Stroke is not a single disease, but rather a pattern of symptoms which arises when a blood clot or ruptured blood vessel obstructs blood flow to parts of the brain and deprives its cells of vital oxygen.
The brain consumes about 20 percent of the body's oxygen and 70 percent of its glucose, though representing just two to three percent of its weight. This high metabolic rate, sensitivity to changes in blood flow, and dependence on continuous blood flow are what make stroke so dangerous. If blood supply to the brain is interrupted for as little as four minutes, brain cells begin to die. They are not replaced.
Types of Stroke
There are three main types of stroke: those caused by (1) hemorrhage, (2) thrombosis, and (3) embolism.
(1) Hemorrhage, causing about 20 percent of strokes, occurs when a tear in a cerebral (brain) artery bleeds into the brain or into the space between the brain and skull.
(2) Thrombosis occurs when a blood clot forms within a brain or neck artery, cutting off blood supply and causing a death of brain tissue, resulting in about 45 percent of stroke occurrences.
Thrombotic and embolic strokes are both ischemic, that is, caused by lack of blood flow to the brain. Ischemic strokes generally result from a decline in vascular health. Clots do not usually form in healthy arteries but tend to form at or adjacent to an area damaged by atherosclerosis, a thick, irregular deposit on the inner lining of arteries.
(3) Embolism occurs when a blood clot forms elsewhere in the body, such as in the heart or a neck artery, and is carried to the brain, causing another 25 percent of ischemic stroke occurrences.
The cause of the remainder of ischemic strokes, (about 25 percent) is not clear, though the latest findings indicate that many appear to be due to embolism. Refinements in scanning technology will make this clearer in the future.
The Impact of Stroke
- Just over one percent of the Canadian population, or about 300,000 persons, are acute or chronic stroke survivors.
- Every year an estimated 50,000 Canadians suffer a stroke. Of these, about a third die within a year and most survivors are left with permanent disabilities.
- Brain damage due to stroke is the leading cause of neurological disability.
- Stroke is the largest cause of unemployable disability (only about ten percent of stroke survivors return to their previous level of activity).
- Stroke is the third leading cause of death - in 1991, about 15,000 deaths, or over 7 percent of deaths in Canada that year.
- The annual total cost in medical care and lost earnings is now over four billion dollars in Canada.
- Clearly, stroke has a huge impact on many lives.
Incidence and Mortality of Stroke
The impact of stroke on a population is generally measured in two ways: the incidence, or number of new cases during a given time period, and mortality, or the number of deaths caused by stroke during that period.
Incidence: The decline in stroke incidence first noted in the 1950s coincided with increasingly effective management of hypertension (high blood pressure) and has continued to this day. Improved quality of health care has also had a beneficial effect on the incidence of stroke, its severity, and on the outcome of treatment.
Mortality: Canada has one of the lowest stroke mortality rates in the world; there has been a steady decline in the death rate from stroke since the 1950s, in all regions of the country. Since 1961, stroke mortality rates in Canada have declined 57 percent in men and 65 percent in women. Canada's declining rates of untreated high blood pressure parallel lower rates of mortality.
Despite these declines, as Canada's population ages the number of people affected by stroke will increase. Stroke remains a major challenge for the health care system, despite improved disease prevention, new drug and surgical treatment, and health promotion. The need for an organization like SRC is clear.