Sleep Apnea and Periodic Breathing
Sleep Apnea and Periodic Breathing
The purpose of this study is to determine the double loop index (DLI) threshold with optimal
 sensitivity and specificity. The investigators hypothesize that the DLI gives a better
 reflection of the pathophysiology of the disease than the apnea-hypopnea-index (AHI).
Sleep apnea syndrome (SAS) is characterized by repetitive events of apnea and hypopnea. These
 events are often part of a periodic breathing pattern, in which relative hyperventilation is
 followed by apnea or hypopnea.

 Recently the investigators 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 is 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. The investigators hypothesize that the DLI derived from
 these signals gives a better reflection of the pathophysiology of the disease than the AHI.
 As a result, the investigators 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 in a higher area under the ROC curve, which describes the sensitivity and
 specificity of the test.
Inclusion Criteria:

 -  Suspected sleep apnea syndrome

 -  > 18 yr

 -  Outpatient

 -  Able and willing to use the necessary equipment for registration of nasal pressure and
 O2 saturation at home

 Exclusion Criteria:

 -  hospitalized patients

 -  < 18 yr

 -  Not able to use the necessary equipment