© 2005 European Society of Cardiology
The effects of long-term β-blockade on the ventilatory responses to exercise in chronic heart failure
Academic Cardiology, Castle Hill Hospital Castle Road, Cottingham Hull HU16 5JQ, UK
* Corresponding author. Tel.: +44-1482-624073; Fax: +44-1482-624071. E-mail address: klauswitte{at}hotmail.com
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Abstract |
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Aims: Chronic heart failure (CHF) patients complain of breathlessness and fatigue. Beta-blockers improve symptoms, echocardiograpahic variables and prognosis in CHF, but their effect on exercise capacity remains unclear. The aim of this study was to describe the effects of long-term beta-blocker therapy on metabolic gas exchange variables and ventilation during exercise in CHF patients.
Methods: 42 patients with symptomatic heart failure due to left ventricular systolic dysfunction (ejection fraction 33.2 (8.2)) on loop diuretics and angiotensin-converting enzyme inhibitors or angiotensin II antagonists, underwent exercise testing with metabolic gas exchange. They were then initiated onto and uptitrated to the maximum tolerated dose of beta-blockers. After 1 year of follow-up, patients were invited back for repeat testing.
Results: 35 patients attended for repeat exercise testing. Four patients had died, and three had not tolerated beta-blockade. After 1 year, exercise time was increased (487 (221) vs. 500 (217), p<0.05), and peak oxygen consumption and VE/VCO2 slope were unchanged (20.9 (5.0) vs. 20.0 (5.4), p=0.15 and 36.7 (8.3) vs. 37.3 (7.8), p=0.70). Peak ventilation, (61.5 (12.9) vs. 57.1 (13.4), p<0.05), peak carbon dioxide production (1629 (404) vs. 1496 (375), p<0.02) and hence respiratory exchange ratio (1.02 (0.08) vs. 0.98 (0.06) p<0.02) and p<0.05) were reduced. Submaximal oxygen consumption and carbon dioxide production were lower at matched workloads. The slope relating symptoms to ventilation (Borg/VE slope) was less steep following beta-blockade (0.18 (0.09) vs. 0.15 (0.06), p<0.05).
Conclusion: Long term beta-blocker therapy increases exercise time but not peak oxygen consumption, and reduces peak carbon dioxide production. CHF patients are less symptomatic for a given ventilation during exercise following beta-blocker treatment.
Key Words: Breathlessness • Beta-blockers • Chronic heart failure
Received August 13, 2003; Revised March 22, 2004; Accepted May 5, 2004
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