Correct option is B
Explanation-
Statement A - The breaking point is shorter in subjects after removal of carotid bodies compared to when they have intact carotid bodies - Incorrect
Carotid bodies are peripheral chemoreceptors sensitive to low O₂ and high CO₂.
Removal reduces the sensitivity to hypoxia and hypercapnia, meaning the drive to breathe is weakened, and the breaking point is delayed, not shortened.
Statement B - The breaking point is prolonged if the subject breathes 100% oxygen before breath holding - Correct
Breathing 100% oxygen saturates hemoglobin and delays the fall in arterial O₂, postponing the activation of chemoreceptors.
Therefore, breaking point is prolonged.
Statement C - When the subject hyperventilates with room air before breath holding, the breaking point is delayed compared to when the subject breathes normally before breath holding - Correct
Hyperventilation lowers CO₂ levels in the blood (hypocapnia), which delays the buildup of CO₂—the main trigger for the urge to breathe. This prolongs the breaking point.
Statement D- The breaking point can be reduced in a subject by making respiratory movements behind a closed glottis - Incorrect.
These are called "false breathing movements" (e.g., Valsalva maneuvers), which may provide psychological relief but do not physiologically lower CO₂. They do not significantly reduce the breaking point.
Statement E - The breaking point is shorter when the subject is told during breath holding that her/his performance is very good compared to a situation when she/he is not told so - Incorrect.
Positive encouragement may improve mental endurance and delay the breaking point. This statement is opposite of the expected outcome.
So, the correct answers is option b - B and C.
