A/Prof Celestial Yap, Department of Physiology, NUS

PHASE I: RESPIRATORY PHYSIOLOGY TUTORIAL – TUTORS’ VERSION

PULMONARY DIFFUSING CAPACITY & ARTERIAL OXYGEN

Read up on the following topics in Respiratory Physiology for this tutorial:

1. Anatomy and histology of the lung2. Process of diffusion from lung to blood; structure of the alveolar-capillary membrane3. Transport and delivery of oxygen4. Control of respiration5. Pulmonary circulation6. Ventilation-perfusion mismatch (alveolar dead space and shunt)

Additional references for alveolar dead space and shunt:

Human PhysiologyVander, Sherman & Luciano

Textbook of Medical PhysiologyGuyton & Hall

Review of Medical PhysiologyWilliam Ganong

Tutors/Case developers

Emergency Medicine, NUHS Dr Winsen KuanDr Zulkarnain Bin Abdul Hamid

Pathology, NUHSDr Seet Ju Ee

Physiology, NUHSA/Prof Celestial YapDr Chen Zhi Xiong

General Surgery, Mount Elizabeth Hospital (Orchard) and SGHDr Goh Yaw Chong

A/Prof Celestial Yap, Department of Physiology, NUS

Case history

Part 1. Mr Chan is a 75-year-old man who complains of breathlessness on walking for about 30 meters, and feels more comfortable at rest. His effort-induced breathlessness has been getting worse over the past few months. He has no history of cough or fever. He has been smoking since young but has stopped for about 10 years.

Physical examination shows that his respiratory rate (RR) is 22 breaths/minute, pulse rate (PR) is 105 per minute, blood pressure is 130/85 mmHg.

Chest X-ray shows diffuse reticular (net-like) and nodular opacities in all zones of both lungs. Heart size is normal.

High resolution CT scan shows that there is diffuse interstitial involvement of all portions of both lungs.

Spirometry tests show that his FEV1 = 2.6 litres, FVC = 2.9 litres, FEV1/FVC = 89.7%. (Normal for person of similar build: FEV1 approximately 4L, FVC 5L, FEV1/FVC approximately 80%)

Arterial blood gas results on ‘room’ air (normal atmospheric air) are: PO2 = 59 mmHg, PCO2 = 33mmHg, saturation of oxygen in arterial blood is 89%.

Mr Chan is diagnosed to have pulmonary fibrosis.

Erect chest X-ray CT scan

Questions for discussion

1. State whether the findings on physical examination are normal. What are the normal ranges of RR and PR?

2. Interpret the spirometry results and suggest reasons why it is different from normal.

3. A. What are the changes in compliance and recoil? B. What are the effects on the work of breathing?

4. A. What is the normal range of arterial PO2?B. Interpret his arterial PO2 result and suggest mechanisms leading to this result

A/Prof Celestial Yap, Department of Physiology, NUS

C.How and why may the arterial PO2 change if Mr Chan exerts himself?

5. A. How may Mr Chan’s arterial PO2 affect the oxygen content in the blood and oxygen supply to tissues?

B. How will his oxygen content change if his arterial PO2 decreases another 15 mmHg? Explain how and why this is different compared to a drop of 15 mmHg in arterial PO 2 in a healthy individual breathing air at sea level.

6. A. What is the normal range of arterial PCO2?B. Interpret his arterial PCO2 result and suggest mechanisms leading to this result.

7. Suggest what may happen to his arterial blood gas results if the disease progresses in severity?

Part 2. Mr Chan is admitted to hospital for treatment of his breathlessness. In the hospital, he develops a fever and cough with sputum. Chest X-ray shows consolidation in the right lower lobe of his lung and he is diagnosed with pneumonia.

8. What histological changes are expected in the right lower lobe of his lung affected by pneumonia?

9. A. What are the effects of pneumonia on ventilation/perfusion matching in his lungs?B. How may you expect his arterial blood gas profile to be further affected?