Respiratory: Lung Volumes and Capacities in Sickness and in Health L15 Flashcards
What is surfactant? What is surface tension? How does surfactant reduce surface tension? How does this affect lung compliance?
Surfactant is a phospholipid produced by the alveolar type 2 cells that lower surface tension in alveoli.
Surface tension stems from the fact that water H2O molecules try to attract each other, thereby contracting the fluid.
The fluid lining the alveoli would tend to cause them to collapse due to these forces if there was no surfactant.
Surfactant lowers surface tension decreases the attractive forces of the water molecules due to hydrogen bonding by interspersing the surfactant through the H2O.
Lowering surface tension will increase lung compliance, the amount of inflation the lung can make, which is required to expand for inspiration. Compliance is a measure of the elasticity of the lung (the change in volume for each unit of pressure change across the lung).
What effect does surfactant decreasing alveolar radius by decreasing surface tension, have?
As alveolar radius decreases, surfactant’s ability to lower surface tension increase. This prevents a pressure gradient forming between small and large alveoli causing the smaller alveoli to empty into the larger ones.
What are the consequences of a lack of surfactant?
Decreased surfactant = Increased surface tension = Alveoli cannot retain shape, fuse together.
Infant respiratory distress syndrome (IRDS) is caused by a lack of surfactant: prematurely born infants (usually those born before 7 to 8 months of gestation) may not have adequate amounts of surfactant and can experience great difficulty inflating the lungs.
What is the value of Total Lung capacity?
What 4 lung volumes makes up total lung capacity?
Total Lung Volume = 6L = Vital capacity + Residual Volume. 'Vital capacity' is made up of 'Inspiratory Reserve Volume', 'Tidal Volume' and 'Expiratory Reserve Volume'.
What is Tidal volume?
0.5L. The volume that is breathed in or out during quiet respiration.
What is Inspiratory Reserve Volume?
3L, the additional air that can be breathed in after a normal inspiration (i.e the maximum volume that can be inspired above and beyond the tidal volume).
What is Expiratory Reserve Volume?
1.5L, the additional air that can be breathed out after the normal expiration.
What is Residual Volume?
1L This quantity of air remains trapped in the lungs, keeping them partially inflated, even after a maximal expiration. It cannot be measured directly by spirometry.
What is Functional residual capacity?
Functional residual capacity (FRC) = 2.5L, the amount of air remaining in the lungs after you have finished breathing out, during normal quiet respiration: it is therefore equal to the expiratory reserve volume plus the residual volume. FRC = RV + ERV (2.5 = 1 + 1.5)
What is Vital Capacity?
Vital Capacity (VC) = 5L: this is the max amount of air that can be forced out of the lungs after a maximal inspiration (i.e if you breathe in as much as you can and then breathe out as much as you can): it is therefore equal to the tidal volume plus the inspiratory reserve volume and the expiratory reserve volume.
What is Inspiratory Capacity?
Inspiratory Capacity (IC) = 3.5L: the maximum amount of air you can breathe in after a normal expiration: equal to the tidal volume plus the inspiratory reserve volume. IC = VT + IRV (3.5 = 0.5 +3)
What is Total lung capacity?
Total lung capacity (TLC) = 6L: the total volume of air that can be contained in the lungs (i.e the amount of air in the lungs if you breathe in as much as you can): equal to all four of the lung volumes added together.
TLC = RV + ERV + TV + IRV
(6=1 + 1.5 + 0.5 + 3)
What is spirometry?
The measurement of breath, and is the most common test of respiratory function. It is performed using an instrument called a spirometer.
What is a spirometer?
A traditional spirometer consists of a hollow bell inverted over water, and it can measure the volume and speed of air inspired and expired from the lungs.
What does 2 important values can be determined by spirometry?
Forced vital capacity (FVC) and forced expiratory volume (FEV):
Forced vital capacity is the volume of air (in litres) that can be forcibly expelled after taking a deep breath.
The FVC is measured by having the subject take the deepest breath that they can and then exhaling as hard as they can for as long as they can (known as performing the FVC manoeuvre).
The forced expiratory volume (FEV) is the volume of air (in litres) that can be forcibly expelled in a particular interval of time during the FVC manoeuvre.
