PhysioEx Lab 7
Respiratory Systems Mechanics Marking Scheme
Complete PhysioEx lab #7. Hand-in all of the pages associated with the lab. Note that
there are 5 activities to be completed. You DO NOT need to hand in the histology review
supplement. (5 marks)
MARKING NOTE: Ten of the questions (activities) below are each worth 0.5 marks.
Activity 1: Measuring Respiratory Volumes
Compute the minute respiratory volume (i.e., minute ventilation) using the following
MRV = TV X BPM = 500 ml X 15 breaths/min = 7.5 L/min.
Does expiratory reserve volume (ERV) include tidal volume (VT)?
No, ERV is the amount of air that can be exhaled following a normal tidal
exhalation. **(0.5 marks)**
Activity 2: Examining the Effect of Changing Airway Resistance on
Copy the FEV a1d vital capacity values from the computer screen to the chart below and
then calculate the FEV1(%) by dividing the FEV1volume by the vital capacity and
multiplying by 100. Record the FEV 1%) (also called FEV1/FVC) in chart 1.
Radius (mm) FEV 1 FVC FEV 1%)
5.0 3541 4791 73.9
4.5 2303 3143 73.3
4.0 1422 1962 72.4
3.5 822 1150 71.4
3.0 436 621 70.2
**(0.5 marks)** (for completing the table)
Explain your answer (should read explain your observations)
FEV , FVC and FEV (%) all decrease as airway radius decreases because airway
diameter (radius) has decreased and it is harder to exhale (increased resistance). This is
akin to an obstructive lung disease. **(0.5 marks)** 2
Activity 3: Examining the Effect of Surfactant
The first two questions in this section are out of place. They should have been in activity
What happened to the FEV (%)1as the radius of the airways was decreased?
FEV 1%) decreased as the radius of the airway was decreased.
How has the air flow changed compared to the baseline run?
Airflow decreased as the radius of the airway was decreased.
Premature infants often have difficulty breathing. Explain why this might be so.
Premature infants don’t produce enough surfactant making it hard for the lungs
Activity 4: Investigating Intrapleural Pressure
What happened to the lung in the left side of the bell jar?
The lung deflated.
How did the pressure in the left lung differ from that in the right lung?
The pressure in the left lung was zero. Pressure in the right lung did not change.
Explain your reasoning.
The left lung deflated because the intrathoracic pressure was equal to
atmospheric pressure. **(0.5 marks)**
How did the total air flow in this trial compare with that in the previous trial when both
pleural cavities were intact?
Total flow was reduced by half.
What do you think would happen if the two lungs were in a single large cavity instead of
Both lungs would have deflated due to equal pressure inside and outside the
thoracic cavity.** (0.5 marks)**
Did the deflated lung re-inflate?
Explain your answer.