Many people experience sleep apnea; it occurs especially in those sleeping on their backs and snoring, when the tongue and soft parts of the upper airway may fall back and partially block the airway. This causes a period of intermittent breathing known as obstructive sleep apnea (OSA).

From the University of Colorado Health Sciences Center comes a report on the effect of sleep apnea on hypertension. As the period between breaths increases, the amount of oxygen in the blood may fall. This sets off the body's 'fight or flight' mechanism, which is a reflex controlled by the sympathetic nervous system. When that happens, the vascular system clamps down and raises blood pressure in an attempt to get the body ready for action.

When normal breathing resumes, blood pressure levels return to normal. Hypertension in awake patients is also associated with increased activity of the sympathetic nervous system. Individuals who have not been identified as OSA patients exhibit this same sympathetic response. A common respiratory therapy, called continuous positive airway pressure, or CPAP, has been shown to lower blood pressure in some hypertensive OSA patients. Effective CPAP therapy moderates this hypertensive effect even in awake patients with undiagnosed OSA.

Source: Zwillich, CW. Obstructive sleep apnea causes transient and sustained systemic hypertension. Int J Clin Pract 1999;53(June):301-5. (Abs)