Screening for sleep apnea using home recording of the double-loop gain as a measure of periodic breathing

Sleep apnea syndrome (SAS) is caracterized by repetitive events of apnea and
hypopnea, usually accompanied by snoring, disturbed sleep and excessive
daytime-sleepiness. These events are often part of a periodic breathing
pattern, in which relative hyperventilation is followed by apnea or hypopnea.
In this pattern ventilation and oxygen saturation usually oscillate with a
period of 30 - 60 seconds.
Recently we described the *double-loop gain* of the respiratory control system
as a measure of periodic breathing. This is a frequency-dependent variable
which describes 1) the tendency of the respiratory system to oscillate at a
given frequency and 2) the degree to which the relation between oscillations in
ventilation and oscillations in arterial blood gas values is linear. The
underlying hypothesis is that periodic breathing results from negative feedback
regulation of arterial O2 and CO2 pressure through the chemoreflexes. The
double-loop gain describes the gain in the negative feedback loop under the
assumption that accidental changes occur in both ventilation and arterial blood
gas pressures. A simple version of the double-loop gain is derived from nasal
pressure changes and arterial O2 saturation . From all-night recordings, the
*double-loop index* (DLI) can be derived, which is determined by the time
during which the double-loop gain exceeds a given threshold.
Currently, the presence of sleep-apnea and its clinical significance are
determined by the apnea-hypopnea index (AHI), using in-hospital sleep
recording. With a growing number of referrals, waiting lists for sleep
registration are emerging. Screening for SAS using home-measurement of nasal
pressure and SaO2 seems to be a good alternative. We hypothesize that the DLI
derived from these signals gives a better reflection of the pathophysiology of
the disease than the AHI, which does not take into account the inherent
periodicity of the breathing pattern. As a result, we expect that the DLI
improves the distinction between healthy and diseased subjects in comparison to
the simple counting of apneas and hypopneas.This is reflected by a higher area
under the ROC curve, which describes the sensitivity and specificity of the
test.

Primary objectives:

1. To determine the DLI threshold with optimal sensitivity and specificity. The
DLI threshold is the DLI value above which the test is considered positive (and
below which the test is considered negative). The optimal DLI threshold will be
taken as the value that gives the highest area under the ROC curve.

2. To test the hypothesis that the sensitivity and specificity of the screening
are higher when the DLI is used instead of the AHI (both derived from the same
home measurements of nasal pressure and SaO2).

Secundary objective:

1. To assess the repeatability of the DLI using home and in-hospital recordings
of nasal pressure and SaO2.

observational study without intervention

In addition to standard in hospital sleep registration patients are asked to
perform a one night registration of nasal pressure and O2 saturation at home.
The have to collect the equipment and return it the next day. No known risks
are associated with this procedure. In the future this screening method may
reduce the number of hospital admissions for sleep registration.