Dynamic response of peripheral chemoreflex loop to changes in end-tidal CO2.

The dynamic ventilatory response of the peripheral chemoreflex loop after isoxic step changes in end-tidal PCO2 (PETCO2) (range 5-30 Torr) was studied in 12 alpha-chloralose-urethan-anesthetized cats. The technique of artificial brain stem perfusion allowed the response to be observed in isolation from the central chemoreflex loop. The data were fitted by an exponential with time delay. During normoxia the mean time constant and time delay (with SD) were 8.6 +/- 7.3 and 3.3 +/- 0.9 s, respectively (9 cats, 56 runs). During hypoxia [arterial PO2 (PaO2) approximately 60 Torr] these values were 6.0 +/- 4.5 and 2.9 +/- 0.9 s (6 cats, 38 runs). In 17 of the 94 runs an augmented breath occurred in the first three breaths after the stepwise increase in PETCO2. For these augmented breaths, tidal volume, inspiratory time, and expiratory time were not different from the next augmented breath occurring in the same run in the steady state. Neither a rate-sensitive component nor a central neural mechanism (central afterdischarge), with the property of maintaining an increased but slowly declining respiratory activity for some minutes after cessation of the PETCO2 challenge, was found. We conclude that the description of the ventilatory response of the peripheral chemoreflex loop to step changes in PETCO2 with a single exponential and time delay is adequate.