Fig 1.
Characterization of a typical model's CBFV response (dotted line) to a BP negative step (dashed line). Δτ is the duration of the transient response. Vbase is the baseline level, which is used to normalize the signal before determining the slope of the straight line that characterize its transient response (thick solid line). The horizontal thick solid straight line is the representation of the constant steady state response (Ks). The angle between the line of transient CBFV response and line of BP recovery is the parameter ϕ. eT and eS are examples of the errors in the transient and steady state phase respectively, their sum is minimized to fit the best set of straight lines.
Table 1.
Grand mean ± SD of physiological variables, TF coefficients and predicted dynamic CA index values in baseline and hypercapnia.
Fig 2.
Signals in spontaneous fluctuations.
Recordings of spontaneous BP (solid line, mmHg), CBFV (dotted line, cm/s), and EtCO2 (dashed line, mmHg) from a female 29-years-old volunteer, in baseline (A) and hypercapnia (B). An increase in all signals can be observed in the latter after 50 seconds.
Fig 3.
Each curve shows the averaged step responses generated for each subject by NAR models (solid line) and NFIR models (long dashed line) in baseline, and NAR models (dashed line) and NFIR models (dotted line) in hypercapnia. Error bars represent ± SD.
Fig 4.
Comparison of the actual and predicted CBFV signals.
The CBFV signal predicted by a non-linear NAR model (dotted line) compared with the actual CBFV signal (solid line) of a 26-years-old male volunteer, in baseline (A) and hypercapnia (B).
Table 2.
ν-SVR hyper-parameters and validation correlations coefficients exhibited by the models selected for both non-linear structures in both conditions.
Fig 5.
In subplot (A) ROC curves achieved by non-linear models with classic ARI values for NFIR (dotted line) and NAR models (dashed line), and with mfARI values for NFIR (long dashed) and NAR models (solid line). ROC curves for TF are presented in subplot (B) with TF gainVLF (dotted line), TF phaseLF (dashed line), TF gainLF (dot dashed line) and TF phaseVLF (solid line).
Table 3.
AUC values obtained by each approach when discriminating between baseline and hypercapnia.