Changes in respiratory disorder parameters during the night in patients with obstructive sleep apnoea

Patients with OSA frequently experience cardiovascular events, especially late at night. This phenomenon raises the possibility that respiratory disorders are progressively aggravated during the course of nocturnal sleep. To test this hypothesis, we investigated the changes in respiratory disorder parameters occurring during the night in patients with OSA, in the supine position and in all sleep positions.

Thirty consecutive patients with OSA were enrolled in the study and categorized into those with moderate OSA (n = 12; AHI <40 events/h) and those with severe OSA (n=18; AHI ≥40 events/h). To identify the time during the sleep period at which changes in respiratory disorder parameters were most pronounced, AHI, mean duration of apnoea and average SaO(2) were assessed during the early, middle and late segments of sleep, in the supine position and in all sleep positions.

AHI decreased significantly with time during the course of the total sleep period, and especially during non-rapid eye movement (NREM) sleep. In the group with severe OSA, prolongation of the mean duration of apnoea and the decrease in average SaO2 were also significant in the late segment of sleep in the supine position, especially during NREM sleep.

In patients with severe OSA, there was progressive prolongation of the mean duration of apnoea late at night and this was associated with aggravation of hypoxia in the supine position during NREM sleep. This phenomenon may contribute to the remarkable rise in blood pressure early in the morning, possibly increasing the vulnerability of these patients to cardiovascular events.