Introduction

Breath holding is an intriguing physiological action where a human voluntarily suspends respiration temporarily. Eventually, an irresistible urge to breathe arises, marking the breaking point of breath holding. This point is critical in understanding respiratory control, chemoreceptor function, and lung mechanics. It is influenced by factors such as oxygen levels, carbon dioxide buildup, lung volume, and psychological state.

This article analyzes five statements proposed to characterize the breaking point and identifies which are accurate based on evidence from respiratory physiology.

Overview of the Breaking Point

• The breaking point occurs when the body’s chemical drives to breathe (high CO2, low O2 levels) or mechanical stretch signals reach a threshold, provoking involuntary respiratory muscle activity despite voluntary suppression.

• It usually happens after a variable time depending on lung volume, pre-breathing gases, chemoreceptor function, and psychological factors.

• Mechanisms involving pulmonary stretch receptors and carotid body chemoreceptors play central roles.

Evaluation of the Statements

A. The breaking point is shorter in subjects after removal of carotid bodies compared to when they have intact carotid bodies.

• True.
  The carotid bodies are critical peripheral chemoreceptors sensing blood oxygen. Removal reduces hypoxic drive, lowering breath-hold duration and hastening the breaking point.

B. The breaking point is prolonged if the subject breathes 100% oxygen before breath holding.

• True.
  Pre-breathing pure oxygen delays the onset of hypoxia during breath holding, extending breath-hold duration and delaying the breaking point.

C. When the subject hyperventilates with room air before breath holding, the breaking point is delayed compared to normal breathing.

• True.
  Hyperventilation lowers carbon dioxide (hypocapnia), decreasing the drive to breathe and hence prolonging breath holding before the breaking point occurs.

D. The breaking point can be reduced in a subject by making respiratory movements behind a closed glottis.

• True.
  Forced respiratory efforts behind a closed glottis increase intrathoracic pressure and stimulate receptors that hasten the breaking point, reducing breath-hold duration.

E. The breaking point is shorter when the subject is told during breath holding that her/his performance is very good compared to not being told so.

• False.
  Psychological encouragement or positive feedback generally prolongs breath-hold duration, delaying the breaking point. Negative feedback or lack of support could shorten it.

Identifying the Correct Statements Combination

• Statement E is incorrect.

• All other statements (A, B, C, D) are correct.

Given the options:

Since the question asks for both correct statements, options (1), (2), and (3) each identify two correct statements.

Physiology Behind These Observations

• Carotid bodies continuously monitor arterial oxygen, stimulating breathing when oxygen drops.

• Pre-breathing 100% oxygen provides a greater oxygen reserve, delaying hypoxia and breath-hold termination.

• Hyperventilation lowers CO2, reducing one of the primary respiratory drives during breath holds.

• Respiratory movements against a closed glottis simulate breathing effort, triggering reflexes shortening breath-hold time.

• Positive feedback enhances motivation and tolerance, typically increasing breath-hold times.

Summary Table

Conclusion

The question asks to select both correct statements from the options, where:

• A, B, C, and D are correct statements about the breaking point,

• Whereas E is incorrect.

Among the given options, the most consistent combinations with correct statements are:

• (1) A and B

• (2) B and C

• (3) C and D

Since the user must select one, any of these three options represent two correct statements.