Ventilation Flashcards
Describe breathing and ventilation
this is the flow in and out of the respiratory system
what is the movement of air into the body due to
the movement of air in and out of the lungs occurs due to pressure differences
how are pressure differences created
- Pressure differences are created by changes in lung volume because air flows from a region of a high pressure to a region of low pressure
describe what drives inhalation
- driven by diaphragm which contracts and flattens leading to an increase in lung size and consequently air moves into the lungs
what drives exhalation
– diaphragm relaxes which leads to a decrease in lung size and therefore pressure increases and air moves out of the lungs
How do we measure lung function
spirometry
define tidal volume
amount of air you move into and out of your lungs during rest, not the sum of the two
define inspiratory capacity
total volume of air that you can breathe in at maximum lung capacity at rest
define expiratory capacity
total volume of air that you can breath out of the lungs at maximum lung capacity at rest
define forced vital capacity
maximum volume of air into and out of the lungs in a single respiratory cycle
define residual volume
volume of air that remains in the lungs even after maximal exhalation
How do you calculate the forced vital capacity
- Inspiratory reserve capacity+ tidal volume + expiratory reserve volume = forced vital capacity
what is FEV1/FVC
• FEVI/FVC is a ratio of Forced Expiratory Volume in 1 sec & Forced Vital Capacity
what is the normal FEV1/FVC ratio
values above 70-80% = normal. Age/gender adjusted
what causes the decrease of the FEV1/FVC
• Airflow limitation (e.g. Asthma)
what generates the pressure differences for breathing
it is the respiratory muscles that generate the pressure differences for breathing
what happens during inspiration of quiet breathing
- inspiration: active part of passive breathing
- Diaphragm and external intercostal muscles
what happens during inspiration in forced breathing
- Inspiration: diaphragm, external intercostal muscles and accessory muscles such as pectoralis major and minor and serratus anterior
what is the diaphragm innervated by
- it is innervated by the phrenic nerve
describe measurements of the diaphragm
- rest – 1-2cm
- forced breathing < 10cm
what are the two muscles that the external intercostal muscles do
- pump handle movements; anterior end of each rib is elevated
- bucket handle movements; dimeter of chest increases
what happens during expiration in quiet breathing
- expiration; largely passive as a result of elastic recoil of the lungs
what happen during expiration in forced breathing
- active
- involves accessory respiratory muscles
- E.g. Anterior abdominal muscles & quadratus lumborum
define alveolar ventilation
- Defined by portion of the total ventilation that reaches the alveoli and participates in gas exchange
How do gasses move between air and blood
move between air and blood by passive diffusion
- movement of gases is defined by partial pressure gradients
what is hypoventilation or hyperventilation a sign of
lung diseases
what decreases as you descend the airways
airway ventilation and perfusion decrease
what is dead space
• Volume of air in the mouth, pharynx, trachea and bronchi up to the terminal bronchioles
it is the volume of air that does not exchange in gas
how large is the anatomical dead space
150 ml does not exchange gas
what is the anatomical dead space made out of which structures
made up of upper respiratory tract, trachea, bronchi, bronchioles, terminal bronchioles
what is alveolar dead space
alveoli that have insufficient blood supply to act as effective respiratory membranes therefore do not take part in gas exchange
How do you work out physiological dead space
anatomical dead space and alveolar dead space
how do you work out the rate at which new air reaches the alveoli
(tidal volume - dead space) x respiratory rate
describe the example of how you work out the rate at which new air reaches the alveoli
tidal volume – dead space) x respiratory rate
- Tidal volume=500 mL
- Anatomic dead space=150 mL
- Fresh air entering the lungs=350 mL
- Respiratory rate=12 breaths/min
- Alveolar ventilation (ml/min)
- 12X350=4200 mL/min (4.2L/min)
- This is the effective ventilation that brings about the exchange of O2 and CO2.
