveoli (reduced surface tension reduces hydrostatic pressure in tissue outside capillaries and keeps lungs dry
what is airway resistance
Force needed to inflate greater than elastic recoil
Airway resistance originates from friction between air and mucosa
Is pressure difference between alveoli and mouth divided by flow rate
how is pulmonary resistance calculated
Pulmonary resistance = tissue + airway
what is a small airway
less than 2mm
what are different types of airflow
Laminar smooth flow, resistance generated is proportional to radius
Turbulent flow is irregular, chaotic with eddie currents. Good for heat transfer but resistance is high.
Reynold’s number helps to predict laminar flow converting to turbulent
why is radius most important to flow
Resistance is inversely proportional to the 4th power of radius, flow is inversely proportional to viscosity of fluid
why is resistance not higher in smaller airways
ohm’s law parallel circuits (all add up to total resistance)
what factors affect airway resistance
Inflammation Mucus Bronchodilators Steroids Gas density (heliox, diving)
how much work is required to breathe
required to stretch elastic tissues of chest wall and lungs, moving inelastic tissues and air through tubes. Amount of energy/O2 needed by respiratory muscles to produce enough ventilation and respiration to meet metabolic needs of the body.
how does elastic work compare to non elastic work
Elastic work
Decreased elasticity in restrictive diseases
Greater WOB
Non elastic work
Obstructive diseases lead to greater WOB to overcome increased airway resistance
