Ventilation Flashcards
What is the anatomical dead space
Volume of conducting airways filled with air - air is not available for gas exchange
What is the alveolar dead space
Air in alveoli that are not perfused or are damged -> no gas exchange occurs in the alveoli
What feature do lungs have that allows them to collapse easily during expiration
Lungs have natural elastic recoil
What seal is formed in intrapleural spaces and what does it do
Pleural seal
Pleural seal ensures visceral and parietal pleura stick together during ventilation - surface tension between the pleural surfaces holds lung against chest wall
Describe the resting expiratory level - what is it and what causes it
Resting expiratory level is a state of equilibrium where forces of lung and chest wall are equal and balance out
Occurs at rest -> tendency to want to return to this resting state
How does ventilation disturb the equilibrium of the resting expiratory level
Inspiration - muscles contract to allow chest wall and diaphragm to overcome inward pull of lungs elastic recoil
Expiration - muscles stop contracting so pull of lung is greater than pull of muscles so return to resting level
What is lung compliance
How stretchy the lungs are
Higher the compliance, the easier it is for lungs to strech/expand
Is determined by elastic tissue in lungs and surface tension
How does surface tension affect the lungs
Surface tension decreases compliancy -> makes it difficult for lungs to expand
How does surfactant limit surface tension
Surfactant breaks down and interrupts water around the alveoli -> decreases surface tension
Is surfactant more effective in smaller or larger alveoli and why
Surfactant is more effective in smaller alveoli as the molecules are closer together so are more effective at disrupting surface tension
How does surfactant prevent small alveoli collapsing into larger alveoli
Surfactant causes small and large alveoli to have the same pressure within them
Without surfactant, small alveoli have a higher pressure so air moves from the small alveoli into large alveoli resulting in small alveoli collapsing into large ones
What are the accessory muscles of inspiration
SCM
Scalene muscles
Serratus anterior
Pectoralis major
What are the accessory muscles of expiration
Internal intercostal muscles
Abdominal wall muscles - external and internal oblique and rectus abdominis
How is the high individual resistance to flow by small tubes overcome
High individual resistance is overcome by having a parallel arrangement of small airways which decreases the overall resistance -> smaller airways have a lower overall resistance to flow
