A Level III Study, also called a "Cardio-respiratory" study is performed while you sleep outside of the lab, such as at home. It does not actually monitor sleep because it does not have an EEG to monitor brain waves. It has tiny tubes in the nostrils that monitor airflow, a belt around the chest to monitor breathing effort, and an oximeter on the finger to monitor blood oxygen levels. The airflow pressure transducer sensor also gives a signal that indicates snoring sounds.
This test can be used for the diagnosis of sleep apnea when the condition is moderate to severe. Because it does not monitor the brain waves of sleep, it may underestimate the arousals caused by mild sleep apnea. Thus it may not be as sensitive as a nocturnal polysomnogram performed in the sleep lab. However, when the test is positive for sleep apnea, it is very useful.