Inspiratory time fraction (Ti/Ttot) during exercise in heart failure: associations with cardiac and ventilatory parameters

Abstract Background Disordered breathing patterns in heart failure (HF) are associated with prognosis and exercise tolerance; however, few studies have assessed changes in total respiratory time (Ttot) and inspiratory time (Ti). Objectives To clarify the association of exercise-induced changes in Ti/Ttot with cardiac function and ventilatory efficiency in HF patients. Methods This retrospective analysis included HF patients who underwent cardiopulmonary exercise testing. ΔTi/Ttot was the difference between Ti/Ttot at rest and peak exercise; patients were divided into decreased and maintained/increased groups. Correlations with echocardiographic and ventilatory parameters were assessed. Results Among the 187 patients with HF, 157 without respiratory diseases were analysed. Based on ΔTi/Ttot, 70 (44.6%) and 87 (55.4%) patients formed the decreased and maintained/increased groups, respectively. The median Ti/Ttot ratio at rest was 0.41 (0.37–0.43), whereas at peak exercise, it was 0.42 (0.32–0.45), with minimal overall change. However, the groups analysis revealed distinct patterns peak exercise Ti/Ttot (0.32 vs 0.44, p0.01). The decreased group exhibited significantly lower LVEF (35.0% vs. 54.0%, p 0.01), LV dilatation, and reduced stroke volume, consistent with HFrEF. Patients with LVEF 30% demonstrated pronounced reductions in ΔTi/Ttot. ΔTi/Ttot was positively correlated with left ventricular ejection fraction (LVEF) (ρ=0.46, p0.01), and negatively with left ventricular diastolic diameter and systolic diameter, and the dead space volume to tidal volume ratio (VD/VT) (ρ=−0.57, p0.01). The decreased group showed higher minute ventilation (37.2 vs 31.5 L/min, p0.01) and tidal volume (1292 vs 1145 mL, p0.05). Respiratory rate did not differ (29.1 vs 28.6 breaths/min, p=0.37). Conclusions These results suggest that, in some patients with HFrEF, expiratory prolongation occurs due to elevated VD/VT and impaired gas exchange. Conversely, the maintained/increased group (predominantly HFpEF) demonstrated lower VD/VT and efficient ventilation. Thus, Ti/Ttot may help characterise HF subtypes beyond severity alone. The ΔTi/Ttot decline observed in some patients with HF may reflect complex interactions between LV systolic dysfunction, pulmonary vascular congestion, and increased alveolar dead space. Changes in ΔTi/Ttot were associated with cardiac function and ventilatory efficiency in HF patients. An elevated VD/VT ratio contributed to expiratory prolongation, suggesting that Ti/Ttot may serve as a physiological marker for characterising HF-related breathing patterns.