Modeling low frequency cardiorespiratory interaction using broadband hypoxic stimulation

The authors investigated cardiorespiratory dynamic interaction within the low frequency region (<0.15 Hz) using broadband hypoxic stimulation during mean inspired oxygen levels of 16.5% and 12.5%. Spectral broadening of O₂ level was obtained by pseudo random binary switching (PRBS) of inspired O₂ level between 21% O ₂ and 4% (12% for mild hypoxia), balance nitrogen. Coherence analysis showed that during moderate hyponia, responses of R-R interval, BP and ventilation were statistically related. Partial coherences showed fluctuations in R-R interval and ventilation were correlated in the low frequency region. Parametric modeling resulted in a model with four poles and two zeros as a best fit between F₁O₂ and R-R interval