Expiratory flow limitation as a determinant of orthopnea in acute left heart failure

OBJECTIVES To assess the contribution of expiratory flow limitation (FL) in orthopnea during acute left heart failure (LHF). BACKGROUND Orthopnea is typical of acute LHF, but its mechanisms are not co mpletely understood. In other settings, such as chronic obstructive pulmona ry disease, dyspnea correlates best with expiratory FL and can, therefore, be interpreted as, in part, the result of a hyperinflation-related increase d load to the inspiratory muscles. As airway obstruction is common in acute LHF, postural FL could contribute to orthopnea. METHODS Flow limitation was assessed during quiet breathing by applying a n egative pressure at the mouth throughout tidal expiration (negative expirat ory pressure [NEP]). Flow limitation was assumed when expiratory flow did n ot increase during NEP. Twelve patients with acute LHF aged 40-98 years wer e studied seated and supine and compared with 10 age-matched healthy subjec ts. RESULTS Compared with controls, patients had rapid shallow breathing with s lightly increased minute ventilation and mean inspiratory flow. Breathing p attern was not influenced by posture. Flow limitation was observed in four patients when seated and in nine patients when supine. In seven cases, FL w as induced or aggravated by the supine position. This coincided with orthop nea in six cases. Only one out of the five patients without orthopnea had p osture dependent FL. Control subjects did not exhibit FL in either position . CONCLUSIONS Expiratory FL appears to be common in patients with acute LHF, particularly so when orthopnea is present. Its postural aggravation could c ontribute to LHF-related orthopnea. (C) 2000 by the American College of Car diology.