Think about the blood vessels in your brain like streets in a growing and changing city. The blood vessels are critical to the movement of necessary nutrients to brain cells and the removal of undesirable toxins and waste products. In the city, the thoroughfares (arteries) move large volumes of traffic whereas the small side streets (capillaries) are able to penetrate deep into neighbourhoods. Arteries and capillaries are the streets of the brain and make sure blood flows to the energy-consuming brain cells in every nook and cranny.
For the brain challenged by trauma, infection, stroke, dementia, Parkinson’s, multiple sclerosis and other disorders, density and quality of blood vessels is critical. Fortunately, the brain has the ability to modify its own blood vessel network just like the city can respond to growth of new suburbs by widening and building new streets. Angiogenesis is the sprouting of new capillaries from preexisting blood vessels while arteriogenesis is the increase in diameter of collateral (neighbouring) vessels in response to blockages in vessels that are the main suppliers of an area of tissue.
Most of what I am discussing here is reviewed exceptionally well by Ergul and group from University of Georgia in the journal Stroke (2012) and Schmidt and colleagues from Charité University Medicine Berlin, Germany in the journal Cerebrovascular Diseases (2013). So for more detail read those. I will focus on angiogenesis since it is believed to be the primary method of growing new blood vessels in the brain.
So why is angiogenesis important? Angiogenesis increases blood flow to brain tissue which is especially important after a stroke or other injury to the brain. This has three beneficial effects 1. Improving the survival of vulnerable cells in the boundary zone around the damaged area, 2. Removing debris and unwanted chemicals and enzymes from the area and, 3. Creating an environment ripe for growth of new synapses and neurons (neuroplasticity). (Read my previous posts on Neuroplasticity for background)
Exercise and Physical Therapy-induced Angiogenesis
What we know from animal studies is that exercise before a stroke, builds tolerance to brain ischemia (is-key-me-ya: lack of blood supply to a region of the brain). Animals engaging in regular moderate exercise before a stroke have less damage and better recovery than inactive animals. After a stroke or brain injury, exercise (and physical therapy) stimulates angiogenesis and improves physical and cognitive functioning.
So how much exercise is required to induce angiogenesis? My colleagues and I have just completed a review of studies examining the effects of exercise on angiogenesis after stroke. Of the 6 studies we examined, all were in animal models of stroke (no human studies) and they all used forced wheel or treadmill running. The studies showed that two weeks of daily, moderate to high intensity exercise (walking or running) beginning 1-3 days following stroke resulted in increased markers of angiogenesis. Although this is exciting, it is difficult to translate to the real world setting. First of all, the strokes in animals are very small, sometimes only a few mm. wide, not at all like stroke rehabilitation in humans. Furthermore, it is not practical to ask stroke patients to walk on a treadmill one or two days after stroke. Most are very ill and sometimes not able to sit up, let alone walk on a treadmill. Clearly the timeline in animals after stroke and in humans is very different, but how different we don’t know. A reasonable approach is to make sure aerobic training is included in the rehabilitation process. For the physiotherapist, begin building tolerance to exercise and get the heart rate above baseline gradually increasing intensity each day. Set goals and try to get family members involved. When the patient is able to walk with help, start using your gym equipment (arm ergometer, recumbent bike, etc) adapting them to support the hemiplegic side as necessary. For the patient and family, try not to spend too much time in bed but if you are there, do your exercises (bridging, lifting your legs and so on). Find out from your therapist how intense you should be training and get help to set up a program. Ask for times you can go to the physio gym to do your aerobic workout.