Perception of what?

To the Editors:

Finding risk factors for severe attacks of asthma is an important issue. The study published in the European Respiratory Journal by Barreiro et al. 1 is of interest as it concluded that blunted perception of dyspnoea may be of importance. It is summarised that “Dyspnoea at peak exercise is the best indicator of the near-fatal asthma condition”. Two small groups of asthmatic patients with (n = 7) and without (n = 8) a recent near-fatal asthma (NFA) attack (“at least one NFA attack within the 5 yrs previous to study entry” 1) were compared.

However, the article gives rise to some questions and comments. What was the definition of NFA? No description was given other than that cited above. Did the patients visit an emergency room? How was lung function? How can one know that the attacks were near fatal without examining consciousness, cyanosis, carbon dioxide retention, or by other appropriate tests?

It is well documented in several studies that symptoms generally attributed to asthma are not well correlated (sometimes not at all) to lung function values, such as forced expiratory volume in one second (FEV₁). For this reason, how can one expect that dyspnoea or perception of dyspnoea (which is one symptom) could be relevant for bronchial obstruction and severe asthma attack? What is the hypothesis? Some of the (believed) asthma symptoms are not indicators of bronchial obstruction (asthma) but of asthma-like disorders 2–5, such as sensory hyperreactivity 4, 6. These disorders are often mixed up with classical asthma 5 and a patient may also have classical asthma and sensory hyperreactivity simultaneously 4, 6. There are reasons to suspect that perception of dyspnoea has a very limited direct association with bronchial obstruction (asthma); more important may be a disturbance of the breathing regulation. Low lung function values in these patients may sometimes be interpreted as asthma, but may in fact be better explained by an inability to perform a forced expiration, e.g. when recording FEV₁ and peak expiratory flow.

Exercise may induce bronchial obstruction (exercise-induced bronchial obstruction), but may also induce symptoms that are similar to those in asthma/bronchial obstruction 7. This is often overlooked in the literature. If one likes to predict the risk for acute bronchial asthma, such as NFA, and use a physical test, it may be logical to also document the degree of bronchial obstruction after exercise, e.g. changes in FEV₁. Where are those data? What was the correlation between the degree of dyspnoea and lung function before, during and after exercise?

Thus, there are several basic questions that have to be answered before it may be concluded that perception of dyspnoea is of any importance for the prediction of severe asthma attacks.