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

2024
Views:

307

Pages:

2
Author:

Mariam A. A.

Inspiration Questions 1. Explain the changes to the intra-pleural pressure during inspiration (3 marks) Answer: • • • • 2. a. b. c. d. e. f. During inspiration the phrenic nerve innervates the diaphragm causing to contract downwards and the intercoastal nerves innervate the external intercoastal muscles, causing the ribs to move up and out in order to expand the thoracic cavity As the ribs and the thoracic cavity are expanding, they pull the parietal pleura with them this causes the pleural cavity to expand in volume. As per Boyle’s law, when volume increases the pressure decreases. Normally the pressure within the pleural cavity at rest is -4 mmHg, but since it is now expanding the pressure becomes -6 mmHg The parietal pleura will pull the visceral cavity as well, which will cause the lungs to expand. Answer the following questions on dead space. Define anatomical dead space (1 mark) What is physiological dead space (1 mark) How much of normal environmental air is composed of oxygen and how much is composed of nitrogen (1 mark) Explain the Fowlers method (2 marks) What are the main principles and assumptions of the anatomical dead space equation? (3 marks) If the partial pressure of carbon dioxide in the alveolar is equal to 40 mmHg and partial pressure of gases is 30. Calculate the dead space (2 marks) Answer: a. The anatomical dead space refers to the conducting airways, as the volume of air there does not participate in has exchange. This includes, the trachea, the main bronchus and bronchioles up to generation 14. b. Physiological dead space is the sum of anatomical dead space and the volume of air in alveoli that is not participating in gas exchange c. N2= 78% and O2=21% d. Fowler’s method 1. Patient breaths 100% oxygen 2. Get patient to expire 3. In phase 1 the volume of air that comes out is purely oxygen 4. In phase 2 the expired air will contain O2 and a high concentration of N2, as N2 takes longer to fill and be emptied by the alveoli 5. In phase 4 there is more N2 6. Calculate the amount of N2 inhaled, this should be the midpoint of phase 2 e. Principles: • Tidal volume = alveolar volume and dead space • All CO2 comes from alveoli that participates in gas exchange • PaCO2 = PACO2 since lung physiology tries to reach an equilibrium between the CO2 in the blood and the alveoli f.