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Lung as Filter

Q. Does the lung filter small clots / debris / chemicals as a normal feature?

A. Yes. 1

  • It is a known 'non-respiratory' function of the lungs and they are adapted for it by having:
  • pulmonary capillary endothelium with lots of fibrinolysin activator which stimulates breakdown of fibrin-to-fibrin degradation products, thus lysing clots in situ,

  • seems to play active role in overall coagulability of blood by being:

    • Richest source of heparin in the body.
    • Richest source of thromboplastin (converts prothrombin to thrombin) thus PROMOTING coagulation.

  • PE appears to be due to significant increase in alveolar perfusion causing V/Q mismatch. And emboli also lead to neutrophil activation -> increased permeability / alveolar oedema >> acute lung injury.

  • The other non-respiratory functions of the lungs are: 1) Reservoir of blood, fine tuning the preload to the heart. 2) Defence against inhaled particles and chemicals. 3) Uptake, metabolism and transformation of both exo and endogenous substance. 4) Pulmonary endothelial binding of some drugs can alter their pharmacokinetics.

  1. Deepak Joseph, MBBS, MD, FRCA, Raju K Puttaswamy, MBBS, FRCA, Hari Krovvidi, MBBS, MD, FRCA, Non-respiratory functions of the lung, Continuing Education in Anaesthesia Critical Care & Pain, Volume 13, Issue 3, June 2013, Pages 98–102, https://doi.org/10.1093/bjaceaccp/mks060 ↩