Polysomnography is a more comprehensive examination than polygraphy, aimed at confirming a diagnosis of sleep apnea and assessing its severity (number, duration and severity of apneas and hypopneas). This sleep recording takes place over one night or one night and one day. It not only studies the electrocardiogram and respiratory movements, but also (thanks to electrodes) various parameters enabling sleep quality to be analyzed: brain activity, muscular activity of the chin and legs, eye movements.[1]
[1] https://www.ameli.fr/assure/sante/themes/apnee-du-sommeil/symptomes-diagnostic-evolution