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A normal results from relaxation of the muscles within the penis and an increase in arterial blood flow to the penis. The resulting swelling of the muscles compresses the penile veins, thus trapping blood within the penis. After ejaculation, the associated adrenaline surge constricts the arteries and relaxes the pressure on the veins, which leads to loss of erection (detumescence).
may be spontaneous or caused by medical treatment (iatrogenic). Some 35 per cent of cases are idiopathic (unknown cause) and 21 per cent are associated with drug therapy or Trauma accounts for 21 per cent and blood disorders 8 per cent. Medically, the important issue is whether the condition is associated with high blood flow when there is little risk of tissue damage, or low blood flow when the risk of damage is higher.
Although controversy exists over the way in which , a widely accepted view is that results from injury or damage to the mechanism that produces detumescence of the penis. This damage can be caused by:
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blood disorders, particularly sickle cell disease, myeloma, thalassaemia and leukaemia.
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trauma, both accidental and surgical.
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damage to the nervous system, especially spinal cord injuries, but rarely multiple sclerosis or diabetes (this usually involves an element of overstimulation, resulting in high blood flow to the penis, as well as defective detumescence).
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drugs used to treat impotence (particularly those given by injection into the penis):
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papaverine
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E1 (alprostadil), which causes increased blood flow by dilating blood vessels in the penis (very rare if given into the urethra or urine tube in the penis)
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phentolamine
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sildenafil (Viagra) virtually unknown unless combined with other medication, eg injections such as prostaglandin.
other drugs, especially in overdose.
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: trazodone and chlorpromazine
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blood pressure drugs: prazosin and nifedipine
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anticoagulants: warfarin and hepari
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miscellaneous: omeprazole, metoclopramide, and tamoxifen
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alcohol
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