Lecture 10 Flashcards
What is compliance?
Distensibility: The ease with which the lungs and thorax expand during pressure changes
What is the equation for compliance?
C= change in Volume / change in Pressure
What does low compliance entail?
More work required to inspire in the muscle and diaphram; need to overcome elastic nature
What is a disease in which low compliance can be seen?
Pulmonary fibrosis - lung paranchyma is more rigid
What does high compliance entail?
Little work to expand lungs and inspire but involved more difficulty expiring (loss of elastic recoil)
What is a disease in which high compliance can be seen?
Emphysema
- breakdown of walls, loss of elastic recoil
- when expiring, tend to collapse the airway because of high compliance
- have to overcome force to open airway
- can cause problems
Why do emphysema patients tend to have a higher starting volume?
It prevents the airways from collapsing
What happens when lungs recoil and collapse down?
Collapse down to residual volume
What are the two major components of elastic recoil?
“Anatomical” component
- elastic nature of cells and extracellular matrix
- tissues binding together: elastin etc
Surface tension generated at air-fluid interface
- helps cause lungs to contract
- has to overcome surface tension to expand lungs
Why is there surface tension at the air-fluid interface?
Due to differences in the forces on water molecules at the air-water interface
- in a gas bubble, there is a balance between the pressure exerted by the gas and the surface tension at the gas-water border
What happens in a gas bubble when it comes to surface tension?
Net downward force on molecules at surface
Droplet contracts to take lowest energy state - sphere
How is the relationship between pressure and surface tension described?
By Laplace’s equation
P = 2T / r
According to Laplace’s equation what would happen to the smaller sacs?
Air will flow down from smaller alveoli to larger alveoli leading to their collapse
What prevents smaller alveoli from collapsing?
Surfactant
Which cells produce surfactant?
Type II pneumocytes
What are surfactants composed of?
Lipids and proteins
What do Surfactant (lipoprotein) Type II cells do?
Prevents alveolar collapse by decreasin the surface tension
Alveolar size regulation - spread of surfactant shows rate of inflation
Increases compliance - allows lungs to inflate much more easily
Prevents edema - reduces fluid entering alveoli
What disease shows a decrease in surfactant production?
Pneumonia - lungs are harder to inflate
When do the surfactants begin to be produced?
Fully forms after 37 weeks of gestation
What happens by partitioning phospholipids?
Disrupts the effect of surface tension
Reduces surface tension
Which has a larger density of surfactant, larger or smaller alveoli? Why?
Smaller alveoli
- reduces effect of surface tension
- helps prevent over-inflation of the alveoli to maintain millions of alveoli of different volumes
What is the type of lung volume that cannot be measured using a spirometer?
Residual lung volume
What are the two types of dead space?
Anatomical dead space
Physiological dead space
What is anatomical dead space?
Volume of conducting airways
- at rest approximately 30% of inspired air volume (150ml)
What is physiological dead space?
Volume of lungs not participating in gas exchange
- conducting zone + non-functional areas of respiratory zone
- normally the two values are almost identical
What are the different lung volumes and their values?
Inspiratory reserve volume (IRV) = 1.9 - 2.5 L
Tidal volume (TV) = 0.4 - 0.5 L
Expiratory reserve volume (ERV) = 1.1 - 1.5 L
Residual Volume (RV) = 1.5 - 1.9 L
Total lung capacity (TLC) = 4.9 - 6.4 L
Inspiratory capacity (IC) = 2.3 - 3L
Functional residual capacity (FRC) = 2.6 - 3.4 L
Vital capacity (VC) = 3.4 - 4.5 L
What changes can be seen in the lung volumes during exercise?
IRV, ERV: decrease
TV: increase
VC and RV: same
What is an equation that shows the relationship between airflow and pressure and resistance?
Airflow = Change in Pressure / Resistance
Change in pressure = Alveolar pressure - Atmospheric pressure
What is Poiseuille’s law?
It shows that airway resistance is proportional to gas viscosity and the length of the tube but is inversely proportional to the fourth power of the radius
What is the equation for Poiseuille’s law?
R = 8 ( viscosity x length) / (pi x r4)
What has the most impact on resistance and flow rate?
Airway diameter (radius)
What is the total airway resistance in a normal individual?
1.5 cm H2O x s / liters
Which anatomical structures contribute to total airway resistance and by how much?
Pharynx-Larynx: 40%
Airways > 2mm diameter: 40%
Airways<2mm diameter: 20%
How is the total resistance in the upper airways determined and why?
Sum of resistance
- resistances are in series
How is the total resistance in the lower airways determined and why?
Inverse resistance is the sum of inverse resistances
- resistances are in parallel
When would the lower airways increase resistance?
inflammation
What are factors that have an impact on airway resistance?
Airway diameter:
Increased mucus secretion will effectively reduce airway diameter - increased resistance
Oedema - increased fluid retention in the lung tissue will cause swelling and narrowing of the airways - increases resistance
Airway collapse - e.g. during forced expiration, narrows airways, increases resistance
What are the two pathways involved in the control of bronchial smooth muscle?
ANS
Humoral factors
How is the ANS involved in the control of bronchial smooth muscle?
Parasympathetic:
ACh is released from the vagus, acts on muscarinic (type 3) receptors = (GPCR)
- leads to constriction
Sympathetic:
Release of adrenaline from nerves
- weak agonist binds to beta-2 adrenergic receptors
- leads to relaxation of smooth muscle then dilation of the airways
How are humoral factors involved in the control of bronchial smooth muscle?
Adrenaline circulating in the blood - better agonist binds to dilation
- acts on beta-2 adrenergic receptor
- stronger agonist than noradrenaline
- leads to dilation
Histamine - released during inflammatory process
- binds to H1 receptor (GPCR)
- leads to constriction
