Lecture 17 - The work of breathing Flashcards
What are 4 things that oxygen has to be able to do in our body?
Get it in - get air from outside
Get it across - get gas from alveoli into the bloodstream and from the bloodstream back into the alveoli
Get it around - gets it to the cells that need it and brings it back the blood to be deoxygenated
Keep it going - need to keep the system running smoothly with neural input
Quantifying liquids vs gases
Liquids are usually quantified in terms of volume
Gases are usually quantified in term of pressure
Boyle’s Law
The pressure of a gas is inversely related to its volume
Creating a pressure gradient
Gas will move from high to low pressure
Right before a breath, the pressure outside the body and inside the lungs are equal, so no air is moving
As you inhale, your diaphragm drops while your rib cage expands. This increases the volume in your chest, which lowers the pressure
Creating a pressure gradient - inhalation
Volume is increasing
Pressure inside the lungs is decreasing
Pressure outside is now greater than the inside so air rushes in
Creating a pressure gradient - exhalation
Volume is decreasing
Pressure inside the lungs is increasing
Pressure outside is now lower than inside, so air rushes out
The two opposing forces that must be overcome to take a breath ….
1- Stiffness of lungs
Lungs must expand to take in air - naturally they do not want to inflate
How compliant are the lungs?
Surface tension holds lungs in place
2-Resistance of the airways to the lungs
Need to move the air from outside into the alveoli
How much resistance is the respiratory tract putting on the movement of air?
Lung stiffness is related to…
Compliance
Compliance = ΔV/ ΔP
Pulmonary fibrosis
Thickening and scarring of the alveolar membranes - kills a lot of the cells associated with the lungs and replaces them with scar tissue
Can arise from chronic inflammation or exposure to industrial chemicals
Scar forming on the surface of the lungs is not as flexible as the normal cells in the lungs so now it is more difficult to stretch that lung and accurate a volume of air
Compliance in normal vs pulmonary fibrosis
Normal
As we add more and more pressure to the lung we see that it takes up more and more volume of gas
Pulmonary fibrosis
Inflexible tissue that does not want to stretch out
Fibrotic lung takes much longer to get to the pressure that you have to put on the lung to accommodate the lung for a certain volume
As you pack more pressure in the difference in between the two gets larger
Fluids surrounding the lungs exert…
Surface tension
Alveoli are lined with fluid that exert surface tension.
Walls of alveoli are very thin, enhancing this effect
Must overcome surface tension in order to expand the lungs
Surrounded by fluid that is mostly water and water molecule are really strongly attracted to one another, they form tight bonds with one another. Water molecules form tight bonds with one another and then water droplets form because of this, they don’t flatten out because the attractive forces of the water molecules to each other is greater than the gravitational force trying to pull it flat
Disadvantage to the surface tension in fluid around the lungs is that the molecule are bound to one another and they don’t want to allows the lungs to expand, they form a barrier against it.
What do alveoli produce to disrupt surface tension?
Surfactant
Relieves surface tension and allows the alveoli to expand during a breath
Failure to produce adequate surfactant results in difficulty in expanding the lungs and reduced oxygen intake
Premature infants don’t produce surfactant, resulting in respiratory distress syndrome (RDS) - the lungs are struggling to overcome the surface tension around them and therefore do not get the oxygen exchange that they need
Surface tension is broken by surfactant being there allows lungs to now expand
Surfactant disrupts the interaction between water molecules
Airway resistance through the respiratory tract
Need to move air from outside to the alveoli
Air is conducted through the bronchi and bronchioles
Exert force (friction) on the air that must be overcome
Resistance to air flow and bronchiole radius
R = 1 / (r^4)
Where r = radius and R= resistance
Spirometry
Is a test to measure pulmonary function, and yields a complex trace with a number of volumes and capacities
Common simple test
Test response to therapy
Can measure how much and how fast you breathe
Spirometry trace volumes
Tidal volume Inspiratory reserve volume Expiratory reserve volume Residual volume Minimal volume
Forced breath
Forcing more air in or out than usual
Tidal volume
VT
Volume of air moved in and out during normal quiet breath
Inspiratory reserve volume
IRV
Extra volume that can be inspired with maximal inhalation
Expiratory reserve volume
ERV
Extra volume that can be exhaled with maximal effort
Residual volume
Volume remaining in lungs after maximal exhalation
Even after exhaling as hard as you can you still cannot completely deflate them - this residual volume is the amount that always stays there
Minimal volume
Volume remaining in lungs if they collapsed
Spirometry trace capacities
Vital capacity
Total lung capacity
Inspiratory capacity
Functional residual capacity
Capacity = ?
A capacity is the combination of two or more lung volumes
Vital capacity
Inspiratory reserve + expiratory reserve + tidal volume
Volume of air you can shift in and out of your lungs
Total lung capacity
Vital capacity + residual volume
Total volume in lungs when you have filled them to the maximum
Inspiratory capacity
Inspiratory reserve + tidal volume
Total volume of air you can inspire from rest
Functional residual capacity
Expiratory reserve + residual volume
Volume remaining in lungs after normal exhalation (whats left when everything has been forced out as much as it can)
Forced expiratory volume in one second
FEV1
i.e. how much of the vital capacity comes out in first second
Reduced in diseases causing resistance to airflow such as asthma
FEV1/VC ration is normally 80%, below 70% indicates airways obstruction
Spirometry can discern between ….
