132 Proc. roy. Soc. Med. Volume 69 February 1976

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bulli and depression of the diaphragm better than the

usefulness of this test compared with the so-called more sensitive tests. The results might be different if only those within 90% of the predicted FEV1 were used for study. Professor Milic-Emili replied that his conclusions were unaffected by raising the cut-off point to 85% but the numbers of subjects were smaller. Mrs M McDermott said that data for people living on Bornholm (Olsen & Gilson, 1960, British Medical Journal i, 450-456, McDermott et al., 1975, Bulletin de Physio-Pathologie Respiratoire 11, 41P-45P) showed the closing volume to be greater in cigarette smokers than in cigar and pipe smokers. However, the closing volume bore no relation to respiratory symptoms at the 'time of the study or to subsequent prognosis. The FEV was a better test in these respects. Dr M Sudlow commented that the iso-volume test performed using three breaths of helium exhibited an up to 70% variation; this was greatly reduced by the subjects breathing helium for ten minutes before the test. The difference reflected the extent of washout of nitrogen from the lung. Dr Sudlow suggested this might be the mechanism underlying Professor MilicEmili's findings, and not airways narrowing associated with loss of elastic recoil pressure. Dr T J H Clark had evidence for asthmatics that the three-breath and the ten-minute helium results were similar. Dr Sudlow agreed that they were similar in the absence of airways obstruction. In the presence of obstruction the variability was reduced by taking the best flowvolume curve after three breaths instead of taking the mean of them. Professor C M Fletcher questioned if the closing volume test which yielded abnormal results in 60% of smokers could be a valid predictor of disability, since only a small proportion of smokers were likely to develop airways obstruction. In answer to Mrs McDermott, there was no information on for how long after smoking a cigarette the helium flow volume test was influenced by the acute effects of smoking. Professor Milic-Emili found it disturbing that many new tests were used before they were fully developed.

P-A films. In answer to Dr G Cumming, he had no evidence on the interpretation to be placed oIn a large retrocardiac space. Dr T J H Clark emphasized the need for grading the emphysema; this was an essential step in determining the prevalence.

Professor J Milic-Emili (Department ofPhysiology, McGill University, PO Box 6170, Station A, Montreal, Canada, H3C3GI) Prevalence of Emphysema: Physiological Features Recently several new tests have been described which can detect abnormalities in lung function in patients in whom the conventional lung function measurements are within normal limits. They include (a) regional lung function using radioactive xenon, (b) frequency dependence of lung compliance, (c) frequency dependence of N2 washout, (d) flow dependence of the intrapulmonary distribution of inspired boluses of '33Xe, (e) closing volume and closing capacity, (f) analysis of the alveolar plateau, (g) analysis of flow-volume curves during helium breathing. The last three are sensitive as well as relatively simple and rapid, and appear potentially suitable for epidemiological studies (see McCarthy et al. 1972, Buist & Ross 1973, Buist et al. 1973, Dosman et al. 1975). Although their precision and reliability has not been as yet fully defined, most of these tests appear sufficiently reproducible for epidemiological studies. However, they lack specificity, in that they reflect abnormalities in both small airways and lung parenchyma and their validity has still to be determined. Future longitudinal epidemiological studies are needed to establish if these new lung function tests are of any prognostic value. Additional fundamental information will also be gained by comparing the results of these tests with findings at autopsy. REFERENCES Buist A S & Ross B B (1973) American Review of Respiratory Diseases 108, 1078 Buist A S, Van Fleet D L & Ross B B (1973) American Review of Respiratory Diseases 107, 735 Dosman J, Bode F, Urbanetti J, Martin R & Macklem P T (1975) Journal of Clinical Investigation 55, 1090 McCarthy D S, Spencer R, Greene R & Milic-Emili J (1972) American Journal of Medicine 52, 747 DISCUSSION

Dr T J H Clark said that the FEV,0 had a smaller intra-subject variability than the other tests. On this account the practice of selecting subjects from amongst those whose FEV lay within 75% of the predicted value could lead to under-estimation of the

Dr R B Cole, Dr N C Nevin, Dr B L Bradley, Dr G Blundell, Dr J D Merrett and Dr J R McDonald

(Departments of Medicine and Medical Statistics, Queen's University of Belfast, and Department of Clinical Chemistry, Belfast City Hospital)' Effect of Variation in Alpha-1-antritrypsin Phenotype upon Incidence of Respiratory Illness in an Unselected Working Population In a population sample of 1995 people of both sexes between 30 and 70 years of age living in Northern Ireland, the percentage frequencies of 'Correspondence may be addressed to: Dr R B Cole, Respiratory Physiology Department, North Staffs Hospital Centre, Stoke-on-Trent

Prevalence of emphysema: physiological features.

132 Proc. roy. Soc. Med. Volume 69 February 1976 6 bulli and depression of the diaphragm better than the usefulness of this test compared with the...
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