mechanics of ventilation

Question 1

pressure volume relationships of gases (Boyles law)
- what is boyles law (calc and description)
- example with the lungs

Answer 1

• Boyle’s Law: P1x V1 = P2xV2 (“P” is pressure and “V” is volume)
  Pressure of given quantity of gas inversely proportional to its volume
  Decrease volume by compression, pressure increases, but new values for p x v still = same as old, vice versa
• Lungs expand during inspiration, volume increases, pressure falls, creates pressure gradient lower than atmospheric pressure, air drawn in. opposite occurs during expiration.

Question 2

flow properties of gases
- airflow relationship with pressure difference between 2 points and resistance created by the airways
- what is the respiratory system reliant on for airflow

Answer 2

• Airflow is directly proportional to the pressure difference between two points (greater pressure difference, greater the airflow)
• Airflow is inversely proportional to the resistance that is created by the airways (greater the resistance, less airflow)
• creation of a pressure difference between lungs and environment driven by the muscular pump

Question 3

airway diameter and flow resistance (pousielles law)
- pousielles law
- which part of the law contributes most
- what allows airways to alter resistance
- 2 factors affecting airway radius and what its caused by

Answer 3

• Resistance= (Lxn)/r4
• airway radius is the main factor affecting resistance in the RS as it can change.
• ones that do not have a rigid cartilage frame can alter
• Bronchodilation- caused by- Carbon dioxide, epinephrine (via b2 receptors)
• Bronchoconstriction- caused by- Parasympathetic stimulation (via muscarinic receptors), histamine

Question 4

muscular pump during inspiration at rest and exercise

Answer 4

• normal breathing- contraction of the diaphragm and contraction of the external intercostal muscles moderately expand the thoracic cavity and create airflow
• breathing rate increases- expansion of thoracic cavity assisted by further contraction of of the diaphragm and recruitment of the accessory inspiratory muscles (sternocleidomastoid, scalenes and pec minor so sternum lifts up and out more further increasing pressure and decreasing volume more so pressure difference larger and more air in)

Question 5

muscular pump during expiration during rest and exercise

Answer 5

• Normal expiration- passive process needing no contraction. The relaxation of the inspiratory muscles and recoil of the lungs cause the thoracic cavity to decrease to its original volume.
• Heavy breathing or forceful expiration- recruitment of expiratory muscles (internal intercostal and abdominal muscles) to compress the thoracic cavity down and in faster and further than at rest creating a higher pressure in thoracic cavity so more air is expired.

Question 6

intra pleural pressure
- what 2 forces oppose each other
- how to describe intrapleural pressure and what does it cause
- what does it prevent happening
- what happens if this thing happens

Answer 6

• outwards (chest wall) and inwards (lungs) elastic recoil
• is negative (sub-atmospheric) created by the two forces and the liquid inbetween them and meaning air will rush in from atmosphere
• the lung collapsing
• intrapleural pressure becomes equal to atmospjheric pressure and the pressure gradient is gone

Question 7

what are the 4 main pressures we will look at
- Patm
- Palv
- Pip
- Ptp

Answer 7

Patm: The ambient atmospheric pressure.
Palv: The pressure inside the lungs (at the alveoli) relative to Patm
Pip: The pressure inside the pleural cavity.
Ptp: The difference between Palv and Pip (Ptp = Palv - Pip).

Question 8

basic principles (the 4 pressures)
- when does inspiration occur
- when does expiration occur
- what is required to keep the lungs inflated
- what happens to 2 diff pressures during inspiration and impact on the lungs and chest
- what happens to the same 2 pressures during expiration and impact on lungs

Answer 8

• when Palv below Patm
• when Palv above Patm
• Ptp must be a positive number
• Pip becomes more negative and Ptp increases. Lungs overcome elastic recoil and chest expands
• Pip becomes less negative but Ptp remains positive which prevents the lungs from collapsing

Question 9

the role of surfactant on alveoli
- the law of LaPlace
- what it means for 2 different sized bubbles with the same surface tension
- what would be the implications for alveoli
- what type of alveoli cell secrete surfactant
- what do the proteins in surfactant do
- 2 things this will mean

Answer 9

• 𝐿𝑎𝑤 𝑜𝑓 𝐿𝑎𝑃𝑙𝑎𝑐𝑒: 𝑃 = 2𝑇/r, T=surface tension P= pressure r=radius
• the smaller bubble will have a higher pressure
• alveoli are all diff sizes, so if true, air would flow from small to big and the smaller bubbles would collapse into bigger ones, and eventually 1 big one, massively reducing surface area
• type 2
• disrupt the forces between water molecules and lowers surface tension at alveolar walls
• The alveolar spaces are less prone to collapsing after exhalation
• The lung is inflated easier