References: Johnson et al, 2000
Johnson BD, Beck KC, Olson LJ, O'Malley KA, Allison TG, Squires RW, Gau GT
Ventilatory constraints during exercise in patients with chronic heart failure
Chest 2000 Feb; 117(2): p. 321-332.
Divisions of Cardiovascular, Department of Internal Medicine, Mayo Clinic and
Foundation, Rochester, MN 55905, USA. johnson.bruce@mayo.edu
ABSTRACT: We examined the degree of ventilatory constraint in patients with a
history of chronic heart failure (CHF; n = 11; mean +/- 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 (VT) that met or exceeded the expiratory boundary of
the MFVL. CHF patients had significantly (p < 0.05) reduced baseline pulmonary
function (FVC, 76 +/- 4%; FEV(1), 78 +/- 4% predicted) relative to CTLS (FVC, 99
+/- 4%; FEV(1), 102 +/- 4% predicted). At peak exercise, oxygen consumption
(VO(2)) and minute ventilation (V(E)) were lower in CHF patients than in CTLS
(VO(2), 17 +/- 2 vs. 32 +/- 2 mL/kg/min; VE, 56 +/- 4 vs. 82 +/- 6 L/min,
respectively), whereas VE/carbon dioxide output was higher (42 +/- 4 vs. 29 +/-
5). In CTLS, EELV initially decreased with light exercise, but increased as VE
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 VT in CHF patients vs. < 25% in CTLS (despite the
higher VE 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 VE
constraint. We conclude that patients with CHF commonly breathe near RV during
exertion and experience expiratory flow limitation. This results in VE
constraint and may contribute to exertional intolerance.