Lung mechanics 2 Flashcards
(30 cards)
What is the name of pressure at the beginning of the respiratory tract?
atmospheric
What is the name of pressure inside the lungs?
alveolar pressure
What is the law that defines the relationship between expansion and gas flow?
Boyle’s law:If the volume of a gas increases the pressure exerted by the gas decreases. As the alveoli are forced to expand (inhalation), the pressure inside them decreases and gas flows in from the conducting airways.
What causes air to enter the lungs? Describe how this works
Pressure difference Lowering the diaphragm in inflation, reduces the pressure around the alveoli. Air moves into the lunges from the outside it has less pressure than outside
How are the lungs and chest wall held together? What implications does that have for when one moves?
By the cohesive forces produced by the intrapleural fluid in the intrapleural space.
Thus, as the chest wall expands during inspiration, the lung is obligated to follow, so the two structures expand as a single unit
What is the intaapleural Pressure and how is it generated?
The Intrapleural Pressure is pressure in the intrapleural space.
Affected by the recoil of the chest and lungs away from eachother
•At the end of an expiration (complete relaxation), there is a tension between the lungs, whose elasticity is causing them to collapse and the chest wall whose elasticity is causing it to spring outwards.
Describe how the intrapleural pressure changes during expiration and inspirartion
- The normal pleural pressure at the beginning of inspiration is slightly negative.
- During inspiration expansion of chest cage pulls outwards on the lungs and intrapleural pressure becomes more negative.
Intrapleural pressure becomes less negative to lead to quiet expiration.
What happens to the Intrapleural presure when damage occurs to the pleural cavity? How is this related to disease?
- 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.
- E.g. pneumothorax
What is meant by the term lung compliance? What is the equation to assess it ?
The ease at which the lungs expand under pressure
It is directly relates to there elasticity
Defined as the the change in volume produced by a change in pressure Across the wall of the structure being investigated.
•
Compliance = Change in volume/Change in pressure
When is the lung volume always highest, inhalation or exhalation?
Lung volume is always higehst during exhalation
Why/how do the lungs always have air located in them?
This is due to airway closure
Small airways trap gas in the laveoli
Increases with age
Name conditions which can increase or decrease lung compliance
Increase- same amount of pressure harder to inflate
- Age
- Emphysema
Reduction- same amount of pressure harder to inflate
- Increase of fibrous tissue in the lung (pulmonary fibrosis)
- Collapse/closure of lung (Atelactasis)
- Increase in pulmonary venous pressure
How does emphysema increase lung compliance?
In emphysema elastic fibers and collagen destroyed
Elastic recoil is impared and lungs do not deflate as easily.
The lung is more easily distended, and the compliance of the lung is increased
How does fibrosis effect lung compliance?
Harder to inflate lungs at the same amount of pressure
Decreases lung compliance
Which two components are responsible for the elastic properties of lungs?
- Elastic fibers and collagen
- surface tension forces caused by alveolar-liquid interface
Why does filling lungs with fluid make it easier to deflate?
For airfilled lungs- inflation follows a different pressure- hysteresis
More pressure is required to reach a specific lung volume when inflating
For saline filled lungs- Hysteresis is abolished, air fluid interface is abolished- so there is no surface tension force inhibiting movment
Only elastic forces are being used
less pressure is required to fill lungs
Describe the formation of suface tension in the alveoli
On the inner surface of alveoli, the water surface is trying to contract
This causes the alveoli to try and collapse as air is forced out through bronchi
An elastic contractile force is produced through the lungs - surface tension elastic force
Describe Laplace’s Law and relate it to surface tension in the lungs
•The pressure in a bubble is equal to twice the surface tension divided by the radius
P = 2T/r
Therefore, the smaller the bubble, the greater the internal pressure needed to keep it inflated
As we have different sized alveoli in the lungs, the smaller ones by the law will need more pressure
How do the lungs compensate for Laplace’s Law (different sized alveoli)
The lungs secrete surfanctan which lowers surface tension more in smaller alveoli to equal out surface tension between different sized alveoli
Also reduces surface tension elastic force
What is surfanctant composed of? How does it reduce surface tension?
Lipids and proetins
The main phsopholipid is Dipalmitoylphosphatidylcholine (DPPtdCho)
It reduces surface tension due to Amphipathic character (hydrophilic/water loving head groups and hydrophobic tails towards air) and resultant packing
Where is surfanctant assembled?
lamellar bodies
What is Infant respiratory distress syndrome (IRDS) and how is it caused?
When infants have difficulty breathing at birth
Caused when premature babies are unable to produce enough surfanctant- lung could collapse
Production starts between 24-28 weeks and reaches optimum at 34
What is airway resistance? Name a condition which increases the resistance and describe how it does this
The resistance to the flow of gas within the airways of the lung.
Asthma
Narrowing of airways due to contraction of bronchial smooth muscle or swelling due to inflammation and mucus production
What is laminar air flow?
Smooth, streamline and orderly
