Measurement of Closing Volume as a Simple and Sensitive Test for Early Dectection of Small Airway Disease

Our plain-English summary of Measurement of Closing Volume as a Simple and Sensitive Test for Early Dectection of Small Airway Disease, by D.S. McCarthy, R. Spencer, R. Greene, et al (1972).

The study

• Authors: D.S. McCarthy, R. Spencer, R. Greene, J. Milic-Emili
• Published: American Journal of Medicine, Volume 52. June 1972
• 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 London study does not concern asbestos; it examined cigarette smokers. The authors measured "closing volume" (the lung volume, during a slow full breath out, at which the lowest lung zones stop being ventilated, presumably because their small airways close) using an inhaled bolus of argon. They also ran standard lung function tests. The subjects were 112 men: 66 nonsmokers aged 18 to 82 and 46 smokers aged 25 to 64. In nonsmokers, closing volume as a share of vital capacity rose linearly with age. Fourteen smokers (30 per cent) had at least one abnormal standard test. In seven of them closing volume could not be measured because of grossly uneven ventilation. Of the other 39 smokers, 26 had closing volumes above the nonsmoker upper limit. In all, 33 seated smokers (72 per cent) showed signs of small airway disease. Twenty of the 32 smokers with normal standard tests had raised closing volumes, nine of them without symptoms. The authors concluded that the test detects small airway abnormalities much earlier than conventional lung function tests and is simple enough for routine or wide-scale studies.

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: cross-sectional comparison of volunteers (nonsmokers and smokers) using a single-breath argon bolus test of "closing volume", recorded during a slow vital capacity breath out, alongside conventional lung function tests
• Who was studied: 112 men studied at the Royal Postgraduate Medical School, Hammersmith Hospital, London: 66 nonsmokers aged 18 to 82 with no history of chronic cardiac or respiratory disease, and 46 smokers aged 25 to 64. On direct questioning, 29 smokers had simple chronic bronchitis. All smokers had chest X-rays passed as normal within five years. The study dates are not stated; the manuscript was received October 1971.
• Exposure: cigarette smoking: 10 to 60 cigarettes a day (average 27) for 8 to 40 years (average 22). No asbestos or other fiber exposure was studied.
• Main results:
  • In both seated and supine nonsmokers, closing volume as a percentage of vital capacity increased linearly with age.
  • Fourteen of the 46 smokers (30 per cent) had one or more conventional lung function results outside normal limits.
  • In seven smokers with abnormal conventional tests, closing volume could not be determined because of a steeply rising expired argon curve indicating gross abnormalities of ventilation distribution.
  • Of the 39 smokers whose closing volume could be measured (seated), 26 had closing volume above the upper limit (+2 SD) for nonsmokers.
  • Overall, 33 seated smokers (72 per cent of all smokers) had either a raised closing volume or a profound abnormality of the expired alveolar plateau.
  • Of the 32 smokers with normal conventional test results, 20 had closing volumes above normal limits.
  • In nine asymptomatic smokers, closing volume was clearly abnormal although by questionnaire, X-ray and conventional tests they would have passed as normal.
  • Symptomatic (bronchitic) smokers tended to have higher closing volumes than asymptomatic smokers, but the two groups overlapped considerably.
  • In nonsmokers, closing volume began to exceed resting lung volume (FRC) at an average age of about seventy-three years when seated and about forty-six years when supine.
• The authors' conclusion: The authors concluded that measuring closing volume detects small airway abnormalities much earlier than conventional lung function tests, and is simple and rapid enough for routine or wide-scale studies.

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