3. Ventilation Flashcards
How do normothermic ex vivo ventilated perfused lungs behave differently to in vivo?
- No restriction by chest wall
* Expand freely
What are the definitions of the following: • minute ventilation • respiratory rate • alveolar ventilation • anatomical dead space • alveolar dead space • physiological dead space
- Minute ventilation - volume of air expired in one minute
- Respiratory rate - frequency of breathing per minute
- Alveolar ventilation - volume of air reaching the respiratory zone
- Anatomical dead space - capacity of the airways incapable of undertaking gas exchange
- Alveolar dead space - capacity of the airways that should be able to undertake gas exchange but cannot
- Physiological dead space - anatomical + alveolar dead space
What are the definitions of the following: • Hyperpnoea • Hypopnoea • Apnoea • Dyspnoea • Bradypnoea • Tachypnoea • Orthopnoea
- Hyperpnoea - increased depth of breathing
- Hypopnoea - decreased depth of breathing
- Apnoea - cessation of breathing
- Dyspnoea - difficulty in breathing (shortness of breath)
- Bradypnoea - abnormally slow breathing rate
- Tachypnoea - abnormally fast breathing rate
- Orthopnoea - positional difficulty in breathing (when lying down)
What are the 2 components of the chest wall?
- Bone + muscle + fibrous tissue (tend to recoil out)
- Lungs (tend to recoil in)
(muscular effort needed to push equilibrium in one direction or the other)
What is the functional residual capacity (FRC)?
- Rib cage and lungs in equilibrium
* End of tidal expiration
Describe the pleural cavity volume and pressure
• Fixed volume • Negative pressure - between lungs and chest wall - expanding chest pulls the lung - negative pressure of pleural cavity allows this
What happens to the lung/chest wall equilibrium if either is punctured?
- Fixed volume pleura is compromised
- Air fills the pleural cavity
- Elastic recoil
- Lungs collapse (pneumothorax)
- Haemothorax is much slower (blood filling the pleural cavity)
What are the definitions of the following: • Tidal volume • Inspiratory Reserve Volume • Expiratory Reserve Volume • Reserve volume
- Tidal volume - volume of air inspired and expired to meet the metabolic demands of the body (500mL in 70kg man)
- Inspiratory Reserve Volume - the maximum volume of air that can be inspired after a tidal inspiration
- Expiratory Reserve Volume - the maximum volume of air that can be expired after a tidal expiration
- Reserve volume - residual volume of the lung that you cannot get rid of
(all change in volumes)
Why is it bad to empty the lungs fully?
- Due to the surfactant in the alveoli
* This could cause the alveoli to stick together and not reopen
What are the definitions of the following: • Total Lung Capacity • Vital Capacity • Functional Residual Capacity • Inspiratory Capacity
- Total Lung Capacity - the volume of air in the lungs when you inspire as much as possible (everything combined)
- Vital Capacity - how much air is within the confines of what we are able to inspire and expire (TLC - RV)
- Functional Residual Capacity - the volume of air present in the lungs at the end of passive expiration (equilibrium, ERV + RV)
- Inspiratory Capacity - how much extra air you can take in on top of the FRC (TV + IRV)
(all from 0 to a certain number i.e. include residual volume)
What factors in a person contribute to their lung volumes?
- Height (most influential)
- Body shape
- Sex (male > female generally)
- Age (chronological and physical)
- Genetics
- Fitness (mainly innate, some training)
- Disease (pulmonary/neurological)
What units are used for pressures in the lungs?
cm H2O
What is a transmural pressure?
Pressure across a tissue or several tissues
What is a transpulmonary pressure?
Difference between alveolar and intrapleural pressure
How do you work out the orientation of the pressure gradient?
Pressure inside minus pressure outside
What is a transrespiratory pressure?
- Tells us whether there will be airflow into or out of the lung
- Negative pressure - air moves in (as pressure inside is lower)
Is it possible to ventilate using positive pressure breathing?
- Yes
- Involves increasing the pressure outside
- Using a ventilator or CPR
Describe the ventilation cycle
- No transpulmonary pressure (difference between alveolar and intrapleural pressure) - no volume change
- Chest wall expands, diaphragm moves down, negative pressure
- Pressure gradient (transrespiratory) - air flows in
- Pressure gradient equalises again at the end of inspiration
- Inspiratory effort removed - positive pressure forces air out
- Volume and pressure return to starting values
What is dead space and describe the anatomy of it?
• Part of the airways and lung that does not participate in gas exchange
• Physiological dead space = anatomical + alveolar dead space
• Anatomical dead space = conducting zone
- 16 generations
- 150mL at FRC (usually the total dead space volume)
• Alveolar dead space = non-perfused parenchyma
- alveoli without a blood supply
- normally alveolar dead space is 0
- part of the respiratory zone which has 7 generations
How can you change someone’s dead space?
