research activities in 2007 - CSEM

the signals with a reference to standard hospital devices. In
addition, the clinical validation was a final test by a third party
to check that all variables are recorded, downloaded and
displayed as described in the user manual, as well as to
medically assess the ECG quality regarding the identification
of the ECG P-, QRS-, and T-waves (see Figure 3).
Figure 4: Typical signals obtained and visualized by the LTMS2 system (from the clinical validation)
The validation was performed on three volunteers in three
sessions of 18 hours and one of 24 hours. All sessions
comprised ‘normal’ daily activities such as office work, walking
around, jogging and night sleeping.
The validation clearly proved that the system is comfortable to
wear for 24 hours and can record data for this period, process
the data and visualize a large number of physiological
parameters in perfect synchronism with time. The accuracy of
the parameters does not, however, always match the
reference. While the bias was negligible for heart rate, oxygen
saturation and respiratory rate, LTMS2 underestimated
temperature by 1 °C and overestimated systolic and diastolic
blood pressure by roughly 10 mmHg, and mean blood
pressure by approximately 5 mmHg. The relatively bad
accuracy of the blood pressure is surprising since for this
parameter LTMS2 simply provides a digital interface to a
CE-marked commercial device.
Motion artifacts were sometimes a problem for oxygen
saturation measurement. This is easily explained though:
during the validation, the reference device was placed at the
fingertip whereas the LTMS2 sensor was placed at the
earlobe (less obtrusive but more subject to artifacts). A similar
explanation holds for ECG and related parameters such as
heart rate that are sometimes altered by artifacts. In this case,
one has to take into account that the reference used a threelead
system, while LTMS2 is limited to one lead. Cross
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Figure 4 shows a typical display of signals measured during
the clinical validation. The ECG P-, QRS-, and T-waves are
clearly identified and the ST, QT, and QRS segment correctly
marked. The figure also shows the heart rate, respiration rate,
ST amplitude and duration, and the QT index.
checking between leads is therefore impossible in LTMS2,
which increases the risk of being deceived by artifacts.
In LTMS2, the activity signal is picked up at the electrode,
while the reference used a watch-like device. Despite this
location difference, LTMS2 and the reference device showed
similar actigraphs. The activity and posture classification was
in accordance with the situations specified by the experiment
protocol (no reference was available for these parameters).
In conclusion, the LTMS2 system has been proven
operational in real conditions. Taking into account the
differences between the location and technology used for the
measuring of the physiological parameters, the LTMS2
system accuracy has been validated. However, a future
enhanced version of the LTMS2 prototype should include
additional means to automatically detect and reject more
artifacts. Other foreseen improvements include more
integration and accuracy, in particular for core body
temperature, oxygen saturation and blood pressure. CSEM is
already conducting research projects on these challenging
topics. Many subsystems of LTMS2 − released from some of
the stringent requirements of the ESA needs − can be readily
converted to commercial applications in several domains,
including physiological monitoring in sport and high-altitude
activities, in firefighting and life-threatening situations, in home
care and telemedicine, or in physiological studies.