Children sometimes inhale foreign objects which lodge in the airways leading to the lungs. All accident and emergency departments have seen cases where worried parents have brought in a child to whom this has happened. It also happens to adults who toss up a peanut in an attempt to catch it in the month. Although this may apply to any object of the right size, peanuts are the main culprits in Britain.
When inhaled, it is the right main bronchus (the airway leading to the right lung) that the peanut seems to favour. But why? (Of course, peanuts do not exhibit choice.) The answer usually given is that the right main bronchus is straighter, more vertical, and broader than the left. This reason continues to be accepted. It was even the response from ChatGPT (when asked in January 2024).
This reasoning lacks experimental evidence. It is based entirely on clinical observation and what is known anatomically about the arrangement of the central airway (the trachea) and its two branches (the left and right main bronchi). A moment’s critical thinking should cast doubt over the reason given.
The right main bronchus may be straighter, more vertical and broader than the left, but none influence whether a peanut ends up on the left or right. The characteristics of the airway AFTER the peanut has entered it can have no bearing on a choice made before entry. The reasoning is flawed. Whether this qualifies as reasoning is a moot point. It takes what we know about the airways and concocts an explanation without testing it. In so doing, it fails to be an explanation as such. It does not follow that what we know about the airways is complete enough to make a judgment. Clinical experience leads us to suspect that an inhaled peanut will more likely lodge in the right main bronchus. Chest radiography is necessary to confirm this. Only then can extraction be attempted. Anatomical knowledge without critical thought does not provide an accurate explanation. Here, critical thinking has been lacking.
Little known is that experimental work on this problem has been performed and published in 1984. (Some 40 years before ChatGPT gave the stock answer.)
It appeared as:
Tracheobronical foreign bodies - The position of the carina
Lowe, D. and Ross Russell, R.I.
The Journal of Laryngology and Otology. May 1984, Vol. 98. pp499-501
A brief, popular science report of this paper also appeared in New Scientist:
Why peanuts prefer the right lung
New Scientist 7th June 1984 - p25
Volume 102 Issue 1413
In a laboratory at St. Bartholomew’s Hospital in London, Lowe and Ross Russell suspended dissected tracheas and bronchi and placed a funnel in the top. They then lobbed peanuts into the funnel to simulate their inhalation. These found their way into the right main bronchus four times more often than the left. Thus, they corroborated clinical experience. They then cut these specimens into front and back halves and photocopied them. Using these, they analysed the geometry of the airways. The key finding was that the position of the carina was typically slightly to the left of the axis of the trachea.
Carina is Latin for the keel of a boat. The anatomical carina is the ridge that points upwards where the main bronchi divide. (Imagine the boat upturned on the seashore.) The carina is slightly to the left of the mid-line of the trachea. As a result, it deflects peanuts to the right when inhaled. (Imagine now a pinball machine.)
As I suggested above, this was an elegant piece of work. By this, I mean that it was clear and concise. What the authors set out to test and how they did it left little or no room for doubt. In that sense, there was something ideal about it. Unfortunately, experiments are rarely like that. Therefore, it was refreshing to find one. So, I can recommend reading it.
Note:
An omission from all accounts of why inhaled peanuts favour the right main bronchus is our upright posture. Gravity has a bearing. However, the role played by gravity is missing. It is not just to do with inhalation of air carrying a peanut. It is much less likely that any quadrupedal animals experience such a problem. Of course, giraffes may inhale things while browsing the treetops. Any such nuts or berries fall a long way and gain considerable momentum as they do so. Gravity may play a role in those cases. But this is conjecture.
