A) Concentration of \[C{{O}_{2}}\] in the blood decreases, lessening the excitatory input to the carotid bodies.
B) He is then using less \[{{O}_{2}}\] as his thoracic muscles are not working as hard.
C) Stretch receptors in his lungs are then not firing as much thus lessening the excitatory input to the expiratory centres.
D) He is preventing the pressure in his lung from increasing too much
Correct Answer: C
Solution :
[c] When the chest is expanded, stretch receptors in the lungs relax and excite the expiratory centre in the mdeulla which tends to produce expiration. Partial exhalation lessens the intensity of this reflex, allowing breath to be held for a longer time. Exhalation does not change the blood \[C{{O}_{2}}\] concentration unless fresh air (low in\[C{{O}_{2}}\]) is brought into the lungs, allowing more \[C{{O}_{2}}\] to diffuse out of the blood.
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