Effects of inspiratory muscle training on leg blood flow and exercise tolerance in COPD

Background: Fatiguing contractions of the inspiratory muscles may increase sympathetic tonus leading to peripheral vasoconstriction in healthy individuals. The so-called “inspiratory muscle metaboreflex” (IMM) is thought to be particularly active during heavy intensity exercise in order to deviate blood flow from locomotor to respiratory muscles. It remains unclear whether this phenomenon is also present in patients with COPD. Aims: To assess the effects of inspiratory muscle training (IMT) on leg blood flow and resistance during inspiratory resistance and exercise tolerance in COPD patients. Methods: Patients were randomized to IMT (30% of maximal inspiratory pressure; MIP) or SHAM (without resistance) intervention 30 min/day, 7 times/week, for 8 weeks using Power-breath TM (Southam, UK). High intensity constant load cardiopulmonary exercise test and IMM induction (60% of MIP until exhaustion) with calf blood flow (CBF) measurement by venous occlusion plethysmography (Hokanson TM , USA) were performed before and after training. Results: 7 patients in IMT and 6 patients in SHAM group completed the study (66.8±9.1yr; FEV 1 = 37±13% pred; MIP=88±32cmH 2 O). When compared to SHAM, IMT significantly improved exercise tolerance (Δtlim; 15±65 vs 191±247s; p=0.05). There were no significant between-group differences regarding to CBF and calf vascular resistance (CVR). In addition, CBF and CVR after both interventions did not differ from baseline (p>0.05). Conclusions: IMT with 30% of MIP enhanced exercise tolerance in comparison to SHAM training in patients with COPD. This finding seems not to be mechanistically related to improvements in leg blood flow.