Flashcards in Mechanics of Breathng Deck (82):
Why is work done during breathing?
• To move the structures of the lungs and thorax and to overcome the resistance to the flow air through the lungs
What is the pleural seal?
• A thin film of liquid which holds the outer surface of the lungs to the inner surface of the thoracic wall
What happens if the lung are removed from the chest cavity?
• The inward elastic recoil of the lungs causes them to collapse
How does a pneumothorax cause lungs to collapse?
• Breaks integrity of the pleural seal
In what direction do the lungs pull?
• In and up
In what direction does the thoracic cage pull?
In what direction does the passive stretch of the diaphragm go?
What is the 'default' setting of the lungs
• The resting expiratory level (end of normal quiet respiration)
What is the function residual capacity?
• The lung volume that exists at the end of expiration
What does breathing in from the equilibrium position require?
• Contraction of the diaphragm and the external intercostal muscles
What does breathing out in quiet expiration require?
• Relaxation and passive recoil
What does forced breathing out require
• Abdominal muscles and the internal intercostal muscles
Give three examples of when passive exhalation is difficult due to an inability to flatten the diaphragm
• Pregnancy• Obesity• Wearing a corset
What does an increase in the volume of the lungs cause?
The lungs to fall under atmospheric pressure, so air flows into them
How far does fresh atmospheric air reach?
• The terminal and respiratory bronchioles • Exchange of O2 and CO2 occurs via diffusion between atmospheric air and alveolar gas
What is lung compliance? What is it measured in?
• The stretchiness of the lungs• Volume change per unit pressure change• Mesasured as volume vs pressure on graph (Y vs X)
What does higher compliance of the lungs mean?
What is specific compliance?
• Compliance depends on starting volume from which it is measured
How is specific compliance measured?
• Volume change per unit pressure change/starting volume of the lungs
From what two sources do the elastic properties of the lungs arise from?
Elastic tissueSurface tension
What is the key factor which reduces compliance?
• Surface tension of lining fluid
What is surface tension caused by?
• Interactions between molecules at surface of a liquid• The higher the surface tension, the harder the lungs are to stretch
Why is it easier to stretch lungs than expected, according to surface tension calculations
• Surfactant produced, which reduces surface tension when lungs are deflated
What is surfactant produced by?
• Type 2 alveolar cells
What are the limits of surfactant?
• Reduces surface tension when lungs deflated, but not when fully dilated• Little breaths are easy• Big breaths are hard
Why is it hard to take big breaths?
• Detergent molecules get further and further spread out, reducing effect
What is hysteresis?
• The energy put into stretchin a film of surfactant• Decreases relaxing, energy lost (Hooke's law in physics!)
Films want to reduce to smallest size - To what point will this continue?
• Until there is an equilibrium between tension and pressure Pressure is inversely proportional to bubble size
Outline laplace's law
• Pressure is inversely related to the radius of a bubble
Why don't big alveoli eat little alveoli?
• Surfactant becomes less effective as bubble size increases• Surface tension increases, keeping pressure similar to small
What is respiratory distress syndrome?
• Babies born prematurely have too little surfactant• Breathing and gas exchange compromised
Outline the features of the lungs of a baby with respiratory distress syndrome
• Lungs stiff• Few, large alveoli
What is poiseulle's law?
• Resistance of a tube increases sharply with a falling radius
What should resistance be like in airways?
• Small tubes have very high resistance
Why is resistance not extortionately high in the lungs?
• At each branch number of airways increases• This causes a set of parallel resistors to be formed with relatively low resistance
Where is the highest resistance in a normal breath?
• The trachea (the biggest tube, but least branches!)
Why does resistance increase in forced expiration?
• Small airways narrowed due to compression • Resistance increases dramatically and air is trapped in alveoli
What is work done against in the lungs?
• Elastic recoil of the lungs and thorax ○ Elastic properties of the lungs ○ Surface tension forces in the alveoli • Resistance to flow through airways ○ Of little significance in health but often affected by disease
What occurs in the lungs in terms of resistance in obstructive airway disease?
• Small airways narrowed by disease (asthma, chronic bronchitis)• Resistance increases much earlier in expiration, making breathing out difficult
How do small airways decrease resistance during inspiration?
• Decrease smooth muscle contraction
What are lung function tests designed to assess?
• The mechanical condition oft he lungs• Resistance of the airways• Diffusion across the alveolar membrane
What factors can lung function be inferred from?
• Volumes• Pressures/flows• Composition
What does the spirometer measure?
