Impact of periodic breathing on VO2 and VCO2:: a quantitative approach by Fourier analysis

Oscillations in oxygen uptake ((V) over dot(O2)) and carbon dioxide production ((V) over dot(CO2)) in patients with chronic heart failure differ in amplitude and phase from the oscillations in ventilation (periodic breathing, PB), leading some to doubt whether they result from PB. We applied Fourier transforms to a pulmonary gas exchange model to quantify the effects of fluctuations in alveolar ventilation ((V) over dotA). We found that PB causes oscillations in (V) over dot(O2) and (V) over dot(CO2), but their amplitude and phase are complex, and vary with workload. At low workloads, the relative oscillations in (V) over dot(O2) and (V) over dot(CO2) closely mirror the relative oscillations in (V) over dotA. But at high workloads, the metabolic oscillations are attenuated ((V) over dot(O2) most severely), and the (V) over dot(O2) peaks precede the ventilatory peaks significantly. This study also explains why normal controls simulating PB at higher workloads fail to reproduce the (V) over dot(O2) and (V) over dot(CO2) oscillations seen in spontaneous PB of heart failure. (C) 1999 Elsevier Science B.V. All rights reserved.