Orthopnea and tidal expiratory flow limitation in chronic heart failure

Tidal expiratory flow limitation (FL) is common in patients with acute left heart failure and contributes significantly to orthopnea. Whether tidal FL exists in patients with chronic heart failure (CHF) remains to be determined.

To measure tidal FL and respiratory function in CHF patients and their relationships to orthopnea.

In 20 CHF patients (mean [+/- SD] ejection fraction, 23 +/- 8%; mean systolic pulmonary artery pressure [sPAP], 46 +/- 18 mm Hg; mean age, 59 +/- 11 years) and 20 control subjects who were matched for age and gender, we assessed FL, Borg score, spirometry, maximal inspiratory pressure (Pimax), mouth occlusion pressure 100 ms after the onset of inspiratory effort (P(0.1)), and breathing pattern in both the sitting and supine positions. The Medical Research Council score and orthopnea score were also determined.

In the sitting position, tidal FL was absent in all patients and healthy subjects. In CHF patients, Pimax was reduced, and ventilation and P(0.1)/Pimax ratio was increased relative to those of control subjects. In the supine position, 12 CHF patients had FL and 18 CHF patients claimed orthopnea with a mean Borg score increasing from 0.5 +/- 0.7 in the sitting position to 2.7 +/- 1.5 in the supine position in CHF patients. In contrast, orthopnea was absent in all control subjects. The FL patients were older than the non-FL patients (mean age, 63 +/- 8 vs 53 +/- 12 years, respectively; p < 0.03). In shifting from the seated to the supine position, the P(0.1)/Pimax ratio and the effective inspiratory impedance increased more in CHF patients than in control subjects. The best predictors of orthopnea in CHF patients were sPAP, supine Pimax, and the percentage change in inspiratory capacity (IC) from the seated to the supine position (r(2) = 0.64; p < 0.001).

In sitting CHF patients, tidal FL is absent but is common supine. Supine FL, together with increased respiratory impedance and decreased inspiratory muscle force, can elicit orthopnea, whom independent indicators are sPAP, supine Pimax and change in IC percentage.