Polysomnographic Data Acquisition and Monitoring
Acquisition settings
The amplifier must be set so the signals of interest are faithfully captured. EEG is sampled at a minimum of 200 Hz and commonly 500 Hz; the Nyquist principle requires sampling at least twice the highest frequency you intend to record, which is why anti-aliasing filters exist. Typical filter settings: EEG and EOG low-frequency 0.3 Hz, high-frequency 35 Hz; EMG low 10 Hz, high 100 Hz; ECG low 0.3 Hz, high 70 Hz. EEG sensitivity is conventionally 7 µV/mm, with a 30-second page (time base 30 mm/s) so one screen equals one scoring epoch. Pulse oximetry averaging is typically 3 seconds - longer averaging falsely smooths desaturations.
Live monitoring
The technologist is not a passive observer. Verify each channel is physiologic before lights out (ask the patient to blink, swallow, breathe deeply, move a foot). Watch for sweating (slow rolling baseline), 60-Hz interference (ground or impedance problem - a notch filter hides but does not fix it), pulse and ECG artifact, and lost signals. Check the plethysmographic waveform, not just the saturation number: a bad waveform yields a bad SpO2. Note every intervention, position change, and oxygen adjustment with a time stamp so the scorer can reconcile the record.
Traps in questions
Changing sensitivity alters displayed amplitude, not the underlying frequency. Filtering out 60 Hz does not eliminate the source. A flat channel usually means a disconnected lead or a failed sensor, not a sleeping patient.
Rule of thumb
Time-stamped, real-time technologist notes are worth more than hours of retrospective video review - annotate as it happens.