Obstructive and restrictive issues
Restrictive issues
Reduced lung capacity - trouble of getting the lungs to expand and accommodate the volume that is needed
Reduced lung compliance such as fibrosis, insufficient surfactant release
Reduced ability to expand the lung. Individuals with this disorder will have reduced ling volumes when performing spirometry
Obstructive issues
Resistance to airflow - ability to move air from the outside environment and down into the alveoli
Asthma - bronchioles restricted so restricting the amount of air that is moving through
Chronic bronchitis
Characterised with by a narrowing of the airways or blockage of the airways and this increases airway resistance. Individuals with this disorder will have decreased expiratory flow rate
What is a peak flow meter?
A peak flow meter is a portable hand-held device used to measure the highest rate at which you can expire air from the lungs (known as peak expiatory flow rate)
This test is commonly used to detect narrowing of the airways. Many people with asthma use a peak flow meter to monitor their condition
What is your peak flow meter recording dependent on?
Dependent on age, sex, height, weight and dependent on experiment and procedure
Peak flow tests before and after a 20 minute run…
Peak flow will most likely increase because the airways relax and get wider (bronchodilate) with exercise
Why can’t residual volume be determined using the spirometry technique?
Only measuring air that is going in and out of the lungs
What is the difference between lung capacity and lung volume?
Capacity comprises of 2 or more volumes
Volume measures the amount of air for one function such as inhalation or exhalation
What volumes make up functional residual capacity?
Expiratory reserve volume and residual volume
What is the functional/physiological significance of the functional residual capacity?
It acts as a reservoir to prevent fluctuations in alveolar gases over breathing cycle. FRC also allows us to talk, sing and play a wind instrument
What volumes make up total lung capacity?
Inspiratory reserve volume
Tidal volume
Expiratory reserve volume
Residual volume
Physiological significance of the FEV1/FVC ratio
Tells us a person’s vital capacity that they are able to expire in the 1st second of forced expiration (FEV1) to the full, forced vital capacity (FVC)
Using a forced expiratory volume test, how would you determine if someone has an obstructive or restrictive lung disorder?
FEV1/FVC ratio is less than 70% which indicates an obstructive disorder
Smaller FVC for their age, sex and height indicates a restrictive disorder
Stereotypical example of obstructive lung disorder?
Asthma (uncontrolled)
Stereotypical example of restrictive lung disorder?
Pulmonary fibrosis
What factors determine the size of an individual’s lung capacity?
Age, sex, body build, and physical conditioning
At rest do the lungs completely fill the lateral, inferior regions of the pleural cavities?
No
How far do the lungs extend superiorly and inferiorly within the thorax?
From the diaphragm inferiorly to just superior to the clavicles
Are there any structures of the upper respiratory tract located within the thorax (chest cavity)?
No, the upper respiratory tract structures are outside of the chest cavity, whereas the lower respiratory tract structures are within the chest cavity
What is the function of the vibrissae and where precisely are these located?
Nose hairs - filter inhaled air
Located in the vestibules of the nasal cavity
Cribriform plate of ethmoid bone
Little holes to allow neutrons from olfactory receptors to pass through the bone and up to the brain
Hard palate
Main division between the nasal cavity and the oral cavity
Purpose of the shape of the conchae?
Increases surface area, makes air flow turbulent ensure all air inhaled through the nose is in contact with the conchae
What is the purpose of the mucus produced in the paranasal sinuses?
Moisturises the inside of the nose - protects the nose and sinuses from dust, dirt, pollutants and microbes
The pharyngeal tonsils sometimes become swollen and inflamed. Which portion of the pharynx would the swelling obstruct?
Posterior wall of nasopharynx
Which bilateral pair of tonsils is commonly removed from the oropharynx in a tonsillectomy?
Palatine
Which of the laryngeal cartilages makes up ‘Adam’s apple’?
The thyroid cartilage
What attaches to the ends of the cartilage rings posteriorly on the trachea?
Smooth muscle
Is the cartilage ring the same thickness all the way around?
Thickest anteriorly for protection
Why is the epithelium called ‘pseudostratified’ and what is its purpose?
Look at different heights but all them are attached to the same basement membrane, aids in protection
Why does the cartilage disappear as the bronchi become bronchioles?
No longer need cartilage to maintain a patent airway. Control of airway resistance more important in the bronchioles. Smooth muscle for bronchodilation and bronchoconstriction
From bronchi to bronchioles what happens?
Epithelium decreases in size and height
The goblet cells are going to reduce in number
Which feature(s) distinguishes a bronchiole from a blood vessel?
Bronchioles are lined with a cuboidal epithelium. Blood vessels are lines with a simple squamous endothelium
Why are the no goblet cells or mucus secreting glands in the bronchioles?
Air doesn’t need to be cleaned by this point
The mucus would be unable to be moved out of the bronchioles
