Features of inspiratory muscle functional state in patients with heart failure with preserved ejection fraction

BACKGROUND: Chronic heart failure contributes to multiorgan dysfunction, including skeletal muscle impairment. AIM: This study aimed to assess the strength and electrical activity of inspiratory muscles in patients with chronic heart failure with preserved left ventricular ejection fraction. MATERIAL AND METHODS: Eighty patients of both sexes aged 45–74 years were included and divided into three groups: group 1 comprised 24 patients with chronic heart failure classified as NYHA functional class II, group 2 included 20 patients with NYHA class I chronic heart failure, and group 3 (control group) involved 36 patients without chronic heart failure. All participants underwent evaluation for serum N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels, a 6-minute walk test, assessment of inspiratory muscle strength, and surface electromyography of inspiratory muscles during three loading tests. The significance of intergroup differences was assessed using the Mann–Whitney and Pearson χ2 tests. RESULTS: When stratified by sex, women in group 1 had 31.5% lower maximal inspiratory pressure than those in the control group (p = 0.006). The patients in group 1 demonstrated a smaller increase in diaphragm electromyography amplitude during the first test—sustained inspiratory effort at 30% intensity for 15 seconds—by 27.9% (p = 0.010), 26.1% (p = 0.025), and 40.7% (p = 0.033) at 5, 10, and 15 seconds, respectively. In the second test—sustained inspiratory effort at 50% intensity for 5 seconds—electromyography amplitude decreased by 32.6% (p = 0.041) at 5 seconds. In the third test—sustained inspiratory effort at 70% intensity for 5 seconds—the reduction was 42.8% (p = 0.009) at 5 seconds compared with the control group. Additionally, a more pronounced decrease in electromyography frequency was observed during the first test—by 24.2% (p = 0.048) and 24.7% (p = 0.030) compared with the control group—indicating fatigue. In the accessory inspiratory muscles, electromyography amplitude gain was higher in group 1 than in the control group, showing activation of additional motor units: in the external intercostal muscles during the first test, by 31.7% (p = 0.032) and 37.9% (p = 0.044) and by 28.9% (p = 0.048) and 43.1% (p = 0.036) during the second test; and in the sternocleidomastoid muscle during the first test by 66.1% (p = 0.033) and 49.4% (p = 0.043) and by 128.6% (p = 0.032) during the second test. CONCLUSION: Surface electromyography with loading tests revealed diaphragm fatigue and increased activation of accessory inspiratory muscles in patients with NYHA class II chronic heart failure.