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B. Venema
4.1 Exploring New Application Sites for PPG
Conventional finger-based photoplethysmography (PPG) systems, like finger pulse
oximeters, are widely used. They belong to the standard devices in almost all areas of
clinical facilities, from examination rooms to operating theaters. Based on decades
of research and development, they provide accurate measurement of heart rate and
arterial oxygen saturation (SaO 2 ), are inexpensive, easy to use, and fully accepted
by medical staff. Therefore, it is noteworthy that PGG has not yet extended beyond
the clinical realm to other areas of application where visualization of vital signs has
long been of considerable interest.
One typical application scenario is that of ‘home care’. This type of health care is
based on the principle ‘outpatient before inpatient’ and aims to provide home-related
health care and therapy. Due to an increasingly aging society, rising healthcare costs
have become a major challenge in many countries. Therefore, the concept of home
care is becoming more important in medical technology and will probably play an
important role in the future. It is expected that the outsourcing of healthcare from
clinical facilities to home-related home care will lead to a significant reduction in
costs [1]. Another application scenario is covered by the term ‘personal health care’
(PHC). PHC signifies accessing, monitoring, and/or recording of vital parameters
that are independent of the usual professional medical attendance. Although PHC
is a relatively new term, many people have always (to some extent) been reliant on
self-help, often due to lack of adequate medical care. Nevertheless, due to improved
technical possibilities, PHC has become increasingly important for various health
departments and users [1]. Whereas healthy users become more interested in their
vital signs during sports activities (ranging, e.g., from jogging to high-altitude mountain expeditions), an ever-aging society hopes for some degree of medical independence based on ambient-assisted living. In addition, rural regions and developing
countries will also benefit from robust health information infrastructure [2].
For this special purpose, these sensors must be unobtrusive and easy in use, since
the correct application may sometimes be difficult to control. Although PPG has
considerable potential for the monitoring of vital signs in PHC and home care, this
has not yet been achieved. One reason for this is the limited interest in measurement
of peripheral capillary oxygen saturation (SpO 2 ) and the slow blood volume shifts in
non-clinical environments. For heart rate monitoring the ECG is generally used (e.g.
long-term ECG, sports application) even though this requires distributed electrodes
and is, therefore, more complicated to use. The preference for ECG is mainly due
to two problems associated with conventional PPG: (i) compared to the ECG which
derives information on the heart based on the electrical activity of the heart, PPG
measures sub-dermal blood volume changes that are highly susceptible to contact
pressure variations caused by motion (i.e. motion artifacts), and (ii) PPG is usually
applied at the periphery (e.g. a finger), which is always strongly affected by motion
artifacts during daily activity.
Therefore, it is useful to apply PPG to body parts that are unobtrusive and less
affected by motion during daily activity. Until the late 1960s and early 1970s, the
B. Venema
4.1 Exploring New Application Sites for PPG
Conventional finger-based photoplethysmography (PPG) systems, like finger pulse
oximeters, are widely used. They belong to the standard devices in almost all areas of
clinical facilities, from examination rooms to operating theaters. Based on decades
of research and development, they provide accurate measurement of heart rate and
arterial oxygen saturation (SaO 2 ), are inexpensive, easy to use, and fully accepted
by medical staff. Therefore, it is noteworthy that PGG has not yet extended beyond
the clinical realm to other areas of application where visualization of vital signs has
long been of considerable interest.
One typical application scenario is that of ‘home care’. This type of health care is
based on the principle ‘outpatient before inpatient’ and aims to provide home-related
health care and therapy. Due to an increasingly aging society, rising healthcare costs
have become a major challenge in many countries. Therefore, the concept of home
care is becoming more important in medical technology and will probably play an
important role in the future. It is expected that the outsourcing of healthcare from
clinical facilities to home-related home care will lead to a significant reduction in
costs [1]. Another application scenario is covered by the term ‘personal health care’
(PHC). PHC signifies accessing, monitoring, and/or recording of vital parameters
that are independent of the usual professional medical attendance. Although PHC
is a relatively new term, many people have always (to some extent) been reliant on
self-help, often due to lack of adequate medical care. Nevertheless, due to improved
technical possibilities, PHC has become increasingly important for various health
departments and users [1]. Whereas healthy users become more interested in their
vital signs during sports activities (ranging, e.g., from jogging to high-altitude mountain expeditions), an ever-aging society hopes for some degree of medical independence based on ambient-assisted living. In addition, rural regions and developing
countries will also benefit from robust health information infrastructure [2].
For this special purpose, these sensors must be unobtrusive and easy in use, since
the correct application may sometimes be difficult to control. Although PPG has
considerable potential for the monitoring of vital signs in PHC and home care, this
has not yet been achieved. One reason for this is the limited interest in measurement
of peripheral capillary oxygen saturation (SpO 2 ) and the slow blood volume shifts in
non-clinical environments. For heart rate monitoring the ECG is generally used (e.g.
long-term ECG, sports application) even though this requires distributed electrodes
and is, therefore, more complicated to use. The preference for ECG is mainly due
to two problems associated with conventional PPG: (i) compared to the ECG which
derives information on the heart based on the electrical activity of the heart, PPG
measures sub-dermal blood volume changes that are highly susceptible to contact
pressure variations caused by motion (i.e. motion artifacts), and (ii) PPG is usually
applied at the periphery (e.g. a finger), which is always strongly affected by motion
artifacts during daily activity.
Therefore, it is useful to apply PPG to body parts that are unobtrusive and less
affected by motion during daily activity. Until the late 1960s and early 1970s, the