Nick Mark MD Profile picture
Sep 4, 2021 26 tweets 13 min read Read on X
The last few weeks have been tough. For those in need of a light hearted thread, here’s a brand new 3rd #tweetorial in my extremes of #physiology series. What can the animal kingdom teach us about our physiology?

Buckle up for some fun animal pulmonary facts 🫁!
1/
CASE 1:
You are performing a bronchoscopy. Upon reaching the main carina instead of the usual TWO airways (right & left mainstem bronchi) you see THREE.

Your assistant says “Whoa! That’s weird”

You say no it’s totally normal because the patient is a:
2/
Answer: 🐖
In pigs, the RUL lobe bronchus originates from the supra-carinal trachea (e.g. before the R & L mainstream branches). The view from the trachea looks like this (see the tracheal bronchus on the right).

image source: casereports.bmj.com/content/12/5/e…
3/
Clinical 🥡:
~1% of humans have a tracheal bronchus as an anatomical variant (usually RUL).

This trachea bronchus can cause RUL collapse when intubated.

So if you have an intubated patient with unexplained RUL collapse always think - could this person have a 🐖 bronchus?
4/ Source: https://journals.sagepub.com/doi/pdf/10.1177/0310057
Other answers:
🦒, 🐑, 🐐, 🐪, & 🐋 also have tracheal bronchi but I don’t think anyone has done a bronch on a 🦒!

It is possible to do bronchoscopy in 🐘 - though not easy! A trunk nerve block apparently works better than nasal lidocaine gel. 🐘 don’t have tracheal bronchi.
5/ Source: https://www.cambridge.org/core/journals/epidemiology
Case 2:
You have just placed a LEFT sided chest tube for a patient with large BILATERAL pneumothoraces. Your assistant asks you if you want to place a second tube on the RIGHT side.

You say no, the procedure is unnecessary because the patient is a:
6/
Answer: 🦬
The American Buffalo has a single pleural cavity. Despite its size (up to 2600 lbs) & speed (runs up to 40 mph) a single arrow can cause bilateral tension PTX, incapacitating the buffalo.

(Aside: note that the Plains bison has one of the best species names ever!)
7/
1st Clinical 🥡:
People who have had thoracic surgery that disrupts the pleura, may also have a single pleural space, just like a Buffalo.
(It can also occur rarely in the absence of thoracic surgery as an anatomical variant).
8/
Source: NEJM nejm.org/doi/10.1056/NE…
2nd Clinical 🥡:
This is why in lung transplant recipients a single transbronchial biopsy can cause bilateral PTX.
It's also why, in rare cases, a single chest tube may suffice to treat bilateral PTX.
9/
jhltonline.org/article/S1053-… pubmed.ncbi.nlm.nih.gov/16714521/
Other answers:
🐖 pleural anatomy is similar to humans, other than tracheal bronchi
🐘It’s impossible to place a chest tube in an elephant! (more on this later)
Some 🐍 also have one pleural space but for a very different reason: they only have one 🫁
vetexotic.theclinics.com/article/S1094-…
10/
CASE 3:
You are performing transbronchial biopsies when (oh no!) you realize that your last biopsy appears to have gotten a bite of pleura.
Horrified your assistant asks if you need a chest tube tray.
“No" you say reassuringly, it's unnecessary because the patient is a ___.
11/
Answer: 🐘 Elephant

