| Deep Sleep | Refers to combined non-REM sleep stages 3 and 4 in sleep studies |
| Delayed sleep phase | A condition occurring when the clock hour at which sleep normally occurs is moved back in time in a given 24 hour sleep-wake cycle. The result is a temporarily displaced (delayed) occurrence of sleep within the 24 hour cycle. |
| Delta sleep | Stage(s) of sleep in which EEG delta waves are prevalent or predominant (sleep stages 3 and 4 respectively). |
| Delta waves | EEG activity with a frequency less than 4 Hz. In human sleep stage scoring conventionally the minimum criteria for scoring delta waves is 75 uV (peak-to-trough) amplitude and 0.5 second duration (2 Hz). |
| DENTAL DEVICE | see Mandibular Advancement Device. |
| DESATURATIONS | see Hypoxic Dips. |
| Diagnostic Sleep Study | Monitoring of several physiological activities in a sleeping individual. Usually performed to determine the absence or presence of a specific sleep disorder. The sleep study can occur in a sleep disorders center or in a patient's home with portable recording equipment. |
| Diaphragm | Large concave muscle attached to the rib cage at bottom of the chest (top of the abdomen). Inhalation occurs when diaphragm contracts. Exhalation is passive as the muscle relaxes. |
| DIAPHRAGM (die-er-fram) | Main muscle of breathing between the bottom of the chest and stomach; pulls the lungs out thus drawing in air. |
| DIMS | Disorders of Initiating and Maintaining Sleep |
| Diurnal | Active and wakeful in the daytime versus active in the nighttime. |
| DME | Durable Medical Equipment |
| DME - Durable Medical Equipment | Equipment such as wheelchairs and walkers which are prescribed for use by or on the order of a physician also includes CPAP and BI-Level machines. |
| DOES | Disorders of Excessive Somnolence |
| Drowsiness | Drowsy - quiet wakefulness occurring prior to sleep onset. |
| DSPS | Delayed Sleep Phase Syndrome |
| Dx | Diagnosis |
| Dyssomnia | A disorder of sleep or wakefulness; not a parasomnia. |
