Why Weather and Barometric Pressure Affect Intracranial Pressure, ver 1.0

(whisper: this page is in the process of being edited to better adhere to my theory that everything can be explained in 25 small words or less.  Or close to that.  Please check back.)

Whisperer’s Wisdom:

“If you know what makes you sick, maybe you can avoid being sick.”

“Yeah, it’s a lot of reading, but we’re not dealing with a simple problem.”

 

IPSCD patients all suffer issues of headaches and neurologic/neuroendocrine alterations when the weather changes, and the most notable weather metric that seems to affect us is barometric pressure.     Medicine acknowledges this problem, but does not yet have any consensus the exact mechanism of how changes in the barometer can render us unable to function.  One doctor postulated that perhaps the dime-sized craniotomy for my shunt catheter was allowing air pressure on my brain?  While this does happen to patients who have suffered the loss of a large section of their cranium, with only a surgically positioned flap of skin in direct contact with the dura/brain, I don’t believe that is the case for me.  I see myself more as a marshmallow.

 

Our bodies are predominantly soft tissue covered with an airtight layer of skin.  Undamaged skin is essentially impermeable to air.  Surrounding us is air, pressing on us from all sides.  This pressure is what we call atmospheric pressure.  The entire body is compressible except for teeth, bones, and the skull.  When air pressure increases on the body, its contents are compressed, and extracellular fluids such as blood and lymph, are squeezed into the incompressible tissues, most notably for this topic, the cranium.  When air pressure drops, our tissues expand, and fluids drain back into the soft tissue of the body, lowering pressures in the cranium.  This is the central tenet of what is known in medicine as the Monro-Kellie Doctrine/Hypothesis.  The time honored version is on Wikipedia.  Interestingly enough, Monro-Kellie is undergoing an evolution prompted by ICPSD/ICP disorders.  Known as Monro-Kellie 2.0, it can be viewed here.

 

In ICPSD patients, the physiologic mechanism that regulates our ICP has become dysfunctional.  Basics of this mechanism are discussed on another section of this site.  This dysfunction is what leads to inability to maintain intracranial pressures in a normal range, potentially leading to pathologically high or low ICPs.  Diagnoses of these disorders go by an alphabet soup of names both current and obsolete; I believe them to be different presentations of the same condition, and thus I personally refer to them as IntraCranial Pressure Spectrum Disorders, or ICPSD.  In my case, the barometer dictates my life.  The area I live in sees wide fluctuations of barometric pressure;  before I was shunted and the barometer ran up, I felt like my head was going to burst.  The day of my shunt surgery the area was experiencing a particularly extreme high pressure system, and I was in utter misery;  after the surgery, my neurosurgeon told my wife that when he opened my dural membrane to place the proximal shunt catheter, CSF “shot across the room” as opposed to “dribbling out.”  My neurosurgeon is a quiet man and chooses his words carefully; his expression when relating this story reminded me of Mr. Spock raising one eyebrow when informed of the latest imminent catastrophe awaiting the Enterprise.  Back to the barometer:  when the barometer would drop, I usually got relief from headaches and reduction of tinnitus, but sometimes I had a different type of headache that felt like an my eyes and eardrums were being sucked into my skull.  After my shunt was placed, I became MORE susceptible to these changes because another avenue of fluid drainage had been added to my already challenged autoregulatory system.  It took me four months to determine what was happening.   Post-shunt, rapid drops in barometric pressure had now became my bane, with symptoms I now recognize as overdrainage or underperfusion.  I define overdrainage to be when CSF is being drained from the brain and faster than it can be replaced, and is primarily due to the marginal total system pressure of my shunt configuration.  When I am experiencing overdrainage, I have a feeling that my skull is under a vacuum and my eardrums feel like they are being sucked into my skull, almost like water pressure when I dive to the bottom of a pool.  The compressible parts of my shunt system like the dome and tubing get hard and distended; the ball valve in my antisiphon device/assist doesn’t rattle when I tap it with my finger; I get one little “tink” instead. These observations are due to high flow rate of CSF in the shunt system, and always occurs above a critical Cerebral Perfusion Quotient discussed elsewhere on this site.  Underperfusion, by comparison, is a nearly similar set of symptoms, but my shunt components aren’t distended; the silicone dome is softer and the tubing feels small and limp; the ball valve in my assist rattles loosely when tapped.  This condition occurs when my Cerebral Perfusion Quotient is below a critical limit, and I’m guessing it’s because my damaged ICP autoregulatory system is letting too much fluid (blood + CSF) out of my skull than can be replaced by the amount of blood flowing into my brain along.  Again, Cerebral Perfusion Quotient is key in determining what is actually happening in my head, and dictates what measures I have to take to improve my condition.  I have had to stop one medication that was limiting my cerebral perfusion and apparently making my damaged autoregulatory physiology more unstable; at certain times I’ve had to pack ice on my head to reduce the brain’s demand for extra blood to cool it.  The most significant was having to geographically relocate to a higher elevation (lower barometric pressure)  for a few days when local  conditions were making me barely functional ( -4 on the ICPSD Comfort Index) and my CPQ20 was indicating increasing tendency to overdrainage.

