Home oximetry studies for diagnosis of sleep apnea/hypopnea syndrome: limitation of memory storage capabilities.
BACKGROUND
Memory oximeters enable diagnostic studies for sleep apnea hypopnea syndrome (SAHS) to be performed in the home. However, memory capabilities may be limited.


OBJECTIVE
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.


METHODS
Prospective cohort study.


METHODS
Patients' homes and a sleep laboratory.


METHODS
One hundred patients with suspected SAHS.


METHODS
Home oximetry and a laboratory full polysomnography. The number of >/= 4% dips in pulse oximetric saturation (SpO(2)) 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 x laboratory) - 0.01 +/- 11.2; r(2) = 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; r(2) = 0.69. Mean difference was 5.2/h (0.04 to 15.4 h), which correlated with the mean of the measurements.


CONCLUSIONS
Home 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.
Wiltshire
N
N
Department of Respiratory Medicine, Bristol Royal Infirmary, Bristol, England.
Kendrick
A H
AH
Catterall
J R
JR
D015331:Cohort Studies; D004867:Equipment Design; D005260:Female; D006701:Home Nursing; D006801:Humans; D016247:Information Storage and Retrieval; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D012891:Sleep Apnea Syndromes / Q000175:diagnosis*