Comparison of chemoreflex gains obtained with two different methods in cats

This study investigates the correspondence between results of the ventilatory response to CO2 obtained using the technique of dynamic end-tidal CO2 forcing (DEF) and results obtained using the technique of artificial brain stem perfusion (ABP). The DEF technique separates the dynamic ventilatory response into a slow and fast component with gains g1 and g2 as well as the extrapolated CO2 tension at zero ventilation (Bk). The ABP technique results in steady-state central (Sc) and peripheral (Sp) chemoreflex gains and extrapolated CO2 tension at zero ventilation (B). Experiments were performed on 14 alpha-chloralose-urethan anesthetized cats. A wide range of relative peripheral chemosensitivities was obtained by subjecting eight cats to normoxic and three cats to hypoxic CO2 challenges and three cats to both conditions. Statistical analysis of the experimental data showed that the vectors (g1, g2, Bk) and (Sc, Sp, B) for each cat did not differ significantly (P = 0.56). This was also the case for the vectors [g2/(g1 + g2), Bk] and [Sp/(Sc + Sp), B] (P = 0.21). We conclude that in the DEF experiments the slow ventilatory response to isoxic changes in end-tidal CO2 can be equated with the central chemoreflex loop and the faster ventilatory response to the peripheral chemoreflex loop. The agreement between the two techniques is good.