OPTIMIZATION OF REBREATHING CO2 METHOD BY THE DETERMINATION OF THE SENSIBILITY THRESHOLD

Abstract

Ventilatory response to CO2 rebreathing is a method which allows to evaluate the reactivity of chemoreceptors. However this method doesn''t study the sensibility threshold, i.e. the Pe.t.CO2 value for which the ventilatory response appears clearly. This sensibility threshold was measured in 10 healthy subjects by rebreathing a gas mixture: 7% CO2 and 50% O2 to avoid hypoxia. It was defined as the value of Pe.t.CO2 for which the ventilation was above the tidal ventilation + 2 standard deviations. The sensibility threshold (51 .+-. 4.35 mm Hg) was independent of the reactivity slope represented by the slope of the linear relation between minute ventilation and Pe.t.CO2 (1.34 .+-. 0.60 l/min/mm Hg/m2) and consequently appears as an interesting parameter in order to evaluate the ventilatory response to CO2 by rebreathing.