6.3 Signals of the Cardiovascular System

|

257

Fig. 6.29: Example of QRS search in an ECG signal using Sedgehamiz’s Matlab-program with Pan-

Tompkins adaptive threshold adjustment procedure [72]: In this illustration, the adaptive threshold

adjustment can be seen, shown as dashed horizontal bars. The top figure shows QRS search in the

filtered ECG at the output of the bandpass, and the bottom figure shows QRS search after window

integration (MA filtering).

Both the sympathetic and parasympathetic parts of the autonomic nervous system

influence heart rate. The sympathetic part can increase the heart rate, while the para-

sympathetic can decrease it. The control of autonomic regulation involves several in-

terconnected areas of the autonomic central nervous system. Furthermore, additional

external nervous system areas such as arterial regulation of blood pressure through

the baroreceptor reflex and regulation of respiration can also cause rapid changes in

heart rate through the sympathetic and parasympathetic nervous systems. The barore-

flex is based on baroreceptors, which are located on the walls of some large blood ves-

sels and register the stretching of the vessel walls when blood pressure increases. The

spectral range of heart rate variation can therefore be divided into different sections

(cf. Figure 6.30):

–

Typically, the most prominent oscillatory component of heart rate variability is

represented by the Respiratory Sinus Arrhythmia (RSA), whereby stimulation by

the vagus nerve is suppressed during inhalation and the heart rate increases as

a result. On exhalation, it can take effect again, so that the heart rate rises again.

This high frequency component (HF: high frequency) of the heart rate is thus

mainly generated by the respiratory rate in the range of 0.15 to 0.4 Hz.