describe alveolar ventilation and respiratory exchange
Room = Almost zero CO2 & alveolar gas = 5.5% giving an output of:
4.2 X (5.5-0/100)=0.231 L/min or 231 mL/min
Oxygen forms 21% of atmospheric air and alveolar gas contains about 14% giving an uptake of:
4.2 X (21-14/100)=0.294 L/min or 294 mL/min
How do you see the spirometers restyles
- look at flow volume loops on the graph, where the Y axis is and X axis is
- after the starting point the curve rapidly mounts to a peak (peak expiratory flow)
- after the PEF the curve descends = the flow decreases as more air is expired, a normal non pathological F/V loop will descend into a straight or a convex line form top PEF to bottom FVC
what is pulmonary ventilation breathing
- It is the process of air flow to the lungs during inspiration (inhalation) and out of the lungs during expiration (exhalation)
why does air flow occur
- Air flows because of pressure differences between the atmosphere and the gases inside the lungs
- muscular breathing and recoil of elastic tissues create the changes in pressure that results in ventilation
in what direction does airflow occur
air like other gases flows from a region with a high pressure to a region with lower pressure
what is the pressure at the beginning of the respiratory tract called
Patm
what is the pressure inside the lungs called
Pa
what happens if - If Patm and Pa are equal
- If Patm and Pa are equal than there is no airflow
what happens when Pa is smaller then Patm
- If Pa
what happens when Pa is larger than Patm
if Pa> Patm airflows out of the lungs
what is the law that defines the relationship between expansion and gas flow
Boyles law
Define Boyle’s Law
- If the volume of gas is made to increase the pressure exerted by the gas decreases
- As the alveoli are forced to expand the pressure inside them decreases and the gas in flows in from the conducting airways
lungs and there elastic properties
- lungs are elastic
- they return to there original shape fi a force that is distorting them is removed
- if you prevent the air escaping by blocking the lungs the recoil of the lungs will produce a recoil pressure
how do you generate inflation
- For an object to be distorted it must be subjected to a force for example pressure
- Inspiration = inflation and expiration – deflation
- Rather than blowing into the balloon: if the balloon = lungs, then they are inflated by reducing pressure outside (like a plunger in a syringe).
- Lowering the plunger (diaphragm) reduces the pressure around the balloon and generates inspiration
How do you work out inspiration
inflation and expiration - deflation
describe the elastic properties of the chest wall
- The thoracic cage is also elastic.
- Under normal conditions the chest wall has a tendency to pull outwards and the lung to pull inwards thus balancing themselves
why does the chest wall not collapse under normal circumstances
Under normal circumstances the chest wall does not collapse, this is because the lungs and chest wall are in close contract by the intrapleural fluid in the intrapleural space
This means that a pressure is created in that space
what is the sign for intrapleural pressure
Ppl
describe intrapleural space
intrapleural space has cohesive forces
- they are difficult to separate when they are adjoined to each other
- therefore as the chest wall expands during inspiration the lung follows therefore the two structures expand as a single unit
how is the intrapleural space generated
At the end of expiration when you are relaxed before you take your next breath there is a tension between the lungs whose elasticity is causing them to collapse and the chest wall whose elasticity is cause it to spring outwards this generates a pressure in the intrapleural space known as the intrapleural pressure Ppl
- Intrapleural pressure is negative with respect to atmosphere (and the air pressure in the alveoli which is connected to the atmosphere)
Describe the changes in the intrapleural pressure
- The normal pleural pressure the beginning of inspiration is negative
- During inspiration expansion of the chest cage pulls outward on the lungs and intrapleural pressure and becomes more negative
- Intrapleural pressure becomes less negative to lead to quiet expiration
describe what happens to the intrapleural pressure in a pneumothorax
- If the pleural cavity is damaged/ruptured air enters the pleural space (because the pleural pressure is less than atmosphere)
- The intrapleural pressure becomes equal to or exceeds the atmospheric pressure and the pressure surrounding the lungs will increase and may cause the lungs to collapse.
what is compliance
- Elasticity is a measure of how easily the lungs can be stretched and is conventionally expressed as compliance.
