Medical Terminology Daily - Est. 2012

Medical Terminology Daily (MTD) is a blog sponsored by Clinical Anatomy Associates, Inc. as a service to the medical community. We post anatomical, medical or surgical terms, their meaning and usage, as well as biographical notes on anatomists, surgeons, and researchers through the ages. Be warned that some of the images used depict human anatomical specimens.

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A Moment in History

Jean George Bachman

Jean George Bachmann
(1877 – 1959)

French physician–physiologist whose experimental work in the early twentieth century provided the first clear functional description of a preferential interatrial conduction pathway. This structure, eponymically named “Bachmann’s bundle”, plays a central role in normal atrial activation and in the pathophysiology of interatrial block and atrial arrhythmias.

As a young man, Bachmann served as a merchant sailor, crossing the Atlantic multiple times. He emigrated to the United States in 1902 and earned his medical degree at the top of his class from Jefferson Medical College in Philadelphia in 1907. He stayed at this Medical College as a demonstrator and physiologist. In 1910, he joined Emory University in Atlanta. Between 1917 -1918 he served as a medical officer in the US Army. He retired from Emory in 1947 and continued his private medical practice until his death in 1959.

On the personal side, Bachmann was a man of many talents: a polyglot, he was fluent in German, French, Spanish and English. He was a chef in his own right and occasionally worked as a chef in international hotels. In fact, he paid his tuition at Jefferson Medical College, working both as a chef and as a language tutor.

The intrinsic cardiac conduction system was a major focus of cardiovascular research in the late nineteenth and early twentieth centuries. The atrioventricular (AV) node was discovered and described by Sunao Tawara and Karl Albert Aschoff in 1906, and the sinoatrial node by Arthur Keith and Martin Flack in 1907.

While the connections that distribute the electrical impulse from the AV node to the ventricles were known through the works of Wilhelm His Jr, in 1893 and Jan Evangelista Purkinje in 1839, the mechanism by which electrical impulses spread between the atria remained uncertain.

In 1916 Bachmann published a paper titled “The Inter-Auricular Time Interval” in the American Journal of Physiology. Bachmann measured activation times between the right and left atria and demonstrated that interruption of a distinct anterior interatrial muscular band resulted in delayed left atrial activation. He concluded that this band constituted the principal route for rapid interatrial conduction.

Subsequent anatomical and electrophysiological studies confirmed the importance of the structure described by Bachmann, which came to bear his name. Bachmann’s bundle is now recognized as a key determinant of atrial activation patterns, and its dysfunction is associated with interatrial block, atrial fibrillation, and abnormal P-wave morphology. His work remains foundational in both basic cardiac anatomy and clinical electrophysiology.

Sources and references
1. Bachmann G. “The inter-auricular time interval”. Am J Physiol. 1916;41:309–320.
2. Hurst JW. “Profiles in Cardiology: Jean George Bachmann (1877–1959)”. Clin Cardiol. 1987;10:185–187.
3. Lemery R, Guiraudon G, Veinot JP. “Anatomic description of Bachmann’s bundle and its relation to the atrial septum”. Am J Cardiol. 2003;91:148–152.
4. "Remembering the canonical discoverers of the core components of the mammalian cardiac conduction system: Keith and Flack, Aschoff and Tawara, His, and Purkinje" Icilio Cavero and Henry Holzgrefe Advances in Physiology Education 2022 46:4, 549-579.
5. Knol WG, de Vos CB, Crijns HJGM, et al. “The Bachmann bundle and interatrial conduction” Heart Rhythm. 2019;16:127–133.
6. “Iatrogenic biatrial flutter. The role of the Bachmann’s bundle” Constán E.; García F., Linde, A.. Complejo Hospitalario de Jaén, Jaén. Spain
7. Keith A, Flack M. The form and nature of the muscular connections between the primary divisions of the vertebrate heart. J Anat Physiol 41: 172–189, 1907.


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Tracheal bronchus (pig bronchus)
Tracheal bronchus (pig bronchus)

After writing an article on the tracheal bronchus, I was asked to describe the anatomy of the pig (Sus scrofa domesticus) lung and a comparison with the human lung. The function and general structure of the pig lung is similar to the human. Anatomy-wise... there are several differences.

It is important to understand that directional terminology used to describe the anatomy of the pig is different than that used for the human. We use the anatomical position for humans, but as the pig is a quadruped, there is no such position for the pig, and veterinary terminology is used.. For further information on this topic, click here.

Following are two images. The first one is an anterior view of the human lungs and their tracheobronchial tree. The second image shows a ventral view of the pig tracheobronchial tree and both lungs.

Anterior view of the human lungs and tracheobronchial treeAnterior view of the human lungs and tracheobronchial tree

Pig lungs, ventral viewVentral view of the pig lungs and tracheobronchial tree

The first difference with the human lung is that there are two cardiac notches, right and left (the left cardiac notch is larger) whereas the human has only one, on the left lung.

The structure of the tracheobronchial tree in both species is similar, with incomplete cartilaginous rings and a posterior (dorsal) membrane that closes both the trachea and bronchi. Similarly, as the bronchial tree is more distal, the cartilaginous rings break up.

The trachea in the human ranges between 10 to 12 centimeters, while in the pig the trachea is longer, between 25 to 30 centimeters. Both bifurcate at the carina into a right and left main stem bronchus. In both species there is a large number of lymphatic nodes at the tracheal bifurcation (carinal nodes) which drain the lungs.

In the pig, the bronchus for the right cranial lobe arises directly from the trachea, and is known as the "tracheal bronchus". This does not normally happen in the human, and when it does it is considered an anatomical variation called a "pig bronchus", "bronchus suis", or "tracheal bronchus", and it can cause serious problems during intubation in surgery.

In the human, there are normally three lobes on the right side (upper, middle, and lower), and two on the left side (upper and lower). Each lobe has its separate lobar bronchus.

The right lung in the pig has 4 lobes: Cranial, middle, caudal, and an accessory lobe that is ventral and is located in the midline. Each lobe has its own separate lobar bronchus.

The left lung in the pig has two lobes: Cranial and caudal. The left cardiac notch splits the cranial lobe in two segments, but since these segments arise from a common bronchus, they are considered one lobe.

Sources:
1. "Essentials of Pig Anatomy" Sack, W.O.; Horowitz, A. 1982 Veterninary Textbooks, Ithaca, New York..
2. “Bronchial tree, lobular division and blood vessels of the pig lung” Nakakuki, S. J Vet Med Sci. 1994 Aug;56(4):685-9. 
3. “Bronchial anatomy and single-lung ventilation in the pig” Muton, WG. Can J Anesth 1999 46:7 p701-703

- Human tracheal bronchus endoscopic image modified from the original. Public domain.
- Anterior view of the human lungs and tracheobronchial tree image by . Patrick J. Lynch, medical illustrator, CC BY 2.5 <https://creativecommons.org/licenses/by/2.5>, via Wikimedia Commons.
- Ventral view of the Ventral view of the pig lungs and tracheobronchial tree image by Dr. Miranda, modified from the original. Public domain.