Respiratory muscle training improves hemodynamics, autonomic function, baroreceptor sensitivity, and respiratory mechanics in rats with heart failure

Abstract

Respiratory muscle training (RMT) improves functional capacity in chronic heart-failure (HF) patients, but the basis for this improvement remains unclear. We evaluate the effects of RMT on the hemodynamic and autonomic function, arterial baroreflex sensitivity (BRS), and respiratory mechanics in rats with HF. Rats were assigned to one of four groups: sedentary sham (n = 8), trained sham (n = 8), sedentary HF (n = 8), or trained HF (n = 8). Trained animals underwent a RMT protocol (30 min/day, 5 day/wk, 6 wk of breathing through a resistor), whereas sedentary animals did not. In HF rats, RMT had significant effects on several parameters. It reduced left ventricular (LV) end-diastolic pressure (P < 0.01), increased LV systolic pressure (P < 0.01), and reduced right ventricular hypertrophy (P < 0.01) and pulmonary (P < 0.001) and hepatic (P < 0.001) congestion. It also decreased resting heart rate (HR; P < 0.05), indicating a decrease in the sympathetic and an increase in the vagal modulation of HR. There was also an increase in baroreflex gain (P < 0.05). The respiratory system resistance was reduced (P < 0.001), which was associated with the reduction in tissue resistance after RMT (P < 0.01). The respiratory system and tissue elastance (Est) were also reduced by RMT (P < 0.01 and P < 0.05, respectively). Additionally, the quasistatic Est was reduced after RMT (P < 0.01). These findings show that a 6-wk RMT protocol in HF rats promotes an improvement in hemodynamic function, sympathetic and vagal heart modulation, arterial BRS, and respiratory mechanics, all of which are benefits associated with improvements in cardiopulmonary interaction.

Fig. 1.

Values are means ± SD; n = 8 for all groups. Two-way ANOVA and Bonferroni post hoc test. Sed-Sham, sedentary sham rats; RMT-Sham, respiratory muscle training-Sham rats; Sed-HF, sedentary heart failure rats; RMT-HF, RMT HF rats. Plots showing the average values of the relationship between mean arterial pressure (MAP) and heart rate (HR) using logistic sigmoidal baroreceptor curve analysis. P < 0.05 comparing RMT-HF with the Sed-HF group. ∙, values related to the highest slope point of the MAP (MAP₅₀; corresponding to the value found at 1/2 of the HR range evoked by the baroreflex response).

Fig. 2.

Values are means ± SD; n = 8 for all groups. Two-way ANOVA and Bonferroni post hoc test. A: Rrs, respiratory system resistance. *P < 0.001 compared with RMT-HF and Sed-Sham; †P < 0.01 compared with RMT-Sham. B: Gti, tissue resistance. *P < 0.001 compared with Sed-Sham; †P < 0.01 compared with Sed-HF; **P < 0.05 compared with Sed-HF.

Fig. 3.

Values are means ± SD; n = 8 for all groups. Two-way ANOVA and Bonferroni post hoc test. A: Ers, respiratory system elastance (Est). *P < 0.001 compared with Sed-Sham; †P < 0.01 compared with RMT-HF and RMT-Sham. B: Hti, tissue Est. *P < 0.001 compared with Sed-Sham; †P < 0.01 compared with RMT-Sham; **P < 0.05 compared with Sed-HF. C: Est, quasistatic Est. *P < 0.01 compared with Sed-Sham and RMT-HF.