| Background Male erectile dysfunction (ED) is defined by the inability to attain or maintain penile erection sufficient for satisfactory sexual intercourse . It has been estimated to affect 1.5 hundred million men in the world , including about 30 million in the United States. Among England and France, 30～40% of men have ED. More than half of men , 40～70 years old , in China disturbed by ED. So, ED is a common disease . With the improvement of life quality and changes in sex, healthy sex has been concerned by more and more people . Recently, a great quantity of people complaints of ED. Some of which were soldiers or technican in a bid to help Tibet, some suffered from pulmonary disease, such as sleep apnea syndrome (SAS). It is the hypothesis that chronic hypoxia can impair male sex function.Penile erection is a neurovascular event modulated by psychological factors and hormonal status. On sexual stimulation, nerve impulses cause the release of neurotransmitters from the cavernous nerve terminals and of relaxing factors from the endothelial cells in the penis, resulting in the relaxation of smooth muscle in the arteries and arterioles supplying the erectile tissue and a severalfold increase in penile blood flow. Within the muscle, nitric oxide activates a soluble guanylyl cyclase, which raises the intracellular concentration of cyclic guanosine monophosphate (GMP). Cyclic GMP in turn activates a specific protein kinase, which phosphorylates certain proteins and ion channels, resulting in the opening of potassium channels and...
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