Table 2.
Feature Definition and Weight Assignment
| Input | Feature Name | Description | Feature Weights |
|||
|---|---|---|---|---|---|---|
| Obstructive |
Central |
|||||
| Present | Absent | Present | Absent | |||
| Effort | Paradoxical breathing (19) | Paradoxical motion of the ribcage and/or abdomen during a sequence of small breaths | 1 | −1 | −1 | 2 |
| Airflow | Flow limitation (18) | Inspiratory flow limitation | 5 | −2 | −5 | 3 |
| Airflow | Prolonged inspiration (12) | Inspiratory time is prolonged relative to baseline inspiratory time | 3 | −1 | −1 | 2 |
| Airflow | Sequence of flow limitation | Flow limitation on adjacent breaths | 3 | −1 | −1 | 0 |
| Airflow | Sudden termination of hypopnea (27) | Sudden increase in flow after a sequence of small breaths | 3 | −1 | −1 | 2 |
| Airflow | Periodic breathing (10, 28) | Crescendo pattern of airflow | −1 | 0 | 3 | 0 |
| Snore | Inspiratory snoring (3) | Inspiratory snoring on reduced-flow breaths that disappears with resumption of flow | 2 | 0 | −1 | 2 |
| SpO2 | Type of desaturation | Symmetric desaturation ⩾ 3% | −1 | 0 | 3 | 0 |
| Asymmetric desaturation ⩾ 3% | 3 | 0 | −1 | 0 | ||
| Effort | Absence of effort* (3) | Absence of effort during apnea | −10 | 15 | 15 | −10 |
Definition of abbreviations: Small breaths = breaths with an amplitude of less than 85% of normalized breath amplitude; SpO2 = oxygen saturation using finger pulse oximetry.
None of the features required manual scoring of either sleep/wake or respiratory events. For each breath, two scores are obtained (obstructive and central).
*
“Absence of effort” feature is only used in case of imputed breaths during apneas. Effort is absent if ΔEffort during apnea is less than 30% of ΔEffort preceding the apnea (see online supplement for detailed derivation). ΔEffort is defined as maximum effort − minimum effort during a breath (start of inspiration to end of expiration).