Breathlessness perception in airways obstruction.

It has been known for many years that there are variations between patients in terms of their perception of breathlessness during airways obstruction. This has led to the concept of "poor perceivers" [1]. Poor perception probably has at least two components; the most widely recognized is diminished awareness of acute exacerbations of obstruction, but a second component is failure to recognize chronic changes. The presence of these two patterns can be clearly seen in the patients studied by RuBINFIELD and PAIN [1]. Subsequent studies have sought to address this problem by measuring breathlessness and a range of physiological variables associated with airflow limitation during the acute induction of airways obstruction or bronchodilatation (2-6]. Tests of the perception of external resistances have also been carried out [7-9]. The common finding is of wide variation in breathlessness perception and awareness of added resistances. No clear overall pattern has emerged with regard to factors responsible for these differences. RUBINFIELD and PAIN [1] were unable to identify any characteristics that distinguished perceivers from poor perceivers. They interpreted their later methacholine studies [3] as indicating that perception of acute exacerbations increased with deteriorating airways obstruction. In contrast, BuRDON et al. [2) found less dyspnoea during histamine induced bronchoconstriction in patients with a lowered baseline forced expiratory volume in one second (FEV1) compared to patients with normal function. Studies using external resistances have produced mixed results. Asthmatics and normals exhibited similar perception of added loads [7, 8) but in chronic obstructive airways disease (COAD) patients, perception was reduced compared to both normals and asthmatics [8]. Attempts have been made to relate dyspnoea perception to bronchial responsiveness. BuRDON et al. [2] found that patients with high responsiveness to histamine perceived less dyspnoea than less responsive subjects. Whilst this observation was statistically significant, the scatter in the data is considerable and one data point appears to be particularly influential. An alternative interpretation may be that less responsive subjects experienced more systemic effects due to histamine because a higher dose was needed and this may have influenced them. In support of this conclusion, a study using methacholine