- Compliance is the ease at which the lungs expand under pressure
what is the compliance of the lungs changed by
- it is changed by most lung diseases
what is the equation of compliance
change in volume/change in pressure
how do you work out the total compliance
- Across the wall of the structure being investigated e.g. lungs (Cl) chest wall (Cw) or lungs and chest wall (Total compliance CTOT)
what happens to lung compliance at a high expanding pressure
- In normal range the lung is very complaint however at high expanding pressure the lung is stiffer and compliance is smaller
at any given pressure
- At any given pressure lung volume during inhalation is less than the lung volume during exhalation
what is airway closure
Even without any expanding pressure the lung always has some air in it. This is due to airway closure, where small airways close trapping gas in alveoli. Airway closure increases in certain conditions, such as age and lung disease
diseases that affect either the chest wall or lung structure will..
affect compliance
what causes a reduction in compliance
- Increase of fibrous tissue in the lung
- Collapse/closure of lung (atelectasis)
increase in pulmonary venous pressure
what causes an increase in compliance
- Age
- Emphysema
what is emphysema
- a lung disease which causes destruction of the normal lung architecture which includes the elastic fibres and collagen
what does emphysema cause to the structure of the lungs
- There is also impaired elastic recoil and lungs do not deflate as easily.
- The lung is more easily distended, and the compliance of the lung is increased (more compliant
what’s the differences between emphysema and fibrosis
Emphysema – same amount of pressure, easier to inflate
Fibrosis – same amount of pressure harder to inflate
what is the effect of kyphoscoliosis on the compliance of the chest wall
- Structural change in the thorax
- Kyphoscoliosis – a disorder characterised by progressive deformity of the spine will affect compliance
- However more usual that lung complacence is affected
what 2 main components generate the elastic properties of the lungs
1) elastic fibres and collagen
2) surface tension forces caused by the alveolar-liquid interface.
name the structure of the elastic fibres in the lungs
- Elastic fibres form the bulk of connective tissue present in the walls of the alveoli
- Elastin fibres act like stocking when stretched
filling a lung with …
fluid makes it easier to inflate
what happens in inflation to an air filled lung
- Inflation of the lung follows a different pressure/volume curve from deflation.
- This is known as hysteresis which literally means “to lag behind”.
- A greater pressure is required to reach a specific lung volume when you are inflating it rather than deflating it.
what happens to inflation in an saline filled lung
- Hysteresis is abolished.- no lagging behind
- Much easier (less pressure) to expand fluid filled lungs.
- In fluid filled lungs only the elastic forces are working - there must be another component that also contributes.
- In the fluid filled lungs the air-fluid interface has been abolished.
What is hysteresis
this is when the inflation of the lung follows a different pressure/volume curve from deflation
where is surface tension presence
in the alveoli
describe what surface tension does
- The cohesive forces between liquid molecules at the surface are responsible for the phenomenon known as surface tension.
- The molecules at the surface of the liquid do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface.
- This forms a surface “film” which makes it more difficult to move an object through the surface than to move it when it is completely submersed.
- the water molecules on the boundary have an especially strong attraction for one another and therefore as a result the water surface is always trying to contract
what is the surface tension elastic force
- On the inner surface of the alveoli the water surface is always trying to contract
- This results in the alveoli trying to collapse (forming air out through bronchi)
- The net effect is to generate an elastic contractile force throughout the entire lungs, this is known as the surface tension elastic force
what does Lapacales law relate to
relates pressure to surface tension and radius
what is the equation of Lapacales law
P = 2T/r
- P = pressure within the bubble
- T = surface tension
- R = radius
explain how Lapacles law works
- the smaller bubble the greater the internal pressure that is required to keep it inflated, the smaller the radius
How do the lungs compensate with problem of pressure differences arising from having alveoli of different sizes
- Surfactant this stabilises the alveoli
what do surfactants do on the alveoli
- Surfactants greatly reduce the surface tension and therefore reduce the surface tension elastic forces
what is the surfactant made up of
- Pulmonary surfactant is a complex mixture of lipids and proteins.
- A major component (approx. 50%) of surfactant is the phospholipid Dipalmitoylphosphatidylcholine (DPPtdCho)
describe the properties of the surfactant
- Amphipathic character (hydrophilic/water loving head groups and hydrophobic tails towards air) and resultant packing reduces surface tension.