Assessment of variability of exercise tolerance limited by breathlessness.

A sequence of questions was designed to quantify the within subject variation of exercise tolerance limited by breathlessness, to serve as a guide to variation in airflow limitation for epidemiological purposes. The questions seek answers about breathlessness in relation to various levels of attempted activity when the subjects are at their best and at their worst. The difference between exercise tolerance at best and exercise tolerance at worst (variation in exercise tolerance) was expressed on a scale ranging from 0 (no variation) to 6 (greatest variation). The effectiveness of these questions has been assessed in 68 patients with airflow limitation attending a chest clinic, by comparing the results with variation in peak expiratory flow rate (PEF). Variation in PEF was expressed as the standard deviation of the first 24 PEF recordings from each patient (equivalent to four days' recordings). There was a highly significant relation between the measure of variation in exercise tolerance obtained from the questionnaire and PEF variation, though each point on the scale of variation in exercise tolerance covered a wide range of variation in PEF. The questions give some guide to the variation in airflow limitation and in combination with other questions may be helpful in epidemiological studies.