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S. Leonhardt
autonomic nervous activity. Yet, the true origin of these skin perfusion phenomena
and their medical value is still being debated and especially the spatial distribution
and spectral formation of these rhythms haven’t really been explained until now.
13.5 Conclusions
Non-invasive, computer-aided and easy-in-use plethysmographic systems have
rapidly gained widespread acceptance for routine diagnostic assessments. Today,
such systems are an indispensable part of the vascular labs around the world. An
important task remaining to be accomplished, however, is to optimize the present
system by improving sensor technology and PPG signal post-processing, especially
the correlative analysis of spectral signal components, related to the central cardiovascular&respiratory and local vasomotion patterns. The presences of the first two oscillators in the human body, namely the heart and the lung, are well known and widely
reported in the scientific literature; their presence and the coupling (see Chaps. 6, 7
and 8) is evident by studying the frequency spectrum of the photoplethysmographic
signal, especially of the heart rate variability patterns. In many studies, the local
perfusion rhythmicity (on frequencies below 0.2 Hz) is unfortunately considered
“more or less as interesting epiphenomena or at best as indicators without essential
functional significance” [26]. In contrast to this general view, however, at RWTH
University we envision these autonomous low frequency perfusion patterns to be
very rewarding area of study.
While current research on dermal rhythmicity concentrates on the frequency range
below 0.1 Hz, the assessment and interpretation of these perfusion rhythms are particularly hindered by the fact that these patterns have a very strong spatial variability
and are highly transient. For example, we found such slow waves in preterm infants,
which have traditionally been thought to be passive due to their not yet mature
thermal regulation system. However, the proper interpretation of these signals is
pending. Furthermore, if these waves truly turn out to reflect the status of the central
autonomous nervous system, many applications, like pain, relaxation and stress monitoring, come to mind. Quantification of emotions as in “affective” or “emotional
computing” may become a method to communicate with persons incapable of verbal
communication, like in dementia, surgery, coma or with neonates.
Hence, it seems fair to say that these phenomena may carry the means for advanced
signal processing and monitoring options, but require raised efforts of research to
fully understand them. For example, controlled skin perfusion studies will be necessary to really quantify the correlation between the state of activity of the autonomic
nervous system and dermal rhythms.
In any case: for future research into skin perfusion dynamics of living skin, a
contact-free measurement technique featuring sufficient spatial resolution is mandatory. Fusion of different optical imaging modalities will give completely new
information and will certainly play an important role.
S. Leonhardt
autonomic nervous activity. Yet, the true origin of these skin perfusion phenomena
and their medical value is still being debated and especially the spatial distribution
and spectral formation of these rhythms haven’t really been explained until now.
13.5 Conclusions
Non-invasive, computer-aided and easy-in-use plethysmographic systems have
rapidly gained widespread acceptance for routine diagnostic assessments. Today,
such systems are an indispensable part of the vascular labs around the world. An
important task remaining to be accomplished, however, is to optimize the present
system by improving sensor technology and PPG signal post-processing, especially
the correlative analysis of spectral signal components, related to the central cardiovascular&respiratory and local vasomotion patterns. The presences of the first two oscillators in the human body, namely the heart and the lung, are well known and widely
reported in the scientific literature; their presence and the coupling (see Chaps. 6, 7
and 8) is evident by studying the frequency spectrum of the photoplethysmographic
signal, especially of the heart rate variability patterns. In many studies, the local
perfusion rhythmicity (on frequencies below 0.2 Hz) is unfortunately considered
“more or less as interesting epiphenomena or at best as indicators without essential
functional significance” [26]. In contrast to this general view, however, at RWTH
University we envision these autonomous low frequency perfusion patterns to be
very rewarding area of study.
While current research on dermal rhythmicity concentrates on the frequency range
below 0.1 Hz, the assessment and interpretation of these perfusion rhythms are particularly hindered by the fact that these patterns have a very strong spatial variability
and are highly transient. For example, we found such slow waves in preterm infants,
which have traditionally been thought to be passive due to their not yet mature
thermal regulation system. However, the proper interpretation of these signals is
pending. Furthermore, if these waves truly turn out to reflect the status of the central
autonomous nervous system, many applications, like pain, relaxation and stress monitoring, come to mind. Quantification of emotions as in “affective” or “emotional
computing” may become a method to communicate with persons incapable of verbal
communication, like in dementia, surgery, coma or with neonates.
Hence, it seems fair to say that these phenomena may carry the means for advanced
signal processing and monitoring options, but require raised efforts of research to
fully understand them. For example, controlled skin perfusion studies will be necessary to really quantify the correlation between the state of activity of the autonomic
nervous system and dermal rhythms.
In any case: for future research into skin perfusion dynamics of living skin, a
contact-free measurement technique featuring sufficient spatial resolution is mandatory. Fusion of different optical imaging modalities will give completely new
information and will certainly play an important role.