Chronic Bronchitis and Decline in Pulmonary Function with Some Suggestions on Terminology

Summary

The history of developments in terminology of obstructive pulmonary diseases is briefly reviewed. An account is given of two prospective studies which have shown that the rate of loss of ventilatory function is independent of indices of bronchial mucus hypersecretion and infections so that there is no casual connection between chronic bronchitis and development of generalised airflow limitation. Since it is also known that mucus hypersecretion arises in large bronchi and airflow limitation in small bronchi, it is inappropriate to use the term ‘chronic obstructive bronchitis’ to describe patients with expectoration and airflow limitation. The term ’chronic bronchiolitis would be more appropriate for subjects with chronic airflow limitation which is not due to asthma or emphysema.

Of all the harmful effects of smoking breathlessness due to irreversible air-flow limitation is perhaps the most distressing and disabling. In the United Kingdom, where death rates from this condition are the highest in the world, this condition is usually referred to as “Chronic Bronchitis” or “Emphysema”. It was largely ignored by chest physicians until the post-war years when, with the decline in tuberculosis the importance of chronic bronchitis became apparent. Its relationship to smoking was completely ignored. At that time there was great confusion about terminology. The first step towards clarification came in 1959 when the report of a CIBA Guest Symposium was published (1). Its proposal t hat emphysema should be defined on an anatomical basis of dilatation and destruction of alveoli has retained universal acceptance. It was also proposed that bronchitis should be defined as hypersecretion of bronchial mucus sufficient to cause persistent expectoration and that generalised limitation of airflow should be described simply by that term and should be separated into a reversible form or asthma — a definition which has been widely accepted but never precisely defined — and an irreversible type. It is in relation to this latter condition, when not manifestly due to emphysema, that confusion in terminology persists, the reasons for which I would like to discuss and about which I hope finally to make acceptable recommendations.

In 1965 a committee of the British Medical Council proposed a classification on bronchitis (2) (Figure 1). This was based on the epidemiological observation (3) of a marked association between volume of sputum, frequency of chest illnesses and reduction of FEV. So it was thought that these three abnormalities were part of a single disease process and it was widely believed in the U.K. (Figure 2) that hypersecretion encouraged infection which in turn damaged the lung causing airflow obstruction (AFO) which was thought to be due to emphysema. At that time it had already been shown that severe obstruction could occur in the absence of emphysema. The pathology of this sort of obstruction was not widely known; but severe bronchiolitis in one such case had been described by Harrison in 1951 (4) and simple methods for distinguishing ‘emphysematous’, ‘mixed’ and ‘bronchial’ types of case in 1966 (5). Pathologist had also described bronchiolar infection in association with emphysema (6, 7) and bronchiolar stenosis had also been described (8), but it was generally believed that excessive mucous in the bronchi caused much of the obstruction.