Inhaler Physics (AT Days 64 & 65)

The skies opened up once again and began dumping rain on me at 1-2 inches and hour. I sighed and resigned myself to getting soaking wet again… The same thing had happened yesterday and the day before. Today, however, I only had two miles of hiking left and then I was headed into town to a nice dry hostel.

Even though I’d resigned myself to getting wet, the thunder, lightning, and really heavy rain weren’t making it the most enjoyable of experiences. I was hiking at about 2 miles/hr so I figured I only had about an hour of uphill in the rain to go. Suddenly I had an epiphany, if I jogged I could be out of the rain in 30 minutes or less… That would be much better than hiking in the nasty nasty weather for an hour!

I tightened the straps of my pack and with water streaming down from the sky and through the trail I started running. It felt good to stretch out my stride and navigate around the rocks and roots.

Not long after initiating this plan the slope of the uphill increased and I realized that I’d forgotten something. I’d forgotten that I have asthma. Doh! I stopped running, pulled out my rescue inhaler (which I always keep handy), and almost hungrily inhaled the medicine that would make it so that I could breath comfortably again.

However, instead of getting the usual easing of my breath as my chest opens up and my lungs full with air, I felt a caustic burning of my throat and lungs and if anything it felt like my lungs constricted even more.

Shocked and confused and now definitely having an asthma attack I looked accusingly at my inhaler. Had I
Accidentally grabbed my pepper spray instead? No, it was definitely my inhaler that I held in my hand. Perhaps it had gotten some sort of particulate in/on it that I had just accidentally propelled into my lungs (everything gets dirty when you’re backpacking). I carefully wiped off the mouthpiece inside and out and took a second puff of the inhaler sure that I’d fixed the problem and would soon be breathing easy again.

F***!!!! Burning, searing, pain as my lungs really ceased up. I threw my inhaler onto the ground; I threw my backpack onto the ground; I threw myself onto the ground. Stupid inhaler, why was it hurting instead of helping?! For the moment I didn’t care. I closed my eyes, leaned forward onto my knees and focused on breathing… It was starting to work, but I was still coughing and feeling short of breath. I reached over and grabbed my water. It soothed my throat and after a couple of minutes I’d stopped coughing.

I was still short of breath, but at least I could think again. What the heck had happened with my inhaler? I remembered the trouble I’d had with my inhaler at the ice hotel in Quebec City over the weekend. It was so cold outside that the inhaler wasn’t working… A common problem with canisters of compressed gases at low temperatures… And suddenly I was thinking about the ideal gas law (PV=nrT), and the compressibility of gases, and thermodynamics.

Was my inhaler acting up because of the weather? It was around 90 degrees out, 100% humidity, plus a low pressure system with a severe thunderstorm raining 2 inches/hr on me. I decided that somehow I must be having the opposite problem from Quebec City, that the compressed gas from the inhaler was still rapidly expanding as it hit the tissue of my throat and lungs. Since the expansion of gas is endothermic, that could essentially burn my throat and lungs with intense cold.

I had a hypothesis… Could I test it? Hmmm… I reached over and picked up my inhaler, which was still sitting in the middle of the trail where I’d thrown it in frustration and anger, and looked at it for a minute. My hypothesis was that the weather conditions were causing the compressed gas in the inhaler to expand over a larger area than usually, so that a noticeable endothermic reaction was still occurring as that compressed air hit my lungs. Based on that hypothesis I would predict noticeable plume as the inhaler was puffed into the open air around me instead of into my lungs.

I pointed the inhaler away from me and delivered a puff over the trail. It looked liked the white plume of breath that you see when someone exhales moist air on a cold winters day… Except that it actually had a propellant, so the plume extended out for about 3 feet.

I was still short of breath, so now I needed a plan. How to get the drugs from my inhaler into my lungs without giving them frostbite? I decided to use my hand as a spacer tube, hoping it would allow the gases to expand in my hand and not my lungs, while still directing the medication into my lungs.

With some trepidation, I squeezed down on the inhaler and inhaled (rather cautiously this time). It worked!!! No horrible burning sensation, and my lungs started to open up. I took a second puff the same way, and my breathing returned to normal.

Now I *really* was drenched. The rain kept pouring down as I walked the rest of the way to the road. I made it in 45 minutes.

Extra credit assignment: Demonstrate mathematically the crucial parameter/s (was it the humidity? the thunderstorm? or a combination of the humidity, thunderstorm, and temperature?) that led to the inhaler doing more harm than good. If I were at home I would have modeled this already and figured out the critical parameters both for this story and for the ice hotel… I miss having pencil, paper, and the easy ability to look things up and research them!

6 thoughts on “Inhaler Physics (AT Days 64 & 65)

  1. Ooh! Ooh! I know!
    I’ll bet it was a combination of extra-rapidly-expanding gas from an overheated and therefore overpressurized inhaler causing the water vapor in the moist air in in your mouth and lungs (extra-moist from the humidity) to condense in your alveoli and bronchioles in a most painful fashion. Either that or cold fusion caused by the electric field from the thunderstorm… ;-)

    Like

    • The propellant is HFA134a, there was 100% humidity. Assuming normal atmospheric pressure at 3000 ft elevation in central Virginia, what is the distance over which the propelled gas is expanding at 0C? 22C? 37C? Looking up local atmospheric pressure during a thunderstorm and using that instead of normal atmospheric pressure answer the same.

      Like

  2. If the humidity was at 100%, rapid cooling of the air inside your lungs would also cause the water vapor to rapidly condense, wouldn’t it? I would think the small relative drop in air pressure (from the storm) compared to the pressure inside the inhaler canister would make that less likely to be a factor. But if droplets of water were suddenly condensing on your lung tissue, that sounds burningly painful to me (having experienced pneumonia before)!
    You also mentioned that you inhaled the first dose “almost hungrily”, so perhaps the slight vacuum from sucking the expanding gas also contributed to the effect.

    It sounds awful, yet I can’t help but smile at the thought of a scientist formulating a hypothesis and devising a workaround in an emergency situation like that. Someone less knowledgeable and resourceful would have fared much worse in that situation, I imagine.

    Like

  3. I made my husband (an engineer) read this post and subsequent comments because I knew he’d thoroughly enjoy the math behind it. Also, so that he could translate for me should I ever need to figure this out for myself. I am glad that it all turned out okay, and hopefully you won’t ever have to test this theory again for the rest of your journey.

    Like

  4. Pingback: Goat Rocks (PCT Days 144-147) | Patches Thru

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s