1 BGYC34 PhysioEx Lab 7 Respiratory Systems Mechanics Marking Scheme Part 1 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 formula: 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. Activity 2: Examining the Effect of Changing Airway Resistance on Respiratory Volumes Copy the FEV 1 and vital capacity values from the computer screen to the chart below and then calculate the FEV 1 (%) by dividing the FEV 1 volume by the vital capacity and multiplying by 100. Record the FEV 1 (%) (also called FEV 1 /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 (for completing the table) Explain your answer (should read explain your observations) FEV 1, FVC and FEV 1 (%) 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.
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 2. What happened to the FEV 1 (%) as 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 to expand. 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. 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 separate cavities? Both lungs would have deflated due to equal pressure inside and outside the thoracic cavity.** (0.5 marks)** Did the deflated lung re-inflate? No. Explain your answer. The left lung remained deflated because the intrathoracic pressure was never restored to its normal value. The lung chamber remained equalised with atmospheric pressure.
3 Why did lung function in the deflated left lung return to normal after you clicked reset? Air was withdrawn from the intrapleural space thereby reducing it to levels less than atmospheric pressure. Activity 5: Exploring Various Breathing Patterns What happens to PCO 2 during rapid breathing? Explain your answer. PCO 2 decreases during rapid breathing because CO 2 excretion has increased. Rebreathing What happens to PCO 2 during the entire time of the re-breathing activity? PCO 2 increases (continually) during re-breathing. Did the depth of the breathing pattern change during re-breathing? The rate and depth of breathing increased during Rebreathing. This is because the increased levels of CO 2 stimulated respiratory chemoreceptors. Breath-Holding What happens to PCO 2 during breath holding? There were large increases in PCO 2 during breath holding. What happened to the breathing pattern when normal respiration resumed? There was a slight increase in tidal volume (the depth of breathing).
4 Part 2 (10 marks) Answer the following questions. Staple the answers to the back of the PhysioEx pages. 1) How might age, gender and body height/size affect the results of pulmonary function tests? Suggest one other physiological factor (other than a disease state) that may affect the results of pulmonary function testing. (2 marks) Age: As people age their lungs become less elastic and therefore do not inflate as easily. This would cause decreases in lung volumes/capacities. (0.5 marks) Gender: Women (on a per weight basis) have smaller lungs than men (therefore smaller volumes/capacities). (0.5 marks) Body height/size: A larger person has larger lungs.(0.5 marks) Other factor: Anything that seems reasonable (0.5 marks) 2) What are restrictive and obstructive breathing disorders? (2 marks) A restrictive breathing disorder is one in which lung expansion (inspiration) is hindered. (1 mark) An obstructive breathing disorder is one in which expiration (lung emptying) is hindered. (1 mark) 3) Using pulmonary function tests, how would you distinguish between a restrictive breathing disorder and an obstructive breathing disorder? (2 marks) An obstructive lung disorder has low FEV 1 /FVC ratio while a restrictive lung disorder has a normal or slightly elevated FEV 1 /FVC disorder. (2 marks) 4) What is infant respiratory distress syndrome? What causes it? (2 marks) Infant respiratory distress syndrome refers to laboured breathing or problems breathing in (premature) infants. (1 mark) It is caused by a lack of surfactant in the lungs which hinders lung expansion. (1 mark) 5) During a re-breathing experiment, what would happen to the p50 value? (2 marks)
During re-breathing, arterial pco2 levels increase. This causes arterial ph levels to decrease. A reduction in ph causes a right shift in the oxygen equilibrium curve and an increase in p50. (1 mark for saying p50 increases; 1 mark for the explanation why) 5