Procedures

Electroencephalography (EEG) is an electrophysiological monitoring method to record electrical activity of the brain. It is typically non-invasive, with the electrodes placed along the scalp, although invasive electrodes are sometimes used such as in electrocorticography. EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain. In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a period of time, as recorded from multiple electrodes placed on the scalp. Diagnostic applications generally focus either on event-related potentials or on the spectral content of EEG. The former investigates potential fluctuations time locked to an event like stimulus onset or button press. The latter analyses the type of neural oscillations (popularly called "brain waves") that can be observed in EEG signals in the frequency domain.

EEG is most often used to diagnose epilepsy, which causes abnormalities in EEG readings. It is also used to diagnose sleep disorders, depth of anaesthesia, coma, encephalopathies, and brain death. EEG used to be a first-line method of diagnosis for tumours, stroke and other focal brain disorders, but this use has decreased with the advent of high-resolution anatomical imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT). Despite limited spatial resolution, EEG continues to be a valuable tool for research and diagnosis. It is one of the few mobile techniques available and offers millisecond-range temporal resolution which is not possible with CT, PET or MRI.

Electromyography and nerve conduction studies: These are diagnostic tests of the peripheral nervous system, especially useful in evaluating diseases of the muscles, nerves, and nerve roots. Records electrical activity of the muscles and the passage of them along nerves in the limbs. Most nerve-muscle disorders that occur fall into one of two types of categories, morphologic or physiologic, which can be seen within the motor unit. These disorders can either be acute or have a slow developing nature.

Polysomnography is a comprehensive recording of the biophysiological changes that occur during sleep. It is usually performed at night, when most people sleep, though some labs can accommodate shift workers and people with circadian rhythm sleep disorders and do the test at other times of day. The PSG monitors many body functions, including brain activity (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG), and heart rhythm (ECG), during sleep. After the identification of the sleep disorder sleep apnea in the 1970s, the breathing functions, respiratory airflow, and respiratory effort indicators were added along with peripheral pulse oximetry.

CPAP:  For moderate to severe sleep apnea, the most common treatment is the use of a continuous positive airway pressure (CPAP) or automatic positive airway pressure (APAP) device.  These devices splint the person's airway open during sleep by means of pressurized air. The person typically wears a plastic facial mask, which is connected by a flexible tube to a small bedside CPAP machine.

With proper use, CPAP improves outcomes.   Whether or not it decreases the risk of death or heart disease is controversial with some reviews finding benefit and others not. This variation across studies might be driven by low rates of compliance—analyses of those who use CPAP for at least four hours a night suggests a decrease in cardiovascular events.  Evidence suggests that CPAP may improve sensitivity to insulin, blood pressure, and sleepiness.  Long term compliance, however, is an issue with more than half of people not appropriately using the device.

Although CPAP therapy is effective in reducing apneas and less expensive than other treatments, some people find it uncomfortable. Some complain of feeling trapped, having chest discomfort, and skin or nose irritation. Other side effects may include dry mouth, dry nose, nosebleeds, sore lips and gums.

Evoked potentials: Diagnostic test evaluating specific tracts of the central and peripheral nervous system. May include visual, auditory, or somatosensory evoked potentials. These record the electrical responses of the brain and spinal cord to the stimulation of the senses.