Lung Mechanics - L2 Flashcards
What are the 3 different pressure considerations important in ventilation?
Atmospheric pressure (barometric)
Intra-alveolar pressure (intrapulmonary pressure)
Intrapleural pressure (intrathoracic pressure)
What relationships are important in ventilation?
Interrelationships among pressures inside and outside the lungs are important in ventilation
When does atmospheric pressure decrease?
It decreases as altitude increases
What is atmospheric pressure at sea level?
760mm Hg at sea level
What is P atm set to?
P atm = 0 mm Hg
What is intra-alveolar pressure?
It is the pressure of air in alveoli - not a closed system, it is opened
When does intra-alveolar pressure vary?
It varies with phases of respiration
What happens to intra-alveolar pressure during inspiration?
It is negative - less than atmospheric
EXAM Q B4: Describe how pressure gradients are involved and how they affect flow rate
What drives ventilation?
The differences between P alv and P atm
What happens to intra-alveolar pressure during expiration?
It is positive - more than atmospheric
What is intra-pleural pressure?
It is pressure inside the pleural sac - it is a closed sysetm
What is intra-pleural pressure at rest?
756 (or -4) mmHg
Is intra-pleural pressure always more or less than P alv?
Always less than P alv
When is intra-pleural pressure always negative?
Its always negative under normal conditions at rest
Why is there negative pressure for intra-pleural pressure? HINT reason and 5 points of how
Negative pressure is due to elasticity in the lungs and chest wall:
1. Lungs recoil
2. Chest wall recoils outward
3. Opposing pulls on intrapleural space
4. Surface tension of intrapleural fluid hold wall
and lungs together (H2O molecules are polar, attract
each other)
5. Sub-atmospheric P: due to vacuum in the pleural cavity
what happens for us to breathe in?
pressure must drop for us to breathe in
What is FRC - Functional Residual Capacity?
It is the volume of air in the lungs between breaths that is defined as rest: P alv = P atm : 2.2L
Formula for Air FLOW?
FLOW = Patm-Palv
—————
R
When is atmospheric pressure constant?
During the breathing cycle
What does changes in alveolar pressure cause?
Changes in alveolar pressure creates or changes gradients
Boyle’s Law:
Pressure is inversely related to volume in a closed system - airtight container.
What does R in the FLOW formula stand for?
R = Resistance to air flow
Resistance is related to radius of airways and mucus
lecture slide figures from diagrams
needed
Thus due to Boyle’s Law how can you change alveolar pressure?
Can change alveolar pressure by changing its volume
2 factors that determine intra-alveolar pressure?
- Quantity of air in alveoli
- Volume of alveoli
Are the intra-pleural sacs independent of one another?
The left intra-pleural sac is independent from the right - so if you damage 1 the other one should be fine
What happens if the lung tissue is broken, for example due to disease?
If lung tissue is broken due to disease it can eventually damage the pleural sac and this can break the sac and eliminate the pressure defence and then the lung will collapse and the thoracic will expand
What happens during inspiration? what happens to the lungs + 5 Points
The lungs expand:
- Alveolar volume increases
- P alv decreases
- Pressure gradient occurs and air is drawn into lungs
- The quantity of air in alveoli rises
- P alv increases
What happens during expiration - to the lungs + 5 points:
Lungs recoil:
- Alveolar volume decreases
- P alv increases
- Pressure gradient occurs and air is pushed out of the lungs
- Quantity of air in alveoli decreases
- P alv decreases
Opened system uses what pressure?
Intra-alveolar pressure
Closed system that follows Boyle’s Law uses what pressure?
Intra-pleural pressure
Respiratory muscle activity during inspiration - ribs?
Elevation of ribs
How much % of total energy expenditure does quiet breathing require?
3%
What do lungs normally operate at?
About 1/2 full
What situations is the work of breathing increased? 4 points and example
- When pulmonary compliance is decreased
- When airway resistance is increased
- When elastic recoil is decreased
- When there is a need for increased ventilation
For instance, COPD: 30% EE at rest
Factors that affect pulmonary ventilation? 2
Lung compliance and Airways resistance
What is lung compliance?
It is the ease at which lungs can be stretched
What is required the less compliant the lungs are?
The less compliant the lungs are, the more work is
required to produce a given degree of inflation
What 2 things is lung compliance affected by?
Affected by (i) elasticity (elastic recoil) and (ii) surface
tension of lungs (alveoli)
What do type 2 alveoli cells make?
They make surfactant to decrease surface tension
When is airway resistance increased?
Increased in pathologies
What is airway resistance affected by? 3
Passive forces, contractile activity of
smooth muscle and mucus secretion
Obstructive lung disease
Resistance is much higher and pressure is reduced and the intra-pleural pressure is also much higher and capacity to recoil lung is also reduced - same pressure
Not able to empty lungs properly - air accumulates
Limits capacity of exercise in individuals - but if its very severe it can happen at rest
What can total energy expenditure go up to in someone with lung disease?
can go to 30%
Tidal Volume? in mL
500 mL
What does the elevation of the ribs during inspiration cause?
It causes sternum to move upward and outward, which increases front-to-back dimension of thoracic cavity
What happens to the respiratory muscle activity during inspiration - external intercostal muscles?
The contraction of external intercostal muscles causes elevation of ribs, which increases side to side dimension of thoracic cavity.
What happens to the diaphragm: respiratory muscle during inspiration? What does this do?
Lowering of diaphragm on contraction increases vertical dimension of thoracic cavity.
What happens to the respiratory muscles - internal intercostal muscles during expiration? What does this do?
Contraction of the internal intercostal muscles flattens the ribs and sternum which further reduces side-to-side and front-to-back dimensions of thoracic cavity
What happens to the respiratory muscles - abdominal muscles during expiration? What does this do?
They contract, the contraction of abdominal muscles causes the diaphragm to be pushed upward, further reducing the vertical dimension of thoracic cavity
What restores the thoracic cavity to pre-inspiratory size?
Return of the diaphragm, ribs and sternum to resting position on relaxation of inspiratory muscles
Inspiratory reserve volume (IRV) in mL?
3000 mL
Inspiratory capacity (IC) in mL?
3500mL
Expiratory reserve volume (ERV) in mL?
1000 mL
Residual volume (RV) in mL?
1200 mL
Functional residual capacity (FRC) in mL?
2200mL
Vital capacity (VC) in mL?
4500 mL
Total Lung Capacity (TLC) in mL?
5700mL