Elephants are the *ONLY* mammal that does not have a pleural space. In utero their visceral & parietal pleura fuse, obliterating the pleural space with dense connective tissue.
Thus elephants can’t develop PTX (and its impossible to place a chest tube)!
12/
But *WHY* are 🐘's pleural cavities unique?
The answer is that elephants snorkel to cross deep water. This creates massive negative intra-pleural pressure, which would in another species cause massive fluid transudation. 🐘 natural pleurodesis enables them to tolerate this.
13/
I *HIGHLY* recommend reading this excellent article by West about the unique physiologic adaptations that enable elephant snorkeling 🐘🤿
Another fun fact: their diaphragms are 3 cm thick (10x ours), enabling them to pull negative pressure underwater
pubmed.ncbi.nlm.nih.gov/11311306/
14/
Clinical 🥡:
Humans who undergo pleurodesis are protected against pneumothorax; in some cases this is why the procedure is performed. In one case series of patients with primary spontaneous PTX, talc pleurodesis prevented recurrent PTX in 95% of them.
erj.ersjournals.com/content/29/4/7…
15/
Other answers:
🐃 Buffalo - PTX are a huge deal in buffalos because they are always bilateral! (see case 2)
🐪 & 🦏 can also develop PTX
Cetacean lungs have abnormally high compliance so they can take *HUGE* tidal volumes (a🐬's TV is 55 ml/kg); even🐬 can develop PTX rarely
14/
CASE 4:
You are called from the PFT lab about an abnormal CPET result: VO2max 255 ml/kg·min
The technicians says this calculation can’t possibly be right. You tell them it’s expected because the patient is a ____
15/
Wrong answers first:
🥇 The highest recorded human VO2max was 97.5 mL/kg/min (set by 🇳🇴 cyclist Oskar Svedsen in 2012)
For comparison, the average in a sedentary non-professional athlete is about 30-40 mL/kg/min (men) and 27-35 mL/kg/min (women).
16/
🐎 Thoroughbred horses running on an inclined treadmill averaged 194 mL/kg/min after 18 weeks of high intensity training (yes horses do HIT classes!)
According to a colleague, the sound made by a horse’s hooves running on a treadmill was deafening!
physoc.onlinelibrary.wiley.com/doi/full/10.11…
17/
Huskies from a champion dogsled team have demonstrated VO2max as high as 240 ml/kg/min.
The dogs who run the 938 mile Iditerod in just 8 days are perhaps the best endurance athletes in the world.
news.cornell.edu/stories/1996/1…
18/
🐁 The tiny 10 gm Pygmy Mouse achieves an incredible VO2max >250 ml/kg/min.
This is a great demonstration of allometric scaling laws at work: smaller animals have much denser mitochondria enabling greater VO2; this is also why they have higher BMR/mass
general.utpb.edu/fac/eldridge_j…
19/
Answer: 🐦
The real champion is the 4 gm hummingbird, with a VO2max of >660 ml/kg/min.
This is close to the theoretical limit of what is possible (e.g. their muscle cells are so dense that adding more mitochondria would take away sarcomeres!)
pnas.org/content/88/11/…
20/
If you are wondering *HOW* they measure the VO2max of a 4 gm hummingbird, they get the birds to insert their beak into a feeder while hovering and measure the CO2 and O2 concentration.
utsc.utoronto.ca/news-events/br…
21/
If you like this, I highly recommend reading this amazingly detailed Quora thread. Just fantastic.

Highlights: hummingbirds VO2max is >1000 ml/kg/min if they fly in thin air (He/O2 mix); IMO this is cheating, like hitting golf balls on the moon.

quora.com/Whats-the-high…
22/
Clinical 🥡:
Elite athletes can have a VO2max that’s ~3x “average.” When evaluating for change in exercise tolerance it’s important to think about what their baseline was; e.g. going from 60 to 40 could be a big drop but still be “normal” range.

Also we got nothing on 🐦!
23/
Hope you’ve enjoyed the 3️⃣rd installment in this series. Hopefully you’ve learned something that will make you a better doctor, or at least increase your enjoyment of the discovery channel.

For earlier installments see:
1️⃣
2️⃣
24/

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More from @nickmmark

Jul 16
The media silence on this is deafening.

Did he have a head CT? What did it show?
Did he have stitches? Tetanus shot?

The NYT ran nonstop stories about Biden’s health after the debate but can’t be bothered to report on the health of someone who was literally shot in the head?
To the people in the replies who say it’s impossible because of “HIPPA”
1. I assume you mean HIPAA
2. A normal presidential candidate would allow his doctors to release the info. This is exactly what happened when Reagan survived an assassination attempt.
washingtonpost.com/obituaries/202…
My advice to journalists is to lookup tangential gunshot wounds (TGSW).

Ask questions like:
- what imaging has he had?
- what cognitive assessments?
- has he seen a neurosurgeon or neurologist?
- he’s previously had symptoms like slurred speech, abnormal gait - are these worse?
Read 4 tweets
Jun 30
You've probably heard "don't give lactated ringers because it raises lactate"

This statement is ~98% false, but there's one crucial practice-changing fact that you need to know.

