Thoracic fluid content — a possible determinant of ventilatory efficiency in patients with heart failure

Abstract Ventilatory efficiency, evaluated by cardiopulmonary exercise testing (CPET), has considerable prognostic value in patients with chronic heart failure (CHF) due to left ventricular systolic dysfunction (LVSD). Its determinants nevertheless remain controversial. Aim To investigate the possible correlation between parameters of ventilatory efficiency obtained by CPET and thoracic fluid content (TFC), assessed by thoracic electrical bioimpedance (TEB), in patients with CHF due to LVSD. Methods We studied 120 patients with LVSD and CHF, referred to our laboratory for CPET: 76% male, age 52.1 ± 12.1 years, 37% of ischemic etiology, left ventricular ejection fraction 27.6 ± 7.9%, 83% in sinus rhythm, 96% receiving ACEIs and/or ARBs and 79% beta-blockers, and 20% treated with a cardiac resynchronization device. TEB studies were performed after 15 minutes of rest, prior to symptom-limited treadmill CPET, using the modified Bruce protocol. CPET-derived peak oxygen consumption (pVO 2 ), the slope of the relationship between minute ventilation (VE) and carbon dioxide production (VCO 2 ), VE/VCO 2 at the anaerobic threshold (AT), and TFC assessed by TEB were considered for analysis. Results TFC ranged between 20.6 and 45.8 kOhm −1 , mean 32.2, SD = 5.7, median 32.7, pVO 2 8.9–40.6 ml/kg/min, mean 21.0, SD 6.2, median 20.2, VE/VCO 2 slope 19.8–60.7, mean 30.7, SD 7.9, median 29.1 and VE/VCO 2 at AT 21–62, mean 33.1, SD 7.5, median 31.5. By linear regression, TFC did not correlate with pVO 2 (r = 0.05, p = 0.58), but showed correlation with parameters of ventilatory efficiency: r = 0.20, p = 0.032, r 2  = 0.04 for VE/VCO 2 slope and r = 0.25, p = 0.009, r 2  = 0.06 for VE/VCO 2 at AT. Conclusion TFC correlates with CPET parameters of ventilatory efficiency in patients with CHF due to LVSD, suggesting that it may be one of its determinants.