Background: Memory oximeters enable diagnostic studies
for sleep apnea hypopnea syndrome (SAHS) to be performed in the home.
However, memory capabilities may be limited.
Objectives: To compare a pulse oximeter used at home with an 8-h
memory, storing data every 12 s, and in the laboratory, with
on-line recording every 2 s.
Prospective cohort study.
Setting: Patients’ homes
and a sleep laboratory.
Patients: One hundred patients
with suspected SAHS.
Measurements: Home oximetry and a
laboratory full polysomnography. The number of ≥ 4% dips in pulse
oximetric saturation (Spo2) was calculated for
each study. Daytime sleepiness was assessed by the Epworth Sleepiness
Scale (ESS) score.
Results: The mean dips per hour
were 5.3/h (range, 0 to 53/h) for home studies and 13.4/h (range, 0 to
106/h) for laboratory studies; the relationship between home and
laboratory studies was as follows:
home = (0.4 × laboratory) − 0.01 ± 11.2;
r2 = 0.64. Mean difference was 8.4/h
(− 2.5 to + 77.9/h), which correlated with the mean of the
measurements. At a cutoff point of 10/h, 52 studies were both negative
and 13 studies were both positive. Nineteen home studies were
false-negatives. Sensitivity was 0.41, and specificity was 1.0. In
these 19 studies, 7 patients had an ESS score > 10 and 4 patients had
an ESS score > 14. To confirm that differences were due to different
sampling rates, 16 additional patients had on-line data and stored data
collected simultaneously in the laboratory. Mean dips per hour were
3.2/h (range, 0.1 to 18.3/h) for the stored data and 8.34/h (0.2 to
22.8/h) for on-line data; the relationship being stored was as follows:
0.5 on-line − 1.17 ± 2.6; r2 = 0.69.
Mean difference was 5.2/h (0.04 to 15.4 h), which correlated with
the mean of the measurements.
studies using a memory storage pulse oximeter may underestimate the
number of hypoxic dips, probably due to sampling rates. Clinically
significant hypoxic SAHS may therefore be missed.