Testing at home can be done using oximetry alone or oximetry with airflow (sensors at nose or mouth) and effort (belts around chest and abdomen) information. Other data can be gathered at home, but the information becomes progressively more expensive to obtain, more prone to problems, and more difficult to interpret. Usually, EEG (brain) data is not collected, so it’s not clear when the patient is asleep or awake or how the data correlates with the sleep state.
Patients must be carefully screened for home sleep testing. The elderly, children/teenagers, patients with cardiopulmonary or neurological problems, those with little if any snoring, uncooperative patients, and patients with other potential sleep problems (parasomnias, narcolepsy, periodic leg movements) are not good candidates for home testing. Patients who have had prior problems with testing or treatment of sleep apnea are also not good candidates for home sleep testing.
Portable home testing is more for the young or middle-aged obese patient who snores loudly, stops breathing at night, and is inappropriately sleepy during the day. Thus, there is a strong suspicion of “pure” obstructive sleep apnea. If this patient is otherwise healthy (no cardiopulmonary or neurological disease, no use of alcohol or drugs, and no suspicion of other sleep problems), then Obesity Hypoventilation Syndrome (shallow breathing) and severe hypoxemia (low oxygen) should be ruled out, and the patient is a candidate for portable testing to diagnose sleep apnea. Home sleep testing does not rule out sleep apnea (though some insurances misinterpret this), but can rule it in. It is also problematic to rule out sleep apnea using home testing in a symptomatic patient with a "critical occupation" (pilots, truck or bus drivers, etc.). If sleep apnea is found, then documented treatment can follow. But if the test is negative, then many authorities would still want a polysomnogram monitored by a sleep technologist in a sleep lab setting. The same line of thinking applies to a dangerously symptomatic (obese, loud snoring, stops breathing, fell asleep while driving) patient with a negative home test. With home sleep testing, patients usually need to apply the sensors themselves and keep them on the whole night, so it is not rare to end up with inadequate data collection.
Treatment is another matter, Here, the physician can make an educated guess as to the PAP (positive airway pressure) settings or whether an “auto-PAP” can be used. An auto-PAP is a “smarter” (technologically advanced) machine that decides its own settings within a range prescribed by the physician. Close follow-up is necessary. Also, the physician needs to guess which mask (nasal pillows, nasal mask, or full face mask — covering nose and mouth) should be used. In the overnight polysomnogram, both the settings on the PAP machine and the mask are carefully selected and proven to work.
Many patients refuse to go to a facility to undergo an overnight study, while others may not have the proper insurance or financial resources. However, given the number and types of available tests, more expertise in the field of sleep medicine is required, not less. The physician must know which test to use, under which circumstances, and in which patient, and then weigh the validity of the results.
An abnormal overnight oximetry (assuming the patient was mostly asleep) by itself only means that the patient’s oxygen saturation dropped during the night. This could be due to obstructive or central sleep apnea (or a mixture of the two), or to lung disease, heart disease, neurological disease, drugs, obesity itself, infection, or technical problems with the study creating artifacts. There are certain characteristic desaturation patterns of sleep apnea, but these aren't specific without data also showing the airflow obstruction causing these oxygen desaturations. Clearly, the study itself is not as important as the physician interpreting the study, who should have considerable experience and knowledge about sleep medicine. (See Instructions for Oximetry under the FORMS tab)
(See also www.sleepeducation.com).