Better parameters of ventilation-CO2 output relationship predict death in CHF patients

Objective: Measures of ventilation-co_2 output relationship have been shown to be more prognostic than peak O_2 uptake in assessing life expectancy in patients with chronic heart failure(CHF). Because both the ratios(V4e/V4co_2) and slopes(V4e-vs-V4co_2) of ventilation-co_2 output of differing durations can be used, we aim to ascertain which measurements best predicted CHF life expectancy. Methods: Two hundred and seventy-one CHF patients with NYHA class II-IV underwent incremental cardiopulmonary exercise testing(CPET) and were followed-up for a median duration of 479 days. Four different linear regression V4e-vsV4co_2 slopes were calculated from warm-up exercise onset to: 180 s, anaerobic threshold(AT), ventilatory compensation point(VCP); and peak exercise. Five V4e/V4co_2 ratios were calculated for the following durations: rest(120 s), warm-up(30 s), AT(60 s), lowest value(90 s), and peak exercise(30 s). Death or heart transplant were considered end-points. Multiple statistical analyses were performed. Results: CHF patients had high lowest V4e/V4co_2(41.0±9.2, 141±30%pred), high V4e/V4co_2 at AT(42.5±10.4, 145±35%pred), and high V4e-vs-V4co_2 slope to VCP(37.6±12.1, 126±41%pred). The best predictor of death was a higher lowest V4e/V4co_2(≥42, ≥141%pred), whereas the V4e-vs-V4co_2 slope to VCP was less variable than other slopes. For death prognosis in 6 months, %pred values were superior: for longer times, absolute values were superior. Conclusion: The increased lowest V4e/V4co_2 ratio easily identifiable and simply measured during exercise, is the best measurement to assess the ventilation-co_2 output relationship in prognosticating death in CHF patients.