Abstract 15018: Inverse Frequency Dependence of the Chemoreflex - is the Gain Measured with Rebreathing Relevant to Periodic Breathing in Heart Failure?
Background High chemoreflex gain in heart failure may result in periodic breathing (oscillations in cardiorespiratory parameters with a period of about a minute). Clinical research generally separates chemoreflexes into central and peripheral components for measurement, and makes the assumption that responses are independent of stimulation frequency. It is however the total ventilatory response to an oscillatory carbon dioxide (CO2) stimulus with a cycle time of one minute that is physiologically-relevant in heart failure.
Design We tested the hypothesis that chemoreflex gain, like other physiological reflexes, is frequency-dependent: i.e. with increasing stimulus administration frequency, the response increases. We administered oscillations of inspired CO2 at stimulus periods of 30-240 seconds, to measure chemoreflex gain in 28 subjects (heart failure and age-matched controls), and compared this to rebreathing in a subset.
Results Chemoreflex gain increased linearly with stimulus period (r=0.99, p<0.0001). This oscillatory gain correlated with the values obtained using the Modified Rebreathing method (r=0.96, p<0.0001), although the latter were higher (161±54 v 752±405 L/min/atm). We confirmed that chemoreflex gain is greater in heart failure patients with periodic breathing than in those with stable breathing measured using both oscillatory CO2 (261±37 v 144±23 L/min/atm, p=0.009)) and Modified Rebreathing (1278±356 v 526±76 L/min/atm,p=0.0004).
Conclusions Over these clinically-relevant timescales, the chemoreflex has a greater gain when the cycle time of the oscillatory CO2 stimuli is longer, in contrast to other physiological reflexes, meaning that the Modified Rebreathing method may not measure the gain relevant to periodic breathing in heart failure.
- © 2011 by American Heart Association, Inc.