lecture 17 - the work of breathing Flashcards
What determines the direction of airflow into/out of the lungs?
The difference between atmospheric and intrapulmonary pressure
What is the pressure inside the lungs?
Intrapulmonary pressure
What is the pressure outside the lungs?
Atmospheric pressure
What are the 2 opposing forces that must be overcome to take a breath?
Stiffness of the lungs, resistance of the airways to the lungs due to friction
What is compliance, in terms of the lungs?
The magnitude of the change in lung volume produced by the given change in pressure - how ‘stiff’ the lungs are
What is the equation for lung compliance?
C= ΔV/ΔP
What distinct condition is characterised by low compliance/ ‘stiff lungs’?
Pulmonary fibrosis
What are the characteristics of pulmonary fibrosis?
Thickening and scarring of alveolar membranes due to chronic inflammation or exposure to industrial chemicals, resulting in decreased lung compliance
What is the cause of surface tension in the lungs?
Fluids surrounding the lungs exert surface tension
What is surface tension?
The tendency of a fluid surface to occupy the smallest possible surface area.
Why does surface tension arise?
Due to hydrogen bonds
What is the cause of surface tension in the alveoli?
They are lined with fluid and have very thin walls which enhances the effects of surface tension
How does surface tension affect lung function?
Causes stiffness that must be overcome to expand the lungs
how does surfactant reduce lung stiffness?
By reducing surface tension in the alveoli and makes them easier to expand.
How does surfactant lower the surface tension in the fluid in alveoli?
Reduces the attractive forces between fluid molecules by inserting hydrophobic ligands between H2O molecules
What is the cause of respiratory distress syndrome in premature infants?
Premature infants have immature type II pneumocytes so do not produce surfactant, which causes lung stiffness
How does bronchial radius influence resistance to air flow due to friction?
Decreasing the bronchial radius increase the resistance to airflow
What is the equation for air resistance in the bronchioles?
R = 1/r^4, where R = resistance, r = radius of bronchiole
What is the main area of airway resistance?
The bronchi
What does a spirometer measure?
Volume of air inspired/exhaled and the rate of breathing
On a spirometry trace, what is tidal volume (VT)?
Volume of air moved in and out during a normal quiet breath
On a spirometry trace, what is inspiratory reserve volume (IRV)?
Extra volume that can be inhaled over and above the tidal volume
On a spirometry trace, what is expiratory reserve volume (ERV)?
The extra volume that can be exhaled voluntarily after completion of a normal, quiet respiratory cycle
On a spirometry trace, what is residual volume?
The volume of air remaining in the lungs are maximal exhalation
On a spirometry trace, what is minimal volume?
Volume remaining in lungs if they collapsed
On a spirometry trace, what is vital capacity?
Inspiratory reserve + expiratory reserve + tidal volume - total volume that can be moved in and out of the lungs in one breath cycle
On a spirometry trace, what is total lung capacity?
Vital capacity + residual volume - the total volume of air that can fit in the lungs
On a spirometry trace, what is inspiratory capacity?
Inspiratory reserve + tidal volume - total volume of air that can be inspired from rest
On a spirometry trace, what is functional residual capacity?
Expiratory reserve + residual volume 0 the volume remaining in the lungs after normal maximal exhalation
What is the typical value of tidal volume?
500mL
