CSA10a module computes the cross-spectrum between two continuous or discrete input signals.
Considering that one signal is the input and the other one is the output of a linear system, cross-spectrum analysis provides information about the transfer function of the system.
A configuration based on CSA10a, for the study of spontaneous baroreflex is shown in figure 1.
Systolic values of the arterial pressure are measured using APR31a and are applied to the first input of CSA10a. RR intervals can be derived from the electrocardiogram or from the beat interval output of APR31a and are applied to the second input of CSA10a.
Three functions are needed to study the relation between the arterial pressure and the cardiac frequency: coherence, phase and gain.
Two band frequencies are configured in CSA10a: low frequency (LF) with a frequency domain 0.04-0.15 Hz and high frequency (HF) with a frequency domain 0.15-0.4 Hz.
The coherence output takes values between 0 and 1. High values show a strong linear relation between the two signals, low values show week relation between them.
The phase is output in radians. For a specific frequency the phase shows the delay between the two signals.
A negative phase shows that the fluctuations of signal connected to the first input of CSA10a precede the fluctuations of the signal connected to the second input.
The cross-spectrum and the individual spectra, calculated by the same CSA10a can be added to the analysis.