Inspiratory Muscle Training Attenuates The Inspiratory Muscle Metaboreflex In Heart Failure With Preserved Ejection Fraction

Heart failure patients with preserved ejection fraction (HFpEF) exhibit inspiratory muscle (IM) dysfunction potentially contributing to exercise intolerance. High IM work elicits IM metaboreflex activation resulting in increases in mean arterial pressure (MAP) and decreases in limb blood flow in healthy adults. In patients with HFpEF, IM metaboreflex activation leads to exaggerated increases in MAP and decreases in limb blood flow than controls. Inspiratory muscle training (IMT) attenuates the IM metaboreflex mediated increase in MAP in healthy adults. PURPOSE: The purpose was to investigate the effect of IMT on the IM metaboreflex mediated cardiovascular responses in patients with HFpEF. We hypothesized that 8 weeks of IMT would attenuate the IM metaboreflex mediated 1) increase in MAP and 2) decrease in limb blood flow in patients with HFpEF. METHODS: 11 HFpEF patients (4 M/7F; 70 ± 9 years; 33 ± 5 kg/m2) were enrolled in this study. Cardiovascular responses to inspiratory resistive breathing tasks (IRBT) were measured pre- and post-IMT. IMT consisted of 30 repetitions/day, 7 days/week, for 8 weeks at 40% of maximal inspiratory pressure (MIP). IRBTs at 60% MIP were performed to activate the IM metaboreflex. The IRBTs consisted of a breathing frequency of 20 breaths/min with a 50% duty cycle. Continuous beat-by-beat blood pressure and heart rate (HR) were measured using finger plethysmography. Vastus lateralis blood flow index (BFI) was measured using near infrared spectroscopy and indocyanine green dye. Responses were reported as absolute (MAP and HR) and percent (BFI) changes from rest (i.e., pre-IRBT values) to task failure. RESULTS: MIP increased from 73 ± 21 to 98 ± 25 cmH2O from pre to post-IMT (p < 0.01). Compared to pre-IMT, the increase in MAP during the 60% IRBT was attenuated post-IMT (Pre: 17 ± 6 vs. Post: 10 ± 6 mmHg; p < 0.01). HFpEF patients also had smaller % decreases in vastus lateralis BFI during the 60% IRBT post-IMT compared to pre-IMT (Pre: -33 ± 14 vs. Post: -23 ± 12 %; p < 0.01). The increase in HR during the 60% IRBT was not different between pre- and post-IMT (pre: 10 ± 7 vs. post: 7 ± 5 beats/min; p = 0.13). CONCLUSIONS: IMT attenuates the IM metaboreflex mediated cardiovascular responses in patients with HFpEF. These data suggest that IMT may improve cardiovascular regulation in HFpEF.