Sleep disorders and cardiovascular risk: Focusing on sleep fragmentation

In this comment, we explored the link between sleep fragmentation and the cardiovascular risk, considering various sleep disorders and methodologies for assessing sleep fragmentation.It is generally known that sleep deprivation increases the cardiovascular (CV) and metabolic risk.Additionally, some data indicates that prolonged sleep is also associated with such risk. 1 In addition to sleep duration, sleep quality is also essential in the assessment of the CV risk.The continuity of sleep is one of its crucial features that contributes to effective rest and refreshment.Sleep may be interrupted by arousals and awakenings, which can result in prolonged wakefulness after sleep onset (WASO).Therefore, it is important to deter mine the threshold for the number of arousals and awakenings during sleep to consider them a normal phenomenon.According to the American Academy of Sleep Medicine (AASM) definition, an arousal is an abrupt shift in electro encephalography (EEG) frequencies, including alpha, theta and/or frequencies greater than 16 Hz (but not spindles), that lasts at least 3 s, with at least 10 s of stable sleep preceding the change. 2The scoring of arousals during rapid eye movement (REM) sleep requires a concurrent increase in the submental electro myography (EMG) lasting at least 1 s. 2 Arousals, which can be accompanied by respiratory events, periodic limb movements in sleep (PLMS) or sleep brux ism events, are usually followed by autonomic activation, resulting in increased heart rate and blood pressure.Nevertheless, they can also occur spontaneously or be elicited by pain, light, noise, or a change in temperature.The arousal index (ArI), counted as the number of arousals per sleep hour, is frequently considered to quantify sleep fragmentation. 3 Sleep fragmentation, character ized by repetitive interruptions of sleep, is one of the factors contributing to excessive daytime sleepiness.The apnea-hypopnea index (AHI) is generally considered an imperfect in dicator of obstructive sleep apnea (OSA) severity.It is strongly believed that oxygen saturation parameters (i.e., the mean oxygen saturation, the oxygen desaturation index (ODI), the nadir oxygen saturation, and the percentage of sleep with oxygen saturation <90%) are more effective predictors of CV complications than the index of respiratory events. 4It is worth noting that