| A | B |
|---|
| Rapid eye movements | Eye movements during waking and R that are sharply peaked, with the first part of the wave movements lasting less than 0.5 seconds. |
| Reading eye movements | A distinctive pattern of eye movements that occur when scanning a page of text. |
| REM sleep behavior disorder (RBD) | A disorder in which the patient acts out dreams, frequently resulting in injury. |
| Respiratory effort related arousals (RERA) | A reduction of airflow that results in an arousal. |
| Respiratory inductance plethysmography (RIP) | A measure of respiratory effort that uses a coiled wire sewn into an elastic belt. |
| Rhythmic anterior theta (RAT) | Rhythmic 5 - 7 Hz EEG activity in the frontal channel used to score Ni sleep in children. |
| Rhythmic movement disorder (RMD) | Movement disorders more common in children and include head banging, body rocking and head rolling. |
| Sampling rate | The number of voltage measurements per second used to convert the continuous sleep study signals into a digital signal. |
| Sawtooth waves | Sharp or triangular waves with a frequency of 2 to 6 Hz usually largest in the central channels. |
| Sino-atrial node | The heart's pacemaker located in the right atrium of the heart. |
| Sleep onset | In a sleep study, the time between lights out and the first epoch of any stage other than W. |
| Sleep spindles | A train of waves lasting at least 0.5 seconds with a frequency of 11 to 16 Hz, largest in the central leads. |
| Slow eye movements | Eye movements around sleep onset with the initial part lasting more than 0.5 seconds. |
| Slow wave activity | EEG activity in the range of 0.5 to 2 Hz with amplitude from zenith to nadir of more than 75µV. |
| Sustained | In scoring cardiac arrhythmias during sleep, sustained tachycardia or bradycardia lasts at least 30 seconds. |
