Lecture 1: Respiratory Cycle and Mechanics Flashcards
What does Boyle’s law say?
Pressure of gas is inversely proportional to volume
What happens when lung volume increases?
Pressure in lungs decrease so air can enter lungs
What happens when lung volume decreases?
Pressure in lungs increases so air can exit lungs
What happens during inspiration?
- Inspiratory muscles (external intercostal muscles) contract
- Diaphragm descends
- Thoracic volume increases
- Intrapleural pressure and alveolar pressure decreases
- Chest wall and lungs will expand due to coupling (lungs want to collapse)
Where is parietal fluid found?
Between parietal and visceral pleura
What is intrapleural pressure?
Pressure everywhere in thorax except lumens of blood vessels, lymphatics, and airways
What is the intrapleural pressure at rest?
-5 cm H2O
What is the intrapleural pressure during inspiration?
Reaches -8 cm H2O
What is the alveolar pressure at rest?
0 cm H20
What is the alveolar pressure during inspiration?
-1 cm H20
What happens during expiration?
- Passive so expiratory muscles not always used
- Diaphragm ascends
- Thoracic volume decreases
- Intrapleural pressure and alveolar pressure increases
- Chest wall and lungs will shrink due to coupling
What is the intrapleural pressure during expiration?
Goes back to rest (-5 cm H2O)
What is the alveolar pressure during expiration?
Reaches +1 cm H2O
What four things does the respiratory cycle show change in?
1) Volume
2) Alveolar Pressure
3) Intrapleural Pressure
4) Air Flow
What is minute ventilation?
What is the normal value?
Volume of air inhaled every minute
How do you calculate minute ventilation?
V(dot) = Tidal Volume x frequency
What is the normal value of minute ventilation?
7 L/min
What is anatomic dead space?
Space in the lungs designed not exchange oxygen
- first 16 generations of airway do not have alveoli
- called anatomic since it is not designed for air exchange
How do you calculate anatomic dead space?
Weight of person –> anatomic dead space
Example: 120 lb person has 120 mL of anatomic dead space
What is alveolar dead space?
Alveoli that receive air but not blood
-this should in theory not exist
What is physiological dead space?
Dead alveolar space so no gas exchange
-this should in theory not exist
How do you calculate minute alveolar ventilation?
V(dot alv) = (Tidal volume-anatomic dead space volume) x (frequency)
When is it easiest for lungs to stretch during inspiration?
After there is a little air in the lungs, a small change in pressure can lead to a huge increase in volume of lungs
What is hysteresis?
Difference between inspiration and expiration
What allows hysteresis to occur?
Surfactant: reduces tension and helps air reach all alveoli
What is compliance?
Measure of stretch ability of lungs
Where is compliance high in lungs?
Tidal volume (middle) -easy to inflate
How is compliance calculated?
Compliance = (Δ volume)/(Δ pressure)
What is the opposite of compliance?
Elasticity: recoil ability
How does fibrosis affect compliance?
Lowers compliance
-lungs have to work harder to bring in air
How does age affect compliance?
Compliance increases with age
-less elastin and more collagen
How does emphysema affect compliance?
Increases compliance
-easier to bring air but air has no where to go since there is an increase in dead space
Where do recoil of lungs and chest wall balance each other?
Functional residual capacity (FRC)
When a pneumothorax occurs, what happens to chest wall and lungs?
Lungs: get smaller
Chest wall: expand
*both get their wish
How is airway resistance calculated?
Resistance = (8 x viscosity of x length of tube) / (radius^4)
What prevents alveoli to collapse?
Interdependence
-shared walls of alveolar and airways prevent collapse as recoil opposes each other
