Pattern of breathing during progressive exercise in chronic heart failure

This descriptive study analyzed serial, individual changes in the exercise pattern of breathing (POB) of patients with stable chronic heart failure (CHF). Twenty-two CHF patients underwent maximal, symptom-limited cardiopulmonary exercise test on a treadmill. Minute ventilation (VE), tidal volume (VT), breathing frequency (f), the ventilatory equivalent for carbon dioxide (VE/VCO2) and estimated dead-space to tidal volume ratio (VD/VT) were continuously recorded. The VE/VCO2 slope was calculated in every subject as the slope of the regression line relating VE to VCO2 during exercising testing. Pattern of breathing was investigated by constructing the individual VT-f relationship for each patient separately. In 16 (73%) patients (group 1), the VT-f plot was initially linear, but subsequently exhibited an inflection point at which VT stopped increasing with further increases in f. In six (27%) patients (group 2) no inflection point was evident on the VT-f relation; in four of these patients the VT-f relation remained linear but shifted to the right throughout testing, and two patients decreased VT before peak exercise achieving high breathing frequencies. Comparing group 1 to group 2 patients, they had higher VEmax (68+/-23 vs. 44+/-10 l/min, P=0.02) and VO2max (17+/-5 vs. 12+/-3 ml/min/kg, P=0.01). In contrast, the two groups did not differ in terms of age, weight, height, diagnosis, ejection fraction or VE/VCO2 slope. In conclusion, patients with CHF adopt variable breathing patterns during exercise; specific patterns are associated with greater impairment in functional capacity.