Inspiratory muscle relaxation rate slows during exhaustive treadmill walking in patients with chronic heart failure

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.