Other Diagnostic Approaches

Actigraphy refers to methods using miniaturized computerized wristwatch-like devices to monitor and collect data generated by movements. Most actigraphs contain an analog system to detect movements. In some devices, a piezoelectric beam detects movement in two or three axes and the detected movements are translated to digital counts accumulated across predesigned epoch intervals (e.g., 1 minute) and stored in the internal memory. While these have been very useful in determining disorders of the sleep-wake rhythm (75) and are even quite good in estimating sleep time in patients with sleep apnea (76), they cannot really be used to diagnose sleep apnea (77).

Other surrogate markers have been used to detect sleep apnea including cyclical changes in heart rate on 24-hour Holter monitoring (78) and pulse transit time (79-81). While both of these reflect physiologic changes accompanying obstructive events, the sensitivity and specificity of these are insufficient (owing to wide extremes in spectrum of disease) to warrant routine use.

In assessing the validity and applicability of any ambulatory diagnostic system, several standards should be met (82). These include: (i) an independent blind comparison with a reference standard; (ii) an appropriate spectrum of patients; (iii) avoidance of work-up bias; (iv) methods for performing the test described in detail, allowing for duplication of the study; (v) adequate description of study population; (vi) adequate sample size (conservative estimate is that there should be greater than or equal to 200 patients in the study, approximately equally divided between those with and without the condition. This allows for confidence intervals of approximately ± 10% for estimates of sensitivity and specificity); (vii) avoidance of a selection bias—in the case of patients with sleep apnea, this means a consecutive sample of patients referred to a sleep clinic rather than those referred to a sleep laboratory, avoiding filtering of patients; and (viii) adequate description of study setting and appropriate setting—for instance, basic descriptors of the study should include whether it is a tertiary referral sleep clinic or a community sleep clinic, types of physicians referring to the sleep clinic, population base, types of patients, and so on.

Because most portable monitors are intended for use outside of the sleep laboratory, this is the setting in which they should be studied. Still, there are very few studies that meet these criteria.

Sleep Apnea

Sleep Apnea

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