Core muscle contractions may help regulate blood flow to the brain, study finds
A Penn State-led study finds that abdominal muscle contractions during movement, coughing or breathing squeeze large veins in the brain, offering a possible mechanism linking exercise to brain health.
Contractions of the abdominal muscles during movement, exercise or even a cough may play a role in regulating blood flow to the brain, according to a new study led by Patrick Drew, professor of biology at Penn State. The research was published on September 21 in PNAS.
The work examined how blood flow in the brain is controlled and how body movement affects it. Blood flow in tissues normally shifts dynamically to match metabolic demand, entering through arteries, passing through the capillary network and leaving through veins. The conventional understanding is that arteries and capillaries are wrapped by cells that contract or relax, widening or narrowing the vessels much like enlarging a pipe allows more water to pass. That regulation does occur in the brain, but the study found that the diameter of veins is also regulated, and that this control is driven by contractions in the abdominal muscles.
When animals move or are startled, the abdominal muscles contract, raising intracranial pressure and squeezing the largest veins in the brain. The contraction compresses blood vessels in the abdomen that are connected to vessels in the spinal cord, pushing blood from the abdomen and squeezing the spinal cord, which is linked to the brain. The researchers describe the effect as similar to a hydraulic system, in which pressure is transferred from one region to another.
The team suggests several possible benefits. The mechanism produces a momentary, very quick increase in blood flow that is faster than normal vasodilation, offering a rapid way to boost cerebral blood flow during activity. Abdominal muscles contract during any postural motion, including exercise, and also when a person is startled or something interesting happens. Respiration can produce a similar effect: when a person breathes, the diaphragm pushes on the abdomen, changing intracranial pressure and squeezing and relaxing the large veins in the brain.
The findings indicate that cerebral blood flow is regulated not only by local neural activity and heart rate but also by how the body moves, suggesting that movement in the periphery is an important regulator of blood flow to the brain. The researchers propose this may be one reason exercise and daily movement contribute to brain health, by altering vessel diameter and regulating blood flow. Abdominal muscles engage during any movement, including a simple reaching motion, tensing to stiffen the core when walking or moving around, so the mechanism is naturally active during exercise.
While activity and body motion are known to help maintain brain health and alertness, the mechanisms involved are not fully understood. The study offers an example of one mechanism linking body motion and activity to a healthy brain. Disruption of this regulation or reduced blood flow is associated with neurodegenerative disorders and other problems, but the underlying reasons remain unclear. Understanding how blood flow functions normally in healthy people and animals could help researchers work out how to correct what goes wrong in disease, the researchers said, drawing an analogy to a car mechanic who can fix a fault more easily when he understands how a vehicle should work.
The work may also shed light on why headaches worsen with movement. While the brain itself lacks pain receptors, the dura surrounding it contains sensory nerves that respond to being pushed or pulled. When vessels constrict or dilate, they press on these sensory neurons. Contracting the abdominal muscles changes intracranial pressure, altering the size and shape of the vessels and pulling and pushing on the dura membrane to which they are connected — a possible explanation for the intensification of headache during movement or coughing.
Earlier work by the group showed that this process causes motion of the brain and potentially circulation of cerebrospinal fluid that can remove waste. The recent paper shows that, in addition to brain movement, the pressure changes compress some of these veins, altering blood flow and potentially other aspects of brain physiology and circulation.