A novel method for the quantitative evaluation of diurnal respiratory instability in patients with heart failure: A pilot study

Abstract Background There is no established method to quantitatively measure the presence and the severity of respiratory instability (RI). The purpose of this pilot study was to propose a novel index of diurnal RI as a surrogate measure of clinical severity of heart failure (HF). Methods and results We prospectively enrolled 60 patients with symptomatic HF [70 ± 14 years, 75% male, and New York Heart Association (NYHA) functional classes II–IV] who underwent right heart catheterization (RHC), and recorded diurnal respiration using a nasal pressure sensor during bed rest while awake within 2 days before or after RHC. Non-uniformity of the breath-by-breath respiratory slopes during 15 min calculated as the ratio of peak expiratory amplitude to corresponding peak-to-peak interval was assessed by histogram-based frequency distribution measurement, and was defined as the “RI-index”. The RI-index was significantly different among NYHA functional classes and was highest in NYHA class IV. The presence of atrial fibrillation ( β coefficient: 0.300, p  = 0.01) and stroke volume index ( β coefficient: −0.462, p Conclusions The RI index stratified functional severity of HF well, and was a significant independent predictor of poor outcomes.