Effect of physical training on breath holding time in Indian subjects.

Breath holding time is the time taken by the subject to hold his breath as long as he can. During voluntary breath holding, tissues continue to utilize oxygen and liberate carbon dioxide. Therefore during breath holding arterial pO2 falls and pCO2 rises. Since both these factors are powerful respiratory stimulants, a point is reached where the respiratory drive becomes so strong that the person cannot hold the breath any longer (1). The point at which breathing can no longer be voluntarily inhibited is called the breaking point. The breaking point is generally reached when alveolar pO 2 is 56 mm of Hg and alveolar pCO 2 is 49 mm of Hg. Either an increase in pCO2 or a decrease in pO2 stimulates central and peripheral chemoreceptors which in turn stimulate respiration through respiratory centers, thus influencing breath holding time.