LETTERS

Ventilation variability inversely correlates to ejection fraction in heart failure To the Editors: Heart failure is currently considered a systemic disease. In this context, there is growing interest in cardiopulmonary interac-tions during rest, sleep and exercise [1]. Periodic breathing during exercise is characterised by regular waxing and waning of minute ventilation (V’E) due to oscillations in central respiratory drive. Periodic breathing independently predicts mortality in heart failure patients [2], but is not directly correlated with low left ventricular ejection fraction. For example, the occurrence of periodic breathing could predict cardiac mortality in patients who were waiting for cardiac transplantation, independent of ejection fraction [2]. Clinical experience shows that some heart failure patients exhibit ventilatory oscillations during exercise testing without achieving the established criteria of periodic breathing (mini-mum of three regular oscillations; deviation of three con-secutive cycle lengths within 20 % of their average; and minimal ventilatory oscillation of 5 L) [2]. We hypothesised that the analysis of time-domain variability of respiratory variables during exercise could add important clinical infor-mation, detecting changes of insufficient magnitude to be classified as periodic breathing. Cardiopulmonary exercise tests in 17 heart failure patients (53 % male; mean¡SD age 59¡9 yrs; ejection fraction 23¡6%) under standard treatment were retrospectively analysed following approval of th