REPRODUCIBILITY OF THE ALTERNATING BREATH TEST OF FRACTIONAL INSPIREDO-2 IN INFANTS

We conducted a reproducibility study of the alternating breath test (A BT) for assessing peripheral chemoreceptor function in infants. The AB T delivers a rapid hypoxic stimulus to the peripheral chemoreceptors w ith breath-by-breath alternations of the inspired O-2 fraction. The re producibility of the ABT performed on a single occasion has not been e xtensively studied in infants. Eight unsedated infants (postnatal age, 22 +/- 19 d; weight, 3.2 +/- 0.4 kg) were studied in standardized con ditions: morning naps, supine position, room temperature 22-24 degrees C, quiet sleep, and face mask attached to a pneumotachograph connecte d to a two-way electric valve. Respiratory gases were analyzed by mass spectrometer. Two ABTs were performed. Each included a 2-min control run (CR) alternating between air and air, and a 2-min test run (TR) al ternating between air and 0.15 O-2. After data preprocessing, on avera ge 13 +/- 11% of the data were rejected because of sighs, apneas, and cycles with the fraction of inspired oxygen above 0.17. Using the rema ining validated breaths, the response to ABT was calculated for the CR , for all breaths in the TR (TRT), and for the first 50 breaths of the TR (TR50). During the ABTs oxygen saturation did not fall below 96%, and heart rate was not affected. Inspired and end-tidal CO2 fractions remained unchanged during the ABTs. Feto(2) oscillated in TRs at a low er values than in CRs and differed significantly between breaths of ai r and hypoxic breaths of TRs. All infants responded to ABT with percen tage alternation coefficients of TRs significantly greater than those of CRs for all respiratory variables. The values of the coefficients w ere not significantly different between both ABT, and between TR50 and TRT. The greatest values of the coefficients were for timing variable s compared with flows and volume. We conclude that the ABT is a reprod ucible test of peripheral chemoreceptor function under standardized co nditions.