Orthopnea and inspiratory effort in chronic heart failure patients

Study objective: Orthopnea is a typical feature of patients with chronic heart failure (CHF), the factors contributing to it are not completely understood. We investigated changes in dyspnea and other respiratory variables, induced by altering posture (from sitting to supine) in II CHF patients (NYHA classes II-IV) and 10 control subjects. Methods and Results: We measured dyspnea (Borg scale), the diaphragm pressure time product per minute (PTPdi/m, index of metabolic consumption), and mechanical properties of the lung (lung compliance (C,_L) and resistances (R,_L). CHF patients also underwent a trial of non-invasive mechanical ventilation (NIMV) inthe supine position in order to ascertain whether unloading the inspiratory muscles could somehow relieve dyspnea. While sitting the PTPdi/min was significantly higher in CHF patients than in controls (181±54 cm H₂O × s/min vs. 96±32; P2O/L × s sitting vs. 79±2.5 supine; P2O sitting vs. 0.07+0.01 supine; PL, and a reduction in C,L so that PTPdi/min increased further. Orthopnea was strongly correlated with the increased diaphragmatic effort.