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was confirmed by including a grey area
characterized by the patient‘s individual need for
diagnosis. The integration of this grey area as an
additional classification group for apnea screening
could significantly improve the reliablity of SAHS
detection. The grey area was implemented in
reference to the actual German guideline that also
earmarks this area for requiring a patient‘s indivi-
dual classification in dependence on coexisting EDS
within these thresholds. The best result was obtained
by a decreasing type algorithm using a decrease
threshold of ≥4% within a moving time window of
30 seconds. The yielded reliability was SE=92.16
and SP=90.32 by a mean deviation of calculated DI
vs. real AHI of -1.68/h. In comparison to the same
algorithms without grey area consideration, this
showed an increase of 7.3% in SE and 8.7% in SP.
In a final manner, we animadvert that generally,
information about the intensity of desaturations gets
lost within existing SAHS screening algorithms.
Extended and deep desaturations (e.g. 40 seconds
and 15%) are not differed from shorter and light
desaturations (e.g. 20 seconds and 5%). In this
regard, we presented the prospects of short-term
frequency analysis of SpO
2
data. Thus, individual
sleep profiles of overnight desaturation
characteristics can be visualized in an easy to
interpret three-dimensional graph. This allows
drawing conclusions on intensity and repetitivity of
desaturation events, even by non sleep medicine
specialists.
5 DISCUSSION
According to sleep medicine guidelines, pulse
oximetry is a reliable medical device for SAHS pre-
test probability assessment; keeping in mind that is
not able to substitute a sleep medical diagnosis via
polysomnography (q.v. Netzer (2001), Wessendorf
(2002)). Thus, pulse oximetry is not able to detect
e.g. neither AHI nor EDS. Convenient SAHS
screening algorithms classify SAHS suspects
according to determinable DI values that can differ
from patients’ AHI. Possible causes of this diversity
of DI and AHI are multiple. For example there are:
- Hypopneas, that by definition are decreases
in breath flow, but that do not have to be
accompanied by pronounced desaturations
(Konietzko, 1998).
- Moving artifacts, that may lead to a over-
estimation of real DI values (Netzer, 2001).
- Physiological dependences like the initial
arterial oxygen saturation or the perfusion at
the point of measurement (Oczenski, 2008).
- Dependences on pulse oximeter model
(Zafar, 2005).
- Dependences of desaturation classifier
definition.
Nonetheless we demonstrated that the reliability
of SAHS pretest results yielded to trustworthy SE
and SP values ≥ 90% in comparison to AHI
diagnosis by polysomnography in sleep laboratory.
Against this background and with regard to the high
prevalence of SAHS we see a high, but still not
exploited potential of pulse oximetry in SAHS
screening and pretest application. Furthermore we
see the requirement and room for improvement of
the analyzability and interpretability of recorded
pulse oximetric screening data even by non-sleep
medicine experts. In this context, we presented
prospects of the short-term analysis of SpO
2
data for
improvement of SAHS screening by individual
SAHS sleep profiles considering desaturation
intensities and its temporal clusters.
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