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