Is serial determination of inspiratory muscle strength a useful prognostic marker in chronic heart failure?

Background Little data exists on the prognostic role of inspiratory muscle strength (Pimax) in chronic heart failure (CHF). Training studies, however, frequently use it as a therapeutic target and surrogate marker for prognosis. The prognostic value of changes of Pimax that allow this extrapolation is unknown. Design Patients with stable CHF were prospectively included and 1-year and all-time event rates recorded for endpoint analysis. Methods In 158 patients (85% men; New York Heart Association functional class: 2.4 +/- 0.6), Plmax was measured along with clinical evaluations at two visits, the initial visit and the second visit, 6.4 +/- 1.4 months apart. The mean follow-up was 59 34 months. Results Overall, 59 patients (37%) reached the primary endpoint of death or hospitalization (endpoint positive), and overall mortality rate (secondary endpoint) was 26% (42 patients). Plmax did not differ between endpoint-negative and endpoint-positive patients, both at the initial and at the second visit (8.3 +/- 5.6 vs. 73 +/- 3.4 kPa and 8.8 +/- 6.0 vs. 7.9 +/- 3.6 kPa, respectively; P = NS), and both groups showed increased Plmax (0.6 +/- 2.6 vs. 0.6 +/- 2.8 kPa; P= NS). Cox analyses found neither the absolute nor the relative change of Plmax to be significant predictors for the primary and secondary endpoints (P= NS for both), both for the 1-year and for the all-time event rates. Endpoint rates did not differ between patients showing increasing or decreasing Pimax (P=NS; relative risk (RR): 0.77; 95% confidence interval: 0.47-1.27). Conclusion Trials focusing on inspiratory muscle function should use the actual levels of Plmax as a surrogate marker to represent prognostic information, rather than relative or absolute changes. This is the first study to investigate the prognostic information of the changes of Pimax over time, regarding both short-term and long-term morbidity and mortality in patients with stable CHF.