Relationships between eupnoeic pattern of breathing and ventilatory control in man II. Early response to transient hypercapnia.

The individual importance of peripheral chemosensitive afferents was studied using a transient hypercapnia (inhalation of a 5% or a 10% CO2 in air gas mixture respectively during 4 or 2 breaths) in human conscious subjects chosen for their different eupnoeic ventilatory patterns. Calculation of the speed of change in end-tidal CO2 pressure in tracheal gas (sPETCO2) and of the rate of change in tidal volume (sVI) gave assessment for quantifying the sensitivity of arterial chemoreceptors to hypercapnia (sCO2=SVI/SPETCO2). Our results showed that, independently of any outside influence of the eupnoeic ventilatory pattern on the components of the chemical stimulus, sVI and sCO2 were found to be much smaller in subjects whose pattern of breathing was slow (i.e. having a large tidal volume). The possible causes of the weak importance of peripheral chemosensitive afferents in such subjects were discussed.