Breathlessness in healthy subjects at physical load.

The aim of the study was to ascertain the reasons which lead to discontinuance of exercise on the bicycle ergometer in healthy untrained subjects and to assess the dependence of dyspnea on breathing pattern and on ventilation. The physical load was progressively increased to the maximum in 11 volunteers at the age of 21 +/- 1 years. During exercise some cardiovascular and respiratory parameters were measured simultaneously with the degree of dyspnea. Breathlessness was rated by means of a scaling according Borg, where 0 indicates no, 10 maximal dyspnea. Dyspnea was not a reason for termination of maximal exercise, its value being 6 +/- 1.9 in men and 4.5 +/- 2.3 in women at the end of exercise. The reasons for termination of exercise were the sensations of general fatigue and pain in lower the extremities. The degree of dyspnea correlated with the minute ventilation, with the decrease of end-tidal CO2 concentration, with the duration of exercise and some other values. The grading varied among subjects. The mathematical dependence of dyspnea was summarised by two regression equations, one without suppression, the other with suppression of interindividual differences in responses.