University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

390

Pages:

2
Author:

Mariam A. A.

Gas Diffusion in the Lungs Concept Questions 1. Explain the difference between diffusion limited and perfusion limited using examples. Explain why CO is used for measuring diffusion capacity. (4 marks) Answer: Diffusion limited refers to gases that can diffuse as long as there is a partial pressure gradient. For example, CO is diffusion limited because it can bind to Hb really quickly, so the rise in PaCO is very slow, this will allow CO from the alveolar to continue moving into the alveolar capillary, because the PACO is greater than PaCO, and gases like to flow from an area of high pressure to an area of low pressure. On the other hand, perfusion limited is when gas diffusion is blood flow limited/dependent. For example, at rest O2 from the alveolar diffuses into the capillary and will oxygenate blood. Once, equilibrium is reached, no more O2 will flow until we get more de-oxygenated blood. CO is used for measuring diffusion capacity, because it quickly binds to Hb, due to the high affinity. Due to this, there will always be pressure gradient hence there will always be diffusion. 1. Measuring gas diffusion is important for determine lung functions. (6 marks) a. Write the formula for gas diffusion (1 mark) b. Write the formula for DL (1 mark) c. If thickness is increased how will this affect gas diffusion. Name ONE condition that may cause this. (1 mark) d. How would you use CO to measure diffusion capacity (3 marks) Answer: a. b. c. Increase in thickness decreases the rate of diffusion. For example, pneumonia d. 1. Give the patient a known concentration of CO and a known concentration of He (He to measure the volume of air the is accessible to CO) 2. Get patient to hold their breath for 10 seconds 3. There will be a decreased concentration and pressure of CO in the lungs as CO is diffusing into the alveolar capillary 4. The steeper the slope (k) the more diffusion 5. The greater the accessible volume the more diffusion