Ventilatory constraints during exercise in patients with chronic heart failure

We examined the degree of ventilatory constraint in patients with a history of chronic heart failure (CHF; n 11; mean a SE age, 62 +/- 4 years; cardiac index [CI], 2.0 +/- 0.1; and ejection fraction [EF], 24 +/- 2%) and in control subjects (CTLS; n = 8; age, 61 +/- 5 years; CI, 2.6 +/- 0.3) by plotting the tidal flow-volume responses to graded exercise in relationship to the maximal flow-volume envelope (MFVL). Inspiratory capacity (IC) maneuvers were performed to follow changes in end-expiratory lung volume (EELV) during exercise, and the degree of expiratory flow limitation was assessed as the percent of the tidal volume (V-T) that met or exceeded the expiratory boundary of the MFVL. CHF patients had significantly (p < 0.05) reduced baseline pulmonary-function (FVC, 76 +/- 4%; FEV1, 78 +/- 4% predicted) relative to CTLS (FVC, 99 +/- 4%; FEV1, 102 +/- 4% predicted). At peak exercise, oxygen consumption ((V) over dot (O2)) and minute ventilation ((V) over dot (E)) vc ere lon er in CHF patients than in CTLS ((V) over dot (O2), 17 +/- 2 vs 32 +/- 2 mL/kg/min; (V) over dot (E), 56 +/- 4 vs 82 +/- 6 L/min, respectively), whereas (V) over dot (E)/carbon dioxide output was higher (42 +/- 4 vs 29 +/- 5), In CTLS, EELV initially decreased with light exercise, but increased as (V) over dot (E) and expiratory flow limitation increased. In contrast, the EELV in patients with CHF remained near residual volume (RV) throughout exercise, despite increasing flow limitation. At peak exercise, IC averaged 91 +/- 3% and 79 +/- 4% (p < 0.05) of the FVC in CHF patients and CTLS, respectively, and flow limitation was present over > 45% of the V-T in CHF patients vs < 25% in CTLS (despite the higher (V) over dot (E) in CTLS), The least fit and most symptomatic CHF patients demonstrated the lowest EELV, the greatest degree of flow limitation, and a limited response to increased inspired carbon dioxide during exercise, all consistent with (V) over dot (E) constraint. We conclude that patients with CHF commonly breathe near RV during exertion and experience expiratory flow limitation. This results in (V) over dot (E) constraint and may contribute to exertional intolerance.