Lecture 6 - Normal Lung Function Flashcards
1
Q
Lung is expandable and retractable
A
Expandable
- compliant
- low resistance network of branching conduits
Retractable
- elastic
- millions of tiny alveolar sacs
2
Q
Pleural space
A
- potential space
- Few mL fluid only
Pressure
- lung, chest wall
- gravity
- Position
3
Q
Mechanics of lung function
A
- Changes in pressure inside thorax are generated by changes in lung volume, which are made possible by the moevement of air, which necessarily requires exchanges of gas
4
Q
What determines lung volume
A
- height: big persons = big lungs
- age: volume increases up to age 20, but alveolar number is determined in utero/infancy (controversial)
- gender: men>women
- Race: Caucasion> others
- in utero history: what happens in lung at old age is determined before birth
5
Q
Height and lungs
A
Height is the most important determinant of a person’s finak TLC (linear relationship)
- kick up at about 160cm because this is when puberty hits -> growth spurt. Dont see this lung growth spurt in females
6
Q
Age and alveolar size
A
- alveolar size increases with age up to age 20
- ADC is a measure of alveolar size
- but studies show that alveolar size doesnt increase as predicted by lung volume - must be new alveoli?
7
Q
Functional residual capacity
A
- at FRC, breathing is most efficient -> highest lung compliance
- 45% of TLC at rest -> FRC
- equilibrium point when outward recoil pressure of chest wall = inward recoil of lung
- in disease, obstruction (asthma) increases
8
Q
Residual volume
A
- in normals, RV is determined by limitation of the chest wall and muscle strength, not by lung.
- the lung itself could still emptyh but the chest wall cant press back down anymore
9
Q
How is residual volume affected by diseases
A
- increased in obstructive lung disease (gas trapping)
- decreased in restrictive neuromuscular disease
10
Q
Measuring lung volume - body plethysmography
A
- relies on boyles law
- PxV is constant
- man in a box
- when airflow is absent, alveolar pressure = mouth pressure
- volume of air inside the box expands if you empty your lung : inject only a known amount of air particle ion the box and measure the difference
- this measures FRC
11
Q
Once MRC is measured, how do you measure other capacities?
A
- TLC = FRC + inspiratory capacity
- RVL TLC - VC
12
Q
Simpler method of lung capacity measurement: Gas dilution
A
- inspire a known concentration of particles.
- measure the expired concentration
- Cinsp x Vinsp = Cexp x Valv
13
Q
Body plethysmography characteristics
A
- measures entire thoracic gas volume
- not affected by degree of obstruction
- complicated, expensive equipment
- high degree of patient coordination
- rapidly repeatable, but limited by effort/fatigue
14
Q
Gas dilution characteristic
A
- single breath
- measures accessible lung volume (alveoli)
- susceptivle to gas trapping/slow gas mixing (obstructive diseases)
- simple and relatively inexpensive
- less coordination required
- need time to washout helium between test
15
Q
Measuring air flow: spirometry
A
- FEV1: Forced expiratory volume in 1 sec
- FVC : Forced Vital capacity
- FEV1/FVC = 0.8
- this is influenced by age (reduces) and diseases)
