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Nervous System Affects Breathing During Exercise in CHF

October 7, 2003 - During the early stages of exercise in
CHFers, oxygen use is lower than in healthy people. This
suggests that nervous system activation - overactive in
CHFers - may be at least partly to blame.
	Dr. K. Witte studied the effect of alpha-blockers
and beta-blockers on ventilation and breathlessness
during exercise in 11 CHFers and in 11 controls. This was
a random, double-blind study. It used:

alpha-blocker versus placebo;
beta-blocker versus placebo;
alpha-blocker and beta-blocker;
two placebos

Patients had repeated peak Vo2 exercise testing. Peak
oxygen consumption was lower in CHFers (20.7 mL/kg per
minute) than in controls (37.6 mL/kg per minute). CHFers
also had quicker increase in carbon dioxide production
than controls.
	In both patients and controls, blood pressure was
lower after alpha-blocker and beta-blocker. After a
beta-blocker, heart rate's relationship to oxygen
consumption was reduced. No changes in exercise time was
seen with beta-blocker or alpha-blocker use.
	Ventilation during less than maximum exercise was
reduced after both alpha-blocker and beta-blocker.
Patients did not feel any difference in how much they
exerted themselves during exercise with any of the
treatments.
	These findings suggest that sympathetic nervous
system overactivity contributes to the reduced ability to
breathe in chronic heart failure.

Source:  Heart 2003;89:1169-1173 and Reuters Health.