Progressive arterial stiffness with age causes hypertension, a state of chronically raised blood pressure, which in turn damages sensitive tissues in the brain and other organs. Over time that means a loss of function and cognitive decline. Researchers here suggest that even without the increase in blood pressure, stiffness in larger blood vessels will redistribute pressure in a way that will harm cells near to smaller capillary vessels. What causes arterial stiffening? A combination of damage and dysfunction such as, for example: persistent cross-links degrade elasticity in the extracellular matrix of blood vessel walls; senescent cells and the chronic inflammation that they cause creates calcification of tissue, as well as poor function of smooth muscle tissue responsible for blood vessel constriction and dilation; mitochondrial dysfunction in smooth muscle cells also contributes.
The fact that human memory is deteriorating with increasing age is something that most people experience sooner or later, even among those who avoid diseases such as Alzheimer's. Similarly, a connection between the ageing of the brain and the body is well known. However, the exact nature of this association is not known. Researchers have created an explanatory model that starts with the heartbeat, and carries through the largest arteries in the body all the way to the finest vessels in the brain. An important feature of the model is that it provides a rationale why some cognitive processes may be particularly at risk for the proposed mechanism.
As the human body ages, large arteries, such as the aorta, stiffen and lose a large portion of their ability to absorb the pressure increase generated as the heart ejects blood into the arteries. Such pressure pulsatility is instead transmitted to smaller blood vessels, for example those in the brain. The smallest blood vessels in the brain, the capillaries, are subjected to an increased stress that causes damage to cells within and surrounding the capillary walls. These cells are important in the regulation of the capillary blood flow. If the smallest blood vessels are damaged, this is detrimental to the ability to increase the blood supply to the brain when coping with demanding cognitive processes.
According to the researchers' model, the hippocampus in the brain is particularly vulnerable. The structure in that part of the brain is important for the episodic memory, that is, the ability to remember events from the past. The vulnerability of the hippocampus relates to the fact that it is located close to the large vessels and thus is exposed to the increased load early in the chain. In a young and healthy person, the pulsations are soft, but in an ageing person the pulsations can be so powerful that they affect the brain tissue and can damage the blood supply to memory processes.