Heat stroke, which conjures up an image of the burning desert, is primarily an urban disease, mostly affecting the old, the poor and minorities, the national Center for Disease Control finds in a study of the severe heat wave of 1980. The study is aimed at helping doctors identify factors that increase the risk of heat stroke, which occurs when body temperature rises above 105 degrees and no sweating occurs. Brain damage, kidney failure and death are some of the consequences. About 1,265 heat-related deaths were reported last year, compared with an average of about 200 a year. "Heat stroke rates in persons 65 or older were 12 to 13 times the rates in the remainder of the population," the CDC said.Poor people and blacks also had high rates of heat stroke, as did alcoholics, people with mental illness and people who could not take care of themselves, the report said. Certain antipsychotic drugs also contributed to heat stroke risk. The study found that old people do not adapt well to heat stress and caonnot dissipate the heat load in hot weather.They are also more likely to have underlying diseases which decrease their resistance to heat stress. Poor people also have a high rate of chronic disease, often resist or delay treatment and do not have air conditioners or fans. Although blacks and other non-whites had a high incidence of heat stroke, it was not clear whether race or low income was the determining factor.