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* From the Divisions of Cardiovascular (Drs. Johnson, Olson, Allison, Squires, and Gau) and Thoracic Diseases (Dr. Beck and Ms. O’Malley), Department of Internal Medicine, Mayo Clinic and Foundation, Rochester, MN. The study was supported by the Mayo Foundation and Human Health Services grant MO1-RR00585, General Clinical Research Centers, Division of Research Resources, National Institutes of Health.
Correspondence to: Bruce D. Johnson, PhD, Division of Cardiovascular Diseases, Baldwin 2B, Mayo Clinic, Rochester, MN 55905; e-mail: johnson.bruce{at}mayo.edu
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%;
FEV1, 78 ± 4% predicted) relative to CTLS (FVC,
99 ± 4%; FEV1, 102 ± 4% predicted). At peak
exercise, oxygen consumption (
O2) and
minute ventilation (E) were lower in CHF patients
than in CTLS (O2, 17 ± 2 vs 32 ± 2
mL/kg/min; E, 56 ± 4 vs 82 ± 6 L/min,
respectively), whereas E/carbon dioxide output was
higher (42 ± 4 vs 29 ± 5). In CTLS, EELV initially decreased with
light exercise, but increased as 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
VT in CHF patients vs < 25% in CTLS (despite the higher
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 E constraint.
We conclude that patients with CHF commonly breathe near RV during
exertion and experience expiratory flow limitation. This results in
E constraint and may contribute to exertional
intolerance.
Key Words: ejection fraction • end-expiratory lung volume • flow limitation • left ventricular dysfunction • ventilatory limitation
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