Abstract
0858 PURPOSE: To examine the reliability and reproducibility of a modified rebreathing procedure and assess its utility as a research/diagnostic tool. METHODS: The rebreathing technique used was modified to include 5 minutes of prior hyperventilation and maintenance of iso-oxia at hyperoxic (150 mmHg) or hypoxic (50 mmHg) oxygen tensions during rebreathing (Duffin et al., Respir. Physiol., 2000). Twentyeight healthy subjects (14 men, 14 women) performed both hyperoxic and hypoxic rebreathing experiments in the morning (AM) and evening (PM) of the same day, with 12–13 hours separating AM and PM tests. Reliability was examined using the Pearson product-moment correlation coefficient. A three-way ANOVA was used to evaluate the reproducibility. Within and between-subject coefficients of variation (CVs) were calculated. RESULTS: Mean hyperoxic and hypoxic ventilatory responses to carbon dioxide (CO2) did not differ between the AM and PM. Significant reliability coefficients were observed for hyperoxic (r = 0.45 – 0.75) and hypoxic (r = 0.67 – 0.78) rebreathing responses. Bland-Altman plots confirmed no systematic bias between AM and PM tests. Between-subject CVs for basal (41.0 and 39.1%) and sensitivity (34.3 and 33.7%) responses, for hypoxic and hyperoxic tests were similar, but the CVs for the chemoreflex threshold for CO2 were much less (4.8 and 4.9%) for both hyperoxic and hypoxic tests. Within-subject CVs for basal (23.9 ± 4.1 and 20.7 ± 3.7%), threshold (2.6 ± 0.4 and 2.6 ± 0.4%) and sensitivity (17.5 ± 3.1 and 19.9 ± 2.6%) responses to CO2, for hyperoxic and hypoxic tests, were reasonably low. CONCLUSIONS: The results support the within-day reliability and reproducibility of the modified rebreathing procedure. These data support the use of the modified rebreathing procedure to investigate the effects of interventions/physiological perturbations on the chemoreflex control of breathing. However, its use to diagnose disorders in respiratory chemoreflex control in individual patients is not supported. Supported by the William M. Spear Foundation and Ontario Thoracic Society.
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