EFFECT OF BREATHING RATE ON OXYGEN-SATURATION AND EXERCISE PERFORMANCE IN CHRONIC HEART-FAILURE

Background In chronic heart failure (CHF), impaired pulmonary function can independently contribute to oxygen desaturation and reduced physi cal activity. We investigated the effect of breathing rate on oxygen s aturation and other respiratory indices. Methods Arterial oxygen satur ation (SaO(2)) and respiratory indices were recorded during spontaneou s breathing (baseline) and during controlled breathing at 15, six, and three breaths per min in 50 patients with CHF and in 11 healthy volun teers (controls). 15 patients with CHF were randomly allocated 1 month of respiratory training to decrease their respiratory rate to six bre aths per min. Respiratory indices were recorded before training, at th e end of training, and 1 month after training. Findings During spontan eous breathing, mean SaO(2) was lower in CHF patients than in controls (91.4% [SD 0.4] vs 95.4% [0.2], p<0.001). Controlled breathing increa sed SaO(2) at all breathing rates in patients with CHF. Compared with baseline, minute ventilation increased at 15 breaths per min (+45.9% [ 9.8], p<0.01), did not change at six breaths per min, and decreased at three breaths per min (-40.3% [4.8], p<0.001). In the nine CHF patien ts who had 1 month of respiratory training, resting SaO(2) increased f rom 92.5% (0.3) at baseline to 93.2% (0.4) (p<0.05), their breathing r ate per min decreased from 13.4 (1.5) to 7.6 (1.9) (p<0.001), peak oxy gen consumption increased from 1157 (83) to 1368 (110) L/min (p<0.05), exercise time increased from 583 (29) to 615 (23) min/s (p<0.05), and perception of dyspnoea reduced from a score of 19.0 (0.4) to 17.3 (0. 9) on the Borg scale (p<0.05). There were no changes in the respirator y indices in the patients who did not have respiratory training. Inter pretation Slowing respiratory rate reduces dyspnoea and improves both resting pulmonary gas exchange and exercise performance in patients wi th CHF.