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