A 🧵 all about lactic acid and lactated ringers!
1/
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First off, we should ackowledge the obvious: Lactated ringers does in fact contain lactate... 28 mEq/L in fact

BUT there's one little detail to remember:
Lactate ≠ Lactic acid

When we measure "lactate" we care about the ACID (H+) which lowers pH & causes organ dysfunction
2/ Image
But the correlation between pH & lactate is really bad!

Look at this analysis of lactate vs pH in 171 ICU patients.

There is a *weak* correlation in people with arterial lactate > 5, but even w/ lactate =10, pH ranged from 7.5 to 7.05. Quite a spread!

3/ ncbi.nlm.nih.gov/pmc/articles/P…
Image
Read 10 tweets
Jun 13
If you intubate you need to read the #PREOXI trial!
-n=1301 people requiring intubation in ED/ ICU were randomized to preoxygenation with oxygen mask vs non-invasive ventilation (NIV)
-NIV HALVED the risk of hypoxemia: 9 vs 18%
-NIV reduced mortality: 0.2% vs 1.1%

#CCR24
🧵
1/

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Hypoxemia (SpO2 <85%) occurs in 10-20% of ED & ICU intubations.

1-2% of intubations performed in ED/ICU result in cardiac arrest!

This is an exceptionally dangerous procedure and preoxygenation is essential to keep patients safe.

But what’s the *BEST* way to preoxygenate?
2/
Most people use a non-rebreather oxygen mask, but because of its loose fit it often delivers much less than 100% FiO2.

NIV (“BiPAP”) delivers a higher FiO2 because of its tight fit. It also delivers PEEP & achieves a higher mean airway pressure which is theoretically helpful!
3/
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Read 15 tweets
Jun 12
Results from #PROTECTION presented #CCR24 & published @NEJM.
- DB RCT of amino acid infusion vs placebo in n=3511 people undergoing cardiac surgery w/ bypass.
- Reduced incidence of AKI (26.9% vs 31.7% NNT=20) & need for RRT (1.4% vs 1.9% NNT=200)

Potential game changer!

🧵
1/
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I work in a busy CVICU & I often see AKI following cardiac surgery.

Despite risk stratification & hemodynamic optimization, AKI remains one of the most common complications after cardiac surgery with bypass.

Even a modest reduction in AKI/CRRT would be great for my patients.
2/ From Nature reviews nephrology  https://www.nature.com/articles/nrneph.2017.119
During cardiac surgery w/ bypass, renal blood flow (RBF) is reduced dramatically. This causes injury, especially in susceptible individuals.

But what if we could use physiology to protect the kidneys?

Renal blood vessels dilate after a high protein meal increasing RBF & GFR!
3/ https://www.jtcvs.org/article/S0022-5223(18)33243-4/fulltext
Read 11 tweets
May 3
A slightly tricky blood gas case:

77 yo with respiratory distress, RR 30, SpO2 80% on non-rebreather at 15 lpm

CXR & TTE are unrevealing

pH 7.58 / PaCO2 24 / PaO2 >500 / HCO3 22

MetHb 0% CarboxyHb 0%

The ABG looks like this: Image
The answer is sulfhemoglobinemia.

Sulfhemoglobinemia is a *permanently* modified hemoglobin associated with exposure to TMP/SMX, dapsone, phenazopyridine, & other amino & nitro compounds.

It has an altered oxy-hemoglobin dissociation curve.

2/

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Sulfhemoglobinemia is easily confused with methemoglobinemia. Both have very dark colored blood & present with cyanosis. Diagnosis typically requires a specialized lab.

Spoiler: you may have heard that SulfHb is green. It isn’t really. You’re thinking of Vulcans’ blood.

3/
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Read 7 tweets
Apr 28
This story is absolutely shocking.

Philip Morris International (PMI) spent millions to influence medical education by buying a series of “CMEs” at Medscape!

How else has big tobacco tried to normalize vaping & influence the medical community?

🧵
1/
theexamination.org/articles/medsc…
Recently it was revealed that Philip Morris International (PMI) had SPONSORED CME materials about smokeless tobacco products on Medscape.

I had the opportunity to review these “CME” materials & they are pretty shocking!
2/

Image
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One truly incredible thing about this “CME” was that it has NO DISCLOSURE SLIDE!

The fact that people teaching about vaping don’t disclose their financial ties to the tobacco industry is absolutely bonkers!

Why isn’t there a sunshine act for this?
3/
Read 19 tweets

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