Pendelluft—The Beast Within

It was dark, the only light coming from the red glowing numerals of my digital alarm clock. I hadn’t set it to alarm—I needed to sleep as long as I could.

It was also quiet in my bedroom, quiet enough for me to hear my breathing as I lay still, trying to sleep. The breath sounds were rhythmic and calming, breathing in with a hiss, and out with a coarser and louder “huh,” endlessly repeated.

I had just been released from our local hospital after five days on oxygen, diagnosed with “respiratory failure” of unknown origin. The medical term for unknown origin is “idiopathic,” but that word added no clarity to what had happened.

What had happened has been described in a previous blog post, a post that correctly warned that if the illness that almost killed me was any indication, we should NOT expect COVID-19 to abate during the hot and humid months in the American South.

Whatever virus I picked up in Thailand in July, seemed to have a predilection for the hot and humid summer weather of Florida. In other words, it had made itself right at home in my lungs. The result was a puzzling but treacherous case of silent hypoxia, or as some have called it, happy hypoxia. In that regard, my respiratory failure was every bit as inexplicable and potentially deadly as COVID-19.

Thankfully, my viral infection had not yet reached the level of transmissibility of COVID-19. Otherwise, my wife of fifty years would certainly have been affected as she sat by my side for those long and frustrating days in the hospital.

But now, it was time for celebration. By sheer willpower and some tricks of the respiratory physiology trade, I had gotten myself discharged from the hospital. But that’s another story.

At home once again, my finger-tip pulse oximeter showed I was oxygenating reasonably well on air (in the low 90 percentile), but I was not back to normal (the high 90s). My lungs still had some healing to do before I could claim I was 100% normal.

As I now lay quietly as night enveloped me, entering almost a meditative state listening to my breathing, I noticed a strange sound. Alerted, I listened more intently. And what I heard scared the hell out of me.

There was something alien in my body. I couldn’t feel it, but I could hear it. When I breathed in, it breathed out. When I breathed out, it breathed in. It was clear as day, something was breathing in my chest, and it wasn’t me.

I had a monster in my chest.

At times like that, it is hard to be objective. But with years of training as a scientist, I forced myself to collect data and analyze the results before, well, FREAKING OUT!   

The first thing I noticed, was that the asynchrony between my breathing and the other’s breathing, was invariant. They were 180 degrees out of phase, and that never changed.

Professionally, I’ve dealt with probability my entire scientific career. So, if there were in fact some other living thing in my chest, the odds that it would never change its breathing rhythm seemed unlikely. Unless—it was waiting for my lungs to have a full “tidal” breath” before IT took a breath.

Of course! That is exactly what I would do if I was in some giant’s chest. I’d wait until their lungs were full before I’d steal air from them. After all, how else could I, as a little monster, breathe?

But wouldn’t X-rays at the hospital have shown its presence? Well, yes, and no. They didn’t do an MRI. If IT was soft bodied, and growing, it might not have been detected. And going an analytical step further, that could explain why my arterial oxygen saturation levels were not back to normal. IT was stealing oxygen from me.

My heart rate was increasing, which was the last thing I wanted it to do. The more blood I sent the thing, the faster IT would grow. I had to stay calm. But how?

I began thinking about physiology text books. That would put anybody to sleep. But that was also the magic moment. That was when I put a name on the creature in my chest.

I called it, Pendelluft.

Until that night, Pendelluft had been to me of little more than academic interest. I’d read about it, but I knew it is primarily found in patients with chronic obstructive pulmonary disease (COPD); which I do not have. I’ve also never been a smoker or asthmatic.

I knew of the diagrams which explain it, but I never thought that I would be able to hear it, in my body, and especially without a stethoscope.

An illustration of the mechanism of Pendelluft from a humorously named web site, Deranged Physiology.

After I explored the medical literature, I’m not sure anyone in the medical field thinks it possible for a patient to hear his own Pendelluft. But it must be true, since the monster never reared its ugly head, and my arterial oxygen level regained its expected normal value only after the “monster” faded away.

 According to a 1985 paper in the Journal of Applied Physiology, the experimental evidence and theoretical aspects of Pendelluft are attributable to varied pulmonary (lung) airway resistance and compliance (the opposite of stiffness), and were first described in a classic paper by Otis et al. in 1956.  

I was pleased when I read that one of my mentors, Dr. Arthur Otis, the one time Department Head of the Physiology Department at the University of Florida School of Medicine, had done the pioneering research on the subject.

However, I found no reference to breath sounds until I came across the 2012 article in the journal Pulmonary Medicine. That study used very complex instrumentation and statistical methodology to detect Pendelluft.

I have to admit that I smiled when I read that 2012 article. I was questioning how much money was spent on that very elaborate medical investigation. Arguably, it was fine work and contributed nicely to the field.

But, I wondered, did they try asking the patient, “Do you hear a monster in your chest?”

For what it’s worth, I did.

And it was scary as hell.