Table 2.

Qualitative sleep disorders and cardiovascular risk

Definition	Description	Association with cardiovascular risk factor	Association with cardiovascular events
Insomnia	Quantitative and qualitative sleep disorder characterized by difficulty falling asleep, frequent nocturnal interruption, early awakening, accompanied by daytime symptoms related to this condition	↑↑	↑↑
Fragmented sleep	Qualitative alteration of sleep characterized by frequent and brief awakenings	↑=	↑↑
Sleep disordered breathing	A group of clinical conditions characterized by abnormal breathing during sleep. They include: obstructive apnoeas, central apnoeas, hypoventilation and sleep-related hypoxemia	↑↑	↑↑
Obstructive sleep apnoea	Episodes of partial or complete closure of the upper airways during sleep leading to respiratory interruption, desaturation and awakening. If accompanied by daytime symptoms, it is called “obstructive sleep apnoea syndrome”	↑↑↑↑	↑↑↑
Periodic limb movements in sleep	Repetitive contraction of the upper or lower limbs during sleep, which often lead to frequent awakenings and fragmented sleep	=	=
Restless leg syndrome	Motor restlessness, uncontrolled movements and contractions of the lower limbs that occurs in the phases of falling asleep, sleep and awakening. When conscious, the patient feels a sensation of discomfort in the legs, accompanied by the need to move them continuously	↑↑	↑
Circadian rhythm sleep disorders	Alterations caused by the desynchronization between the endogenous sleep–wake rhythms and the normal external light–dark cycle, from endogenous causes (delayed or advanced sleep phases) or exogenous (intermittent night shifts)	↑↑↑	↑↑

The arrows and the equal sign indicate the strength of the association (equal sign: no association; one, two, three, or four arrows: mild, moderate, strong, very strong association). See text for details