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Tuesday, January 28, 2014

Pulmonary functioning and high altitude climbing...

Twenty weeks ago, I completed my pulmonary functioning test.  The results were somewhat confusing and I thought I would investigate them further and report back what I found out.  Here are the main findings:
  1. I have asthma - no great surprise but it was nice to get confirmation.
  2. My peak flow is roughly 75% of what it ought to be given my age, body size, and sex.
  3. My lung volume is moderately compromised but not severe enough to warrant too much attention
Why are these results relevant to climbing Mt. Everest?  The most obvious answer is that breathing is essential for life and you cannot climb unless you are alive.  A more subtle and yet obvious answer is that climbing at altitude taxes your breathing.  There is an even subtler answer, however, that requires some explanation.  Bear with me while I go through the mechanisms and then arrive at my final answer.

Some Background

Most of you know the mechanisms of breathing but I figured a quick refresher might help us all understand the same language.  The respiratory system looks like this....


Oxygenated air comes in through the mouth/nose, down the trachea and eventually ends up at the alveolar sacs where oxygen transport takes place.  Experts typically refer to that stage of respiration as "ventilation."  Asthma affects ventilation.  An asthmatic has blocked airways that limit the transportation of oxygenated air into the lungs and exhausted, less-oxygenated air out of the lungs.  All of us living in congested areas know how traffic gets fouled up with just one lane closed; asthma is no different.  We all need to breath and some of us cannot catch a breath when we most need one.  Below is a great picture showing how the blockage occurs with asthma.  

So how do these diagrams relate to high-alpine climbing?  Several ways but I need to provide a bit more detail.  Consider the full oxygen transport cascade depicted in the figure below.


The x-axis in the figure above shows the cascade (stages) from inspiration to the final delivery to the blood (Venous).  The y-axis in the figure represents how much oxygen is available at each stage.  Asthma affects the first stage by limiting inspiration  (really by limiting expiration) and also the second stage by restricting airflow to the alveoli.  Each of these limitations leads to bad outcomes.  Here is how....

Breathing at high altitude

Here is what we know about the affects of high altitude.
  1. Altitude reduces the percent of oxygen in the atmospheric air (pre-stage 1).
  2. Reduced oxygen in the air means that inspired air has less oxygen to be absorbed.
  3. The reduced oxygen and consequently the increase in CO2 in the air causes the carotid bodies to signal the body to breath more frequently (i.e., increased respiration rate).
  4. Increased respiration rates are generally good BUT the increased rate leads to a greater expiration of CO2  and that results in a higher blood pH (more alkaline) - two bad outcomes.
  5. Higher blood pH - a situation call blood alkalosis - is not fatal but it does compromise your body's ability to function properly.  More importantly....
  6. Lower CO2 concentration in the blood REDUCES your breathing rate.  While this last consequence seems less problematic than the blood pH, I came to realize that this outcome is the part that causes the greatest problem for mountaineers.  
Breathing is essential - as we all know - but breathing is what helps us acclimatize to high altitude environments.  As your respiration rate decreases, your chances of HAPE (High Altitude Pulmonary Edema) and HACE (High Altitude Cerebral Edema) increase.  Both HAPE and HACE end your climb immediately.

Asthma

Now, back to asthma.  How does asthma affect your ability to acclimatize?  Asthma, as my brother explained to me, is a disease that affects expiration mostly.  Yes, it does affect inspiration but it is the expiration that is the greatest concern.  If an asthmatic person is less able to expire air then that person's body does not expel CO2 as rapidly as a person without asthma.  Sounds like a good situation, right?  Well, not exactly.  If you cannot expel the residual air from your lungs, you are less able to inhale new, oxygenated air.  Thus, asthmatics are less likely to function well at altitude than non-asthmatics because of an air exchange problem.  Less air out means less air in and if that air is already oxygen compromised then the little you take in creates an even bigger problem for the oxygen starved body.

Is asthma a big deal in mountaineering?  Simply put - YES.  Cold dry air often triggers asthma attacks.  There is little moisture in high altitude air and the temperature is pretty obvious.  Combined, the cold and dry air inhibits the exhalation of air from the lungs (good if you are only concerned about alkalosis) and increases the CO2 concentration in the blood.  Why?  Asthmatics cannot expel the CO2 rich air after the respiratory process.  To make matters worse, the increased CO2 leads to a higher respiration rate but a rate that is not beneficial to the asthmatic because the air that now comes in at a faster rate is also cold and dry.  The picture gets really simple.  Imagine having a drink of water from a hose.  If the hose offers you a trickle and you can use that trickle of water to slake your thirst then you come away from the experience satisfied.  What happens when the hose is attached to a fire hydrant?  That hose no longer provides the refreshments you desire.  Instead, you drown.

Asthma is akin to drowning because the failure to exchange oxygen depleted air with oxygen rich air leads to suffocation - much like drowning.  The greater the limits on this exchange, the greater the likelihood of HAPE or HACE.  

So what do I do about my asthma?  Manage it prior to, during, and after climbing via sound judgement, modest use of drugs (prescription not recreational), and preparation.  I had an asthma attack on Denali upon my descent from the summit and it was hardly a fun experience.  Rarely have I been so affected by asthma.  I am taking every step possible to avoid that situation on Everest.  Thanks to my brother and his colleagues at Allergy Partners, I am a well-managed asthmatic.