Week 1 Flashcards
What makes up the bony skeleton of the thorax?
-12 ribs, 12 vertebrae, sternum
Which muscles are involved in quiet inspiration and expiration?
Inspiration: diaphragm, external intercostals Expiration: largely passive recoil of the lungs
Which muscles are involved in forced inspiration and expiration?
Forced inspiration: diaphragm, external intercostals, accessory muscles (scalenes, sternocleidomastoid)
Forced expiration: abdominal, internal intercostals, neck and back muscles
How are pressures in the lung measured?
in mmH20, relative to atmospheric pressure
What is the normal tidal volume?
What is the normal dead air space?
What is the normal functional residual capacity?
- 500 mL
- Anatomic (in conducting airways): 150 mL (~ 1mL per pound of body weight)
- Alveolar (in respiratory airways): 25 mL
- Physiologic= anatomic + alveolar
- FRC=2400 mL
Conduction airways vs. gas-exchange airways?:
- which structures are part of wach category?
- how many divisions in the lungs and names of the divisions, starting with trachea
Conducting airways are: nasal cavities, nasopharynx/oropharynx, larynx, trachea, bronchi, bronchioles.
Gas exchange (respiratory) airways are: respiratory bronchioles, pulmonary alveoli
Divisions:
- Conducting zone is from trachea (0) to 16 trachea–>bronchi–>bronchioles–>terminal bronchioles
- Gas exchange zone (17-23) respiratory bronchioles–>alveolar ducts–> alveolar sacs .
2 general ways to get a pneumothorax
- air can penetrate directly from the atmosphere into the pleural space, or can go through a rupture pulmonary bullae
The static lung volumes and what they are
Resting tidal volume: what you normally breathe in and out.
Inspiratory reserve volume: how much you can breathe in on top of the resting tidal volume
Expiratory reserve: how much you can breathe out past your normal tidal volume
Residual volume: dead air. The volume of air always in the lungs
The lung capacities and what they are
Inspiratory capacity (IC): tidal volume+ inspiratory reserve volume
Vital capacity (VC): tidal volume + inspiratory reserve volume + expiratory reserve volume
Functional residual capacity (FRC): expiratory reserve volume + residual volume
Total lung capacity (TLC): everything!
Which volume cannot be directly measured by spirometry?
The residual volume and therefore the functional residual capacity (FRC) and the total lung capacity (TLC) cannot be measured by spirometry.
Volumes are determined by… Capacities are determined by..
Volumes are determined mostly by respiratory effort (except RV). Capacities are determined mostly by the size of the chest/lungs
What are the mechanical properties of the chest wall and lungs at rest?
The chest wall wants to EXPAND due to:
- the tendency of the ribs to spring outwards
- the resting tension of the muscles of respiration
The lungs want to RECOIL due to:
- the elasticity of the lungs
- surface tension in alveoli
What is intrapleural pressure at rest and what is it determined by?
Pressure in the intrapleural space (Ppl). The inward recoil of the lungs and the outward recoil of the chest wall create a partial vacuum that is -5 mmH20
**it will fluctuate with breathing, but is always less than atmospheric**
What is transpulmonary pressure and what is it determined by?
The transpulmonary pressure is the alveolar pressure minus the intrapleural pressure. It is a distending force that determines the volume of alveoli
Ptp= Palv - Ppl
How to increase the Ptp?
You can force air into the alvoeli (increase Palv ) or make the intrapleural space more negative by sucking air out of it (Ppl)
What is Boyle’s law?
pressure is inversely proportional to volume
How and why does air flow into the alveoli during respiration
1) expand the chest –> makes intrapleural pressure even more negative
2) therefore the transplural pressure increases and the alveoli expand
3) an expanded alveoli with the same volume has a lower pressure
4) air flows from high to low pressure until pressures are equal
How and why does air flow out of alveoli during expiration?
1) inspiratory muscles relax–> intrapleural pressure becomes less negative
2) transpulmonary pressure decreases–>alveoli decrease in size
3) Pressure increases in alveoli (via Boyle’s law)
4) air flows out of alveoli until the pressure in the alveoli is the same as atmospheric
What forces must respiratory muscles overcome to initiate inspiration?
1) the recoil of the lung from elastin and surface tension
2) frictional resistance to air flow (and to a much lesser extent the friction from the deformation of the lungs –> tissue resistance)
What happens to the elastic recoil of the lung in emphysema and pulmonary fibrosis? How do the static volumes and capacities change.
Emphysema: loss of elastin makes the lung easier to inflate (loss of elastic recoil), but more likely to collapse during expiration. Airways are then narrower and resist flow more. The residual volume (RV) increases, so FRC and TLC also increase.
Fibrosis: deposition of collagen makes the lung more difficult to inflate (increased elastic recoil). RV decreases, so FRC and TLC decrease too.
What are two big actions of surface tension in alveoli?
1) Contributes to elastic recoil of lung because it acts to make the alveoli as small as possible
2) Promotes alveolar instability
Laplace’s Law for alveoli
- what does this mean for alveolar stability?
- what reduces the pressure in an alveoli?
P=(2*surface tension/ radius)
Small alveoli are higher pressure and will collapse into larger alveoli.
Surfactant helps reduce the pressure generated from the surface tense and opposes alveolar instability
What is compliance? What does it assess?
A measure of the distensibility of an elastic structure (e.g. the lung): change in volume/change in pressure. It is a way of assessing the elastic recoil against which the muscles of the chest have to work to expand the thorax.
What do the static compliance curves for a normal lung, a fibrosed lung and an emphysemic lung look like?
