THE HUMAN VENTILATORY RESPONSE TO STEP CHANGES IN END-TIDAL PO2 OF DIFFERING AMPLITUDE

This study assessed whether the form of the peripheral chemoreflex res ponse to hypoxia depends on the magnitude of the stimulus. Two amplitu des of square-wave hypoxic stimulation were employed: small amplitude (SO) PET(O2), from 63.2 to 54.9 Torr, and large amplitude (LO) PET(O2) , from 73.0 to 48.0 Torr. Each was studied at two levels Of PET(CO2):2 Torr above resting PET(CO2) (EC), and 7 Torr above resting PET(CO2) ( HC). Each protocol was repeated 6 times on 5 subjects. To assess the f orm of the response, a simple first-order model was fitted to the data which incorporated a pure delay (Td) and time constant (tau). Average parameter values (sec) were: ECSO tau = 4.07, Td = 6.69; ECLO tau = 8 .82, Td = 4.9 1; HCSO tau = 5.22, Td = 7.08; HCLO tau= 9.96, Td = 4.39 . ANOVA demonstrated modest but significant differences for log(e)(tau ) (P<0.01) and Td (P<0.02) between the two hypoxic step magnitudes, wi th tau longer and Td shorter for the larger step size, but no differen ces were found between the parameter values for the two CO2 levels. We conclude that the form of the response of the peripheral chemoreflex to hypoxia depends upon the magnitude of the stimulus.