“Don’t forget to breathe” is a constant mantra of Elizabeth, my Yoga trainer, when I instinctively hold my breath executing a demanding pose. And what does the nurse tell patients who experience pain during a procedure? “Take slow deep breaths.” As many runners would attest, some of their clearest thinking and most creative ideas come to them when they go out for a run.
I can add here my personal experience: My thinking became far less emotional and a lot more rational about problems at work or home at about a mile or two into my run. I once conceived of a new, innovative research program on the run, so to speak. So what’s going on here? Is it just the touchy-feely of Yoga practitioners, or the anecdotal testimonials of runners? Turns out, there is a solid physiological basis for all that.
Breathing and the brain
To start, a very short lesson (I promise) in brain anatomy.
The brain sits inside the hard shell of the skull. Great for protection of this soft mass that controls the functions of our lives: breathing, blood circulation, the senses that allow us to maneuver in the environment, our reactions to environmental threats, our memory, our thinking. Come to think of it, here is an astonishing fact: Such protection was deemed by evolution so vital that the skull was only exoskeleton feature that our ancient invertebrate ancestors bequeathed to us vertebrates. There were plenty of occasions for traumatic head injuries. So the brain protected itself from bashing against the hard shell of the skull by surrounding itself with a liquid layer of shock absorber: the cerebrospinal fluid (CSF).
This shock absorbing function is so important to maintaining the integrity of the brain that the CSF circulates not only in the periphery, but also through a system of four internal cavities, called ventricles, providing internal cushioning. CSF originates from its primary production sites at the choroid plexus (intertwined cellular structures in the ventricles; choroid = highly vascularized tissue; plexus = braid, anything twined) through the brain ventricles to reach the outer surface of the brain in the subarachnoid spaces from where it drains into the venous bloodstream and cervical lymphatics. Recent studies of brain fluid transport in rodents showed that CSF from the brain surface also enters the brain tissue along para-arterial routes and exits through para-venous (para = adjacent, next to) spaces and return into subarachnoid compartments.
Of course, even evolution in its great wisdom couldn’t foresee the ingenuity of Homo sapiens (“the thinking man”) in devising ways to overcome the natural shock absorber and bash their brains with high impact in games and wars. But mentioning evolution, violent games, and wars in one breath is too politically fraught in today’s environment, so let’s go on with the strictly scientific narrative.
Deep breathing and CSF flow?
As implausible as it sounds, not hard to believe. Why? Because as we learned from human intellectual history, once you provide a tool for one purpose, unforeseen uses are sure to follow. Take the invention of the steam engine, the computer, the internet. The latter, for instance, was invented to facilitate communication between certain (not all) academic institutions. Today, we are talking about communication between your car and your home appliances. So could natural selection, with many millions of years on its hands, be far behind?
Of course not. Once we were able to measure flows of liquids in the body, it was evident that the CSF is not static—it is somehow being pumped, and its ebb and flow regulates to a large extent the flow of blood in the brain. Also, remember that the CSF from the peripheral subarachnoid space penetrates the brain tissue. Could this extensive bathing end up being as inert as a shock absorber?
Like every important discovery, it raises even more questions. An obvious one: What regulates this pumping action of the CSF? The answer came only recently from Steffi Dreha-Kulaczewski and her co-workers at the University Medical Center Göttingen in Germany.
To investigate how CSF flow is regulated in humans, the investigators applied a novel real-time magnetic resonance imaging technique in healthy human subjects. They observed significant CSF flow exclusively with inspiration. In particular, during forced deep breathing, high CSF flow was elicited during every inspiration, whereas breath holding suppressed it. Only a minor flow component could be ascribed to cardiac pulsation. These results unambiguously identify inspiration as the most important driving force for CSF flow in humans.
Why is it important?
This finding has an obvious clinical importance. Hydrocephalus (“water on the brain”) is a medical condition in which there is an abnormal accumulation of CSF in the ventricles of the brain. This can occur when there is an obstruction to the CSF flow, for whatever reason. The new insight into the regulation of this flow may lead to new diagnostic and therapeutic procedures.
But about non-pathological implications? Consider: CSF is recycled (flushed) 4 times per day in order to clean out metabolites and toxins like beta amyloids (the stuff that accumulates in Alzheimer’s disease). Hence the choroid plexus must produce about 500 milliliters of CSF daily (or 21 mL per hour). With this extensive flushing action going on, is it possible that the technique of pain control by taking “slow deep breaths” actually works by removing stress proteins from the brain? And what about the clarity of thinking that runners claim to have during a run? And the feeling of well-being after a yoga session?
The possibilities are endless. But until all the evidence is in just obey your Yoga trainer’s admonition: Don’t forget to breathe!
Featured photo credit: Matt Madd