Mechanics Of Breathing Flashcards
Which extra muscles are needed for deep inspiration?
Sternocleiodomastoid (elevates the sternum) Middle, anterior and posterior scalene (elevate and fix the upper ribs)
Which muscles are used in normal inspiration?
External intercostals Diaphragm Interchondral parts of internal intercostal muscles
Which muscles are required for normal expiration?
None Results from passive recoil of the lungs and ribcage Expiration is passive
Which muscles are required forced expiration?
Internal intercostals Rectus abdominis External and internal obliques Transversus abdominis
What is a pneumothorax?
When the integrity of the pleural sac is broken by air, causing the lungs to collapse
What is in the pleural space?
Fluid
What holds the lungs to the thoracic wall?
Surface tension of the fluid in the pleural space
Define compliance of the lungs
Stretchiness of the lungs So equals the volume change per unit of pressure change
What does it mean if the lungs have a high compliance?
The lungs are easier to stretch
How does compliance change with lung volume?
The greater the lung volume, the greater the compliance
What are the main factors that affect compliance of the lungs?
Surface tension Surfactant Bubbles
How does surface tension affect the compliance of the lungs?
Interactions between molecules at the surface of a liquid makes the surface resist stretching
As surface tension increases, how does this affect lung compliance?
As Durga e tension increases, the harder the lungs are to stretch
Why is the surface tension of the lungs much lower than expected than if lungs were lined with saline?
Presence of surfactant
How does surfactant reduce surface tension?
Disrupts interactions between the surface molecules The hydrophilic ends of molecules lie in alveolar fluid while the hydrophobic ends project into alveolar gas
What is surfactant?
A mixture of phospholipids and proteins
What is surfactant produced by?
Type II alveolar cells
What is hysteresis?
The energy put into stretching a film of surfactant is not all recovered when the film recoils because need to overcome the surface tension when inhaling https://uk.answers.yahoo.com/question/index?qid=20100605085048AAbWQGy
When is the energy loss in hysteresis greatest?
When tidal volume is maximal - reason why little breaths are best
What is the equilibrium in a bubble?
When the film shrinks around gas until an equilibrium between tension and pressure is reached
What is Laplace’s law?
Pressure is inversely related to the radius of the bubble As radius increases, pressure decreases Bigger the bubble, lower the pressure
What will happen if a big bubble is connected to a smaller bubble?
Air will flow from high to low pressure -small bubble collapses into the big bubble
What prevents the alveoli (bubbles) from swallowing eachother and how?
Surfactant Keeps a high pressure in the larger bubbles As alveoli get bigger, the surface tension increases because surfactant is less effective - stops them eating the little bubbles
What is respiratory distress syndrome?
When premature babies have too little surfactant in their lungs so they are very stiff with fewer, larger alveoli. Breathing and gas exchange is compromised.
What is Poiseulle’s law?
Small rubes have high flow resistance
Where is the respiratory system is the highest resistance and why?
Trachea In the lung there are many small airways but there are many in parallel, reducing the resistance
Why is there such a thing as residual volume?
When the lung is compressed in forced expiration, small airways are narrowed so resistance increases dramatically and air is trapped in the alveoli
What is obstructive airway disease and what does it do?
When small airways are narrowed by disease Increases the resistance much earlier in expiration so breathing out can become difficult
What are all the forces in equilibrium at resting respiratory level?
Lungs trying to pull inwards and upwards Thoracic cage trying to pull outwards Diaphragm pulling downwards
What are lung function tests used to assess?
Mechanical condition of the lungs Resistance of the airways Diffusion across alveolar membrane
What does a spirometer measure?
The vital capacity (max inspiration to max expiration)
What does maximum inspiration test?
Compliance Force of inspiratory muscles
What does max expiration measure?
Airway resistance
How is single breath spirometry done?
Fill lungs with air Breath our as far and as fast as possible through a rapid responding spirometer
What is the name of the graph that spirometry gives you?
A vitalograph trace
What does single breath spirometry show?
FEV1.0 - forced expiration in one second. Affected by how quickly airflow slows down Can work out the FEV1.0/FVC ratio which is normally >70% So FEV1.0 should be more that 70% of the FVC a
Define forced vital capacity. Typical value?
Maximum volume that can be expired from full lung. 5L
What is a restrictive deficit?
Problem with inspiration
What can cause a restrictive deficit?
Due to stiffness, weak muscles, problem with chest wall
How does a restrictive deficit affect FEV1.0 and FVC?
FVC will be reduced (PICTURE) FEV1.0 will be normal
What is an obstructive deficit?
Problem with expiration
What causes an obstructive deficit?
When airways are narrowed so increased resistance in expiration.
What happens to FEV1.0 and FVC in an obstructive deficit?
FEV1.0 will be reduced FVC will be normal PICTURE
What are on the axes of a flow volume curve?
Volume expired against flow rate Derived from a vitalograph
Explain the shape of a flow volume curve
When lungs are full, little air expired. Airways are stretched so resistance is minimum Flow rate will reach its maximum (peak expiratory flow rate PEFR) As lungs are compressed, airways narrow and resistance increases so flow rate decreases The narrower the airways to begin with, the more rapidly it falls
Why is a flow volume curve better than a vitalograph trace?
It is a more sensitive indicator of airway narrowing Can discriminate between large and small airway narrowing
What can peak expiratory flow rate be used to measure?
Screening test for airway narrowing Very insensitive
How is residual volume measured?
Use a spirometer with helium dilation
How does helium dilation work?
Helium is not normally present in the air and is insoluble in blood Patient breaths in a known concentration starting at a functional residual capacity See how much the helium concentration reduces by mixing it with air already in the lungs to give a measure of residual volume
What does a nitrogen washout measure?
Serial dead space Ventilation perfusion matching (indirectly)
How is a nitrogen washout done?
Patient takes one normal breath of pure oxygen and breaths out via a meter measuring percentage nitrogen Initially, only oxygen will be breathed out, then a mixture of oxygen and air with nitrogen from the alveoli. Volume expires at transition is the serial deadspace.
How is diffusion conductance measured?
See how easily carbon monoxide crosses from alveolar air to the blood.
How does an obstructive deficit affect a flow volume curve?
