Higher brain function is disturbed with sleep disruption (see Chapter 19), cognitive dysfunction3 and the development of mood impairment.
The development of ill health due to chronic disease does not follow a simple linear path (Figure 31.1) and within each pathway there may be multiple mechanisms. For example breathlessness may be due to expiratory airflow limitation, an increase in static lung volume, dynamic hyperinflation and hypoxia-induced stimulation of breathing. Furthermore, some of these paths are circular. Perhaps, the simplest to understand is the effect of exercise limitation. This causes muscle wasting due to disuse atrophy, which itself will induce exercise limitation. The existence of such feedback loops leads to ‘local autonomy’ with the induction of secondary selfmaintaining disease processes that are entirely unrelated
to the original disease trigger. It is clearly inappropriate to consider COPD just as a condition of the lungs; it is a multisystem disease and so its assessment should reflect this.