Sudden disruptions of brain function known as "strokes" are the result of either bleeding or infarction. Bleeding in the brain tends to have a better prognosis than does infarction of brain if one survives the initial event. Bleeding results from the bursting of weakened abnormal blood vessels -- either from an aneurysm, or in Sen Johnson's case an abnormal tangle of blood vessels (arterio-venous malformation, or AVM) that was present when he was born (i.e. congenital). Blood then escapes into the space around the outside of the brain (sub-arachnoid hemorrhage), and sometimes also produces a concentrated space-occupying clot within the substance of the brain in the region of the AVM. This is to be contrasted to an infarction of the brain, which is caused by an obstruction of blood flow within an artery that supplies a region of brain. Death of that region occurs fairly quickly as a result of lack of oxygen, glucose, and impaired removal of waste products. In contrast, following a bleed, the affected region of brain may cease functioning as a consequence of physical distortion, local metabolic changes, or other reasons -- but dysfunction of that region of brain doesn't necessarily imply its permanent loss.
Thus recovery from a bleed is quite different from recovery from an infarct. It takes a lot longer to know what won't recover. Following an infarct, we usually can have a reasonable idea of what magnitude of permanent deficity there is likely to be from the neurologic examination and the findings on MRI scans of the brain. Much of the remaining uncertainty will be resolved by the pattern of improvement over the next few days to weeks. This short term recovery comes with resolution of local swelling. Longer-term recovery from an infarct results from other regions of brain taking over the functions lost. Following a bleed there may, or may not, be a substantial problem with function of the brain region affected. Recovery after a bleed is generally better than that after an infarct of similar size. Sometimes recovery can be absolutely stunning despite substantial early deficit. Senator Johnson's relative youth and vigor are an important factor here. Recovery after a bleed can take a long time, though -- usually measured in weeks to months, or even a year. So it isn't easy to postulate that recovery won't happen until one allows for this much time.
What we've heard so far, if true, is enough to make me fairly confident that he will be physically able to vote as a senator, and probably fairly soon. Whether or not he will have all the complicated intellectual capacity necessary to being an effective legislator may take a lot longer to know. The initial symptom of a language disorder leads me to guess that the AVM was in the left parietal region, where many language functions are controlled. The local injury to brain of the bleed and surgery could be responsible for anywhere from subtle to substantial cognitive problems – unfortunately, we can only wait. It is probably worth noting that more than a few senators probably have cognitive deficits that are well hidden from the voting public.
A political question. If he is unable to vote, but does not resign, this changes the Senate to 50 to 49, and the Dems retain control, no?
I'm a first-time poster, but long-time lurker and admirer of the DK community. Its interesting that my specialty has had a major roll in the politics of the last couple years! My last comment was on Schiavo...