Sleep physicians have two well-established objective tools at their disposal to measure daytime sleepiness.
Multiple Sleep Latency Test (MSLT)
The MSLT measures daytime sleepiness in a sleep lab after a whole-night polysomnography (PSG), which evaluates sleep and identifies sleep disorders such as obstructive sleep apnea. In the morning, the patient remains connected to the polygraph to measure brain activity, eye movement and muscle tonus during four to five 20-minute nap opportunities at 2-hour intervals. The time to sleep onset (if it happens at all) during these opportunities and the sleep stage reached are recorded and compared to normative values. The process yields a validated measure of daytime sleepiness.
Maintenance of Wakefulness Test (MWT)
The MWT is another measure of daytime sleepiness that is also used after a whole-night PSG. Four to five events at 2-hour intervals allow the patient to sit quietly in an armchair in dim light for 45 minutes. He/she is asked expressly to make a maximum effort to remain awake. As with the MSLT, the times to sleep onset (if it happens at all) are recorded, along with the sleep stage reached. Those measurements are compared to normative values to evaluate the degree of daytime sleepiness.