 

In short, when barometric pressure rises, it squeezes our bodies. Fluids are displaced into areas that cannot be compressed, i.e. the bones, the teeth, and most notably, the skull.  This increases pressure inside of those structures.  When the barometer drops, the body relaxes and fluid drains out of these incompressible spaces, lowering pressure.  This is why inflamed joints and teeth ache with weather changes, and also why the incidence of seizure activity and migraine-like headaches increases with as little as a 5mb change in barometric pressure.

 

Speaking of millibars/hectopascals/inches of mercury and other measurements of barometric pressure, I was stunned to discover how significant these units are when compared to “normal” Intracranial Pressures”.  I’ve been told that in the general population of non-ICPSD patients, intracranial pressures range from 30 to 200 column mm of water, that is, the pressure at the base of a column of water 1mm in diameter from 30 to 200 mm high, with the bell curve at Y H20.  Now take a millibar:  one millibar equals 10.97mm of water (conversions and values taken from this website only because it popped up first in a Google search)!  That is huge considering that the average weather system bringing rain is accompanied by a drop in the barometer of 10-20mb, or ~110-220 mmH20; more severe weather systems bring changes of 30mb, and I’ve seen (and suffered) as much as 40mb, translating into 440mm H20!  This fact alone should leave no doubt that not only do changes in the weather/barometer have an impact on human physiology, but that this impact is arguably very significant.  It also explains why I have more pain and a more brittle ICP regulation during the spring and fall when weather patterns are more unstable.

 

FOR ICPSD PATIENTS:  The exact impact of barometric pressure changes likely depends on several variables, which I will attempt to address on a “crime wall” page (you know, like on “police procedural” shows, where detectives have a wall of pictures and threads strung between the push-pins holding related pictures or newspaper clippings together).   These variables I’ve noticed/suspect  “include but are not limited to” individual physiology, shunted/not shunted, stented/not stented, shunt pressure setting and flow rate/flow rate limit, geographic location, and factors that affect blood flow to the brain including environmental temperature, mental processing of information (gaming, number crunching),  exercise, medications.  I strongly recommend that if you have been diagnosed with any of the alphabet soup insurance code related names currently assigned to ICPSD conditions that you begin monitoring your Cerebral Perfusion Quotient (CPQ20), again discussed in detail elsewhere.  Record the following:  blood pressure, heart rate, barometric pressure*, temperature, and your ICPSD Comfort Index.  Within two weeks you should begin to notice a CPQ20 range where you are most functional, if not necessarily comfortable, as well as how barometric pressure and activity affect your Comfort Index.  It is my hope that you can take this to your doctor and use it to plan and manage treatments for ICPSD.

 

 

*Note:  I am becoming aware that barometric pressure is playing a role in determining my CPQ20 comfort range; I’m not ready to put it up yet, but as the saying goes, it ain’t rocket surgery…