The relationship between breathlessness and ventilation during steady-state exercise.

In clinical studies on breathlessness, the relationship between breathlessness and ventilation is a convenient way of summarizing the responses of single subjects or groups of subjects. This relationship is usually based on measurements during progressive exercise. The objective of this study was to determine whether the relationship was maintained in different conditions or whether breathlessness could alter independently of ventilation. Six healthy subjects undertook progressive exercise so that the relationship of breathlessness to ventilation could be described; the reproducibility was established. The same subjects also undertook exercise at two constant workloads. After 4 min, stable values of ventilation were achieved but the breathlessness scores continued to increase (p less than 0.05). These findings show that the relationship between breathlessness and ventilation may be disturbed without external intervention, and this provides further evidence that breathlessness is not simply a sensing of the ventilation achieved.