Assessment of the Autonomic Control of the Cardiovascular System by a Frequency Domain Approach

This chapter discusses how a frequency domain approach can be used to assess the autonomic control of the cardiovascular system. Power spectrum analysis based on Fast Fourier Transform (FFT) or autoregressive modeling (AR) provides the center frequency of rhythmic fluctuations of the different cardiovascular variables. Normalization procedure is obtained by dividing the absolute power of each oscillatory component by total variance and then multiplying by 100. Frequency domain analysis of heart rate and arterial pressure variability enabled to disclose subtle changes in the neural cardiovascular control that would be hidden when considering the simple variations of heart rate and blood pressure mean values. The high frequency (HF) component of systolic arterial pressure variability reflects the mechanical influence of respiratory activity. The other oscillatory component is indicated as low frequency (LF). The LF component of RR variability (LFRR) when expressed in normalized units (n.u.) reflects primarily the sympathetic efferent modulation of the sino-atrial node. Rhythmic discharge activity is a general property of the nervous system. A 0.1 Hz rhythmicity linked with low frequency fluctuations of RR interval and arterial pressure variability was found to characterize sympathetic neurons located in areas within the central nervous system involved in cardiovascular regulation.