Chapter 6
Low-Frequency Blood Volume Rhythms
in the Skin Perfusion Obtained
by Optical Sensing
Hans J. Schmitt
Abstract Optical sensing of physiological rhythms has been the subject of intensive research in past years. Photoplethysmography (PPG) is well established for
optical reflection and/or transmission measurements of dermal blood volume changes
phenomena. PPG recordings from the skin exhibit a rich spectrum including components around 1 Hz (and harmonics) due to heart pulse, breathing periodicity normally
around 0.25 to 0.3 Hz, but varying over a wide range down to 0.1 Hz and less,
depending on workload and wilful control, and a periodic low frequency component
at around 0.12 to 0.14 Hz, which usually occurs for a number of minutes, then may
disappear and possibly reoccur from time to time. The origin of this frequency component is still being debated. Its importance rests in the belief, that it is somehow related
to a certain state of mind and awareness. This in turn could have therapeutic consequences if such oscillations and the corresponding mental state could be induced by
outside control.
Various theories have been brought forward as to the origin of these low-f oscillations:
as a sub-harmonic of breathing via parametric-, coupling- or hysteresis effects, either
mechanically by thorax motion or by unspecified nervous effects [1], as a frequency
modulation due to a slight heart arrhythmia known to occur with inhaling and exhaling
[2], nonlinear coupling processes of blood flow and pumping between left and right
sections of the heart [3], rhythmic exchange of brain fluid, such as palpable by
osteopathy [4] or natural mechanical oscillations in the vascular system, various
metabolic processes, or the action of a so far unknown ”internal clock”. This chapter
was previously published in [5].
H. J. Schmitt—is Deceased.
H. J. Schmitt (B)
Institute for High Frequency Technology, RWTH Aachen University, Aachen, Germany
e-mail: perfusion.group@hia.rwth-aachen.de
© Springer Nature Singapore Pte Ltd. 2021
V. Blazek et al. (eds.), Studies in Skin Perfusion Dynamics,
Biological and Medical Physics, Biomedical Engineering,
https://doi.org/10.1007/978-981-15-5449-0_6
105
Low-Frequency Blood Volume Rhythms
in the Skin Perfusion Obtained
by Optical Sensing
Hans J. Schmitt
Abstract Optical sensing of physiological rhythms has been the subject of intensive research in past years. Photoplethysmography (PPG) is well established for
optical reflection and/or transmission measurements of dermal blood volume changes
phenomena. PPG recordings from the skin exhibit a rich spectrum including components around 1 Hz (and harmonics) due to heart pulse, breathing periodicity normally
around 0.25 to 0.3 Hz, but varying over a wide range down to 0.1 Hz and less,
depending on workload and wilful control, and a periodic low frequency component
at around 0.12 to 0.14 Hz, which usually occurs for a number of minutes, then may
disappear and possibly reoccur from time to time. The origin of this frequency component is still being debated. Its importance rests in the belief, that it is somehow related
to a certain state of mind and awareness. This in turn could have therapeutic consequences if such oscillations and the corresponding mental state could be induced by
outside control.
Various theories have been brought forward as to the origin of these low-f oscillations:
as a sub-harmonic of breathing via parametric-, coupling- or hysteresis effects, either
mechanically by thorax motion or by unspecified nervous effects [1], as a frequency
modulation due to a slight heart arrhythmia known to occur with inhaling and exhaling
[2], nonlinear coupling processes of blood flow and pumping between left and right
sections of the heart [3], rhythmic exchange of brain fluid, such as palpable by
osteopathy [4] or natural mechanical oscillations in the vascular system, various
metabolic processes, or the action of a so far unknown ”internal clock”. This chapter
was previously published in [5].
H. J. Schmitt—is Deceased.
H. J. Schmitt (B)
Institute for High Frequency Technology, RWTH Aachen University, Aachen, Germany
e-mail: perfusion.group@hia.rwth-aachen.de
© Springer Nature Singapore Pte Ltd. 2021
V. Blazek et al. (eds.), Studies in Skin Perfusion Dynamics,
Biological and Medical Physics, Biomedical Engineering,
https://doi.org/10.1007/978-981-15-5449-0_6
105