Glossary of 2 - Whole Lung Ventilation and Compliance
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- What is minute ventilation? How is it calculated? What is a normal value?
- *the amount of air inspired/exipired in one minute
*equal to tidal volume minus air trapped in physiological dead space times resp rate
*(0.5L - 0.15L) x (12bpm) = 4.2L/min
- What are the two general types of resistance to air flow?
- *airways resistance
*lung and chest wall compliance
- What is lung compliance? How can it be calculated from a graph of volume vs. pressure?
- *CPL is the ease with which the lung changes volume per unit pressure
*CPL would be the slope of this graph
- How does compliance vary during inspiration?
- CPL decreases during inspiration, becoming less compliant as maximum inspiratory capacity is approached.
- How does elastic recoil of the lung work? In other words, what processes does this assist and which are hindered by it?
- Elastic recoil assists in deflation and works against inflation.
An air-inflated lung has higher compliance during inspiration as compared to expiration.
- What two factors are the primary determinants of lung compliance?
- *elastic recoil
- Why does inflation of an isolated lung with saline show higher compliance than one inflated with air?
- Because in the saline-filled lung there is no surface tension.
- How is surface tension created?
- At the interface between two phases, molecules of one phase are unable to H-bond with molecules of the other phase - this creates a force on the surface.
- How can surface tension be calculated? In which direction is this tension exerted?
- *LaPlace equation: P = 2T/r
*the tension is directed inside - to collapse the alveoli
- What are the two means of counteracting surface tension in the human lung?
- How does surfactant work? What does it consist of?
- *provides a layer of amphipathic molecules that can H-bond with both phases
*phosphotidylcholine and proteins
- How does surfactant lessen surface tension during expiration?
- *compression of the alveoli leads to an increase in the density of surfactant
*the more dense surfactant has less surface tension
*collapse is opposed
- What is the primary cause of infant respiratory distress syndrome?
- Immature type II alveolar cells do not produce enough surfactant leading to alveolar collapse.
- How does alveolar interdependence oppose alveolar collapse?
- *the walls of the alveoli are interconnected
*as any one gets smaller this stabilizes adjacent alveoli
- How does lung compliance change in emphysema and fibrosis?
- *emphysema leads to increased compliance
*fibrosis leads to decreased compliance
- How can chest wall compliance be calculated? How is it affected by obesity?
- *1/CPL(tot) = 1/CPL(lung) + 1/CPL(wall)
*obesity decreases chest wall compliance
- What is airway pressure at mechanical equilibrium?
- What occurs at mechanical equilibrium?
- *the tendency of the ribs to spring out is balance by the tendency of the lung to collapse
*i.e. lung compliance is balanced by chest wall compliance
- Describe the energy transfer between the chest wall and lung during inspiration.
- *the chest wall moves to its preferred position and transfers energy to the lungs
*the lungs are moved away from their preferred position and thus require energy released from the chest wall
- Describe the transfer of energy between the chest wall and the lungs during exhalation.
- *lungs move from a position of high energy to one of low energy and transfer the difference to the chest wall
*the chest wall moves from a position of low energy to one of high energy and require energy
- What lung volume defines total system equilibrium?
- In normal patients, what percentage of the O2 taken in is used to power the work of respiration? How does this change during heavy exertion of exercise?
- *5% of O2 taken in is used to power tidal breathing
*this can increase to as high as 30% during heavy exertion
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