The hyperoxic test in infants reinvestigated

The hyperoxic test (HT) examines peripheral chemoreceptor function (PCF) by measuring the decrease in ventilation ((V)over dot(E)) after 100% O-2 inha lation. A 30-s HT has been previously used in infants with calculation of t he ventilatory response (VR) as the mean percentage change in (V)over dot(E ) during HT as compared with normoxia. However, it has been shown that duri ng hyperoxia (V)over dot(E) rises secondarily after the initial drop becaus e of loss of PCF. We hypothesized that the mean ire change over a 30-s HT m ay underestimate the strength of PCF and may be poorly reproducible. We per formed breath-by-breath analysis during 30-s HTs, calculating VR at the res ponse time (RT) defined as the time from HT onset to the first significant MT-related change in (V)over dot(E) . Eighteen infants (postnatal age, 21 /- 4 d) underwent two HTs (quiet sleep, face mask attached to a pneumotacho graph, and inspired and expired O-2 and CO2 fractions measured using mass s pectrometry). (V)over dot(E), V-T, and V-T/T-I decreases at the RT were sig nificantly greater than the corresponding means (-21 +/- 7 versus -15 +/- 7 %, -21 +/- 8 versus -13 +/- 8%, and -22 +/- 11 versus -17 +/- 11%, respecti vely). Intra-individual coefficients of variation of (V)over dot(E), V-T an d V-T/T-I were significantly smaller when RT values were considered rather than means. We conclude that calculation of the VR to HT at RT improves ass essment of PCF and enhances HT reproducibility in infants.