lung resistances Part 2: static resistances Flashcards
static resistance: chest wall
what is the relationship between the force of movement of the chest wall and the force of movement of the lung?
the force of movement of the chest wall is the OPPOSITE of the lung
what does the chest wall have a tendency to do and what opposes this
- chest wall has tendency to expand or “spring out”
- negative pleural pressure opposes this
what percentage of your lung capacity does your chest wall reach if its force to spring open is unopposed?
the chest wall will reach 70% of the total lung capacity if unopposed.
what is the name for the resting volume in the lungs when the thorax volume is in equilibrium with the lung volume?
functional residual capacity
when does the functional residual capacity occur?
when there is no air flow ( at the end of a normal breath )
causes of increased chest wall resistance
what are 5 things that can cause increased chest wall resistance
5 things that can cause increased chest wall resistance are:
- structural abnormality - decreased flexibility/expansion
- chest trauma
- loss elasticity
- blockage of smaller respiratory passages with mucus or fluid
- raised abdominal pressure
what are 3 examples of structural abnormality, causing increased resistance of the chest wall
- deformities of thorax
- ossification of the costal cartilage
- paralysis of intercostal muscles
what are 3 examples of chest trauma that cause increased resistance of the chest wall
- paralysis
- strain
- pain
what is an example of loss of elasticity of the lungs, causing increased resistance of the chest wall
- burns
what are 3 examples of raised abdominal pressure that can cause increased chest wall resistance?
- obesity
- pregnancy
- scoliosis
static resistance: lungs
what is elastic recoil, why do lungs have natural tendency to collapse and what holds the lungs open and what establishes this?
- tendency of an elastic structure to oppose stretching
- lungs have tendency to collapse because of elastic recoil
- held open by intrapleural pressure established by lymphatic pumping of fluid
what 2 things can cause lung collapse, and what are their overall proportions in causing collapse?
- elastin and collagen in lung tissues (1/3 of collapses)
- surface tension abnormalities ( 2/3 of collapses)
what 2 fibres are interwoven in the lung parenchyma
- elastic fibres
- collagen fibres
what are elastin fibres for?
to help expand the lungs and allow them to return to their normal shape due their elastic properties
surface tension
what do small alveoli have a greater tendency to do and why?
- small alveoli (smaller radius) have a greater tendency to collapse and empty its air into connected larger alveoli as smaller alveoli are unstable
what are collagen fibres for?
to stiffen the lung tissue once they have expanded
what does reduction in ST forces allow for?
allows for interdependence and stability
why do smaller alveoli need a larger inflating pressure?
because they have a larger collapsing pressure
what is the equation linking inflating pressure, collapsing pressure and radius?
P = 4ST/f
where:
- P = inflating pressure
- 4ST = collapsing pressure
- f = radius
what is surfactant
a secretory product that is composed of lipids & proteins that lowers the surface tension at the air-liquid interface to prevent alveolar collapse
when is surfactant synthesised in babies?
surfactant is synthesised between weeks 24-28 in babies
what synthesises surfactant?
Type II pneumocytes
benefits of surfactant
what 4 things does surfactant do?
- makes the transmural pressure needed to expand the lungs 3x smaller
- keeps alveoli dry
- maximises area for ventilation and perfusion
- maintains alveolar interdependence by acting as additional splints to keep alveoli open
how does surfactant keep the alveoli dry?
surfactant keeps the alveoli dry by lowering the inwardly directed pressure that draws water into the alveoli
how does surfactant maximise area for ventilation and perfusion
surfactant maximises area for ventilation and perfusion by reducing surface tension for small alveoli compared to larger alveoli as surfactant molecules crowd into the smaller space.
how does surfactant maintain alveolar interdependence
surfactant maintains alveolar interdependence by aiding fibrous tissue in septal walls between alevoli of different sizes, thus acting as an additional splint
disorderes influencing surface tension
what 3 disorders can alter/destroy surfactant
- Neonatal respiratory distress syndrome caused by prematurity
- adult respiratory distress syndrome
- oxygen toxicity
what is the most prevalent component in surfactant?
dipalmitoyl phosphatidylcholine (DPPC)
