2.17 - Pressure Changes & Airflow During Breathing

Question 1

Draw a spirometry curve and label all measurable volumes and capacities

Answer 1

Question 2

What are the two different types of spirometers? Provide pros and cons for each

Answer 2

Bell Spirometer: bell dome filled with air immersed in water. Pros: direct volume measurement, very precise. Cons: poor dynamics due to inertia, expensive

Pneumotachographs: based on ohm’s law. Pros: excellent dynamic response, cheap. Cons: fiddly - small pressure changes can cause “drifts”, need repeated calibrations, need a computer

Question 3

What two methods are used to measure residual volume?

Answer 3

Body plethymosgraph and Helium dilution technique

Question 4

What are the six important lung pressures?

Answer 4

P_b = barometric pressure

P_pl = intrepleural pressure (difference between pleura and outside world)

P_A = alveolar pressure (0 at beginning/end of inspiration and expiration)

P_L = translung pressure (P_A - P_pl) this pressure tracks the flow.

P_W = transthoracic pressure

P_rs = respiratory system pressure

Question 5

Describe the respiratory cycle at tidal volume

Answer 5

1. FRC (end of expiration). P_pl = -P_pl(as P_A=0).
2. Inspiration - muscles contraction. P_pl and -P_L drop. The drop in -P_L lags behind the drop in P_pl due to airway resistance and lung compliance.
3. End of inspiration/start of expiration. P_pl=-P_L, but at a larger magnitude.
4. Expiration: muscles relax –> recoil of system –> increase in P_pl with a delayed increase in -P_L. P_A>0 –> airflow out of lungs

Question 6

Why does translung pressure lag behind pleural pressure?

Answer 6

Two major factors: airway resistance and total compliance of the lung

Question 7

What is PEF and PIF?

Answer 7

PEF: Peak Expiratory Flow Rate

PIF: Peak Inspiratory Flow Rate

Question 8

Which of PEF and PIF is more sensitive to airway resistance?

Answer 8

PEF

Question 9

What forced volume or peak flow is a good test for airway resistance?

Answer 9

Forced Expiratory Volume in One Second (FEV1)

Question 10

Describe the changes of resistive work and elastic work as respiratory rate increases. And based off this why baseline respiratory rate is approximately 16bpm.

Answer 10

Resistive work increases as respiratory rate increases. Elastic work on the other hand decreased with respiratory rate.

The baseline respiratory rate of 16bpm is at this point because it is here that total work is at a minimum

Question 11

Draw a Volume-Flow Rate Diagram

Answer 11

Question 12

A 17 year old woman presents to emergency with an acute asthma exacerbation of moderate severity. Which of the following sets of lung function tests best describes her current condition?

Answer 12

A: Decreased FVC, FEV1, FEV1/FVC, PEF and increased RV