Autonomic Arousals in Sleep Related Breathing Disorders: A Link Between Daytime Somnolence and Hypertension?

WE HAVE READ WITH EXTREME INTEREST THE RECENT ARTICLE PUBLISHED ON YOUR JOURNAL BY KAPUR ET AL.1 THE FINDINGS OF THIS STUDY EMPHASIZE the important role of daytime sleepiness in determining the risk of hypertension in patients with sleep-related breathing disorders. In particular, in Figure 1 the authors clearly show that only in patients with daytime somnolence there is an increase in the risk of hypertension, in parallel with the increase in apnea-hypopnea index. The important and clinically relevant contribution carried by this excellent study, is the identification of daytime sleepy patients as a group at greater risk of cardiovascular events. However, this study was not designed to investigate the mechanisms responsible for the association between sleepiness and hypertension, an important issue which thus remains unresolved. We have hypothesized that excessive daytime sleepiness (EDS) in patients with sleep related breathing disorders may be associated with subcortical arousals. Apnea-related autonomic arousals may not produce detectable EEG changes. However, since they involve brainstem neurons controlling both sleep/ vigilance and cardiovascular regulation, they may simultaneously trigger daytime somnolence and appreciable changes in cardiac autonomic regulation. Therefore alterations in cardiac autonomic control might be considered as markers of the occurrence of autonomic arousals in patients with sleep related breathing disorders. These alterations can be easily assessed by estimating changes in spontaneous baroreflex sensitivity2 or in specific indexes of heart rate variability3 from polysomnographic recordings.