[Analysis of the imperative stimulus restricting voluntary breath holding].

In 5 healthy young men, the maximal voluntary breath holding--was studied under conditions of different initial values of PACO2--after oxygen inhalation at ordinary minute volume of respiration or at hyperventilation, or after breathing with oxygen mixtures with 2, 4, 6, 8 or 10% CO2. PACO2 was recorded at the moment of resuming of the intercostal muscles electric activity and at the point of breaking up the apnoea. A mathematical model was constructed. The hypothesis of participation of two independent factors (chemo- and mechanoreceptive) in genesis of the imperative stimulus for breathing was checked. The data obtained suggest that, in fact, the only factor restricting the duration of voluntary breath holding--is the summed up in time chemoreceptive stimulation. The involuntary contractions of respiratory muscles observed during apnoea are, apparently, a connecting link in formation of the imperative stimulus which breaks up the cessation of breathing.