Inefficient ventilation and reduced respiratory muscle capacity in congestive heart failure

Abstract

The extent and time-course of changes in lung volumes, ventilatory efficiency at rest and during exercise, and respiratory muscle function and their influence on exercise limitation in congestive heart failure (CHF) are unclear. It is unknown whether respiratory muscle function may predict changes in exercise limitation or may be impaired in patients with poor outcome. 145 male patients (54±1 years) suffering from CHF (NYHA class I–III, mean 2.3±0.1), with a LVEF of 23±1 %, and a mean peak O₂ uptake (V_O2peak) 15.0±:0.5 mL×min⁻¹×kg⁻¹, were studied. They were grouped in Weber functional classes A to D according to their V_O2peak. Significant increases in ventilatory equivalents for O₂ and CO₂ (V_E/V_CO2peak) and in dead space ventilation at rest and during exercise were found with increasing exercise limitation. Moreover, there was a correlation of static and dynamic lung volumes (inspiratory vital capacity, IVC, r = 0.43, P < 0.01), as well as of maximal inspiratory pressure (MIP; r = 0.46, P < 0.01) with V_O2peak. Patients who died (n = 26) or were heart transplanted (n = 20) during a follow-up (mean 800 ± 10 days) had a reduced MIP (6.4 ± 0.4 kPa) as compared with survivors (n = 82; 9.3±0.7 kPa, P < 0.01). In a subgroup of 33 patients re-evaluated after six months, individual changes in IVC and V_E/V_CO2peak, but not in MIP, correlated to changes in V_O2peak (r = 0.69 and r = 0.72 respectively; P < 0.01).

In CHF, exercise limitation is associated with reversible lung restriction and inefficient ventilation at rest and during exercise. Patientss with severe CHF have a significant reduction in MIP, a finding that is associated with poor outcome.