Information Technology Reference
In-Depth Information
decrease in the blood oxygen saturation (the percentage of haemoglobin saturated
with oxygen) during sleep.
The gold standard for the diagnosis of OSA is an overnight in-clinic polysomnog-
raphy. The sleep study measures the frequency of apnea and hypopnea events. In
general, the diagnosis of OSA uses two scores: Apnea-Hypopnea Index ( AHI )and
Apnea Index ( AI ). The apnea-hypopnea index ( AHI ), the most commonly used
score, is calculated as a number of apnea and hypopnea events per hour of sleep;
The apnea index ( AI ) is calculated as a number of apnea events per hour of sleep.
Additionally, many definitions of apnea/hypopnea events require one or both of two
factors: oxyhemoglobin desaturation of 4% or more and brief arousals from sleep.
Thus, the definition of apnea event varies.
The diagnosis of OSA can be based on two approaches: (1) a score of apnea/hy-
popnea events ( AHI ) or (2) a combination of AHI scoring and symptoms. In the
diagnosis based solely on the AHI index, apnea is classified as mild for AHI be-
tween 5 and 14
30.
The International Classification of Sleep Disorders (ICSD) [16] defines the severity
of OSA in terms of the frequency of apnea events, the degree of oxygen desaturation,
and the severity of daytime sleepiness.
The differences between the scoring and definitions of apnea have important im-
plications for the conceptual data modeling in data mining. Most published medical
research studies base the diagnosis of OSA on AHI or a combination of apnea index
( AI )and AHI obtained from overnight in-clinic PSG. For example, the authors of
two articles on craniofacial predictors [9] and [5] define respectively two criteria:
(1) OSA defined as AHI
.
9, moderate for AHI between 15 and 29
.
9, and severe for AHI
>
>
10. To il-
lustrate the difference between diagnostic criteria based on AHI and a combination
of AI and AHI , we applied these two criteria to 233 records from the data set ob-
tained from the authors of the first publication [3]. Figure 13.2 shows the number of
records classified into OSA and non- OSA using two diagnostic criteria: OSA defined
by AHI
5and(2) OSA defined as AI
5or AHI
10 (col-
umn to the right). The second criterion is more restrictive and excludes 26 records
(26
5 (column to the left) and OSA defined by AH
>
5OR AHI
>
233) from the OSA group and classifies them as a non- OSA .
The definition of OSA is fuzzy.
/
Different studies use different cut-off values
to indicate OSA , for example AHI
15. To illustrate the
differences in prevalence of OSA , we applied three cut-off values to 795 records
obtained from a sleep clinic [7, 8]. Figure 13.3 shows the changing proportions
between non- OSA and OSA records for AHI
5, AHI
10, AHI
15.
OSA is operationalized using diverse methods. Thus, the conceptual model for
data must define precisely the scoring criteria. The use of AHI or AI and three
cut-off values can result in significant differences in classification of the patients
(non- OSA , OSA ), especially for patients with low AHI scores [13]. Furthermore,
the difficulty with the scoring of AHI is compounded by the natural night-to-night
variability in the severity of apnea and the differences in diagnostic equipment.
5, AHI
10, and AHI
 
Search WWH ::




Custom Search