Respiratory muscles performance is related to oxygen kinetics during maximal exercise and early recovery in patients with congestive heart failure

Background-Dyspnea and fatigue are the main causes of exercise limitation i n chronic heart failure (CHF) patients, whose peak inspiratory (Pi(max)) an d expiratory pressures (Pe(max)) are often reduced. The aim of this study w as to examine the relationship between respiratory muscle performance and o xygen kinetics. Methods and Results-A total of 55 patients (NYHA class I to III) and 11 hea lthy subjects underwent cardiopulmonary exercise tests (CPET) on a treadmil l. In 45 of the 55 patients (group I) and in healthy subjects (group II), p ulmonary function tests, Pi(max), and Pe(max) were measured before and 10 m inutes after exercise, and oxygen kinetics were monitored throughout and du ring early recovery from CPET. The first degree slope of oxygen consumption ((V) over dot O-2) decline during early recovery ((V) over dot O-2/t-slope ) and (V) over dot O-2 half-time (T-1/2) were calculated. In 10 of the 55 C HF patients (group III), the measurements of Pi(max) were repeated 2, 5, an d 10 minutes after CPET. A >10% reduction in Pi(max) after CPET (subgroup I A) was measured in 11 of 45 patients. In contrast, 34 of 45 CHF patients (s ubgroup IB) and all central subjects (group II) had Pi(max)>90% of baseline value after CPET, Subgroup IA patients had significantly lower peak (V) ov er dot O-2, (13.5+/-2.1 versus 17.8+/-5.6 mL.kg(-1).min(-1); P<0.001), lowe r anaerobic thresholds (10.1+/-2.4 versus 13.6+/-4.6 mL.kg(-1).min(-1); P=0 .003) and lower (V) over dot O-2/t-slopes (0.365+/-0.126 versus 0.519+/-0.2 27 L.min(-1).min(-1); P=0,008) than subgroup IB patients. Conclusions-The reduction of Pi(max) after exercise is associated with prol onged early recovery of oxygen kinetics, which may explain, in part, the ro le played by respiratory muscles in exercise intolerance in CHF patients.