• Vital capacity - Maximum inspiration to maximum expiration
What is required before you can predict vital capacity of an indiviual?
Knowledge of age, sex and height
What causes vital capacity to be less than normal?
• Filled normally in inspiration• Emptied normally in expirationBoth
What is vital capacity?
• Maximum inspiration to maximum expiration
What limits vital capacity?
• Maximum inspiration ○ Compliance of the lungs ○ Force of inspiratory muscles• Maximum expiration ○ Increasing airway resistance as the lungs are compressed
What may be the reason if vital capacity is less than normal?
• Cannot breathe in maximallyCannot breath out maximally
What is single breath spirometry?
• Subject fills lungs from atmosphere and breathes out as far and fast as possible through spirometer
What is a vitalograph trace?
• Plot of volume expired vs time• Will show an initial rapid rise which tails off to a plateau
What is the forced vital capacity?
• The maximum volume that can be expired from full lungs• Typically 5l in normal adults
What is the FEV 1.0
• Volume expired in first second of exhalation• Affected by how quickly air flow slows down• Less if airways narrows • >70%
How can obstructive and restrictive deficits be separated?
By asking patients to breathe out rapidly from maximal inspiration
What does a single breath spirometer do?
Plots volume expired
What is a restrictive deficit?
If lungs are difficult to fill
What is an obstructive deficit?
• If airways are narrowed and lungs will be easy to fill• Resistance will increase in expiration
What factors would cause the lungs to be difficult to fill?
• Stiff• Weak muscles• Problems with chest wall
What will an vitalograph show with a restrictive deficit?
• FVC will be reduced• FEV will be normal (>70% FVC)
What will a vitalograph show with an obstructive deficit?
• FEV 1.0 will be reduced (
What is a flow volume curve?
• Plot of volume expired against flow rate, derived from a vitalograph tract
Why is expiratory flow rate highest at state of expiration?
• Airways stretched, so resistance at a minimum• Known as peak expiratory flow rate
What are the two types of graphs we can us for flow volume?
• Volume expired against time• Flow against volume expired
What does mild obstruction of the airways cause?
• A scooped out expiratory curve• More severe obstruction will cause reduced PEFR (peak expiratory flow rate)
What does restrictive disease show on a flow-expiratory graph?
Peak then rapid decline
What can't be measured by spirometer?
• Functional Residual Capacity
What can measure residual volume?
What is helium dilution?
• Patient breathes in helium of known concentration at end of quiet expiration• See how much conc reduced by mixing with air already in lungs
Why is helium used to detect lung function?
• Not present in normal air• Insoluble in blood, so not remains in alveolia
Outline exactly what happens in Helium Dilution Test (Use equation!)
• Patient inhales gas with known Helium Concentration (C1) and Volume (V1)• End of tidal expiration ○ Lung volume = Functional Residual Capacity = Expiratory Reserve Volume + Respiratory Volume • Patient keeps breathing until equalised • Functional Residual capacity - Expiratory reserve volume = Residual Volume
How is Transfer Factor calculated?
• Carbon Monoxide Transfer Factor
What is CO transfer factor?
• Rate of transfer of CO from the aveoli to the Blood in ml/min/kPa• Way of measuring diffusion capacity of the lung
Why is CO used?
• High affinity for haemoglobin• Concentration gradient between blood plasma and alveoli constant as CO removed immediately by RBC• Thus, only limiting factor is diffusion capacity of lung
Why is only a small amount of CO used?
What exactly occurs in a CO Transfer Factor?
• Gas containing CO inhaled• Held for 10 seconds• Patient exhales and gas collected mid expiration to gain an alveolar sampleCan detect con of CO and inert gas
What does nitrogen washout measure?
• Serial dead space and ventilation perfusion
What happens in nitrogen washout test?
• Takes one normal breath of pure oxygen• Breathes out via meter measuring %nitrogen• Initially only oxygen expired from airways• Then mixture of o2 and air from aveoli
What do you measure in nitrogen washout test?
• Time it takes for nitrogen to appear in mixture is amount of dead space
What are you measuring in a diffusion conductance test?
• Measure how easily CO crosses from alveolar air to blood
Why is CO used in the diffusion conductance test?
• Uses CO because binding to Hb means no partial pressure in mixed venous blood
What four things are found in a lung function report?
• Vital capacity• FEV 1.0• Ratio FEV1.0/FVC• Peak expiratory flow• FRC• RV• TLC• RV/TLC• Transfer factor• CO conductance
Give an example of a restrictive airway disease