Our brains are washed by a constant flow of cerebrospinal fluid, which plays the important role of carrying away waste substances, such as harmful proteins and excess water.
The rhythm of your heart is one of the factors that affects how well this fluid flows through the brain. Now a new study shows that breathing also affects how well the spinal fluid flows.
“It’s not impossible that yoga breathing techniques can affect the flow of cerebrospinal fluid and promote the removal of brain wastes,” says Vegard Vinje of the Simula Research Laboratory, where he is a PhD candidate.
The study was recently published in the journal Nature Scientific Reports and is part of Vinje’s doctoral thesis on the topic.
Heart rate and sleep promote flow
Some waste substances accumulate in the brain as a result of functional brain disorders. One well-known example is amyloid beta, which accumulates as plaque when a person has Alzheimer’s disease. But much remains unknown about how the brain gets rid of waste products.
In 2013, however, researchers discovered that cerebrospinal fluid plays a role in cleansing the brain. The fluid flows into the brain along the small spaces around the arteries and washes away waste material through the brain tissue itself.
“This really got people’s attention,” Vinje says.
How well the brain fluid flows can thus determine how efficiently waste materials are flushed away.
The flow is driven by the heartbeat, among other things, because the arteries in the brain expand with each beat. In addition, previous research suggests that the flow increases as we sleep.
Measured brain pressures over a long period
Vinje was named Engineering Student of the Year in 2016 by Universum when he was a student at the Faculty of Mathematics and Natural Sciences at the University of Oslo. His master’s degree was about calculations of fluid flows in the brain.
Previous MRI studies have shown that breathing can affect the flow of spinal fluid.
“But these studies have been limited to short periods of time, due to the limitations of the MRI technology,” Vinje says.
He and his colleagues had access to pressure measurements from the brains of patients with hydrocephaly, or water on the brain, who were at Rikshospitalet, Ullevål University Hospital. These pressure measurements are done routinely to determine which patients need surgery.
The advantage, for Vinje’s research, is that the pressure readings extended over 15 hours and more.
Breathing versus heartbeat
Two pressure sensors were located in two different locations in the patients’ brains, giving 200 pressure measurements per second.
From these pressure measurements, Vinje and colleagues were able to calculate the spinal fluid flows using Navier-Stokes equations. They then calculated the percentage of the changes in the flow that were due to breathing in relation to heartbeats.
The measurements showed that the pressure pulsations are three times greater for the heart pulsations than for the breath.
“Although the pressure pulse cycles are dominated by heart pulsations, the velocity of the fluid is as much affected by the breath as by the heartbeat. The amount of cerebrospinal fluid volume that pulsates in and around the brain is far greater for a breathing cycle than for a heartbeat,” Vinje said.
The volume that was moved during a breathing cycle was more than four times the volume moved by a heartbeat. That’s because each inhalation lasts longer than each heartbeat — with around 15 inhalations per minute versus 60-70 heartbeats per minute, he explains.
Deep breathing better than rapid
Vinje explains why fewer deep breaths have a greater impact on the flow of brain fluid than faster, shallow breathing. Essentially, the longer waves that result from deep breaths can carry more volume. He compares it to ocean waves hitting the land.
“Imagine a beach with rubbish. A long wave will remove garbage and clutter on a beach more efficiently than a short one,” he said.
Short, choppier waves won’t come as far up on the beach compared to longer waves of the same height, he explains.
May explain the value of breathing exercises
The patients in Vinje’s study took as many as 15 breaths per minute, on average, which is normal. But for some kind of yoga deep breathing exercises, practitioners may only take five breaths a minute, he says.
Much research has been done into whether and how breathing may have a health-promoting effect.
“It is not impossible that some of the answer may lie in the effect of breathing techniques on the flow of spinal fluid, which in turn has been linked to the removal of waste materials from the brain,” Vinje said.