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N. Blanik
can be made. These include recordings of individuals or their body parts while at rest
in a relaxed sitting or lying position, and cooperative patients who follow instructions
to keep still except for involuntary respiration. These two categories present an ideal
state from the point of view of analysis. Further descriptions of analyzing method as
well as examples of application are outlined in [38].
In addition to the detection of breathing patterns, heartbeat synchronous movements can be similarly analyzed from recorded sequences. The amplitude of the
heartbeat signal, though significantly smaller than the breathing amplitude, possesses
a high level of regularity (with the exception of alterations due to pathological conditions), and a frequency band shifted to higher frequencies, making it easier for separation by band-pass filtering. This approach corresponds to an optical ballistocardiography method. Instead of usual pressure sensors below the patients, here the
movements recorded in the PPGI sequences are analyzed in the heartbeat frequency
band. Since the forces arising from heart activity get distributed along the arteries by
pressure waves, heartbeat correlated movements are also measureable in the extremities, for example, the pulsatile influx of blood into the head causes spontaneous head
movements which can be described as micro head-nodding.
11.6 Conclusion
The PPGI concept opens up new possibilities for the unobstusive assessment of a
wide range of bodily signals. Its basic evaluation principle is derived from classical
skin-contact PPG, thereby rendering it possible to,adapt and apply existing analyzing
algorithms.
In contrast to the simple PPG, the requirements of the PPGI measurement setup are
quite demanding—a camera with high dynamic range and suitable scene illumination
enable high quality perfusion signal detection. Furthermore, interpretation and analysis of the substantially large recorded data require sufficient computational power.
The heartening fact is that with constant improvements in camera design as well as
computer technology, acquisition cost decreases progressively, and is accompanied
by a simultaneous upswing in scope of application of this technique. By analyzing
perfusion signals with spatial resolution, new phenomena of movements in perfusion
distribution could be found (so called “blood volume clouds”).
In summary, it could be pointed out that:
• Photoplethysmography Imaging (PPGI) is a functional, non-invasive, and contactless measurement technique for assessing dermal perfusion;
• Usage of a high-sensitivity camera as optical sensor, enables detection of
rhythmical phenomena in dermal perfusion, with multidimensional resolution;
• Low-cost cameras are available for evaluating basic vital parameters;
• The detection scope covers numerous vital parameters like HR, HRV, RR, RRV,
PI, and S p O 2 which can be calculated automatically and simultaneously;
• Either ambient or artificial light can be used as a source of illumination;
N. Blanik
can be made. These include recordings of individuals or their body parts while at rest
in a relaxed sitting or lying position, and cooperative patients who follow instructions
to keep still except for involuntary respiration. These two categories present an ideal
state from the point of view of analysis. Further descriptions of analyzing method as
well as examples of application are outlined in [38].
In addition to the detection of breathing patterns, heartbeat synchronous movements can be similarly analyzed from recorded sequences. The amplitude of the
heartbeat signal, though significantly smaller than the breathing amplitude, possesses
a high level of regularity (with the exception of alterations due to pathological conditions), and a frequency band shifted to higher frequencies, making it easier for separation by band-pass filtering. This approach corresponds to an optical ballistocardiography method. Instead of usual pressure sensors below the patients, here the
movements recorded in the PPGI sequences are analyzed in the heartbeat frequency
band. Since the forces arising from heart activity get distributed along the arteries by
pressure waves, heartbeat correlated movements are also measureable in the extremities, for example, the pulsatile influx of blood into the head causes spontaneous head
movements which can be described as micro head-nodding.
11.6 Conclusion
The PPGI concept opens up new possibilities for the unobstusive assessment of a
wide range of bodily signals. Its basic evaluation principle is derived from classical
skin-contact PPG, thereby rendering it possible to,adapt and apply existing analyzing
algorithms.
In contrast to the simple PPG, the requirements of the PPGI measurement setup are
quite demanding—a camera with high dynamic range and suitable scene illumination
enable high quality perfusion signal detection. Furthermore, interpretation and analysis of the substantially large recorded data require sufficient computational power.
The heartening fact is that with constant improvements in camera design as well as
computer technology, acquisition cost decreases progressively, and is accompanied
by a simultaneous upswing in scope of application of this technique. By analyzing
perfusion signals with spatial resolution, new phenomena of movements in perfusion
distribution could be found (so called “blood volume clouds”).
In summary, it could be pointed out that:
• Photoplethysmography Imaging (PPGI) is a functional, non-invasive, and contactless measurement technique for assessing dermal perfusion;
• Usage of a high-sensitivity camera as optical sensor, enables detection of
rhythmical phenomena in dermal perfusion, with multidimensional resolution;
• Low-cost cameras are available for evaluating basic vital parameters;
• The detection scope covers numerous vital parameters like HR, HRV, RR, RRV,
PI, and S p O 2 which can be calculated automatically and simultaneously;
• Either ambient or artificial light can be used as a source of illumination;