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Collateral ventilation
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  1. E J Cetti,
  2. A J Moore,
  3. D M Geddes
  1. Department of Respiratory Medicine, Royal Brompton Hospital, London, UK
  1. Correspondence to:
    Dr E J Cetti
    Department of Respiratory Medicine, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK; e.cetti{at}rbht.nhs.uk

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Understanding collateral ventilation is probably central to planning new bronchoscopic techniques for treating emphysema

The phenomenon of collateral ventilation in the human lung is defined as “the ventilation of alveolar structures through passages or channels that bypass the normal airways”. This phenomenon seems to be prominent in emphysema and is emerging as a key issue for those working in the new and exciting field of bronchoscopic techniques for treating emphysema.

The existence of channels within the lungs through which such collateral flow could occur was realised a century ago,1 but it was not until the 1930s that the possible significance of this flow was recognised.2 This significance was largely ignored by physiologists and physicians alike,3 apart from a select band of investigators in the 1960s and 1970s.4–7 However, with the emergence of new bronchoscopic techniques for treating emphysema, the phenomenon of collateral ventilation has gained a renewed importance and the paper by Higuchi et al8 in this issue of Thorax casts some welcome light on the issue of collateral ventilation in the emphysematous lung.

ANATOMICAL, PHYSIOLOGICAL AND CLINICAL EVIDENCE FOR THE EXISTENCE OF COLLATERAL VENTILATION

In order for collateral flow of air to occur within the lungs, there must exist collateral channels with a pressure gradient across them. Candidate pathways for collateral ventilation include interalveolar pores,9 accessory bronchiole-alveolar communications,10 and accessory respiratory bronchioles connecting bronchiole to bronchiole.4 As Higuchi et al8 point out in this issue of Thorax, interlobar collateral flow across fissures has been demonstrated, and while this may be via some of the above pathways, in the context of lung destruction by emphysema new channels may develop. The resistance to collateral flow in human lungs has been measured and found to be 50 times greater than the resistance to flow through the normal airways.5,11 It therefore …

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