problems, decreased cognitive functioning, and reduced quality of life. other associated problems include cerebrovascular diseases (hypertension, coronary artery disease, and stroke) and diabetes. these problems could be, at least in part, caused by risk factors of osa. central sleep apnea main article: central sleep apnea screenshot of a psg system showing a central apnea. in pure central sleep apnea or cheyne–stokes respiration, the brain's respiratory control centers are imbalanced during sleep. blood levels of carbon dioxide, and the neurological feedback mechanism that monitors them, do not react quickly enough to maintain an even respiratory rate, with the entire system cycling between apnea and tachypnea, even during wakefulness. the sleeper stops breathing and then starts again. there is no effort made to breathe during the pause in breathing: there are no chest movements and no struggling. after the episode of apnea, breathing may be faster (tachypnea) for a period of time, a compensatory mechanism to blow off retained waste gases and absorb more oxygen. while sleeping, a normal individual is "at rest" as far as cardiovascular workload is concerned. breathing is regular in a healthy person during sleep, and oxygen levels and carbon dioxide levels in the bloodstream stay fairly constant. any sudden drop in oxygen or excess of carbon dioxide (even if tiny) strongly stimulates the brain's respiratory centers to breathe. in any person, hypoxia and hypercapnia have certain common effects on the body. the heart rate will increase, unless there are such severe co-existing problems with the heart muscle itself or the autonomic nervous system that makes this compensatory increase impossible. the more translucent areas of the body will show a bluish or dusky cast from cyanosis, which is the change in hue that occurs owing to lack of oxygen in the blood ("turning blue"). overdoses of drugs that are respiratory depressants (such as heroin, and other opiates) kill by damping the activity of the brain's respiratory control centers. in central sleep apnea, the effects of sleep alone can remove the brain's mandate for the body to breathe. normal respiratory drive: after exhalation, the blood level of oxygen decreases and that of carbon dioxide increases. exchange of gases with a lungful of fresh air is necessary to replenish oxygen and rid the bloodstream of built-up carbon dioxide. oxygen and carbon dioxide receptors in the blood stream (called chemoreceptors) send nerve impulses to the brain, which then signals reflex opening of the larynx (so that the opening between the vocal cords enlarges) and movements of the rib cage muscles and diaphragm. these muscles expand the thorax (chest cavity) so that a partial vacuum is made within the lungs and air rushes in to fill it. physiologic effects of central apnea: during central apneas, the central respiratory drive is absent, and the brain does not respond to changing blood levels of the respiratory gases. no breath is taken despite the normal signals to inhale. the immediate effects of central sleep apnea on the body depend on how long the failure to breathe endures. at worst, central sleep apnea may cause sudden death. short of death, drops in blood oxygen may trigger seizures, even in the absence of epilepsy. in people with epilepsy, the hypoxia caused by apnea may trigger seizures that had previously been well controlled by medications. in other words, a seizure disorder may become unstable in the presence of sleep apnea. in adults with coronary artery disease, a severe drop in blood oxygen level can cause angina, arrhythmias, or heart attacks (myocardial infarction). longstanding recurrent episodes of apnea, over months and years, may cause an increase in carbon dioxide levels that can change the ph of the blood enough to cause a respiratory acidosis. mixed apnea some people with sleep apnea have a combination of both types; its prevalence ranges from 0.56% to 18%. the condition is generally detected when obstructive sleep apnea is treated with cpap and central sleep apnea emerges. the exact mechanism of the loss of central respiratory drive during sleep in osa is unknown but is most likely related to incorrect settings of the cpap treatment and other medical conditions the person has. management the treatment of obstructive sleep apnea is different than that of central sleep apnea. treatment often starts with behavioral therapy. many people are told to avoid alcohol, sleeping pills, and other sedatives, which can relax throat muscles, contributing to the collapse of the airway at night. changing sleep position more than half of people with obstructive sleep apnea have some degree of positional obstructive sleep apnea, meaning that it gets worse when they sleep on their backs. sleeping on their sides is an effective and cost-effective treatment for positional obstructive sleep apnea. continuous positive airway pressure person using a cpap mask, covering only the nose cpap machine with two models of masks