- Tracheostomy - upper part of the airway is no longer dead space, decreasing dead space
- Ventilator - extra tubing becomes dead space
Why is it impossible to use a 100m snorkel?
- Extra dead space
- Dead space is 76x greater than resting TV and 7x greater than TLC at 100m
- Can’t push the CO2 all the way and get O2 at that depth
- More pressure on respiratory muscle at greater depths too
- All oxygen used - death
What does the chest-wall pressure relationship allow us to understand?
- Considers the respiratory mechanics of: independent chest wall and independent lung
- Intact lung is the sum of both
- If chest wall pressure is -5 cm H2O and lung pressure is 5 cm H2O, Intact lung pressure (FRC) is 0
What is the significance of the sigmoid shape of the chest-wall pressure relationship?
Easier to ventilate the lungs around the FRC (functional residual capacity)
Why do we not use our entire vital capacity when exercising?
- Inefficient
- Lot of energy and effort
- Higher ventilation performance is good but not good to tire out muscles
What is the protocol for using a patient to create a volume-time curve?
1) Patient wears noseclip
2) Patient inhales to TLC
3) Patient wraps lips around mouthpiece
4) Patient exhales as hard/fast as possible
5) Exhalation continues until RV is reached or six seconds has passed
6) Visually inspect the curve, looking for slow starts, early stops and intramanoeuver variability
• Tests airway resistance and FVC
What is FEV1, FET and FVC?
- FEV1 - amount of air forced out of the lungs in 1 second (around 75%)
- FET - forced expiratory time, time take to expel all the air from the lungs
- FVC - Forced Vital Capacity
What happens to FEV1, FET and FVC in obstructive lung disease e.g. COPD?
- FEV1 is much lower (can’t expel air fast)
- FET is much higher (takes longer to expel all air)
- FVC is much lower
What happens to FEV1 and FVC in restrictive lung disease e.g. sarcoidosis?
- FEV1 is relatively high - air conducting airways are quite clear and can expel air relatively easily
- FVC - lower, due to the overall lower volume in the lungs
How does the FEV1/FVC ratio change in obstructive and restrictive lung disease?
- Obstructive - lower (e.g. 53%)
- Restrictive - higher (e.g. 97%)
(normal e.g. 73%)
What is the protocol for using a patient to measure peak expiratory flow?
1) Patient wears nose-clip
2) Patient inhales to TLC
3) Patient wraps lips around mouthpiece
4) Patient exhales as hard/fast as possible
5) Exhalation does not have to reach RV
6) Repeat at least twice, taking the highest measurement
- Tests airway resistance
- Graph made comparing peak expiratory flow rate (y-axis) to age (x-axis)
What is the protocol for using a patient to create a Flow-Volume loop?
1) Patient wears nose-clip
2) Patient wraps lips around mouthpiece
3) Patient completes at least one tidal breath (small loop)
4) Patient inhales steadily to TLC (volume decreases)
5) Patient exhales as hard/fast as possible (graph peaks)
6) Exhalation continues until RV is reached (flow rate decreases)
7) Patient immediately inhales to TLC (volume decreases as the graph loops down)
8) Visually inspect for inconsistencies and interrupted flow data
(graph is like a clockwise spiral)
How can you measure residual volume?
- Inhaling and exhaling something with a known concentration of an inert gas
- Therefore none of it enters circulation
- Measure the concentration difference after a while - determine the residual volume
How does the Flow-Volume loop change in an obstructive disease?
- Disease - indentation (coving) in top right line - last bit of expiration
- More severe - deeper indentation
- Alveolar walls degraded - increased volume - loop moves left
(• Residual volume expands - air trapped in alveoli)
(• TLC might increase)
How does the Flow-Volume loop change in a restrictive disease?
- Narrower loop - restriction makes it harder to get to a high TLC
- May be some decrease in flow rate
- Loop moves right
How does the Flow-Volume loop change in a Variable Extrathoracic Obstruction?
Inspiratory curve is blunted (bottom dome flattened) - flow rate is limited but something in the way
How does the Flow-Volume loop change in a Variable Intrathoracic Obstruction?
Expiratory curve is blunted (top peak flattened)
How does the Flow-Volume loop change in a Fixed Airway Obstruction?
- Blunted inspiratory curve
* Blunted expiratory curve
Distinguish the mechanical force involved in tidal and maximal ventilation
- Tidal - diaphragm induced (‘syringe’)
* Maximum ventilation - full inspiratory muscle recruitment (‘syringe’ and ‘bucket handle’
Explain the regional differences in ventilation and perfusion
- Gravity favours ventilation and perfusion of the basal lung
- Basal lung has wasted perfusion
- Apical lung has wasted ventilation
