Pd. Hughes et al., Inspiratory muscle relaxation rate slows during exhaustive treadmill walking in patients with chronic heart failure, AM J R CRIT, 163(6), 2001, pp. 1400-1403
Exercise intolerance is a feature of chronic heart failure (CHF). We hypoth
esized that excessive loading of the respiratory muscle pump might contribu
te to exertional breathlessness. One marker of excessive muscle-loading is
slowing of maximum relaxation rate (MRR) and, therefore, to test our hypoth
esis, we investigated the effect of exhaustive treadmill walking on inspira
tory muscle MRR in patients with CHF. We studied eight stable patients with
mild-moderate CHF walking on a treadmill until termination because of seve
re dyspnea. Inspiratory muscle MRR was determined from esophageal pressure
(Pes) change during submaximal sniffs (Sn) before and immediately after exe
rcise to a mean (SD) minute ventilation of 77 (18) L/min. For comparison, n
ine healthy subjects performed a similar protocol; exercise was terminated
either by severe dyspnea or when minute ventilation reached 100 L/min. Ther
e were no significant differences in terms of heart rate, respiratory rate,
tidal volume, or inspiratory duty cycle at cessation of exercise. The mean
slowing of Sn Pes MRR in the first minute after termination of exercise in
the CHF group was 22.4% and in the normal control group it was 2.8% (p < 0
.01). Our data show that slowing of inspiratory muscle relaxation rate occu
rs in patients with CHF walking to severe breathlessness. We conclude that
severe loading of the inspiratory muscles is a feature of exertional dyspne
a in CHF.