Breath-holding and the sensations due to chemical and mechanical stimuli to breathing.

EVERY medical student and, indeed, every schoolboy knows that it is possible to hold the breath for a longer time with lungs fully inflated than at a smaller lung volume, and that the breath-holding time can also be prolonged by hyperventilation beforehand. This prolongation is possible because the onset of the unpleasant sensations which arise during breath-holding is delayed. Thus both mechanical and chemical factors are able to modify the development of the intolerable sensations which causes the subject to break off the breath-hold. The object of the present paper is to review the experiments which have been performed to study this subject and to show how they can help in understanding the origins of respiratory sensation.