There is no reliable way to determine who will have an intracranial bleed post-treatment versus who will not. In those with findings of savable tissue on medical imaging between 4.5 hours and 9 hours or who wake up with a stroke, alteplase results in some benefit.Its use is endorsed by the American Heart Association, the American College of Emergency Physicians and the American Academy of Neurology as the recommended treatment for acute stroke within three hours of onset of symptoms as long as there are no other contraindications (such as abnormal lab values, high blood pressure, or recent surgery). This position for tPA is based upon the findings of two studies by one group of investigators which showed that tPA improves the chances for a good neurological outcome. When administered within the first three hours thrombolysis improves functional outcome without affecting mortality. 6.4% of people with large strokes developed substantial brain bleeding as a complication from being given tPA thus part of the reason for increased short term mortality. The American Academy of Emergency Medicine had previously stated that objective evidence regarding the applicability of tPA for acute ischemic stroke was insufficient. In 2013 the American College of Emergency Medicine refuted this position, acknowledging the body of evidence for the use of tPA in ischemic stroke; but debate continues. Intra-arterial fibrinolysis, where a catheter is passed up an artery into the brain and the medication is injected at the site of thrombosis, has been found to improve outcomes in people with acute ischemic stroke.
Signs and symptoms
Fear, discomfort or anxiety may be triggered both by the presence and the anticipation of the specific object or situation. The main behavioral sign of a specific phobia is avoidance. The fear or anxiety associated with specific phobia can also manifest in physical symptoms such as an increased heart rate, shortness of breath, muscle tension, sweating, or a desire to escape the situation. Causes
The exact cause of specific phobias is not known. The mechanisms for development of specific phobias can be distinguished between innate (genetic and neurobiological) factors, and learned factors. In neurobiology, one explanation proposed for specific phobia is that the typical activation of the amygdala in response to stimuli may be exaggerated due to pathological changes. According to this theory, a deficiency in amygdala habituation may also contribute to the persistence of non-experiential phobia. Certain phobias that are less lethal (e.g. dogs) seem to be more frequently observed and easily acquired in comparison to potentially lethal fears which are more relevant to developed human society (e.g. cars and guns). This was theorised to be due to biological adaptation being passed through evolution which makes recent threats less prone to easy acquisition. However, a 2014 study found evidence against this evolutionary theory, which stated: "Our findings are inconsistent with the hypothesis that fears/phobias of individual stimuli result from genetic and environmental factors unique to that stimulus. Instead, we observed substantial sharing of risk factors across individual fears."