Quantitative Sleep Monitoring - Quantitative EEG Analysis Methods and Clinical Applications - page 285

observed agreement among the system and the expert to the chance agreement. The
chance agreement measures the amount of agreement to be expected by chance
alone [45].
Although evaluation of the performance of a sleep detection algorithm is more
complicated than evaluating the performance of a binary classification problem,
many metrics do exist that could be used. Unfortunately, no standard evaluation
has been used across techniques, so it is difficult to say which technique works the
best. It would be very beneficial to the field of automated sleep detection to apply a
standard metric, such as a contingency table or the kappa index, to the different
techniques for comparison purposes.

10.17 Positive Airway Pressure Treatment for Obstructive Sleep Apnea

The primary treatment for obstructive sleep apnea is positive airway pressure
(PAP). This treatment is available in a number of forms, including continuous PAP
(CPAP), bilevel PAP (BPAP), autotitrating PAP (APAP), and flex settings with
patient-selected pressure releases. All of these systems work under the same princi-
ple—pneumatic splinting of the retropharyngeal space and upper airway.
Airway resistance (AR) is proportional to the inverse of the radius r of the air-
way to the fourth power:

4

AR ∝ 1 r

Therefore, even small improvements in the airway radius result in very signifi-
cant improvements in airway resistance. PAP increases the radius by the above
described pneumatic splinting.
Most PAP devices run at a given setting with little or no variation. Autotitrating
systems attempt to match the apparent need for pressure to a given setting on the
machine. This theory is very appealing, but the machines do not fully achieve this
goal.

10.17.1 APAP with Forced Oscillations
The use of the forced oscillation technique (FOT) measures airway impedance and
was initially applied to the measurement of obstruction in the lower airway [58].
The technique can also be applied to obstruction involving the upper airway, for
example, obstructive sleep apnea. The impedance measured by FOT correlates with
esophageal pressure recordings.
Forced oscillations of externally applied airflow are used to determine the
mechanical response of the respiratory system. The system requires the use of
low-amplitude oscillations to maintain linearity. It is possible that this limitation
could mask important and as yet incompletely described nonlinear components.

10.17.2 Measurements for FOT
The impedance ( Z ) and the spectral relationship between pressure ( P ) and airflow
( V ) comprise the key variables in forced oscillation analysis. Depending on the sites