Besides heart rate and arterial blood pressure, several parameters of the cardiovascular system fluctuate spontaneously. In the current study, the fluctuations of tissue blood content and blood volume pulse were investigated using two parameters of the photoplethysmographic (PPG) signal: the parameter BV, defined by: BV=Const−BL where BL is the baseline of the PPG signal, and the amplitude (AM), which are related to the blood volume and to the systolic blood volume increase, respectively. The PPG measurements were performed on the fingertips of ten healthy male subjects for 5 to 10 min and the PPG signal was digitally analyzed. Both BV and AM show low frequency fluctuations, which, for 23 out of 26 examinations, were positively correlated, with a lag of BV relative to AM. In three examinations, however, the two parameters were inversely correlated. A lower correlation was found between each of these parameters and the PPG period, which is actually the cardiac period. The results show that several mechanisms are involved in the spontaneous periodic fluctuations in the vascoconstriction level, which are known to be mediated by the sympathetic nervous system. The digital PPG provides, therefore, a potential tool for evaluating the role of the sympathetic nerves in the regulation of the microcirculation.
Several parameters of the cardiovascular system such as heart rate, arterial blood pressure and blood flow fluctuate spontaneously. These fluctuations are related to the autonomic nervous system activity. In particular the low frequency fluctuations are mediated by the sympathetic nervous system. In the cuttent study, the low frequency fluctuations of the tissue blood volume and the blood volume pulse in the fmgertips of healthy subjects were investigated using photoplethysmography (PPG). The baseline of the PPG signal (BL) is inversely related to tissue blood volume so that the parameter BY, defmed by: BY = Const. -BL is directly related to the blood volume. The amplitude (AM) is directly related to the systolic blood volume increase. For most of the examinations BY and AM show positive correlation but in some examinations the two parameters were inversely correlated. PPG measurements performed in near infrared radiation, showed better correlation between BY and AM than for red light PPG. The results show that several mechanisms are involved in the low frequency fluctuations in the tissue blood volume. The analysis of the PPG signal provides, therefore, a potential tool for studying the mechanism of the regulation of the microcirculation by the sympathetic nerves.Yarious parameters of the cardiovascular system show spontaneous oscillations in well defmed frequencies. Heart rate and arterial blood pressure variability is associated with the activity of the autonomic nervous system. Its power spectrum is mainly composed of three frequency ranges: low and medium frequencies (below 0.05 Hz and at about 0. 1 Hz, respectively) which are attributed to the activity of the sympathetic and the parasympathetic nervous systems, and high frequency (around 0.3 Hz), which is caused by the influence of respiration on the cardiovascular system via the parasympathetic nervous system [1][2][3] Spontaneous fluctuations were also found for other parameters of the peripheral blood circulation system. Low frequency fluctuations were found in the blood content in the fmgertip and 84 ISPIE Vol. 2631 O-8194-1995-8/96/$6.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
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