A hypothesis for pulmonary clearance and its implications

Our plain-English summary of A hypothesis for pulmonary clearance and its implications, by K. H. Kilburn (1968).

The study

• Author: K. H. Kilburn
• Published: American Review of Respiratory Disease, Vol. 98, 1968 (pp. 449-463)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This paper was not a study of asbestos and did not mention asbestos. It was a hypothesis paper that organized published information on how the lungs clear inhaled particles. It was partly supported by the author's observations of an opened-out (evaginated) bullfrog lung, which were reported in detail elsewhere. The author proposed that the air sacs (alveoli) are cleared of insoluble particles and cells on a thin fluid film that moves by surface forces toward the ciliated small airways. The author also proposed that failure of this clearance is a major disease-causing process in certain lung diseases. In the frog lung, India ink, graphite, lamp black, carmine or silicone particles were moved by moisture and by cilia. With more fluid, transport to the glottis took only minutes, while materials on a dry surface were not moved. The author calculated that mucus secretions must be reduced in volume more than 4,000-fold between the sixteenth-generation bronchioles and the windpipe (trachea). The author suggested that bronchitis, bronchiolitis, asthma and centrilobular emphysema may be related to failure of clearance.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Hypothesis paper organizing existing published information on lung clearance, partly supported by the author's own observations of an evaginated bullfrog lung (details reported elsewhere)
• Who was studied: No human study population. Observations were made on evaginated bullfrog lungs viewed under a dissecting microscope; the number of animals is not given in this paper.
• Exposure: In the frog lung model: small drops of India ink and particles of graphite, lamp black, carmine or silicone dusted onto the lung surface. Asbestos is not discussed.
• Main results:
  • In the bullfrog lung, when more fluid was present, transport of particles to the glottis took only minutes.
  • In the bullfrog lung, materials on a dry surface were not moved.
  • In the bullfrog lung, clearance was reversibly slowed by cooling, by surface drying and by particle overload.
  • Using published airway measurements (Weibel), the author calculated that mucus secretions moving from the sixteenth-generation bronchioles to the trachea must be reduced in volume more than 4,000-fold (4320 times in the author's table).
• The authors' conclusion: The author suggested that alveolar clearance occurs through movement of thin (sol) fluid from its secretion by type II alveolar cells and Clara cells to its reabsorption higher up the airways. The author also suggested that the pathogenesis and many manifestations of bronchitis, bronchiolitis, asthma and centrilobular emphysema may be related to failure of clearance from alveoli and small bronchioles.
• Limitations the authors state:
  • The author stated that the process of delivering material from alveoli to the ciliated transport system cannot be observed in the mammalian lung, so the simpler bullfrog lung was used.
  • The author stated that the frog clearance model as described does not include phagocytosis (removal by scavenger cells).

Topics

Medical terms in this study, explained in our Lexicon: Alveoli, Emphysema.

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