E-Mail IMAGE: Data available from clinical sleep studies could be utilised more extensively by, for example, paying closer attention to heart rate and heart rate variability. view more Credit: UEF / Raija Törrönen Longer nocturnal respiratory events in patients with obstructive sleep apnoea (OSA) cause higher immediate heart rate variability, and greater changes in beat-to-beat intervals are associated with reduced daytime alertness, according to new research from the University of Eastern Finland. Obstructive sleep apnoea affects approximately 1 billion people worldwide. It is one of the most prevalent sleeping disorders, putting a great strain on national economies and on public health. Nocturnal respiratory events, be they complete or partial blocking of the airways, often cause repeated oxygen desaturations and interrupted sleep in patients with OSA, leading to abnormal nervous system function.