The influence of varying inspired fractions of O2 and CO2 on the development of involuntary breathing movements during maximal apnoea

► Involuntary breathing movements (IBMs) occur during the last phase of breath-holding. ► We test whether the IBM are initiated at critical level of hypercapnia and/or hypoxia. ► Arterial blood gasses were sampled at the onset of IBM and at apnoea cessation. ► A possible threshold level for PaCO2 at IBM onset was observed ► Interaction of PaCO2 and PaO2 at IBM onset was found.