VOLUNTARY DECREASE IN BREATHING FREQUENCY IN EXERCISING ASTHMATIC SUBJECTS

Exercise rehabilitation programmes are increasingly recommended in you ng asthmatics, but it is unclear whether or not training should incorp orate instructions on breathing pattern, In this study, we examined th e effects of voluntarily decreasing breathing frequency on their venti latory equivalents for oxygen and carbon dioxide (minute ventilation ( V'E)/oxygen consumption (V'O-2) and V'E/CO2 production (V'CO2), respec tively), noninvasively determined physiological dead space/tidal volum e (VD/VT) and dyspnoea. Fifteen young asthmatic subjects were assigned to two groups: low frequency breathing (LFB) and controls, They first underwent an exercise test at a cardiac frequency of 150 beats . min( -1). They were trained at this level for nine sessions, LFB subjects w ere instructed to decrease respiratory frequency by 40% during exercis e. Control subjects received no instructions, A second test was then p erformed in the same conditions. LFB subjects decreased V'E/V'O-2, V'E /V'CO2, and VD/VT by 22, 19 and 12%, respectively, Arterial oxygen sat uration (Sa,O-2) fell to 89+/-4% and end-tidal carbon dioxide tension (PET,CO2) rose to 65+/-0.7 kPa (49+/-5 mmHg). In controls, these varia bles were identical in the two tests, Dyspnoea was lower in the second test in all subjects. In conclusion, breathing pattern may be profoun dly altered during exercise without concomitant increase in dyspnoea. However, directing breathing patterns for exercise rehabilitation requ ires an individual assessment of the desired pattern in order to preve nt hypercapnia or hypoxia.