Variability of the ventilatory response to Duffin's modified hyperoxic and hypoxic rebreathing procedure in healthy awake humans

We quantified the magnitude of within- and between-day, within-subject variability of the ventilatory response to Duffin's modified rebreathing procedure in 20 healthy humans. The P-ETCO2 at which ventilation increased with progressive increases in P-ETCO2 during rebreathing was identified as the ventilatory recruitment threshold (VRTCO2); the ventilatory response below and above the VRTCO2 was taken as an estimate of non-chemoreflex drives to breathe ((V) over dot(EB)) and chemoreflex sensitivity ((V) over dot(ES)), respectively. Within- and between-day intraclass correlation coefficients for each of these parameters were >0.60 (range: 0.62-0.93), indicating good-to-excellent test-retest reliability. Within- and between-day, within-subject coefficients of variation for hyperoxic and hypoxic (V) over dot(EB) (range: 24.6-30.7%) and (V) over dot(ES) (range: 18.5-32.7%) were relatively high but acceptable, while those for the VRTCO2 were very small (range: 3.0-3.8%). In conclusion, Duffin's modified rebreathing procedure, in both its hyperoxic and hypoxic form, is a highly reliable tool for measurement of chemoreflex and non-chemoreflex ventilatory control characteristics over short and long periods of time in healthy humans. (C) 2009 Elsevier B.V. All rights reserved.