Answer: mechanical nerve receptors in the airways, lung, respiratory muscles and chest wall detect the increased work of breathing during inhalation and exhalation and transmit this to the brain as a sense of breathing discomfort. (i.e., shortness of breath).

Question 2: In this demonstration, as in emphysema, why do the neck muscles contract with each inhalation?

Answer: the sternocleidomastoid neck muscles contract in order to elevate the clavicles and upper rib cage. This enlarges the thoracic cavity and makes more space for the already hyperinflated lungs to receive more air during the inhaled breath which must be forced.

Question 3: Why do emphysema patients have airflow limitation during exhalation? (as simulated by exhaling through a narrow straw in demonstration A). Why is the airflow limitation less during inhalation?

Answer: The airways are narrowed because of less elastic traction from the surrounding lung holding them open (emphysema) and also because of swelling, secretions and scar from associated bronchitis which obstruct the airways (see Slide q). Airflow limitation is less during inhalation because increased negative intrapleural pressures during inhalation expand the airways.

Question 4: Why do emphysema patients have to inhale using their neck muscles even when breathing at rest? (as simulated in demonstration A).

Answer: Since in emphysema the obstruction to airflow is primarily expiratory, air flows into the lung easier than it flows out (i.e., like a one way valve), air becomes trapped and the lungs become chronically hyperinflated (slide p). As a result, emphysema patients try to force more air into already hyperinflated lungs during a regular resting inhalation and they must use their neck muscles to do it, as discussed in Question 2 above. Normally, only the diaphragm and intercostal (chest wall) muscles function when breathing at rest. The neck muscles only come into play during strenuous exercise where very deep and forced inhalation is required. In the Video, Tadge Bredwell, who had advanced emphysema, can be seen fighting for air, having to use his neck muscles for each inhaled breath, even though he was at rest, sitting in a chair! (Video Script pgs 45-46).

Demonstration B: Have students hold their breath for as long as they can to again simulate the severe shortness of breath that occurs in patients with advanced emphysema. What is causing the shortness of breath in this case?

Answer: The lung serves to take up oxygen into the blood stream and remove carbon dioxide from the blood stream during the act of breathing. When breathing stops (or is severely impaired as in emphysema) the level of blood oxygen progressively falls and